Tool wear

In the illustrative wear trial, flank wear rises from 0.140 mm at 20 cutting minutes to 0.230 mm at 30. Linear interpolation gives 26.67 cutting minutes at an assumed 0.200 mm endpoint. At 0.75 cutting minute per part, 35 complete parts use 26.25 min and 36 use 27.00 min. The endpoint and interpolation are trial assumptions. Variability, sudden failure and part acceptance still need separate evidence.

Seco distinguishes progressive flank or crater wear from edge chipping. Plastic deformation and adhered material can coexist with wear. Seco Tools, Understanding Tool Wear.

Tie a wear endpoint to the tool, workpiece and operation.

Location and morphology describe different quantities

Seco describes relatively uniform flank wear as more predictable than abrupt failure and discusses temperature-dependent contributions to flank and crater wear. Its chipped-edge discussion includes instability, inclusions and interrupted cutting. These descriptions relate morphology to candidate mechanisms; they do not make a photograph a unique diagnosis. Seco, flank, crater and chipped-edge discussion.

Explanatory synthesis: A wear-land width, a crater depth and a missing corner are not interchangeable measurements. The same apparent surface-finish problem can result from different edge conditions, while an insert can exhibit more than one condition at once. Average wear can conceal a local defect that controls part quality or failure risk.

Why a correction depends on the mechanism

Sandvik’s thread-turning troubleshooting illustrates the distinction. For plastic deformation associated with excessive cutting-zone temperature, its responses include lower cutting speed and a grade more resistant to deformation. For built-up edge associated with unsuitable grade or low edge temperature, it instead includes increased speed and a tough insert. Opposite responses can therefore be reasonable for different diagnosed problems in the same operation. Sandvik Coromant, thread-turning troubleshooting.

The same guide notes that built-up material can tear away with insert material, producing chipping. An adhered deposit is consequently not proof that the underlying cutting edge is undamaged. Its examples remain specific to thread turning and do not establish feed or speed changes for an unrelated milling operation. Sandvik, built-up edge and chipping.

Sandvik’s milling troubleshooting separately treats flank wear, notch wear, thermal cracking, chipping and plastic deformation. Interrupted engagement and changing thermal conditions give milling a different loading history from a continuous turning cut. A general recommendation to add coolant or reduce feed cannot replace the applicable operation-specific analysis. Sandvik, milling troubleshooting.

Chip formation and wear interact

Workpiece material, tool geometry, engagement and cutting conditions determine how chips form and leave the cutting zone. Seco’s chip-formation guidance explains that chip thickness and width/depth relationships can create excessive nose loads or difficult ribbon chips. It also describes unstable built-up material breaking away and leaving material on the machined surface. Seco, chip-formation guidance.

Thus, a wear comparison made after changing chip evacuation or engagement is not a comparison of cutting speed alone. A tool grade can have adequate abrasion resistance yet fail because of mechanical instability or chip interaction. Surface roughness, tool loss and chip behavior are related observations, not substitutes for one another.

Tool life requires a defined endpoint

ISO 3685:1993, edition 2, specifies recommended tool-life testing procedures for high-speed-steel, cemented-carbide and ceramic single-point turning tools used on steel and cast iron. Its public abstract identifies workpiece, tool, fluid, cutting conditions, equipment and deterioration assessment among the test factors. The scope is narrower than all cutting processes and materials. ISO 3685:1993, public scope.

Explanatory synthesis: “Thirty minutes of tool life” is incomplete without the end criterion and time basis. Cutting time, spindle-running time, elapsed shift time and number of accepted parts can differ substantially. A dimensional failure, a chosen wear limit and catastrophic breakage also represent different endpoints. Consequently, a longer measured life need not mean a more economical or more capable process if cutting time per part or scrap increases.

A tool-life model is conditional on the behavior used to fit it. A smooth empirical relationship cannot establish the probability of a sudden breakage caused by an inclusion or an unstable setup. It also cannot turn an arbitrary wear criterion into a universal acceptance limit.

Original example: an illustrative wear endpoint

Assume invented measurements of one specified flank-wear quantity, using the same method and location convention throughout a trial:

Suppose the chosen trial endpoint is 0.200 mm, purely as an example. Linear interpolation between the bracketing 20- and 30-minute observations gives:

T = 20 + (0.200 − 0.140)/(0.230 − 0.140) × 10 = 26.67 cutting minutes.

This is an interpolation of invented data, not a standardized wear limit or a validated replacement policy. The observations do not prove linear wear between measurements, and they provide no evidence of the wear curve beyond the measured interval.

Now assume each complete part uses 0.75 cutting minute on the same edge. The interpolated time corresponds to 26.67/0.75 = 35.56 part-equivalents. Thirty-five whole parts consume 26.25 cutting minutes; thirty-six consume 27.00 minutes. Rounding to 36 would therefore exceed the interpolated endpoint under this simplified balance. Even 35 is not a guaranteed safe production count: part variability, measurement uncertainty and sudden failure were excluded.

Original example: edge cost versus production cost

Continue with a hypothetical 16-currency-unit insert providing four equally usable edges, so purchase cost is 4 per edge. At 35 accepted parts per edge, the insert allocation is 4/35 = 0.1143 currency/part. If an edge change takes 1.5 minutes and the relevant machine-time cost is 1 currency/minute, change time adds 1.5/35 = 0.0429 currency/part. Their combined allocation is 0.1571 currency/part.

This excludes machining time, scrap, offsets, inspection, other consumables and any unused edges. It is not a quoted selling price. A faster cut with shorter edge life can still have a lower total cost, or a higher one, depending on those omitted terms. More minutes per edge alone does not decide the economic comparison.

Interpretation limits

Explanatory synthesis: Wear evidence is strongest for the material, tool condition, engagement and cutting interval actually represented. A favorable trial does not establish long-run variation, the condition of every indexed edge or conformity of every produced feature. Machine-load and vibration signals may reflect tool deterioration, but they can also change with engagement, material or setup; a signal trend alone is not a direct wear-land measurement.

Part dimensions and surface requirements remain distinct from an insert’s measured wear. A chosen wear endpoint may occur before or after a part-quality limit, depending on the operation. This distinction explains why comparative tool tests, economic calculations and production acceptance answer different questions.

Source versions

Reviewed 2026-11-02 PST. ISO identifies 3685:1993, edition 2, November 1993, last confirmed in 2017; its live record also shows a later review stage, not a newly published replacement edition. No separately verified issue date is assigned to the cited Seco and Sandvik web guidance. No numerical wear allowance is taken from an unread normative table. Examples and explanatory synthesis are original and bounded to the stated assumptions.