How to Choose Right Metalforming Processes?---Casting

April 04, 2022

Casting is one of the earliest known methods of metal forming. It generally pours molten metal into a refractory mold cavity and solidifies it. After solidification, the desired finished product is removed from the mold, this processing is known as casting.

After years of development, today’s casting is subdivided into sand casting, investment casting, centrifugal casting, gravity casting, extrusion casting, lost foam casting, etc.

(1) Sand Casting: a casting method for producing castings in sand.

Steel, iron and most non-ferrous alloy castings can be produced by sand casting.

Advantage:

① Suitable for making complex shapes, especially blanks with complex inner cavities

② Wide adaptability and low cost;

③ For some materials with poor plasticity, such as cast iron, sand casting is the unique forming process for manufacturing its parts or blanks.

(2) Investment Casting: usually refers to making a pattern by fusible material, coating the surface on the pattern with several layers of refractory materials to make a mold shell, and then melting the pattern to obtain the mold without parting surface, which can be filled with sand and poured after high temperature roasting. This process is often referred to as “lost wax casting”. It is suitable for produce small parts with complex shapes, high precision requirements, or difficult to be produced by other processing, such as blades of turbine engines.

Advantage:

① High accuracy in dimensional and geometric.

② High surface roughness;

③ It can make castings with complex shapes, and the alloys materials are not limited.

(3) Centrifugal Casting: It is a casting method in which molten metal is poured into a rotating mold, and the mold is filled and solidified under the action of centrifugal force. Centrifugal casting was first used to produce cast pipes. Centrifugal casting processes are used in metallurgy, mining, transportation, irrigation and drainage machinery, aviation, national defense, automobiles and other industries in domestic and foreign to produce steel, iron and non-ferrous carbon alloy castings. Among them, the castings such as centrifugal cast iron pipes, internal combustion engine cylinder liners and shaft sleeves is the most common.

Advantage:

① There is almost no metal consumption of the gating system and the riser system, which improves the process yield;

②It doesn’t need the cavity core for producing hollow castings, so the metal filling capacity can be greatly improved in the production of long tubular castings, the ratio of the castings wall thickness to the length or diameter can be reduced, and the production process of sleeve and tube castings can be simplified;

③The casting has high density, less defects on pores and slag inclusions, and high mechanical properties;

④It is convenient to manufacture cylinder and sleeve composite metal castings, such as steel-backed copper sleeves, bimetallic rolls, etc. When forming castings, centrifugal motion can be used to improve the metal filling ability, the thin-walled castings can be produced.

(4) Gravity Casting: refers to a molding method in which liquid metal fills a metal mold under the action of gravity, then cools and solidifies in the mold to obtain a casting. Metal mold casting is not only suitable for mass production of non-ferrous alloy castings such as aluminum alloys and magnesium alloys with complex shapes, but also for the production of iron and steel metal castings and ingots.

①The internal pores of aluminum castings are small, and heat treatment can be carried out.

②The cost of the mold is low, and the service life of the mold is long.

③The process is simple and suitable for large-scale operations.

④Special aluminum alloy with low fluidity can be used.

⑤The use of materials is wide.

(5) Lost foam casting (also known as solid casting):Lost foam casting is a process used to create complex metal pieces and parts in which molten metal evaporates a foam mold being held still with sand. The process starts with a polystyrene foam as the mold material which can be carved, machined from a foam block, or created using a process similar to injection molding.. It is suitable for the production of precision castings of various sizes with complex structures, unlimited types of alloys and unlimited production batches. Such as gray cast iron engine case, high manganese steel elbow, etc.

Advantage

①The casting has high precision and no sand core, which reduces the processing time;

②No parting surface, flexible design and high degree of freedom;

③Clean production, no pollution;

④Reduce investment and production costs.

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Author:

Ms. SU LAN RONG

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