Patent Application
20120264528
This application claims the benefit of Japanese Patent Application No. 2009-294915 filed Dec. 25, 2009 in the Japan Patent Office, the whole disclosure of which is incorporated herein by reference.
The present invention relates to a screw manufacturing method by a thread whirling method, and a whirling cutter and a screw manufacturing machine used in the thread whirling method. Accordingly, the present invention can be applied to a field of manufacturing ordinary screws, such as medical screws, worm screws, metric screw threads, and others.
A conventionally known method of manufacturing ordinary screws (mechanical screws) is, for example, thread rolling. In thread rolling, thread rolling dies corresponding to a specific screw-thread shape are used. Thus, thread rolling is preferred in the case of manufacturing a mass of single products.
Other than thread rolling, a screw manufacturing method by turning is known. In the method by turning, a work piece being rotated is cut by a turning tool. Turning is preferred in the case of manufacturing a wide variety of products in small quantities.
Separately from these screw manufacturing methods, a thread whirling machining is known as a manufacturing method of medical screws such as implant screws and bone screws, for example (see Patent Document 1).
The thread whirling machining is a screw manufacturing method which uses an annular whirling cutter that is fixed to a tool spindle of a lathe and is rotatable around its rotation axis, and a main spindle that holds a rod to be machined (work piece) which is a material for manufacturing a screw and is rotatable.
In detail, the machining method uses a whirling cutter in which a plurality of inserts are radially arranged. A work piece held by the main spindle is inserted into a center through hole of the whirling cutter. Also, the whirling cutter is inclined at a predetermined angle (mount angle) with respect to a center axis of the work piece. In this state, the work piece is moved forward in an axial direction while being rotated in a predetermined direction. At the same time, the whirling cutter is rotated at a rotation speed higher than a rotation speed of the work piece, thereby cutting a thread by one or a plurality of inserts.
The mount angle set upon the above-described thread whirling machining has been generally set equal to a lead angle in a design drawing of a screw.
In case that screws are manufactured by the above-described thread rolling, thread rolling dies corresponding to a specific screw-thread shape are used. Thus, thread rolling is not adequate to manufacturing of a wide variety of products in small quantities.
Also, in case that screws are manufactured by turning, the turning is performed by a turning tool. Due to a cutting load, it is difficult to cut a screw thread in one pass. The screw thread is formed in a plurality of passes. Thus, the machining requires time. Especially in a case of manufacturing a long screw, it is difficult to do the cutting work piece at a time. It is necessary to form the screw thread in a sequential manner of, after forming several threads, forming another several threads, for example. Since the machining includes joining, there is a problem that machining accuracy at a joined part is low.
Further, in the case of medical screws, as compared to screws used in ordinary machines, there are exceptional circumstances such that a difference between a valley diameter and an outer diameter is large, a shape of the screw thread is special (cross-sectional shape is orthogonal to a direction of a series of threads), etc. Thus, upon machining of medical screws, a problem as below exists.
Particularly, as noted above, if a mount angle in thread whirling machining is set equal to a lead angle, it has been difficult to manufacture a screw of a desired shape, depending on a targeted work piece shape (screw-thread shape).
The first reason why it is difficult to obtain the targeted screw-thread shape is because medical screws have special shapes. The second reason is because, since thread whirling machining is a machining method by a milling tool in which inserts are attached toward a center of a whirling cutter and the whirling cutter rotates, moving paths (machining paths) of the inserts interfere with a curved line of a screw. That is, the inserts may shave a portion which should not be ground when going in and out of the work piece.
In other words, the problem is that shaving is performed in both inward and outward cutting (as shown in
However, if the interference occurs to either of the portions on the screw outer diameter side or the screw base end side (valley side), there is not much problem in using the manufactured screw.
The problem due to the above noted interference is significantly exhibited when a screw having a special shape such as a medical screw is manufactured. The same problem may sometimes occur to other ordinary screws.
The present invention was made in view of the above problem. One object of the present invention is to provide a screw manufacturing method by thread whirling machining, and a whirling cutter and a screw manufacturing machine used in thread whirling machining, wherein the problem due to thread rolling and turning can be solved. In the present invention, moving paths of the inserts are inhibited from interfering with a desired curved line of a screw upon both going in and out. Thereby, a targeted curved line of a screw is provided in a preferred manner.
A first aspect of the present invention in order to achieve the above object provides a screw manufacturing method for manufacturing a medical screw. The method uses: an annular cutter member (e.g., whirling cutter) that has a plurality of inserts radially arranged and is rotatable on its rotation axis; and a holding portion (e.g., main spindle) that holds a work piece for forming the medical screw and is rotatable. The cutter member is inclined with respect to an axial center of the work piece at a predetermined angle (mount angle). When a lead angle of the medical screw is different from the mount angle, the mount angle is calculated by formulae (1), (2), (3), (4) and (5) below.
mount angle=tan−1{n×pitch/(π×D1)} (1)
D1={(screw valley diameter+screw outer diameter)/2}+ΔT (2)
screw valley diameter≦D1≦screw outer diameter (3)
{(screw outer diameter−screw valley diameter)/2}×0.2<ΔT<{(screw outer diameter−screw valley diameter)/2} (4)
{(screw outer diameter−screw valley diameter)/2}×0.2<ΔT<−{(screw outer diameter−screw valley diameter)/2}×0.2 (5)
where D1≠0, ΔT≠0, and n indicates a number of threads.
