Rheocasting becomes a new solution to applications in many sectors, especially the telecom, automotive and transportation, EV, and power-sports markets.
Dynatool partnered in March 2020 with Comptech of Sweden to become their first North American provider of Rheocasting technology and components. We now have several castings in production on our 1650t Die Casting machine and are adding a 900t DCM in the coming months.
The advantages of Rheocasting:
Rheocasting basically combines the best of Low Pressure and High Pressure Die Casting.
Rheocasting is a high integrity die casting / semi solid casting process.
• Based on conventional HPDC, but eliminates major issues of the process (turbulent injection at high speed, die soldering, porosity, alloy limitations) => offering new opportunities for part quality/properties/applications
• The melt is modified to become thixotropic (like soft butter)
• This allows a laminar flow (no turbulence, almost no porosity) and slower injection speed and lower metal temperature (less die soldering, extended die life)
• Has longer fill time and feeding due to high viscosity and globular microstructure with low shear strength => allows casting very large castings (flow length of up to 730mm per 1 mm wall thickness) and extremely thin sections down to 0.4mm wall thickness – especially in combination with vacuum!
• With simplified gating – reduced projected area, and reduced intensification pressure required (less shrinkage) – significantly reduced DCM size possible!
• Ability to cast many otherwise very difficult/impossible to cast alloys (anything but eutectic) gives opportunities for excellent properties (mechanical/physical – see tables below), and therefore improved functionality of components
• High freezing rate allows higher Fe content than PM/Sand casting and therefore higher recycling content (lower carbon footprint)
• With the A356 alloy we can achieve a wide range of mechanical properties for different applications.
• The most common temper we use is T5, as it offers an economical compromise between properties and distortion in large parts.
• The alloy is easily available and can be sourced as primary or secondary (100% post consumer) alloy for lowest carbon footprint.
The structural Rivian door hinge pillar Rheocasting for the Rivian Electric Delivery Van demonstrates the process capabilities for structural applications (using A356-T5): Long flow length (part is 1.475m long). Thick (22mm) and thin (2mm) walls possible in the same part. Produced on a 1650 ton DCM (instead of a 2600 ton DCM if it was liquid die cast). Welded, crash relevant, with high requirements on mechanical properties.
Rivian Hinge Pillar Casting and how it is integrated into the largest Electric Deliver Van door on the market NADCA winner of casting of the year award 2022-Aluminum Semi Solid
Functions of hinge pillar casting and 23 spot weld locations.
The Comptech Rheocasting process:
• Simple process using a carousel (Permanent Mold) to create an EEM (Enthalpy Equilibration Material) that is carefully stirred in the liquid metal of the dosing ladle, creating the semi-solid slurry with the desired solid fraction
• Very high slurry quality with absolutely minimum oxide inclusions
• Solid fraction can be tailored (15-45%)
• Cost-efficient process (minimum addition to conventional HPDC process, significant increase in machine capability of HPDC cell) with small footprint for additional equipment
The following video shows how the semi-solid slurry making process works:
Rheocasting is the ideal process for telecom and heat sink applications:
Silicon content in die casting is important for long flow-length and good castability, but it reduces thermal conductivity. In Rheocasting low-silicon alloys can easily be cast and provide best conductivity, especially in combination with the special microstructure and heat treatments.
The special microstructure of Rheocasting (globular 𝛼1-Al) improves conductivity compared to standard casting processes.