Gratbildung

Gratbildung, often translated as burr formation, is the formation of a sharp projection or irregularity along the edge of a workpiece that remains after a cutting, shearing, or forming operation. It commonly occurs in processes such as milling, turning, drilling, punching, stamping, laser cutting, and water jet cutting, and can affect metal, plastic, or composite materials.

Grat forms when material is plastically deformed and displaced rather than cleanly separated, or when brittle fracture tears away material at the edge. Depending on the process and material, burrs may be short, hairlike projections or broader raised edges that extend along the edge. Burr morphology can vary from tiny, almost invisible remnants to more pronounced and jagged features.

Consequences of burr formation include interference with subsequent assembly, impaired sealing or clearance, and altered fit. Burrs can concentrate stress and initiate fatigue cracking, promote corrosion, or pose safety hazards to operators handling the parts.

Mitigation and removal strategies focus on process optimization and post-processing. This includes selecting appropriate tool geometry, cutting speeds, feeds, and depth of cut; maintaining sharp tools; use of proper lubrication or cooling; and controlling tool wear. In many cases burrs are removed after machining by deburring operations such as brushing, grinding, tumbling, or electrochemical or thermal methods. Design for manufacturability and tolerance specification also help minimize burr formation.

Measurement and acceptance criteria for burrs depend on the part’s function and fit requirements. Common metrics include burr height and length, contour, and protrusion relative to mating surfaces, assessed by visual inspection, profilometry, or dedicated measurement devices.