Difference Between Gravity Casting and Pressure Casting

  • What is Gravity Casting?
    In conjunction with the pouring process of liquid metal, casting can also be divided into gravity casting and pressure die casting. Gravity casting refers to the process by which molten metal, also known as casting, is injected into the mold under the gravity of the earth. In the general sense, sand casting, metal casting, investment casting, clay casting, etc. are included in gravity casting; gravity casting applies to metal casting in the narrow sense.

    In gravity casting, the liquid aluminum is normally poured by hand into the gate. It fills the mold cavity, exhausts, cools, and opens up the mold to receive the sample, depending on the self-weight of the liquid metal. The flow of the gravity casting process is usually: molten aluminum smelting, filling of material pouring, exhausting, cooling, mold opening, production of clearing, heat treatment, and processing.

    The Gravity Casting Advantages
    1. In aluminum casting, there are few pores, so it can be handled with heat.

    2. The cost of the mold is small and the mould's service life is long.

    3. The method is quick and sufficient for mass manufacturing.

    4. It is possible to use special aluminum alloys with low fluidity.

    5. The materials are used extensively.

    Disadvantages of Casting with Gravity

    1. The product's surface finish is not big, and after shot blasting, it is simple to create pits.

    2. The low efficiency of production increases the cost of production.

    3. The method is straightforward and not acceptable for thin-walled pieces.

    What is Pressure Casting?
    Pressure casting is a procedure in which the mold is injected with liquid metal under the action of other external forces (excluding gravity). The general sense of pressure casting involves die casting machine pressure casting, vacuum casting, low-pressure casting, centrifugal casting, etc. The narrow sense of pressure casting applies explicitly to die casting machine metal pressure casting, referred to as die casting. The most widely used and the lowest price for non-ferrous metal casting are these kinds of casting methods.

    The casting of pressure is subdivided into casting of high pressure and casting of low pressure. High pressure casting is a type of casting in which the molten metal is poured into the pressure chamber to fill the high-speed steel mould cavity and solidify the molten alloy under pressure. High pressure and high speed are the major characteristics of high-pressure die casting.

    Low Pressure Casting Characteristics
    1. Quick prototyping, high productivity in manufacturing

    2. The product has high density, high strength and surface hardness, and low elongation under high-pressure moulding.

    3. The product's surface finish is high, usually up to Ra6.3.3.

    4. It can generate components for thin-wall

    5. Filling block, more interested in internal gas, bad product porosity of the product

    6. The internal gas can expand during heat treatment, resulting in product bulging or cracking and other defects can not be heat treated.

    7. Limited machining allowance, too much machining can impact the thick surface layer, exposed to internal pores, resulting in a decrease in product strength

    8. Elevated mould costs

    Low Pressure Casting Characteristics

    1. The casting utilization rate is exceptionally high. The gate is small, so the cost of the material and the manufacturing time can be drastically reduced. There is no riser and runner.

    2. Get the ideal casting solution. With few internal defects, it is simple to shape directional solidification.

    3. There is less interest of gas and debris. It is possible to adjust the pressure level, and the molten soup is filled by laminar flow.

    4. It is possible to use sand cores.

    5. Automation is simple to realize and can work in different devices and processes.

    6. It is not determined by the competence of the operator.

    7. There is extensive use of materials.

    Difference between die casting for gravity and pressure - gravity casting vs pressure casting
    1. The theory of gravity casting is to rely on the position of gravity, so that gravity naturally fills the liquid aluminum into the mold. Of necessity, centrifugal casting, which also belongs to the scope of gravity casting, is also used; the idea of die casting is to inject liquid aluminum by mechanical force, such as an injection rod, into the injection chamber. The pressure is created by the linear motion of the injection rod and the head of the injection, causing the mold to be filled with liquid aluminum;

    2. For parts with complex internal shape (such as gasoline refueling gun), gravity casting is usually used, while die casting is usually used for components with complex external shape but simple internal shape (such as the gearbox, etc.)