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How to Design a Die Casting Mold

Workers pouring molten metal into a casting moldDie casting is a technique for mass-producing metal products and components. Mold design is one of the most important steps in the process because the shape and attributes of the mold will directly affect the final product. The die casting procedure forces molten metal into molds using high pressure and it requires a mold with exact specifications to achieve the task.

The Importance of Mold Design

Mold design affects the shape, configuration, quality, and uniformity of a product created through the die casting procedure. Improper specifications can result in tool or material corrosion, as well as inferior product quality, while an effective design can improve efficiency and production time.

Factors Contributing to Quality Mold Design

There are a number of mold design factors to consider when deciding on the appropriate specifications for a project. Some of these factors include:
• Die draft
• Fillets
• Parting lines
• Bosses
• Ribs
• Holes and windows
• Symbols
• Wall thickness

Draft

Draft is the degree to which a mold core can be tapered. A precise draft is needed to smoothly eject the casting from the die, but since draft is not constant and varies according to the angle of the wall, features such as the type of molten alloy used, shape of the wall, and depth of the mold can affect the process. Mold geometry can also influence draft. In general, untapped holes require tapering, due to the risk of shrinkage. Likewise, inner walls can also shrink, and therefore require more drafting than outer walls.

Fillets

A fillet is a concave junction used to smooth an angled surface. Sharp corners can hinder the casting process, so many molds have fillets to create rounded edges and reduce the risk of production errors. With the exception of the parting line, fillets can be added nearly anywhere on a mold.

Parting Line

The parting line, or parting surface, connects different sections of the mold together. If the parting line is imprecisely positioned or becomes deformed from work strain, material may seep through the gap between the mold pieces, leading to non-uniform molding and excessive seaming.

Bosses

Bosses are die cast knobs that serve as mounting points or stand-offs in mold design. Manufacturers often add a hole to the interior structure of the boss to ensure uniform wall thickness in a molded product.  Metal tends to have difficulty filling deep bosses, so filleting and ribbing may be necessary to alleviate this problem.

Ribs

 

Die cast ribs can be used to improve material strength in products lacking the wall thickness required for certain applications. Selective rib placement can reduce the chance of stress cracking and non-uniform thickness. It is also beneficial for decreasing product weight and improving fill capabilities.

Holes and Windows

Including holes or windows in a die cast mold directly affects the ease of ejecting a completed molding and enables the creation of substantial drafts. Additional features, such as overflows, flashovers, and cross feeders may be necessary to prevent unwanted casting within the holes or poor material flow around the holes.

Symbols

Manufacturers often include brand names or product logos in the mold design of die-cast products. While symbols do not typically complicate the die casting process, their use can affect production costs. In particular, a raised logo or symbol requires additional molten metal volume for each manufactured part. Conversely, a recessed symbol requires less raw material and can reduce expenses.

 

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