Broach

Details Broach Broach

1986-09-19

1988-04-26

Godici, Nicholas P.

Cutters, for shaping

Rectilinear broach

Including holder having seat for inserted tool

407 18, 407114, 409260, B23D 4304, B23D 3700

Patent

active

047401150

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The invention relates to a surface working broach for working the surfaces of forged cylindrical pins on workpieces, particularly for crankshafts, during rotation of the workpieces.
Customarily, crankpins as well as the major pins and the journal pins of cast or forged crankshafts are worked by rough turning or circular milling with subsequent finish turning and grinding. Roughing of the crankpins as produced by circular milling results in a polygonal surface configuration. To produce a round surface in the individual regions of the pin already at the end of the machining process, it is absolutely necessary to add the turning or grinding process.
The customary use of two different cutting processes to produce crankshaft pins involves considerable expenditures for machinery. To avoid these expenditures, it has already been proposed to effect the machining, particularly of crankshaft pins, by so-called rotary broaching. In this process, the workpiece is caused to rotate about the axis of the pin to be worked as in milling. The broach is then guided tangentially along the pin or pins to be worked. If a plurality of coaxial pins are to be worked on the crankshaft, all pins are worked simultaneously by separate broaches in one broach feed. With this proposed, rotary broaching, processing speeds of about 250 m/min result while conventional broaching at stationary workpieces takes place at speeds between 35 and 45 m/min, depending on the material involved.


SUMMARY OF THE INVENTION

It is an object of the invention to configure a broach of the above-mentioned type so that it is suitable for mass production meeting high precision requirements. This is accomplished by the feature wherein the cutting edges of the broaches are parts of exchangeably fastened cutting elements made of a hard cutting material and, in order to perform a trailing cut, enclose an acute angle with the longitudinal broach axis at least in the roughening section of the broach.
During rotary broaching there exists the additional problem that one cutting edge of the broach must be in cutting engagement with the workpiece over at least one revolution of the latter. This results in a certain minimum chip length which normally cannot be reduced in size. It is here assumed that the cutting edges of the broach perform a trailing cut. This means that the chips are not discharged at a right angle to the cutting edges but that the cutting region on the cutting edge travels during the cutting process from the inner end of a cutting edge in the region of the longitudinal center axis to its outer end, i.e. starting in the center of the groove to be broached and moving toward its outer region. This travel of the chip cutting region and the discharge of the chips in a direction other than at a right angle to the cutting edge makes the arrangement of conventional chip breaking grooves, chip breaking projections or the like at or on the cutting surfaces of the cutting element ineffective.
It is therefore a further object of the invention to give a broach of the above-mentioned type such a configuration that the chip formed by each cutting edge of the broach which extends from the longitudinal center axis to the side edge of the broach is effectively broken at comparatively short intervals and thus the removal of chips is enhanced even in workpiece materials which cause problems with respect to chip formation. This is accomplished by the characterizing features wherein the cutting edges of the broach enclose a bow angle which opens in a direction opposite to their direction of feed and the cutting edges are interrupted between their inner and outer ends. Thus, the chip of a cutting edge performing a trailing cut starts at the longitudinal center axis and moves only to an interruption where it breaks off. The continuation of the cutting edge between the interruption and the outer edge of the broach or a further interruption forms a new, separate chip.
According to the characterizing feature of claim 32, the interruptions are formed

REFERENCES:
patent: 3548474 (1970-12-01), Meyer
patent: 4243347 (1981-01-01), Clapp et al.
patent: 4273479 (1981-06-01), Raupp, Jr. et al.

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