Tier 2 Automotive Supplier Boosts Output with Improved Fixturing

Hydraulic Workholding Yields High Accuracy on Machined Cast Parts

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Precision CNC Machining As a Tier 2 supplier to the automotive industry, Southland CNC of Cornelia, Georgia provides machined aluminum sand-cast components to all three American and the six largest foreign auto manufacturers. The company started 19 years ago with a single machine in the garage of its owner and president, Keith Armour, and has since grown to 30 employees using 21 high-capacity machining centers.

Southland machines a variety of parts on production runs ranging from very high volumes to those of relatively low volume. For its high-volume production runs, the company uses dedicated hydraulic clamping fixtures on Okuma Howa vertical machining centers. According to the company, these fixtures greatly decrease production time and are highly cost-effective. By providing clamping pressure that is consistent and repeatable, the hydraulic fixtures are also said to improve machining accuracy.

According to Keith Armour, the company typically holds tolerances to 20 microns true position, and critical dimensions to +/- 6 microns, which he credits largely to the hydraulic fixturing supplied by Southland's longtime supplier, Advanced Machine & Engineering (AME) of Rockford, Illinois. Because low-volume production runs do not justify dedicated fixturing, Southland uses manual fixturing for its adaptability and lower cost of acquisition, when appropriate.

Southland currently has four horizontal machining centers that use hydraulic tombstone fixturing, and three vertical machining centers that use hydraulic tombstone fixturing. All of the fixturing is designed and built by AME. These fixtures are dedicated to high-volume production of single parts or single families of parts.

According to Southland CNC, the company chose AME to provide its first tombstone hydraulic fixture because the fixturing solution was competitively priced and specifically designed by AME engineering to fit Southland's production needs. Delivery, which was very important to Southland's production scheduling, was also significantly better than what any other designer or supplier was able to deliver, according to Armour. The first AME fixture that Southland used was a specific replacement for customer-supplied fixturing, which Southland had determined was not providing the efficiency needed to meet cost and schedule goals for the high-volume production run.

The advantages provided by the AME-designed fixture included reduced load/unload time, reduced cycle time, reduced scrap rates, and error-free loading, Southland said. The initial application of the fixture reportedly reduced Southland's cycle time by more than 50 percent, which allowed Southland to meet the high production volume without additional machines. On one bearing plate for a supercharger assembly, according to Keith Armour, production has gone from 50 units to 110 units per day with the same superior tolerances and a 1.67 Cpk, critical to the Six Sigma conformity required by its major automotive customers.

The fixture, which provides automatic clamp and release, is designed with locating dowels to ensure error-free handling. Each component to be machined is handled only twice--once as it is loaded into the fixture, and a second time as it is unloaded. Because the fixture is a windowed fixture, the component is completely machined on all four sides without additional handling. Typically, on the vertical machining centers, a second loading pallet is used to mount workpieces while another fixture is running in the machine. This further enhances Southland's throughput.

Keith Armour says that the AME-produced fixturing has been very reliable. One fixture has been in operation 20 hours a day, five days a week, for more than seven years without a single problem. Because of this reliability, and because of the cooperation and innovation that AME has provided, Southland added a second fixture for use on the vertical machining centers, plus a fixture dedicated to horizontal machines.

The fixture configurations we designed for Southland include cast tombstones, as well as welded tombstones," said AME Fixturing Group Manager, Alvin Goellner. "Depending on the intended use for the fixtures, they were provided with external surface-mounted hydraulics, as well as internally cored hydraulics.

One particular application is a bearing plate for a supercharger. The aluminum sand-cast part, measuring 8 inches long x 4 inches wide x 1-½-inch deep, requires two operations per side. The workpieces are loaded in less than 20 minutes on a second fixture, using the secondary pallet on the VMC. Southland produces approximately 30,000 of these parts annually for a Tier 1 supplier to Jaguar, BMW, and Mercedes.

"The fixture was designed specifically for this part, though it's flexible enough to allow us to use it for other jobs," Keith Armour explains. "AME had a very short turnaround time, plus their knowledge of workholding and the components they selected were all first-rate. We have experienced zero downtime because of the fixturing they supplied us for this particular part. Although we tweak the rest pads for enhanced accuracy, that's normal with the machining centers we use."

Armour further noted that the design and development work was done via CAD drawings, and that the entire project was completed on schedule and at the quoted price. "When we began to go from 50 parts per day to 110 or better, with absolutely no loss of accuracy and finish quality, we knew we'd made a wise choice," says Armour. All accuracies are checked on the in-house CMM at Southland for verification.

Advanced Machine & Engineering Co. (AME) provides design and build services as a manufacturer of workholding fixtures, tombstones, and components for CNC horizontal and vertical machining centers, as well as other CNC machines. The company, which began as a full-service machining company, provides custom fixturing dedicated to meeting customers' part and production requirements.

Edited by Design-2-Part.

For more information on Advanced Machine & Engineering, contact Alvin Goellner, Fixturing Group Mgr.; 2500 Latham Street, Rockford, IL 61103; phone: (815) 962-6076; Web: www.ame.com; Email: info@ame.com.

For more information on Southland CNC, contact the company's main office at 5691 Duncan Bridge Road, Cornelia, GA 30531; phone: (706) 778-0369; fax: (706) 776-6138; E-mail: slcnc@southlandcnc.com.

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