Metal working – Method of mechanical manufacture – Gear making
Patent
1996-01-17
1999-02-09
Echols, P. W.
Metal working
Method of mechanical manufacture
Gear making
298933, B21D 2800
Patent
active
058679014
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION GROUP 3200
The present invention relates to methods for forming bevel gear shafts. In particular, the present invention relates to a method for forming a bevel gear shaft having a desired recess shape, such as an involute spline, in its longitudinal direction.
Known methods for producing bevel gear shafts are useful for a variety of applications. The methods can be applied to the production of drive pinions on limited slip differential gears. For example, referring to FIG. 7 of the present invention, a bevel gear I having an involute spline 2 is utilized as a driving pinion on a limited slip differential gear.
Conventionally, when manufacturing bevel gear shafts, involute spline 2 is produced by a material removal process such as machining. The main disadvantages of material removal processes are low productivity and decreased mechanical strength. Forming involute spline 2 by machining requires 1-5 minutes and the resulting structure has only 75-80% of the mechanical strength of the same structure formed by forging. This lower mechanical strength of machined -vs- forged structures is known to be due to the interruption of the stabilized grain structure by the shearing action of the machining process.
Referring now to FIG. 8, when the involute spline is produced on a bevel gear shaft by conventional forging techniques, a shoulder 4 and an approach angle 5 are required for guiding the blank into the die, for stabilizing it during the punching process, and for drawing the shaft in the bevel gear. Therefore, forging an involute spline on the entire length of the shaft with no shoulder 4 and no approach angle 5, as in FIG. 7., cannot be accomplished with a conventional die forging process.
Referring now to FIG. 9, involute splines 2 can be formed before producing bevel gear portion 3. However, in order to make the involute spline fit smoothly in a gear die, the involute spline is required to be of smaller dimension than gear die. Moreover, in the next step the involute spline is required to be uniformly enlarged. It is impossible to accurately enlarge the spline uniformly. Furthermore, with this process a protruding portion 6 is produced in forming the bevel gear portion, thereby reducing the yield rate.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the present invention to overcome the drawbacks of the prior art by producing a bevel gear formed entirely by forging.
To overcome the drawbacks of the prior art, it is a further object of the present invention to provide a method for forging an involute spline on a bevel gear shaft which shortens manufacturing time, increases yield per unit material, and improves product strength.
In a first embodiment of the first invention there is provided a method for producing a bevel gear shaft. An upward pressure by a lower punch creates a desired bulging portion, such as an involute spline, on a bevel gear which has a bevel gear portion previously formed by a machining or forging process. The preformed bevel gear portion is blocked to prevent damage to the bevel gear while forging the shaft. Thus the involute spline can be produced on the entire length of the bevel gear shaft at a high rate of yield, and in a short period of time.
In a second embodiment of the present invention there is provided a method for producing a bevel gear shaft wherein the upper and lower dies, as a unit, sink downward around a stationary lower punch. The pressure between the lower punch and the workpiece, generated by the sinkage rate of the downward moving upper and lower die unit, creates a desired bulging portion on the shaft of a bevel gear blank. At the same time, the bevel gear portion is also coined. Accordingly, it is possible to recoin the bevel gear portion exactly, even if the bevel gear used as a blank has different dimensions from the final specification. Using this method the involute spline can be accurately produced on the entire length of the bevel gear shaft with a high yield rate and a short manufacturing time.
In both embodiments it is
REFERENCES:
patent: 3780413 (1973-12-01), Burgdorf
Noda Katsunori
Okajima Kazuaki
Echols P. W.
Nichidai Corporation
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