🧪 COBALT-CHROME · HARD WORK-HARDENING ALLOY

Cobalt-Chrome Deep Hole Drilling

Cobalt-chrome combines outstanding wear and corrosion resistance with a machinability that is outright punishing. Used in medical implants, turbine hardware and wear components, it work-hardens the instant a tool rubs — deep holes in CoCr are drilled slowly, sharply and relentlessly.

HRC 30–45hardnessAnnealed to solution-treated

8–20m/minGundrill Vc

Work-hardenshardEdge-grabbing behavior

Medical / aerosectorsImplants, turbines

PRINCIPLE

Why CoCr Is So Demanding

Cobalt-chrome (ASTM F75, F799, F1537 for implants; Stellite-type wear alloys) is a Co-Cr-Mo alloy that forms a hard, strain-hardening surface at any frictional contact. It has low thermal conductivity, so cutting heat concentrates at the edge; it welds to a dull tool; and its chips are abrasive. Every one of these pushes the same conclusion: sharp tools, low speed, positive feed, relentless coolant.

💡 The hardness trap: even “annealed” CoCr is ~HRC 30–35, and the cut surface immediately strain-hardens toward HRC 45+. Parameter creep is fatal — treat every pass like hardened steel.

PARAMETERS

Starting Parameters

Parameter	CoCr (F1537 / F75)
Gundrill Vc (m/min)	8–20
BTA Vc (m/min)	8–15
Feed @ Ø10 mm (mm/rev)	0.01–0.02
Coolant	Neat oil, high EP
Coolant pressure	100–200 bar (micro/small gundrills)

⚠️ Never dwell: any pause lets the tool rub, which hardens the hole wall and welds the edge. Continuous feed only — and index/regrind the tool at the first sign of edge wear.

CHALLENGES

Failure Modes & Countermeasures

Work hardening: keep the edge engaged and sharp; stop rubbing by holding a true cutting feed.
Edge welding / BUE: built-up edge tears out, notches the tool, and ruins the hole. High-EP oil and sharp edges fight it.
Heat: concentrate coolant at the cutting zone; through-tool delivery is mandatory.
Tool wear: flank wear accelerates once the coating goes — run a wear budget (e.g. regrind every 20–60 m of drilled length).

TOOLING

Tooling for CoCr

Grade: micro-grain carbide (K10–K20) or CBN for the hardest grades.
Coating: TiSiN or TiAlN hold up; uncoated sharp edges work where BUE is the problem.
Geometry: positive rake, strong edge, well-designed guide pads to share the load.
Monitoring: torque and coolant-pressure trend; a climb signals dulling — retract before the tool snaps in the bore.

APPLICATIONS

Where CoCr Bores Are Drilled

🧸 Hip & Knee ImplantsStem bores and taper connections in CoCr implants.

🧸 DentalCoCr frameworks and abutment bores.

⚙️ Turbine HardwareCoCr vane and seal components.

🛡 ValvesWear-grade CoCr valve seats and bodies.

🔧 PumpsWear sleeves and shafts in abrasive service.

📝 DownholeCoCr wear components for well tools.

Cobalt-Chrome Deep Hole Drilling

Why CoCr Is So Demanding

Starting Parameters

Failure Modes & Countermeasures

Tooling for CoCr

Where CoCr Bores Are Drilled

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