Chip Types
Chip types are the forms cut metal takes as it leaves the tool — the ribbons, the crumbs and the welded lumps of the swarf that every cutting process makes — and they matter because the chip is the cut’s report on itself. The same metal cut under different conditions does not leave the tool the same way: it peels off in a long continuous ribbon, breaks into short separate segments, or welds itself onto the edge and cuts with its own stuck-on tip. Which of these a cut makes is not an accident but the signature of the speed, the feed, the rake angle and the material — and reading that signature is one of the machinist’s oldest skills. This entry names the main chip types, explains what makes each form, and sets out what each one says about the cut that made it.
Where the chip comes from
A chip type is decided in the instant when the tool edge pushes into the work and the metal ahead is sheared away. As the entry on chip formation describes, the edge compresses the material until it yields along a shear plane, and the layer that yields slides up the rake face and becomes the chip. Whether that chip comes off whole, comes off broken, or welds to the edge is set by how the material behaves under that shearing. Three variables govern the outcome more than any others: the ductility of the work material, the cutting speed, and the tool geometry — the rake angle and edge sharpness that this wiki treats under tool geometry. Move any of them and the chip type changes, which is why the swarf shows in one glance whether the cut is what the setup intended.
Discontinuous chips
The discontinuous chip — the short broken segment, sometimes no more than a crumb — forms when the material fractures rather than flows. It is the chip of the brittle work materials, the cast irons and the harder, less ductile alloys, which cannot stretch into a ribbon before the shear breaks them again; it also forms at low cutting speeds and with small rake angles, where the compressed material cracks rather than flows. The discontinuous chip has a practical virtue: it falls away and clears itself, needing no chip breaker and posing little tangle hazard — one reason cast iron machines so easily dry. But each separate fracture is a small shock to the edge and a small variation in the cut, so it tends to leave a rougher surface and wear the edge more erratically than a clean flow. A related type, the segmented or serrated chip, forms in the tougher alloys — the titaniums and the nickel superalloys — under heavy cuts: the metal flows in a saw-tooth of concentrated shear bands, and the cutting force pulses with every segment.
Continuous chips
The continuous chip is the long smooth ribbon of the ductile metals cut at higher speeds with a positive rake — the steel and aluminium chip that streams off a properly cutting tool, its underside polished by sliding on the rake face. It forms when the material flows plastically without fracture, and it is in most ways the sign of a healthy cut: the metal shears cleanly, and the surface it leaves is generally the finest of the chip types. But a long steel ribbon at speed is a live hazard — hot, razor-edged, quick to whip and tangle around the tool, the holder and the work — and it must be controlled, which is the job of the chip breaker: the groove or step in the insert’s rake face that forces the flowing chip to curl until it breaks under its own strain, turning the endless ribbon into manageable commas. The continuous chip is also the type most worth reading, for its curl, its colour and its underside all speak of the cut.
The built-up edge
The built-up edge — BUE for short — is the odd one of the family: not a form the chip takes but a lump of work material that welds onto the cutting edge and then does the cutting in the tool’s place. At the low-to-moderate speeds and pressures where work metal, softened by the heat of sliding but not yet hot enough to flow away cleanly, cold-welds itself to the rake face behind the edge, it builds a pad there and cuts with a changing, unstable tip. It is the bane of the sticky, work-hardening materials — the low-carbon steels, the stainless steels, the softer aluminiums. The built-up edge damages in several ways at once: it blunts the effective edge, it roughens the surface as fragments break away and are carried across it, and it feeds the built-up-edge wear and vibration that this wiki treats under tool wear. The cure is to change the conditions that weld it: raise the cutting speed so the metal flows instead of sticking, increase the rake so the chip leaves more easily, keep the edge sharp and honed, and use the lubrication of a cutting fluid to stop the welding at its source.
Reading the swarf
Because each chip type answers to the cutting conditions, the chip is the machinist’s continuous read-out of the cut. A long ribbon that will not break tells the operator that the chip breaker or the feed is wrong for the job. A chip that comes off blue or burnt in steel tells of a cut running too hot — too fast, too dry or too dull an edge — and of a tool wearing faster than it should. A chip with a rough, torn underside is the mark of a built-up edge building and breaking, and a signal to change speed or rake before the surface suffers. A segmented chip in a titanium or nickel alloy is the ordinary signature of those metals, but its pitch and its colour still tell whether the cut is steady or overloaded. Even the colour scale of the steel chip is a language — straw, then brown, then blue as the heat climbs. The machinist reads that report against the feeds and speeds the job was given, and adjusts the cut until the chip coming off the tool is the chip the job should make.
The chip as feedback
The chip types are not a taxonomy to be memorised but a diagnostic to be used — the visible half of the chip-formation physics this wiki describes, joined to the tool geometry that shapes them, the speeds and feeds that drive them and the wear they leave behind. Every machining job makes its chips, from the first part of the day to the production run on a CNC machine, and the machinist who can name what the chip is doing and why is the one who can fix the cut before the part is spoiled. Whether the swarf streams in long steel ribbons, crumbles as brittle segments, or threatens to weld itself onto the edge, it is the material’s honest answer to the tool — read it, and the cut is no longer a guess.