Metals.
Forming, redistribution and addition processes · Technical principles
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Metal Processes
METAL PROCESSES
Redistribution processes (casting)
Redistribution processes involve melting metal and pouring it into a mould, where it cools and solidifies into the required shape. These processes are used for complex shapes that are difficult to form by deformation.
Die casting
Die casting uses permanent metal moulds to produce accurate, high-quality castings with good surface finish. It is mainly used for non-ferrous metals.
Types of die casting:
Gravity die casting
Pressure die casting (hot chamber)
Pressure die casting (cold chamber)
Gravity die casting
Gravity die casting is a permanent mould casting process where molten metal fills the mould using gravity only.
Process overview
The metal mould (die) is preheated and coated to improve flow and release.
Molten metal is poured slowly into the mould cavity using a ladle, with no external pressure applied.
The metal is allowed to solidify before the mould is opened and the casting removed.
The part is machined or finished as required.
Key characteristics and applications
Produces stronger and more consistent castings than sand casting due to controlled cooling.
Initially used for simple shapes, but modern gravity casting can produce complex parts using sand cores.
Typically used with low melting point metals such as aluminium and zinc.
Moulds must be relatively thick to withstand repeated heating and cooling.
Suitable for large-scale mass production.
Pressure die casting (hot chamber)
Hot chamber pressure die casting is used for low melting point metals where the injection system is submerged in molten metal.
Process overview
Molten metal is stored in an integrated furnace.
A plunger forces the molten metal through a gooseneck into the closed mould under high pressure.
The metal cools rapidly, the mould opens, and the casting is ejected.
Key characteristics and applications
Very fast cycle times, making it ideal for mass production.
Produces excellent surface finish and dimensional accuracy.
Typically used for zinc and low-melting aluminium alloys.
Not suitable for high-melting-point metals, as they would damage the injection system.
Pressure die casting (cold chamber)
Cold chamber die casting is used for higher melting point metals, where molten metal cannot be stored inside the machine.
Process overview
Molten metal is poured into a separate shot chamber.
A hydraulic plunger forces the metal into the mould under high pressure.
The metal solidifies, the mould opens, and the casting is removed.
Key characteristics and applications
Suitable for metals such as aluminium alloys with higher melting points.
Slower cycle times than hot chamber casting but still suitable for mass production.
Produces strong, accurate components with good surface finish.
Investment casting (lost wax casting)
Investment casting is used to manufacture highly detailed and intricate metal components with excellent surface finish.
Process overview
An exact wax replica of the product is produced.
The wax pattern is coated in layers of ceramic slurry and fired in a kiln, causing the wax to melt away.
Molten metal is poured into the ceramic mould and allowed to cool.
The ceramic shell is broken away and the runner is machined off.
Key characteristics and applications
Produces extremely accurate parts with minimal machining required.
Ideal for complex or awkward shapes that cannot be machined easily.
Used in aerospace, medical, and high-precision engineering components.
Metal Forming processes
Forming processes shape metal by deforming it, often using heat and/or mechanical force, without removing material. These processes are chosen when strength, structural integrity, and efficient material use are required.
Press forming
Press forming is an industrial forming process used to create 3D shapes from flat sheet metal.
How the process works
A die-cut base is prepared with the required shape machined into it, and the sheet metal is clamped securely in position.
A draw force is applied using a press, forcing the sheet metal into the die to create the required 3D form.
Key characteristics and applications
Produces accurate and repeatable 3D shapes from flat sheet.
Commonly used in mass-production environments where consistency is critical.
Often used for automotive panels and pressed metal components.
Cupping and deep drawing
Cupping and deep drawing are forming processes used to produce deep, hollow, tube-like shapes from sheet metal.
How the process works
The sheet metal blank is die-cut to a rough shape and clamped over a deep-drawing die using a pressure pad (retainer).
A hydraulic press pushes a punch into the blank, forming an initial cup shape.
The cup is then drawn further through the die to create the final deep or tubular shape, and excess material may be trimmed.
Key characteristics and applications
The draw force goes significantly deeper than standard press forming.
Used to manufacture products such as aerosol cans and similar containers.
A multi-operational process with high setup costs, making it suitable only for mass production.
Bending
Bending is a forming process used to create straight bends along the edge of sheet metal.
How the process works
Sheet metal is clamped between a punch and die, usually in a press brake machine.
A mechanical brake holds the metal securely while the punch is lowered to form the bend.
Key characteristics and applications
Used for seams, casings, housings, and folded edges.
