JPH0818181B2 - Broach for helical internal gear machining - Google Patents

Description

The present invention relates to a broach used for cutting a helical internal gear.

(Prior Art) A broach generally used for cutting a helical internal gear has an outer diameter in which a blade height increases from a tension portion 1 to a rear support portion 2 in a main body 10 as shown in FIG. Direction cutting cylindrical blade portion 3 and, following the blade portion, tooth thickness direction cutting cylindrical blade portion 4
And a finishing cylindrical blade portion 5 are provided. Axis (X-
X), a large number of cutting edges 6, 6a are formed in the outer diameter cutting cylindrical blade portion 3 and the tooth thickness direction cutting cylindrical blade portion 4 along the spline twist angle (β).

As shown in Fig. 4, the conventional helical internal gear machining broach has a predetermined spline helix angle (β) in the longitudinal direction of the cylindrical blade portions 4 and 5 constituting the broach, and the blade height is increased rearward. A large number of blade rows 8 or a large number of blade rows 8a whose blade width gradually increases in the tooth thickness direction are formed, and a large number of blade grooves 7 orthogonal to the axis (XX) of the broach.
A large number of cutting blades 6 are formed in each of the blade rows 8 and 8a (hereinafter referred to as a shaft straight blade groove). Further, a broach similar to that shown in FIG. 2 is used in which the blade groove 7a is twisted at a right angle to the spline twist angle (β) (Japanese Patent Publication No. 46-5669). In this case, β (spline twist angle)
≉α (helix groove helix angle), and in the following, the blade groove 7a is referred to as a tooth straight blade groove.

(Problems to be Solved by the Invention) In recent years, highly accurate internal gears that have been broached have been required, but in the broach having the shaft straight blade groove described above, FIG. "Dog legs" shown in
In many cases, an error referred to as "high-precision gear" cannot be satisfied. In FIG. 6, 11 is a gear to be cut,
E is a read error, and β is a spline twist angle. On the other hand, the broach having the above-mentioned tooth straight blade groove does not always sufficiently improve the gear accuracy.

(Means for Solving the Problem) In a broach for machining a helical internal gear with a spline twist angle β of 19 ° <β ≦ 34 °, a large number of blade groove twist angles α and spline twist angles β intersect in the longitudinal direction. The cutting edge angle δ of each cutting edge of the obtuse flank is 90 ° + (β-19) by forming the cutting edge and limiting the groove helix angle α in the range of 0 ° <α <38 ° -β.゜) × 2 <δ <90 ° +
Set to the range of β, so that the axis of the broach body (X
-X), the working angle θ of the cutting edge is arranged on the side where the resultant cutting force acts in the machining surface direction, that is, the side where the force acts in the direction of escape of the workpiece (hereinafter referred to as the minus side). The present invention relates to a broach for machining a helical internal gear that enables highly accurate machining of a helical internal gear. The reason for limiting the spline helix angle β to 19 ° <β ≤ 34 ° is that the broach for helical internal gear machining is the easiest to process with a straight groove on the shaft, and then the one with a straight groove on the blade. It is easy to process, and the other things including the present invention are the most difficult to process, but the work gear finished with the brooch of the present invention with a spline helix angle β of 19 ° or less is the easiest straight groove for machining. Compared with the work gear finished with the broach, and the work gear finished with the broach of the present invention in which the spline twist angle β exceeds 34 °, the work gear finished next is the broach with straight flutes that are easy to machine. Compared with the cut gear
This is because the superiority in performance of reducing the lead error, which exceeds the difficulty of manufacturing and processing the broach of the present invention, is not seen, and the economical effect of the present invention is small. Here, the inequality between the cutting edge angle δ and the spline twist angle β is δ = 90 ° +
When arranged by the identity β-α, the inequality between the groove groove helix angle α and the spline helix angle β is 0 ° <α <38 ° -β
It is equivalent to making the relationship of. Note that the formula δ =
90 ° + β-α is shown in FIG. The inequality described here is
Originally based on experimental data.

