• Document: NetShape - MIM. Metal Injection Molding Design Guide. NetShape Technologies - MIM Phone: Solon Road FAX:
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NetShape - MIM Metal Injection Molding Design Guide NetShape Technologies - MIM Phone: 440-248-5456 31005 Solon Road FAX: 440-248-5807 Solon, OH 44139 solutions@netshapetech.com 1 NetShape - MIM Frequently Asked Questions Page What is metal injection molding (MIM)? 3 What materials can be made in MIM? 3 How does MIM compare to other metalworking technologies? 4 Why are sintered densities higher in MIM than in powder metallurgy? 4 What types of components are suitable for MIM? 5 Can existing MIM tools be transferred to NetShape MIM? 6 Can different materials be run with the same tool? 6 Are multi-cavity tools used in MIM? 6 What can be done to minimize tooling costs? 6 What is the expected tool life? 6 What secondary operations can be performed on MIM parts? 7 Design Material Properties 7 Surface finishes 7 Tolerances 8 Shrinkage 8 Maximum/Minimum Cross Sections 8 Tooling Threads 9 Surface Details 10 Changeable Inserts 10 Draft 11 Sintering Supports 12 “Lightweighting” Parts 12 Uniform Wall Thickness 13 Turning Assemblies into a Single Component 13 2 NetShape - MIM What is metal injection molding (MIM)? MIM produces complex, high-volume, repeatable components out of high melting temperature alloys. The most common alloys done in MIM are ferrous. All MIM processes have these four elements in common: 1. Mix a fine (<20 um) metal powder with a binder (usually polymer-based). 2. Mold the mixture using slightly modified plastic injection molding machines & molds. 3. Remove some or all of the binder from the molded component without disturbing its shape. 4. Sintering the component in a high temperature furnace, where it shrinks 15-20% & densifies to >95% of the alloy’s theoretical density. What materials can be made through MIM? Alloys with a higher melt temperature than copper are the most common materials done in MIM. Lower melting materials, like zinc & aluminum, are better suited for die casting. Alloys that form strong oxides (e.g. titanium) are difficult to process. Alloy Type Examples Low-alloy steels 4650; 4140 Stainless steels 304L; 316L; 17-4 PH; 420; 440 Magnetic steels 50% Fe - 50% Co; Fe-3% Si Controlled expansion alloys Fe-Ni alloys like Invar High density alloys W-Ni-Fe; up to 18 g/cc High Temperature Superalloys Inconel 625, Hastalloy X 3 NetShape - MIM How does MIM compare to other processes? Die Casting: MIM can handle higher-temperature alloys than die casting, since the MIM alloys are never melted - the polymer binder allows the powder to make the desired shape in a die at temperatures similar to plastic injection molding. This also results in very long tool life, with cavity lifetimes of over 250,000 shots without needing substantial rework. Stamping/ Fine Blanking/ Screw Machining: By using tooling similar to plastic injection molding tooling, complex 3-dimensional geometries impossible to produce by stamping, fine blanking or screw machining are easily produced in MIM. Powder Metal: Small powder sizes (typically < 25 um) can be used in MIM, smaller than the powder used in traditional powder metallurgy. The small size leads to a relatively high amount of free surface area, which during sintering allows MIM components to sinter to near full density. Also, the MIM molding process allows for more complex designs. CNC/EDM: The use of multi-cavity tooling can provide high production rates (100,000

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