Can be carried out in industry or school workshops and is often cold formed.
Does not involve trimming or die cutting, and is similar to press forming but produces only a single bend rather than a full 3D shape.
Spinning
Spinning is a forming process used to create axisymmetric (radially symmetrical) shapes from sheet metal.
How the process works
A former, known as a mandrel, is mounted in a chuck and the sheet metal blank is clamped between the mandrel and tailstock.
The blank is rotated at high speed while a roller tool presses against it, gradually stretching the metal over the mandrel.
The roller tool is moved along the mandrel until the final shape is formed, after which the product is removed and excess material trimmed.
Key characteristics and applications
Produces smooth, seamless shapes with good surface finish.
Commonly used to make stainless steel kettles, saucepans, and light shades.
Suitable for mass production and can be automated using CNC spinning machines.
Rolling
Rolling is a forming process used to reduce the thickness of metal by passing it between rotating rollers.
How the process works
Hot metal is passed repeatedly through rollers, which compress and elongate the material.
The thickness is gradually reduced while maintaining uniform properties.
Key characteristics and applications
Hot rolling produces material with uniform mechanical properties throughout the section.
Used to manufacture structural steel such as I-beams, as well as thinner materials like sheet and foil.
Cold rolling is used for finished products such as chairs, drums, and saucepans, where improved surface finish is required.
Rolling often produces a metal billet that can later be drawn or further processed.
Wrought iron forging
Wrought iron forging is a traditional forming process used for decorative and bespoke metalwork.
How the process works
Iron with a carbon content of less than 0.08% is heated to a cherry-red colour.
The hot metal is repeatedly struck and shaped over an anvil using a hammer.
The work is allowed to cool before undergoing further heat treatment for enhancement.
Key characteristics and applications
Traditionally carried out by blacksmiths, though modern versions may use hydraulic hammers.
Produces strong, decorative components such as gates, railings, and ornamental items.
Typically used for one-off or small-batch bespoke products rather than mass production.
Drop forging
Drop forging is a mass-production forming process used to manufacture tough, high-strength components.
How the process works
Dies made from cast tool steel are mounted on an anvil and a hydraulic ram.
A metal billet is heated above its recrystallisation temperature to prevent work hardening.
The heated billet is placed into the lower die and struck by the ram, forcing it into shape.
The finished product is removed and allowed to cool.
Key characteristics and applications
Produces very strong components with refined grain structure.
Commonly used for tools such as spanners, pliers, and screwdrivers.
Suitable for high-volume production where durability is essential.
Wastage processes (metal)
Wastage processes shape metal by removing material to achieve the required form. They are used where accuracy, surface finish, and tolerance are important.
Turning
Turning is carried out on a centre lathe, where the workpiece rotates and cutting tools remove material.
A metal bar is held in a rotating chuck and machined to reduce diameter, face off ends, cut threads, and drill holes.
Cutting tools held in a tool post move inwards, outwards, and along the bar to shape the material.
Turning can be manual or CNC-controlled, with CNC improving accuracy and repeatability.
Flame cutting (A-level only)
Flame cutting is a thermal cutting process using oxy-acetylene gas.
A flame-cutting torch produces a focused flame above 3500°C, with an additional jet of oxygen to intensify the flame and pierce the metal.
Used to cut low-carbon and alloy steel plate and does not require electricity.
Difficult to achieve parallel cuts with high tolerance.
Plasma cutting (A-level only)
Plasma cutting uses super-heated, ionised gas to cut conductive metals.
The ionised gas conducts electricity, transferring energy from the power supply to the metal.
Temperatures can reach 28,000°C, melting the metal and blowing it away from the cut.
Produces fast, clean cuts and is more accurate than flame cutting.
Laser cutting (A-level only)
Laser cutting is a high-precision process mainly used for flat sheet metal.
A high-powered laser beam is focused through optics and a lens to create a very fine cutting beam.
Produces extremely tight tolerances, often less than 1 mm, and can also be used for engraving.
More accurate and energy-efficient than plasma cutting, but cannot cut material as thick.
Lower-powered lasers are commonly used in schools for boards and acrylic.
Punching / stamping
Punching and stamping are computer-controlled sheet-metal processes that remove material by shearing.
Sheet metal is placed between a punch and die, and sections are stamped out.
Very fast and accurate once tooling is set up, making it suitable for small- and medium-scale production.
Typically used for sheet metal thicknesses between 0.5 mm and 6 mm.
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