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Mixing is the process of mixing metal powder with binder to obtain uniform feeding. Because the properties of the feed determine the properties of the final injection moulding product, the mixing process is very important. This involves many factors, such as the way and sequence of binder and powder addition, mixing temperature, characteristics of mixing device and so on. At present, this process has been staying at the level of experiential groping. An important index to evaluate the mixing process is the uniformity and consistency of feed.

Mixing of MIM feeds is accomplished under the combined action of thermal effect and shear force. Mixture temperature should not be too high, otherwise the binder may decompose or two-phase separation of powder and binder may occur due to low viscosity. As for the shear force, it varies with the way of mixing. MIM commonly used mixing devices are twin-screw extruder, Z-impeller mixer, single-screw extruder, plunger extruder, double planet mixer, double cam mixer, etc. These mixing devices are suitable for preparing mixtures with viscosity in the range of 1-1000Pa.s.

The mixing method is usually to add high melting point components to melt first, then to cool down, then to add low melting point components, and then to add metal powder in batches. This can prevent the gasification or decomposition of low melting point components. Batch addition of metal powder can prevent the sharp increase of torque caused by too fast cooling and reduce equipment losses.