SAND CASTING
Sand casting is a versatile and cost-effective metal casting process ideal for producing large components and complex shapes. It involves creating molds from a mixture of sand, clay, and other additives. This method is economically advantageous for large volume productions, offering design flexibility, material versatility, and lower tooling costs. Sand casting supports a wide range of product sizes and features shorter lead times. However, there are other processes that provide higher dimensional accuracy and smoother surface finishes.
THE PROCESS
Pattern Making
A pattern, which is a replica of the desired part, is created from wood, metal, or plastic. It includes the part geometry as well as provisions for the gating and riser systems.
Mold Making
A flask or mold box is filled with specialized sand, typically green sand (a mixture of silica sand, clay, moisture, and other additives). The pattern is pressed into the sand, creating a cavity. The pattern is then removed, leaving the mold cavity.
Common products
Core Making
(optional)
For internal cavities or complex shapes, separate sand cores are made and placed into the mold cavity.
Bearings, gears, bushing, brackets, nuts, flanges, clamps, fittings, pipe plugs, engine blocks, cylinder heads, exhaust manifolds, gearboxes, connecting rods, pump housings, valves, machine tool bases, pulleys, transmission cases
Melting
The desired metal alloy is melted in a furnace to its molten state.
Common materials
Both ferrous + non-ferrous metals like aluminum alloys, brass alloys, bronze alloys, steel (BS3100), grey Iron (BS EN1561), spheroidal Graphite Iron (BS EN 1563)
Size range
A few ounces to a few hundred pounds
Pouring
The molten metal is poured into the mold cavity through the gating system.
Solidification
The metal is allowed to cool and solidify inside the mold cavity.
Shakeout
Once solidified, the sand mold is broken apart, and the casting is removed, a process known as shakeout.
Finishing
The casting may undergo further processes like grinding, machining, or heat treatment to achieve the final desired specifications.
INVESTMENT CASTING
Investment casting, also known as lost wax casting, is a precision casting process ideal for producing intricate parts with excellent surface finish and dimensional accuracy. This method involves creating a wax or plastic pattern of the final part, coating it with ceramic material to form a mold, and then pouring molten metal into the mold. It is particularly suited for industries requiring detailed and accurate components, such as aerospace, medical, and jewelry sectors. Investment casting supports complex geometries and thin walls while offering lower tooling costs and compatibility with both ferrous and non-ferrous materials. However, there may be better processes to support high volume productions.
THE PROCESS
Pattern Making
A pattern, which is a replica of the desired part, is created from metal.
Mold Making
Wax patterns are created by injecting wax into metal dies. The wax patterns are exact replicas of the desired final part.
Assembling Wax Pattern
The wax patterns are assembled onto a central wax sprue, forming a "tree" configuration. This allows multiple parts to be cast simultaneously.
Common products
Pump housings, nozzle rings, turbine scroll, injection clamps, rocker arms (parts that require precision - aerospace, automotive equipment, agriculture equipment)
Investing Wax
Tree
The wax tree is dipped into a ceramic slurry and then coated with sand or stucco. This process is repeated to build up multiple layers of the ceramic shell around the wax.
Dewaxing
The ceramic shell is heated to melt and drain out the wax, leaving a hollow cavity in the shape of the part.
Common materials
Stainless steel alloys, brass, aluminium, carbon steel, glass
Size range
A few ounces to a few hundred pounds
Firing the Shell
The ceramic shell is fired in an oven to strengthen it and remove any remaining wax.
Pouring
The fired shell is placed in a bed of sand and molten metal is poured into the cavity.
Knockout
After solidification, the ceramic shell is removed, typically by mechanical means like vibration or high pressure water blasts.
Finishing
After solidification, the ceramic shell is removed, typically by mechanical means like vibration or high pressure water blasts.
DIE CASTING
THE PROCESS
Die casting is a high-efficiency metal casting process perfect for producing small to medium-sized parts with excellent dimensional accuracy. In this method, molten metal is forced under high pressure into a mold cavity created by two hardened tool steel dies, similar to an injection mold. There are two types of die casting:
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Hot chamber die casting - suitable for low melting point metals (i.e. zinc, magnesium)
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Cold chamber die casting -- ideal for higher melting point metals (i.e. aluminum)
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Die casting offers high production rates, excellent surface finishes, & is cost-effective for large production volumes due to reusable molds. However, there may be better processes to support smaller runs.
Mold Design
& Preparation
Metal
Preparation
Injection
A mold is created via CNC machining.
Non-ferrous alloy is melted & poured into shot sleeve or injection cylinder.
Two halves of the mold are clamped together under high pressure & molten metal is injected at high speed and pressure (10-175 MPa or 1,500-25,400 psi) into the mold cavity through the shot sleeve.
Solidification
Injected molten metal is allowed to solidify inside the mold cavity by cooling while pressure is maintained until object solidifes.
Common products
Automotive, aerospace, and electronics industries for parts like engine blocks, transmission cases, & heat sinks
Common materials
Ejection
Once solidified, the mold is opened, and the cast part is ejected using ejector pins.
