Chrysler Closes Dimensional-Data Collection Loop
Partnering with PC-DMIS developer allows automation of CMM programming and management of plant-initiated changes
By Howard Casey
Sheet Metal Leader
Advanced Metrology Group
Auburn Hills, MI
By Joe Zink
Global Product Manager
Hexagon Metrology Co.
"Everybody talks about the weather," said Mark Twain, "but nobody does anything about it." Much the same can be said about the chaotic state of measurement data-collection programs once a CAD model is released from the pristine confines of design engineering to manufacturing plants for product prove-out.
A CMM programmer's interpretation of marked-up drawings, notes, and/or conversations with designers typically determines what gets measured as a design progresses through product testing. As a result, there are many opportunities for misunderstandings and programming errors that lead to disconnects between the design intent and the measurement programs used to validate that intent.
What's more, the ultimate measurement program, once changes have been made to accommodate factory-initiated part modifications or fixturing on the CMM, may be very different from the original version. Several versions for the same components may even be circulating at various manufacturing and design locations.
That's the way it is throughout many large-scale manufacturing operations. Chrysler is a notable exception. When the Advanced Metrology Group at the Corporation's Scientific Lab transitioned to CATIA V4 as its CAD tool, it recognized the need for a way to append design-intent information to the CAD model automatically—the goal being to automate creation of measurement programs and minimize the opportunities for error enumerated above.
So, engineers at the Lab developed some homegrown tools. One called CMM Data automatically collects lists of data required to generate inspection programs from CATIA V4 models. Another, CMM Inspect, transforms these lists into measurement programs imported by various CMM software products, primarily as DMIS files. These tools worked well, saving the programmers a lot of time, and reducing programming errors.
When the transition to CATIA V5 was on the horizon in 2006, however, the Advanced Metrology Group recognized the need for new software tools. They saw this as an opportunity to improve upon what they already had, while filling a major hole in the system by incorporating capabilities for automatically managing changes made to CMM programs at various manufacturing locations. The objectives were to improve inspection programming productivity by an additional 60%, and close the loop between evolving CAD models and measurement programs built from them by automatically reconciling their differences.
As part of their upgrade to CATIA V5, Chrysler developed a software module called eTool. It automatically creates an inspection plan for verifying a part. While designers do their jobs, eTool is a silent partner that captures the information necessary for inspection programs, including datum definitions, feature measurement, and dimensional-evaluation information. Because eTool resides inside CATIA V5, the inspection plan it creates resides in the CATIA file.
Once they had clearly defined the eTool module, Chrysler's engineers turned their attention to how to generate programs from the eTool inspection plans they created. The engineers assembled as a group (author Howard Casey and three other programmers), and decided that, since PC-DMIS is the CMM software used in 90% of the company's own and supplier facilities, they would prefer to use it for off-line part programming. However, to link it to eTool-generated inspection plans, they needed a way to read the eTool data from CATIA directly into PC-DMIS.
The team approached the developers of PC-DMIS, Wilcox Associates, to see if they would like to work with Chrysler as partners to develop the pieces necessary for completing the project. Wilcox proved very interested, since the firm had already been working on similar technology (see sidebar page 80). The project was a good fit for Wilcox, because working with Chrysler on its proprietary system would also move Wilcox forward in the development of a commercial product.
Software engineers from Wilcox and the Chrysler team worked at the project for two years, getting everything in synch to meet all of Chrysler's needs. Much of that work entailed accommodating precise Chrysler-specific definitions for hundreds of feature types. These definitions use 47 fields just to store the information for each feature. This information includes XYZ, IJK, size, approach vector, surface vector, and tolerance fields. This comprehensive approach ensures that features will be coded the same way by the measurement software every time.
To create a CMM program for a part, the programmer accesses the CATIA V5 model from a workstation running PC-DMIS Offline using a CATIA Direct CAD Interface so that no translators are required. PC-DMIS reads the design intent information built into the CAD file by eTool, and from it produces a neutral inspection plan "extract file." The file format is essentially the same as that which Wilcox developed for its commercial PC-DMIS Planner product.
Using the model and the extract-file information, PC-DMIS automatically builds the measurement program. Among other things, it creates features and dimensions, inserts clearance moves, and optimizes probe paths. In most instances this step eliminates 98% of the work associated with part programming. The job of interpreting marked-up drawings, conferring with engineers, and manually entering data—which formerly required several weeks—is now performed automatically in an hour or two.
The project also made provisions for the 10% of Chrysler's CMMs that are not running PC-DMIS. In Chrysler's case, the PC-DMIS software has a proprietary module that sends the generic extract file data to inspection systems not currently running PC-DMIS, allowing users of these systems to use this data for developing part programs.
