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MIM parts manufacturability design (process design & sintered post processing)-(1)

Categories: ZCMIM NewsStars: 3StarsVisit: -Release time: 2019-09-23 08:32:00
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The design of MIM parts is similar to plastic injection molding. Unconstrained by traditional metal molding processes, from the beginning, designer can re-imagine parts with a new perspective, how production processes reduce material weight, how multiple parts can be combined into one part, or how functional and decorative features can be formed. In order to give full play to advantages of MIM technology in design MIM parts, following criteria are proposed:

I. technological design

Mold core is internal structural of parts, while cavity is external structural of parts.

All design must be solidified and can be drafted from cavity and core by means of push rod. As complexity of MIM parts increases, sliders, cores, and other tools commonly used in injection molding can be added to form parts. 

At the same time, complexity of parts increases, and economic benefits of MIM parts can be obtained by eliminating subsequent processing or assembly operations.


At every stage of design, these benefits and costs must be carefully balanced against each other.

The following key points must be taken into account when designing MIM parts to fully reap all  benefits of this process: uniform wall thickness, thickness transition, core holes, release inclination, stiffened ribs and spokes, chamfering and roundness, threads, holes and grooves, root cutting, gating systems, parting lines, decorative features, sintered supports, etc.

Each will be described below.

1.1 Uniform wall thickness

If possible, wall thickness of whole MIM parts should be same. Different thickness can lead to distortion, internal stress, holes, cracks and dents. In addition, it will lead to uneven shrinkage, affecting size tolerance and control.

Thickness of parts should be within 1.3~6.3mm.

1.2 Thickness transition

 Some occasions cannot meet wall thickness uniform, then different thickness should be designed to gradually transition. As shown in figure 1


                                                                                                                                                                                                  Figure 1- thickness transition

1.3 Remove cored hole

Using core hole can reduce cross section to criterion limit, reach uniform wall thickness, reduce material consumption and reduce or eliminate cutting operation.

 As shown in figure 2, preferred direction is parallel to parting direction, in other words, perpendicular to parting line.


Because core rod is supported at both ends, so it is better to use through hole, not blind hole, blind hole is use of cantilever rod.

1.4 De-molding inclination

De-molding slope is a small angle on surface parallel to movement direction of parts.

For core rods, should be particularly precise. De-molding inclination is to facilitate de-molding and ejection. De-molding inclination is generally 0.5 ~2 degrees. Actual inclination degree increases with hole depth or the depth of indentation or complexity of parts or number of cores.

1.5 Strengthen rib and spoke plate

Reinforcing ribs and spokes are used to reinforce thin walls and avoid thick sections.

In addition to increasing strength and stiffness of wall thickness, it also improves material flow and limits distortion.

The thickness of reinforcing rib shall not exceed thickness of adjacent wall. On structure needs thicker reinforcing rib, should use multiple reinforcing rib to replace.

1.6 Chamfer and round

Figure 3 shows chamfering and rounding.

Chamfer and chamfer can reduce stress at junction of structural features. It eliminates sharp Angle which may cause cracking and corrosion, facilitates material flow into cavity and helps parts to draft from mold, which is beneficial to molding operation.

Keywords in the article: MIM parts injection molding
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