Patent Application
20090180862
The present invention relates generally to a VGS turbocharger for use in an automobile engine or the like, and more particularly to a novel method of manufacturing a turbine frame to be incorporated therein for rotatably holding adjustable blades, which method is capable of eliminating a time-consuming cutting operation to the utmost.
A turbocharger is known as a supercharger used as means for improving the power output and the performance of 20 an automobile engine. The turbocharger is an apparatus in which a turbine is driven by the exhaust energy of the engine to rotate a compressor with the power of the turbine, whereby the engine is supercharged to have more air fed into it than fed into it by natural suction. In the case of an engine capable of running at up to a high rotational speed region, when the engine is running at low rotational speeds, the exhaust turbine of the turbocharger hardly functions due to the reduced flow rate of the exhaust gas, so that the engine can not avoid giving a slow-moving feeling until the exhaust turbine runs efficiently, and necessitating a subsequent time or a so-called turbo-lag before the turbine rapidly reaches the full-running state. Furthermore, in the case of a diesel engine which runs inherently at low rotational speeds, there is a disadvantage in that it is difficult to produce an effect of the turbocharger.
Therefore, a VGS turbocharger that works efficiently even when the engine is running at low rotational speeds has been developed. The turbocharger of this type is adapted to obtain a high power output when the engine is running at low rotational speeds by throttling a flow of exhaust gas at a low flow rate with a plurality of adjustable blades (vanes) disposed on an outer periphery of the exhaust turbine to increase the velocity of the exhaust gas and increase work of an exhaust turbine. For this reason, in the VGS turbocharger, an adjusting mechanism for the adjustable blades is required additionally, and it is required that the associated constituting parts be formed to have a complicated shape or the like in comparison with those of the conventional one.
It has been common that, when a turbine frame for rotatably holding adjustable blades in such a VGS turbocharger is manufactured, a metal material (or a shaped material having a starting form for the turbine frame) including a boss portion and a flange portion that are integrally formed is first formed, for example, in accordance with a precision casting method represented by a lost wax casting method, a metal injection molding method or the like, and the shaped material is then suitably subjected to cutting or the like, to thereby finish the turbine frame to have a desired shape and dimensions.
However, in the technique using cutting operations applied to the shaped material, the following problems arise. Since this kind of turbo apparatus is constructed so as to introduce exhaust gas and utilize energy of the exhaust gas, a surface member thereof is naturally exposed to a high-temperature atmosphere of the exhaust gas. Since the exhaust gas contains constituents that can corrode the metal material, a heat resisting stainless steel such as SUS310S having excellent heat resistance, oxidation resistance and the like is also used for the turbine frame. However, since such a material is generally difficult to cut and therefore requires a lot of time to cut it, there is a problem in that a lot of trouble is taken for processing it. Therefore, a problem has arisen in achieving mass production of the turbine frame and exhaust guide and, by extension, VGS turbocharger that cutting operations are eliminated to the utmost from the turbine frame manufacturing process.
Additionally, recent years have seen tighter regulation of exhaust gas emission into the atmosphere particularly from diesel vehicles from a viewpoint of environmental protection and the like. For a diesel engine which inherently runs at low rotational speeds, mass production of a VGS turbocharger capable of improving the engine efficiency from a low rotational speed region has been strongly desired in order to reduce NOx, particulate matter (PM) and the like.
A method of manufacturing a turbine frame for a VGS turbocharger according to a first aspect of the present invention , wherein the turbine frame rotatably holds a plurality of adjustable blades at the outside of an outer periphery of an exhaust turbine wheel, the turbine frame being incorporated in the VGS turbocharger, and wherein exhaust gas discharged from an engine at a relatively low flow rate is suitably throttled by the adjustable blades to increase the velocity of the exhaust gas so that the exhaust turbine wheel is rotated by energy of the exhaust gas and a compressor directly coupled to the exhaust turbine wheel feeds more air into the engine than is fed into it by natural suction, whereby a high output power of the engine is obtained at low rotational speeds, is characterized in that: a blank which is punched out from a metal material having a substantially constant thickness in such a manner as to integrally include a boss forming portion and a flange forming portion is used as a shaped material serving as an original member for the turbine frame; when the shaped material is processed, the boss forming portion is formed into a projecting state by a press forging tool; and receiving holes for rotatably holding the respective adjustable blades are formed in the flange forming portion by punching.
