Fixturing and Workpiece Articulation

April 01, 2010

One way to survive—and even thrive—during an economic downturn is to help your customers increase their productivity. Here's how AME achieves that goal.


It would be unwise to challenge some companies in the Rockford, Illinois area to an engineering contest if the subject is machining metal parts. This is home to a wealth of engineering firepower, and it all results from real-world, hands-on experience, building the machine tools and related equipment that won a couple of world wars, changed the face of American industry, and even helped put a man on the moon. Despite recent hard times and a crippled economy, the master craftsmen and toolmakers in Rockford take those titles quite seriously.

Advanced Machine & Engineering (AME) is no exception to that rule, which has helped us to weather the economic downturn. The length to which we will go in meeting our customers’ needs provides a valuable case study in surviving a recession. A longtime leader in spindle interface products, fixturing, workholding devices, carbide sawing systems, numerous safety innovations, and other engineered solutions for the machine tool and general metalworking industry, AME engineers literally bring hundreds of years of experience to the challenges they face with customers as they seek to help them devise better machining techniques and improved part handling and transitioning within the metal-cutting theater.

Examples abound of how we apply our extensive knowledge to customer problems in the area of fixturing and workholding devices. In one recent case a major Illinois construction equipment builder needed two solutions for its machining inside large MAG centers. The workpieces were assorted shafts and splines, parts of a transmission gearbox assembly. After we reviewed and evaluated the challenge—which I handle along with Lonnie Miller, project engineer—we devised a centering vise fixture and hydraulic indexing fixture. These fixtures were to be mounted on a tapped center plate for a rotary table assembly, and machining was to be done in stages.

The key challenges were the numerous diameters and lengths of shafting to be machined, as well as the substantial chip volumes generated. Hydraulic centering jaws, plus a cradle assembly and chip guard, were devised and engineered by our team. Previously, each workpiece was being handled manually and individually fixtured, thereby wasting very expensive machine time. Fig. 1A

The centers on the vise jaws were kept to +/- 0.005” while the workpieces being secured ranged up to 6.88” diameters. All the hydraulics were isolated in the center plate, another solution configured by AME engineers, who also devised the entire porting arrangement. On the indexing fixturing a combination of a steady rest, face driver, and rotary indexer were all incorporated into the overall design to maximize the accuracy of the cutting and the indexing, regardless of the workpiece diameter being machined on any given cycle. According to the customer, this solution has proven very successful in decreasing the changeover time from piece to piece, plus its improved accuracy over the length of all individual components; a vital element in the buildup of a transmission or other drivetrain assembly where gearing and splines are involved. When assembled into position, this substantial spline-indexing fixture measured a full 84” mounted to a 95” plate. Fig. 1B

Another example of AME’s fixturing expertise is found in a vertical machining center built for an automotive engine component manufacturer. Southland CNC of Cornelia, Georgia is a tier-two supplier to the automotive industry, providing machined aluminum sand-cast components to all three American and the six largest foreign auto manufacturers. The company, which was launched 19 years ago in President/Owner Keith Armour’s garage on a single machine, has now grown to 30 employees using 21 high-capacity machining centers.

Southland machines a variety of parts that include production runs of very high volumes, and other production runs of relatively low volume. It uses dedicated hydraulic clamping fixtures on Okuma Howa vertical machining centers for its high volume production runs, because these fixtures greatly decrease production time, which makes the fixturing highly cost-effective. The dedicated hydraulic fixtures also provide clamping pressure that is consistent and repeatable, which improves machining accuracy. According to Armour, the typical tolerances are held to 20 microns true position, with critical dimensions to +/- 6 microns, which he credits largely to the hydraulic fixturing that we have provided. Because low volume production runs do not justify dedicated fixturing, Southland uses manual fixturing for its adaptability and lower cost of acquisition, when appropriate. The company currently has four horizontal machining centers that use hydraulic tombstone fixturing and three vertical machining centers that use hydraulic tombstone fixturing, all designed and built by AME. These fixtures are dedicated to high volume production of single parts, or single families of parts. Fig. 2A

Southland chose us to provide its first tombstone hydraulic fixture because the fixturing solution was competitively priced and specifically designed by AME engineers to fit its production needs. Delivery, which was very important to its production scheduling, was significantly better than any other designer/supplier, according to Armour. The first AME fixture specifically replaced the customer-supplied fixturing the company had been using, which 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, cycle time, and scrap rates, along with error-free loading. The initial application of the fixture reduced Southland’s cycle time by over 50 percent, which allowed it to meet the high production volume without additional machines. According to Armour, on one bearing plate for a supercharger assembly production has gone from 50 units to 110 units per day with the same superior tolerances and a 1.67 Cpk, which is critical to the Six Sigma conformity for its major automotive customers. Fig. 2B

The fixture, which provides automatic clamp and release, is designed with locating dowels to insure 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. On the vertical machining centers, a second loading pallet is typically used to mount workpieces while another fixture is running in the machine. This further enhances Southland’s throughput.
Armour states 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 due to the cooperation and innovation AME has provided—Southland added a second fixture used 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. Depending on the intended use for the fixtures, they were provided with external surface mounted hydraulics as well as internally cored hydraulics.

On one particular part, a bearing plate for a supercharger, the part is aluminum sand cast and measures 8” long x 4” wide x 1-1/2” deep. A two-operation part 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 this part annually for a tier-one 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,” 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.”

He further notes that the design and development work was done via CAD drawings, and the completion of the entire project was done 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,” he says, adding that all accuracies are checked on the in-house CMM for verification.

Trying times require extra effort and creative solutions, and that’s what AME brings to the table when helping our customers overcome the challenges they encounter while developing efficient and successful production strategies.  

About The Author

Alvin Goellner is vice president of the fixturing group at Advanced Machine & Engineering. To
learn more contact Kris Drennen at (815) 962-6076, or send e-mail to info@ame.com. Go
online to [www.ame.com] or [www.hennigworldwide.com].