tool-wear

name	tool-wear
description	Tool wear mechanisms — flank wear (V_B), crater wear, built-up edge, chipping, notch wear, Taylor tool life equation, cutting tool materials, wear monitoring, ISO 3685 standards.
metadata	{"priority":7,"promptSignals":{"phrases":["tool wear","flank wear","crater wear","Taylor tool life","cutting tool wear","VB wear","tool life equation"],"minScore":3}}

Tool Wear — Complete Skill

Wear Mechanisms

Adhesive Wear

Material transfer from workpiece to tool via cold-welding at asperity contacts Built-up Edge (BUE): workpiece material welds to rake face; changes geometry; unstable; breaks off → surface damage Dominant at: low-moderate cutting speeds; ductile materials (low-C steel, aluminum); poor coolant Reduction: increase speed above BUE speed, use coated tools, apply coolant

Abrasive Wear

Hard particles (carbides, oxide inclusions) in workpiece scratch tool surface Two-body: hard material directly scratches softer tool Three-body: loose particles roll between tool and chip Dominant at: machining cast iron, composites, hardened steels, ceramics Reduction: harder tool material (ceramic, PCBN, PCD)

Diffusion Wear

Atomic diffusion from tool to chip at high temperatures; weakens tool surface Dominant: high speeds (T > 800°C); continuous cutting; uncoated carbide WC-Co: Co diffuses; W diffuses into iron → crater wear; TiN, TiAlN coatings prevent diffusion

Oxidation Wear

Tool oxidizes at high temperature in air; oxide softer → removed easily Dominant at: highest cutting speeds; dry machining Reduction: TiAlN coating (Al₂O₃ forms as protective barrier at T > 800°C)

Fatigue Wear (Chipping)

Cyclic thermal/mechanical loads cause crack initiation and propagation Thermal fatigue: interrupted cutting (milling); cooling/heating cycles → comb cracks Mechanical chipping: intermittent cutting, hard spots in workpiece Reduction: tougher grade carbide (higher binder Co%); avoid flood coolant in milling of hot materials

Wear Types and Location

Flank Wear (V_B)

Most measurable: wear land on flank face ISO 3685 limits: V_B = 0.3 mm (uniform flank wear) — standard tool life criterion V_B_max = 0.6 mm (maximum; localized areas) V_B_notch = 0.5 mm (notch at depth of cut line)

Measurement: optical microscope; tool maker's microscope; focus-variation microscopy

Crater Wear (K_T)

Concave cavity on rake face from diffusion/abrasion by chip K_T: crater depth [mm]; K_M: crater center distance from edge; K_B: crater width ISO limit: K_T = 0.06 + 0.3 × f [mm; f = feed in mm/rev] — feed-dependent

Relationship: crater weakens cutting edge → chipping when K_T/K_M > 0.4–0.6

Notch Wear

Groove at depth-of-cut boundary; from abrasion by work-hardened layer at free surface Dominant in: stainless steel (highly work-hardened), titanium, Inconel Reduction: vary depth of cut slightly between passes; sharp lead angle

Deformation Wear

Plastic deformation of cutting edge (high T + high P) Occurs with: excessive speed on high-speed steel; insufficient binder in carbide Tool edge rounds, loses geometry → poor surface finish

Taylor Tool Life Equation

Basic Taylor: V × T^n = C (or equivalently: T = (C/V)^(1/n))

V = cutting speed [m/min]; T = tool life [min]; n, C = material constants

n values: HSS: n = 0.10–0.125 Uncoated carbide: n = 0.20–0.30 Coated carbide/TiAlN: n = 0.25–0.40 Ceramic: n = 0.30–0.45 PCBN: n = 0.45–0.55

Extended Taylor (speed, feed, depth): T = C / (V^a × f^b × a_p^c) a ≈ 1/n; b ≈ 0.5/n; c ≈ 0.3/n (empirical approximations)