According to the invention, it is possible to obtain a turbine frame as a finished product by press forging a blank (shaped material) blanked to a substantially constant thickness, a cutting operation can be eliminated to the utmost from processing steps of the turbine frame, resulting in mass production of the turbine frame being actually achieved. The conventional turbine frame is extremely difficult to draw or burr by press forging due to the fact that the turbine frame is made of a difficult-to-cut heat resisting material and that it has a relatively large thickness of about 5 mm, so that unavoidable time-consuming cutting operations are required after casting, resulting in the conventional turbine frame being unfit for mass production.
A method of manufacturing a turbine frame for a VGS turbocharger according to a second aspect of the present invention is characterized in that: in addition to the features of the first aspect of the invention, when the shaped material is processed, some or all of the manufacturing processes are carried out in a warm condition.
According to the invention, some or all of the manufacturing processes of the turbine frame are conducted in a warm condition, to thereby improve the degree of freedom for deforming the shaped material and the like, resulting in more efficient processing being performed. The invention also provides a highly accurate turbine frame as a finished product.
A method of manufacturing a turbine frame for a VGS turbocharger according to a third aspect of the invention is characterized in that: in addition to the features of the first or second aspects of the invention, an austenitic heat resisting material is applied to the shaped material; and when the shaped material is processed, either one or both of the shaped material and a processing device are heated depending on an Md30 value which is a strain induced martensitic transformation index of the shaped material.
According to the invention, it is possible to determine the optimal heating temperature based on the Md30 value of the type of material used, to thereby ensure a further efficiency in processing.
A method of manufacturing a turbine frame for a VGS turbocharger according to a fourth aspect of the invention is characterized in that:
in addition to the features of the first or second aspects of the invention, when the shaped material is processed, an appropriate temperature gradient is imparted to the shaped material to be processed.
According to the invention, an appropriate temperature gradient is imparted to the shaped material to be processed, to thereby ensure a more actual use of deep drawing and the like, which has never been hitherto achieved. Such a temperature gradient can also reduce defects such as wrinkles, cracks and local insufficient thickness associated with projection forming (deep drawing).
A method of manufacturing a turbine frame for a VGS turbocharger according to a fifth aspect of the invention is characterized in that: in addition to the features of the first, second, third or fourth aspects of the invention, when the shaped material is processed, a water-soluble heat-resistant lubricant is interposedly disposed at a contact portion between the shaped material and the processing device.
According to the invention, the use of a water-soluble heat-resistant lubricant, for example, in a burring step, can not only ensure the burring to be performed smoothly and reliably, but can also provide improved properties associated with the use of the lubricant such as coatability, dryability, high-temperature lubricity and removability, leading to an extremely high efficiency in manufacture of the turbine frame. Incidentally, ordinary lubricants deteriorate in lubricity as a result of reduced viscosity due to heating, thus making them hardly usable in a high-temperature atmosphere. On the other hand, high-viscosity lubricants such as WS2 and MoS2 are poor in workability and particularly in removability, so that they are unfit for manufacture of the turbine frame in the invention after all.
A method of manufacturing a turbine frame for a VGS turbocharger according to a sixth aspect of the invention is characterized in that: in addition to the features of the first, second, third, fourth or fifth aspects of the invention, the press forging tool includes as its main members a die, a punch and a blank holder; and the punch is subjected to either one or both of low-speed control and inching control in the vicinity of a bottom dead point.
According to the invention, it is possible to form a projection on a difficult-to-machine turbine frame that must have a heat-resistance with added reliability, resulting in the dimensions and shape of the finished product being attained with high accuracy.
