Patent Grant
7794306
The present invention relates to a surface finishing apparatus and a related method and, more particularly, to a surface finishing apparatus and a related method for surface finishing a workpiece in a desired geometrical profile contoured along an axial direction of the workpiece.
In the past, various attempts have been undertaken to lap a target shaped periphery, such as a journal portion or a pin portion, of a crankshaft of an automotive engine and subsequently to roller burnish the resulting surface in a desired surface roughness.
The preceding lapping operation in such surface finishing is achieved by permitting the target shaped periphery of the workpiece to be covered with a lapping film and placing a plurality of shoes on a rear side of the lapping film whereupon, under a condition where the lapping film is held in pressured contact with the workpiece, the workpiece is rotated to allow an abrasive surface of the lapping film to lap the target shaped periphery of the workpiece. To this end, a lapping apparatus includes an urging mechanism that urges shoes against the workpiece through the lapping film, a drive unit to drivingly rotate the workpiecce, and an oscillating mechanism arranged to apply an oscillating force to at least one of the workpiece and the lapping film along an axial direction of the workpiece, as disclosed in Japanese Patent Application Laid-Open Publication No. H07-237116, with reference to
However, since such mere lapping operation results in an outer circumferential periphery with an insufficient profile or in an undesired surface roughness, an attempt has been made to allow a burnishing roller to be brought into pressured contact with the outer circumferential periphery of the workpiece to collapse uneven surface portions of the outer circumferential periphery of the workpiece to provide an improved surface nature in the workpiece while permitting the outer circumferential periphery of the workpiece to be formed in a mid-concave profile for use as an oil sump to enable lubricating oil to be suitably supplied as disclosed in Japanese Patent Application Laid-Open Publication No. H06-190718, with reference to
In the meantime, there is a probability where one type of workpiece needs to be surface finished in a highly accurate straightness, and the other type of workpiece is intended to have a geometric geometrical profile, positively formed in mid-convex or mid-concave shapes.
Also, depending on circumstances, for the purpose of improving a surface quality of the workpiece, a probability exists where the workpiece resulting from grinding operation is directly roller burnished without lapping the workpiece
However, the lapping apparatus of the related art is arranged to achieve lapping operation under a fixed lapping condition, involving a shoe pressure force to be applied during lapping operation, and in actual practice, the use of such mere fixed lapping condition results in an inability of controlling lapping operation so as to obtain a desired geometrical profile.
Further, the roller burnishing operation of the related art encounters an issue in that it is troublesome to achieve and a roller burnishing tool per se is expensive.
In particular, when roller burnishing the pin portion of the crankshaft into a geometrical profile, having a mid-concave shape, shaft ends of the workpiece should be supported between a headstock and a tail stock to allow a pair of support rollers to be brought into abutting engagement with the target shaped periphery of the workpiece in a direction perpendicular to the axial direction of the workpiece while keeping the burnishing roller to be held in pressured contact with the target shaped periphery of the workpiece.
Since such a burnishing roller serves to transfer an outer profile of the burnishing roller to the pin portion of the crankshaft, the specific relationship should be present between individual workpieces and the associated burnishing rollers. Therefore, in order to carry out the above-described roller burnishing, there is a need for preparing burnish rollers with centrally ridged profiles in compliance with the mid-concave shapes of the individual workpieces. For this reason, it is hard to provide generalized burnishing rollers and it is hard to manufacture such generalized burnishing rollers, resulting in increased cost.
Further, although the pin portion of the crankshaft has both ends formed with fillet portions for permitting the surface finishing tool to escape, roller burnishing proximities of the fillet portions cause distal ends of the fillet portions to be collapsed to form sags that protrude into the fillet portions, resulting in a difficulty in finishing the pin portion in a desired straightness.
For this reason, the pressure force, produced by a hydraulic cylinder, to be applied to the proximities of the fillet portions and a central portion of the pin portion of the workpiece should be precisely controlled at different levels or the burnishing roller per se should have a particular hardness distribution pattern such that a hardness of the burnishing roller to be held in contact with the fillet portions is different from that of a central area of the burnishing roller.
However, adjusting the pressure force to be applied to the burnishing roller needs to perform troublesome control operation, resulting in occurrence of fear in a drop in productivity of the workpieces. Also, if the burnishing roller per se is formed to have the different hardness distribution pattern varying along a length of the burnishing roller, it is troublesome to form the burnishing roller, resulting in high cost.
Additionally, when in roller burnishing, since the burnishing roller is held in pressured contact with a whole axial surface of the crankshaft to improve the surface roughness, the whole axially extending surface of the crankshaft is entirely formed in too excellent surface finish. The presence of excessively small unevenness in the surface roughness of the pin portion of the crankshaft results in no formation of unevenness to form the oil sump in the sliding surface of the pin portion of the crankshaft. This causes deterioration in a retaining capacity of lubricating oil and depending on circumstances, there is a fear of occurrence of shortage in oil film, seizure and biting.
Therefore, the present invention has been completed upon such careful studies conducted by the present inventors and has an object to provide a surface finishing apparatus and its related method which allow a workpiece to be surface finished into a given geometrical profile through adjustment of surface finishing conditions.
To achieve the above object, in one aspect according to the present invention, a surface finishing apparatus, for surface finishing a workpiece, comprises: a workpiece supporting mechanism supporting a workpiece having a target shaped periphery to be surface finished; a surface finish tool adapted to be in abutting contact with the target shaped periphery of the workpiece; a pressure applying mechanism operative to apply a pressure force to the surface finish tool to cause the surface finish tool to be held in pressured contact with the target shaped periphery of the workpiece, with the pressure force exhibiting a distribution pattern depending upon an axial direction of the workpiece; and a drive mechanism rotating the workpiece about the axial direction during operation of the pressure applying mechanism to allow the surface finish tool to surface finish the target shaped periphery of the workpiece into a given geometrical profile, while exhibiting the distribution pattern of the pressure force of the surface finish tool.
Stated another way, in another aspect according to the present invention, a surface finishing apparatus, for surface finishing a workpiece, comprises: workpiece supporting means for supporting a workpiece having a target shaped periphery to be surface finished; a surface finish tool adapted to be in abutting contact with the target shaped periphery of the workpiece; pressure applying means for applying a pressure force to the surface finish tool to cause the surface finish tool to be held in pressured contact with the target shaped periphery of the workpiece, with the pressure force exhibiting a distribution pattern depending upon an axial direction of the workpiece; and rotating means for rotating the workpiece about the axial direction during operation of the pressure applying means to allow the surface finish tool to surface finish the target shaped periphery of the workpiece into a given geometrical profile, while exhibiting the distribution pattern of the pressure force of the surface finish tool.
In the meanwhile, in another aspect according to the present invention, a method of surface finishing a workpiece comprises: supporting a workpiece having a target shaped periphery to be surface finished; holding a surface finish tool in abutting contact with the target shaped periphery of the workpiece; applying a pressure force to the surface finish tool to cause the surface finish tool to be held in pressured contact with the target shaped periphery of the workpiece, with the pressure force exhibiting a distribution pattern depending upon an axial direction of the workpiece; and rotating the workpiece about the axial direction to allow the surface finish tool to surface finish the target shaped periphery of the workpiece into a given geometrical profile, while exhibiting the distribution pattern of the pressure force of the surface finish tool.
Other and further features, advantages, and benefits of the present invention will become more apparent from the following description taken in conjunction with the following drawings.
Hereunder, a surface finishing apparatus and its related method of each of various embodiments according to the present invention are described below in detail with reference to the accompanying drawings. In the following description, directional terms, such as “laterally”, “horizontally” and “vertically”, are used for convenience in referring to the accompanying drawings. Additionally, it is to be understood that the various embodiments of the present invention described herein may be utilized in various orientations, such as inclined, inverted, horizontal, vertical, etc., without departing from the principles of the present invention. Also, for the sake of convenience of explanation, an axial direction (a lateral direction, for example, as viewed in
Referring now to
As shown in
More particularly, in the lapping apparatus 1 of the presently filed embodiment, the workpiece supporting mechanism WS comprises a base 49A, a workpiece support table 49 disposed on the base 49A for sliding movements in the X-direction, a biasing member 52 resiliently coupled to the workpiece support table 49 to allow the same to be horizontally oscillated as described below, a first slidable table 47 disposed on the workpiece support table 49 and a second slidable table 48 disposed on the workpiece support table 49, with the first and second slidable tables 47, 48 being slidable in the Y-direction, a headstock 42 carried on the first slidable table 47 and rotatably supporting a spindle 41 by which a chuck 43 is connected to grip one end of the workpiece W, and a tailstock 46 having a center 46a to support the other end of the workpiece W.
