Casting process

Casting

• Casting is a manufacturing process where liquid material is poured into a mold containing a hollow cavity of the desired shape, then allowed to solidify.
• The solidified part is also known as a casting, which is then ejected or broken out of the mold to complete the process.
• Casting materials are usually metals or time setting materials that cure after mixing, such as epoxy, concrete, plaster, and clay.
• Gravity or other forces help in process in which molten metal flows into a mold where it solidifies into the shape of the mold cavity.
• The term "casting" also refers to the part made in the process.
• Casting is used for making complex shapes that would be difficult or uneconomical to make by other methods.
• Heavy equipment such as machine tool beds and ship propellers can be cast easily in the required size.
• A successful casting process needs preparation of molds and patterns, melting and pouring of liquefied metal, solidification and cooling to room temperature and defect inspection.

Capabilities and Advantages

• Complex part geometries that could not be made by other processes can be made.
• Can create both external and internal shapes.
• Some casting processes result in a net shape; others are near net shape.
• Produces very large parts with weights of more than 100 tons, like m/c beds.
• Can shape any metal that can melt.
• Some methods are suited to mass production.

Disadvantages

• Limitations on mechanical properties
• Poor dimensional accuracy and surface finish depending on the process; e.g., sand casting.
• Safety hazards exist for workers due to hot molten metals
• May cause environmental problems

Parts Made

• Big parts, such as engine blocks and heads for automotive vehicles, machine frames, railway wheels, pipes, bells, pump housings, and mill rolls.
• Small parts, such as dental crowns, jewelry, small statues, and frying pans.
• All varieties of metals can be cast, ferrous and nonferrous.

Overview of Casting Technology

• Casting is usually performed in a foundry.
• A foundry is a factory equipped for making molds, melting and handling molten metal, performing the casting process, and cleaning the finished casting
• Workers performing casting are called foundrymen

Sand Casting Process

• Sand casting is a versatile casting process that can be used to cast any metal alloy, ferrous or non-ferrous.
• It is widely used for mass production in industrial units, such as automotive metal casting parts, like engine blocks, cylinder heads, crankshafts, etc.

Advantages of Sand Casting

• Relatively inexpensive in terms of production costs, especially in low-volume production.
• Fabrication of large components can be achieved.
• Can be used for casting both ferrous and non-ferrous alloys.
• Is a recyclable process for materials
• Used for processing of metals with high melting temperatures, such as steel and titanium.

Disadvantages of Sand Casting

• Lower degree of accuracy as compared to alternate methods
• Difficult to use this method for products with pre-determined size and weight specifications.
• Produces products with a rough surface finish.

Gravity Die Casting

• Gravity die casting, also called permanent mold casting, uses reusable molds made of metal (steel, graphite, etc.) to fabricate metal and metal alloys
• Used to manufacture various parts such as gears, gear housings, pipe fittings, wheels, and engine pistons.
• Direct pouring of molten metal into the mold cavity takes place under the effect of gravity, and the die can be tilted to control the filling.
• The molten metal is then allowed to cool and solidify within the mold to form products.
• This process makes casting of materials such as lead, zinc, aluminum, magnesium alloys, certain bronzes, and cast iron more common.

Advantages of Gravity Die Casting

• Provides better surface quality due to rapid solidification.
• Produces casting products with high precision and tight tolerance.
• Reusable molds save time and increase productivity, which reduces production costs.
• Produces components with better mechanical properties
• Can be used to produce thin walled products

Disadvantages of Gravity Die Casting

• Casting complex objects is difficult.
• Manufacturing costs of molds are higher.
• The ejection mechanism to remove the casting from the mold sometimes forms a dent in the product.

Pressure Die Casting

• Two types of pressure die casting, depending on the pressure: low-pressure and high-pressure.
• High-pressure die casting is more popular for mass production of complex geometries needing high precision.
• Low-pressure die casting is preferable for large and simple parts production.
• In this type of metal casting, non-ferrous metals and alloys such as zinc, tin, copper, and aluminum are injected into a reusable mold coated with a lubricant at high pressure.
• High pressure is maintained during the rapid injection process to avoid metal hardening.
• Extraction of casting and finishing remove excess material after process completion.

Advantages of Pressure Die Casting

• High precision and dimensional tolerance in finished products
• High efficiency and good product quality.
• Reduced need for post-casting machining.
• Rapid cooling of molten metal leading to faster production rates.
• Longer run times for given die

Disadvantages of Pressure Die Casting

• Relatively high tool costs
• Mechanical properties of products are difficult to ensure, so the process is not typically used for structural parts
• The set-up needs a large capital investment

Investment Casting

• Investment casting, known as lost-wax casting, involves investing a wax pattern with refractory material and a binding agent to shape a disposable ceramic mold
• Molten metal is poured into the mold to make metal castings.
• It is an expensive and labor-intensive process for mass production or in complex castings to produce metal casting products.
• Products can range from gears and bicycle trunks
• Can be used for moto discs, and spare parts in blasting machines.