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Toolholders enhance flexible machines.

In 1986, when talks first began between HR Krueger Machine Tool Inc, Farmington, MI, and a major American automotive manufacturer, engineers set a goal to build a piece of equipment capable of machining aluminum alternator housings, processing multiple parts, and performing multiple operations on a number of parts with varying configurations while holding critical tolerances.

"The only way the expenditure could be justified was to build a single machine capable of machining all of the configurations," says Bruce Chapin, tooling engineer at HR Krueger. The 14-station machine drills, bores, mills, reams, and taps eight different part configurations in 10 sec per part. The machine has hole-size tolerances of 0.002" and positional tolerances of 0.0035".

Housing variety

Alternator housings come in eight different configurations and two different bore sizes. There are similarities between the eight configurations, but typically more than half of the machining parameters must be altered to accommodate the running of a new part. Sometimes this means changing the size of the drill, but in most cases it's a matter of changing drill locations. Holes are drilled in sizes ranging from .177" to 0.422" dia, and from less than 1" to more than 3" deep. In some cases, holes have a depth-to-diameter ratio greater than 10 to 1. Some holes are machined through solid material, while most have cored holes. In a few cases, the holes required step drilling.

"We designed these machines with part changes in mind. They can be programmed on the floor with a portable terminal on a station-by-station basis, from the central control console through the system's dedicated control computer, or off-line on a personal computer and then transferred to the machine via floppy disk," says Mr Chapin. Once the machine has been programmed, different part configurations can be run by selecting the part number on the master control console. The machine automatically reconfigures itself to accommodate a new set of machining requirements.

Multiple-parts processing

The initial problem was designing a machine with the ability to machine a family of parts. When the project first began, there were four different types of housings. That number soon changed to nine. But the solution, because of its programmability, is able to handle an unlimited number of part configurations.

One challenge HR Krueger faced was devising a means to machine eight or nine holes with stringent size and location tolerances. Though most instances required 0.0035" positional tolerance, sometimes they were required to hold 0.002", with one machining pass.

Stub-style tooling was chosen instead of bushing plates-a move that saved costs and eliminated changing and maintaining an inventory of bushing plates. Solid carbide drills were used to maintain optimum rigidity and keep machining time to a minimum. "The selection of holders became critical where we were simultaneously drilling and counterboring three bearing retainer holes on a common head and needed to hold size and location tolerances of 0.002". In those conditions, the toolholders have to be very accurate," says Mr Chapin.

After reviewing various holder systems, HR Krueger decided to use the Tru-Taper[R] system developed by TM Smith Tool International, Mt Clemens, MI. The Tru-Taper system delivers a high degree of precision, based on mating 50-deg angles in the toolholder and machine spindle, eliminating bushing plates through the use of stub-style tooling. Another advantage to using the system is that, once modified, spindles will still work with Acme and straight-shank holders. "We were impressed with the Tru-Taper concept. Tru-Taper is the best drill holder we have found for holding location. Tapering of the contact surfaces ensures maximum precision and consistently accurate centering," says Mr Chapin.

Maintaining a precision bore

The stator bore of the housing also proved to be a particularly tricky machining effort. Operators were running a 5"-dia bore 1 1/4" through a portion of the part characterized by lugs, ears, and other protrusions, thus making the wall thickness vary from as little as 1/8" to over 1/2". To avoid the tendency of the part to contract unevenly because of the varying wall thickness, the Krueger team decided to machine on the return stroke as well as the advance stroke. This enabled the setup to maintain roundness to within 0.002".

For more toolholder information, contact TM Smith Int'l, 360 Hubbard Ave, Mt Clemens, MI 48046

Boring eccentric auto Wheel hubs

In response to the automotive industry's increased use of aluminum wheels with eccentric bore designs, Jack Haines Co, Detroit, MI, a machine-tool builder, is developing precision-machining equipment that processes wheels previously machined on lathes and boring mills.