(Operation) The brooch according to the present invention, as shown in FIG.
When the cutting edge angle δ = 90 ° + β-α, the working angle θ is located on the minus side. Where α is the helix angle of the flute, β is the helix angle of the spline, F _{1 is the} main cutting force component, F _{2 is the} cutting back force component, F _{3 is the} F ₁ ,
Resultant force of F _2, phi: Synthesis angle _{^{= tan -1 (F 2 / F}} 1), δ: cutting angle, in F ₁ with respect to the axis X-X, F ₂ working angle of the resultant force θ is
θ = β−φ.

As described above, the working angle θ (θ = β-φ) is on the negative side, that is, the side where the resultant force acts in the direction of the machining surface in which the cutting resultant force acts on the axial center (XX) of the broach body to escape the workpiece. Therefore, the gear accuracy is improved. By the way, FIG. 5 shows the main part of the conventional broach of the tooth straight blade groove, and it is found that the position of the working angle .theta. Is opposite to that of the present invention, that is, the plus side. At this position, the combined cutting force acts to pull the workpiece.

(Example) Blade groove helix angle α is 7.5 °, spline helix angle β is 25
When an internal gear having a helix angle of 25 ° was cut with a broach having a cutting edge angle δ of 107.5 ° and a working angle θ of -2.7 °, the results shown in Table 1 were obtained. As a result, it can be seen that the broach of the present application improves the accuracy of the gear to be cut.

The composite angle φ changes depending on the cutting edge angle δ. Cutting edge angle δ and working angle θ of materials commonly used for automobile internal gears
The relationship is as shown in Table 2.

The present invention is an area in which the numerical values in Table 2 are circled. That is, in the present invention, the spline twist angle β exceeds 19 ° and is 34 ° or less, and the obtuse flank (the cutting edge angle exceeds 90 °). The angle of cutting edge δ on the corresponding side of 90 ° + (β-19 °) ×
The blade groove helix angle α is arranged so that 2 <δ <90 ° + β. Therefore, the working angles θ are all negative, in other words, they are located on the side where the resultant cutting force acts in the machining surface direction with respect to the axis (XX) of the broach body. In Table 2, the area without numerical values is a conventional broach and is the area where gears can be machined with desired accuracy. The area surrounded by triangles is the range where gear accuracy is not obtained. Not subject to the invention.

(Effect) According to the present invention, as described above, a large number of cutting edges are formed in the longitudinal direction of the broach body, and the spline twist angle β is 19 ° <β ≦.
In a 34 ° helical internal gear machining broach, by limiting the blade groove helix angle α to the range of 0 ° <α <38 ° -β, the cutting edge angle δ of each cutting edge of the obtuse flank is 90 ° +
The range of (β-19 °) × 2 <δ <90 ° + β is set, and the working angle θ of the cutting edge is arranged on the side where the resultant cutting force acts in the machining surface direction with respect to the axis (XX) of the broach body. Therefore, it is possible to perform high-precision machining without causing a lead error in a gear to be machined, which is a so-called dog leg, such as a conventional broach.

[Brief description of drawings]

1 is a schematic view of a general broach for processing a helical internal gear, FIG. 2 is a side view of a cylindrical blade portion of the broach of the present invention,
FIG. 3 is an explanatory view of a main part of the present invention, FIG. 4 is a side view of a conventional broach having a shaft straight blade groove, and FIG. 5 is an explanatory view of a main part of a conventional broach having a tooth straight blade groove. , FIG. 6 is a schematic view of a lead error called a dog leg formed on a gear to be cut. 1 ... Brooch body, 6 ... Cutting edge, 6a ... Cutting edge, 7 ...
Blade groove, 7a: Blade groove, α: Blade groove helix angle, β: Spline helix angle, δ: Cutting edge angle, θ: Cutting edge working angle.

Claims (1)

[Claims] 1. In a broach for machining a helical internal gear having a spline helix angle β of 19 ° <β ≦ 34 °, a large number of cutting edges are formed in the longitudinal direction by intersecting the blade groove helix angle α and the spline helix angle β. By forming and forming the blade groove helix angle α in the range of 0 ° <α <38 ° -β, the cutting edge angle δ of each cutting edge of the obtuse flank is 90 ° + (β-19 °) × 2 <
Set within the range of δ <90 ° + β, so that the cutting blade acts on the side where the resultant cutting force acts in the machining surface direction with respect to the axis of the broach body (XX), that is, the side where the force acts in the work escape direction. A broach for machining helical internal gears that enables highly accurate machining of helical internal gears by arranging the angle θ.