Knowledge Centre - What Is Casting?
Casting is a manufacturing process with around 6,000 years of history. During the process, a liquid such as hot metal is poured into a container, or a mould. After the metal is solidified, the resulting cast, also called a model or an object, will have the desired shape.
Modern metal casting could be classified into 4 types (Figure 1). Ming Ming’s gravity casting is based on permanent mould casting.
Materials used in casting
Materials used for casting include metal, plaster, concrete, and plastic resin. Most commonly used materials in metal casting include gray iron, ductile iron, aluminium, steel, copper, and zinc. Ming Ming specialises in aluminium metal casting and provides tailor-made applications for various industries.
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Moulds are negative forms used for shaping casting materials.The type of mould technique depends on the complicity of the desired model and the mould can be open or closed for metal casting, the closed mould is the common form.
Depending on whether it can be repeatedly used, the mould can be expendable or long-lasting.
The long-lasting mould can be used to create many metal objects and is often made of metals or a refractory ceramic.
In gravity casting,moulds are often made of metal or Graphite. Ming Ming’s gravity casting process uses non-expendable or long-lasting moulds and produces objects using only metal moulds coated with a mould wash.
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Difference between gravity casting and die casting
Both gravity casting and die casting are permanent mould casting using moulds made of steel materials. In gravity casting, molten metal is poured from a crucible into a mould by using the force of gravity, instead of using the pressure from gases, vacuums or centrifugal forces.
In contrast, die casting relies on pressure to inject molten metal into the mould. This process is the most common approach in permanent mould casting.
The advantage of permanent mould casting and gravity casting
Advantages of permanent mould casting include:
- The reusable mould
- Rapid solidification
- High productivity
- Cost-effectiveness in the long run
- A lower scrap rate
Gravity casting, as one type of permanent mould casting, also has the above advantage. Besides, the model produced through gravity casting has better cast surface finish, high consistency, good dimensional accuracy, and good mechanical properties.
Applications of gravity casting
Gravity casting is often used on non-ferrous metals and alloys, such as aluminium, zinc, and copper, among which aluminium alloy gravity cast objects are more common. The applications of aluminium gravity casting include:
- Robotic arms
- The machinery/hydraulic presses
- Engine parts for the automobile
- E-bike parts
- Engine parts for the motorbike
- Aerospace parts
- Parts for the medical device
- Parts for the construction industry
Ming Ming’s gravity casting has served customers in various industries and from different countries and produced a wide range of gravity cast components.
The smallest object Ming Ming has produced weighs 0.1 Kg and the largest object reaches the size of 1500mm x 900mm x 400mm.
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The process of gravity casting
The gravity casting process often involves the following steps:
- Understand the customer’s needs. The procedure should start with understanding the customer’s needs, such as the application of the cast, the choice of alloys, size, shape, wall thickness, technical properties (e.g.,tensile strength,yield strength, and elongation), structure, and weight.
- Design of the cast and ‘pattern’ making. This is important for industrial parts, which need precise calculation to make sure that pieces could fit and work together. Currently, the pattern making is assisted by computer simulation so that high precision can be achieved. Then the pattern is moulded into a three-dimensional shape so that the accuracy of the core could be measured before the final casting. Wood, clay or plastic is often used here. Due to the development of technology, now this can be done through 3D-printing
- Creation of a mould. Based on the confirmed pattern, a mould is created. In the case of gravity casting, reusable metal moulds are created for the desired pattern.
- Melting and pouring of metal or alloys. Metal is melted and then the molten metal is poured into the mould under gravity. Traditionally, this is done by hand. Thanks to modern technology, this pouring process is automatised and the productivity is tremendously improved.
- Fettling. The cast object is removed from the mould and then fettled. During this process, any moulding materials on the model are removed and rough edges and surfaces are smoothed. The cast object might need to be further processed.
Gravity casting process monitor and quality control
The quality control in gravity casting should be done through the whole process, from the design of the pattern to the inspection of the end product. During the discussion with the customer, the chosen casting process, the choice of alloys, and technical properties are an important start.
In the casting process, the following parameters must be monitored and controlled: shrinkage allowance and machining allowance for the pattern, the design and control of the core and the mould, the heating temperature of the metal, the amount of gases inside the molten metal, directions of pouring, the velocity and friction during the pouring, and the solidification time, and shrinkage of the cast object.
The final cast should go through quality inspection such as dimensional measurement, chemical composition analysis, mechanical properties testing, metallurgical analysis, and non-destructive testing.
At Ming Ming, we serve customers based on our T.O.R.S. principle and are earnest in bringing customers the premium-quality cast objects with reasonable prices.