Automated CMM Verification Helps Engine Manufacturer Build Best-In-Class Engines

This manufacturer's new verification system measures part dimensions to ensure accurate machining, supporting process control and production volume objectives.

Case Study From: 10/1/2003 Modern Machine Shop

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Prismo VAST CMM

The Prismo VAST CMM scans thousands of data points per minute and is equipped with 18 different probe configurations. This CMM is measuring an engine block and cylinder head at International's Huntsville, Alabama, plant.

International Truck and Engine Corporation (Warrenville, Illinois) is the operating company of Navistar International Corporation and producer of mid-range diesel engines. International recently remodeled a 680,000-square-foot manufacturing facility in Huntsville, Alabama. Together with its sister engine plant in Indianapolis, Indiana, it produces the next generation V-8 diesel engine for International brand trucks.

At each location, new diesel engines make their way through machining and assembly production lines that are nearly 1 mile long. The process includes multiple integrated manufacturing quality verification stations, where line operators conduct specified quality checks. In addition to the integrated quality verification checkpoints, manufactured components undergo random in-process and final product inspections using coordinate measuring machines (CMMs).

When International developed the manufacturing processes at these facilities, it incorporated a fully automated quality verification process for engine crankcases, cylinder heads and crankshafts that combines Prismo CMMs from Carl Zeiss IMT Corporation (Minneapolis, Minnesota) and an overhead gantry loading system provided by Fibro Inc. The new verification system measures part dimensions to ensure accurate machining, supporting process control and production volume objectives.

“We needed an optimized CMM verification system without the complexities and throughput hindrances that a quality lab sometimes includes,” says Chuck Sibley, business team leader of machining and assembly at International in Huntsville.

While the Huntsville product represents a low-volume, high-complexity focus, the Indianapolis product is the outcome of a high-volume, lower-complexity system. The CMM verification process had to function efficiently within both plants. Other strategic design objectives for the twin verification processes included high functionality, operational control, automated material handling and a safety module for worker safety.

“We knew there were automated CMMs on the market that incorporated loading systems using automated pallets or pick-and-place robotics, but we required a solution that would increase throughput even further,” says Donald Brown, senior manufacturing engineer. “The system had to fully automate the CMM inspection process, optimizing manpower and providing efficient, accurate inspections on production lines.

“In addition to fully automated inspection capability and the option to be used in a stand-alone capacity, the CMMs needed to provide accurate measurement and real-time inspection results to verify the consistency and quality of our products,” he explains. “We also needed adequate capacity for the CMMs to support our 85 percent uptime goal for production equipment.”

Mr. Brown predicted that a CMM equipped with scanning technology and a library of software programs would provide the accuracy and real-time results to meet the quality verification system objectives.

Working with a concept from International’s John Foley, Steve Zike and their manufacturing engineering team, the design team of Carl Zeiss, International, Fibro and TAC developed a CMM inspection strategy that would complement the integrated process validation checkpoints at each facility and contribute to a robust manufacturing process overall.

Each CMM is equipped with 18 probe configurations and measurement programs to verify the thousands of features on each crankcase, cylinder head and crankshaft. Measurement time is dependent upon process or product complexity, with results for each feature downloaded and sent electronically to the manufacturing line’s real-time shopfloor application to let machine operators know when to change worn tools or make alignment adjustments.

Quality verification system components at the two plants are nearly identical, with the exception that the Huntsville plant uses four automated CMMs, while the Indianapolis facility uses three. Both automated systems use overhead gantry loading and computerized controls. Each manufacturing process is verified at a frequency documented by the control plan for each process.

Components are loaded (and unloaded) at a station outside the environmentally controlled enclosure. Parts are loaded on the load shuttle pallet capable of holding three components each (crankcase, cylinder head and crankshaft). Operators enter sample data at the load control station, using operator prompts and bar codes. The load shuttle delivers the sample into the room and to the gantry system through an automated door. The gantry then picks the part from the load shuttle and places the sample in one of three locations on each storage seat (up to 24 samples can be loaded to fill the system). The system selects samples by priority and order, then delivers the sample to the next available CMM shuttle (or a selected CMM). Based upon the sample data entered, the CMM performs the specified program and returns the CMM shuttle to the gantry for post inspection storage. The operator receives the report via the intranet. The inspected sample is removed from the system, similar to the method of entry.

“We believed a single overhead gantry system would enable us to easily load parts for inspection on a CMM without disrupting the routines of the other CMMs,” Mr. Brown says. “Unlike pick-and-place robotics, the overhead gantry can handle the larger part size and weight to easily transfer the part from the queue to one of the four CMMs.” The four Prismo CMMs at International’s Huntsville plant are positioned in the corners of a rectangular room, with two CMMs facing each other at each end. The gantry runs above the CMMs, and the pallet system runs between them. The three Prismo CMMs at International’s Indianapolis plant are set in a straight line, with the gantry above loading the pallets below.

Each facility contains a safety module system, with multiple camera views that allow load operators to monitor the room from their control station. In addition, safety glass and light curtains surround moving components that automatically shut the system down if the beams are broken.

The CMMs are equipped with Zeiss Umess, Holos, Kum and Strata software programs. Umess programming software, along with the Kum and Holos graphical software programs, enables International to report inspection results several ways.

Umess software supports true geometric tolerancing, which considers both the size and the position of holes (true position). This is critical in measuring machined bores on the engine crankcases, cylinder heads and crankshafts. The system accurately measures size and hole positions to within 0.0002 inch. In addition to using scanned data points to produce a 3D digital image of a part, Umess networks with other CAD systems. This provides the capability to download CAD files to the CMM to develop automated inspection programs. Umess also can create a CAD file by using reverse engineering to digitize dimensions directly from an unknown part profile.

Holos software enables analysis of a part by comparing CAD data to actual scanned measurement data. The software also creates CAD data right from digitized measurement data without using other programs. The Strata software provides statistical process control (SPC) to compare data to precise engineering specifications.

There was a two-fold purpose in establishing this system at both manufacturing facilities. “We wanted the identical quality verification system in two locations so the systems can support each other in every conceivable way,” Mr. Sibley says. “We now have a powerful system that meets all requirements and allows us produce a reliable, best-in-class diesel engine.”

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