Metal Injection Molding (MIM) and traditional machining are two common manufacturing processes for producing metal parts. While they have some similarities, they also have key differences that impact design, performance, and cost.
Traditional CNC machining cuts metal pieces to shape from bulk stock material like a bar or sheet. The machinist has precise control over geometry, surface finish, and dimensional accuracy. However, machining metal requires more raw material, generates metal chips as waste and tooling costs can be higher for complex parts.
What is Metal Injection Molding?
Metal Injection Moulding (MIM) is a manufacturing process that allows for the production of complex metal parts with tight tolerances. It involves mixing metal powder with a polymer binder to create a feedstock that is then injection moulded in a die cavity, much like plastic injection molding. If you are looking for MIM suppliers, connect to a Global Sourcing Company in India.
Metal Injection Molding (MIM) Process
The key steps of MIM are: metal powder made from stainless steel and other alloys is mixed with a polymer binder to create a feedstock. This feedstock is injected into a mould cavity under high pressure, forming a “green” part that has the desired shape. The green part is then sintered in a furnace at high temperatures to densify the metal powder and evaporate the polymer binder.
The sintering process causes the metal particles to fuse together, yielding a solid metal part. MIM allows for the production of complex metal components with intricate geometries that would be difficult to machine conventionally. However, powders, binders and the sintering process can impact the final material properties. Still, MIM is often used for high-volume production of small to medium-sized metal parts.
Quality Control and Inspection in MIM
MIM inspection begins with the incoming raw materials, including metal powders and binders, to establish baselines and specifications. In-process inspection of moulded green parts focuses on dimensional checks using tools like coordinate measuring machines, microscopy and laser scanning. Properties like density and mechanical strength are also measured at this stage.
After sintering, the final inspection examines parts for conformance to specifications for dimensions, tolerances, material properties and surface finish. Statistical process control methods are often employed to monitor key quality indicators and drive process improvements. Together, thorough inspection and effective quality control can minimize waste and rework while ensuring the production of parts that meet requirements.
Moulding Process Advantages and Disadvantages
ADVANTAGES
- Metal injection molding (MIM) allows for the production of complex parts with intricate geometries that are difficult or impossible to machine conventionally.
- MIM enables the manufacture of parts with tight tolerances and smooth surface finishes.
- MIM results in lower material waste since parts are formed, not carved out from stock.
- Production costs tend to be lower for high volumes due to lower tooling costs with MIM.
DISADVANTAGES
- The sintering process can impact material properties like strength and ductility, especially for stainless steel parts.
- Residual stresses induced during molding can also cause dimensional distortions in MIM parts.
- MIM feedstocks have a limited shelf life which constrains production planning.
- Material options tend to be limited compared to traditional machining.
- Part properties and costs tend to be more variable and less predictable with MIM.
- MIM is best suited for medium to high-volume production of complex metal parts that require tight tolerances and net-shape fabrication.
Materials Used in Metal Injection Molding
A wide range of metal powders can be used in metal injection molding, including stainless steel, tool steel, titanium, cobalt chrome, and superalloys. The choice of the metal powder depends on the required properties of the final part, with stainless steel and tool steel being the most common. Metal powders typically range from 5 to 20 microns in particle size to achieve optimal flow and density after sintering.
The metal powder is mixed with an organic binder to form the feedstock that is injection molded. Common binder materials include waxes, thermoplastics and thermosets. The binder serves to hold the metal particles together during molding but is removed during sintering. The properties of the binder affect the moldability of the feedstock as well as the density and integrity of the final part.
Other additives may also be included in the feedstock to control rheology, improve mold release or act as lubricants. The metal powder loading, or ratio of metal to binder and additives, is typically 65% to 72% by weight to achieve suitable moldability while maintaining the mechanical strength of the green parts.
MIM vs. CNC Machines: Which One is Better?
Both metal injection molding (MIM) and CNC machines can produce high-precision metal parts. However, each manufacturing process has its own advantages and suitabilities for different applications. MIM is better for complex components that would be difficult or impossible to machine. Due to its net-shape capability, MIM results in less material waste and lower tooling costs compared to machining. MIM is also a more efficient option for medium to high-volume production since setup times are relatively independent of part complexity.
However, CNC machines offer superior control over part properties and consistency. The material properties of parts made by MIM can vary more from batch to batch due to factors like variations in powder size and inconsistencies in the sintering furnace. CNC machining also supports a wider range of feedstock materials. While MIM is suitable mainly for powder metallurgy materials like stainless steel and tool steel, CNC machines can machine almost any common metal including aluminium, titanium, and brass. Connect to India Sourcing Company for CNC Machines.
In summary, MIM is best for producing medium to high quantities of complex metal components, especially those that require tight tolerances and net shapes. For simpler geometries, lower production volumes, or when more precise control of properties is required, CNC machining often provides a better manufacturing solution.
Conclusion
As discussed, MIM is better suited for complex, high-volume production while CNC machining offers more control, flexibility and consistency, especially for simpler geometries. Catalyst Sourcing, the best India Sourcing Company, can help you find the right supplier of MIM and CNC machining services based on your specific requirements. Our experts can provide a personalized quote and source the best suppliers to meet your needs in terms of part specifications, quality, cost and delivery. Get in touch with Catalyst Sourcing today to leverage our full-service sourcing solutions.
