Improved Manufacturing Process with Artec 3D Scanner and Geomagic Control X Software

Pattern Making

AM has been used in aerospace and automotive applications to produce sacrificial casting patterns for decades. With recent advances in 3D printing, industrial-grade patterns can be printed in wax or polymer at a significantly lower cost, which work seamlessly in the investment-casting process. 3D Systems is seeing more distributed adoption of tool-less additive pattern making and will continue to grow as the technology becomes more accessible, rapid, and precise.

For any additive process that involves heat energy in material deposition or post processing, there is some amount of part warpage and settling that could occur. Parts that have significant mass or a significant cross-sectional area will retain heat for longer than smaller or thinner parts.

Based on this knowledge, 3D Systems tested two printing methods with the goal of having the lowest possible cost of printed goods and the highest level of dimensional stability: a completely solid wax-printing method as well as a thin, shell/sparse wax-infill method. Both were prepared with 3D Sprint build client software and printed on the ProJet MJP 2500 IC 3D printer that produces wax casting patterns. From prior experience, we found that a 2 mm shell with a 50% sparse infill ratio produces high-quality, stable parts when printing relatively large parts.

After post processing and cooling time, we used the same Artec 3D Space Spider scanner to scan the two patterns with relative ease. The unique shape of the parts, the green wax color, and the slight dulling and whitening effect of the post process enabled our scanning technician to capture the models smoothly using Geometry + Texture tracking.

Using Geomagic Control X, we imported the 3D Sprint build file directly and inspected each part in its exact print orientation for the inspection routine. Knowing that we would be scanning the subject part iteratively to improve the process, we were able to set up one detailed inspection project and duplicate it several times while maintaining the entire process development history in a single Geomagic Control X file. After completing the scans, we simply dropped each new STL file into the Geomagic Control X project and the evaluation process automatically took over, resulting in high-quality, repeatable reports.

We found that, generally, all areas with machining offsets were within the casting tolerance, but the more free-form areas presented trends outside a tight tolerance band. We believe this properly correlated our assumptions that large cross-section areas retain heat and potentially change shape when cooling.

Our comprehensive analysis for this stage helped us draw some conclusions that 3D printing with the wax pattern was not only more cost-effective, but also more dimensionally-compliant after post processing.

• Material usage was reduce by about 35%.
• Material cost was reduced by about 27%.
• Overall compliance with tolerances were increased by about 10% (using 3D comparison).
• The solid part did not pass the tolerance threshold
• The infill part passed the tolerance threshold.
• Long-term dimensional stability at room temperature was improved over the solid part.

Shrinkage is a known result of the casting process. Typically, a foundry provides customers some guidance to compensate for the known shrinkage for a specific material for a part size defined by the bounding box. Because of the geometric complexity and compounded by the physical casting process, it is common to see non-uniform shrinkage with most parts. As a result, casting can be regarded generally as a loose-tolerance process.

During the casting processes for the steering knuckle, we investigated a shrinkage rate that would be suitable for the model and material. After consulting with the casting facility, a 2% uniform scale was recommended to produce an accurate part. To investigate the effect that 3D scanning and a precision scale factor can have on end-part accuracy, we produced a wax pattern with a 2% scale factor as advised and supplied it to the foundry.