In the lapping apparatus 1, a target shaped periphery of the workpiece W is lapped using the lapping film 11 in a manner described below. The lapping film 11 includes a thin-walled base member 11a (as shown
In the lapping film 11, the thin-walled base member has a surface provided with a large number of abrasive grains, such as aluminum oxide, silicone carbide and diamond, with a grain diameter ranging from approximately several micron meters to 200 μm, with the abrasive grains (such as aluminum oxide, silicone carbide and diamond) being fixed to the thin-walled base member by adhesive. The lapping film 11 may take a structure wherein the abrasive grains are adhered to an entire surface of the thin-walled base member or a structure wherein non-abrasive regions, each with a given width, that are intermittently formed along a length of the thin-walled base member. It is a usual practice for the other surface of the thin-walled base member to be applied with a back coating layer composed of resisting material (not shown) such as rubber or plastic resin, but non-slip surface treatment may be carried out on the other surface of the thin-walled base member if desired.
As best shown in
Disposed in the vicinity of the supply reel 15 and the winding reel 16 are lock mechanisms (not shown) which are selectively actuated to cause the lapping film 11 to be entirely applied with a given tension and to remain tensioned for lapping operation.
As best shown in
In addition, the pressure applying mechanism 10 further includes an upper presser arm 22 and a lower presser arm 23 which are pivotally supported by upper and lower pivot shafts 24, 24, respectively, to allow front end portions 22a, 23a to be moved into or out of operative positions, respectively. The actuator 30 is comprised of a fluid cylinder 25 (adapted to be actuated by hydraulic pressure or air under pressure) operatively disposed between rear end portions 22b, 23b of the upper presser arm 22 and the lower presser arm 23, respectively, to selectively apply shoe pressure forces to the front end portions 22a, 23a, respectively, through a rod. 26 such that the shoes 28A, 28B are held in pressured contact with the target shaped periphery of the workpiece W to be lapped at given pressure forces.
With such a structure of the pressure applying mechanism 10, upon actuation of the fluid cylinder 25, both the presser arms 22, 23 move about the centers of the pivot shafts 24, 24 for opening and closing capabilities. Opening and closing movements of both the presser arms 22, 23 are carried out in association with the lapping film 11 and, during closing movements of both the presser arms 22, 23, the shoes 21A, 21B are brought into pressured contact with the workpiece W by means of the lapping film 11 whereas, during opening movements of both the presser arms 22, 23, the shoes 21A, 21B are brought out of abutting engagement between the workpiece W and the shoes 21A, 21B.
Moreover, the lapping apparatus 1 further includes shoe pressure force adjusting units 31A, 31B as shown in
During lapping operation, heat builds up in the shoe cases 28A, 28B and a cooling unit 70 is disposed on a front side of the pressure applying mechanism 10 to supply coolant to cooling areas proximate to the workpiece W and the lapping film 11 associated therewith for cooling these components.
Turning back to
With the structure set forth above, the workpiece W is set between the headstock 42 and the tailstock 46. Then, the main motor M1 is operated and the workpiece W is rotated through the spindle 41 and the chuck 43 for lapping operation. Operatively coupled to the spindle 41 is a rotary encoder S1 that detects a rotary position of the workpiece W during lapping operation and delivers a detection signal, indicative of the rotary position of the workpiece W, to a controller 100. The controller 100 is responsive to this detection signal to allow a rotational speed of the main motor M1 to be varied to enable the workpiece W to be driven at a workpiece rotational speed Vw of a given value.
Moreover, the oscillating mechanism 50, serving as the tool shifting mechanism, oscillates the workpiece W along a horizontal axis thereof for a specific reason as will be described below in detail. To this end, the oscillating mechanism 50 is comprised of an eccentric rotary element 51 rotatably supported by the frame body in abutting engagement with a distal end of the workpiece support table 27, a motor M2 connected to and drive the eccentric rotary element 51 for oscillating the workpiece support table 49 and the urging unit 52 that urges the workpiece support table 49 in the lateral direction to cause the eccentric rotary element 51 into abutting engagement with the distal end of the workpiece support table 49. Cooperation between rotation of the eccentric rotary element 51, caused by the motor M2, and the urging unit 52 enables the workpiece support table 49 to be operated in reciprocating movements in an X-direction such that the entirety of the workpiece W is oscillated in the X-direction. Additionally, for the purpose of detecting an oscillating position of the workpiece W relative to the lapping film 11 during oscillating operation in the X-direction, a rotary encoder S2 is mounted for detecting a rotary position of the eccentric rotary element 51 to allow resulting detection signal to be delivered to the controller 100.
An oscillating stroke in which the workpiece W travels in a lateral direction is determined based on eccentric displacement of the eccentric rotary element 51 with respect to an axis of an output shaft of the motor M2. The rotary position of the eccentric rotary element 51 is detected by the rotary encoder S2, and adjustment of eccentric displacement may be executed by inserting one or more number of adjustor plates into an engaged area between the motor M2 and the eccentric rotary element 51 or by using a hydraulic unit.
Also, while the presently filed embodiment has been described above with reference to a particular example wherein the oscillating mechanism 50 oscillates the workpiece W along the X-direction, the present invention is not limited to such a particular structure. The oscillating mechanism 50 may be modified in such a way as to directly oscillate the lapping film 11 along a longitudinal direction thereof. This is achieved through the use of a structure wherein the lapping film 11 is pulled out from the shoes 21A, 21B in a radial direction once to be wound on a roller whereupon the lapping film 11 is restored to the initial position near the shoes 21A, 21B, with the roller being connected to an oscillating means to be oscillated in the radial direction.
Incidentally, as shown in
Especially, the presently filed embodiment contemplates to provide an arrangement in which the upper and lower shoes 21A, 21B are offset in contact position, in which the lapping film 11 is urged, with the target shaped periphery with respect to a center line thereof to enable the target shaped periphery of the crankshaft W to be lapped in the mid-concave profile. Here, by the term “target shaped periphery W1 of the crankshaft W” is meant the outer circular-arc shaped periphery between the fillet portions Wf.
As shown in
With such an offset arrangement of the upper and lower shoes 21A, 21B with respect to the target shaped periphery W1 of the workpiece W, the lapping film 11 is apt to be pressured against the central region C of the target shaped periphery W1 of the crankshaft W through all of the upper and lower shoes 21A, 21B to increase a lapping time interval for the target shaped periphery W1 of the crankshaft W whereas, in the terminal regions D of the target shaped periphery W1, the lapping film 11 is intermittently brought into pressured contact with the target shaped periphery W1 with the upper and lower shoes 21A, 21B, resulting in reduction in the time interval for which the workpiece W is lapped.
As a result, the target shaped periphery W1 of the crankshaft W has a surface profile having the central region C formed in a concave profile Wa and the terminal regions each formed in a convex profile Wb, resulting in formation of an entire structure with a mid-concave profile as shown in
The surface profile of the workpiece W was tested to provide quantitative results in terms of offset displacement between the upper and lower shoes 21A, 21B in a manner as described below.
When conducting tests, use was made of the lapping film 11 with a width N in compliance with a width S of the target shaped periphery W1 of the workpiece W and the even number of shoes 21A, 21B formed in the same width S that was made smaller than the width S of the target shaped periphery W1 to be lapped as shown in
Then, operations were carried out to lap the target shaped periphery W1 of the workpiece W in offset displacement at differing values of 3, 6, 9, 12%, respectively, and straightness were measured for respective surface profiles resulting from lapping operations, with measured results being shown in
With respect to the results shown in
Further, as set forth above, with the lapping apparatus 1 of the presently filed embodiment having the oscillating mechanism 50 enabling the workpiece W to oscillate in the X-direction, it is preferable for the relationship between the oscillating stroke, provided by the oscillating mechanism 50, and the offset displacement δ such that the offset displacement δ is made smaller than the oscillating stroke. However, it is preferable for the shoes 21A, 21B associated with the lapping film 11 not to be dislocated from the target shaped periphery of the workpiece W even when the shoes 21A, 21B are disposed in the offset positions with respect to the lapping film 11.
