By implementing a software package that can compare data obtained with a CMM with a CAD model, technicians at Chrysler Belvidere are helping assure quality builds of the Neon. Importantly, the software makes it possible to measure parts without checking or holding fixtures.
"There were perhaps 20 to 25% of the parts and assemblies that we might want to have measurement data on that we were not able to measure," remarks Don Pollock, engineering supervisor, Body Shop, Chrysler Belvidere plant, home of the Neon. The issue was this: they needed manufacturing data on parts and sub-assemblies for which there were no holding or checking fixtures. And the solution to this problem was not going to be found in investing in the fixtures, as the corporation wasn't interested in having that happen. Yet quality is a key aspect of what Chrysler Manufacturing is all about.
So is innovation.
Which lead to a solution: the acquisition of graphics-coupled measurement software capable of aligning and measuring parts free-standing on coordinate measuring machines (CMMs). The software, PC-DMIS for Windows, was developed by Automation Software (North Kingstown, RI). It incorporates a CAD-generated graphic representation into the measurement program's data base. The graphics engine is integrated with the measurement program to automate part programming both on- and off-line. What's more, it can:
- Provide a user-friendly interface for measuring parts;
- Relate measurement data directly to the part graphic;
- Automate the alignment and measurement of complex, free-standing parts, including those with contoured surfaces.
Benefits Beyond Measure
The software is used at Chrysler Belvidere with two surface plates and four Brown & Sharpe horizontal CMMs. The software's iterative alignment feature is used to electronically put the part to be measured in body position in reference to the part program's resident CAD model. Observes Pollock, "Without this scheme, our layout technician is left with the responsibility to try to set the part in body position. This is almost impossible to do because any deviation from nominal in the part itself will create noise in your setup. Iterative alignment averages out that noise so that electronic alignment of the part is far more accurate."
Iterative alignment makes it possible to measure a variety of parts without holding or checking fixtures, which means that there are significant savings. Just how big those savings are is difficult to calculate because some of the components and assemblies being measured hadn't been measured before. Pollock remarks, "We have been able to measure some pretty strange stuff, like air conditioning units for cars, which we never would have tackled before because there would be no way we would be able to define a setup and an alignment scheme without this software." What's more, there are avoided costs associated with maintaining and certifying fixtures. QS 9000 requires certification of fixtures on a regular basis. It is simpler to certify a few CMMs than dozens of fixtures.
Among the other parts that they are measuring include steering brackets, rear suspension cross members, tail lamp modules, trim panels, trim garnish moldings.
Because some parts—such as the trim garnish moldings—are flexible, the PC-DMIS is used with another software package from Automation Software, a best-fit analysis software called AutoFit, which fits measured data to an electronic model of the part.
Resolving Problems Fast
The measurement data obtained is automatically associated with a wire-frame model. This can be viewed on-screen or printed. "This gives us a clear visual presentation of the points measured so that we can easily share this information within our own organization or with suppliers," Pollock says, adding, "If they send me a bad part, I simply fax them a wire-frame with callouts representing the bad points, and we are all instantly on the same page. They now resolve problems faster."
Sharing data will be even easier in the future because the software is fully networkable.
"When the word got out that we were able to perform certain measurements that we could never pull off before," Pollock comments, "it brought people out of the woodwork. The number of requests we receive to measure parts and assemblies has tripled."
The increase of new customers in the department initially caused some problems. The combination of new software with previously unmeasurable parts resulted in some early misinterpretations of data and an erosion of confidence. Pollock and his colleagues regrouped and introduced the measurement capability in a more controlled fashion, which restored confidence as the measurement data was used consistently to solve problems.
Pollock observes, "It is very frustrating to have manufacturing problems you can't solve because you can't get dimensional data. What you can't measure you don't even want to think about. Now we have the tools to do a root-cause analysis on problems we would probably not have been able to address before.
"We can now assess the problem and methodically determine if the root case is tooling, processes, supplier parts, or all of the above. Corrections enter into the system quicker, and we get a faster turn-around on the necessary reworks or repairs. Ultimately, we can implement corrective action faster and reduce our warranty service costs and produce more satisfied customers, which is our ultimate intent."
Pollock says that they've requested enhancements for the software, such as support for scanning. This would mean the ability to use non-contact (e.g., vision, laser) probes, so massive volumes of data could be obtained from contoured sheet metal parts without touching the parts.
"We want to be able to scan a part at a section," explains Pollock, "then take that scanned data and overlay the scan to the model to see precisely how the part form fits or doesn't fit the model. That kind of technology, when we get it, will be a boon to us."