technique. Fig1a: Cavity Filling Time. Fig1b: Shrinkage Porosity plot highlighting the main hot spots in the casting. profile, it could also be decided on which die STEP 4: DIE DESIGN & PROCESS (mobile/fixed) should the ingates be posi- VALIDATION connected to the gates through liquid metal, tioned. Ideal gate velocities are assumed thereby compressing porosity levels. based on the theoretical cavity fill time as a Die design is now developed completely, boundary condition for this simulation. including cooling system and it’s time to go Atleast 3 possibilities can already be thought for a comprehensive validation of the part about at this stage to reduce the possible The main goals to achieve from this step quality on this full die design. This stage is also porosity risk: would be: important, as it allows early (pre) definition of • The locations of hot spots outside of the Ingate position/dimension validation what will be the process conditions in terms indicated region in Fig 1b, are mostly • , keeping in mind the flow balancing, of cycling times, casting temperature, cooling allowed as no specific mechanical flow lengths and as much as possible management, sleeve fill ratio, slow shot, slow characteristics are requested, and hot lesser air entrapment at locations to fast switch, fast shot, 3rd stage pressure, … sealing post machining could be an where the venting will not be acceptable solution. possible. First thermal cycling is run till a steady state die • The cooling system which will evolve Last filling regions to determine the temperature is reached (operating die tem- later in the die design, could be an • overflow positioning. peratures on the shop floor), and then the full option to extract heat out of these Hot spot identification in the casting, filling & solidification results are run on this die. regions and reduce the probability of • as these could be potential porosity porosity formation. However, on locations. >>> SIMULATION RESULTS AND careful observation, the bosses and rib network around these hotspots STEP 2: ANALYSIS are too thick, giving it a low chance to INJECTION SYSTEM DESIGN change drastically the defects in STEP 1: these areas. Once the die designer has the product design MANUFACTURABILITY CHECK • Change in product design seems to in front of him, he must first define the clus- (BARE CASTING) be the best way. However, this ter size and position, in link to the HPDC filling solution was not considered during rules available, and hence the HPDC press that The cavity fill time in Fig 1a, shows the last the 1st physical test loop in 2011, as is going to be used. Designing of the full die regions to fill. An overflow in these last filling the design was frozen before the die comes later. Design of the injection system regions, opposite of the ingates and the encir- design started. But finally, it was including overflows must be validated (posi- cled area will normally function well to trans- understood and redesigned much tion & dimensions) in terms of air entrapment port the air out of the cavity. No high risk of any later. For our further analysis in this and shrinkage risks.Rules are also available for major air entrapment can be seen at this stage. paper however, we shall continue overflow dimensioning. An assumption of a with this unchanged product design. simple die around continues in this step as well. Fig1b, highlights massive hot spots in the cas- ting, which may lead to porosity. The porosity STEP 2: STEP 3: DIE DESIGN in the highlighted region is the main area of INJECTION SYSTEM DESIGN concern, as indicated in Fig 5ashowing the (BISCUIT/RUNNER/INGATE/OVER- After having designed the injection system, quality requirements for this part. It must FLOWS) die designer can now start to design his com- be noted here that an intensification pres- plete die shapes. This part allows a flat par- sure of 900 bars, appropriate with the HPDC Filling through an injection system biscuit ting line, with the mobile and fixed dies able press was considered. The physics behind (means without a shot piston) helps a quick to form the entire casting part. The cooling the Advance Porosity Model (APM) of Pro- analysis of the runnr design and the overe - system however, can only be dimensioned CAST allows to compute shrinkage porosity flow validation. The progressive filling in Fig after having simulated some cycles (shots) risks considering the effect of intensification 2a confirms good positioning of the initial to identify where the hot spots are in the die. pressure which helps in force feeding regions overflows as the flow pushes the air in the 38 • N°10 • AVRIL 2019