Optimal cutting speed (minimum cost): V_opt = C × n / ((1-n) × (t_ct + C_t/C_m))^n

t_ct = tool change time [min]; C_t = tool cost per edge [$]; C_m = machine rate [$/min]

Maximum production speed: V_max_prod = C × n / ((1-n) × t_ct)^n [slightly higher than V_opt]

Cutting Tool Materials

High-Speed Steel (HSS)

M2 (6W-5Mo-4Cr-2V): V_c = 20–40 m/min for steel; T_max = 600°C PM-HSS (powder metallurgy): more uniform; higher V_c; M42 (8%Co) excellent for SS and Ti Used: drills, taps, end mills (low speed), broaches

Uncoated Cemented Carbide (WC-Co)

P-grade (TiC-added): for steel (P01–P40); K-grade (pure WC-Co): cast iron, non-ferrous V_c = 80–250 m/min for steel; T_max = 900°C Grade by ISO: P (steel), M (stainless/ductile iron), K (cast iron), N (non-ferrous), S (super-alloys), H (hardened)

Coated Carbide

TiN (gold): wear and BUE resistance; V_c increase 30% TiCN (grey): harder than TiN; better for abrasive materials TiAlN (black): excellent hot hardness to 900°C; dry machining; best for steel AlTiN (black): Al-rich; Al₂O₃ barrier at 1000°C; highest speeds CVD Al₂O₃: best crater resistance; used in indexable turning inserts nACo/nc-TiAlSiN: nanocomposite; excellent hot hardness; Ti-Al with Si

Ceramics

Al₂O₃ (white): high-speed cast iron; interrupted cuts limited Al₂O₃-TiC (black mixed ceramic): better toughness; steel at 300–600 m/min Silicon nitride (Si₃N₄, grey): cast iron; aggressive interrupted cuts; not for steel SiAlON: whisker-reinforced; better toughness; nickel superalloy rough turning

Cubic Boron Nitride (PCBN)

Hardness 4500 HV (vs. diamond 9000 HV; WC 1800 HV) Used: hardened steel (HRC 45–70); chilled cast iron; powder metal alloys Low-CBN content (45–55%): better toughness; for interrupted cuts High-CBN content (80–90%): better wear; for continuous cuts V_c = 100–400 m/min in hardened steel

Polycrystalline Diamond (PCD)

Hardness: 9000 HV; V_c = 100–1000 m/min for aluminum Used: aluminum (Si-containing), copper, graphite, CFRP, fiberglass Cannot use for: steel (diamond dissolves into iron above 700°C — carbon solubility)

Wear Monitoring Methods

In-process:

• Cutting force measurement: F_c increases with V_B (force ratio: F_thrust/F_cutting > 0.5 → worn)
• Acoustic emission (AE): frequency content changes with tool condition
• Vibration accelerometers: increased vibration amplitude → wear
• Thermal imaging: IR camera or thermocouple in tool → temperature rises with wear

Post-process:

• Optical microscopy: V_B measurement per ISO 3685
• SEM/EDX: identify wear mechanism, element diffusion
• Profilometry: surface finish Ra increases with wear; Ra > 3× initial → replace

ISO 3685:1993

Standard tool life testing: defines criteria (V_B = 0.3 mm); test conditions (cutting speed, material grades) Test procedure: step-down or CNC test; measure V_B periodically; plot V vs T on log-log → find n, C Acceptance: report T [min] at specified V_c and criteria

Output

Provide: dominant wear mechanism (adhesive/abrasive/diffusion/thermal), V_B [mm] expected at given V_c and t_cut, Taylor n and C constants for material-tool pair, optimal V_opt [m/min] and V_max_prod [m/min], tool life T [min] at operating V_c, recommended tool material/grade and coating, wear monitoring method for production, applicable ISO grade (P01–P40), and applicable standard (ISO 3685, ISO 513 for tool classification).