A turbine frame according to a seventh aspect of the invention comprises: receiving holes disposed at the outside of an outer periphery of an exhaust turbine wheel, for rotatably holding a plurality of adjustable blades, the turbine frame being incorporated in the VGS turbocharger, wherein exhaust gas discharged from an engine at a relatively low flow rate is suitably throttled by the adjustable blades to increase the velocity of the exhaust gas so that the exhaust turbine wheel is rotated by energy of the exhaust gas and a compressor directly coupled to the exhaust turbine wheel feeds more air into the engine than is fed into it by natural suction, whereby a high output power of the engine is obtained at low rotational speeds; and the turbine frame is characterized in that: the turbine frame is manufactured by the manufacturing method as defined in the first, second, third, fourth, fifth or sixth aspects of the invention.
According to the invention, the turbine frame can be manufactured with minimal time-consuming cutting operations, to thereby enable actual mass production of the turbine frame, ensuring a stable supply of the mass-produced turbine frames to the market. It is also possible to obtain mass-produced turbine frames which are precise ones, for example, by making proper improvements in heating conditions in accordance with the amount of strain induced martensitic transformation of the type of material used.
An exhaust gas guide assembly for a VGS turbocharger according to an eighth aspect of the invention comprises: adjustable blades for suitably adjusting the flow rate of exhaust gas discharged from an engine so as to rotate an exhaust turbine wheel; a turbine frame for rotatably supporting the adjustable blades at the outside of an outer periphery of the exhaust turbine wheel; and an adjusting mechanism for suitably rotating the adjustable blades so as to adjust the flow rate of the exhaust gas; wherein the exhaust gas at a relatively low flow rate is throttled by the adjustable blades to increase the velocity of the exhaust gas so that a high output power is obtained at low rotational speeds; and the exhaust gas guide assembly is characterized in that: a turbine frame according to the seventh aspect of the invention is applied to the turbine frame.
According to the invention, mass production of the exhaust gas guide assembly having a high heat-resistance and high accuracy can be actually achieved.
A VGS turbocharger according to a ninth aspect of the invention is so constructed that an exhaust turbine is driven by exhaust energy of an engine to rotate a compressor coupled to the exhaust turbine with the power of the exhaust turbine, whereby the engine is supercharged to have more air fed into it than is fed into it by natural suction; and the turbocharger is characterized in that: the turbocharger has an exhaust gas guide assembly as defined in claim 8 incorporated therein; whereby flow of the exhaust gas at a relatively low flow rate is suitably throttled to increase the velocity of the exhaust gas so that a high output power is obtained when the engine is running at low rotational speeds.
According to the invention, mass production of the VGS turbocharger having a high heat-resistance can be actually achieved. The turbocharger has a highly accurate turbine frame capable of reliably rotating adjustable blades incorporated therein, to thereby ensure accurate and reliable adjustment of the flow rate of the exhaust gas, allowing the turbocharger to sufficiently withstand use in a high-temperature exhaust gas atmosphere.
a) is a perspective view showing a VGS turbocharger having a turbine frame incorporated therein according to the present invention, and
The present invention will be described hereinbelow with reference to embodiments shown in the drawings. A description will be made of a turbine frame 2 according to the present invention while a description will be given of an exhaust gas guide assembly A for a VGS turbocharger in which the turbine frame 2 is used, followed by a description of a method of manufacturing the turbine frame.
The exhaust gas guide assembly A suitably controls the flow rate of exhaust gas G by throttling the exhaust gas G as necessary while an engine is running at low rotational speeds. The exhaust gas guide assembly, as shown in
First, the adjustable blade 1 will be described. As shown in
The blade portion 11 is formed to have a certain width corresponding mainly to a width of the exhaust turbine wheel T and an airfoil shape in cross-section in a width direction such that the exhaust gas G is effectively directed to the exhaust turbine wheel T. Hereinafter, the width dimension of the blade portion 11 is referred to as “blade height h”.
The shaft portion 12 is formed to be continues to and integrated with the blade portion 11, so that the blade portion 11 serves as a rotation shaft for the blade portion 11 to be moved.