In operation, both the presser arms 22, 23 are brought into the open condition and under such a condition, the lock unit associated with the supply reel 15 is locked whereupon the motor M3 is operated to rotate the winding reel 16. This causes the lapping film 11 to be moved in a given length with a new abrasive surface of the lapping film 11 being set to face the target shaped periphery W1 of the workpiece W while applying the lapping film with a given tension.
And, when locking the lock unit associated with the winding reel 8, the lapping film 11 is applied with tension to fall in a stretched state with no looseness.
Under such a circumstance, the workpiece W is set between the headstock 42 and the tailstock 46. After such setting operation, the fluid cylinder 25 is actuated and the both presser arms 22, 23 are brought into the closed condition. When this takes place, the lapping film 11 is set onto the target shaped periphery W1 of the workpiece W, with both shoes 21A, 21B being brought into abutting engagement with the target shaped periphery W1 of the workpiece W with a given urging force. In the presently filed embodiment, the workpiece W takes the form of the crankshaft that has a plurality of pins with the target shaped peripheries, respectively, and the lapping films 11 are set onto these target shaped peripheries in pressured contact, respectively.
Then, the main motor M1 is operated and the workpiece W is rotated, causing the target shaped peripheries of the workpiece W to be lapped with the associated abrasive surfaces of the lapping films 11. Depending on shapes of the pin portions, a probability occurs in which some of the pin portions eccentrically rotate with accompanied rocking movements of both the presser arms 22, 23 in a normal practice, with resultant lapping operations being similarly executed on the associated pin portions.
In the presently filed embodiment, particularly, due to the presence of the shoes 21A, 21B disposed in the offset positions with respect to the center line O-O of the target shaped periphery W1 of the workpiece W, the contact regions A of the shoes 21A, 21B held in contact with the target shaped periphery W1 overlap one another at the central region C of the target shaped periphery W1 of the workpiece W and do not overlap one another at the terminal regions D. When this takes place, in the central region C of the target shaped periphery W1 of the workpiece W, both the shoes 21A, 21B are effective to press the lapping film 11 onto the target shaped periphery W1 of the workpiece W to allow the central region C of the target shaped periphery W1 to be lapped at a greater rate than those at which the other regions are lapped, resulting in the workpiece W having surface profiles each formed in a mid-concave profile.
Thus, when carrying out lapping operation to provide the target shaped periphery formed in the mid-concave profile, it is extremely advantageous in that the number of processing steps is decreased to a lower value than that required in using a burnishing roller and no specific roller is required in use with a resultant decrease in a cost performance. Additionally, no probability occurs in the workpiece to have a surface roughness formed in an undesirably smoothed extent and thus, an oil sump area is advantageously formed in the central region of the target shaped periphery of the workpiece to be highly advisable in a lubricating capability.
In the meantime, during lapping operation of the lapping apparatus 1, the motor M2 is operated to allow the eccentric rotary element 51 of the oscillating mechanism 50 to rotate against the biasing force of the urging unit 52, thereby oscillating the workpiece support table 49 in the X-direction to cause the workpiece W to oscillate in the X-direction.
During oscillating operation of the oscillating mechanism 50, there occurs an increase in a distance in which the target shaped periphery W1 of the workpiece W and the abrasive grains of the lapping film 11 are held in contact, resulting in an increase in the number of abrasive grains acting upon the target shaped periphery per unit time for thereby enabling lapping operation to be achieved within a shortened time interval to surface finish the workpiece at an increased efficiency. Due to the presence of the offset displacement δ between the associated shoes 21A, 21B to be made smaller than the oscillating width, the oscillation and lapping operation can be reliably performed.
Further, as shown in
With such concave and convex portions being filled with lubricating oil, the concave and convex portions serve as desired oil reservoirs, exhibiting a desired function to provide am improved lubricating capability while preventing the journal or pin portions from being seized. However, in actual practice to provide a final product, it is preferable for the sharp edges T1 to be subjected to burnishing operation so as to remove the sharp edges T1 such that the sharp edges T1 is lowered to some extent. In so doing, it becomes possible to prevent the sharp edges T1, that would otherwise be caused during an initial stage of start-up of an engine from being worn, with a resultant increase in a durability.
The present invention is not limited to the presently filed embodiment set forth above, and various alterations may be made. While the presently filed embodiment has been described with reference to a particular structure where the pin portions of the crankshaft are mainly processed, lapping operations may be performed not only for the pin portions but also for the journal portions of the crankshaft and, if the occasion demands, lapping operation may be carried out on the target shaped peripheries with non-complete round shape in cross section, such as cam lobe portions or journal portions of a cam shaft. In addition, the present invention may also be applied to the other objective with a target profile in other circular-arc shaped configuration.
Further, while the surface finishing apparatus of the presently filed embodiment has been shown and described in conjunction with an structural example wherein the tool shifting mechanism is comprised of the oscillating mechanism 50 that is arranged to oscillate the workpiece support table 49 by which the workpiece W is oscillated in the lateral direction, the tool shifting mechanism may be modified such that the main spindle 41 is oscillated to cyclically move the workpiece along the axis thereof. In another alternative, the tool shifting mechanism may take a structure to directly oscillate the lapping film 11 or to directly oscillate both workpiece W and the lapping film 11. Also, the oscillating mechanism 50 is not limited to the particular structure that employs the eccentric rotary element 51, and the oscillating mechanism 50 may include an ultrasonic oscillator.
While the surface finishing apparatus of the presently filed embodiment has been shown and described in conjunction with an structural example wherein the oscillating position of the workpiece W is detected based on the rotational position of the eccentric rotary element 51 through the use of the rotary encoder S2, the surface finishing apparatus may take a modified structure upon using an optical sensor to directly detect the terminal end of the workpiece W for thereby detecting the oscillating position of the workpiece W.
Moreover, the surface finishing apparatus of the presently filed embodiment has been shown and described in conjunction with a structural example that includes the convex-shaped shoes, the surface finishing apparatus may use other types of shoe configurations.
A surface finishing apparatus 1A of a second embodiment of the present invention is described below with reference to
The surface finishing apparatus 1A of the second embodiment differs from the surface finishing apparatus 1 of the first embodiment in that a cam shaft is employed as a workpiece and a controller 100A is arranged to control a pressure force to be applied by a pressure applying mechanism 10A in dependence on an oscillating position of the workpiecee resulting from a rotational position, indicative of an oscillating angle θc, of an eccentric rotary element 51 of an oscillating mechanism 50. In the presently filed embodiment, the same component parts as those of the surface finishing apparatus of the first embodiment bear like reference numerals and the surface finishing apparatus 1A is described below aiming at differing points in structure with explanation for the same component parts being simplified or omitted.
Referring to
Likewise, a pair of guide rollers R7 and R8 are located on a front portion of the forward end 23a of the lower presser arm 23, and the guide roller R6 is located in an inside area of the upper presser arm 23 at a position close proximity to the lower pivot shaft 24. With such an arrangement, the lapping film 11 is pulled out from the supply reel 15 and guided with the pair of first guide rollers R3 and R4, the second guide roller R5, the third guide roller R6 and the pair of fourth guide rollers R7 and R8 whereupon the lapping film 11 is taken up on the winding reel 16.
Supported in an intermediate area of the upper presser arm 22 between the guide roller R4 and the guide roller R5 is an upper shoe 21A, and supported in an intermediate area of the lower presser arm 23 between the guide roller R6 and the guide roller R7 is a lower shoe 21B. A cam lobe portion 61 of the cam shaft WA, that is rotatably supported with the headstock 42 and the tail stock 46 (see
Connected to the winding reel 16 is a motor M3. With the motor M3 being operated, the winding reel 16 is rotated and the lapping film 11 is progressively fed from the supply reel 15. In order to detect the amount of lapping film 11 delivered from the supply reel 16, a rotary encoder S3 is mounted onto a shaft of the winding reel 16 as a detection unit to detect rotational displacement thereof. The lock units are mounted to the frame body (not shown) in the vicinity of the supply reel 15 and the winding reel 16, respectively, and operative to apply the given tension force to an entirety of the lapping film 11.