Trimming
Excess metal from gates, runners, and overflows is removed from the cast part, often using a trim die.
Non-ferrous metals like zinc, copper, aluminium, magnesium, lead, pewter, and tin-based alloys.
Size range
A few ounces to a few hundred pounds
SHELL MOLD CASTING
Shell mold casting is a precision casting method that utilizes an expendable mold made from a sand and resin mixture formed around a metal pattern. The pattern is heated, and the sand-resin mixture is blown or poured over it, creating a thin, hardened shell. Two shell halves are then joined to form the complete mold. This process allows for complex geometries and offers good dimensional accuracy. Shell mold casting boasts better dimensional accuracy, higher productivity rates, and lower labor requirements compared to some more traditional processes.
THE PROCESS
Pattern Making
Two metal pattern pieces are created in the desired shape.
Mold Creation
Patterns are heated, coated with a lubricant, and covered with resin-covered sand in a dump box.
Assembly of Pattern Parts
Pattern pieces are joined together and inserted into a flask.
Common products
Cylinder heads, gears, bushings, connecting rods, camshafts, valve bodies
Exposure of
Molten Metal
Molten metal is poured into the mold's cavity.
Cooling
The molten metal cools and solidifies within the shell mold.
Common materials
Both ferrous metals like cast iron and steel + non-ferrous metals like aluminum and copper alloys, grey cast iron, ductile cast iron, carbon steel, allow steel, stainless steel, aluminum alloys, copper alloys
Ejecting the
Casting
The shell mold is opened, and the casting is removed.
Size range
Up to 1,000mmx800mmx500mm, between 0.5kg-100kg, up to 12in in diameter and 30lbs
PERMANENT MOLD CASTING
Permanent mold casting is a reliable process for medium-volume production, offering good dimensional accuracy and surface finish. This method involves filling a reusable steel or cast iron mold with molten metal, typically through gravity pouring or machine-controlled tilt pouring. The molds are reused multiple times, making this process cost-effective for high-volume production. Permanent mold casting produces parts with tight tolerances, low porosity, and strong mechanical properties due to rapid cooling and a finer grain structure. It is a highly repeatable process that supports complex shapes better than sand casting. Permanent mold casting is not ideal for highly intricate products with multiple cores or large parts, as uniform cooling is needed and the metal molds have poor gas permeability.
THE PROCESS
Mold Creation
Uses a reusable mold typically made from steel or cast iron that gets preheated and coated with a ceramic material to prevent sticking.
Material Pouring
Molten metal is poured into the mold cavity, usually using gravity or low-pressure/ vacuum methods.
Cooling &
Removal
Metal cools and solidifies in the mold, which is then opened to remove the casting (mold can be re-used).
Common products
Gears, splines, wheels, gear housings, pipe fittings, pistons
Common materials
Aluminum, magnesium, copper alloys, tin, zinc, lead alloys
Size range
Small to medium parts
CENTRIFUGAL CASTING
THE PROCESS
Centrifugal casting is a process ideal for producing cylindrical parts with high material integrity. It involves using a reusable cylindrical mold that spins at high speeds, causing the molten metal to spread towards the mold's edges, forming a hollow cylindrical shape. There are three types of centrifugal casting:
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True centrifugal casting for cylindrical parts
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Semi-centrifugal casting for parts with rotational symmetry
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Centrifuging for smaller components.
Centrifugal method offers numerous advantages, including high material integrity due to centrifugal forces pushing impurities to the outer surface, resulting in reduced porosity and shrinkage cavities. It also provides high structural strength through directional solidification, improving tensile strength, fatigue resistance, and grain structure. Centrifugal casting is highly reliable and efficient, suitable for large-scale manufacturing, and allows for customizable wall thickness along with good dimensional accuracy with no need for cores and reusability of molds. However, the process is restricted to round shapes, making it unsuitable for complex alloys and non-cylindrical parts.
Mold
Preparation
Inner surface of the mold is coated with a refractory material to prevent the molten metal from sticking and to ensure a smooth surface finish. The mold is preheated and the refractory coating is applied while the mold is spinning.
Mold Making
A flask or mold box is filled with specialized sand, typically green sand (a mixture of silica sand, clay, moisture, and other additives). The pattern is pressed into the sand, creating a cavity. The pattern is then removed, leaving the mold cavity.
Core Making
(optional)
For internal cavities or complex shapes, separate sand cores are made and placed into the mold cavity.
Melting
The desired metal alloy is melted in a furnace to its molten state.
Pouring
The molten metal is poured into the mold cavity through the gating system.
Common products
Pipes, bushings, rings, cylinder liners, and other cylindrical components
Common materials
Ferrous & non-ferrous material, but no complex alloys or lead bronze
Solidification
The metal is allowed to cool and solidify inside the mold cavity.
Shakeout
Once solidified, the sand mold is broken apart, and the casting is removed, a process known as shakeout.
Finishing
The casting may undergo further processes like grinding, machining, or heat treatment to achieve the final desired specifications.
Size range
Small to large products (outer d = 1in to 6 m; length = up to 15m; minimum 2.5mm thickness, up to 800 lbs