IN THE SIMULATED PROCESS
Definition of the parameters
Since the details regarding the conditions surrounding the process are not known in detail, for this industrialization project for a cover we decided to consider pejorative values compared to those that will be actually used. This should leave us a good margin for improvement. We therefore assumed a 650°C temperature for the metal inside the cavity after pouring. As regards the study of the die casting alone, without the presence of the actual mould, we placed the die temperature at 200°C. Without the complete thermodynamic analysis we could not base ourselves on the definitive layout, so we decided to approximate the results using an average temperature. As regards the simulation of the actual mould, instead, we simulated the thermal values of each circuit that can be water or oil cooled according to need. The aim was to achieve dies at 230-250°C.
First of all we did the casting study. Based on our experience, we decided to use a speed at the gates ranging from 40 to 45 m/s. This value is not too high – so as to avoid premature mould wear problems – but not too low either, so as to prevent the material from cooling so quickly as to create cold drops in the part. In this case also, in order to ensure a margin of machine improvement, we chose to keep a 2nd phase speed of not more than 3.5 m/s.
We then proceeded to calculate the specific pressure and the press and, based also on certain safety parameters, we finally defined the press necessary. The casting volume, the plunger diameter and the data regarding the press used then allowed us to calculate the filling rate. Once the parameters were defined, we went on to perform the simulation and the tests regarding temperature, speed, material trace and air pressure. Result analysis led us to make a few additional changes, especially on the gates, and to test a second version of the mould before arriving at the satisfactory result.
In detail, the analysis of the first model revealed the metal’s tendency to fill the central area of the part first and only then the external area. We decided therefore to slightly widen the gates to make filling more homogeneous. In this second model, the speed and temperature values proved to be correct and filling improved. We then decided to add exhausts and 2 chill vents (35 mm²) in the two areas where the highest pressure peaks were generated. These changes gave positive results. In some areas a few small pressure peaks remained but they were to be checked again by simulation once the piece was industrialised.
At this point, we checked deformation and the simulated process showed part deformation that was in compliance with the maximum dimensions of the die.