In the screw manufacturing method of the present invention, even if a lead angle of a medical screw, for example, is designed to satisfy a formula (X) below or the medical screw has a special shape specific to medical screws, it becomes difficult for inserts to interfere with the medical screw upon rotating the work piece and the cutter member, as shown in TABLES 1 to 3 of later-explained first to third embodiments.
Particularly, if the mount angle is set smaller (shallower) than the lead angle (i.e., 0<ΔT), it becomes difficult to hit especially a side face of a tip end of the screw thread. Conversely, if the mount angle is set larger (deeper) than the lead angle (i.e., 0>ΔT), it becomes difficult to hit especially to a side face of a base end of the screw thread. Here, ΔT indicates an adjustment range of the mount angle.
Hereinafter, the above-described respective formulae will be explained.
As shown in the above formula (3), a minimum value of D1 is the screw valley diameter, and a maximum value thereof is the screw outer diameter. As shown in the formula (2), when D1=the screw valley diameter, ΔT={(screw valley diameter)−{screw valley diameter+screw outer diameter)/2}. Similarly, when D1=the screw outer diameter, ΔT={(screw outer diameter)−{screw valley diameter+screw outer diameter)/2}. Accordingly, when D1 is equal to the screw valley diameter or the screw outer diameter, the fluctuation range ΔT with respect to {screw valley diameter+screw outer diameter)/2} takes a maximum value (also referred to as a maximum fluctuation range).
Here in D1, explanation will be given on a value of D1 between the minimum value and a pitch diameter, and the value of D1 between the pitch diameter and the maximum value.
By setting the fluctuation to 100% when ΔT=maximum fluctuation range, values of ΔT in fluctuations from 0 to 100% can be calculated. Particularly, when the fluctuation is 50%, ΔT=maximum fluctuation range/2. The values of ΔT determined as such are given to the above formula (2) so that the value of D1 between the minimum value and the pitch diameter, and the value of D1 between the pitch diameter and the maximum value can be determined. By providing the acquired D1 to the above formula (1), the mount angle can be calculated.
Further, as shown in TABLES 1 to 3 of the later-explained first to third embodiments, by setting the range of ΔT to the above formulae (4) and (5), it becomes difficult for the inserts to interfere with the medical screw.
lead angle=tan−1{n×pitch/(n×pitch diameter)} (X)
Here, “n×pitch(P)” is a value called a lead (L), which is a distance of move when the screw is rotated once. The pitch diameter (D) is defined by JIS B0101 1215, the lead angle is defined by JIS B0101 1208, and the pitch is defined by JIS B0101 1206. Other terms also indicate meanings defined by JIS, respectively. Using the pitch diameter in calculation of a lead angle is general to a person skilled in the art (the same applies to below).
According to the present invention, moving paths of the inserts are inhibited from interfering with a desired curved line of a screw upon both going in and out. Thereby, the screw provided with a targeted curved line can be manufactured in a preferred manner.
Particularly, in the present invention, the interference can be inhibited from occurring to both the portions on the outer side of the screw and the base end side (valley side) of the screw. Thus, upon fastening, etc., using the manufactured screw, the screw can be rotated without problem. That is, there is no big problem in using the manufactured screw.
Here, the interference upon going in means the interference when the insert enters the curved line of a screw, and the interference upon going out means the interference when the insert goes out of the curved line of the screw, upon machining the screw.
Also in the present invention, as compared to thread rolling, a wide variety of products in small quantities can be easily manufactured. Moreover, as compared to turning, machining time can be shortened. Also, continuous machining can be applied to one piece of work piece. Thus, a joining process is not necessary. Machining accuracy is advantageously high.
mount angle=tan−1{n×pitch/(n×D1)} (1)
D1={(screw valley diameter+screw outer diameter)/2}+ΔT (2)
screw valley diameter≦D1≦screw outer diameter (3)
{(screw outer diameter−screw valley diameter)/2}×0.2<ΔT<{(screw outer diameter−screw valley diameter)/2} (4)
−{(screw outer diameter−screw valley diameter)/2}<ΔT<−{(screw outer diameter−screw valley diameter)/2}×0.2 (5)
where D1≠0, ΔT≠0, and n indicates a number of threads.
The present invention is an invention of manufacturing a worm screw. The same effect as in the first aspect can be achieved.
Particularly, the screw manufacturing method of the present invention has effect such that it becomes difficult for the inserts to interfere with the worm screw, as shown in TABLES 4 and 5 for later-explained fourth and fifth embodiments, upon rotating the work piece and the cutter member, for example, in order to manufacture the worm screw of which lead angle is designed to satisfy the formula (X) above.
