US20140213156A1

US20140213156A1 - Method for modifying plunge shaving cutters

Info

Publication number: US20140213156A1
Application number: US13/751,808
Authority: US
Inventors: Chin-Lung Huang; Shi-Duang Chen; Kuang-Rong Chang
Original assignee: Luren Precision Co Ltd
Current assignee: Luren Precision Co Ltd
Priority date: 2013-01-28
Filing date: 2013-01-28
Publication date: 2014-07-31

Abstract

A method for modifying plunge shaving cutters aims to modify a plunge shaving cutter through a grinding tool. The plunge shaving cutter has a plurality of helical teeth spaced from each other. The helical teeth have a machining-intended side. The method of modification includes the steps of: positioning the plunge shaving cutter on a gear forming grinder with the machining-intended side in contact with the grinding tool; moving the plunge shaving cutter according to a variable rotation amount and a first variable movement amount; moving the grinding tool according to a second variable movement amount to perform a helical movement against the plunge shaving cutter and a modification process on the machining-intended side. Thus the existing gear forming grinder can be applied to the plunge shaving cutter for machining to improve machining speed.

Description

FIELD OF THE INVENTION

The present invention relates to a plunge shaving cutter and particularly to a method for modifying plunge shaving cutters.

BACKGROUND OF THE INVENTION

Gears are fundamental elements for transmission of power and movement, and have the advantages of higher transmission efficiency, longer lifespan, safer, more reliable and the like, hence have become indispensable transmission elements in many machinery products.
Design and manufacture quality of the gears directly affect the performance and quality of machineries. To meet higher quality requirement, the gear surface needs precise machining that mainly can be accomplished by two types of methods, i.e. grinding and shaving. The grinding method can produce greater precision, but the grinding process is time-consuming and also generates a lot of oil smoke and grinding particles, thus is less environmental-friendly and not economic justified. Hence modifying the medium and high precision gears mostly adopts the shaving technique. The shaving cutters can be repeatedly used, and modifying the gear workpieces takes less time than the grinding process, thus offers higher economic benefits.
U.S. Pat. No. 4,831,788 discloses a method and device for shaving tooth flanks of shaving cutters. It adopts a rolling-generation method to shave the tooth flanks of the shaving cutters. But during the shaving process it requires additional steps of installing and disassembling the shaving cutters on the grinder. Japan publication No. JP2005-103749A proposes another shaving method for shaving cutters. It provides a rotary-gear-shaving-cutter grinder which comprises an upright machine pillar, a roller slide bracket movable linearly on the upright machine pillar, a spinning workpiece spindle located on the roller slide bracket, a transmission device to drive spinning of the workpiece spindle and linear movement of the roller slide bracket, a grinding wheel and an actuation device to drive the grinding wheel to rotate. The grinding wheel has a conical second work area to form a tangent contact with the tooth addendum of the rotary gear shaving cutter for grinding in an undulant fashion to get a required crest circle diameter. Thus the crest circle diameter of the rotary gear shaving cutter can be shrunk to a desired dimension.
However, after the shaving cutter has shaved the tooth surfaces of gears for a number of times, its cutting edge in contact with the tooth surfaces is gradually worn off that results in decrease of the tooth profile precision of the gears. Hence the shaving cutter has to be modified. Moreover, the conventional five-axis shaving cutter grinder, such as the model Gleason-Hurth SRS 410 produced by U.S. Gleason Co., adopts dry machining for modifying the shaving cutter. Its machining speed is slower, and the grinder has to be designed according to special grinding requirements of the shaving cutter, hence equipment cost is higher. All these show that there are still rooms for improvement.

