Designing Die-Cast Parts For Manufacturability

Update:Dec 01 2016
Summary:

Casting is one of the oldest procedures done on metals. […]

Casting is one of the oldest procedures done on metals. Many products are formed using this method. Here is an attempt to share the knowledge of casting.

Casting is one of four types: sand casting, permanent mold casting, plaster casting and Die casting. All these types of castings have their own advantages and disadvantages. Depending on the properties of the product requited, one of the casting is selected.

Sand Casting: Sand casting is the oldest casting of the above. This method of casting is in use since 1950.The texture of the product depends on the sand used for casting. The end product is given smooth finishing at the end. Usually iron, steel, bronze, brass, aluminium, magnesium alloys which often include lead, tin, and zinc are used.

Permanent mold casting: Permanent mold casting uses two pieces of mold. This molds are joined together and molten metal is pored into this mold. The hot metal is allowed to cool and the mold pieces are separated. Some products have metal extrusion which are removed by flash grind or by hand. Tin, lead and Zinc are commonly moulded using this method.

Draft - The mold used to create a die-cast part has to be designed so that the part can be easily removed from the mold after the part has been cast and has cooled. Draft is a slight angle designed into the vertical surfaces of the die to allow easier ejection of the part from the die after the die-casting process. Draft angles between 1º and 3º are common.

Fillet - A fillet is a radius at a corner where two surfaces meet, rather than having a sharp corner. An internal fillet reduces the stresses that occur in that location when the part is bent or stressed. An external fillet radius is used to eliminate sharp edges.

Undercut - An undercut is a feature of the die-cast part that prevents the piece from being ejected from the die after casting. Designs that require an undercut necessitate complex dies with removable slides so that the part can be extracted after casting. It is generally more cost effective to redesign the part to eliminate undercuts.

Plaster casting: Plaster casting is one of the easiest methods. How ever it is used for metals with low melting point like Coper, Zinc and Aluminum. This is the easiest process because mold can be made easily in case it brakes in the procedures.

Die casting: Die casting is done by introducing molten metal into the mold at high or low pressure. Earlier only low-pressure die-casting was used but now a days high pressure die casting is used more extensively. Molds are well designed to give complex products with stunning accuracy and smooth finishing. They are made of high quality steel as steel has higher melting point. These molds can be reused thousands of times. Casts can be single cavity that produces only a single component, multiple cavity that produces multiple identical parts at a time, unit die that produces different parts and combination die that produces different parts in one go. Usually zinc, copper, aluminium, magnesium, lead, pewter and tin based alloys are used for die casting.