Specifically, in a worm screw having a large difference between a valley diameter and an outer diameter and having a special shape of the screw thread (cross-sectional shape is orthogonal to a direction of a series of threads), use of the screw manufacturing method of the present invention can shorten machining time while maintaining machining accuracy.
mount angle=tan−1{n×pitch/(n×D1)} (1)
D1={(screw valley diameter+screw outer diameter)/2}+ΔT (2)
screw valley diameter≦D1≦screw outer diameter (3)
where D1≠0, ΔT≠0, and n indicates a number of threads.
The present invention is an invention of manufacturing a metric screw thread. The same effect as in the first aspect can be achieved.
Particularly, the screw manufacturing method of the present invention has effect such that it becomes difficult for the inserts to interfere with the metric screw thread, as shown in TABLES 7 to 12 for later-explained sixth to eleventh embodiments, upon rotating the work piece and the cutter member, for example, in order to manufacture the metric screw thread of which lead angle is designed to satisfy the formula (X) above.
Also, as is clear from the later-explained embodiments, if the lead angle in a design drawing of the metric screw thread falls below 7°, the interference is not necessarily heavy upon going in and going out even if the fluctuation is 0%. Depending on a level of inspection, the manufactured screw may be accepted. However, if the lead angle exceeds 7°, the interference becomes heavy upon going in and going out when the fluctuation is 0%. Thus, it is preferable to set the mount angle to conform to the above formulae (1), (2) and (3).
in case ΔT>0,
{(screw outer diameter−screw valley diameter)/2}×0.6≦ΔT≦{(screw outer diameter−screw valley diameter)/2} (6)
in case ΔT<0,
−{(screw outer diameter−screw valley diameter)/2}≦ΔT≦{(screw outer diameter−screw valley diameter)/2}×0.6 (7)
By setting as above, as is clear from later-described TABLES 1 to 12, the interference upon both going in and out between the curved line of the screw and the moving paths of the inserts can be further reduced.
By setting as above, as is clear from the later-described TABLES 1 to 12, the interference upon going in or going out between the curved line of the screw and the moving paths of the inserts can be null.
mount angle=tan−1{n×pitch/(n×D1)} (1)
D1={(screw valley diameter+screw outer diameter)/2}+ΔT (2)
screw valley diameter≦D1≦screw outer diameter (3)
in case ΔT>0,
{(screw outer diameter−screw valley diameter)/2}×0.2<ΔT<{(screw outer diameter−screw valley diameter)/2} (4)
in case ΔT<0,
−{(screw outer diameter−screw valley diameter)/2}<ΔT<−{(screw outer diameter−screw valley diameter)/2}×0.2 (5)
where D1≠0, ΔT≠0, and n indicates a number of threads.
Even if a lead angle of the medical screw, for example, is designed to satisfy the formula (X) above or the medical screw has a special shape specific to medical screws, as in the first aspect, when the medical screw is manufactured using the whirling cutter of the present invention, it becomes difficult for the inserts to interfere with the medical screw upon rotating the work piece and the whirling cutter.
Particularly, if the mount angle is set smaller (shallower) than the lead angle (i.e., 0<ΔT), it becomes difficult to hit especially a side face of a tip end of the screw thread. Conversely, if the mount angle is set larger (deeper) than the lead angle (i.e., 0>ΔT), it becomes difficult to hit especially to a side face of a base end of the screw thread.
Accordingly, when a medical screw is manufactured using the whirling cutter of the present invention, moving paths of the inserts are inhibited from interfering with a desired curved line of the screw upon both going in and out. Thereby, the screw provided with a targeted curved line can be manufactured in a preferred manner.
Also in the present invention, as compared to thread rolling, a wide variety of products in small quantities can be easily manufactured. Moreover, as compared to turning, machining time can be shortened. Also, continuous machining can be applied to one piece of work piece. Thus, a joining process is not necessary. Machining accuracy is advantageously high.
mount angle=tan−1{n×pitch/(π×D1)} (1)
D1={(screw valley diameter+screw outer diameter)/2}+ΔT (2)
screw valley diameter≦D1≦screw outer diameter (3)
in case ΔT>0,
{(screw outer diameter−screw valley diameter)/2}×0.2<ΔT<{(screw outer diameter−screw valley diameter)/2} (4)
in case ΔT<0,
−{(screw outer diameter−screw valley diameter)/2}<ΔT<−{(screw outer diameter−screw valley diameter)/2}×0.2 (5)
where D1≠0, ΔT≠0, and n indicates a number of threads.
The present invention is an invention of a whirling cutter that manufactures a worm screw. The same effect as in the sixth aspect can be achieved.
Particularly, use of the whirling cutter of the present invention has effect such that it becomes difficult for the inserts to interfere with the worm screw, upon rotating the work piece and the whirling cutter, in case that a lead angle of the worm screw, for example, is designed to satisfy the formula (X) above.
mount angle=tan−1{n×pitch/(π×D1)} (1)
D1={(screw valley diameter+screw outer diameter)/2}+ΔT (2)
screw valley diameter≦D1≦screw outer diameter (3)
where D1≠0, ΔT≠0, and n indicates a number of threads.
