Tolerances

MIM processing normally requires a dimensional tolerance of ±.003 inches/inch (±0.3percent). As part size decreases, increasingly tighter total tolerances can be achieved, as would be expected. However, the reduction in tolerances is not directly proportional to decreasing dimensions and may depend on material, part shape, and process requirements. A tolerance of ± 0.1 percent can generally be held on a small, selected dimension when the mold has been “fine-tuned”. Typical tolerances for MIM parts, over a range of dimensions, are shown in Table II for both standard and specialprocessing. Geometrical tolerances are shown in Table III.

As can be seen, it is possible to improve tolerances with tighter process control but this may reduce process efficiency and increase cost.

Extremely tight tolerances may have to be obtained through machining:

Tolerances

Tolerances specified should be no closer than absolutely required for satisfactory performance.
Close tolerances should not be specified for parts having major wall thickness variations.
Close tolerances on several dimensions of a part usually result in increased part cost.
Close tolerances should not be specified across a parting line or for dimensions controlled by movable cores or sliding cams.

 

 

 

Table II - Typical Tolerance
in thousandths of an inch

Dimension (Inches)

Standard Tolerance Special Control

 3.000

+/- .009

-

 2.000

+/- .006
-

 1.000

+/- .003

+/- .0020

 0.500

+/- .0025
+/- .0015

 0.250

+/- .0020

+/- .0010

 0.100

+/- .0015

+/- .0010

 0.050

+/- .0010

+/- .0010


Table III - Geometrical Toleraces

Characteristic Related Surface Typical Tolerance (IN/INCH)

Flatness

A

.002

Parallelism

A to B
.003

Perpendicularity

C to B

.002

Concentricity

C to D
.003

Roundness

C

.003