The pair of upper and lower presser arms 22 and 23 are pivotally supported on the upper and lower pivot shafts 24, 24 to allow the forward end portions 22a, 23a of the upper and lower presser arms 22, 23 to be movable with respect to one another in the Z-direction for opening and closing capabilities. The upper and lower presser arms 22 and 23 are actuated by the fluid cylinder 25. With such a structure, if the piston rod 26 of the actuator 30 protrudes from a retracted condition, the upper and lower presser arms 22, 23 are pivoted in a direction to allow the forward end portions 22a, 23a of the upper and lower presser arms 22, 23 to fall in the closed position shown in
Although the upper and lower presser shoes 21A, 21B may be classified into convex type shoes and concave type shoes depending on outer profiles of the forward end portions of the shoes, in the illustrated second embodiment, the upper and lower presser shoes 21A, 21B are shown as concave type shoes, respectively, each of which has a concave distal end portion formed with plural lobes (shown as two lobes in the second embodiment) that are selectively brought into abutting engagement with a target shaped periphery of the cam lobe portion 61 by means of the lapping film 11. The distal end of each shoe is indented but has a pair of engaging surfaces per se, which mate with the workpiece WA, that are formed in convex circular arc configurations in cross section, respectively. Thus, the upper and lower presser shoes 21A, 21B are able to be brought into abutting engagement with the target shaped periphery of the cam lobe portion 61 at two line contacts though the lapping film 11 is intervened. Due to the presence of the cam lobe portion 61 being supported with the upper and lower presser shoes 21A, 21B at four contact points, the cam lobe portion 61 can be rotated in a stable and reliable fashion. Here, by the term “contact” used in the presently filed embodiment is meant that the upper and lower presser shoes 21A, 21B are brought into indirect abutting engagement with the target shaped periphery of the workpiece WA via the lapping film 11, and by the term “contact surface area” is meant the surface area in which the upper and lower presser shoes 21A, 21B are brought into indirect abutting engagement with the target shaped periphery of the workpiece WA via the lapping film 11.
As shown in
The pressure applying mechanism 10A includes upper and lower pressure adjusting units 31A, 31B associated with the forward end portions 22a, 23a, respectively, of the upper and lower presser arms 22, 23 for enabling the shoes 21A, 21B to hold the lapping fill 11 in pressured contact with the target shaped periphery, i.e., the cam lobe portion 61, of the workpiece W under the given pressure distribution pattern. Also, as conceptually shown in
As shown in
Also,
In
The abrasive grains 12 of the lapping film 11 encounter damages, such as cracks or fallouts in the worst case, resulting from the edge portions We, We of the workpiece WA that moves in oscillation. For this reason, as shown in
Here, the removal quantity of the target shaped periphery W1 of the workpiece WA per unit time due to the abrasive grains 12 of the lapping film 11 increases with an increase in the shoe pressure force P (see
Accordingly, in the comparative example, as shown in
Therefore, the surface finishing apparatus 1A of the second embodiment contemplates the provision of a structure wherein the rotational position (the oscillating angle θc) of the eccentric rotary element 51 using the rotary encoder S2 and the oscillating position of the cam shaft 60 is detected using the oscillating position θc whereupon the controller 100A operates to variably control the shoe pressure force P, to be applied to the lapping film 11 in the given distribution pattern depending upon the axial direction of the workpiece WA, in dependence on the oscillating position of the workpiece WA during surface finishing operation for thereby enabling the target shaped periphery W1 to be formed into a desired geometric profile along the axis of the workpiece WA.
A basic sequence of operations in control set forth above is described in detail with reference to
Referring to
The controller 100A is responsive to the detection signal related to the rotational position of the eccentric rotary element 51 delivered from the rotary encoder S2 and discriminates to find whether the oscillating position of the cam shaft 60 is located. And, the controller 100A variably controls the shoe pressure forces P to be applied to the shoes 21A, 21B in dependence on the oscillating position of the cam shaft 60 along the axial direction thereof.
The shoe pressure forces P are variably controlled by the controller 100A in a manner described below. As shown in
More particularly, the controller 100A outputs a control signal to the presser motor M4 to allow the presser motor M4 to be controllably rotated such that the eccentric angle θe of the eccentric rotary element 35 is angled at 180 degree when the oscillating position of the cam shaft 60 reaches the leftmost end (at the oscillating angle θc=zero degree) whereas the eccentric angle θe of the eccentric rotary element 35 is angled at zero degree when the oscillating position of the cam shaft 60 reaches the central position (at the oscillating angle θc=90 degree) and the eccentric angle θe of the eccentric rotary element 35 when the oscillating position of the cam shaft 60 reaches the rightmost end (at the oscillating angle θc=180 degrees) is angled at 180 degrees. With the eccentric angle θe being angled at 180 degrees, since the shoe pressure forces P are maximized (see
When controlling the shoe pressure force P to be applied to the shoes in such a manner set forth above, as compared to the shoe pressure force P applied as shown in the comparative example in
Also, while in
In usual practice, there are workpieces some of which are intended to have the geometric profiles each positively formed into a mid-convex configuration. In order to contemplate reduction in friction by decreasing a contact region between the cam lobe portion 61 and a valve lifter (not shown), there are some occasions where the axially extending geometric profile is desired to be formed into the mid-convex profile in cross section.
The shoe pressure force P when contemplating to obtain the axially extending geometric profile formed into the mid-convex shape is variably controlled in the same manner as described above. That is, as shown in
When controlling the shoe pressure force P in such a manner set forth above, the damage D in the abrasive grains, encountered in the region where the edge portion We of the workpiece WA is shifted, further decreases. The degree of resulting damage D in abrasive grains is assigned to be “c” (which is expressed as a>b>c). By a further decrease in the damage D in the abrasive grains is meant the further increase in the removal quantity of the target shaped periphery W1 per unit time as a result of lapping with the abrasive grains 12 under the same shoe pressure force P. Also, since the shoe pressure force P, related to the central portion on the oscillating stroke of the workpiece W oscillating in the lateral direction, further decreases, the removal quantity caused per unit time at the central portion on the oscillating stroke also further decreases. These actions are combined to allow the both terminal portions of the workpiece WA to be further promoted in lapping than the central portion of the workpiece WA to be performed, thereby enabling the axially extending geometric profile to be surface finished into the mid-convex shape.
In usual practice, there are workpieces some of which are intended to have axially extending geometric profiles each positively formed into a mid-concave configuration. That is, there are some occasions where pin portions 63 of a crankshaft 62 (see
The shoe pressure force P when contemplating to obtain the axially extending geometric profile formed into the mid-concave shape is variably controlled in a manner as shown in
More particularly, the controller 100A outputs a control signal to the presser motor M4 to allow the presser motor M4 to be controllably rotated such that the eccentric angle θe of the eccentric rotary element 35 is angled at zero degree when the oscillating position of the crankshaft 62 reaches the leftmost end (at an oscillating angle θc=0 degree) whereas, when the oscillating position of the cam shaft 60 reaches the central position (at an oscillating angle θc=90 degrees), the eccentric angle θe of the eccentric rotary element 35 is angled at 180 degrees and, when the oscillating position of the crankshaft 62 reaches the rightmost end (oscillating angle θc=180 degrees), the eccentric angle θe of the eccentric rotary element 35 is angled at zero degree. With the eccentric angle θe being angled at 180 degrees, since the shoe pressure force P is maximized (see
When controlling the shoe pressure force P in such a manner set forth above, the damage D in the abrasive grains, encountered in the region where the edge portion We of the workpiece WA is shifted, becomes larger than the that obtained when applied with the shoe pressure force P shown in the comparative example of
Also, since the change rate between the shoe pressure force P related to the terminal portions on the oscillating stroke of the workpiece W oscillating in the lateral direction and the shoe pressure force P related to the central portion on the oscillating stroke of the workpiece W oscillating in the lateral direction varies depending on the axially extending geometric profile (to be formed into the flat, mid-convex and mid-concave shapes in cross section) of the workpiece, the surface finishing conditions (such as the shoe pressure force, the workpiece rotating speed and respective fundamental values in the oscillating speeds) based on which lapping operation is performed, and the surface roughness that is demanded, the change rate in the shoe pressure force should not be determined in a univocal fashion and a final change rate of the shoe pressure force may be determined in trial and error.
Further, in order to vary the shoe pressure force P in synchronism with the oscillating position of the workpiece WA, when designing the eccentric rotary element 35, a base circle radius and an operation start angle associated in terms of the X-direction are determined taking an oscillating cycle into consideration and, in respect of the Z-direction, the cam lift h and the operation start angle are determined.
