Material-Removal Process Families

Start with what removes the material

A machine tool controls motion between a tool and the workpiece, the part being made. In material removal, the final shape is what remains after unwanted material is taken away.

CNC is a control method, not a removal family. Computer numerical control can guide a mill, lathe, grinder, EDM machine or cutting jet. See G-code and Toolpaths. Forming moves material without removing it; see Manufacturing Process Categories for the wider manufacturing map.

Conventional cutting uses defined cutting edges

• Turning rotates the work past a cutting tool; milling rotates the cutter and feeds it relative to the work.
• Drilling makes holes; sawing separates stock, the starting material, with successive teeth.
• Broaching uses a sequence of teeth to progressively cut a profile, such as a keyway. Dedicated tooling often suits repeated production, but broaching is not limited to large runs.
• Shaping and planing use a back-and-forth straight cutting stroke. A shaper normally moves the tool; a planer normally moves the work.

A process name describes the action, not every possible shape. Milling can make curved contours as well as flat faces.

Abrasive processes use many small cutting grains

Grinding wheels hold abrasive grains that remove material. Precision grinding controls size and surface texture, often on hardened parts. Grinding can also remove substantial stock; it is not restricted to light finishing.

Honing commonly uses abrasive stones with combined motions to refine a bore's size, form and surface. Lapping uses fine abrasive between a lap and the work to refine a surface. Neither is simply another name for grinding.

Nontraditional processes change the removal mechanism

• Thermal: EDM, laser and plasma remove material with concentrated heat. EDM's energy supply is electrical, but its removal mechanism is thermal.
• Electrochemical: ECM uses electric current to dissolve metal.
• Chemical: Chemical Milling and Etching uses an etchant to dissolve exposed material.
• Mechanical energy: waterjets and Ultrasonic Machining erode material with moving water or abrasive particles.

Use Selecting a Material-Removal Process to narrow the candidates. Safety references: Machine Hazards and Housekeeping, Equipment Operating Procedure and Chemicals and Safety Data Sheets.