As manufacturers in worldwide are purchasing to produce high-quality metal components with complex geometries. They prefer freedom design components without sacrificing cost. Traditional casting methods is no longer able to satisfy these special requirements, so new molding process like metal injection molding (MIM) and powered metallurgy (PM) is becoming more suitable for metal parts with high tolerance, excellent surface and material properties.
Metal Injection Molding(MIM) and Powered Metallurgy(PM) process
Powered Metallurgy (PM) basic process:
Mix or blend specific metal powder and lubricant
Form certain shape in die by compact press
Sinter compressed parts in furnaces to final parts with powder metallurgical bonds
Mix metal powders with polymer binders for feedbock
Inject feedbock in to molding machines for parts certain shape
Chemical or thermal process to remove binders
Sinter parts to densify powder and form metallurgical bonds
Although, MIM and PM use same base metal powders and custom alloys, the key difference of material is particle size. MIM powder (2-15 micron µm) is smaller than PM powder(50-100 micron µm), which give rise to less parts porosity in MIM process. So MIM parts density will achieve to more than 95% after sintering, while PM parts can only get 92% in maximum.
PM forms parts sharp in use of high-pressure uni-axis compaction, so it is suitable for simple shape with easily ejection form mold cavity. With MIM technology, there are very few geometrical restriction for 3D design freedom, in addition, MIM can combine 2 or more sub-components into one MIM parts. In following, there are normal MIM design improvement:
Uniform wall thickness: MIM can uniform all parts wall thickness to produce high tolerance products.
Coring and mass reduction: MIM utilize coring to reduce material waste, and never affect parts application in further usage.
Holes and slots, Undercuts, Threads: All these items are used for further assembly with other components.
Knurling, letter, and logos: MIM use these items to improve metal parts surface appearance.
As PM form parts shape in unique axis, so the friction and tension between metal powder mold surface will result to final parts non-uniform. By contrast, MIM parts can uniform friction and tension in all directions. Finally, MIM parts will display higher physical properties like surface appearance, corrosion resistance than PM parts. In addition, MIM sintering temperature is much higher than PM for same material, combine with very fine powder cause MIM parts has significant toughness and fatigue strength comparing with PM parts.
Reason to Choose MIM
Excellent for complex geometries
MIM is excellent for intricate design parts, liquid feedstock and injection molding means it can be formed into any structure with corresponding mold cavity. Unlike die cast metal powder into required shape in PM process, MIM can create complex geometries by various mold cavity structures. In addition, it is cost-effective to combine several departed components into 1 MIM parts.
On contrary, PM technology only have to produce these components respectively, and then, assemble them into final production with manual power. As consideration in these case, we can easily recognize MIM is an more cost-effective way than PM for parts with complex geometries.
High temperature sintering
In MIM and PM process, sintering temperatures are different from each other, even for same alloy materials. As we consider that MIM heating process will add substantial cost in manufacturing process compare to PM. On the other hand, we need to consider other outstanding returns as following:
High tolerance: MIM technology utilize smaller size powders and higher temperature sintering to remove binders and other impurities, in order to achieve actual dimension with higher tolerance as design than PM.
High density: Higher sintering temperature encourage more metal powder molten to elimination surface pores in process, as result MIM parts density is higher than PM parts.
Delicate surface: MIM parts surface toughness can reach to 1 µm, this is perfect for further secondary operation without additional machining process. By contrast, PM pasts need polishing process before further surface treatment.
Corrosion resistance: MIM parts with high density and delicate surface guarantee its higher corrosion resistance than PM.
High fatigue strength: Higher temperature sintering process will no doubt increase metal physical properties like fatigue strength. MIM parts will performance better than PM parts with same materials.
Choose Cost-effective Manufacturing Way
Volume & Complexity
In order to select the most cost-effective way of metal parts manufacturing, we need to analyze your projects of parts volume and complexity. PM May be cost-effective for simple parts, However, MIM is able to produce complex geometry metal parts with significant cost saving in secondary operation. Especially for two or more substantial components, which need to be assembled in further operations. MIM technology can produce these kind of component as only one MIM part, this will save the total cost of materials, design, assembly and logistic. In addition, MIM will reduce failure rate in manufacturing process.
As illustrated in the following graph, we should consider parts complexity and volume degree to select the most economical manufacturing choice. PM only can satisfy simple structure metal parts requirement, MIM is able solve complex geometries option.
Metal parts manufacturing is a complex process, which is affected by various factors. Once you are planning your next projects, you need to consider all of them. As following, we provide critical factor you should notice:
Size & Weight limitation: Your metal parts size&weight will determine main manufacturing way, PM and MIM are both suitable for small metal parts in size & weight range of 1-200 grams.
Tolerance limitation: MIM is most suitable for metal parts with high tolerance, if you need high precision metal parts, MIM is the only optimum choice.
Secondary operation: MIM parts are convenient for further secondary operations, once you are planning to add further surface treatment like coating, painting or anodizing, MIM is the most perfect manufacturing way.
Property requirement: MIM parts have almost 100% physical properties as raw materials, if your metal parts need special metal physical properties as electrical and thermal conductivity, high fatigue strength, MIM technology will satisfy all your requirement easily.