HIGH PRESSURE DIE CASTING
Die Casting also known as high pressure die casting (HPDC) is a metal casting technique that uses high pressure to inject a steel die cavity with molten metal.
This method of metal casting is especially suited for the mass production of small to medium sized metal parts because it:
- is mostly automated
- is able to produce net shape castings of geometrically complex parts
- produces parts with excellent dimensional accuracy
- is able to cast parts with a thinner wall thickness than other casting techniques
- allows for multiple finishing techniques
Die cast components are used in a wide variety of industries.
Among the industries that are heavy die-cast component users we see:
- the automotive industry which uses die cast parts as power-train components, body in white, seat structures, casings, gears, connecting rods and many other parts
- the white goods industrial sector including household appliances such as refrigerators and pasta machines, furniture and sporting goods
Notwithstanding this, die casting can also be the most “defect generating” of the high-volume metal casting techniques because of the high number of process variables involved and the non-synchronization of the process control units. One of the major sources of these defects is caused by air entrained during the cavity filling process, resulting from the shot curve profile adopted by the plunger and the layout of the gating system. Other common defects include shrinkage porosity, cold fills, oxide films and soldering, all of which affect the mechanical properties of aluminum or magnesium alloys.
High Pressure Die Casting: the Numerical Simulation
The die casting foundries are turning to numerical simulation to reduce their production costs while improving their production quality. In order to optimize the process layout of a die casting system through numerical simulation, a full fluid-dynamics simulation (using the Navier-Stokes equations) is required. Free-surface, turbulent flows, phase changes and friction all need to be included in the simulation. Thermo-physical properties which vary significantly over the temperature range of the process must be accounted for. Some typical aspects that a simulation should cover are:
- the pressure of entrained air, a key factor in the prediction of the location and size of gas porosity
- the thermal behavior of the die and its role during the metal-solidification phase, and the energy balance of all that contributes to this thermal behavior such as the die mass, thermoregulation channels, and the lubrication systems
Mastering the Die Casting Process through Simulation
Healthy competition in the die casting sector is why more and more foundries are turning to engineering simulation experts to help them achieve:
- "0 defect manufacturing”, reducing the current scrap rate of 5-6% to as close to 0% as possible by acting on the process variables in the design phase, resulting in substantial financial savings
- a throughout prediction of quality
- a reduction in casting trials
- a longer die life, minimizing any extraordinary maintenance needed
- reduced lead times for the finished product