Injection-molded plastic parts often show warpage after production due to cooling effects and other production parameters. The parts then don’t correspond with the CAD data or show many out of tolerance dimensions. To reduce warpage, it is possible to adjust some production parameters. However, this is very complex and not compatible with production goals such as very fast production and thus short cooling times. Therefore, it is often necessary to inspect the produced parts in the current state to assure their quality.
For this quality control, CT scans, which deliver 3D volume data of the parts, offer high efficiency combined with accuracy and the ability to measure the inside of a part. Solutions like the ZEISS METROTOM 1 can scan small to medium-sized parts and are easy to operate. The CT software GOM Volume Inspect offers powerful features to qualify and analyze characteristics like shape and positional tolerances, material defects and wall thicknesses.
Distortions caused by warpage make it difficult to assess the part quality correctly. The overall question is whether the warpage really affects the functionality of the part or whether it easily can be compensated with the forces that are applied during assembly. When using optical metrology, clamping devices help to simulate later mounting conditions with fixed points. Thus, the parts can be measured with a compensated warpage, the measuring data can be correctly interpreted and the part rejection rate diminished. But these clamping fixtures can be problematic due to issues like lack of process stability and time consuming operation. With CT scans, clamping fixtures can’t be used altogether because of disturbances of the measuring process.
To address this problem, GOM Metrology has developed a new software package: De-Warp. The software function can virtually compensate warpage of parts with powerful and efficient algorithms. Users can define virtual fixing points and evaluate measuring data of unstressed parts. With a mouse click users can then generate measurement results of the virtually clamped state. Completely without a clamping fixture!
The results also provide a lot of additional information and answer these questions: What is the real warpage? Is it possible to mechanically compensate the warpage in an assembled state? Are the parts functional despite small warpage? This enables plastic manufacturers to accelerate their product development process, to reduce costs resulting from time-consuming measurement processes and complex clamping devices and to minimize the rejection rate of totally functional parts.
De-Warp is a new technology and a real innovation for the quality assurance of plastic parts as it makes possible for the first time to realize over-constrained datum conditions without using mechanical fixtures.
For more information visit: www.gom.com