Now, operation of the surface finishing apparatus of the presently filed embodiment is described in conjunction with an exemplary case where the target shaped periphery of the axially extending geometric profile is surface finished in the flat shape in cross section.
First, the cam shaft 60 is set between the headstock 42 and the tail stock 46 as the workpiece WA, and the upper and lower presser arms 22, 23 are moved toward the cam lobe portion 61. When this takes place, the fluid cylinder 25 is operated to retract the piston rod 26, thereby operating the upper and lower presser arms 22, 23 in the opening directions. Subsequently, the fluid cylinder 25 is actuated to cause the piston rod 26 to protrude the upper and lower presser arms 22, 23 in the closing directions. These closing movements allow the lapping film 11 to be set on the target shaped periphery W1, i.e., of the cam lobe portion 61, of the cam shaft 60 by means of the shoes 21A, 21B.
During opening movements of the upper and lower presser arms 22, 23, the motor M3 is operated to rotate the winding reel 16. Then, the lapping film 11 is shifted by a given length and a new abrasive grain surface is set onto the target shaped periphery W1. Thereafter, upon locking of the lock device disposed in the vicinity of the supply reel 15, if the winding reel 16 is rotated, the lapping film 11 is applied with a given tension force. Next, when locking the lock device in the vicinity of the winding reel 16, the lapping film 11 is brought into an operative condition with no looseness in tension.
When the cain lobe portion 61 is thus clamped in a manner set forth above, the pressure applying mechanism 10A is operated to cause both the shoes 21A, 21B to be brought into abutting engagement with the cam lobe portion 61, thereby compelling the abrasive grain surface of the lapping film 11 to be brought into pressured contact with the target shaped periphery W1.
And, the drive mechanism 40 is operated to cause the cam shaft 60 to rotate about the axial direction thereof while operating the oscillating mechanism 50 to allow the cam shaft 60 to oscillate in the X-direction along the axis thereof, the cam lobe portion 61 rotates followed by reciprocating movements of the shoe cases 28A, 28B, retaining the upper and lower shoes 21A, 21B, respectively, within the cavities 27A, 27B for expanding and retracting movements, thereby causing the target shaped periphery W1 of the cam lobe portion 61 to be lapped.
During such lapping operation, the controller 100A controls the oscillating mechanism 50 and the pressure applying mechanism 10A to be operated in synchronism with respect to one another. The controller 100A discriminates the oscillating position of the cam shaft 60 in dependence on the rotary position of the eccentric rotary element 35 detected by the rotary encoder S2 and variably controls the shoe pressure force P, to be applied to the shoes 21A, 21B, depending on the oscillating position of the cam shaft 60 during lapping operation. That is, the controller 100A controls the operation of the presser motor M4 such that, when the oscillating position of the cam shaft 60 reaches the leftmost end or the rightmost end, the eccentric rotary element 35 is angled at the eccentric angle θe of 180 degrees. This allows the shoe pressure force P related to the terminal portions on the oscillating stroke in the radial direction of oscillation of the workpiece WA to become greater than that related to the central portion on the oscillating stroke in the radial direction of oscillation of the workpiece WA (see
This improves the unevenness in the removal quantities that would occur between the both terminal portions and the central portion on the oscillating stroke of the cam lobe portion 61, and the axially extending geometric profile is formed in the flat shape in cross section, thereby suppressing a drop in the straightness. Thus, by merely adjusting the lapping conditions, it is possible to controllably surface finish the geometric profile of the target shaped periphery W1 along the axial direction of the workpiece WA.
The cam shaft 60 has a plurality of cam lobe portions 61, which are concurrently subjected to lapping operation. When lapping operation is completed, the fluid cylinder 25 is operated to contract the piston rod 26 for operating the upper and lower presser arms 22, 23 in the opening directions, thereby placing the cam shaft 60 in a condition available to be taken out. After the cam shaft 60 has been taken out, another cam shaft 60 is newly set and is enabled to be subjected to similar lapping operation.
When surface finishing the axially extending geometric profile in the mid-convex shape in cross section, the lapping operation is controlled in such a manner set forth above. That is, the lapping operation is performed such that the change rate ΔP, related to the axially extending geometric profile to be surface finished in the mid-convex shape in cross section, between the shoe pressure force P related to the both terminal portions on the oscillating stroke of the workpiece W oscillating in the lateral direction and the shoe pressure force P related to the central portion on the oscillating stroke of the workpiece W oscillating in the lateral direction, is set to be greater than that required when lapping the geometric profile of the target shaped periphery in the flat shape in cross section (see
This allows the both terminal portions of the target shaped periphery, i.e., the cam lobe portion 61, to be lapped in a further promoted extent than that at which the central portion is lapped, resulting in formation of the axially extending geometric profile in the mid-convex shape in cross section. Thus, by merely adjusting the lapping conditions, it is possible to controllably surface finish the geometric profile of the target shaped periphery W1 in a desired shape in cross section along the axis of the workpiece WA.
When lapping the axially extending geometric profile of the workpiece WA (such as the crankshaft 62) in the mid-concave shape in cross section, the controller 100A controls the operation of the presser motor M4 such that when the oscillating position of the crankshaft 62 reaches the central position, the eccentric angles θe of the eccentric rotary elements 35A, 35B are angled at 180 degrees, and the shoe pressure forces P related to the both terminal portions on the oscillating stroke of the workpiece W oscillating in the lateral direction are set to be smaller than that related to the central portion on the oscillating stroke of the workpiece W oscillating in the lateral direction (see
This allows the central portion of the target shaped periphery W1 of the crankshaft 62 to be lapped in a further promoted extent than that at which the both terminal portions are lapped, resulting in formation of the axially extending geometric profile in the mid-concave shape in cross section. Thus, by merely adjusting the lapping conditions, it is possible to controllably surface finish the geometric profile of the target shaped periphery W1 in a desired shape in cross section depending upon the axial direction of the workpiece WA.
As set forth above, with the surface finishing apparatus 1A of the presently filed embodiment, due to the provision of the lapping film 11, the shoes 21A, 21B, the pressure applying mechanism 10A operative to urge the shoes 21A, 21B toward the workpiece WA to cause the abrasive surface of the lapping film 11 to be held in pressured contact with the target shaped periphery of the workpiece WA while enabling the shoe pressure forces P to be freely adjusted, the oscillation mechanism 50 serving as the tool shifting mechanism to cyclically move at least one of the workpiece WA and the lapping film 11 in the given stroke defined in relation to the given width of the target shaped periphery such that the working position of the lapping film 11 is shifted in variable positions with respect to the target shaped periphery, the rotary encoder S2 that detects the current relative oscillating position of the workpiece WA with respect to the lapping film 11 during oscillating movement and generates a detection signal indicative of the detected relative oscillating position, and the controller 100A responsive to the detection signal to variably control operation of the pressure applying mechanism so as to vary the shoe pressure forces P to be applied to the shoes 21A, 21B, with the pressure force exhibiting the given distribution pattern depending on the current oscillating position of the workpiece WA, the geometrical profile of the target shaped periphery W1 of the workpiece WA can be controlled along the axis of the workpiece WA. An advantageous effect is that upon mere adjustment of the lapping conditions, lapping operation can be carried out to surface finish the geometrical profile of the target shaped periphery W1 of the workpiece WA in any desired shape (flat, mid-convex or mid-concave shapes) in cross section along the axis of the workpiece WA.
Further, due to an ability of the controller 100A to control the operation of the pressure applying mechanism 10A in a way to allow the shoe pressure forces P appearing when the current oscillating position of the workpiece WA assumes both the terminal portions on the oscillating stroke of the workpiece W oscillating in the lateral direction to be set greater than those appearing when the current oscillating position of the workpiece WA assumes the central portion on the oscillating stroke, mere adjustment of the lapping conditions enables the geometrical profile of the target shaped periphery W1 of the workpiece WA to be surface finished in the flat or mid-convex shapes in cross section.
Furthermore, by operating the pressure applying mechanism 10A in a way to allow the lapping film 11 to be held in pressured contact with the target shaped periphery of the workpiece WA, with the pressure force exhibiting the given distribution pattern depending upon the axial direction thereof such that the change rate ΔP, between the shoe pressure force P related to the both terminal portions on the oscillating stroke of the workpiece W oscillating in the lateral direction and the shoe pressure force P related to the central portion on the oscillating stroke of the workpiece W oscillating in the lateral direction when required to surface finish the axially extending geometric profile in the mid-convex shape in cross section, is set to be greater than that required when surface finishing the geometric profile of the target shaped periphery in the flat shape in cross section, the geometrical profile, can be surface finished either in the flat or mid-convex shapes in cross section.
