Microcellular form injection moulding process for auto components

MuCell? microcellular foam injection moulding process is getting attention with the recent announcement by Ford that it has been testing the use of such technology to reduce component weight and cut down fuel consumption. The technology was invented and patented by the Massachusetts Institute of Technology (MIT). In 1995, Trexel Inc. was granted an exclusive worldwide license for the further development and commercialisation of the technology.

The MuCell microcellular foam injection moulding process for thermoplastics materials provides unique design flexibility and cost savings opportunities not found in conventional injection moulding. It is a complete process and equipment technology which facilitates extremely high quality and greatly reduces production costs. The process involves the use of highly controlled gas such as CO2 or nitrogen in its supercritical state (SCF) in the injection moulding process to create millions of micron-sized voids or bubbles in uniform configurations. The voids are created as a result of homogeneous nucleation that occurs when a single-phase solution of polymer and gas passes through the injection gate into the mould. The MuCell technology is targeted at precision and engineered plastic components with maximum wall thicknesses of less than 3mm. It allows for plastic part design with material wall thickness optimised for functionality, and not for the injection moulding process.

The combination of density reduction and design for functionality often results in material and weight savings of more than 20%. The MuCell process generally offers a 50-75% improvement in key quality measures, such as flatness, roundness, and warpage, also eliminating all sink marks.

Direct economic advantages ensured

As a direct result of the uniform stress and shrinkage associated with the MuCell process (which occurs because the pack and hold phase of the moulding cycle is eliminated), the parts that are produced tend to comply far more closely with the mould shape and, presumably, the dimensional specifications of the part itself.

The quality advantages of the MuCell Process are complemented by certain direct economic advantages - including the ability to produce 20-33% more parts per hour on a given moulded machine, and the ability to mould parts on lower
tonnage machines as a result of the viscosity reduction and the elimination of the packing requirement that accompanies the use of supercritical gas.

Virtually all polymers will develop a cellular structure with the MuCell process except for LCP. Filled materials tend to offer the greatest value as fillers act synergistically with the supercritical fluid to provide the best combination of weight reduction and cycle time reduction. Unfilled amorphous materials also foam very well and can provide good weight reductions but with less cycle time benefits than filled materials. High temperature materials such as PEEK, PEI and PSU also provide significant cost reduction based on material price.

With the target to reduce the weight of its cars and improve fuel efficiency, Ford has turned to the Mucell technology citing that the process will enable the weight of plastic components to drop by 10% Ford wants to reduce the weight of its vehicles by between 250 and 750 pounds per car by 2020, citing that the technology is an example of eco innovations that automakers can utilise to meet such targets. In its research, Ford also found that even while reducing weight, the components retain all necessary properties for a nonvisible part without sacrificing durability and quality.

Ford will continue to conduct research on other potential uses of the Mucell technology for theNike