Why Tungsten Steel Is Difficult to Machine

Tungsten steel — also called cemented carbide — ranks among the hardest materials we machine at AOOM Technology. With a Vickers hardness approaching 10K, it sits just below diamond on the hardness scale. This makes it incredibly wear-resistant and heat-resistant, which is exactly why dies, punches, and cutting tools are made from it.

But that extreme hardness creates real machining challenges. Tungsten steel is brittle. It chips easily under vibration or shock. And it destroys cutting tools quickly if parameters are not set correctly. I tell new clients: treat tungsten steel with respect. It will not bend, but it will crack if you push too hard.

We see this material most often in mold inserts, stamping dies, and wear-prone tooling components. Clients come to us because they cannot machine it in-house — their standard CNC equipment and tooling cannot handle the hardness.

What Tools Cut Tungsten Steel

The answer surprises many people: tungsten steel is typically ground, not cut. Diamond grinding wheels are the primary tool for tungsten steel machining. They remove material through abrasion rather than shearing.

For milling operations, we use PCD (polycrystalline diamond) end mills or specialized tungsten carbide end mills with ultra-fine grain structure. Grades like KF10 and NR11 perform better than standard carbide grades because their finer grain structure resists chipping at the cutting edge.

For small-diameter precision features like M2 internal threads, ultrasonic-assisted machining increases tool life by up to 3 times. The ultrasonic vibration reduces cutting forces and helps clear chips from the cutting zone.

Tungsten Steel CNC Machining Parameters

These are our recommended starting parameters. Every machine and tool combination behaves differently, so consider these a baseline, not a final setting.

Spindle speed: 10,000–30,000 RPM. Too high generates excessive heat. Too low causes chipping at the cutting edge. Start in the middle range and adjust based on tool wear observations.

Feed rate: 20–60 mm/min. Slow feeds reduce tool impact but extend cycle time. We optimize feed based on the specific tool geometry and surface finish requirement.

Depth of cut: 0.01–0.1 mm per pass. Multiple light passes are safer than one deep cut. Tungsten steel does not deform — it fractures. Stay conservative on depth.

Cooling: High-pressure oil cooling directed at the cutting zone. Tungsten steel is heat-sensitive. Inadequate cooling causes micro-cracks that propagate into part failure during use.

I keep a log of parameter adjustments for every tungsten steel job. Small changes — 10% adjustment in feed or speed — produce measurable differences in tool life and surface quality. Record your results and build your own reference data.

Lessons from Our Shop Floor

Machine rigidity is everything. A rigid CNC machine absorbs the cutting forces that would otherwise chip the tungsten steel. Light-duty machines vibrate too much for reliable tungsten steel work.

Inspect tools frequently. Do not push a worn tool to finish the job. A chipped edge on the tool creates a stress riser in the part that may cause cracking during use. Replace tools at the first sign of edge degradation.

Use climb milling. Climb milling reduces the cutting force compared to conventional milling. This prevents edge chipping and produces a better surface finish on tungsten steel parts.

Is Tungsten Steel CNC Machining Expensive?

Yes. The cost comes from three sources. Diamond grinding wheels and PCD tools are expensive compared to standard carbide. The CNC equipment must be high-rigidity and often requires ultrasonic add-ons. And cycle times are long because conservative parameters mean slow material removal.

For high-precision applications — medical device components, aerospace tooling, precision dies — the cost is justified. One set of tungsten steel dies can produce millions of parts before needing replacement. The per-part cost is lower than using softer materials that wear out quickly.

Advice for Beginners

Start with aluminum or copper to learn the basics. Tungsten steel is not a beginner material. Build experience with chip formation, tool wear patterns, and parameter optimization on forgiving materials first.

When you are ready, work with a tool supplier who offers technical support. A good supplier recommends specific tool geometries and coating options for your application. They can also suggest starting parameters based on their own testing data.

Document every tungsten steel job. Parameters that work on one machine may not transfer directly to another. Your own data is more reliable than any table in a handbook.

Send your CAD files to chen@aoomtech.com for a quote within 24 hours.