Further design considerations

The impact of sintering on dimensional tolerances

Other details in the MIM product emerge from the physics of the process. For example, sintering involves heating the powder body to a point where there is little strength.

The material strength is often in the MPa range during sintering densification. At this temperature, gravity is a significant force. Accordingly, distortion due to non-uniform heating and gravity impact the final size and shape. Sintered tolerances are often quite tight prior to sintering, but more scattered after sintering.

Depending on the equipment and technology used the as-sintered dimensional tolerances are ± 0.3% and in some cases ± 2% or ±0.1%. Much dispute emerges over the tolerance issue, but in a few cases ± 0.02% has been demonstrated using sorted parts, but at a cost since there is only 80% process yield.

Further design considerations - Fig_9

Fig. 9 Sketches of some viable feature combinations seen in MIM

 

The advantages of PIM

To appreciate the inherent advantages of MIM, Fig. 9 shows sketches of some of the possible geometries and feature combinations encountered already with the technology. This collection is only illustrative of the possibilities.

Table 1 shows typical variations observed in MIM component production, illustrating what can realistically be expected from the technology.

Since the small powders used in MIM can be costly, good candidates for MIM tend to have high machining costs when compared to the material cost. And even for high volume materials, such as surgical stainless steel, the raw powder cost is probably twice that of the cast material. For this reason, MIM is not cost competitive with respect to castings, but can be competitive if there is considerable machining on the casting.

 
Feature Best possible ± Best possible ±
Angle 0.1°
Density 0.2% 1%
Weight 0.1% 0.4%
Dimension 0.05% 0.3%
Absolute dimension 0.04 mm 0.1 mm
Hole diameter 0.04% 0.1%
Hole location 0.1% 0.3%
Flatness 0.1% 0.2%
Parallelism 0.2% 0.3%
Roundness 0.3% 0.3%
Perpendicularity 0.1% or 0.1° 0.2% or 0.3°
Average surface roughness 0.4 µm 0.8 µm

Table 1 Typical variations observed in MIM component production (these are relative to the specified feature and the actual values encountered in production depend on many site-specific and component-specific factors)

 

Continue to next page: MIM material options and component properties

 

Industry News

Read the latest issue of PIM International

The latest issue of PIM International magazine is available to view online or download in PDF format.

As well as an extensive MIM and CIM industry news section, this 104-page issue includes the following exclusive articles and reports:

  • Threat or opportunity? The MIM industry as a partner, a target and a market for metal AM
  • WORLDPM2018 Congress: Global MIM markets show healthy growth
  • Ceramic Injection Moulding and Ceramic Additive Manufacturing side by side: Opportunities and challenges
  • Euro PM2018: Innovations in Metal Injection Moulding highlighted in Bilbao
  • > Go to magazine page

Connect with us

E-newsletter

Register for our e-newsletter and we'll let you know each time a new issue of PIM International magazine is available, as well as keeping you informed of MIM and CIM industry developments.

Industry News