The present invention is an invention of a whirling cutter that manufactures a metric screw thread. The same effect as in the sixth aspect can be achieved.
Particularly, use of the whirling cutter of the present invention has effect such that it becomes difficult for the inserts to interfere with the metric screw thread, upon rotating the work piece and the whirling cutter, in case that a lead angle of the metric screw thread, for example, is designed to satisfy the formula (X) above.
mount angle=tan−1{n×pitch/(π×D1)} (1)
D1={(screw valley diameter+screw outer diameter)/2}+ΔT (2)
screw valley diameter≦D1≦screw outer diameter (3)
in case ΔT>0,
{(screw outer diameter−screw valley diameter)/2}×0.2<ΔT<{(screw outer diameter−screw valley diameter)/2} (4)
in case ΔT<0,
−{(screw outer diameter−screw valley diameter)/2}<ΔT<−{(screw outer diameter−screw valley diameter)/2}×0.2 (5)
where D1≠0, ΔT≠0, and n indicates a number of threads.
When a medical screw is manufactured using the screw manufacturing machine of the present invention, in the same manner as in the first aspect, for example, even if the lead angle of the medical screw is designed to satisfy a formula (X) above or the medical screw has a special shape specific to medical screws, it becomes difficult for inserts to interfere with the medical screw upon rotating the work piece and the whirling cutter.
Particularly, if the mount angle is made smaller (shallower) than the lead angle (i.e., 0<ΔT), it becomes difficult to hit especially a side face of a tip end of the screw thread. Conversely, if the mount angle is made larger (deeper) than the lead angle (i.e., 0>ΔT), it becomes difficult to hit especially to a side face of a base end of the screw thread.
Accordingly, when a medical screw is manufactured using the screw manufacturing machine of the present invention, moving paths of the inserts are inhibited from interfering with a desired curved line of the screw upon both going in and out. Thereby, the screw provided with a targeted curved line can be manufactured in a preferred manner.
Also in the present invention, as compared to thread rolling, a wide variety of products in small quantities can be easily manufactured. Moreover, as compared to turning, machining time can be shortened. Also, continuous machining can be applied to one piece of work piece. Thus, a joining process is not necessary. Machining accuracy is advantageously high.
mount angle=tan−1{n×pitch/(π×D1)} (1)
D1={(screw valley diameter+screw outer diameter)/2}+ΔT (2)
screw valley diameter≦D1≦screw outer diameter (3)
in case ΔT>0,
{(screw outer diameter−screw valley diameter)/2}×0.2<ΔT<{(screw outer diameter−screw valley diameter)/2} (4)
in case ΔT<0,
−{(screw outer diameter−screw valley diameter)/2}<ΔT<−{(screw outer diameter−screw valley diameter)/2}×0.2 (5)
where D1≠0, ΔT≠0, and n indicates a number of threads.
The present invention is an invention of a screw manufacturing machine that manufactures a worm screw. The same effect as in the ninth aspect can be achieved.
Particularly, use of the screw manufacturing machine of the present invention has effect such that it becomes difficult for the inserts to interfere with the worm screw, upon rotating the work piece and the whirling cutter, in case that a lead angle of the worm screw, for example, is designed to satisfy the formula (X) above.
mount angle=tan−1{n×pitch/(π×D1)} (1)
D1={(screw valley diameter+screw outer diameter)/2}+ΔT (2)
screw valley diameter≦D1≦screw outer diameter (3)
where D1≠0, ΔT≠0, and n indicates a number of threads.
The present invention is an invention of a screw manufacturing machine that manufactures a metric screw thread. The same effect as in the ninth aspect can be achieved.
Particularly, use of the screw manufacturing machine of the present invention has effect such that it becomes difficult for the inserts to interfere with the metric screw thread, upon rotating the work piece and the whirling cutter, in case that a lead angle of the metric screw thread, for example, is designed to satisfy the formula (X) above.
Here, screws subject to the present invention include ordinary mechanical screws and medical screws. The present invention is a manufacturing method which is preferred to manufacture screws especially having special shapes such as medical screws.
Examples of the ordinary mechanical screws include various screws defined in JIS, e.g., metric screw threads, worm screws, unified threads, trapezoidal threads, buttress threads, and others.
The medical screws mean screws (implants) used inside bodies of humans and animals.
Examples of cases where the interference between the screw and the inserts becomes large in a medical screw include cases where: its pitch is larger than that of an ordinary mechanical screw (e.g., equal to or larger than 2.0 mm); a number of thread is larger than that of a single-threaded screw, e.g., double-threaded screw; a screw is deep threaded (a difference between an outer diameter and a valley diameter is large, e.g., equal to or larger than 2.0 mm); and a lead angle of a target screw is large (e.g., equal to or larger than 15°).
Hereinafter, embodiments of the present invention will be described together with the accompanying drawings.
a) First, an outline will be provided on a manufacturing method of a medical screw by a thread whirling method.