In a portion connecting the blade portion 11 and the shaft portion 12, a taper portion 13 tapering from the shaft portion 12 to the blade portion 11 and a flange portion 14 having a somewhat larger diameter than that of the shaft portion 12 are formed continuously. A bottom face of the flange portion 14 is formed to be almost flush with an end face of the blade portion 11 on the side of the shaft portion 12 of the adjustable blade 1, to thereby ensure a smooth rotation of the adjustable blade 1 through the bottom face serving as a sliding surface in a state where the adjustable blade 1 is fitted to the turbine frame 2. Furthermore, at a distal end of the shaft portion 12, reference planes 15 serving as a basis for mounting of the adjustable blade 1 are formed. These reference planes 15 are a portion fixed by caulking or the like to the blade adjusting mechanism 3. The reference planes 15, as shown in
Next, the turbine frame 2 will be described. The turbine frame 2 is constructed as a frame member for rotatably holding the plurality of adjustable blades 1. The turbine frame 2, as shown in
The holding member 22 is formed to have a disk shape having an opening at the center thereof as shown in
In the illustrated embodiment, the flange portion 23 of the frame segment 21 comprises two flange parts, i.e. a flange part 23A having almost the same diameter as that of the holding member 22 and a flange part 23B having a somewhat larger diameter than that of the holding member 22. These flange parts are formed of a single member. However, in the case where it is too complicated to make the flange parts 23A and 23B by processing the same member, the flange parts 23A and 23B may be constructed in such a manner that two flange parts having different diameters are formed separately and then joined to each other by caulking, brazing or the like.
Here, the wording “method of manufacturing a turbine frame” recited in the title of the present invention substantially refers to the method of manufacturing the frame segment 21. The frame segment 21 uses, as a starting material, a blank which is blanked or punched out from a heat-resistant metal material of a substantially constant thickness so as to integrally include the flange portion 23 and the boss portion 24. The frame segment 21 is obtained as a finished product by subjecting the blank to suitable processing. It is to be noted that a blank that will serve as a staring form for the segment is referred to as a shaped material w (the blank in processing prior to completion is also referred to as the shaped material W).
Next, the blade adjusting mechanism 3 will be described. The blade adjusting mechanism 3 is provided on the outer periphery of the boss portion 24 of the turbine frame 2 to rotate the adjustable blades 1 so as to control the flow rate of the exhaust gas. The blade adjusting mechanism 3, as shown in
In the initial state where the plurality of adjustable blades 1 are attached, in order to align them on the circumference, it is necessary that each of the adjustable blades 1 and a respective one of the driven elements 32 B are attached to form a predetermined angle. In the illustrated embodiment, the reference planes 15 of the adjustable blade 1 mainly perform such an alignment function. Furthermore, in the case where the rotating member 31 is simply fitted into the boss portion 24, it is feared that the engagement of the transmitting member 32 is released when the rotating member 31 slightly moves away from the turbine frame 2. Therefore, in order to prevent this, a ring 33 or the like is provided on the side opposite to the turbine frame 2 such that the rotating member 31 is interposed between the ring 33 and the turbine frame 2, to thereby urge the rotating member 31 toward the turbine frame 2.
By such a structure, when the engine is running at low rotational speeds, the rotating member 31 of the blade adjusting mechanism 3 is rotated as necessary, and the rotation is transmitted to the shaft portions 12 through the transmitting members 32, so that the adjustable blades 1 are rotated as shown in
The exhaust gas guide assembly A using the turbine frame 2 according to the present invention has the basic structure as described above. The method of manufacturing the turbine frame will be described below. It is to be noted that the wording “turbine frame” herein substantially denotes the frame segment 21 as described above. To form the frame segment 21, a blank which is blanked to a substantially constant thickness (shaped material W) is used as a starting material. Appropriate processing is performed on the shaped material W, such as forming the boss portion 24 to be a projection on the shaped material and forming the receiving holes 25 and the pin insertion holes 27, to thereby obtain the frame segment 21 as a finished product. When a distinction is necessary between the flange portion 23 and the boss portion 24 in the shaped material W prior to a finished state and those in the finished state, the formers are respectively referred to as a flange forming portion 23a and a boss forming portion 24a.
