technique. Fig2b: Filling time plot (left), confirming the overflow locations to have filled the last and Shrinkage Porosity (right) highlighting the hot spots in the casting. Fig2a: Progressive filling in the cavity. Fig 3a: Die temperature profile taken at hottest mold/ casting interface. cavity into these and no major air entrapment. The plot indicates the fraction of element that Fig 3b: Die temperature profile of Mobile Die (Top) and Fixed Die (Bottom) at the end of 8 cycles (shots). is filled. The filling time plot in Fig 2b (left) Light blue circles and bars indicate the cooling circuits of the 2011 die. confirms the overflow location validation, confirming the Step 1 analysis. Shrinkage Poro- Cooling lines at appropriate locations will only ture decrease of about 70°C at die skin on the sity plot inFig 2b (right) shows mostly similar help this in the next step. hottest mold/casting interface point. risks than what was observed in Step 1. We do notice some additional regions of porosity than Fig3b shows the hot spots in the both the Sleeve filling seems to be quiet enough to what was noticed before. This could be because mobile & fixed dies, as well as the cooling cir avoid any major turbulences inside the sleeve - of the change in thermal gradients and filling cuits (indicated in light blue circles and bars) (Fig 4c). The slow shot V1, shows a wave that profile we create by adding the biscuit and used in the 2011 die are highlighted. Some encloses slight air in the sleeve, which can lead runner into the simulation, as opposed to the riht in unfortunately to oxides and air entrainment ideal gate velocities in Step 1. If these regions, front of the hot spots, and some not. inside the part that are very difficultto antici- don’t request strong mechanical characteris- pate without simulation.Fig 4d shows possible tics, and hot sealing can cover them up (if) post Such simulation results during the die design air entrainment locations at the end of the machining, this is an acceptable solution. stage, enable the designer to determine the filling. These are qualitative results and shall locations of the cooling channels in a more be validated further as experience grows. The STEP 3: DIE DESIGN (WITHOUT smarter way, thereby arriving at an optimized current locations indicated are close to core COOLING LINES) die design. The dimensions of the cooling chan- pins, and overflows,which can help pulling out nels, are determined based on the amount of this air and lead to fortunately no gas problem Pre-shot timings are assumed to simulate heat still required to extract from those hot for this DT1 loop. Part fill time plot (Fig 4e left) this step, including the spray sequence. spots in the available time during the shots. shows very similar behavior to previous steps, confirming this to be an interesting parameter Fig 3a shows a temperature profile through STEP 4: FULL DIE DESIGN & PRO- to follow during all the simulation. the shots taken on the hottest mold/cas- CESS VALIDATION ting interface. The trend line indicates the Finally concerning shrinkage porosity risk (Fig reduction in the delta of peak temperatures Thermal Cycling simulation results shows that 4eright), the critical regions continue to have between shots, indicating reaching of the die thermal steady state is achieved almost the porosity. Cooling lines positively influence stabilized die temperatures. It means that same way compared to previous simulation reduction in porosity in boss B (Fig 5b), while the current external cooling is designed well without cooling systems (Fig 4b left). Even if doesn’t influence or slightly counter-produc- to ensure quick thermal stability of the die. temperature profile is equivalent, internal die tive in the boss C & boss D regions (Fig 5b). It Ofcourse temperatures are at a higher end. cooling has a clearly visible effect on tempera- must be noted here that the cooling lines used N°10 • AVRIL 2019 • 39