What Can MIM Offer?
Depending on size and component design, accuracy is generally from ±0.05mm on a 10mm dimension, and pro-rata for other dimensions, as shown in the tolerance chart.
| General tolerance =1% of dimension
with minimum of ± 0.05mm. Examples: |
| DIMENSION |
TOLERANCE |
| up to 10mm |
± 0.05mm |
| 12mm |
± 0.06mm |
| 18mm |
± 0.09mm |
| 24mm |
± 0.12mm |
| 40mm |
± 0.20mm |
Surface Finish
Generally 1.6 microns (63 CLA, N7). Surface treatments can be applied to MIM components by conventional methods, including polishing, grinding, plating, case hardening, etc.
Quantities
Typically 20,000 or more per year, but smaller quantities of metal injection mouldings can be economically viable, depending on size, complexity etc.
Size Range
Generally from 2mm to an envelope size of approximately 50mm, but lengths up to 150mm are possible. Maximum weight – approximately 100 grams.
Hardened steel dies are used, similar in design to injection dies for plastics or pressure die-casting.
Materials
Metal injection mouldings can be made in carbon and low alloy steels; stainless steels; tool steels; nickel and cobalt alloys; Invar and Kovar and magnetic irons. see Materials
Quality
Approval - BS EN ISO 9001:2008. Certification can be supplied if required, including Chemical Analysis, Mechanical Testing and Non-Destructive Testing.
Design Guide
The full advantages of Metal Injection Mouldings are best exploited by designing specifically for the MIM process and full assistance will be given by our experienced technical staff. The following guidelines cover the general design principles which are similar to those used for plastic injection mouldings and pressure die castings
Complexity - The more complex the design, the more economically advantageous metal injection moulding becomes. Most shapes that can be injection moulded are also suitable for the MIM process following the well-developed guidelines used for plastic injection mouldings and pressure die -castings. Intricate features can be produced by MIM, such as serrations, teeth, odd-shaped holes, flat-bottomed holes, blind recesses, lettering, internal and external threads.
Wall Thickness - Uniform wall thickness is preferred for metal injection moulding, but not essential. A wall thickness of between 1mm and 5mm is preferable but thicknesses ranging from 0.3mm to 10mm are possible, depending on overall geometry. Any weight reduction could reduce cost - webs or ribs can be used to improve rigidity and strength.
Dimensional Tolerances - Typical MIM tolerances are shown in the table above. Where closer tolerances are required, additional operations such as coining and setting can be carried out. It is good practice to only add tolerances to the critical features on a drawing, as even non-toleranced dimensions will have excellent repeatability. A fine surface finish is achieved by metal injection moulding, in the order of 1.6 microns (63 CLA,N7).
Corner Radii - Sharp internal corners and notches can act as stress raisers. Radii of 0.4mm or more should preferably be used although internal corner radii of 0.15mm minimum may be possible on critical features. External corners can be square or have any size of radius.
Holes and Threads - Holes with a minimum length to diameter ratio of 10 to 1 can be produced by the MIM process, with a minimum diameter of 0.5mm. Virtually any shape of straight hole can be formed, whether through holes or blind holes. Internal and external threads can be moulded, depending on thread size, tolerance and orientation.
Ejection Pins and Parting Lines - Draft taper is not generally necessary but injection pins and gates are required and these may leave witness marks on the component surface. Small parting lines may be apparent, along the die split lines. The above points need discussion at the design stage.