Moreover, due to the presence of the controller that controls the operation of the pressure applying mechanism such that the shoe pressure forces related to both the terminal portions on the oscillating stroke in the lateral direction of oscillating movement becomes smaller than those related to the central portion on the oscillating stroke, merely adjusting the lapping conditions allows the geometrical profile of the target shaped periphery W1 of the workpiece WA to be surface finished in the mid-concave shape in cross section.
In addition, the surface finishing apparatus 1A of the presently filed embodiment achieves to realize a lapping method for controllably surface finishing the geometrical profile of the target shaped periphery W1 of the workpiece WA by detecting a current relative oscillating position of the workpiece WA relative to the lapping film 11 during oscillating movement using the rotary encoder S2, and variably controlling the shoe pressure forces to be applied to the shoes depending on the current oscillating position of the workpiece WA detected by the rotary encoder 52 during lapping operation. As set forth above, an advantageous result resides in that merely adjusting the lapping conditions allows the lapping operation to be carried out to surface finish the geometrical profile of the target shaped periphery W1 of the workpiece WA in a desired shape (flat, mid-convex or mid-concave shapes) in cross section depending upon the axial direction of the workpiece WA.
The modified form shown in
While the presently filed embodiment has been described with reference to a particular structure where the cam lobe portions 61 of the cam shaft 60 or the pin portions 63 of the crankshaft 62 are lapped to obtain the desired geometrical profile along the axial direction of the workpiece WA, the lapping operations may be performed not only for the cam lobes 61 of the cam shaft 60 but also for the journal portions 63 of the crankshaft 62. And, if the occasion demands, the lapping operation may be carried out for circu1ar-arc shaped target peripheries with an incomplete circular shape in cross section, and the present invention may also be applied to the other objective with a target profile in other circular-arc configuration.
In particular, the target shaped periphery of the workpiece is not limited to the pin portions of the crankshaft or the cam lobe portions of the cam shaft, the surface finishing apparatus of the presently filed embodiment may have other applications to a variety of workpieces.
Further, although the presently filed embodiment has been shown and described with reference to the pressure applying mechanism 10A, for adjustably controlling the shoe pressure forces to be applied to the shoes 21A, 21B to allow the lapping film 11 to be held in pressured contact with the target shaped periphery of the workpiece, with the pressure force exhibiting the given distribution pattern depending upon the axial direction thereof, that includes the pressure adjusting units 31A, 31B composed of the workpiece clamp springs 33, the eccentric rotary elements 35A, 35B and the presser motors M4, M4, the pressure applying mechanism 10A may be suitably altered. In particular, a fluid cylinder adapted to be actuated by air under pressure may be employed to allow the shoes 21A, 21B to be pressed such that the abrasive surface of the lapping film 11 is brought into pressured contact with the workpiece WA, with the pressure force exhibiting the given distribution pattern depending upon the axial direction thereof. In such case, air under pressure to be supplied to the fluid cylinder may be adjusted or a direction in which air under pressure is supplied to the fluid cylinder may be switched over through the use of electromagnetic valves for thereby adjusting the pressure distribution pattern in which the shoe pressure forces P are applied to the shoes.
Further, while in the surface finishing apparatus of the presently filed embodiment, the tool shifting mechanism has been shown and described as comprised of the oscillating mechanism 50 that is arranged to oscillate the workpiece support table 49 by which the workpiece W is oscillated in the lateral direction, the tool shifting mechanism may be modified such that the main spindle 41 adapted to support the workpiece WA is oscillated to cyclically shift the workpiece depending upon the axial direction thereof. In another alternative, the tool shifting mechanism may take a structure to directly oscillate the lapping film 11 or to directly oscillate both workpiece W and the lapping film 11. Also, the oscillating mechanism 50 is not limited to the particular structure that employs the eccentric rotary element 51, and the oscillating mechanism 50 may include an ultrasonic oscillator.
While in the surface finishing apparatus of the presently filed embodiment, a structural example has been shown and described wherein the oscillating position of the workpiece W is detected based on the rotational position of the eccentric rotary element 51 detected by the rotary encoder S2, the surface finishing apparatus may take a modified structure in which an optical sensor is employed to directly detect the terminal end of the workpiece W for thereby detecting the oscillating position of the workpiece W.
Moreover, the surface finishing apparatus of the presently filed embodiment has been shown and described in conjunction with an structural example that includes the shoes having engaging surfaces formed in the concave shapes, the present invention may be applied to a case where the distal end of each shoe is formed in a convex-shaped circular-arc profile.
The surface finishing apparatus of the third embodiment differs from the first embodiment in that the surface finishing apparatus of the presently filed embodiment takes the form of a roller burnishing apparatus which allows roller burnishing process to be applied to the workpiece W, which is preliminarily lapped in a surface finish with a mid-concave profile in cross section as shown in
The surface finishing apparatus 100 of the third embodiment contemplates to perform roller burnishing on the sharp edges of both the terminal portions of the mid-concave profile formed in the target shaped periphery, i.e., the pin portion, of the crankshaft W subsequent to preceding lapping operation for thereby flattening the sharp edges on both the terminal portions of the mid-concave profile of the target shaped periphery. In particular, the surface finishing apparatus 100 of the third embodiment operates to roller burnish the sharp edges T1 (see
Referring now to
In actual practice, the workpiece supporting table 102 may includes a slidable table, carrying the headstock and the tail stock, of a machining apparatus such as a lath.
In alternative, the roller burnishing apparatus 100 may further include a tool holder 105′ connected to the pressure source 106, and a tool support 107′ retained by the tool holder 105′ and rotatably supporting a burnishing roller 108′ coaxially aligned with the burnishing roller 108 to be concurrently operated by the pressure source 106. In further alternative, the varnishing rollers 108, 108′ may be formed in a single elongated burnishing roller with an axial length substantially equal to a length of a target shaped periphery (pin portion) of the workpiece W except for the fillet portions Wf. In this alternative, the elongated burnishing roller is held out of abutting engagement with a mid-concave area Wa of the target shaped periphery and concurrently brought into abutting engagement with both the convex areas Wb, Wb of the target shaped periphery, enabling roller burnishing to be performed on both the convex portions Wb, Wb at one time. The use of any one of two structures mentioned above enables the convex portion Wb of the target shaped periphery to be burnish finished, preventing the above-described sags from protruding to the fillet portion Wf.
The pressure source 106 may include a structure similar to the pressure applying mechanism 10 of the first embodiment shown in
Here, by the term “convex portion” is meant the protruding portion Wb that protrudes in a radial direction from a bottom of a mid-concave portion Wa as a result of preceding lapping operation carried on the workpiece W. By the terms “sharp edges ” are meant the sharp projections T1 formed in zigzags in terms of the surface-roughness sectional curve as shown in
In operation, the crankshaft W having the target shaped periphery, preliminarily lapped in a profile with the mid-concave portion Wa and the convex portions Wb, Wb, is set between the headstock and the tail stock (not shown) on the workpiece support table 103, such that the target shaped periphery of the crankshaft W rests on the pair of rollers 103, 103. Then, the pressure source 106 is operated to press the burnishing roller 108 against the surface portion (pin portion) of the crankshaft W, with the pressure force exhibiting the given distribution pattern depending upon the axial direction of the workpece W. Here, the burnishing roller 108 is held in pressured contact with the convex portion Wb of the workpiece W so as to allow the axial direction of the burnishing roller 108 to lie in parallel to the axial direction of the workpiece W. During operation of the pressure source 106, the workpiece W is rotated with the drive mechanism 109 under such a condition. Thus, the sharp edges of the convex portion Wb of the target shaped periphery are crushed and flattened, resulting in an increase in a strength of the target shaped periphery. Accordingly, there is no need for preparing a crankshaft having an undesirably increased diameter or no need for manufacturing a crankshaft in a large size, resulting in miniaturization and light weight in structure of the workpiece.
Since such burnishing operation is not performed over an entire area of the target shaped periphery of the workpiece but merely on the convex portion Wb, a margin for roller burnishing to be performed can be remarkably minimized, realizing burnishing operation in a short period of time.