This step is intended to prepare a blank (a shaped material W) of a substantially constant thickness which is blanked or punched out so as to obtain the aimed at frame segment 21. Here, the blank having an approximately circular shape in plan view and a thickness of about 5 mm is blanked or punched out from a steel strip or the like. As the material for the shaped material W (blank), heat resisting rolled materials such as SUS304, SUS316, SUS310S, SUH310, SUH660, NCF800H (Incoloy 800H) and Inconel 625 are used. Incidentally, to obtain the shaped material W by casting, that is, when a heat-resistant casting is used as the material for the shaped material W, projection formation on the blank by burring or deep drawing in a later stage is extremely difficult to perform. Therefore, a blank blanked from a heat resisting rolled material is used as the shaped material W in the present invention.
It is to be noted that the blank need not always be prepared by blanking from a plate-shaped material. If a blank blanked into an appropriate shape in advance (commercially available product in particular) is applicable, bringing-in of such a blank may be regarded as the step of preparing the shaped material.
(2) Forming Boss Portion into Projection
Following the preparation of the shaped material W, the boss forming portion 24a is formed to be projected on the shaped material W having a flat plate-like shape. Here, burring, deep drawing or the like is carried out using a press forging die. It is to be noted that, for purposes of distinction herein, the method in which a preparatory hole for burring is first formed in the shaped material W and then the boss forming portion 24a is formed to be in a projecting state is called burring while the method in which a projection of a cup shape is formed on the shaped material W without a preparatory hole being formed is called deep drawing. These methods are collectively called projection forming. Burring and deep drawing will be described below.
To cause the boss forming portion 24a to project by burring, a preparatory hole for burring is formed substantially at the center of the shaped material W first. This preparatory hole is noted by reference number 24b because the hole is formed to correspond to the boss forming portion 24a. A piercing device 6 having a die 61 and a punch 62 as main component members is used, for example, to form a preparatory hole 24b. Naturally, the preparatory hole 24b is formed to have a diameter smaller than an inner diameter of the boss portion 24 in a finished state. As an example, the preparatory hole 24b is formed to have a diameter approximately 70% of the boss portion 24 in the finished state. The shaped material W with the preparatory hole 24b has an approximately donut-shape in plan view as shown in
Thereafter, the shaped material W is formed to have a projection substantially tubular in shape (pipe-shaped) by a burring device 7 so as to expand the preparatory hole 24b. At this time, the burring device 7 includes, as main members, a die 71, a blank holder 72 for holding the flange forming portion 23a that is a peripheral edge portion of the shaped material W such that the flange forming portion 23a is sandwiched therebetween and a punch 73 for pressing out the boss forming portion 24a. The shaped material W is pressed into a substantial forming acting portion 74 formed on the die 71 when pressed by the punch 73. The burring device 7 is provided as appropriate with an opposed punch 75 for pressing the shaped material W from the side opposite to the punch 73. The opposed punch 75 flattens a distal end of the boss forming portion 24a to be on the same plane. It is also possible to provide the opposed punch 75 with a knock-out function to eject the burred shaped material W out of the forming acting portion 74.
A deep drawing device 8 is used to perform deep drawing on the shaped material W having a flat plate-like shape with no preparatory hole 24b so as to form the boss forming portion 24a in a projecting state. The deep drawing device 8 will be described first. The deep drawing device 8 is configured substantially similarly to the burring device 7, for example, as shown in
The shaped material W removed from the deep drawing device 8 is formed to have a so-called bottomed cylinder shape as shown concurrently in
Though the boss forming portion 24a (boss portion 24) is formed to have an appropriate length by burring and deep drawing as described above, it is also possible to form the boss portion 24 to have a desired length, for example, by a multi-stage projection forming step so to speak, that is, by performing ironing on the boss forming portion 24a that has already been formed to be in a projecting state to some extent. In this case, ironing can be conducted by a press forging device similar to the burring device 7 and the deep drawing device 8 mentioned above (illustration omitted).
As the frame segment 21 shown in
At the completion of the aforementioned projection forming, the flange forming portion 23a of the shaped material W has no receiving hole 25 or pin insertion hole 27 formed therein. Such holes are formed as appropriate by piercing or the like, and other portions are formed as necessary into desired shapes or dimensions. It is possible to finish the receiving holes 25 and the like to have a diameter with a desired accuracy by so-called swaging in which a steel ball is pressed into the holes.