As shown in
The whirling cutter 9 is an annular device which is rotated by a not shown tool spindle. As shown in
Each of the inserts 13 is secured to the cutter head 11 by a fixation screw 15. A machine that includes the main spindle 7 and the whirling cutter 9 and manufactures the screw 1 by the thread whirling method is referred to as a screw manufacturing machine 10.
For example, when the screw 1, as shown in
First, as shown in
Next, the work piece 3 is inserted to a through hole 17 in a center of the whirling cutter 9. Also, the whirling cutter 9 is inclined at a predetermine angle (mount angle β) with respect to a center axis of the work piece 3. In this state, the work piece 3 is forwarded at a predetermined speed to its axial direction (upward direction in
In detail, as shown in
The medical screw 1 to be manufactured in the present embodiment is a single-threaded screw. Here, in order to prepare a single-threaded screw, the insert 13 having one-ridged cutting portion 19 as shown in
b) Next, how to set the mount angle β will be described.
The mount angle β is determined by a shape of the screw 1 to be prepared.
Thus, first of all, as shown in
For example, typical data which specify the shape of the screw 1 is as below. Other than below, there are data for specifying a three-dimensional surface shape (curve) of the screw portion 5. Here, the numerical data of the screw 1 to be prepared by the inserts 13 are shown.
Whole screw length in axial direction: 50.0 mm
Screw portion length in axial direction: 30.0 mm
Screw outer diameter: φ6.0 mm
Screw valley diameter: φ4.0 mm
Pitch: 5.0 mm
Thread lead angle: 17.66°
The mount angle β is different from the lead angle of the screw 1. That is, D1 in the above formula (1) is different from a pitch diameter of the above formula (X).
c) Next, an example of the method of manufacturing the screw 1 using thread whirling machining will be described.
Here, a case of preparing the screw 1 having the aforementioned measurements will be described.
As shown in
The mount angle β is calculated using formulae (1), (2), (3), (4) and (5) below. Here, the mount angle β is an angle at which the whirling cutter 9 is inclined with respect to the center axis of the work piece 3 upon thread whirling machining.
mount angle=tan−{n×pitch/(π×D1)} (1)
D1={(screw valley diameter+screw outer diameter)/2}+ΔT (2)
screw valley diameter≦D1≦screw outer diameter (3)
in case ΔT>0,
{(screw outer diameter−screw valley diameter)/2}×0.2<ΔT<{(screw outer diameter−screw valley diameter)/2} (4)
in case ΔT<0,
−{(screw outer diameter−screw valley diameter)/2}<ΔT<−{(screw outer diameter−screw valley diameter)/2}×0.2 (5)
where D1 (mm)≠0, ΔT (mm)≠0, and n indicates a number of threads.
As for the work piece 3, a cylindrical rod made of titanium alloy was used which has a length of 2.5 m×an outer diameter of 0.0 mm.
Then, according to machining conditions below, the screw 1 having a target shape shown in
Main spindle rotation speed: 10 rpm
Work piece forward speed: 2.75 mm/rev
Tool spindle rotation speed: 2000 rpm
As shown in TABLE 1 below, the screw 1 was prepared by changing D1 to change the mount angle β. At that time, presence/absence of interference (interference between a curved line of the screw 1 and moving paths of the inserts 13) was studied. In detail, a simulation was conducted by a known CAD. Also, the screw 1 was actually prepared to check a state of interference.
As for the CAD, a three-dimensional CAD USG NX4 was used.
The result is shown in the TABLE 1 and
In the above TABLE 1, “Fluctuation” indicates a proportion of fluctuation (in case that a maximum fluctuation range of 1.00 is set to be 100%) in D1 from an intermediate value (D1=5.00: ΔT=0). “Revised fluctuation” indicates a value obtained by converting the fluctuation of 200% to 100%. “Fluctuation range” indicates a range of actual fluctuation (corresponding to the above ΔT) from D1=5.00.
In the result of Determination, “⊚” indicates that “interference upon either going in or out is completely avoided so that a targeted screw-thread shape can be substantially obtained”. “◯” indicates that “interference upon either going in or out is not completely avoided, but machining to an extent not to be called a shape defect can be performed. “A” indicates that “interference upon either going in or out is frequent, but products can be accepted depending on the inspection level”. “X” indicates that “interference upon both going in and out is frequent, and only the products determined to have a shape defect can be produced”.
Here, the “targeted screw-thread shape” is not only an ideal screw-thread shape which follows a screw curved line, but also a screw-thread shape in which interference can be caused only in either of portions on a screw outer diameter side or on a screw base end side (valley side).
Further, in
As is clear from TABLE 1 and
Particularly, for example, as shown in
Accordingly, it is understood that the screw 1 having a smaller interference (or no interference) either upon going in or out can be obtained.
Moreover, as is clear from comparison between
Also, as is clear from
e) As noted above, in the present embodiment, by setting values of the mount angle β to be different from the lead angle, the screw 1 in the shape which reduces interference between the moving paths of the inserts 13 and the curved line of the screw 1 upon going in or out can be obtained in a preferred manner. Further, since interference does not necessarily occur to both the portions of the screw outer diameter side and the screw base end side (valley side), there is no problem in use of the manufactured screw 1.
