Finite Element and CFD Based Simulation of CastingUsing Sophisticated FEA and CFD technologies, ESimLab Engineers can predict deformations and residual stresses and can also address more specific processes like investment casting, semi-solid modeling, core blowing, centrifugal casting, Gravity Casting (Sand / Permanent Mold / Tilt Pouring), Low Pressure Die Casting (LPDC), High Pressure Die Casting (HPDC), Centrifugal Casting and the continuous casting process. The metal casting simulation using FEA and CFD based technologies, enable us to address residual stresses, part distortion, microstructure, mechanical properties and defect detection include:
- Solidification: Micro Porosity, Gas Porosity
- Stress: Hot Tears, Surface Cracks, Residual Stresses, Cold Cracks, Distortion, Die Fatigue
- Metallurgy Specifications: Stray Grain, Freckle, Segregation, Distortion
- Pouring: Misruns, Air Entrapment, Oxides, Surface Defects, Cold Shuts, Turbulences, Inclusions, Core Gases
Reduce Development Cost
Test Before Manufacturing
Low pressure die casting
Low pressure die casting, LPDC, is a process in which a ceramic tube is connected to a steel die above and extends into a furnace of molten metal below. The furnace is then pressurized to fill the part by forcing fluid up through the sprue. Once the casting has solidified the air pressure is reduced allowing the rest of the metal still in liquid form in the tube to recede back into the furnace. Low pressure die casting is used for high production rates, thicker parts up to 2.5 mm, for better surface quality, and when high temperature heat treatment is needed to improve strength.
Based on problem description, FEA or CFD tools used with ESimLab engineering team to better design many aspects of a low pressure die casting through modeling thermal die cycling, filling, and solidification including thermally induced stresses and displacements. Better designs before production help alleviate trial and error through experimentation and bring designs to production more quickly. Both of which help save time and reduce costs.
High Pressure Die Casting (HPDC)
The simulation of die casting needs to replicate the following typical problems: Patterns and temperatures in the melt flow: last filled areas, venting of the die, aggregation of die agents, ‘dead areas’ in the runner, turbulences in the melt, disintegration of the melt and merging of melt fronts, cold shuts, or weld lines. Temperatures of the die: the complete die filling (especially during thin-wall casting), cycle times, core wear, adhesive tendency, or heat loss when spraying. Solidification of the casting: the creation of shrinkage cavities and pores, hot tears, microstructure formation, possible feeding in the final pressure phase or during local squeezing, as well as the formation of residual stress and consequently arising distortion.
Thermal Die Cycling
Thermal die cycling simulations are essential for high pressure die casting, since the same die is used repeatedly to produce thousands of castings. Maintaining consistent die temperature becomes more challenging over time due to warping in the die pieces leading to dimensional instabilities. With using Advanced CFD an FEA tools based on problem, the temperature distributions resulting from the combined effects of die heating, spraying and air blow-off, as well as the location of cooling channels and inserts can be accurately and efficiently predicted.
Shot Sleeve Optimization
The goal of a properly designed shot sleeve profile is to push the metal into the die quickly enough to avoid premature solidification, which can cause incomplete or defective filling. However, if the piston moves too fast, the liquid metal will fold over, trapping air that may appear as internal defects in the final cast part.
The most complex challenge in HPDC simulation is accurately tracking metal as it enters the die cavity under high pressure and at speed. The resulting splashing of the metal throughout the cavity presents a significant challenge to prediction of defects for any software. Using advanced simulation tools, we can determine the location of gates to ensure the best flow pattern, the location of overflows to ensure the defects flow to them, and the presence of early solidification.
FEA and CFD helps engineers investigate the formation of internal porosity that can affect the quality of the final part. Also enables the investigation of segregation in binary alloys. Finally, a detailed temperature history helps determine whether chills or cooling lines need to be added or modified, and whether the initial metal temperature should be changed. Numerical Simulation with FEA or CFD enables engineers to investigate the formation of internal porosities, thermally induced stresses, and segregation in binary alloys.
