What Is High-Speed Milling in CNC Machining?

What Really Makes Milling “High-Speed”

Many people think high-speed milling (HSM) is just spinning the spindle really fast. That’s not correct. Real HSM depends on four main factors that work together:

· cutting speed at the tool edge (vc)

· spindle RPM (n)

· feed rate (vf)

· material removal rate (Q)

The big difference from normal milling is simple. Conventional milling takes slow, deep cuts. HSM in CNC machining takes fast, shallow cuts. Deep cuts create heavy loads and a lot of heat. Shallow, fast cuts keep forces low and heat under control. Important: HSM is NOT high RPM plus deep cuts. It’s a completely different way of working that gives longer tool life, better accuracy, and smoother surfaces.

History of High-Speed Milling

The idea started in the 1920s with early tests. In 1931, Carl Salomon published his famous curve. He showed that once cutting speed passes a certain point, the temperature at the cutting edge actually drops because the chip becomes thinner and carries heat away faster. Research continued through the 1950s–1970s, mostly in universities and aerospace companies. Real factory use began in the 1980s for hard metals and thin-wall aircraft parts. From the 1990s onward, better CAD/CAM software and stronger machines made HSM common in mold making, aerospace, medical, and automotive shops.

Conventional Milling vs. High-Speed Milling

Old-style milling uses long “racetrack” paths. The tool stays in the cut for a long time. Chip load keeps changing. Forces get high. Heat builds up. Tools wear fast. Surfaces look rough. HSM uses very short contact time and constant chip load. Forces stay low. Heat goes out with the chips. You get better finish, longer tool life, and parts stay accurate. Most HSM services need little or no coolant. Dry machining or a tiny amount of mist works fine.

Tooling Requirements for Successful High-Speed Milling

Never use the same tool for roughing and finishing. Keep different tools for each job. Keep tool overhang as short as possible. Rigidity is everything. Use good tool holders: HSK, shrink-fit, or hydraulic. Many shops now choose Momaking shrink-fit holders because they stay perfectly balanced even above 30,000 RPM. Clear chips fast. Through-tool air or mist is usually enough.

Core High-Speed Milling Techniques

· Trochoidal milling: looping paths that keep radial engagement low but chip load steady. Great for slots and hard materials.

· Plunge roughing: the tool goes straight down instead of sideways. Less side pressure.

· Constant-Z roughing: even layers in 3D shapes.

When stepover is under 50 % of tool diameter, chips get thinner than you expect. You must raise feed per tooth to keep proper load. That’s radial chip thinning. Use smooth “golf-club” transitions and good look-ahead in corners. Modern CAM can track remaining stock so roughing flows right into finishing.

Machine Tool Capabilities Required for True High-Speed Milling

l Spindle: 20,000–60,000 RPM with stiff bearings.

l Drives: linear or torque motors that hit 1–2 g acceleration.

l Base: polymer concrete or similar for damping.

l Thermal control: the machine must stay the same size even when it warms up.

l CNC control: needs 1000–4000 block look-ahead and nano-level smoothing. Shops running Momaking high-speed machining centers often hit these numbers without extra tuning.

Summary of Key Technical Advantages

· Much better surface finish

· Tools last longer

· Parts stay accurate

· Faster overall cycle time even with light cuts

· Cleaner shop floor

· Works on hard steel, titanium, graphite, etc.

Conclusion – When to Choose High-Speed Milling

Choose HSM when you need excellent finish on complex shapes, thin walls, hardened material, or graphite electrodes. You need three things to make it work:

1. Modern CAM that creates smart paths

2. A stiff, fast machine — many users report good results with Momaking platforms

3. Proper tooling strategy

High speed milling factory is not just a spindle setting. It’s a complete system that combines the right machine, software, tools, and strategy.

FAQ

Q: What is the real definition of High-Speed Milling (HSM)?

A: It’s high spindle speed + high feed rate + very light cuts + constant chip load. The goal is higher removal rate with much lower forces and heat.

Q: Can any CNC machine with a high-RPM spindle do High-Speed Milling?

A: No. You also need fast acceleration, extreme rigidity, big look-ahead, thermal control, and balanced tooling.

Q: Why does High-Speed Milling often run dry or with almost no coolant?

A: The heat leaves with the thin chips. Very little heat goes into the tool or part.

Q: When should I switch to High-Speed Milling?

A: Use it for molds, dies, aerospace thin-wall parts, hardened steel finishing, graphite electrodes—any job where finish, accuracy, and speed really matter.