Metal co-injection moulding (Co-MIM) originated in the 1990s and is a sandwich powder injection moulding technology.

The process is to inject two kinds of materials with different characteristics into a mold simultaneously or in batches for a composite injection molding. It can combine metal materials and a material with completely different properties in the same part.

With this method, core/shell structures with functional and complex shapes can be obtained without subsequent processes such as coating, heat treatment and assembly. Finally, a process is realized to prepare functionally gradient materials, which greatly reduces the process and costs.

Co-MIM technology provides a new idea for the development and design of functional parts. Li Yimin have proposed a new bio-implant structure using Co-MIM technology, which is widely used in compact cortical bone structure and dense cancellous bone structure in the outer foramen.

The pore volume ratio of the outer porous structure is 5%-60%, and the maximum pore size is 400 microns.