JP7793178B2 - Gear finishing grinding wheel and its manufacturing method - Google Patents

Description

The present invention relates to a gear finishing grinding wheel for honing gears and a method for manufacturing the same.

Patent Document 1 discloses a gear finishing grinding wheel for grinding internal gears. This gear finishing grinding wheel is barrel-shaped and has helical teeth for finishing. This grinding wheel is manufactured and dressed using tools such as internal gear-shaped dressing gears and disk dressers.

Japanese Patent Application Laid-Open No. 2013-230554

The tools, consisting of the dressing gear and disc dresser, are specially designed and prepared for each gear specification of the gear to be machined by the gear finishing wheel. Therefore, manufacturing these tools is time-consuming, and many different types must be prepared to correspond to the gear specifications. This makes it difficult to avoid high costs in manufacturing gear finishing wheels. For this reason, it is not suitable to prepare a small number of different types of gear finishing wheels for test machining, etc.

The gear finishing wheel of the present invention is characterized by having multiple finishing teeth formed by cutting tooth grooves into the peripheral surface of a barrel-shaped substrate containing dispersed abrasive grains using a single blade of a cutter, and by forming crowning in the tooth trace direction on the tooth surface of each of the finishing teeth.

The method for manufacturing a gear finishing wheel of the present invention is characterized in that abrasive grains are dispersed in a substrate, and finishing teeth are formed by cutting tooth grooves into the outer surface of a barrel-shaped workpiece using one edge of a cutter.

In this way, because tooth surface finishing wheels are cut using a single-edged tool such as a milling cutter, there is no need for specially designed internal gear-shaped or overall-shaped tools. In other words, there is no need to machine tools to match the gear specifications. This allows tooth surface finishing wheels to be manufactured inexpensively. In other words, according to the present invention, by attaching a tool such as a milling cutter to the tool shaft of a numerically controlled (NC) machine tool, tooth surface finishing wheels of various sizes and shapes can be manufactured.

The present invention has the advantage of making it possible to easily manufacture barrel-shaped gear finishing wheels without using tools tailored to the gear specifications.

(a) is a perspective view of a gear finishing wheel with helical finishing teeth, (b) is a perspective view of a gear finishing wheel with spur finishing teeth, and (c) is a perspective view of a workpiece before being cut with the gear finishing wheel. FIG. 1A is a front view of a gear finishing grindstone having helical finishing teeth, and FIG. 1B is a front view of a gear finishing grindstone having straight finishing teeth. FIG. 10 is a perspective view showing a state in which the internal gear is being finished by a finishing grindstone. FIG. 1A is a front view showing the helical teeth of a finishing grindstone, and FIG. 1B is a front view showing the straight teeth of the finishing grindstone. FIG. 1A is a front view showing the processed state of the helical teeth, and FIG. 1B is a simplified diagram showing the helix angle of the helical teeth. 1A is a longitudinal cross-sectional view showing an initial state of cutting a helical tooth by a milling cutter, and FIG. 1B is a longitudinal cross-sectional view showing a final state of cutting the helical tooth. FIG. 10 is a cross-sectional view showing the cutting of helical teeth using a fly cutter. FIG. 1A is an explanatory diagram showing the relationship between the milling blade and the helical teeth, and FIGS. 1B to 1D are explanatory diagrams showing the cutting process. 10 is a cross-sectional view showing the process of cutting helical teeth using a milling cutter. (a) is a perspective view showing a naturally crowned tooth; (b) is a perspective view showing a positively crowned tooth. FIG. 4 is an explanatory diagram showing the shape of a finishing tooth having a ridge line.

(Embodiment)
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the present invention will be described with reference to the accompanying drawings.
<Configuration of gear finishing wheels>
First, the structure of the gear finishing wheel will be described.

As shown in Figures 1(a), 1(b), 2(a), and 2(b), a gear finishing wheel (hereinafter referred to as a finishing wheel) 11 has flat surfaces 12 on both ends, and the outer peripheral surface 13 between the flat surfaces 12 is formed in a barrel shape. This outer peripheral surface 13 is a curved surface whose radius of curvature decreases as it approaches the flat surfaces 12. Therefore, the diameter of the finishing wheel 11 decreases toward both ends. A shaft hole 14 is formed between the centers of the flat surfaces 12.