However, if an excessive degree of roller burnishing is carried out to excessively minimize the surface roughness on the target shaped periphery, a probability occurs where insufficient oil sump is provided in the flattened area of the convex portion Wb and, therefore, it is preferable for the target portion to be roller burnished to an extent where only the sharp edges T1 (see
Test was conducted to burnish a crankshaft using a commercially available hydraulic type ball-point tool (manufactured by ECOROLL Company) as a roller burnish tool. The crankshaft was set between the headstock and the tail stock of a lathe and rotated. First, the crankshaft was grounded in a surface quality of a value less than 0.63 μmRa. Then, the crankshaft was lapped in lapping step (for coarse lapping) of a first stage using a lapping film with an abrasive surface covered with abrasive grains of approximately 30 μm, resulting in the surface quality of a value less than 0.2 μmRa. And, lapping step (for finish lapping) in the second stage was carried out using a lapping film with an abrasive surface covered with abrasive grains of approximately 20 μm, resulting in the surface quality of a value less than 0.1 μmRa.
After finish lapping, roller burnishing was conducted on the resulting crankshaft, but it was hard to flatten the sharp edges of the crankshaft resulting from lapping operation. Because, it was considered that the presence of an arithmetic average roughness on the order of the value less than 0.1 μmRa meant the surface roughness lying at a value of approximately 1 μm and the crankshaft had a fairly good surface roughness with the presence of the small sharp edges, in terms of the surface-roughness sectional curve, which deemed to be densely distributed.
Therefore, lapping operation in the second stage was abolished, and burnishing operation was conducted on the crankshaft resulting from lapping operation in the first stage. Upon such burnishing operation, the sharp edges T1 (see
With the roller burnishing apparatus of the presently filed embodiment, since the workpiece is first subjected to lapping operation to allow the target shaped periphery to be formed in the mid-concave profile and the convex portions on both sides of the mid-concave profile of the workpiece are roller burnished, with the pressure force exhibiting the given distribution pattern depending upon the axial direction of the workpiece to form the flattened surfaces, even in the occurrence of a pressure force applied to the flattened surfaces, on both ends of the pin portion of the workpiece to which an associated component part is held in abutting engagement, an initial quality of surface finish resulting from roller burnishing can be maintained for an extended period of time with a resultant increase in a durability with no occurrence of so-called initial wear.
Further, by roller burnishing the convex portions on both sides of the mid-concave profile of the workpiece, the pin portion of the workpiece can be surface finished in a favorable straightness. Also, due to the presence of compression residual stress applied to the flattened convex portions, on both sides of the mid-concave profile, to which the associated component part is held in abutting engagement, the workpiece has an improved strength, enabling miniaturization and light weight in structure without causing the workpiece to be undesirably formed in a large diameter or in a large size.
Furthermore, since the sharp edges, in terms of the surface-roughness sectional curve, of the pin portion of the workpiece are roller burnished, compression residual stress can be applied to the flattened surfaces in given limited regions in intended depths and, as a result, the workpiece is able to have an improved strength, thereby realizing miniaturization and light weight in structure. Also, the both ends of the pin portion of the workpiece, to which the associated component part is held in abutting engagement, can be formed with oil sumps, resulting in an increase in a durability. Especially, since the roller burnishing is performed on only the convex portions of the pin portion of the workpiece, the roller burnishing can be successfully achieved even without being applied with an extremely high pressure force, and it becomes possible to preclude the sags from occurring on the burnished areas, resulting in surface finish in a favorable straightness.
If a crankshaft having a journal portion or a pin portion with both ends thereof formed with fillet portions is used as the workpiece and the journal portion or the pin portion are lapped followed by roller burnishing, the above described advantages are further enhanced. That is, when mounting a bearing or a connecting rod to the journal portion or the pin portion of the crankshaft as the associated component parts, not only the avoidance of sags described above, increased strength, miniaturization, light weight in structure and the superiority in surface finishing can be further enhanced, but also the concave shaped central portion of the journal portion or the pin portion may serve as an oil sump from which oil is supplied to both the end portions of the finished product with a remarkable improvement in a lubricating property and a durability.
The surface finishing apparatus of the fourth embodiment differs from the third embodiment in that a workpiece WB to be roller burnished includes a target shaped periphery (of a pin portion or a journal portion) Wp formed in a cylindrical outer configuration as a result of preliminary operation such as preliminary machining, heat treatment and grounding, to which an associated component part, such as a connecting rod or a bearing, is mounted and in that a surface finish tool in the form of a burnishing roller is held pressured contact with the target shaped periphery Wp of the workpiece WB in a given pressure distribution pattern along an axial direction of the workpiece WB so as to roller burnish the target cylindrical profile of the workpiece WB in surface finish with a mid-convex profile wherein a central area of the target shaped periphery is larger in diameter than both terminal areas of the target shaped periphery. The same component parts as those of the third embodiment bear like reference numerals to simplify or omit description.
Referring now to
The burnishing roller 118 includes a normal roller having an outer cylindrical shape. The burnishing roller 118 preferably has an axial length R1 slightly larger than an axial length L1 of the target shaped periphery Wp (pin portion) such that both edges of the burnishing roller 118 slightly protrude into fillet portions Wf, Wf formed adjacent the target shaped periphery Wp in the lateral direction. In particular, the axial length R1 of the burnishing roller 118 is sized to be slightly larger than the axial length L1 by an extent that causes no interference with a balancer (not shown) that would move closer to the pin portion Wp of the crankshaft during the maximum inclination of the burnishing roller 118.
The rocking mechanism 122 is comprised of a rocking source 124 fixedly supported by the support bracket 120 and including a piston 124a slidably disposed in a cylinder 124b and a piston rod 124c having a central portion connected to the piston 124, a pair of support members 126, 126 whose upper ends connected to distal ends of the piston rod 124c to be laterally movable depending on the position of the piston 124a, and pinch members 128, 128 fixedly secured to lower ends of the support members 126, 126, respectively, in abutting engagement with the upper end 116a of the tool holder 116 at contact points S, S to translate lateral movements of the support members 126 into rocking movement of the tool holder 116.
In the presently filed embodiment, the rocking source 124 may be preferably of the type that is able to control a rocking angle θ of the tool holder 116 and, to this end, a piston/cylinder mechanism of fluid actuation type is used as the rocking source 124. When controlling the rocking angle θ, a longitudinal length of the cylinder 124b is set to a given length to enable stroke of the piston 124a to be restricted.
The piston/cylinder mechanism forming the rocking source 124 has both ends connected to conduits Pa, Pb through which fluid under pressure is selectively and cyclically supplied to both sides of the cylinder 124b to cause the piston 124a to move to both of left and right positions to allow the support members 126, 126 to move in opposing directions through the piston rods 124c, 124c, respectively, whereby the pinch members 128, 128 rock the tool holder 116 at the angle θ about the center of the pivot shaft 114 through the head 116a of the tool holder 116 for thereby causing the burnishing roller 118 to be cyclically brought into contact with the pin portion Wp of the workpiece W at an inclined angle θ to roller burnish the pin portion Wp in surface finish with the mid-convex profile in a manner as described below in detail.
In actual practice, the rocking angle θ at which the tool holder 116 is caused to rock about the center of the pivot shaft 114 is selected such that though depending on a ratio (A1/A2) between a distance A1, between the contact position S between the pinch member 128 ad the head 116a of the tool holder 116 and the center O of the pivot shaft 114, and a distance A2 between the center O of the pivot shaft 114 and a lower end of the burnishing roller 118, it is suffice for such a dimensional ratio to lie at a value ranging from 1 to 2 and for the rocking angle to lie at a value ranging from 0 to 1 degree. Thus, a stroke of the piston 124a may be determined to fall in an extremely small value.
In operation, a pin portion Wp of a crankshaft WB for use in an automobile is machined and subjected to heat treatment and, then, is grounded to be finished into a straight cylindrical shape between filet portions Wf, Wf. This crankshaft is mounted between the headstock and tail stock (not shown) and set in place with the pin portion Wp being held in abutting contact with the pair of rollers 103, 103.
And, the pressure source 106 is operated to allow the burnishing roller 118 to be brought into pressure engagement with the pin portion Wp against the pair rollers 103, 103. Under such a condition, the drive mechanism 109 is operated to rotate the crankshaft WB and, then, the rocking mechanism 122 is operated to cause the burnishing roller 118 to rock through the tool holder 116 to roller burnish the pin portion Wp.
