Metal Injection Molding Design

In order to take full advantage of Metal Injection Molding process, we need to consider many critical aspects in MIM parts design. A clear understanding of these principles will guarantee the best manufacturing results for your MIM parts. In addition, we will assist you to analyse benefits versus cost in designing stage.

MIM design guideline is a reference to apply new components design principles, and evaluate exist components manufacturing possibility. Proper MIM design will maximize economic benefits, guarantee MIM parts with targeted geometries and dimensions.

MIM Design Guideline

In MIM designing process, you need to consider the Design for Manufacturing principles, in order to eliminate expensive secondary operations.

Sintering Support

In sintering process, green parts shrink about 20% in volume. In order to minimize distortion possibility, we need to support green parts adequately.

It is ideal to design MIM part with large flat surface, or several component with a common plane, so standard fixture can be used. Part-specific fixtures or setters will be required for parts with long spans, cantilevers, or delicate points.

Draft

This is small angle on parts surface, which is parallel to mold movement direction. Draft is used to facilitate molded form release and ejection. Its normal range is 0.5° to 2.0°, greater draft should be used once longer component element with text on surface.

Fillets and Radii

These two are used to reduce feature intersection stress for production function. They are instrumental in molding process, eliminating sharp corners, feedstock flow, part ejection. It is an effective way to handling sharp corners. Fillets and radii of 0.4–0.8 mm are generally preferred.

Ribs and Webs

Ribs and webs are usually used to reinforce relative thin walls and avoid thick section. In addition, they can improve material flow, limit distortion, increase thin wall strength and rigidity. Rib thickness should be less than adjoining wall, multiple ribs should be used for structural requirement.

Gating

As gate always leaves a mark on a finished part, so its location should balance demand of manufacturability, function,dimensional control and esthetic. It is normally best located on parting line of mold, positioned to make flow path impinges on cavity wall or core pin. We need to consider other factor of gate location, such as subgate, pin point gate and tunnel gate. For MIM parts with different wall thickness, we will place gate at the thickest cross section, in order to make MIM material flows from thick to thin section. This way will reduce voids, sink marks, concentration stress and flow line on part surface. In multiple cavities MIM process, we must consider gate size and placement to assure material is deliver to each cavity at balanced fill rate.

Sink

Minimize sink and knitlines in design process. Sink always occurs around thick section of same thickness wall and rib. Reduce rib thickness to 75% of wall will eliminate potential sink.

Uniform Wall Thickness

MIM parts overall size and design will determine cross sectional wall thickness. Generally, optimum wall thickness is 1mm to 6mm, which is variable for different overall size. We should uniform wall thickness in feasible condition, avoid non-uniform shrinkage, distortion, internal stress, voids, cracking, sink marks , dimensional and tolerance interference lead by thickness variations. Thickness in 1-6mm is preferred. We still can remove material in both direction to create wall thickness uniformity, in order to save cost of fine metal powder in economic way.

Parting Line

Parting line is the plane where two halves of mold meet, all features need to be perpendicular to parting line for removal facilitate from mold. Normally, parting line will transfer to part surface as witness line, we can design parting line to separate along inconspicuous edge to hiding it. It is preferred to contain parting line in one single plane.

ZCMIM projects

Start Your MIM Project Now


ZCMIM provide professional technology and experience team.

We are you reliable partner for every MIM project.

We also notice the Design of Part Improvement as following:

Coring Holes

Cored holes are normally used to reduce MIM parts cross section, uniform wall thickness, reduce metal material consumption, reduce or eliminate secondary machining operation. Its preferred direction is parallel to mold opening and perpendicular to parting plane. When length/diameter ratio is great than 4:1, through hole is preferred because both ends support core pin, otherwise, blind holes will be used with cantilevered pin.

Holes and Slots

Hole and Slots can provide functional features in MIM parts without additional cost, besides reduce part mass and uniform wall thickness. Holes are perpendicular to parting line is easy to mold with least cost, these are parallel require mechanical sliders or hydraulic cylinders. For internal connected holes, we need to consider carefully of potential sealing-off problems and flashing issues.

Undercuts

External undercuts can be formed on a parting line by split mold. Internal undercuts can be produced by slides, or collapsible cores. In MIM design, avoid internal undercuts because of additional cost and potential flashing problems.

Threads

Both internal and external threads can be formed in MIM process, internal thread is more precise and cost effective than unscrewing cores. External threads optimum location is on a parting line. To hold thread tolerance on thread diameter, narrow flat is typically 0.005”.

Decorative Features

MIM can easily mold features as logo, knurl, part number and identification marks in place without added cost, all these feature can be raised or sub-surface. We also can pride high level feature detail like diamond knurling in MIM process.

Thickness Transition

Although MIM part wall thickness is uniformed desirably, coring for thickness uniformity is not a perfect option, and it is difficult to avoid variations. We need to design a gradual transition between different thickness.