Case Study 1101: Failure Mode Analyis

The first three case studies are pertaining to a very critical part - a crank case used in an automobile compressor application.

During the production process, the die was found to wear very frequently resulting in high rejection rates, frequent breakdowns resulting in interrupted production for die maintenances.

The process audit revealed a very high injection veloc­ity of more than 2 m/sec whereas the theoretical velocity needed was less than 1 m/sec. This high velocity results in a very high gate velocity, thereby causing the rapid die ero­sion especially near the gate area (Figure 1a).

The design of the experiment revealed that the high veloc­ity is required, without which the part will not fill properly. On the other band the part geometry does not allow any more increase in gate area, creating a deadlock situation.

Figure 1a - Moving Core of the Die showing high wear near the gate area.

Figure 1b - Potential Defect Concentration at theoretical velocity of < 1 m/sec.

Figure 1c - Potential Defect Concentration at higher veloc­ity of > 2 m/sec.

The flow simulations for defect predictions were done for velocity of0.8m/sec (Figure 1b) and 2.2m/sec (Figure 1c).

The effect of the high velocity filling was very clear from the results, and it correlated with the process parameters, hence confirming that this part design requires such a short cavity filling time.

Discussion with the customer, based on the results of the simulations, resulted in the following decisions:

  • To change the moving core portion of the die at a frequency of every 25000 shots.
  • To work together to improve the Part Design and reduce the filling velocity.
  • To revisit the acceptance criteria without affecting the form, fit and function of the part, considering the Intricacy of the part as revealed by the simulation.
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