More particularly, with fluid under pressure being supplied to the conduit Pb of the rocking source 124, the piston 124a of the rocking source 124 moves leftward in the cylinder 124b to cause the support member 126 and the pinch member 128 associated therewith to move leftward through the piston rods 124c, 124c, thereby causing the upper end 116a of the tool holder 116 to rock leftward about the center O of the pivot shaft 114. Since the stroke of the piston 124a is restricted by the cylinder 124b, the rocking angle θ is restricted to a value of approximately 0 to 1 degree. As a result, the burnishing roller 118 supported by the lower bracket portions 116c, 116c of the tool holder 116 to fall in a rocked condition in a right direction.
Accordingly, under such a condition, if the pressure source 106 is operated while causing the pin portion Wp to be rotated by the drive mechanism 109, the burnishing roller 118 is brought into pressured contact with the pin portion Wp at a slightly inclined angle as shown in
In the meanwhile, with fluid under pressure being supplied to the conduit Pa of the rocking source 124, the piston 124a of the rocking source 124 moves rightward in the cylinder 124b to cause the support member 126 and the pinch member 128 associated therewith to move rightward through the piston rods 124c, 124c, thereby causing the upper end 116a of the tool holder 116 to rock rightward about the center O of the pivot shaft 114. As a result, the burnishing roller 118 rock leftward about the center of the pivot shaft 118 and comes to a halt.
Accordingly, under such a condition, if the pressure source 106 is operated while causing the pin portion Wp to be rotated by the drive mechanism 109, the burnishing roller 118 is brought into pressured contact with the pin portion Wp at a slightly inclined angle as shown in
Thus, when burnishing the left and right shoulder portions of the pin portion Wp using the burnishing roller 118 while rocking the burnishing roller 118, even in the presence of the burnishing roller 118 having the outer cylindrical shape extending straight, the outer shape of the burnishing roller 118 under an inclined state is transferred to the pin portion Wp and longitudinal end portions of the pin portion Wp are collapsed at a greater rate than a central portion of the pin portion Wp.
As a result, an outer peripheral profile of the pin portion Wp is entirely shaped in a centrally ridged configuration, that is, a drum shape. Further, as shown in
Especially, upon formation of the pin portion with the centrally ridged profile, when the pin portion Wp is mated with an associated component part in sliding contact, since the pin portion Wp comes to be brought into contact with the associated component part at one contact point in the central area of the pin portion Wp, the pin portion Wp and the associate component part comes to mate with one another in a favorably balanced condition without causing any deviated loading, enabling deviated wear from occurring with a decrease in change of contact surface area for thereby increasing stability in operation for long-term use and a durability.
Further, since formation of the centrally ridged profile on the pin portion Wp enables compression residual stress to be applied to a contact area of the associated component part, with which the pin portion Wp mates, without suffering from any issue of a drop in a circularity due to the sags, a strength of a whole of the pin portion Wp is improved, enabling miniaturization and light weight in structure to be realized with no need for the crankshaft to be undesirably formed in a large diameter or to be sized in a large scale. In addition, the presence of the piston/cylinder mechanism forming the compact rocking source 124 to cause the burnishing roller 118 to be rocked enables the workpiece with the centrally ridged profile to be simply formed even in a limited narrow space, providing a capability of easily achieving burnishing operation for a short period of time followed by reduction in costs.
Furthermore, since the presence of the pin portion Wp with the centrally ridged profile allow the pin portion Wp and the associated component part to be brought into engagement a restricted contact area while enabling a load to be applied to a center of the pin portion Wp in a longitudinal direction thereof, the pin portion Wp is subjected to a stable loading condition at all times, resulting in reduction in wear.
First, a crankshaft was grounded in a surface quality of a value less than 0.63 μmRa and, then, the crankshaft was set between the headstock and the tail stock of a lathe. Next, roller burnishing was carried over the resulting pin portion of the crankshaft using a commercially available hydraulic type ball point tool (made by ECOROLL Company). Roller burnishing was completed at a timing at which a height m shown in
A connecting rod was mounted to the resulting crankshaft subsequent to roller burnishing, and an assembly of the crankshaft and the connecting rod was incorporated into an engine whereupon the engine was operated. Upon conducting tests, it was proved that the resulting crankshaft was found to be favorable and to be free from stress concentration and an issue of a lubricating property.
With the surface finishing apparatus 110 of the presently filed embodiment, since the target shaped periphery of the workpiece is burnished by rocking the cylindrical burnishing roller, that is placed on the target shaped portion along the axis thereof to be pressed, with the pressure force exhibiting the given distribution pattern depending upon the axial direction of the workpiece, the longitudinal terminal portions of the target shaped portion are roller burnished at a greater degree than that roller burnished at the central portion. This results in an improved surface roughness, an increased fatigue strength of dynamically loaded components, an improved surface nature, an improved surface profile, a saved production time and improved fatigue resistance. The target shaped periphery of the workpiece can be formed in the centrally ridged profile with the central area being larger in diameter than both the end portions of the target shaped periphery. Especially, the use of the burnishing roller having the straight cylindrical configuration provides a lower cost in manufacturing than that required when using a high cost burnishing roller and results in significant economic benefits at rather low investment.
Further, in the presence of the workpiece with the target shaped periphery burnished in the centrally ridged profile, the target shaped periphery of the workpiece mates with the associated component element in contact at one central point to allow the relevant component parts to be held in engagement with one another in a favorably balanced condition with no occurrence of deviated loading. This results in no deviated wear and reduction in change in the contact area, enabling an operating stability to be enhanced for long-term use while increasing a durability. Also, since the target shaped portion of the workpiece becomes free from the burrs set forth above and compression residual stress can be applied to the area with which the associated component part is held in engagement, the product has an increased strength.
Additionally, since burnishing operation can be achieved through mere rocking movement of the burnishing roller, it is easy to perform burnishing operation and surface finishing can be carried out in a short time period, providing an advantage in cost in view of work.
Moreover, due to the provision of the tool holder having the central portion pivotally supported on the pivot shaft and the end portion adapted to be rocked by the rocking source at a given rocking angle while enabling the pressure applying mechanism to apply a pressure force to the burnishing roller, the burnishing roller can be subjected to rocking movement and pressured against the target shaped portion of the workpiece in a smooth and easy fashion.
Furthermore, due to an ability of the rocking source to allow the tool holder supporting the burnishing roller to be rocked about the center of the pivot shaft and an ability to adjust the inclined condition of the burnishing roller with respect to the workpiece, the burnishing roller can be inclined with respect to the axis of the workpiece even within a slight space for thereby providing a remarkably improved workability. Also, since the burnishing roller can be brought into pressured contact with the workpiece by the action of the pressure applying mechanism while permitting the burnishing roller to be inclined by the rocking source, the inclined condition and the pressure applying condition for the workpiece can be independently adjusted, enabling the workpiece to be burnished in a profile with a desired, centrally ridged portion in a precise and an extremely easy fashion.
In addition, the provision of the rocking source comprised of the piston/cylinder mechanism enables the tool holder to be rocked in an extremely compact space.
Moreover, upon selection of the workpiece having the journal portion or the pin portion each of which has both ends formed with fillet portions, the spaces of the fillet portions can be utilized for rocking the burnishing roller, providing a further ease of carrying out burnishing operation.
The entire content of a Patent Application No. TOKUGAN 2003-036704 with a filing date of Feb. 14, 2003 in Japan, a Patent Application No. TOKUGAN 2003-034073 with a filing date of Feb. 12, 2003 in Japan, a Patent Application No. TOKUGAN 2003-066592 with a filing date of Mar. 12, 2003 in Japan and a Patent Application No. TOKUGAN 2003-036700 with a filing date of Feb. 14, 2003 in Japan, are respectively hereby incorporated by reference.
Although the invention has been described above by reference to certain embodiments of the invention, the invention is not limited to the embodiments described above. Modifications and variations of the embodiments described above will occur to those skilled in the art, in light of the teachings. The scope of the invention is defined with reference to the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2003-034073 | Feb 2003 | JP | national |
| 2003-036700 | Feb 2003 | JP | national |
| 2003-036704 | Feb 2003 | JP | national |
| 2003-066592 | Mar 2003 | JP | national |
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| Number | Date | Country | |
|---|---|---|---|
| 20040166776 A1 | Aug 2004 | US |