With the process of automatic inspection program creation from the CATIA embedded design intent resolved, there was still one very important missing component for Chrysler: the ability to identify, evaluate, and incorporate changes made to the design into the inspection programs returned to the Scientific Lab after a development cycle.
Launching a new vehicle typically involves a two-year evolutionary process. Consequently, many changes to the inspection programs take place as the design changes. Essentially the product is built, measured, crashed, changed, and measured again, for six development phases.
In the past, the Sheet Metal Team at the Advanced Metrology Lab would have to manually compare returned inspection programs to the inspection plan in the current CAD model to flag any differences between them. Doing so allowed them to determine if they needed to add, delete, or modify any features in the measurement program based on the latest design. This process was enormously tedious, time-consuming, and prone to error.
Fortunately, Wilcox engineers were already developing a change management tool for their own inspection planning software. They adapted it to satisfy Chrysler's requirements. This capability allows the programmer to compare the updated inspection plan from the CATIA V5 model with its associated CMM program. The results highlight any changes between the new plan and the original CMM program, including feature modifications, additions, or deletions. The programmer can then use Change Manager either to process the changes automatically or to accept or reject them on a case-by-case basis. In either instance, the time savings are substantial.
The four members of the Sheet Metal Team are responsible for creating, as well as managing, changes in all of the CMM programs used in the development of gasoline-powered Chrysler trucks and passenger cars. Their workload currently includes all model launches scheduled for 2010 and 2011.
As of February 2009, the team was looking at April and May deadlines for the delivery of nearly 200 inspection programs to the six Chrysler plants. Most of these programs are exceptionally complex. With only four programmers, meeting the deadlines could have been quite a daunting prospect.
However, the team is already 30–40% more productive than previously, and well on its way to achieving its goal of a 60% total productivity improvement. In addition to dramatically improving the team's programming productivity, there are three systemic advantages of the new approach to creating and managing measurement programs.
- Better Information: The DMIS programs that formerly shipped to customers were "dumbed down." This was because they had to maintain compatibility among a range of metrology software products of varying capabilities. By necessity, these programs represented the, lowest common denominator. Now, with most measurement systems in Chrysler using PC-DMIS, compatibility isn't such a serious issue for engineers and programmers.
- Change Management: After a prove out, the team would have to run the returned measurement program on a CMM to review all the probe paths, tip changes, moves to avoid clamps, and so forth to see what was happening. Then they had to rewrite the program to reconcile all of the differences between the returned inspection program and the original. Now, Change Manager automatically does this review off-line, and the user makes reconciliations within the software. This capability reduces the time spent in the process by as much as 70%.
- Same Page: For all of Chrysler to receive the same benefits that the team achieves in the Lab, it was important that everyone at Chrysler was using the same set of tools. To achieve this objective, Chrysler negotiated a Corporate SMA (Software Maintenance Agreement) with Wilcox which ensures that all of the PC-DMIS seats at the Science Lab and the six plants can be running the same version of the software, and be ready to take advantage of the latest enhancements upon release.
Chrysler is eager to proliferate the eTool system throughout its second and third-tier supplier network and to its various factories using a wide range of CMMs for sheetmetal work, so they can share in the benefits Chrysler now enjoys. The goal is to get everyone on the same page, and Chrysler takes that goal very seriously.
eTool For Everybody Else
Chrysler's proprietary eTool software module resides inside CATIA V5 CAD. It collects design intent information that allows PC-DMIS to generate measurement programs automatically. This technology is only available to Chrysler plants and suppliers using the CATIA V5 software.
What if you are not a Chrysler supplier, or use other brands of CAD software?
The newest release of PC-DMIS metrology software allows the automatic generation of inspection programs based on data collected from any CAD product using optional PC-DMIS Planner software. A stand-alone application, PC-DMIS provides an automated, paperless method for transforming design intent into inspection routines. With it, part designers record their requirements for validating or verifying a part without getting involved in the technology of the inspection process or measurement device. It's a matter of defining datums, identifying what needs to be measured, and establishing the relationships and tolerances among features. Subsequently, PC-DMIS uses this plan—along with the associated CAD model—as the basis for automatically generating a measurement program.
Much like Chrysler's eTool system, PC-DMIS Planner includes a full range of tools for developing plans, optimizing paths, and generating clearance moves. It also includes a version of Change Manager for keeping the inspection programs, the inspection plans, and the CAD drawing in sync.
This article was first published in the September 2009 edition of Manufacturing Engineering magazine.