SUMMARY OF THE INVENTION

The primary object of the present invention is to solve the problems of wearing off of the cutting edge of a shaving cutter after having shaved the tooth surfaces of gears for a number of times that results in decrease of the tooth profile precision of the gears and dry machining of the conventional five-axis shaving cutter grinder that results in slow machining speed and requiring a specially designed grinder for grinding the shaving cutter to cause higher equipment cost for users.
To achieve the foregoing object, the present invention provides a method for modifying plunge shaving cutters implemented through a gear forming grinder. The gear forming grinder includes a tool stand and a workpiece stand. The tool stand has a machining spindle to drive a grinding tool to spin. The workpiece stand is movable against the tool stand along a first axis and has a workpiece spindle rotating about the first axis. The method comprises the steps as follows:
providing a plunge shaving cutter which includes a plurality of helical teeth spaced from each other;
defining an machining-intended side on the helical teeth;
positioning the plunge shaving cutter on the workpiece spindle with the machining-intended side in contact with the grinding tool; and
spinning the grinding tool and rotating the plunge shaving cutter about the first axis according to a variable rotation amount and moving the plunge shaving cutter along the first axis according to a first variable movement amount at the same time, and moving the grinding tool along a second axis perpendicular to the first axis and the machining spindle according to a second variable movement amount such that the grinding tool moves helically against the plunge shaving cutter to perform a modification process on the machining-intended side.
During the modification process, the ratio of the variable rotation amount and the first variable movement amount is a first variable obtained through calculation of a tooth profile parameter of the plunge shaving cutter, and the ratio of the second variable movement amount and the first variable movement amount is a second variable obtained through calculation of the tooth profile parameter of the plunge shaving cutter.
Thus, the plunge shaving cutter of the invention can rotate about the first axis according to the variable rotation amount and move along the first axis according to the first variable movement amount, and the grinding tool can also move along the second axis according to the second variable movement amount. Such a technique provides at least the following advantages:
1. The grinding tool moves helically against the plunge shaving cutter to perform the modification process on the machining-intended side so that the helical teeth whose tooth profiles have been modified can be used for shaving the teeth of the gears.
2. The variable rotation amount, first variable movement amount and second variable movement amount can be adjusted according to the tooth profile parameter of the plunge shaving cuter, hence the machining amount of the grinding tool to the plunge shaving cutter can be evenly adjusted according to the wearing condition of the plunge shaving cutter. The grinding tool uses wet grinding that can increase grinding speed.
3. The invention uses the existing gear forming grinders, hence no extra equipment cost is required.
4. The invention not only can modify the conventional plunge shaving cutters, also can be used for grinding the new plunge shaving cutters.
The foregoing, as well as additional objects, features and advantages of the invention will be more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an embodiment of the invention.

FIG. 2A is a schematic view showing the modification process according to an embodiment of the invention.

FIG. 2B is another schematic view showing the modification process according to an embodiment of the invention.

FIG. 3A is a schematic view showing a machining-intended side before the modification process according to an embodiment of the invention.

FIG. 3B is a schematic view showing a machining-intended side after the modification process according to an embodiment of the invention.

FIG. 4A is a chart showing a first variable according to an embodiment of the invention.

