Six Sigma systems approach to precision molding

GE Plastics intends to help its customers make the impossible possible when it comes to repeatably molding dramatically more consistent micron-toleranced parts. It has installed a Precision Molding Lab (PML) at its Polymer Processing Development Center (PPDC). Using Six Sigma methodology, the PPDC defines, measures, analyzes, improves, and controls attributes of a project their customers consider to have the most impact on quality. The PML gives the PPDC a means of better quantifying the impact of materials and process variations on the critical-to-quality attributes of precision-molded products.

The low-noise PML has a precision molding development cell fully instrumented with top-of-the-line analytical instruments and data acquisition systems. The cell runs at a quiet 75dB, but that is not the kind of "noise" the PPDC is concerned about. What they mean is "measurement noise." Measurement noise in the PML's machine, its auxiliaries, and its ambient environment has been reduced. This allows engineers to precisely quantify differences in materials and process performance normally masked by the noise generated by other, more conventional molding systems.

The nucleus of the cell is a Netstal Synergy 1500, a 165-ton press with switchable 4- and 5-oz barrels owned by GE Plastics. Injection-compression capabilities are included. The press also is equipped for gas-assist and high-temperature molding. When first putting it through its paces against other machines, one engineer at PPDC said he saw a CPK-doubling, 50-percent improvement with the Netstal's tolerancing in one application, particularly in terms of Six Sigma critical-to-quality characteristics like flatness and critical dimensions.

In another test involving 1000 consecutive shots, the Synergy performed with less than a .02/second variation in fill time. For some very thin thinwall applications, the Netstal's accumulator-juiced fill time is .06 second. "Explosive molding" is how one member of the PPDC team describes that kind of speed. Even with the best equipment from the top vendors in their field, PPDC engineers say they often find the Netstal to be faster than their ability to record its performance.

The PML will help speed new IT, E/E, and media applications to market by scientifically integrating materials and processing. Pen bodies for printers, chip trays, and next-generation data storage are examples of the types of proprietary applications the PML is working on.

Work on thin-walling also is underway. Some parts have already been molded with nominal .006-inch- to .008-inch-thick walls in materials like Lexan and Noryl. Future lab work will involve automotive connectors.