福建Tolerances for MIM products

When receiving MIM injection molded parts, the company often has more dimensional requirements than conventional powder metallurgy pressed products, which requires several dimensional docking and even changes in product drawings. Although MIM can complete geometric and complex parts, there are many dimensional factors to consider.

Two aspects should be considered when determining the tolerance of MIM products during design. 1 Tolerance level that MIM technology can achieve. 2 What tolerance grade is required for the product?

Dimensional tolerance

The tolerance of MIM parts is affected by many factors, such as mold design, size, shape, material, gate position, cavity number, mold structure, annual production layout and maintenance technology.

But generally speaking, the tolerance control ability will gradually improve with the accumulation of experience in the production process*** Initially, the linear dimension tolerance of MIM products can only be controlled within 0.5% of the soil. By strictly controlling the MIM process parameters, the linear dimension tolerance can be controlled within 0.3% of the soil. If the part size is reduced, a narrower dimensional tolerance can be obtained. However, the tolerance reduction is not proportional to the size reduction, and depends on the raw materials, part shape and process requirements. For some small products, 0.1% of the soil dimensional tolerance can usually be expected if the mold works well. According to the development of new binder system and the whole process control, the above tolerance values are expected to increase.

The size change of MIM in isotropic and all directions is almost the same, but the influence of anisotropy is secondary and weak. However, the size of formed parts will change when they are affected by weak external forces. These weak external forces include the adhesive force of the mold during injection molding filling, the gravity when removing the adhesive, and the friction resistance of the chassis during sintering shrinkage. Therefore, small deformation of this part must be considered in die design.

At present, powder metallurgy manufacturers are working hard to overcome the problem of dimensional tolerance, especially titanium alloy MIM injection molded parts, to produce parts made of special materials, such as titanium alloy eyeglass frames, which are hard and light. The frame is very long. During sintering, it is very easy to deform. If deformation occurs, the finishing will be very troublesome, so the tolerance is difficult to control. There are also medical devices, such as surgical instrument parts or medical suture guns, which require very high dimensions and appearance. Technicians need to communicate many times to determine the final production plan.

At present, the default shape tolerance range of the MIM products produced by the MIM industry is as follows: flatness 0.002mm, parallelism 0.003mm, perpendicularity 0.002mm, coaxiality 0.003mm, roundness 0.003mm, but these are not * * *, and the structure of the parts should also be considered to determine the size tolerance.