JPS6327127B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for creating cylindrical gears by means of a hob.

A method is known in which a hob and a blank are rotated at a constant rotational speed ratio and the hob is used to create teeth on the periphery of the blank.

The hob center axis is always placed on a plane parallel to the blank rotation center axis at a distance equal to the sum of the rolling pitch cylinder radii of the gears on which the hob is to be created,
Moreover, it is attached so as to always maintain a constant angle with respect to the main plane of the blank. This mounting angle Γ is given by Γ=β−γ...(1) where β is the helical angle on the pitch cylinder of the gear to be generated and γ is the helical advance angle on the pitch cylinder of the hob to be used. It will be done.

In addition, in the area where cutting generation is being performed, the same number of teeth of the hob as the number of teeth to be generated must be encountered within a certain period of time, so Z is the number of teeth of the gear to be generated and Z is the blank rotation speed. When φ, the number of threads of the hob, and the rotation speed are respectively n and ω, it must be as follows: φ/ω=n/Z (2).

In the conventionally known method, the hob is moved in the direction of the blank rotation center axis while being given the above-mentioned position, mounting angle, and rotation speed. That is, the hob and the pitch cylinder of the gear to be generated circumscribe each other at the same angle as the mounting angle Γ, and the hob cuts the blank while moving along one generatrix on the pitch cylinder of the gear to be generated. and create teeth.

When the hob moves a small distance along the above generatrix line, the tooth surface of the hob will be inconsistent with the tooth surface created before the hob moved, so the rotation angle relationship between the hob and the blank can be expressed by the formula ( This is to make corrections to the values determined in 2) so that the correct teeth are created.

In this way, a desired cylindrical gear can be manufactured with extremely high precision, so gear cutting machines based on this method are widely used and widely used.

However, according to research conducted by the present inventors, it has been found that this conventionally known method has several problems.

The first problem is that with this method, the cut starts at the corner between the end face and side face of the blank, and
The same applies to the end of the cut, so the shock associated with cutting is large at the beginning and end of the cut, which limits the cutting speed, and the damage to the hob is severe because the load on the hob is uneven, making it particularly difficult to use a multi-hole hob, which is highly efficient. This was difficult.

Not being able to increase the number of hob holes not only means that machining efficiency cannot be increased, but also that it is not possible to increase the number of hob teeth that are involved in creating one tooth surface.
There were also limits to the accuracy of the tooth surfaces.

Further, in the conventionally known method, relatively small diameter and thick gears can be efficiently cut, but there is a problem in that the gear cutting efficiency of large diameter and thin gears is low.

It is the approach and recess time, that is, the time from time t ₁ when the hob starts contacting the upper end surface of the blank to the time when the correct tooth profile appears on the upper end surface.
The time up to t ₂ and the time from time t ₃ when cutting begins on the bottom edge of the blank to time t ₄ when the correct car shape is finally completed on that edge are accounted for in the total machining time. This is because the weights are significantly different. In other words, for small-diameter, thick gears, this approach time has a low weight and causes few problems, whereas for large-diameter, thin gears, time _t3 arrives earlier, so almost the entire surface of the hob contributes to machining at the same time. death,
This is because the period during which cutting can be performed efficiently is lost.

Further, in the conventionally known method, there was a problem that the cutting load on the cutting edge of the hob was not uniform over the entire length of the hob, and the central part of the hob was particularly damaged due to the high load.

The present invention has been made to solve the above-mentioned problems, and the gist of the present invention is to align the hob not parallel to the blank center axis, but within the main plane of the gear to be created. The purpose is to create teeth while moving parallel to the tangent.

The details of the present invention will be explained below with reference to the drawings.

1 and 2 are a side view and a plan view showing the mutual relationship between a blank processed by the method of the present invention and a hob. In these drawings, the hob and blank are shown as rolling pitch cylinders of gears created with the hob. The figure also shows the hob movement path in the conventional method for reference.

In the figure, 1 is a generated gear, and 2 is a hob.
In addition, the figure shows pitch cylindrical spiral winding lines 1a and 2a, respectively.

The gear 1 to be created has the number of teeth Z, the helix angle β on the pitch cylinder, the thickness W, and the normal pitch P _N , and the hob to be used has the number of teeth n, the normal module m _N , and the helix angle β on the pitch cylinder. The lead angle of the winding wire is γ.

