forming metals

FORMING METHODS

press forming - used to creates 3D forms of aluminium and low carbon steel, often automated for mass production reducing the cost per unit. the dies are made from hardened steel that are hand burnished and spark eroded to give a high quality finish

turning (spinning) - used to make long and round objects, spun products are often CNC produced to create accurate complex forms or in batch production combined with a lathe it is suitable for making screws

cupping and deep drawing - used to make tubes from sheets. cupping is known as deep drawing where the depth is larger than the diameter, the corners are rounded to create stretches instead of shearing. when setting up cupping or deep drawing it is often expensive and requires a die making it suitable for mass or continuous production

drop forging - drop forging is used on hot metal to make a tough and hard product. metals are forced into a shape with a lot of pressure, this is used for mass production and requires a die to form the hot metal

wrought iron forging - this is used for low carbon content metal which is malleable and easy to shape. it can be made using hydraulic and mechanically powered rams or handmade using hammers and an anvil. scroll formers are used to twist metal to make an intricate shape, this is often used for small batches or one time pieces

bending - bending is used to shape sheet metal where it is clamped around a punch and die formed, a press brakes and lower to form the metal

rolling - rolling is used to make thinner products from structural steel, it is manufactured and heated a lot, the final piece can have carbon on the surface but will not have any stress points. and alternative is to roll at a low temperature to create a tolerance for very thin metal

die casting - die casting is used on metals with a low melting point such as aluminium, pewter and zinc, tool steel is produced to make the dies, as they are very expensive it is more suitable for mass production that make a high-quality finish, die casting is very accurate and allows repeatable shape to be produced, die casting can either be done by pressurising metal into a form with a hot chamber pressure die casting where ejector pins release the die or using gravity to make the metal flow down into the die. locator pins are used to make sure the mould is accurate to avoid defects and lubrication or a releasing agent must be used. there is also cold chamber die casting where the molten metal is added to the plunger, this is used for high melting point metals

sand casting - sand casting is used to form metals with very high melting points using sand, it is very slow and requires lots of work as the moulds can only be used once, it is used for one off or batch items that do not need a high quality finish as it looks grainy. sand casting often used to different patterns with open risers to stop air pockets and patterns inside for hollow parts. sand must be strickled off when making the mould and sprue pins are placed to create vents and risers.

investment casting - investment casting is for awkward shape production that is used on lots of different metals, it produces a nice finish and is easily repeatable by using a master mould to make wax patterns, the tree is then coated with stucco and the patterns are removed

pewter casting - pewter casting is used for school workshops as it does not require a high temperature (around 200°C) it is made as one off production, however moulds can be scaled up for batch production

CONSIDERATION

when forming metals you must consider metal grain orientation. cast metal has no grain and so can fracture anywhere, rolled pieces have a parallel grain and has weak points that can snap easily, whereas drop forged pieces have a grain that fits around the die meaning there are no areas of weakness