That is, in the present embodiment, since interference can be avoided from occurring to both the portions on the screw outer diameter side and the screw base end side (valley side), the screw 1 can be rotated without problem when fastening, etc. is performed using the manufactured screw 1.
In detail, as is clear from the above TABLE 1, interference between the curved line of the screw 1 and the moving paths of the inserts 13 upon going in or out can be all the more reduced by setting as below.
in case ΔT>0,
{(screw outer diameter−screw valley diameter)/2}×0.6≦ΔT≦{(screw outer diameter−screw valley diameter)/2}
in case ΔT<0,
−{(screw outer diameter−screw valley diameter)/2}ΔT≦−{(screw outer diameter−screw valley diameter)/2}×0.6
The above “(screw outer diameter−screw valley diameter)” indicates the maximum fluctuation range. For example, if the fluctuation is +60% (revised fluctuation=+30%), ΔT={(screw outer diameter−screw valley diameter)×0.3}.
Specifically, by setting D1 upon calculating the mount angle β to the screw outer diameter (+100% fluctuation) or the screw valley diameter (−100% fluctuation), no interference between the moving paths of the inserts 13 and the curved line of the screw 1 occurs upon either going in or out.
Also, even the screw 1 having a special shape such as a medical screw can be advantageously prepared by a single process, and not by processes including a plurality of passes.
Now, a second embodiment will be described. Descriptions of the same contents as those in the above first embodiment will not be repeated.
A medical screw to be manufactured in the present embodiment is a double-threaded screw. As shown in
In the present embodiment, an example of typical data which specify the shape of the screw is as below.
Whole screw length in axial direction: 50.0 mm
Screw portion length in axial direction: 30.0 mm
Screw outer diameter: φ4.0 mm
Screw valley diameter: φ2.4 mm
Pitch: 3.42 mm
Thread lead angle: 18.79°
The mount angle β is calculated using the formulae (1), (2), (3), (4) and (5) in the above first embodiment.
As shown in TABLE 2 below, the screw was prepared by changing D1 to change the mount angle. At that time, presence/absence of interference was studied. The result is shown in the TABLE 2 and
Meanings of words in TABLE 2 and meanings of colors (thickness) in
As is clear from TABLE 2 and
Accordingly, in the present embodiment, the same effect as in the first embodiment is achieved.
Also in the insert 21 for the double-threaded screw, its cutting surface is larger in its width direction as compared to its height direction, in order to form a double-threaded screw portion at once, than that the insert for the single-threaded screw. Since interference is easy to occur between the insert 21 and the screw portion, it is not easy to form a desired screw thread. However, the manufacturing method according to the present embodiment allows easy preparation of a screw having a desired shape.
Further, a double-threaded screw can be advantageously prepared by a single process, and not by processes including a plurality of passes.
Now, a third embodiment will be described. Descriptions of the same contents as those in the above second embodiment will not be repeated.
A screw to be manufactured in the present embodiment is a double-threaded medical screw 31, as shown in
In the present embodiment, an example of typical data which specify the shape of the screw is as below.
Whole screw length in axial direction: 30 mm
Screw portion length in axial direction: 20 mm
Screw outer diameter: φ5.5 mm
Screw valley diameter: φ4.0 mm
Intermediate value of screw: φ4.75 mm
Pitch: 5.35 mm
Thread lead angle: 19.72°
The mount angle β is calculated using the formulae (1), (2), (3), (4) and (5) in the above first embodiment.
As shown in TABLE 3 below, the screw was prepared by changing D1 to change the mount angle. At that time, presence/absence of interference was studied. The result is shown in the TABLE 3 and
Meanings of words in TABLE 3 and meanings of colors (thickness) in
As is clear from TABLE 13 and
Accordingly, in the present embodiment, the same effect as in the second embodiment is achieved. In this way, the effect of the present invention can be achieved regardless of designs such as an outer diameter/valley diameter of a screw.
Now, a fourth embodiment will be described. Descriptions of the same contents as those in the above first embodiment will not be repeated.
A screw to be manufactured in the present embodiment is a double-threaded worm screw (JIS B1723/3) 35, as shown in
In the present embodiment, an example of typical data which specify the shape of the screw is as below. Unit of length in
Whole screw length in axial direction: 11 mm
Screw portion length in axial direction: 10 mm
Screw outer diameter: φ6 mm
Intermediate value of screw: φ5.125 mm
Screw valley diameter: φ4.25 mm
Pitch: 2.872 mm
Thread lead angle: 10.1141°
The mount angle β is calculated using the formulae (1), (2), (3), (4) and (5) in the above first embodiment.
As shown in TABLE 4 below, the screw was prepared by changing D1 to change the mount angle. At that time, presence/absence of interference was studied. The result is shown in the TABLE 4 and
Meanings of words in TABLE 4 and meanings of colors (thickness) in
As is clear from TABLE 4 and
Accordingly, in the present embodiment, the same effect as in the first embodiment is achieved even with the ordinary double-threaded worm screw 35.