These wheels require special fixturing and machining techniques because the hub or pilot bore of the wheel is designed eccentric or offset to the wheel diameter by 0.004" to 0.007". The reason for this design is to accommodate the overlap of the steel belts in tire design so the tire and wheel will run in balance. This design prevents lathe boring or boring on standard machines.

Jack Haines offers two machines that solve processing problems for different automotive wheel designs. Each machine handles wheels from 14" to 17" dia and widths from 7" to 11.5".

The first machine is a double-end drilling, boring, and facing machine for processing aluminum wheels. It finish-bores the pilot hub, generates a stepped-hub face, and drills and chamfers the five lug holes. The machine is designed with a one-piece base that mounts two standard slide units. A centering fixture mounted between the units holds the wheel in proper orientation for machining from both sides.

The second machine is a double-end drilling and boring machine that drills, reams, and chamfers the valve-stem hole and precision bores the eccentric bore. It features a one-piece T-shaped base design that mounts a combination drilling, reaming, and boring head on one side and a chamfering head on the other. A self-centering fixture locates the parts for processing at 90 wheels/hr.

For more information, contact jack Haines Co, 2761 Stair St, Detroit, MI 48209.

Metalizing process restores worn axles

Electrochemical metallizing, manufactured by Selectrons Ltd, Waterbury, CT, is an in-shop process that repairs and restores worn freight-car axles. This process reduces axle scrapping and replacement costs, vendor repair costs, and salvage expenses by producing adherent, controlled metal build-up on metal surfaces at room temperature. The Selectron[R] process combines the concepts of arc welding and electrochemistry to provide hardnesses from 100 Knoop to 58 Rc. Thickness control is so accurate that secondary machining is not necessary. For example, railroad axles can be rebuilt without postmachining. Thermal distortion is not a concern because no heat is generated.

Electrochemical metallizing can also be used for other railroad applications including transit-car axle aluminum-wheel seat resizing; bearing support diameter reconditioning; water-jacket seal restoration; and hydraulic pit, score, and groove rebuilding.

For more information, contact Selectrons Ltd, 137 Mattatuck Heights Rd, P 0 Box 115, Waterbury, CT 06725-0115.

Milling machine cuts manufacturing time

Ferrostaal Machine Tool Corp, Placentia, CA, has announced that its installation of an SHW UFDZ 1200 universal milling center has reduced manufacturing time on a series of parts for Van Dorn Corp's Greenville, SC, operation by 60%.

Before installing the UFDZ 1200, a CNC milling, drilling, and turning cell capable of five-sided machining in one setup, Van Dorn was producing the front head and rear head for its line of plastic-injection-molding machines on two CNC lathes and four separate vertical machining centers. The total production time on the six machines was 10.6 hours.

Both parts were being produced from flame-cut 1119 steel, and the front head was 12.5" x 12.5" x 5". A great deal of handling and setup time was required to produce each part using the old method. Ron Taylor of Van Dorn says, "...using the UFDZ 1200, we have reduced our setup time from 6 hours to 1 Vt hours and our manufacturing time from 4.6 hours to 2.9 hours." "We are pleased with the results of the UFDZ 1200 and with the cost savings that it is producing for Van Dorn," says Ferrostaal's VP of sales, Helmut Pongs. "It's an efficient method for producing families of parts that require multiple operations such as milling, turning, and drilling. And, with the flexible head moving from the vertical to the horizontal in 3 sec, very little machining time is lost between operations."

Ferrostaal is a subsidiary of MAN AG. For more information, contact Ferrostaal Machine Tool Corp, 1981 Miraloma Ave, Placentia, CA 92670.
COPYRIGHT 1991 Nelson Publishing
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1991 Gale, Cengage Learning. All rights reserved.

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Title Annotation:Manufacturing in Action
Publication:Tooling & Production
Date:Jan 1, 1991
Previous Article:Temperature control boosts push-rod quality.
Next Article:Hidden benefits of CNC turning.

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