Design / Tolerances / Materials

The full advantages of Metal Injection Mouldings are best exploited by designing specifically for the process and full assistance will be given by our experienced technical staff.
Virtually any shape capable of being moulded can be produced by Metal Injection Moulding, offering a new freedom to designers, new possibilities to production engineers and cost savings to the purchasing manager.

The following guidelines cover the general design principles...

DIMENSIONAL TOLERANCES - Tolerances can be calculated generally as ±0.5% of the related dimension with a minimum tolerance of ±0.05mm. If closer tolerances are required, this may be possible if the feature is suitable for a setting or coining operation.
A fine surface finish is achieved in the order of 1.6 microns (63 CLA, N7)

MATERIALS - MIM parts have excellent strength, ductility, magnetic response and can be bent, welded, hardened and treated like any other metal.

• Low Alloy Steels
• Stainless Steels
• Magnetic Alloys
• Invar & Kovar
• Tool Steels

Aluminium and Zinc are not suitable for MIM.

COMPLEXITY - The more complex the design, the more economically advantageous MIM becomes. Almost any shape can be produced by MIM, following the well developed guidelines used for plastic injection mouldings. Intricate features can be made such as serrations, teeth, odd-shaped holes, flat-bottomed holes, blind recesses, cantilevered forms, lettering, internal and external threads.

WALL THICKNESS - Uniform wall sections are preferred, but not essential. A wall thickness of between 1mm and 5mm is preferable but sections ranging from 0.3mm to 10mm are possible, depending on overall geometry. Any weight reduction could reduce costs. Webs or ribs can be used to improve overall rigidity and strength.

CORNER RADII - Sharp internal corners can act as stress raisers. Radii of 0.4mm or more are preferred, although smaller radii may be possible. External corners can be sharp or have any size of radius.

HOLES AND THREADS - Holes with a maximum length to diameter ratio of 10 to 1 can be produced, with a minimum diameter of 0.5mm. Virtually any shape of straight hole can be formed. Internal and external threads can be moulded, depending on thread size, tolerance and orientation.

EJECTION PINS & 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.

Metal Injection Mouldings Ltd Davenport Lane, Altrincham, Cheshire, England WA14 5DS Tel: +44 (0) 161 928 4247   Fax: +44 (0) 161 927 7023   Email: mim@metalinjection.co.uk