GM Daewoo of Korea, which is now part of the General Motors’ family, shortened die duplication tryout processing time by 30 percent through innovative reverse engineering process utilizing a 3D scanner and Design X.
The process of duplicating a stamping die is generally a painstaking and time-consuming task. GM Daewoo of Korea, which is now part of the General Motors’ family, shortened die duplication tryout processing time by 30 percent through innovative reverse engineering process utilizing a 3D scanner and Design X.
Replacing or duplicating a stamping die leads to unnecessary costs, inefficiencies and delays. Even though the original die has been through an exhaustive quality check, making duplicates involves more than another round of machining and assembly operations. Instead, stamping die engineers must repeat the entire die tryout process to produce quality stampings.
When General Motors announced a second Chevy Aveo production facility in Poland, the stamping die engineers at the GM Daewoo facility sought an alternative that would condense, or eliminate, the multi-week tryout process. With more than 25 large die sets for the Aveo, which is called Kalos in Korean markets, the gains in efficiency, cost reduction and lead time would be enormous.
Culminating a three year search, the GM Daewoo team found and implemented a 3D scanning procedure that uses Design X scan-to-CAD software. By documenting the as-built condition of operational dies, GM Daewoo slashed die tryout times by five weeks. It also ensured that the Polish-built Aveos would have the same fit and finish as the South Korean-made Kalos.
Die Tryouts
Following CAD design and simulation, stamping dies go through a rigorous tryout process. Samples are stamped, measured and scrutinized to uncover tolerance deviations and surface defects. When flaws are discovered, the die is handworked to fine-tune it so that stampings match print specifications. For parts like the Aveo’s tailgate, the tryout process is a 16-week endeavor.
The challenge in duplicating an operational die is that the handmade adjustments create an as-built condition that no longer matches the original CAD data. Therefore, the 16-week tryout process is repeated for each replacement or duplicate die set. The ideal alternative is to eliminate this costly redundancy by measuring the die and documenting the modifications in the CAD data.
GM Daewoo’s stamping die engineers had considered using a Coordinate Measuring Machine (CMM) and 3D scanners for the task but found each to be impractical. CMMs required too much time and labor to capture all the necessary measurements. 3D scanning resolved this issue, but the scanning software could not produce surfaces sufficient for tool path creation. This lead to a cumbersome and convoluted effort that divided the point cloud processing and solid modeling efforts between two separate software programs. In the end, there was little benefit because the time saved in die tryouts was offset by the time and effort to generate the as-built CAD data.
Parametric Modeling
The Chevy Aveo’s tailgate was the first sheet metal part to be stamped from a die that was duplicated using a new 3D scanning methodology. GM Daewoo converted 3D scanner point cloud information into a full-function CAD model using only Design X. According to the stamping die engineers, correcting the CAD data to as-built conditions in Design X yielded 85 to 90 percent time savings, when compared to previous 3D scanning attempts. The time saved gave them a viable solution for die duplication with minimal die tryout delays.
The GM Daewoo engineers noted that the key to making this possible was Design X’s combination of point cloud processing tools with parametric, solid modeling. In previous 3D scanning attempts, surface data was exported from the 3D scanning software and imported to UGS NX, where it was used as reference data for the manual recreation of the CAD model. In contrast, Design X performed the CAD modeling functions. It created parametric solids, with the full history tree, that drove the automated update of GM Daewoo’s UGS NX models.
With Design X, the die engineers used a variety of CAD Correct™ tools for refitting and redesigning the original Siemens NX files. These functions were supported by the Redesign Assistant™ that aids in interpreting the design intent of features of the handworked, and slightly worn, dies. Although these functions are not available in CAD packages, the GM Daewoo team noted that the user interface was intuitive because it had a familiar, CAD-like functionality and layout.
3D Scanning for As-Built CAD
GM Daewoo selected a CogniTens Optigo scanner for the Chevy Aveo project. The Optigo captured dense point clouds that documented measurements for both the untouched and handworked features of the tailgate die set. For the four-operation stamping process, there were eight die components for drawing, punching and bending. Following scanning, the point cloud data and original UGS NX solid models were imported into Design X. The point clouds were then cleaned, merged and aligned to the CAD model.
The first step in the CAD refitting process was identifying “regions of interest,” which are the areas where the scan data does not match the CAD model. To do so, GM Daewoo’s die engineers used Accuracy Analyzer™, which is a visual tool that highlights discrepancies between the two die descriptions. As the redesign progressed, Accuracy Analyzer also monitored the changes, in real time, to confirm that the modifications were within user-defined tolerances.
Another tool the die engineers relied on was Redesign Assistant. This Design X function automatically extracts the design intent of individual features. For example, Redesign Assistant determines the radius and center point of fillets even if there are slight changes in curvature resulting from imprecise, hand grinding or tool wear. Having extracted the design intent, the die engineers remodeled features with CAD-like solid modeling functions such as sweep, extrude and revolve.
While the standard CAD modeling functions were used throughout the project, the bulk of the time savings came from automated tools that have been developed specifically for 3D scanning. For example, GM Daewoo’s engineers turned to Design X’s automated refilleting tools. Other examples included Refit and Loft Wizard™. Refit automatically generates new, parametric faces that have G1 and G2 continuities for surface smoothness. For sculpted surfaces, the Loft Wizard automatically creates smooth, lofted surfaces and profile curves.
Manufacturing Duplicate Stamping Dies
After completing the modification of the CAD data to reflect the as-built stamping die, the parametric model, with its history tree, was transferred to UGS NX. Although time reduction for the CAD refitting process was important, the true test of this new approach to die duplication was the quality of the surfaces for machining of the production die. According to a GM Daewoo die engineer, “We have had no problems with Design X. It has proved its ability to rapidly create machinable surfaces for our body and chassis stamping dies.”
Machined from the Design X-generated solid model, the Aveo tailgate stamping die is now in operation in Warsaw, Poland. It is an exact duplicate of the Kalos die that has been stamping parts in South Korea. Replicating all of the original handworked modifications, this duplicate die is producing stampings that match the quality of the Kalos tailgate, and it is doing so without duplicating the lengthy tryout process.
Using 3D scanning and Design X, GM Daewoo cut five weeks from the tryout and approval process. For the tailgate, this 30 percent reduction resulted in an estimated savings of US$200,000. Extended over all large die sets for the Aveo, GM Daewoo estimated total saving of $5 million.