The axial lead l of the hob is given by l = π・n・m _N /cosγ ...(3), and its normal lead l _N is given by l _N = l・cosγ = π・n・m _N ...( 4) is given by. Also, the residual pitch h is given by h=l/2π (5).

Furthermore, between the normal pitch P _N of the gear and the normal lead l _N of the hob, P _N · n = l _N ... (6) holds true.

The rotation angles of the blank and the hob at time t=t are Φ and Ω, respectively, and the hob is at the reference position F=
0, then Φ=φt...(7) Ω=ωt...(8), and equation (2) holds true between φ and ω.

In the method of the present invention, gear cutting is performed by moving the hob 2 from the position 2' to 2'' shown in FIG. (The gear was cut by moving from 20' to 20''.) To simplify the explanation, let's consider the hob and blank as they stop rotating.

Assume that the hob 2 has moved in the above-mentioned direction, the direction indicated by the arrow F in the figure, by a distance F from the reference position.

The amount of movement of the cutting edge due to this movement, measured in the axial direction of the hob, is l′, and the value measured in the direction perpendicular to the hob teeth is
If l′ _N , then l′ _N = l′cosγ = Fcosβ ...(9) ∴l′ = Fcosβ/cosγ ...(10) holds.

If the advance of the teeth corresponding to l' is compensated for by rotating the hob, then the compensation rotation angle θ is determined by h·θ=l′ (11). Here, h is the residual used pitch determined by equation (5).

Therefore, from (10) and (11), θ＝Fcosβ／hcosγ……(12) is obtained.

The direction of θ is determined according to the rotating direction of the hob and blank, the moving direction of the hob, and the helical direction of the hob and teeth to be created.

That is, instead of equation (8), Ω=ωt+θ(F) (13) is used, and the blank and hob are rotated so as to match equations (7) and (13).

In this way, the cutting edge of the hob and the tooth surface of the generated gear can always maintain a correct meshing state even when the hob moves in the F direction, so that the teeth can be generated correctly. It is.

In the method of the present invention, as shown in FIG. 1, a minute portion d _W of a blank having a thickness W is mainly cut by a minute portion d _L of the hob. The cutting load is applied almost uniformly to each part of the hob, and all cutting is performed in a small area centered on the contact point of the rolling pitch cylinder from the start to the end of the cut. Therefore, when using the conventional method, As shown in the figure, the cut is made at the corner of the blank without causing large shocks or vibrations, and there is less wear and tear on the hob.

In addition, in the method of the present invention, in order to process a blank with a thickness of W as shown in FIG.
It is only necessary to have a hob having a length L given by WcosecΓ, and therefore, if the gear is thin, a short hob is sufficient.Moreover, as can be seen from the figure, only a small amount of movement in the F direction is sufficient, so the present invention Thin gears can be efficiently cut regardless of their diameter.

In addition, since the method of the present invention is similar to the tangential feed method using a worm hob, many hob blades act to create one tooth profile, resulting in good finished teeth. Even if the tooth surface is increased, a smooth tooth surface can be obtained.

[Brief explanation of drawings]

1 and 2 are a side view and a plan view showing the mutual relationship between a blank processed by the method of the present invention and a hob. 1...gear to be created, 2...hob.

Claims (1)

[Claims] 1. A hob is rotatably supported on a blank rotatably supported around a predetermined central axis, and the central axis is always aligned with the sum of the pitch cylindrical radius of the hob and the gear to be generated. on a plane parallel to the blank rotation center axis with an equal distance between them, and always maintain a constant angle with the main plane of the blank, and within the main plane of the gear to be created with the gear axis. The blank and the hob are supported so as to be relatively movable in orthogonal directions, and the blank and the hob are rotated at a rotational speed ratio equal to the ratio of the number of teeth of the hob to the number of teeth of the gear to be generated, and the hob rotation angle is The amount of relative movement from the reference point that can be determined arbitrarily is F, the helix angle on the pitch cylinder of the gear to be generated is β, the helical advance angle on the pitch cylinder of the hob is γ, and the registration stop pitch of the hob is h Then, the hob is moved in the above direction while making a correction by the compensation rotation angle θ given by the formula θ=F・cosβ/h・cosγ to create teeth around the blank. Cylindrical gear gear cutting method.