As shown in Figures 1(a) and 2(a), multiple thread-like tooth grooves 15 are engraved on the outer peripheral surface 13 of the finishing grindstone 11. As a result, multiple helical finishing helical teeth 16 are formed at equal intervals on the outer peripheral surface 13, centered on the grindstone axis α.

As shown in FIGS. 1(b) and 2(b), the finishing grindstone 21 has straight teeth 26 as finishing teeth formed by tooth grooves 25 parallel to the grindstone axis α.
The finishing wheels 11 and 21 are constructed by dispersing abrasive grains (not shown) in a polymeric substrate (not shown). The substrate is typically a ceramic material with little elasticity, such as vitrified ceramic. Alternatively, the substrate may be a material with some elasticity, such as urethane resin or a resin mixture of urethane resin and epoxy resin. Furthermore, highly elastic materials such as nitrile rubber are also used. Diamond, CBN (cubic boron nitride), white alundum, and the like are used as abrasive grains.

The helical teeth 16 and straight teeth 26 of the finishing grindstones 11 and 21 have a substantially involute tooth profile. Furthermore, as shown in Figures 4(a) and 4(b), the helical teeth 16 and straight teeth 26 are machined so that the tooth flanks 17 have a crowning shape, as described below. Therefore, the tooth thickness of the helical teeth 16 and straight teeth 26 decreases toward both ends of the axial direction of the finishing grindstones 11 and 21, and the involute tooth profile is shifted toward the negative side.

<How to use gear finishing wheels>
As shown in Figure 3, a finishing grindstone 11 having helical teeth 16 is engaged with the teeth Gr of the internal gear G to be finished, and both are rotated. In this way, slippage occurs between the helical teeth 16 of the finishing grindstone 11 and the teeth Gr of the internal gear G. As a result, the teeth Gr are polished by the abrasive grains of the helical teeth 16, improving the surface roughness. When using a finishing grindstone 21 having straight teeth 26, it is necessary that the teeth Gr of the internal gear G to be polished have helical teeth. Gears that can be finished by the finishing grindstones 11, 21 are not limited to internal gears G, and external gears can also be used.

<Method for manufacturing gear finishing wheels>
Next, a method for manufacturing the finishing grindstone 11 having mainly helical teeth 16 will be described.
In this manufacturing method, a milling cutter 32 having a plurality of milling blades 31 evenly spaced around a central axis, as shown in Figures 5 and 6, is used as a tool. As shown in Figures 8(a) to 8(d), the milling blade 31 has a leading cutting edge 31a and side cutting edges 31b on both sides. This milling cutter 32 is held by a tool shaft (not shown) of a machine tool and rotated at high speed in the direction of arrow P in Figures 6(a), 6(b), 7, and 9 for cutting. Note that Figures 6(a), 6(b), and 9 illustrate the workpiece 20 that will become the finishing grindstone 11 being cut along the tooth trace at the tooth grooves 15, with the milling cutter 32 tilted by a set angle θ1, described below, without cutting.

A workpiece 20 shown in FIG. 1(c) has a polymeric base material with abrasive grains dispersed in it, and is held by its axial hole 14 on the workpiece shaft (not shown) of the machine tool.
In manufacturing the finishing grindstone 11, the workpiece 20 is index-rotated around its own grindstone axis α at equal angular intervals at a pitch equal to the arrangement pitch of the helical teeth 16. Then, at each index position, the workpiece 20 is further rotated for cutting (this is called intra-index position rotation).

At each index position, as shown in Figures 5(a) and 5(b), the rotation surface of the milling cutter 32, which rotates at high speed in the cutting direction, is set at a set angle θ1 relative to the grinding wheel axis α of the workpiece 20. This angle is called the set angle. This set angle θ1 is often within a range of a lower limit of 5 degrees and an upper limit of 60 degrees. In the case of a straight tooth 26, the set angle θ1 is 0 degrees.

That is, as shown in Figures 5 to 7, the milling cutter 32 is moved in the direction of arrow Q shown in Figure 6 while following the curved shape of the outer peripheral surface 13 of the workpiece 20 and maintaining a set angle θ1 in a direction along the grinding wheel axis α of the workpiece 20, cutting a predetermined amount into the outer peripheral surface 13 of the workpiece 20. At this time, as shown in Figure 7, the workpiece 20 rotates within a certain range at the index position around the axis α. As a result, the tooth groove 25 cut by the milling blade 31 becomes a spiral groove 15a with a twist angle θ (see Figure 5(b)) that corresponds to the amount of rotation within the index position relative to the grinding wheel axis α of the workpiece 20.

