Technology suitable for both serial and small quantity production

In Injection molding the polymer material is heated and melted and then forced into the tool cavity using high pressure. Usually the tool temperature is relatively low compared to the material. Metal injection molding is a recently developed method, where a mixture of metal powder and binder is injected into the mold.

The material solidifies under a maintained pressure before it is ejected out of the tool. In micro injection molding very low shot weights (0.01 g) and even smaller part weights have to be realized. Because of the small parts size many cavities can be implemented into one tool in this way making the process cost effective. The tool manufacture is totally relying on manufacturing technologies that can create the necessary microstructures (milling, laser machining, electroforming). An important parameter is holding pressure that influences the product quality since increased pressure improves mould filling. The most important requirement is that the mold must be evacuated before molding, because proper venting during molding is not possible from such microcavities. Although the dimensions of the products are precisely specified during the process, some deformation usually occurs after demolding. The causes include release of compression stress, temperature change, chemical post-reaction and shrinkage by sintering. However, the deformation rate does not change much in repeated operations. After molding, the demolded product is debinded and sintered, and a metal product is finally obtained. As an extension of conventional investment casting, microcasting is also possible.

Micro structures with wall thicknesses of 20 µm, structural details in the range of 0,2 µm and surface roughness Rz < 0,5 µm are obtainable. It is possible to produce 2D, 3D and 2,5D micro products by injection molding. With this technology structural details in the order of 10-50 µm and aspect ratios of 10-15 can be obtained.

In microMIM (Metal Injection Moulding) the feeedstock material (metal plus binder) is heated and melted and then forced into the tool cavity using high pressure. Usually the tool temperature is relatively low compared to the material. The material solidifies under a maintained pressure before it is ejected out of the tool. In microMIM very low shot weights (0.01g) and even smaller part weights have to be realised.

The tool manufacture is totally relying on other micromanufacturing technologies that can create the necessary micro structures (e.g. milling, laser machining, electroforming). The dependence of the product quality on process parameters is reported. Tool temperature was found to have more effect on product quality than melt temperature. Holding pressure also influences the product quality since increased pressure improves mould filling. Micro structures with wall thickness of 20 µm, structural details in the range of 0.2 µm and surface roughness of about Rz < 50 nm can be manufactured. Aspect ratios exceeding 20 are obtainable. It is possible to produce 2D, 2,5D and 3D micro products by injection moulding. The main challenge is the manufacture of the mould. Further sintering and debinding are required in a very stable and controlled manner.