When the boss forming portion 24a is formed to be a projection by deep drawing, the receiving holes 25 and the pin insertion holes 27 are concurrently formed at the time a hole is formed in the boss portion 24 in the end.
It is preferred that the receiving holes 25 and the pin insertion holes 27 be made after burring when projection forming is performed by burring. These arrangements are intended to minimize geometric distortion of the shaped material W caused by stress during forming of the preparatory hole 24b and burring (including tensile and compressive stresses caused by processing and thermal stress during heating if any). However, in a case where the receiving holes 25 and other holes are not particularly adversely affected, the receiving holes 25 and the pin insertion holes 27 may be formed concurrently with burring.
In this embodiment, the so-called rigid pressing technique is adopted in which forming is conducted with tool members such as a die and a punch for pressing out the shaped material W (boss forming portion 24a) that are formed by a metal material having an appropriate rigidity, the present invention is not limited thereto. The hydraulic pressing technique may be used in which forming is conducted by directly applying a hydraulic pressure to the shaped material W instead of using the die and the punch. When the shaped material W is formed to have a projection by the hydraulic pressing technique, it is easier to control the applied pressure, pressure application speed and the like as compared with the rigid pressing technique, to thereby prevent wrinkles and the like, resulting in the shaped material W being processed with a higher accuracy.
Thus, processing (plastic working) conducted in the present invention is substantially press forging, and cold forging to which the shaped material W is subjected at room temperature or at a temperature close thereto is preferred among press forging techniques from the viewpoints of cost reduction, simplification of step control and the like. However, for the purpose of providing improved formability or improved degree of freedom for deforming the shaped material W, the shaped material W and the processing devices (hole 20 forming, burring and deep drawing devices 6, 7 and 8) are heated as appropriate in some or all of the processing steps described above. Such embodiments will be described below.
(1) Heating or the like Depending on High-Temperature 5 Strength of Shaped Material
This technique determines the heating temperature and processing speed in accordance with a high-temperature deformation resistance or high-temperature strength of the shaped material W. For example, projection forming on the shaped material w is carried out by press forging in a warm condition where the shaped material W is heated to about 300° C. More specifically, for example, in the case where the high-temperature strength of the shaped material W is 500 MPa or more, the shaped material W is heated to approximately 300 to 350° C. and processed at the speed of 1000 mm/s or more. This reduces the force required for press forging and provides improved formability to the shaped material W, to thereby allow forming to an extent extremely close to the desired shape and dimensions.
In the case where ironing is, for example, conducted following projection forming by press forging, the ironing is performed in a cold condition in a room temperature atmosphere. This minimizes defects such as expansion, contraction, spring-back, excess metal, shrinkage and the like.
In this technique, either one or both of the raw material (shaped material W) and the processing device is heated to 50 to 200° C. in accordance with an Md30 value which is a strain induced martensitic transformation index of the shaped material W. Herein, the term “Md30”, which is typical of austenitic (stainless steel) materials, denotes the temperature at which 50 vol % of an austenitic phase transforms into a ferromagnetic high-strength martensitic phase, when uniaxial tensile stress true strain is imparted to a raw austenite plate, and which indicates that the higher the value, the likelier the raw material is to change into martensite. Md30 is the value predetermined by the composition and micro grain size of the heat resisting material used as the shaped material W.
Thus, the shaped material W is processed under proper heating conditions according to the type of material used, to thereby enhance flow of the metal material of the shaped material W, facilitating not only processing in the heated condition but also processing in later stages. That is, a small amount or several vol % or less of martensite is uniformly transformation distributed while being associated with the dislocation density equivalent to that of austenite, with the result that deformation margin is enhanced during processing in the heated condition and processing in later stages. The assignee of the present invention has confirmed that when this heating technique (heating according to the Md30 value) is used during burring, the bore expansion ratio improves considerably to about 1.5 as compared with about 1.2 in a conventional technique although the value may vary depending on the material used. The term “bore expansion ratio” refers to the value obtained by dividing the limit burring diameter by the diameter of the preparatory hole 24b, which indicates that the larger the value, the larger the deformation margin.
