The five categories are additive manufacturing, subtractive manufacturing, forming, joining, and finishing. They classify manufacturing techniques according to what happens to the material or components during production.
How the five categories differ
| Category | Core mechanism | Typical examples |
|---|---|---|
| Additive | Material is added progressively to build a three-dimensional form, often directly from digital data. | Fused deposition modelling (FDM), stereolithography (SLA), selective laser sintering (SLS) |
| Subtractive | Material is removed from a larger piece of stock until the required shape is produced. | Drilling, turning, milling, routing, laser cutting |
| Forming | Material is reshaped using force, heat, pressure, a mould, or a die, without building it layer by layer. | Injection moulding, casting, vacuum forming, bending, forging |
| Joining | Two or more separate components are assembled into one product using permanent or temporary connections. | Welding, brazing, soldering, riveting, adhesives, screws |
| Finishing | A surface is treated to improve its appearance, protection, texture, durability, or other properties. | Sanding, polishing, painting, powder coating, anodizing |
The categories describe the primary purpose of a process. For example, sanding removes a small amount of material, but it is normally classified as finishing because its main purpose is to improve surface quality rather than create the product’s overall geometry.
A common misconception is that all processes involving moulds are additive. Injection moulding and casting are classified as forming because material is shaped inside a mould; additive manufacturing builds geometry through successive deposits or layers.
Manufacturing a single product may involve several categories. A metal chair could have tube sections cut by a subtractive process, bent through forming, welded through joining, and powder-coated through finishing.
IB exam technique
For A4.1 Manufacturing techniques (HL only), define each category by its mechanism and give a suitable example. When explaining process selection, link the technique to material properties, production quantity, cost, precision, geometry, waste, and required surface finish rather than merely naming the process.