Warranty costs are a growing concern in the auto industry, where manufacturers are under intense pressure to cut costs while maintaining quality. Even the smallest defect can siphon off millions of dollars in profit and create big headaches for engineers.
What happens when a noncompliant automotive part ships from a supplier to an OEM varies, depending on the problem. For instance:
- The supplier may send someone to the customer's facility to inspect all shipped parts.
- The OEM may ask the supplier to take back the entire shipment of parts and replace it with a new batch.
- The OEM may charge the supplier for servicing the warranty claim at approximately $55 per hour.
- The OEM may force the supplier to hire a third party to fully inspect each batch before shipment. That could cost approximately $20,000 per month for a single shift.
- In the worst-case scenario, the supplier could be forced to pay $500 or more for each minute the production line is down.
New Product, Old Problem
When someone puts an ignition key in a luxury sedan, they expect the $50,000 vehicle to work flawlessly. A critical component in the 275-hp V-8 engine of a new front-wheel drive car is the water crossover assembly. It houses a water pump that dispenses coolant throughout the engine to keep it at the optimum operating temperature.
The most important function of the water crossover is to get coolant from one side of the engine to the other. But, the device also contains the throttle body, which meters the air flow allowed into the intake manifold.
In addition, the water crossover assembly houses the exhaust gas recirculation valve. It takes some exhaust gas and recirculates it back to the inlet side of the head, resulting in cleaner emissions.
The water crossover assembly measures 24 inches long, 12 inches wide and 8 inches high. Because the engine is mounted sideways in the vehicle, the component sits near the left front tire.
The 28-pound water crossover assembly contains more than 50 parts, which are assembled by Enterprise Automotive Systems (EAS, Warren, MI). The company casts, machines, assembles and tests powertrain and chassis components for OEMs such as DaimlerChrysler (Auburn Hills, MI), Ford Motor Co. (Dearborn, MI) and General Motors Corp. (Detroit).
One automaker recently turned to EAS after it encountered quality problems on earlier versions of the water crossover assembly. The previous supplier had too many nonconformance issues. The customer would receive an assembly that was missing components or was incorrectly assembled. Apparently, this supplier depended on its operators to verify that the components were present and correctly assembled.
To avoid that same problem, the EAS engineering department evaluated the process and determined that they needed to eliminate the risk of human error during the quality audit inspection process. Their goal was to find a way to identify any problems before the water crossover assemblies ship to the OEM's engine plant, which is located 25 miles away.
Up-front Error Proofing
Errors and defective parts are cheapest to address early in the assembly process. The EAS engineers determined that an automated inspection station would be required at the end of the water crossover assembly line to ensure that all parts are present and attached correctly.
A local systems integrator, Total Automation (Marine City, MI), was assigned the task of building the device. The company built a standalone station that eliminates the containment costs typically associated with shipping noncompliant assemblies. It verifies that 54 components are attached before the water crossover subassembly is approved for shipment.
The machine features 11 cameras and ring lights sequenced to perform the vision checks and complete data storage in less than 7 seconds. The frame-mounted enclosure includes automatic doors that eliminate ambient light, in addition to a light screen for operator safety.
"The major challenge was defining the scope of the project and how the station would ultimately function," says Brian Kirchner, president of Total Automation. "For instance, more than 250 e-mails went back and forth between our engineers and the customer during the course of the 5-month project."
Kirchner's team used CAD design tools to create a 3D model of the enclosure, part and fixture. "This allowed us to position the cameras in space to pick up the features we needed in each field of view," he explains.
What makes the machine unique is the shear number of cameras and vision tools-more than 140-that are used to discern the various part features. It was determined that 11 cameras were needed to optimize the view of all the details.
"A single camera may verify up to eight components by using a wide field of view," says Kirchner. "However, when we needed to measure the gasket thickness of 0.02 inch to make sure it was present, or not doubled up, we would have to zoom that camera in for finite details and only check one feature per camera."
The cameras are located on all sides-top, back and bottom-of the part. "We pretty much have it surrounded once the part is placed into the enclosure," notes Kirchner. Each camera looks for various things. For instance, one camera verifies the leak test marks. Another verifies that the four bolts and the water pump housing are in place. Another measures the angle of a pressed in plenum. Ten red LED array lights are used for feature detection, and one blue LED array is used to read a 2D bar code that identifies each assembly.
The first camera triggered reads the bar code. A file folder is created and identified with that particular serial number. All the pertinent part data and individual camera shots are saved for 90 days on the PC's hard drive. The remaining cameras will trigger in no particular order, but each verifies two to 13 features of the water crossover assembly. The total capture time is about 6 seconds.
Total Automation engineers developed and installed an intuitive operator interface, which features a 17-inch flat-screen monitor. Visual BASIC programs control all I/O functions and the operator interface. "There are over 1,200 man-hours of development in the operator touch screen and diagnostic functions to allow anyone to operate the system with minimal training," says Kirchner.
An operator swipes his or her employee badge at the start of each shift. That ID is stored along with data on each part. Passed parts are ink-marked to show they have been inspected.
If a part fails, the operator must call a supervisor to remove the part. The supervisor has to turn a key switch to remove the part. A label is printed with the failed component listed by item number. The supervisor is forced to remove the failed part label and place the part onto a conveyor where it is acknowledged and quarantined before the audit station will be allowed to cycle again. All measurement data and video captures are saved for up to 6 months. This archive could be beneficial if there are future assembly audits.
The main components selected for the project included a Vision Pro computer system from Cognex Corp. (Natick, MA). "It allowed us to keep the cost down by using simple CCD cameras tied back to one common, powerful processor," Kirchner points out. "The built-in tool library enabled us to develop a robust audit system that not only identifies part presence, but also measures the pressed tube angle of rotation, and eight overall bolt lengths at extremely high speeds."
The machine uses a Dimension 8300 series computer from Dell Inc. (Round Rock, TX), with dual 250-gigabyte hard drives to provide massive amounts of data storage. All programming is done in Visual BASIC Pro 6.0 from Microsoft Corp. (Redmond, WA), which is designed to offer a closed loop system. According to Kirchner, the PC with the installed 64-channel I/O card, combined with the Visual BASIC programming, handled all of the motion commands and sensor feedback that would normally be handled by a PLC.
Other components of the automated inspection system include 11 XC-ST-50 cameras from Sony Electronics Inc. (Park Ridge, NJ) and a S-600 industrial label printer from Zebra Technologies Corp. (Vernon Hills, IL).
A team of seven operators at EAS currently build 420 water crossover assemblies a day. But, the company is ramping up to produce more than 500. In addition to the luxury sedan, the V-8 engine is now used in one of the automaker's other vehicles.
Operators work in a U-shaped workcell that features six different assembly stations. Station 1 machines the raw casting. Station 2 washes and dries the parts. Station 3 presses two tubes. Station 4 performs the first leak test. Station 5 assembles 49 components, which require approximately 20 fasteners. Station 6 performs the final leak test.
The quality audit inspection station is the last operation in the workcell. "The station determines if the part is suitable to be shipped to the end user, or if it must be put into the reject quarantine," says Ray Casper, manufacturing project manager at EAS.
With OEMs demanding perfection today, Enterprise Automotive Systems has recognized the value of error-proofing before shipment. "Today's customers are very demanding of supplier quality," Casper points out. "The up-front cost of error prevention and elimination will pay dividends over the long haul."
"EAS realized that human error must be removed from the scenario if it is going to have a completely satisfied customer," adds Kirchner. "It has uncovered the weak areas of the overall assembly process. This has allowed EAS to quickly identify the root cause of problems, and implement accurate and permanent solutions."