Now, a fifth embodiment will be described. Descriptions of the same contents as those in the above first embodiment will not be repeated.
A screw to be manufactured in the present embodiment is a triple-threaded worm screw (JIS B1723/3) 41, as shown in
In the present embodiment, an example of typical data which specify the shape of the screw is as below. Unit of length in
Whole screw length in axial direction: 12 mm
Screw portion length in axial direction: 12 mm
Screw outer diameter: φ7 mm
Intermediate value of screw: 6.000 mm
Screw valley diameter: φ5.000 mm
Pitch: 4.867 mm
Thread lead angle: 14° 28′ 39″
The mount angle β is calculated using the formulae (1), (2), (3), (4) and (5) in the above first embodiment.
As shown in TABLE 5 below, the screw was prepared by changing D1 to change the mount angle. At that time, presence/absence of interference was studied. The result is shown in the TABLE 5 and
Meanings of words in TABLE 5 and meanings of colors (thickness) in
As is clear from TABLE 5 and
Accordingly, in the present embodiment, the same effect as in the first embodiment is achieved even with the ordinary triple-threaded worm screw 41.
Now, a sixth embodiment will be described. Descriptions of the same contents as those in the above first embodiment will not be repeated.
Screws to be manufactured in the present embodiment are ordinary single-threaded metric screw threads 51 and 53, as shown in
The screw 51 is an external screw and the screw 53 is an internal screw. In these metric screw threads 51 and 53, a relation among its pitch (p), fundamental triangle height (H), and others in case that an outer diameter of the screws is φ5 mm, for example, is defined as shown in TABLE 6 below.
Although not shown, inserts used in a thread whirling method by which the metric screw threads 51 and 53 are manufactured include a one-ridged cutting portion.
In the present embodiment, an example of typical data which specify the shape of the screw (e.g., the metric screw thread 51 as an external screw) is as below.
Whole screw length in axial direction: 15 mm
Screw portion length in axial direction: 10 mm
Screw outer diameter: φ5 mm
Intermediate value of screw: φ4.567 mm
Screw valley diameter: φ4.134 mm
Pitch: 0.8 mm
Thread lead angle: 3.19°
The mount angle β is calculated using formulae (1), (2) and (3) below.
mount angle=tan−1{n×pitch/(n×D1)} (1)
D1={(screw valley diameter+screw outer diameter)/2}+ΔT (2)
screw valley diameter≦D1≦screw outer diameter (3)
As shown in TABLE 7 below, the screw was prepared by changing D1 to change the mount angle. At that time, presence/absence of interference was studied. The result is shown in the TABLE 7 and
Meanings of words in TABLE 7 and meanings of colors (thickness) in
As is clear from TABLE 7 and
Accordingly, in the present embodiment, even in the ordinary metric screw thread 51, the screw 51 which is shaped to reduce the interference between the moving paths of the inserts and a curved line of the screw 51 upon going in and out can be obtained in a preferred manner by setting different values to the mount angle β and the lead angle. Further, since the interference is not caused on both portions on the outer side of the screw and the base end side (valley side) of the screw, there is no problem in using the manufactured screw 51. To sum up, in the present embodiment, the interference can be inhibited from occurring to both the portions on the outer side of the screw and the base end side (valley side) of the screw. Thus, upon fastening, etc., using the manufactured screw 51, the screw 51 can be rotated without problem.
Now, a seventh embodiment will be described. Descriptions of the same contents as those in the above sixth embodiment will not be repeated.
A screw to be manufactured in the present embodiment is an ordinary single-threaded metric screw thread (external screw), as in the sixth embodiment, which is not shown. Especially, while its outer diameter is φ5 mm which is the same, its pitch is larger, i.e., 1.0 mm.
Although not shown, inserts used in a thread whirling method by which the metric screw thread is manufactured include a one-ridged cutting portion.
In the present embodiment, an example of typical data which specify the shape of the metric screw thread is as below.
Whole screw length in axial direction: 15 mm
Screw portion length in axial direction: 10 mm
Screw outer diameter: φ5 mm
Intermediate value of screw: φ4.459 mm
Screw valley diameter: φ3.917 mm
Pitch: 1.0 mm
Thread lead angle: 4.08°
The mount angle β is calculated using the formulae (1), (2), and (3) in the above sixth embodiment.
As shown in TABLE 8 below, the screw was prepared by changing D1 to change the mount angle. At that time, presence/absence of interference was studied. The result is shown in the TABLE 8 and
Meanings of words in TABLE 8 and meanings of colors (thickness) in
As is clear from TABLE 8 and
Accordingly, the present embodiment achieves the same effect as the sixth embodiment.
Now, an eighth embodiment will be described. Descriptions of the same contents as those in the above sixth embodiment will not be repeated.
A screw to be manufactured in the present embodiment is an ordinary single-threaded metric screw thread (external screw), as in the sixth embodiment, which is not shown. Especially, while its outer diameter is φ5 mm which is the same, its pitch is larger, i.e., 1.25 mm.
Although not shown, inserts used in a thread whirling method by which the metric screw thread is manufactured include a one-ridged cutting portion.