FIG. 4B is a chart showing a second variable according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Please refer to FIG. 1 for an embodiment of the invention. It provides a method for modifying plunge shaving cutters through a gear forming grinder 1. The gear forming grinder 1 includes a workpiece stand 20 and a tool stand 10. The workpiece stand 20 is movable against the tool stand 10 along a first axis Z and has a workpiece spindle 21 rotating about the first axis Z. The tool stand 10 has a machining spindle 11, an upright movement portion 12, a swing portion 13 and a horizontal movement portion 14. The machining spindle 11 spins about a third axis X perpendicular to the first axis Z to drive a grinding tool 40 to spin. The grinding tool 40 is formed in a disk shape with an outer annular surface 41 (referring to FIG. 2A) and a grinding edge 42 jutting and extending radially (also referring to FIG. 2A). The grinding edge 42 is conical and symmetrical on left and right. The grinding tool 40 can be, but not limit to, an emery wheel. The upright movement portion 12 is coupled with the machining spindle 11 to allow the machining spindle 11 to move along the third axis X. The swing portion 13 is coupled with the upright movement portion 12 to allow the upright movement portion 12 to swing about a second axis Y perpendicular to the first axis Z and third axis X. The horizontal movement portion 14 is coupled with the swing portion 13 to allow the swing portion 13 to move along the second axis Y.
Please refer to FIGS. 2A, 2B, 3A and 3B for an embodiment of the invention in a modification process. The method of modification according to the invention comprises the following steps:
Step 1: providing a plunge shaving cutter 30 which has a front end surface 32, a rear end surface 33, a circumferential surface 34 and a plurality of helical teeth 31. The rear end surface 33 is remote from the front end surface 32. The circumferential surface 34 bridges the front end surface 32 and rear end surface 33. Any two of the helical teeth 31 are spaced by a backlash 35 and the helical teeth 31 are located on the circumferential surface 34. Each helical tooth 31 is extended from the rear end surface 33 to the front end surface 32 along the first axis Z in an oblique manner.
Step 2: defining a machining-intended side 311 and a cutting-intended thickness 313 for the helical teeth 31. The machining-intended side 311 includes a plurality of cutting blades 312 facing and protrusive towards the backlash 35. The cutting blades 312 are arranged along the first axis Z and spaced from each other, and have a greater thickness at positions close to the front end surface 32 and rear end surface 33, thereby form an unmodified thickness 314 decreasing gradually inward from the outer side. The cutting-intended thickness 313 is the thickness to be modified from the unmodified thickness 314 of each cutting blade 312 on the machining-intended side 311.
Step 3: positioning the plunge shaving cutter 30 on the workpiece spindle 21 so that it can be rotated about the first axis Z. The grinding tool 40 is moved via the horizontal movement portion 14, swing portion 13 and upright movement portion 12 to a contact-intended position. The plunge shaving cutter 30 is also moved from the workpiece stand 20 along the first axis Z to the contact-intended position. The grinding tool 40 is moved against the plunge shaving cutter 30 to let the grinding edge 42 of the grinding tool 40 enter the backlash 35 through the front end surface 32 of the plunge shaving cutter 30 to contact with the machining-intended side 311.
Step 4: The workpiece spindle 21 controls the plunge shaving cutter 30 to rotate about the first axis Z according to a variable rotation amount; meanwhile, the workpiece stand 20 moves the plunge shaving cutter 30 along the first axis Z according to a first variable movement amount, and the machining spindle 11 drives the grinding tool 40 to spin, and the horizontal movement portion 14 moves the grinding tool 40 along the second axis Y according to a second variable movement amount, thereby the grinding tool 40 moves helically against the plunge shaving cutter 30 to perform a modification process on the machining-intended side 311, and grinds the cutting blades 312 on the machining-intended side 311. Thus a modified thickness 315 is formed by subtracting the cutting-intended thickness 313 from the unmodified thickness 314, and the modified thickness 315 shrinks gradually inward from the outer side, and is smaller than the unmodified thickness 314.
Also referring to FIGS. 3A and 3B, it is to be noted that before the modification process the junctions of two flanks 316 and top edge 317 of each cutting blade 312 on the machining-intended side 311 have been worn to become a smooth curve after a long duration. In the event that a precise tooth profile modification process is performed at this stage, the precision decreases to affect the quality and performance of the gear.
Hence, before the modification process, a tooth profile parameter related to the plunge shaving cutter 30 has to be set that can include but not limit to the aforesaid cutting-intended thickness 313. During the modification process, the variable rotation amount, first variable movement amount and second variable movement amount are appropriately adjusted through the workpiece spindle 21, workpiece stand 20 and horizontal movement portion 14 according to the set tooth profile parameter of the plunge shaving cutter 30 and grinding tool 40 so that the ratio of the variable rotation amount and first variable movement amount becomes a first variable a as shown in FIG. 4A, and the ratio of the second variable movement amount and the first variable movement amount becomes a second variable b as shown in FIG. 4B. The first variable a and second variable b form a nonlinear cubic curve as an example, but this is not the limitation of the invention. Thus the contact position between the plunge shaving cutter 30 and grinding tool 40 can be adjusted, and the contact angle of the grinding tool 40 against the plunge shaving cutter 30 also can be adjusted via the swing portion 13 to evenly modify the plunge shaving cutter 30 by subtracting the cutting-intended thickness 313 of the cutting blade 312 to form the modified thickness 315 as shown in FIG. 3B. The junction of the top edge 317 and flank 316 of the cutting blade 312 forms a cutting edge 318.
As a conclusion, the plunge shaving cutter of the invention can be rotated about the first axis according to the variable rotation amount and also moved along the first axis according to the first variable movement amount, and the grinding tool can be moved along the second axis according to the second variable movement amount to proceed a helical movement against the plunge shaving cutter to perform the modification process on the machining-intended side, thereby the helical teeth of the plunge shaving cutter can be modified further for a gear shaving operation. Moreover, the variable rotation amount, first variable movement amount and second variable movement amount can be adjusted according to the tooth profile parameter of the plunge shaving cutter to adjust each machining amount evenly of the grinding tool to the plunge shaving cutter according to the wearing condition thereof to reduce error of the modified thickness. In addition, the grinding tool employs wet grinding, hence grinding speed is faster. The invention can be adaptable to the existing gear forming grinder without increasing extra equipment cost, hence it not only can be used for modifying the conventional plunge shaving cutter, also can be used for grinding the new plunge shaving cutters. Thus the invention provides significant improvements over the conventional techniques.
While the preferred embodiments of the invention have been set forth for the purpose of disclosure, they are not the limitation of the invention, modifications of the disclosed embodiments of the invention as well as other embodiments thereof may occur to those skilled in the art. Accordingly, the appended claims are intended to cover all embodiments which do not depart from the spirit and scope of the invention.

