A manufacturing process does more than create geometry: it can only produce certain combinations of material, shape, size, accuracy, surface condition and production rate.

A process capability envelope is the range of requirements that a process can achieve reliably. Important parts of that envelope include:

• compatible materials;
• feasible shapes and minimum feature sizes;
• attainable dimensional and geometric accuracy;
• attainable surface condition;
• part size and mass;
• production rate;
• tooling and equipment requirements.

Major process families create shape in different ways:

• subtractive processes remove material from a larger workpiece;
• forming processes permanently reshape solid material without removing most of it;
• casting and moulding processes place a flowable material into a cavity where it solidifies or hardens;
• additive processes build a part by placing or consolidating material only where it is needed.

Process selection therefore begins by screening. A process that cannot satisfy a hard requirement should be removed before cost optimization begins.

A process does not always need to create every final feature directly. A near-net-shape process produces a part close to its final geometry, after which one or more finishing operations create tighter tolerances, smoother surfaces or local features.

For example, a casting may create the main body of a component economically while a later machining operation produces one precisely sized hole.

Manufacturing requirements are therefore coupled: geometry, material, accuracy, surface condition, production volume and cost all influence which process or sequence of processes is appropriate.