The Process

Remington’s InjectAlloy® parts start as very fine metal powders, typically less than 20 microns in diameter, which are mixed in precise proportions with expendable thermoplastic binders. The combination of metal powder and polymer is then pelletized and fed into conventional injection molding machines. Under heat and pressure, the feedstock flows into and assumes the shape of the mold cavity. After removal from the mold, parts are subjected to thermal processing to remove the binders and are finally high-temperature sintered to achieve the required metallurgical properties.

Composition


  FE-2% NI2 FE-3% SI 316L Stainless 410 Stainless 17-4 Stainless W Heavy Alloy

 Density(g/cm3)

 

7.5

7.8

7.8
7.5
7.6
17.5

 % of full density

 

95

99
98
97
98
98

 Tensile Strength x103psi)

 

55

75

78
220
190
110

 Elongation(% of 1 inch)

 

25

25
50
5
6 5

 Hardness, Rockwell

 

B55

B85

B68
C40
C41
C25


Selected Property Data
A variety of metal alloys can be made with the MIM Process. Remington works primarily with compositions of low alloy steels, soft magnetic materials, stainless steels and tungsten heavy alloys.Since final density is typically 95 to 98% of wrought metal, excellent mechanical and magnetic properties can be achieved. The properties included in Table 1 are not guaranteed minimums, but are typical values provided as an indication of the expected range for design consideration. For minimum property data, please refer to MPIF Standard 35: Materials Standards for Metal Injection Molded Parts.

Part Parameters
As with any process, there are limits of applicability. The following paragraphs will help to establish the general characteristics of MIM parts. These guidelines are not absolute, and are influenced by a number of factors related to part design.

Size Range
Metal injection molding is best suited for relatively small to medium size parts. On a volume basis, parts should typically be smaller than a tennis ball, with the process being most cost effective when parts are smaller than a golf ball. Irregularly shaped parts can be produced with a major axis of up to about 4 inches (102mm) in length. The lower limit of the size range is determined only by the limitations of the injection molding process itself. Parts as small as 0.25 X 0.10 X 0.05 inches (6.4 X 2.5 X 1.3mm) are feasible. The upper limit of part size is established by processing economics, not technical limitations.

Wall Thickness
The cross-section or wall-thickness is what ultimately determines whether it is feasible to produce a particular InjectAlloy® part. The part thickness must be kept relatively low to facilitate efficient binder removal. The practical range of section thickness is from 0.03 inch (0.75 mm) to 0.22 inch (5.6 mm). Parts can be molded with thinner cross-sections, but are limited with regard to flow length. MIM parts are sensitive to the relationship of cross-section to length, and it is difficult to form long, tubular parts with thin walls.

Weight
Parts can be made which weigh from 0.1 to 150 grams or more. However, InjectAlloy® parts are most cost-effective in the range of 1 to 50 grams per part, which reflect size and wallthickness considerations.