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ASMs meet a tough challenger.

ASMs meet a tough challenger

The shop is new, and so is the technology. Management at Production Screw Machine Co, Dayton, OH, helped pioneer SPC, segregated CNC lathes in a "softer" area suited to electronic controls, and developed manufacturing cells that now include some alternatives to the automatic screw machine (ASM).

Pete Mauro and Gene McQuinn started the company ten years ago, with just three used Davenports. It took three months and new spindles to get the first one going. The previous owners had used the wrong oil, causing bearings to seize. Now the firm has a battery of Davenports, Brown & Sharpes, Acme-Gridley multiple-spindle machines, three Hydromat rotary-transfer machines, and the CNC group.

"We learned about statistical process control (SPC) about the same time General Motors' engineers were going through their learning curves," Pete Mauro told T&P. "GM awarded us important contracts, and they taught us about SPC as they were learning themselves... We've grown with them to provide Quality On Time, which is a mutual goal."

Mike Mauro, Pete's son, told us just how it was done in specific cases. "We were running 303 stainless-steel hex masts for a major automaker's radio antennas. We were running them for five years, but we never had all the business, and we wanted to expand that job," he said.

"We could have bid using our existing machines, but the job would have tied up six or seven ASMs. Instead, we got a commitment from the customer, then invested in machines to do the full hex-mast job," said Mr Mauro. "It turned out we needed just one double-production machine, a 16-station Hydromat(R) Model HB32/16 (8+8) rotary-transfer machine using a two-bar feeder system. We run two parts at a time and have gone from making 20,000 pcs/week to 100,000 pcs/week. That's five times the part production we previously had."

Complete in one operation

In the original setup using conventional ASMs, the Davenport five-spindle machine would spot face, rough form, and drill the back end, shave the OD, and drill and tap the center hole, then cut it off. These operations took about 14 sec total cycle time.

Next the part went to a washing station and on to a Brown & Sharpe No 00 for secondary operations. Parts loaded into the spindle automatically, but operators first had to place the parts on a tray manually. The machine finish-drilled the back end of the hole, which took four operations. Cycle time here was 11 sec.

Finally, operators checked the parts. Maximum gross production was just 170 pcs/hr.

Using the rotary-transfer machine, supplied by Hydromat Inc, St Louis, MO, Production Screw makes two parts every 9 sec, and the machine runs at 90% efficiency or better. Engineers set up the following operations in eight stations: cut-off; drill 5.5-mm hole; face and drill 0.196"; tap M6 x 1; turn workpiece 180 deg; drill 0.138" dia and taper plunge the OD; taper finish; and step ream, face, and chamfer OD.

Identical operations take place on stations 9 through 16. Stock enters from an automatic barfeeder, and a circular cut-off saw on each side cuts it off. Then the machine performs the listed operations. An automatic transfer station turns the part around, reloads it and finishes the drilled hole for the antenna mast. The machine kicks out some 800 pcs/hr. In using the Hydromat, three part-handling operations and one machine operation are eliminated.

Tooling and uptime

To minimize toolchange time, Production Screw uses presetting in extra drill chucks. Parts still have to be approved after each toolchange, but it's quicker using presets. Also, there are extra collets for the tapping units.

Tools are carbide wherever possible, usually Micro 100 tools with indexable inserts. The only highspeed-steel tools used on the Hydromats are drills and taps. We asked how often operators must change the tools. Mr Mauro replied, "Out of an 8-hr day, we may be down a total of 30 to 45 min for tool changes. We don't change all tools at once, but we've kept records for the past four years, so we know in advance when most tools will wear out.

"As for the machine itself, we've had total documentation on everything in the five years we've had it. We stock hydraulic units, computer boards, etc, so we can fix most problems ourselves. We keep the records on this and our other two Hydromats, so if we have a failure, we can find out if it ever happened before, and, if so, the cure. Of course, we have regular inspection and maintenance, checking of hydraulics, etc, to reduce unexpected downtime.

"Actually, the uptime is phenomenal. Our average shop efficiency is 75%, but the Hydromats run at 90% or better. They're all hydraulic, with no cams to wear and change work-piece dimensions. All that wears in a hydraulic system is the seals, and we can replace O-rings easily."

Cell operation

Mike Mauro notes that most of the work in his plant is done in cells, each with about 10 individuals and a cell adviser. "We try to eliminate all indirect labor, and make it direct labor. It works out well, improving our efficiency tremendously," he says. Of course, there is no cell for the hex mast; it comes off the Hydromat complete.

While Production Screw originally purchased the Hydromat to solve volume-requirement problems, Mike Mauro says that, after working with the machine for a period of time, other advantages were realized including: lower maintenance, improved part quality, reduced material usage, and reduced work-in-process.

ASM still viable

Is the rotary-transfer machine the way of the future? Definitely for the right job. But it won't replace the automatic screw machine totally. It takes longer to set up than a screw machine, but it can eliminate costly secondary operations.

You have only five spindles to work with on a screw machine, six on an Acme; but there are 16 stations on the Hydromat, not counting vertical units. Conceivably, you could have 8 vertical, for a total of 24 spindles or stations. It's a very versatile machine.

Close concentricities may require more attention in setup, because the rotary uses a different machining concept. The Hydromat system uses modular components that can be easily adapted for various applications, similar to a standard screw machine. The workpiece is stationary, and the tools revolve around it - as opposed to a screw machine with rotating workpiece and tools on slides and fixed spindles. (Of course, the same thing happens when you add live spindles to a lathe.) Mr Mauro says you must indicate tools very closely, and, if you take the part out of one spindle and put it in another, or rotate from station to station, concentricity is generally limited to a tolerance of 0.002".

Why didn't Production Screw just get more screw machines instead of the Hydromat to do the hex-mast job? The answers are simple: too much direct labor cost, and too much maintenance. With a Hydromat, you can double your hourly rate in labor costs and still be competitive, according to Mike Mauro. And it's hard to beat all that uptime.

PHOTO : Hydromat rotary-transfer machine makes 100,000 hex masts a week from 303 stainless-steel bar stock. Production Screw Machine Co has two 16-station machines and one 12-station model.

PHOTO : Mike Mauro says he couldn't meet the hex-mast Quality On Time schedule without the Hydromat machine.
COPYRIGHT 1991 Nelson Publishing
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Copyright 1991 Gale, Cengage Learning. All rights reserved.

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Title Annotation:automatic screw machines
Author:Miller, Paul C.
Publication:Tooling & Production
Date:Oct 1, 1991
Previous Article:CMM's go portable.
Next Article:Sheet-metal FMS: too big a jump?

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