It is preferred that when burring is performed on contact surfaces between the device and the shaped material W during processing, or in the case where, for example, the shaped material W is burred, contact portions between the punch 73 and the inner surface of the boss forming portion 24a be subjected to the so-called bonderizing in which a water-soluble heat-resistant lubricant is interposed to reduce friction therebetween. The bonderizing is a treatment by which a heat-resistant special lubricant is applied or a coating thereof is formed, wherein the lubricant is prepared by adding wax as appropriate to trimethyl borate or phosphate or both thereof and mixing the resultant mixture into an organic solvent or water and the lubricant is applied by direct coating, a roll coater, a drip feed lubricator, pre-reaction treatment or the like. Since ordinary lubricants deteriorate in lubricity as a result of reduced viscosity due to heating, they are hardly usable in a high-temperature atmosphere. Since lubricants of high viscosity such as WS2 and MOS2 are poor in workability and particularly in removability, they are unfit after all. Unlike such lubricants, the aforementioned water-soluble heat-resistant lubricant ensures smooth and reliable projection forming such as burring and provides improved properties associated with use of the lubricant such as coatability, dryability, high-temperature lubricity and removability, whereby the turbine frame 2 can be manufactured more efficiently.
This technique imparts an appropriate temperature gradient to the shaped material W to be processed and will be described here by taking as an example the shaped material W that undergoes deep drawing as shown in
Here, a temperature gradient is imparted to the shaped material W under deep drawing in such a manner that the boss forming portion 24a (center portion) is the low-temperature side and the flange forming portion 23a (peripheral edge portion) is the high-temperature side. For this purpose, the punch 83 comprises appropriate cooling means such as cooling water circulation and is configured so as to bring the bottom portion thereof for pressing the shaped material W into a low-temperature state. The die 81 and the blank holder 82 comprise appropriate heating means such as an electric heater and are configured so as to heat the peripheral edge portion of the shaped material W (held portion). In the embodiment shown in
Further, this embodiment is so configured that the point a of the shaped material W is kept substantially at a constant low temperature and the point e of the shaped material W is heated to an appropriate temperature by controlling the current flowing through the heater or the like. The reason for this is that it is often necessary to heat the point e side of the shaped material W as deep drawing progresses in order to maintain the temperature gradient in the range of about 0.5 to 3° C./mm, due to elongation of the points b to d of the shaped material W during deep drawing. However, in the case where the temperature gradient does not depart from the range of approximately 0.5 to 3° C./mm even when the point e of the shaped material W is maintained constant in a heated condition, it is possible to maintain the current flows through the heater constant during processing.
Though, in this embodiment, the flange forming portion 23a (point e) of the shaped material W is heated and the boss forming portion 24a (point a) is cooled, it is sufficient to only heat the point e in the case where it is possible to obtain the desired temperature gradient which allows the point e to be the high-temperature side without actively cooling the punch 83 so as to provide sufficiently improved formability (deep-drawability). The case in which the punch 83 does not require active cooling is, for example, when the Md30 value which is the strain induced martensitic transformation index of the material is as high as about 20° C. or more.
Here, the following briefly describes the reason why the boss forming portion 24a of the shaped material W is set at a low temperature and the details as to how the assignee acquired the knowledge that a temperature gradient of approximately 0.5 to 3° C./mm would be favorable. In deep drawing, for example, formation of the wall portion (points b to d in
In addition, to satisfy ease of deformation in each of the modes, uniformity therein, enhanced rupture resistance and the like, imparting of a temperature gradient to the wall portion is effective. From various tests conducted in relation to imparting a temperature gradient, the assignee has attained the knowledge. that the proper range thereof is approximately 0.5 to 3° C./mm. The limit drawing ratio data shown in
Further, during deep drawing of the shaped material W, it is possible, for example, to control the stroke speed of the punch 83 to be 1 cm/s or less immediately before the punch reaches the bottom dead point or perform, or in addition to the low-speed control, to perform inching control in which the punch 83 is stopped once when the punch 83 reaches the bottom dead point, resulting in the deep-drawability being further improved.
