What automotive customers look for in machining centers

Automotive Manufacturing & Production, March, 1997 by Joe Jablonowski

Right now, the tooling development unit of Kelsey-Hayes Co. (Livonia, MI) is working with Daewoo Machinery Corp.'s systems division (Plymouth, MI) on special fixturing for their horizontal-spindle machining centers. The work is being done on behalf of a new joint-venture plant in China, where Volkswagen components for Beijing taxicabs will be manufactured.

"It's typical of the kind of jobs we're getting involved in now," says Daewoo engineer Len Elliott. "We're putting four steering knuckles on a two-sided upright fixture that can be rotated in 0.001-deg increments. That allows machining on any feature of the knuckle." Other aspects of the job include employing 180-psi coolant nozzles on each side of the machine's work area, plus through-the-spindle coolant, to control chips; using step drills and backfacing cutters that reduce out-of-cut time; and perfecting a specialized straddle mill that cuts both sides of the steering arms of both knuckles on each face of the fixture.

An interesting aspect of the project: While tooling and fixtures are being developed on a demonstration machine in Michigan, the six production machines are being delivered from their builder in Seoul, South Korea, and installed in China for preproduction operator training. The machining center (MC), Daewoo's ACE-H50S, has several features specifically aimed at the Tier-One automotive parts market, including four controlled axes using the Fanuc 16, twin automatic pallet changer with pallet rotation at the load station, a screw conveyor for chips, and an oil jacket cooler for the spindle that helps deliver guaranteed 0.002-mm repeatability. The design items fit today's demand, says Jim Janis, VP of sales at the builder's U.S. headquarters in Carlstadt, NJ. "The call is for quick setup and changeover, easy chip removal and part access, and simple maintenance, as opposed to the previous tendency toward single-purpose transfer-type concepts."

Ever Faster. If faster throughput in order to compete with dedicated metalcutting lines is the aim, many MC designers seem to be getting the hang of it. Cincinnati Milacron, Inc. (Cincinnati, OH) conceived a proof-of-concept exercise not long ago that shows how gains can be made. Mark Adkins, director of market development for the Mill's machine-tool group, recalls that the three-scenario project involved machining typical features on an aluminum exhaust manifold for a vintage, 1989-design Chrysler four-cylinder engine.

The baseline first scenario uses an old-generation Milacron T-10 horizontal-spindle machining center with a changer for its 500-mm pallet. Operating two shifts per day, output is calculated at 14,000 parts per year.

The second-generation situation involves upgrading to the builder's present-day 500-mm-pallet horizontal, the Maxim 500, and using features like axis speeds to 100 ipm, fast pallet shuttle, and tool-storage capacity to 180 tools. Hypothetical two-shift production of the same exhaust manifold grows to 35,000 parts per year.

The third scenario entails moving to what Adkins terms the "coming generation" of machining centers. It includes features like an indexing pallet that allows eight parts on a cubic tombstone fixture (two on each side), toolchange speeds that are triple those of the old T-10, an improved spindle carrier that enables acceleration to cutting rpm in one-third the time, and triple-speed slides. Production of that Chrysler exhaust manifold now zooms to 70,000 parts per year.

Over the past 10 years or so there has emerged a new class of machining centers designed for high production while retaining the flexibility that endeared MCs to generations of job-shop owners. The newest ones in that class - whether they are called "production machining centers" as in the PMC-V750 from Monarch Machine Tool Co. (Cortland, NY), "production centers" as in the SPN50 from Niigata Machinery (USA) Co., Inc. (Rolling Meadows, IL), or simply have no special class designation as in the FS-510 horizontal that Mazak Corp. (Florence, KY) introduced at IMTS-96 or the new A77 horizontal from Makino Inc. (Mason, OH) - all tend to challenge the conventional idea of where machining centers fit in the overall scheme of things.

You remember the old conceptual scatter graph from all those 1980s articles and promotional materials for flexible manufacturing systems. As you ascend the graph's vertical axis, production volumes increase. Move out along the horizontal axis, and part variety grows. So in the upper-left portion of the graph (high volume, low variety), transfer lines rule. Out at the bottom-right (low volume, lots of variety), stand-alone machining centers dominate. The middle cluster (mid volumes, moderate variety) was to be the natural dwelling place for FMSs, those multi-machine installations linked with rail-guided cars and mind-melded with a central supervisory computer the size of a Jeep Grand Cherokee.

Costly, full-blown flexible manufacturing systems may not have caught on as predicted, but many of their elements were incorporated into smaller-scale manufacturing automation in the form of flexible cells of two or three linked machines. What we're seeing today are the elements of those cells being integrated into single machining centers. These, then, can be operated singly or ganged for increased output and/or redundancy.