Laser Scanning Reduces Time And Cost To Reverse Engineer Auto Stamping Dies

Submitted by GKS Inspection Services

Many of the stamping dies used by Japanese automobile manufacturers to produce body and chassis components in their United States plants are built in Asia under very tight deadlines. The dies are generally modified during the proving out process but as soon as they are capable of building acceptable parts it is usually necessary to rush them onto a boat for the trip to the United States. So there often is not enough time to produce the dimensional data that is needed later to produce replacement parts when the die becomes worn or is damaged.

In the past, before they began production, the stamping companies that used the dies sent them out to engineering firms or tool and die shops for reverse engineering with a coordinate measuring machine (CMM). This was expensive and time-consuming because of the need to manually move the machine probe around the die in order to capture each of the thousands of points needed to accurately characterize its geometry.

.dwg Design Services, Columbus, Indiana, has improved on the traditional approach by using a laser probe to scan the die surface while viewing the reflected light with a camera that captures millions of points in minutes. With laser scanning, most all die components can be scanned in under an hour to an accuracy of 0.0005 inches, enabling the stamping companies to generate additional revenues by getting the dies into production faster.

.dwg Design Services' primary business is designing metal stamping dies, special machines, and fixtures. The company's designers have over 70 years of combined experience in the tool and die industry in designing progressive dies, transfer dies, blank dies, compound blank and pierce dies, draw dies, form dies, line dies, and model trim dies for the automotive, appliance, lawn and garden, and heating/ventilation/air conditioning industries. .dwg Design Services also designs special machines including material handling systems, metalworking machines, assembly machines, and lubrication machines.

Need to quickly digitize die components

"Many of the metal-stamping dies used in the United States to produce automotive components are supplied by overseas resources," said Dirk Rader, Owner/Designer of .dwg Design Services. "A high percentage of these dies are delivered to domestic stamping companies without accurate die design information or 3D surface data need to build replacement components. A major reason for this is that the tooling is typically hand-worked at the overseas tool shop during the die tryout, debug, and part quality inspection process. With short tooling delivery leadtimes, this leaves no time for reverse engineering of the final "as-built" tooling configuration before shipment. The digitized data may be used for several different purposes such as the machining of a spare stock cage die component or the replacement of a broken or worn out component."

This leaves the domestic stamping company to deal with the challenge of getting the critical die components reverse engineered either before the die goes into production or between production runs. In either case, the existing die components are usually available only for a very short period of time before they are needed to make production parts. The dies are usually sent out to die engineering firms or tool & die shops that use CMM's to capture their geometry point by point. But it has become increasingly difficult to utilize CMM's for this purpose as the complexity of dies tends to increase with each new model introduction. At a minimum, tens of thousands and, in some cases, millions of points are needed to accurately define the die geometry. The result is that the amount of time needed to capture points one by one has grown considerably.

Rader found himself facing a particular challenge when a customer asked him to digitize four die components with trim lines and pockets for die button inserts. These components require a high degree of reverse engineering accuracy because the die has only 0.002 inch punch-to-die clearance. Another challenge was that most of the holes in the components are on compound angles. It would have taken a huge amount of time to reverse engineer these parts to the required levels of accuracy using a CMM. Also, the parts were somewhat worn so the model produced by reverse engineering needed to be updated to eliminate the wear. In this case Rader only had three days to work with the parts before they needed to be returned to the stamping company.

Switching from CMM to laser scanning

Rader searched for a better way to meet the needs of his customer and identified laser scanning as a possible solution to this problem. Laser scanning systems work by projecting a line of laser light onto surfaces while cameras continuously triangulate the changing distance and profile of the laser line as it sweeps along, enabling the object to be accurately replicated. The laser probe computer translates the video image of the line into 3D coordinates, providing real-time data renderings that give the operator immediate feedback on areas that might have been missed. Laser scanners are able to quickly measure large parts while generating far greater numbers of data points than probes without the need for templates or fixtures. Since there is no contact tip on a laser scanner that must physically touch the object, the problems of depressing soft objects, measuring small details, and capturing complex free form surfaces are eliminated.

Instead of collecting points one by one, the laser scanner picks up tens of thousands of points every second. This means that reverse engineering of the most complicated parts can often be accomplished in less than an hour. Laser scanning can reverse engineer parts that are so complex that they would be practically impossible one point at a time. Finally, the software provided with the scanner greatly simplifies the process of moving from point cloud to computer aided design (CAD) model, making it possible in minimal time to generate a CAD Model of the scanned part that faithfully duplicates the original part. Special, but readily available software can be used to compare original design geometry to the actual physical part, generating an overall graduated color error plot that shows in a glance where and by how much, surfaces deviate from the original design. This goes far beyond the dimensional checks that can be performed with touch probes on CMMs.

Scanning four components in less than one day

Rader researched the Internet for laser scanning systems with the idea of purchasing a system to provide in-house reverse engineering services. "I found the website of Laser Design Inc. (Minneapolis, Minnesota) to be very comprehensive and contacted the president of the company, Marty Schuster, regarding my idea of purchasing a laser scanning system," Rader said. "Schuster suggested that I use their GKS Inspection Services division, a laser scanning service bureau, to familiarize myself with the process. I emailed him pictures of the four components that needed to be quoted. I received a quote and contracted with GKS Inspection Services to scan the components. I personally delivered the components to GKS and observed the scanning of the components. Each component only took about 30 minutes to scan. In a single day the operator scanned all four components generating point clouds for each with millions of coordinates. I returned home the next day with the die components, making it possible to deliver them to my customer ahead of schedule."

After Rader left, GKS Inspection Services' engineers uploaded the point clouds into Geomagic Qualify software from Raindrop Geomagic, Research Triangle Park, North Carolina. They used this software to convert each point cloud to a surface model of the part geometry and also to correct the model to account for die wear. The software also allows the user to create a graphical comparison called a color error map of the manufactured part vs. the CAD model, by displaying differences between the two in a range. This makes it possible to easily compare the as-built die to the original part geometry to see what changes were made during the debugging process.

"The new high definition laser scanning systems available today in conjunction with high-end data processing software have given the metal stamping industry the resources to provide very quick and accurate reverse engineering data for the manufacturing of complex surfaced die components," Rader concluded. "The ability to accurately digitize the existing component to within 0.0005 inches and then, if necessary, virtually recondition the component using the tools within the data processing software have dramatically improved this process. The higher scanning speed provided by the new method is another important advantage. An average-sized die component can typically be scanned on all surfaces in about 30 minutes and a large component generally takes less than an hour. This compares to several hours or days that are typically required to digitize similar parts on a CMM."