Claims

What is claimed is:

1. A method for modifying plunge shaving cutters through a gear forming grinder which includes a tool stand and a workpiece stand movable against the tool stand along a first axis, the tool stand including a machining spindle for driving a grinding tool to spin, the workpiece stand including a workpiece spindle rotating about the first axis, the method comprising the steps of:

providing a plunge shaving cutter which includes a plurality of helical teeth spaced from each other;

defining a machining-intended side of the helical teeth;

positioning the plunge shaving cutter on the workpiece spindle to make the machining-intended side in contact with the grinding tool; and

spinning the grinding tool and rotating the plunge shaving cutter about the first axis according to a variable rotation amount and moving the plunge shaving cutter along the first axis according to a first variable movement amount, and moving the grinding tool along a second axis perpendicular to the first axis and the machining spindle according to a second variable movement amount such that the grinding tool moves helically against the plunge shaving cutter to perform a modification process on the machining-intended side;

wherein during the modification process a ratio of the variable rotation amount and the first variable movement amount is a first variable obtained through calculation of a tooth profile parameter of the plunge shaving cutter, and a ratio of the second variable movement amount and the first variable movement amount is a second variable obtained through calculation of the tooth profile parameter.

2. The method of claim 1, wherein the tooth profile parameter includes a cutting-intended thickness on the machining-intended side.

3. The method of claim 2, wherein the machining-intended side includes a plurality of cutting blades spaced from each other along the first axis, each of the plurality of cutting blades being formed at an unmodified thickness gradually decreasing inward from an outer side before the modification process is performed.

4. The method of claim 3, wherein the machining-intended side includes a plurality of cutting blades spaced from each other along the first axis, each of the plurality of cutting blades being formed at a modified thickness by subtracting the cutting-intended thickness from the unmodified thickness that gradually decreases inward from the outer side after the modification process is finished.

5. The method of claim 1, wherein the machining spindle spins about a third axis perpendicular to the first axis, the tool stand further including an upright movement portion coupled with the machining spindle to move the machining spindle along the third axis.

6. The method of claim 5, wherein the tool stand further includes a swing portion coupled with the upright movement portion to swing the upright movement portion about the second axis.

7. The method of claim 6, wherein the tool stand further includes a horizontal movement portion coupled with the swing portion to move the swing portion along the second axis.