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The many faces of external broaching.

Unlike internal broaches, which are usually singlepurpose tools, many external broaches can be reused for new applications. in addition, they can be easily adjusted for varying surface dimension and cut depth requirements. Standards can be used for simple cuts, such as flats, double flats, and slots. When specials are required, they usually can be adapted to standard tooling components.

Broaching uses a built-in feed function to make chips. Every tool is composed of groups of tapered roughing/semifinishing/finishing teeth. Each tooth is designed to produce a single chip by cutting slightly deeper than the preceding tooth. The shape of finishing teeth duplicates the final form to be produced.

Maximum cut depth is a function of overall broach length and tooth taper. Even complicated contours can be cut in one stroke; however, very deep cuts may require two or more strokes. Since many teeth are used to make the cut, the workpiece surface finish is usually very fine, and deburring may not be necessary.

The broach is usually just one part of the standard broach tooling package. The broachholder, for example, is required to maintain uniform rigidity throughout the stroke. One holder can accommodate several external broaches; e.g., short broaches, which produce shallow cuts, can be used in long holders by adding spacer bars to fill the gaps.

In addition, standard broach fixtures accept interchangeable workholding details, including various types and sizes of jaws, nests, and clamps configured to the workpiece.

With simple dial-in controls, the external broaching machine allows an operator to program automatic or semiautomatic sequences of uP/ down ram motions interlocked with work clamping/unclamping and table motions. Workpiece unloading, however, may still be manual.

Producing chips

Townsend manufactures printing attachments that add second-color capability to single-color offset duplicators. The equipment uses rollers and shafts of different types and sizes. High precision is a must because micro-adjustments are required to produce accurate registration of colors.

Cuts range from simple flats and slots to complicated contours, mostly on shaft parts. A single 36"-stroke vertical broaching machine from Ty Miles Inc, Westchester, IL, has replaced five milling machines in manufacturing parts.

The following one-stroke broaching applications show how Townsend is using individual standard and special tooling packages to accommodate a variety of part sizes and cut requirements.

Broaching flats

Figure 1 shows a standard Miles vise fixture that Townsend engineers fitted with simple fabricated jaws and outboard supports with adjustable stops. This allows positioning of up to seven different lengths 21.5 " maximum) of ink fountain roller shafts. The standard flat broach, used for all cuts, is shown in foreground.

The broached shaft in the fixture is ready for unloading. The shafts with flats at both ends were broached in separate operations. Cycle time has decreased from 35 min with milling to about 5 sec/cut.

Shaft materials are 416 stainless, plus 12L14 and 11 13 leaded Tellurium. Broached flats are approximately 1/32" deep x 1" long. Flats that are broached at short distances from the ends use the full width of the broach. For flats at the ends of shafts, the broach is easily adjusted to cut shorter lengths. Simple adjustments produce shallow or deep cuts.

An air-over-oil power clamping mechanism is mounted to the top of the fixture. This automatic clamping/unclamping function is interlocked with the broaching machine's up/down ram operation to provide fast, safe reloading.

Straddle flats

Figure 2 shows a standard Miles front-load fixture, used for onestroke broaching of precision tangs on a family of 416 stainless torsion rods. The front-load type is used when workpieces are difficult to load otherwise. Again, a simple fabricated workholding nest attached to the fixture can accommodate all workpieces during a 5-sec cycle.

Straddle broaches with facing teeth are shown in the foreground. Since both cuts are made simultaneously, no other machining method can beat straddle broaching when two or more cuts must maintain a precise dimensional relationship.

Rod lengths from to 21 Y, are accommodated by changing stop positions. All the tang lengths are 1 3/32". Dimension over flats is 0.200". To produce other tang dimensions, broaches can be adjusted closer or farther apart in the holder. Broach holder capacity is the only limitation.

End slotting

Figure 3 shows a standard collet fixture mounted on the broaching machine. A standard slotting broach can be seen at the top, mounted in a holder. The family of form shaft stubs is shown at the right.

Shafts range from 3 1/8 to 4 1/8," long; and up to 1 1/16" dia. A stop is adjusted in the collet to position different stub lengths. Orientation is critical. The 1/16" x 1/16 " Slot must be broached within +/- 1 degree inline with an eccentric hole at the opposite end of the part. Cycle time is 4 sec. This operation replaced an awkward, time-consuming slitting-saw procedure.

The same standard slotting broach was used for all of the parts because slot widths were identical. The flatbroach holder is reused in this application. Simple spacers are fitted on both sides of the slotting broach to provide holder rigidity. Side slotting

Figure 4 shows a 416 stainless oscillator shaft. The deep radiused slots at each end were broached in separate operations, and oriented via a hole drilled in the shaft. Part lengths range from 133/." to 153/.@'. Slots in all shafts are 0.25 " deep x 0. 219 " wide, with a 7/64" radius.

This side-slitting operation required a special broach. All other tooling components were standard. A 36"-stroke broaching machine produced the deep cuts in one stroke; smaller machines might require two strokes.

Contour broaching

Figure 5 shows another standard fixture/special broach setup for one-stroke contouring. The frontload fixture is fitted with workholding details fabricated in our shop to accommodate a family of latch-stop parts. A simple screw-stop is adjusted for different part lengths, ranging from 4 7/8" to 7 1/2". This application requires a special contour broach (foreground). Shape of the tool teeth changes to final form of the contour at the right end. The workpiece material is cold-drawn flat C 10 1 8 steel. Cycle time is 5 sec. (The flat at the opposite end of the part was broached separately, using a standard flat broach.)

Tips

* If your workpieces include unusual shapes, it's probably best to have a specialist design the required broaches. Specials usually can be integrated with standard tooling components; e.g., broach holders, fixtures, and workhandling devices.

* Since a broach stroke can take only a second, the limiting factor in some applications is workhandling. In high-production operations, for example, the objective is to try to match workhandling with ram speed. This can be done by mounting the fixtures on automatic shuttle tables to facilitate faster reloading. In this manner, reloading is done while the broach is returning to its up position.

* When multiple strokes are required to make unusually deep cuts, mount the fixture on an automatic reciprocating infeed table. Then, within a single setup, roughing teeth of the broach take quick, heavy bites, and a final full stroke finishes the cut.

For more information on external broaching equipment, contact Ty Miles Inc, 9855 Derby Lane, Westchester, IL 60153.
COPYRIGHT 1989 Nelson Publishing
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Copyright 1989 Gale, Cengage Learning. All rights reserved.

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Author:Townsend, Don
Publication:Tooling & Production
Date:Jan 1, 1989
Words:1204
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