Case Study 0904: Porosity Prediction and Part Design

It is a common practice to make dies with interchange­ able inserts and core pins to produce different variants from a same die to overcome the cost implications.

This is more so in the case of low volume parts where die cost per piece is very high. This case study is an example of one such die for a part that needs to be free from external porosity.

There are two variants from the same die with part numbers 1200 and 1201. The center core pin is inter­ changeable between a diameter of 62 mm and 67 mm.

Figure 5 -Machining of bore in variant #1200 results in shrinkage pores of Level 4 exposed to surface in-between the circled area indicated in almost all the parts after machining.

Figure 6 - Comparative solidification results at same time intervals -Left: 620(#1200) Right: 670(#1201).

Heavy blow holes are noticed in the variant #1200 in almost all the parts whereas the variant #1201 was free from any blow holes (Figure 5).

Analysis of Results
The comparative analysis of the solidification simu­lation at same time intervals as shown in Figure 6, clearly indicates that the variant #1200 is hotter near the core area as well as very slow in cooling, resulting in heavy blow holes.
Heavy shrinkage of Level 4 as per ASTM E505, noticed on variant #1200, because of higher wall thickness of 10 mm around 62 mm die bore, in simulation, in radiographic inspection and after physi­cal machining of the bore.

Figure 7 - Proposed suggestion far improvement.

The variant #1201 is free from the blow holes at all times. Hence, the correlation is well-established between the blow holes and the wall thickness in the area. So, a proposal for redesign of the variant #1200 to maintain the wall thick­ ness as per the variant #1201 is pending for customer approval (Figure 7). Earlier proposal of two separate dies has not been approved by the customer due to higher investment cost.

Key Benefits

  • Blow holes will be totally eliminated .
  • Uninterrupted supply
  • Low additional investment
  • Quick and easy to implement
  • Increased die life
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