Metal Injection Molding Introduction

MIM Technology Guide

Metal Injection Molding (MIM) is a cost-effective way of metal manufacturing technology, in order to achieve great successful adoption of MIM technology, we should consider some effective guidelines in MIM designing process.

As trained designers with high experience will envision MIM technology to form parts design phase at start, in order to enable higher process yields, lower cost, and faster processing. During the design process, prior adjustment will avoid any difficulties in production process, which will interrupt or delay production schedules. As cost in designing process has little impact on final product price, but design decisions have major implication on final production cost. It is critical to involve MIM manufacturer in the early MIM design phase, we will help the most to deal with design factors and improve final production. Our experienced engineering team will consult with you to save agony and cost during final high-volume production.

Which part is suitable for metal injection molding

Metal Injection Molding (MIM) is able to produce complex net-shape composition with a variety of composition. Main cost in MIM is determined by MIM materials, parts mass, tooling complexity, molding cycle time, debinding and sintering time. We will pose some initial points to verify whether MIM is viable.

Production volume

In reason of mold cost, Metal injection molding is not usually used for low volume production, but is very effective for large quantities. Generally, production quantity more than 5,000 are attractive.

Three dimension geometry complexity

MIM is most effective for components with holes, slot, ribs, protrusions and multiple features. On the other hand, simple two dimensional shape are easier produced by stamping, rolling or die casting, like flat parts with uniform section thickness.

MIM technology feasibility

MIM technology feasibility is best measured by typical part profile. Most MIM parts are small-size, complex with thin walls and appropriate number of features. The following items provide the typical attributes:

1. Typical mass is between 0.1g to 200 g, while the best is around 10g.
2. Typical maximum dimension is 25mm to 35mm, while the largest is 250mm.
3. Typical wall thickness is 2mm to 3mm, while the thinnest is 0.3mm.

Available MIM metal

As most common engineering metal alloys have been demonstrated in metal injection molding process. However, we recommend the best selection of stainless steel. In our company, over 60% of MIM components are fabricated from stainless steel, we have the largest vendor base, production knowledge, and lowest materials cost in reason of high volume production. Generally, MIM is most suitable for higher molten temperature metal, and try to avoid easy oxidized and reactive metal, volatile and toxic metal. Such as beryllium, lead, manganese and magnesium.

MIM cost

Metal injection molding projects viability depends on not only parts cost, but also molds cost and producing time. In addition, complex geometries parts in MIM projects also require engineers skills and experience, corresponding operation time to achieve. Tooling cost and delivering time are the most significant factors to effect final MIM cost. While smooth surface and tight tolerance will also increase production cost.

Optimize MIM design

As in MIM design, we should optimize several aspects to improve the ease of MIM manufacturing, in addition, avoid some design features to reduce potential production cost.

Desirable features:

Gradual variation of section thickness

Wall thickness between 0.1mm to 10mm

Low mass weight

Supporting structure for sintering process

Permitted design features:

Free-form features, Axis symmetric, non symmetric, prismatic and square features

cantilever and non symmetric shapes

Retainers and stiffening ribs for assembly

protrusions, bosses, and studs

Blind and through holes,

External and internal threads

Undercuts, grooves, slots, depressions

Knurled and waffle surface

Identification logo, parts number and other text

Avoidable features

Closed inside cavities

Sharp corners or edges (radius less than 0.1mm)

Long piece without draft or taper for ejection

Undercut on internal bores

Holes diameter less than 0.1mm

Wall thickness than 0.1mm

Parts size limitation

In Metal Injection Molding process, the parts size is not an inherent process limitation, but an issue from the capacity of molding equipment. In addition, section thickness is another parts size issue, since molding, debinding, and sintering process are faster with thinner wall thickness. There is clear advantage in shorter cycle time with hollowed thinner section in MIM components.

Sintering impact

Sintering impact on tolerance is the most obvious issue for MIM design. As during sintering densification process, non-uniform heating and gravity force will impact final size and shape significantly. Depending on our forming equipment and technology, as-sintered dimensional tolerance will reach to ±0.3%.

Design modification

As our 10 years experience in MIM practice, we identify several design adjustment to ease MIM production greatly, there are design suggestion as follow: