The Piston Group (Redford, MI and Liberty, MO) builds cooling modules for seven different vehicles. These cooling modules are built on five different assembly lines, with each line building more than 50 different variants in sequence to the customer’s demand. Many different inspections need to be performed on each module, including verifying the build variation, checking electrical connections, and all dimensional requirements.

In the past, inspections were performed in an automatic check station that utilized multiple pneumatic actuated slides fitted with linear probes, vision systems, and a wide variety of sensors to inspect the different components. The problem with this approach was that each individual slide cost about $15,000, and the slide had to be replaced whenever the corresponding part specifications or design changed.

The vision system mounted on a robot in the checker station.

The conventional approach to replacing the slides with machine vision would have required as many as 30 different fixed cameras, each with special lighting requirements. The Piston Group developed a much less expensive and more flexible solution by mounting a single Cognex® In-Sight® 5603 vision system on a Fanuc® robot. The robot moves the vision system into position to capture the 30+ images in less than 45 seconds, completely inspecting the module. The In-Sight vision system can be modified to inspect for future design changes with a few hours of programming time. The new inspection system has substantially improved quality by inspecting more points at a higher level of accuracy, while reducing initial investment by 40% and retool cost by 80%.

The Piston Group provides sequenced and non-sequenced sub-assembled components for complex modular assemblies. The company assembles modules such as front-end cooling systems, suspension and chassis systems, interior systems, and power train systems. The cooling module produced in this application consists of essentially everything between the motor and front bumper: the core support, radiator, electric fan, AC condenser, power steering and transmission coolers, reservoirs, hoses, wiring harnesses, and many other small components. The modules are built in many different configurations. For example, most lines have over 20 different wiring harnesses, depending on the model and options selected by the customer. The customer sends The Piston Group a daily release that indicates the required front module configurations and their build sequence.

Demanding Quality Requirements

The quality requirements for the modules are demanding. First, each module must be correctly configured for the vehicle in which it will be installed, with the proper wiring harness and other components. Second, many components need to be installed within tight dimensional tolerances. Several hoses and clamps must be installed within 1 mm of a specified location. All electrical connectors must be fully seated and engaged.

In the past, many of these inspections were performed in a check station by mechanical probes mounted on slides. Whenever the dimension was changed, the slide had to be modified or replaced with a new design. Retooling required approximately two weeks of downtime to retrofit the entire check station. Prior to model changeover, the company would build small quantities of pre-production new model parts, and these parts had to be inspected manually due to the station not being changed over. Many inspections, such as determining whether parts were identified and installed properly, were performed by 200% visual inspection by quality engineers. The flexibility of the new system allows for accommodation of both current and new model production, reducing this reliance on visual inspection.

“Every time the customer made a single engineering change, the cost was a minimum of $15,000,” said Kevin Miller, Director of Manufacturing Engineering for The Piston Group. “We wanted to implement a flexible vision system to reduce cost and turnaround time on changes. We also wanted to reduce the amount of required manual inspection to improve quality. The normal practice is to use one camera per inspection point. This approach would have taken up too much space on the existing equipment and the cost was too high.”

Imaging Technology Magazine

This article first appeared in the June, 2010 issue of Imaging Technology Magazine.

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