High-pressure die casting is a cost-effective method for manufacturing high-fidelity metal pieces in medium to high volumes. It can produce complex components to tight tolerances with excellent surface finishes when it is performed correctly. However, many issues may arise during production operations that can affect the quality of the cast parts and products.
A Quick Look at the High-Pressure Die Casting Process
The high-pressure die casting process involves injecting molten metal under high pressure into a pre-fabricated steel die or mold. High speed-injection ensures that the liquid material is forced into every section of the die cavity. The result is highly accurate components with exceptional details and smooth finishes once the material is allowed to cool and harden.
Top Four Common High-Pressure Die Casting Defects
High-pressure die casting relies on highly accurate and precise metal temperatures, mold temperatures, gas ventilation, and injection pressure. The cast component can also be air- or water-cooled, depending on the material. If the temperature, cooling method, or injection pressure are not correct, a number of die casting defects can occur.
The four most common defects found in components made using the high-pressure die casting process are porosity, blisters, cold shuts, and misruns.
Porosity refers to holes or voids in solid cast metal components. They can range from very small (microscopic) to very large (several cubic millimeters or larger). The two main causes of porosity are solidification shrinkage and gas porosity.
- Solidification shrinkage occurs when the molten metal cools too quickly after being injected into the mold. The metal shrinks as it solidifies against the cooler mold wall, creating pores in the still-liquid metal away from the wall.
- Gas porosity refers to pockets formed by air or gas trapped in the mold. It can occur due to many conditions, including insufficient venting or material mixing during the mold filling stage.
Manufacturers can correct these issues by modifying the mold design and/or casting operation to ensure even cooling, reduce shrinkage, or decrease the risk of entrained air. The right solution depends on the root cause of porosity.
Blisters are a form of gas porosity that occurs closer to the surface of the component, often appearing as visible raised bubbles. They are formed when high-pressure air or gas trapped within the casting pushes the material outward after it is removed from the mold.
The solutions for blisters are based on the same principle as the solutions for internal gas porosity: reduce entrained air. They may involve cooling the mold at a different rate, adjusting water flow, increasing cooling time, or quenching the component upon ejection from the mold. You can also change the temperature of the alloy to reduce the thermal difference between the mold and the metal.
3. Cold Shuts
Cold shuts—also known as cold laps—occur when metal molten flows into the mold via two or more channels but cools too quickly. As a result, the streams solidify before meeting, which prevents them from forming a seamless piece.
This defect typically occurs because of poor gating system design or lack of material fluidity. Manufacturers can prevent it by modifying the gating system, increasing pour temperatures, or improving the mold’s gas permeability.
Misruns occur in similar conditions to cold shuts. However, the molten metal cools so quickly that it does not completely fill the mold, resulting in incomplete components.
The solutions for misruns are similar to the solutions for cold shuts. Manufacturers should check the mold design, the gating system design, and/or the fluidity of the molten metal.
High-Pressure Die Casting Solutions at DyCast Specialties
Manufacturers may encounter a variety of issues during high-pressure die casting operations. Knowing why they occur and how to avoid them is an indicator of a good die casting partner.
At DyCast Specialties Corporation, we provide high-pressure die casting solutions to customers in a broad range of industries. Our experts carefully set up and conduct operations to avoid metal casting defects in components. To learn more about our die casting services, contact us or request a quote today.