During this cutting, as shown in Figures 8(a) to 8(d), the workpiece 20 is cut by the leading cutting edge 31a and one side cutting edge 31b of the milling blade 31. In this way, the leading cutting edge 31a and one side cutting edge 31b involved in cutting are called a single edge.

The above-described predetermined cutting is performed multiple times, with the cutting depth of the milling blade 31 increasing each time. In this way, helical helical teeth 16 with a helix angle θ are formed at equal pitch on the outer peripheral surface 13 of the workpiece 20. As shown in Figure 11, the tooth flanks of these helical teeth 16 are composed of multiple continuous flat surfaces 16a that follow an involute shape, with ridgelines 16b formed between the flat surfaces 16a. A tooth flank shape with these flat surfaces 16a and ridgelines 16b is also formed in a similar manner on a straight-tooth finishing grinding wheel 21.

Here, as shown by the solid and two-dot chain lines in Figure 9, the outer peripheral surface 13 of the workpiece 20 has a barrel shape. Therefore, even when the milling cutter 32 moves along the outer peripheral surface 13 of the workpiece 20, the amount of cutting by the milling blade 31 varies in the axial direction of the workpiece 20. Therefore, as shown in Figure 4(a), the solid lines in Figure 10(a), and the two-dot chain lines in Figure 10(b), the helical teeth 16 become continuously thinner at both ends of the tooth trace and are shifted to the negative side. As a result, as shown in Figure 10(a), crowning naturally occurs on the tooth flank 17 of the helical teeth 16. The dot-dash line in Figure 10(a) indicates the crowning curve C. Figures 10(a) and 10(b) show the helical teeth 16 with a shortened tooth trace and a straight tooth shape. Additionally, the two-dot chain line in Figure 10(a) indicates the finishing teeth of the finishing grindstone, which are not barrel-shaped but are imaginary cylindrical.

In this embodiment, as shown by the solid lines in Figures 4(a) and 10(b), the helical teeth 16 are cut so that the thickness of the tooth trace is further reduced at both ends. In other words, a larger amount of crowning is formed, and as shown in Figure 10(b), the curvature of the crowning curve C increases toward both ends of the tooth trace. To achieve this, the rotational speed of the workpiece 20 within the index position can be increased or the feed rate of the milling cutter 32 in the workpiece axial direction can be decreased so that the amount of cutting increases as the milling blade 31 moves toward both ends of the tooth trace of the helical tooth 16. In the case of a finishing grindstone 21 for the straight teeth 26, the workpiece 20 is rotated within the index position at a speed that increases toward both ends of the tooth trace during cutting at both ends of the tooth trace. In this way, crowning is achieved to adjust the tooth surfaces of the helical teeth 16 and spur teeth 26.

The order in which the helical teeth 16 and spur teeth 26 are formed using one blade of the milling cutter 32 may be as follows: After forming one tooth surface of the helical teeth 16 and spur teeth 26 around the entire circumference of the workpiece 20, the other tooth surface is formed using the other blade. Alternatively, one tooth surface on each side may be formed using one blade and then the other blade.

To change the helix angle θ of the helical teeth 16, change the set angle θ1 of the milling cutter 32, and also change the rotation speed within the index position of the workpiece 20 or the feed speed of the milling cutter 32.

When cutting the straight-toothed finishing grindstone 21 shown in Figures 1(b) and 2(b), the set angle θ1 of the milling cutter 32 is set parallel to the grindstone axis α of the workpiece 20 when the workpiece 20 is indexed. Then, the milling cutter 32 is moved along the grindstone axis α.

(Effects of the embodiment)
Therefore, this embodiment has the following advantages.
(1) The gear finishing wheels 11, 21 can be machined using a general milling cutter 32, without using expensive internally toothed or formed tools. In other words, there is no need to prepare tools for each gear specification of the gear finishing wheels 11, 21. This allows the gear finishing wheels 11, 21 to be manufactured at low cost, making them suitable for machining a wide variety of workpieces in small quantities, for example, for test machining.

