Delta Gantry Keeps Auto Body Panels Fit and Trim
American Tooling Center Inc. is an ISO 9002 and QS-9000-TE registered full service tool and die facility that specializes in the machining, construction and tryout of stamping dies for automotive sheet metal body panels. Among the company's customers are major automotive OEM's such as, DaimlerChrysler, Ford and General Motors, and a number of stamping companies.
Cutting the sophisticated dies that shape complex contours in sheet metal requires advanced CNC machining equipment, and American Tooling Center operators six large capacity CNC mills. Four Pratt & Whitney Wolverine CNC vertical mills have a master/slave capacity and are interfaced with two Pratt & Whitney master duplicators. One of the Pratt & Whitney duplicators is fitted with Lemoine digitizing equipment for surface scanning.
All CNC work is produced from CAD-generated surface and cutter path information. The company operates four CATIA workstations and one workstation each for SDRC/IDEAS, PDGS and Unigraphics, plus three WORK NC and three SOLID WORKS Die Design workstations.
An integral part of this design and production system is the use of coordinate metrology to check the accuracy of the machining process. The company uses a high throughput, high accuracy Brown & Sharpe DEA DELTA gantry-type CMM to handle large dies and sheet metal components. The DELTA was installed as part of an equipment upgrade and expansion at the facility that included four Danly 180" presses.
"We've used coordinate metrology in the past, checking the stamped parts to determine if the die machining was accurate, but the machines were smaller and couldn't accommodate the larger dies and parts were producing and plan to be making in the future," said Dave Knox, American Tooling Center Plant Superintendent.
At the American Tooling Center Inc. facility, the DELTA CMM is installed in a separate, climate controlled room between two large cranes ways near the production operation. Because of the massive size of many of the parts, some of the dies weigh up to 50,000 pounds and measure up to 10 feet long by 6 feet wide; the DELTA is augmented with an automated loading table. The table's plate is built on a four-wheel cart that rests on rails set into the room's concrete floor. One of the cart's axles is powered by an electric motor. The table measures 72" x 120" and has 6" grids with 1/2" holes so that work pieces can be tied down.
Dies and stamped components are loaded on the table from either crane way and then delivered to the CMM. The automated table moves between the pillars to a position underneath the bridge of the DELTA CMM. Once in position, the table is raised with bottle jacks and the wheels are cranked up so that the table doesn't move during the inspection process.
Checking Masters
In the inspection process, when the master die comes off the CNC machine, it is immediately delivered to the CMM room for a dimensional check prior to barbering and hardening.
"Generally, the lower die is the master of the set," Knox said. "The sheet metal panel pins on it and the upper die is spotted to the lower to produce the stamped body component. Consequently, the position of the guide pins and bushings is crucial to the proper functioning of the die set."
In addition to checking the position of the locating pins and bushings, the location of coordinating holes, used to pin the parts on the post are checked.
"If these locations check accurately, we'll check the entire surface of the panel at 100 mm grids, " Knox said. "All of the surface data is downloaded to the DELTA from the CAD system, so we can check anything on the die. If we find tight areas on flanges, we'll move those points to wherever we need them."
The inspection routine usually takes four to five hours to complete. Dimensional data is used to adjust the machining process and verify accuracy of the CNC machines.
Running Capabilities Studies
The company uses PC-DMIS tm measurement and inspection software in the measurement process, accompanied by DATAPAGE and DATAVIEW module for data analysis and reporting. Using these software programs in conjunction with the PC-DMIS inspection software gives American Tooling Center the ability to analyze the quality of parts runs and provide customers with a variety of capability studies.
Part checking routines use customer-supplied checkpoints. "Typically, we run six and 30 piece studies to check the location of critical characteristics as identified by the customer and put into a report," Knox said.
DATAPAGE uses high speed querying tools to reduce large volumes of data to critical variables needed for process control applications. Its process report feature condenses all necessary information about a critical variable on a single sheet. A comprehensive statistical package allows any combination of SPC analysis and reports and uses extensive graphic presentation and reporting tools for GR & R and process control studies.
"I particularly like the feature that allows us to insert an arrow to indicate specific check points on an actual drawing of the part," Knox said. "We can also create a list to indicate deviation from nominal and include the Cp or Cpk of a specific check point."
Every part produced by American Tooling Center has its own fixture. In order to insure quality production, the DELTA is used to certify fixtures. "We check them on the DELTA even if they have been certified before arriving here." Knox said. "Each fixture's net surfaces and master locator holes or pins are checked to the latest design data, and all the hole locations are verified."
The integration of coordinate metrology with advanced CAD/CAM techniques has helped American Tooling Center Inc., stay at the forefront of its field, and has also helped the company develop an expertise in building low volume production dies. This tooling process, which reduces production time and costs, is geared toward niche vehicle production and has helped make American Tooling Center Inc., one of the premier die makers in the world.
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Brown & Sharpe, Inc.