FundamentalsChip formation

Chip types and chip forms

The four chip types (continuous, built-up edge, discontinuous, serrated), the eight chip forms of ISO 3685, and how a chip breaker makes a long chip break.

LiveUpdated 11 October 20266 min read

The four chip types

Chip types by the way the material deforms: 4
Chip forms in ISO 3685, Annex G: 8
Forms rated favourable in a study using ISO 3685: 4.2, 6.2, 7
Classifies chip control zones of chip breakers: ISO 10910

The chip is the most honest report a cut gives. Its type tells you how the material deformed; its form tells you whether it will leave the machine on its own or wrap around the tool and the part.

Four chip types

Textbooks group chips into four types by the way the material deforms in the shear zone.

Type	How it forms	Typical conditions	What it means
Continuous	Continuous plastic deformation without fracture	Ductile materials, high cutting speed and/or large rake angle, sharp edge	Stable cutting and good surface, but the chip must be broken or it wraps around tool and part
Continuous with built-up edge (BUE)	Work material welds to the rake face, grows, becomes unstable and breaks away	Ductile materials at low to medium speed, high friction, small rake angle, ineffective cutting fluid	Fragments of the BUE stick to the surface and roughen it; the effective tool geometry keeps changing
Discontinuous	The chip fractures into separate segments	Brittle materials such as grey cast iron, hard inclusions, small rake angle, large depth of cut, low machine stiffness	Normal for cast iron; on ductile steel it signals unsuitable conditions
Serrated (segmented)	Semicontinuous chip with narrow bands of very high shear strain between wide zones of low strain	Titanium alloys, nickel superalloys and austenitic stainless steel at higher speeds	Cyclic force, a sawtooth chip and heavy edge loading

In serrated chips, heat cannot leave the primary shear zone fast enough. The material softens locally and the shear concentrates in a thin adiabatic shear band.

The eight chip forms of ISO 3685

Annex G of ISO 3685, titled “Chip characteristics”, classifies chip forms for tool-life testing in turning. Six of the eight forms have sub-forms: four by length (long, short, snarled), the spiral by shape, and the arc by whether the pieces stay connected.

1Ribbon
2Tubular
3Spiral
4Washer-type helical
5Conical helical
6Arc
7Elemental
8Needle

Chip forms after ISO 3685:1993 Annex G, drawn schematically. Sub-forms: 1, 2, 4 and 5 are long, short or snarled; 3 is flat or conical; 6 is connected or loose.

No.	Form	Sub-forms
1	Ribbon	1.1 long, 1.2 short, 1.3 snarled
2	Tubular	2.1 long, 2.2 short, 2.3 snarled
3	Spiral	3.1 flat, 3.2 conical
4	Washer-type helical	4.1 long, 4.2 short, 4.3 snarled
5	Conical helical	5.1 long, 5.2 short, 5.3 snarled
6	Arc	6.1 connected, 6.2 loose
7	Elemental	—
8	Needle	—

Long and snarled forms tangle around the tool, the part and the chuck, and they are hard to remove from the machine. A study that classified chips according to ISO 3685 lists short washer-type helical (4.2), loose arc (6.2) and elemental (7) chips as favourable, and long ribbon (1.1), snarled tubular (2.3), flat spiral (3.1) and long or snarled washer-type helical (4.1, 4.3) chips as unfavourable.

How a chip breaker works

A chip breaker does not cut the chip. It bends it until it breaks. Tungaloy describes the sequence in four steps:

The material is sheared and lifted off the work.
The groove and wall of the chip breaker force the chip to curl tightly.
The tighter the curl, the larger the bending strain inside the chip.
When that strain exceeds the fracture strain of the material, the chip breaks.

Sheared and lifted off the work
Groove and wall curl the chip
Tighter curl, larger bending strain
Strain exceeds the fracture strain: it breaks

The four steps on an insert with a land, a groove and a backwall, drawn schematically. The bar under each step shows how the bending strain in the chip rises as the curl tightens, until it passes the fracture strain of the material. It shows the order of events, not values.

The chip breaks in one of three ways: against the tool, against the workpiece, or by bending on its own.

The chip-breaking window

Every chip breaker works only within a range of feed and depth of cut. Tungaloy puts the limits plainly: if the feed is too low, the chip is thin and hard to break; if it is too high, the chip is restrained too much and the edge is overloaded. If the depth of cut is too shallow, the chip is not wide enough for the breaker to act on. Tool makers draw the working range as an area on a chart of feed against depth of cut, and ISO 10910 defines how such chip control zones are classified and designated. Both Tungaloy and Mitsubishi note that the range generally becomes narrower as cutting speed rises: the hotter chip is softer and harder to break.

1feed too low: thin chip, hard to break
2feed too high: chip restrained too much, edge overloaded
3depth of cut too shallow: chip too narrow for the breaker to act on
4higher cutting speed: the window narrows

schematic, no values

The chip-breaking window, drawn schematically after the limits above. Each chip breaker has its own chart with real values for feed and depth of cut; the dashed area stands for the narrower range at higher cutting speed.

Reading the chip at the machine

Long ribbon or snarled chips: the feed or depth of cut is probably below the breaker’s range. Raise the feed, or choose a chip breaker designed for lower feeds; the full list in order is on the long, tangling chips page.
Shiny material welded on the rake face, torn surface: built-up edge. Raise the cutting speed and use a sharper, more positive edge.
Sawtooth chip on titanium or a nickel alloy: expected for these materials. Keep the edge strong and the setup rigid.
Short arcs or tight short helices: the chip breaker is working.

Sources (10)

Every value and quotation on this page comes from the documents below.