Goals & Objectives of HPDC Simulation:
- Reduce iterations in tooling development
- Reduce process development time: faster achievement of a stable process window
- Better process understanding: helpful when negotiate with customers about necessary part design changes
Typical defects in high pressure die casting:
- Misruns: Melt solidifies before filling is completed
- Cold shuts: Imperfect fusing of molten metal coming together from opposite directions in a mold
- Porosity: small holes caused by insufficient feeding or dissolved gas
- Air and oxides inclusions
- Cold flakes: floating crystals, solidified at shot sleeve walls and transported into cast par
Sand casting, the most widely used casting process, utilizes expendable sand molds to form complex metal parts that can be made of nearly any alloy. Because the sand mold must be destroyed in order to remove the part, called the casting, sand casting typically has a low production rate. The sand casting process involves the use of a furnace, metal, pattern, and sand mold. The metal is melted in the furnace and then ladled and poured into the cavity of the sand mold, which is formed by the pattern. The sand mold separates along a parting line and the solidified casting can be removed.
Some smaller sand cast parts include components as gears, pulleys, crankshafts, connecting rods, and propellers. Larger applications include housings for large equipment and heavy machine bases. Sand casting is also common in producing automobile components, such as engine blocks, engine manifolds, cylinder heads, and transmission cases.
Can produce very large parts
Poor material strength
|Applications:||Engine blocks and manifolds, machine bases, gears, pulleys|
In centrifugal casting, a mold is rotated at high speed while the molten metal is poured into it. The molten metal is thrown radially outwards to the interior of the mold, where it solidifies as it cools. The higher pressure associated with the centripetal acceleration forces pushes the defects towards the rotational axis.
Tilt pour casting simulations
Lightweight aluminum parts used in water sports rafting equipment require high-quality finish and are cast to be ideally devoid of surface and entrained defects. This simulation of the tilt pour casting process shows potential regions of trapped surface oxides and entrained air through the filling process. Knowing the movement of these defects helps metal casters design better gating, runners and risers to eliminate defects within the casting.
Continuous casting is the process where molten steel is solidified into semi-finished billets, blooms, or slabs for subsequent rolling in finishing mills. In continuous casting, liquid steel is transferred in a ladle to the casting machine. When the casting operation starts, the sliding shutter at the bottom of the ladle is opened and the steel flows at a controlled rate into the tundish and from the tundish into one or more molds.
Casting Simulation Features:
Thermal aspect of Casting Simulation
The heat release associated with phase changes such as solidification and solid phase transformations is described by an enthalpy formulation. Casting issues addressed by the thermal solver include:
- Hot spots and Thermal Modulus
- Macro and micro shrinkage
- Die cooling and heating optimization
- Runner and riser design
- Pin Squeeze
Stress field in Casting Simulation
Coupled stress calculations for precise prediction of casting, using fully coupled thermal, fluid and stress simulations with elasto-plastic or elasto-viscoplastic material behaviors for investigating :
- Thermal and mechanical contact
- Hot tearing and crack
- Distortion and deformation
- Stresses in the casting and die
Shrinkage and Gas Porosity
The phase transformations in solidification of metal are accompanied by shrinkage and sudden changes in the solubility of alloying elements, resulting in negative side effects as micro- and macrosegregation and the formation of gas and shrinkage porosities.
The mixed gas and shrinkage nature of porosity makes it difficult to identify and indicate the dominant source. It is usually believed that formation of gas and shrinkage porosity has different dependencies on the process conditions, and consequently, the gas and shrinkage pores are usually regarded as independent microstructural features.
In this contribution, it is shown that in high-pressure die-castings, gas pores can lead to the formation of shrinkage porosity under specific conditions. This is because the air/gas in the gas pores is an efficient heat-insulating medium. Therefore, presence of gas porosity can retard heat transfer in the liquid melt as compared to similar regions without gas porosity. Consequently, the local solidification rate is lower in such regions, leading to shrinkage porosity formation.For the computation of the porosity criterion the thermal gradient, cooling rate and solidification rate must be known. Using advanced FEA softwares, ESimLab engineers simulate detailed casting to determine parameters and further calculations of the shrinkage and Gas cavity.
Microstructure & Heat treatment
The formation of microstructures associated with solid state phase transformation during cooling or heat treatment simulated with special FEA or CFD tools using models based on Time-Temperature-Transformation (TTT) or Continuous Cooling- Transformation (CCT) diagrams. Mechanical properties determined from the calculated microstructure.
FEA Simulation of Grain Structure
The casting industry has seen rapid advancements in commercially available numerical simulation technology. FEA based Software enable us not only for thermal and flow modeling, but for calculation of grain structure, porosity, hot tearing, and solid-state transformation. In this investment casting process, the alloy starts to solidify at the contact with a chill under the form of very fine grains. In the ultimate case, when a single crystal is required for extreme applications, then one grain is selected through a narrow channel under highly controlled solidification conditions. ESimLab Engineers computes the grain structure formation during solidification using FEA based Softwares.