Though burring and deep drawing a metal plate material and performing such processing in a warm condition have been proposed, these techniques are exclusively used for processing thin stainless steel plates and the like, whereas the techniques have still remained unapplicable to difficult-to-machine heat resisting metal materials, and more particularly to plates of such materials having a relatively large thickness of about 5 mm. However, in this embodiment, it is possible to carry out burring and deep drawing on relatively thick heat-resistant metal materials by various engineering improvements applied thereto including warm processing according to Md30 of the material, bonderizing (coating with a special lubricant), imparting an appropriate temperature gradient to the shaped material W and processing speed control (low speed/inching control of stroke near the bottom dead point of the punch).
Where there is a concern over deterioration in high-temperature wear resistance as a result of use of a heat-resistant rolled material as the shaped material W, it is possible to perform a surface modification by applying a coating such as Cr—C coating (chrome carbide coating) to the surface of the turbine frame 21 (shaped material W) so as to improve high-temperature wear resistance. While Cr-N coating (chrome nitride coating) is also applicable as the surface modification in addition to Cr—C coating, Cr—C coating is preferred in consideration of the working temperature of the turbine frame 21 ranging from about 800 to about 1000° C. because Cr-N coating may decompose or degrade during use.
As for the effects of the present invention, it is possible according to the first or seventh aspects of the invention to carry out all of the processing steps of the frame segment 21 by pressing (forging) including the steps of blanking the blank (shaped material W), forming the boss forming portion 24a into a projection and forming the receiving holes 25, whereby the cutting operations can be eliminated to the utmost from the manufacturing processes, resulting in mass production of the frame segment 21 being actually achieved.
According to the second aspect of the invention, some or all of the manufacturing processes of the turbine frame 2 are carried out in a warm condition, the force required for processing is reduced, to thereby ensure a reduced load imposed on the punch and the die. Processing in a warm condition provides improved formability to the shaped material W, whereby a product (turbine frame 2) which is extremely close to the desired shape and dimensions can be obtained.
According to the third aspect of the invention as, the shaped material W is subjected to projection forming and the like under appropriate temperature conditions in accordance with the amount of strain induced martensitic transformation of the heat-resistant material used, to thereby manufacture the turbine frame 2 with a higher accuracy.
According to the fourth aspect of the invention, for example, in a case of deep drawing of the shaped material W, a temperature gradient is imparted to the shaped material in such a manner that the peripheral edge portion (flange forming portion 23a) thereof is the high-temperature side and the center portion (boss forming portion 24a) thereof is the low-temperature side, so that the deformation resistance of the peripheral edge portion (flange forming portion 23a) decreases through heating and the rupture resistance of the center portion (boss forming portion 24a) through cooling increases, to thereby allow processing under a favorable deep-drawability condition.
According to the fifth aspect of the invention, a water-soluble heat-resistant lubricant is disposed between the shaped material W and the processing device, for example, during burring of the shaped material W, to thereby effectively reduce frictional resistance between the burring device 7 and the shaped material W and provide improved coatability, removability and the like.
According to the sixth aspect of the invention, low-speed or inching control of the punch 63 is performed near the bottom dead point, for example, during deep drawing of the shaped material W, to thereby obtain the turbine frame 2 with a much higher accuracy.
According to the eighth or ninth aspects of the invention, mass production of the exhaust gas guide assembly A and the VGS turbocharger with an excellent heat resistance and a high accuracy can be realized. It is also possible to ensure accurate and reliable adjustment of the flow rate of the exhaust gas G in a high-temperature exhaust gas atmosphere.
As set forth hereinabove, the present invention is suitable to manufacture a turbine frame for rotatably holding adjustable blades in a VGS turbocharger with minimal time-consuming cutting operations, whereby mass production of the turbine frame and, by extension, the VGS turbocharger can be realized.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2001-235746 | Aug 2001 | JP | national |
| 2001-235754 | Aug 2001 | JP | national |
| 2001-235761 | Aug 2001 | JP | national |
This application is a continuation of U.S. application Ser. No. 10/485,687 filed Feb. 3, 2004.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10485687 | Jun 2004 | US |
| Child | 12382287 | US |
