Several instances of repeated failures of the die casting process resulted in high rejects, premature failure/short life of the die, etc., which are yet to be resolved.
This case study is an example of one such die for a part, a filter head of a fuel filtering system of an automobile. This part must be free from leak and external porosity in the machined area. Figure 8 shows an original shot along with an enlarged view of the part where there were heavy die erosions. These failures occurred in less than 20,000 shots. Several experimentations in terms of die material, heat treatments, shot parameters, metal temperature and cooling systems did not yield any improvement.
Heavy rejections due to blow holes in the 3x3 mm O-ring groove areas were also a perennial issue. This will be exposed only after the expensive machining operations were also completed.
The shot design change in terms of changing the metal feeding area was never contemplated. This is because of the collective and unanimous view of the team that feeding elsewhere from the original location would result in more failures. The reason for this opinion was the critical and thin groove areas. Since the die fails more frequently anyway, it was decided to experiment with the feeding system. Several versions of shot designs were developed and flow analyzed, including a version to increase the 3x3 groove area boss length as an alternate to overflows.
Figure 8 - Original shot with enlarged view of erosion area.
Figure 9 - a) Flow Simulation results of original design showing velocity >50 m/sec; b) Flow Simulation results of optimized design showing velocity <25 m/sec.
Figure 10 - Comparison of simulation results of original design (top) and optimized design (bottom).
Analysis of Results
The flow simulations for velocity profile and defect predictions were done. The velocity near the gate area of the original design was more than 50 m/sec, whereas it was reduced to less than 25 m/sec in the optimized design (Figure 9). This will result in significant reduction of die wear. The defect predictions of the original design as well as optimized design were correlated exactly with the actual data of blow holes in the 3x3 mm O-ring groove area (Figure 10). This has resulted in elimination of defects at the groove area.
The existing die was modified to convert into the new design. As the verification process is successfully completed, a new die is under development.