(2) By adjusting the rotation speed of the workpiece 20 within the index position or the feed speed of the milling cutter 32, the helix angle θ of the tooth trace can be set to any angle.
(3) By adjusting either or both of the rotation speed of the workpiece 20 within the index position and the feed speed of the milling cutter 32, it is possible to obtain helical teeth 16 with a desired helix angle θ.

(4) A crowning curve C with an appropriate curvature can be obtained on the tooth flanks of the helical teeth 16 and straight teeth 26. This allows the finishing teeth to smoothly enter and leave the tooth flank of the gear being finished, improving finishing accuracy.

(Example of change)
The present invention is not limited to the above-described embodiment, and may be embodied in the following forms. The embodiment and the following modified examples may be combined with each other within the scope of technical inconsistency.

As shown by the two-dot chain line in Figure 8(b), the gear finishing wheels 11, 21 can be cut with a single-edged milling blade 31 that has a side edge cutting edge 31b formed on only one side and no cutting edge formed on the other side edge 31c. In this case, two types of milling cutters 32 are prepared, each with a single cutting edge of the milling blade 31 that has a symmetrically opposite shape, and a pair of tooth flanks facing the tooth grooves 15, 25 are cut with a different type of milling cutter 32.

- In the above embodiment, the outer peripheral surface 13 of the gear finishing grindstones 11, 21 is a curved surface whose radius of curvature decreases as it approaches both flat surfaces 12. In contrast, the outer peripheral surface 13 of the gear finishing grindstones 11, 21 can be a curved surface whose radius of curvature does not change, or a curved surface whose radius of curvature increases as it approaches both flat surfaces.

Instead of the milling cutter 32, a cutter made of a grinding wheel can be used to cut the gear finishing wheels 11, 21 using one of its edges.
The set angle θ1 is continuously changed within one index position, and the set angle θ1 is maximized when the milling cutter 32 is cutting both axial ends of the workpiece 20, in other words, the ends in the tooth trace direction. This makes it possible to obtain a tooth flank with a surface shape close to the ideal tooth flank shape calculated by the formula.

Other technical ideas
The technical ideas grasped from the above-described embodiments and modifications are as follows.
(A) A gear finishing grindstone according to claim 1 or 2, wherein the curvature of the outer peripheral surface increases toward both ends.

(B) A method for manufacturing a gear finishing grindstone according to any one of claims 3 to 6, in which, when cutting spiral teeth, the set angle of the milling cutter is increased toward the ends in the tooth trace direction.

DESCRIPTION OF SYMBOLS 11...Gear finishing grinding wheel 13...Outer peripheral surface 15...Tooth space 16...Helical tooth 11...Gear finishing grinding wheel 16...Helical tooth 17...Tooth surface 20...Workpiece 21...Gear finishing grinding wheel 25...Tooth space 26...Straight tooth 31...Milling blade 31a...Tip cutting edge 31b...Side cutting edge 32...Milling cutter Gr...Tooth α...Grinding wheel axis

Claims (5)

A gear finishing wheel having a barrel shape, a plurality of finishing teeth formed by a single edge of a cutter on the peripheral surface of a substrate containing abrasive grains dispersed therein, and a crowning formed in the tooth trace direction on the tooth surface of each of the finishing teeth ,
The cutter is a milling cutter, and the peripheral surface is cut by the leading cutting edge and one side cutting edge of the milling blade of the milling cutter . A gear finishing wheel according to claim 1, wherein the finishing teeth are helical with respect to the wheel axis. Abrasive grains are dispersed in the substrate, and tooth grooves are carved into the outer peripheral surface of the barrel-shaped workpiece by one edge of the cutter, thereby forming finishing teeth ;
The cutter is a milling cutter, and the method for manufacturing a gear finishing grindstone cuts with the tip cutting edge and one side cutting edge of the milling blade of the milling cutter . The method for manufacturing a gear finishing wheel according to claim 3, wherein the tooth grooves are carved by cutting one edge of the cutter into the workpiece multiple times. 5. A method for manufacturing a gear finishing wheel according to claim 3 , wherein the depth of cut of the finishing teeth at both ends in the axial direction of the wheel is increased to form crowned tooth surfaces.