Moulding Processes

• Sand casting is a single-use moulding process for metals where a sand mould is created using a pattern and the molten metal is poured into the mould. It is very labour-intensive and requires lots of finishing as parts will have a rough surface texture.
• Investment casting produces high-quality and complex parts by dipping a mould in wax and coating it with ceramic slurry. The wax is then melted out of the ceramic and molten metal is poured into the mould. The part is then finished and checked using radiation to check for any impurities.
• Gravity die-casting is a process where molten metal is poured into a mould and allowed to cool, the metal pushes its way through the mould using gravity. Gravity die-casting is a mid volume process that creates high quality castings with limited accuracy, and minimal wall thickness of 3-5mm.
• Pressure die-casting uses pressure to force molten metal into a mould at high speed. This allows for thinner walls than gravity die-casting but still has limitations on minimum wall thickness due to the need to fill the mould quickly.
• Injection moulding is a process in which molten metals or plastic is squeezed into a mould and cooled to create a solid object. Injection moulding creates complex and accurate parts which have great surface quality. Products that are injection moulding have ejector marks, sprues and visible flash.
• Extrusion moulding is the process of forcing molten plastic or metal through a die to create a long length of material. Extrusion moulding creates pipes, beams and sheets, with complex forms. Using complex internal detailing, designers ensure that extruded parts stay strong and prevent warping.
• Drop forging is used to create high strength metal parts. Hot drop forging involves heating the metal billet to a high temperature and then hammering it into shape using a power or drop hammer. The flash is removed and then the part is heated again to be condensed by a high-pressure machine. However, cold drop forging is the same but the metal isn't heated so it requires a larger amount of force to create the parts.
• Drop forging creates small to large parts with low accuracy and surface quality in low volumes. It also has high tooling costs but is a quick process.
• Rotational moulding creates hollow plastic forms using rotating moulds within an oven which are filled with powdered resin or plastic pellets. The rotation of the moulds while the plastic is melted and cooled ensures the walls are uniform.
• Rotational moulding is low cost and creates forms with high surface quality and medium accuracy. However, it is low speed and the size of the product is limited by the size of the ovens available during manufacturing.
• Compression moulding uses high pressure to form plastic sheets into a heated mould. This creates products with higher impact strength and thicker walls than injection moulding.
• Compression moulding creates parts with high accuracy and surface quality. It has medium speeds, tooling costs and volume potential.
• Injection blow moulding starts with a parison which is lowered into a cooled mould and cut using a hot blade. A blow nozzle inflates the parison into the shape of the mould, creating a hollow form with thin even walls. The tail and head of the moulded parison are removed and the bottle is left to cool.
• What is the main features of injection blow moulding?

  Thin walls, symmetrical forms, detailed screw top
• Where is the sprue mark located on a injection blow moulded product?

  Bottom
• Unlike injection blow moulding, extrusion blow moulding is formed by a hollow tube created via extrusion moulding which is then lowered in a die that grips the top and bottom. The form is then inflated and cooled.
• Extrusion blow moulding creates thicker walls and chunkier screw tops than injection moulding and forms can have built in handles. However, this process commonly causes inconsistent wall thickness and trimming is usually required because of material that escapes the mould.
• Extrusion blow moulding creates hollow forms with high surface quality and mid-high accuracy. The process is high volume and speed but it also has high tooling costs.
• What process is used to make this product?

  Injection moulding

  
• Sprues are an indication of what manufacturing process?

  Injection (blow) moulding
• Ejector pin marks are an indicator of what moulding processes?

  Die casting, injection moulding and compression moulding
• What are webs and ribs used for?

  Strengthening parts
• What do bosses aid in the production process?

  Assembly
• Why are draft angles used in parts?

  Easier release from moulds