In the present embodiment, an example of typical data which specify the shape of the metric screw thread is as below.
Whole screw length in axial direction: 15 mm
Screw portion length in axial direction: 10 mm
Screw outer diameter: φ5 mm
Intermediate value of screw: φ4.323 mm
Screw valley diameter: φ3.647 mm
Pitch: 1.25 mm
Thread lead angle: 5.26°
The mount angle β is calculated using the formulae (1), (2), and (3) in the above sixth embodiment.
As shown in TABLE 9 below, the screw was prepared by changing D1 to change the mount angle. At that time, presence/absence of interference was studied. The result is shown in the TABLE 9 and
Meanings of words in TABLE 9 and meanings of colors (thickness) in
As is clear from TABLE 9 and
Accordingly, the present embodiment achieves the same effect as the sixth embodiment.
Now, a ninth embodiment will be described. Descriptions of the same contents as those in the above sixth embodiment will not be repeated.
A screw to be manufactured in the present embodiment is an ordinary single-threaded metric screw thread (external screw), as in the sixth embodiment, which is not shown. Especially, while its outer diameter is φ5 mm which is the same, its pitch is larger, i.e., 1.5 mm.
Although not shown, inserts used in a thread whirling method by which the metric screw thread is manufactured include a one-ridged cutting portion.
In the present embodiment, an example of typical data which specify the shape of the metric screw thread is as below.
Whole screw length in axial direction: 15 mm
Screw portion length in axial direction: 10 mm
Screw outer diameter: φ5 mm
Intermediate value of screw: φ4.188 mm
Screw valley diameter: φ3.376 mm
Pitch: 1.5 mm
Thread lead angle: 6.5°
The mount angle β is calculated using the formulae (1), (2), and (3) in the above sixth embodiment.
As shown in TABLE 10 below, the screw was prepared by changing D1 to change the mount angle. At that time, presence/absence of interference was studied. The result is shown in the TABLE 10 and
Meanings of words in TABLE 10 and meanings of colors (thickness) in
As is clear from TABLE 10 and
Accordingly, the present embodiment achieves the same effect as the sixth embodiment.
Now, a tenth embodiment will be described. Descriptions of the same contents as those in the above sixth embodiment will not be repeated.
A screw to be manufactured in the present embodiment is an ordinary single-threaded metric screw thread (external screw), as in the sixth embodiment, which is not shown. Especially, while its outer diameter is φ5 mm which is the same, its pitch is larger, i.e., 1.75 mm.
Although not shown, inserts used in a thread whirling method by which the metric screw thread is manufactured include a one-ridged cutting portion.
In the present embodiment, an example of typical data which specify the shape of the metric screw thread is as below.
Whole screw length in axial direction: 15 mm
Screw portion length in axial direction: 10 mm
Screw outer diameter: φ5 mm
Intermediate value of screw: φ4.053 mm
Screw valley diameter: φ3.105 mm
Pitch: 1.75 mm
Thread lead angle: 7.83°
The mount angle β is calculated using the formulae (1), (2), and (3) in the above sixth embodiment.
As shown in TABLE 11 below, the screw was prepared by changing D1 to change the mount angle. At that time, presence/absence of interference was studied. The result is shown in the TABLE 11 and
Meanings of words in TABLE 11 and meanings of colors (thickness) in
As is clear from TABLE 11 and
Accordingly, the present embodiment achieves the same effect as the sixth embodiment.
Now, an eleventh embodiment will be described. Descriptions of the same contents as those in the above sixth embodiment will not be repeated.
A screw to be manufactured in the present embodiment is an ordinary single-threaded metric screw thread (external screw) as in the above sixth embodiment, which is not shown. Especially, while its outer diameter is φ5 mm which is the same, its pitch is larger, i.e., 2 mm.
Although not shown, inserts used in a thread whirling method by which the metric screw thread is manufactured include a one-ridged cutting portion.
In the present embodiment, an example of typical data which specify the shape of the metric screw thread is as below.
Whole screw length in axial direction: 15 mm
Screw portion length in axial direction: 10 mm
Screw outer diameter: φ5 mm
Intermediate value of screw: φ3.917 mm
Screw valley diameter: 2.835 mm
Pitch: 2 mm
Thread lead angle: 9.23°
The mount angle β is calculated using the formulae (1), (2), and (3) in the above first embodiment.
As shown in TABLE 12 below, the screw was prepared by changing D1 to change the mount angle. At that time, presence/absence of interference was studied. The result is shown in the TABLE 12 and
Meanings of terms in TABLE 12 and of colors (thickness) in
As is clear from TABLE 12 and
Thus, the present embodiment achieves the same effect as the sixth embodiment.
Accordingly, as is clear from the sixth to the eleventh embodiments, the same effect as in the first embodiment is achieved in ordinary metric screw threads.
The embodiments of the present invention have been described in the above. However, the present invention should not be limited to the above described embodiments, and may be practiced in various forms within the technical scope of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-294915 | Dec 2009 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2010/073442 | 12/24/2010 | WO | 00 | 6/25/2012 |
