A beginner's guide to High Speed Machining

High Speed Machining is milling at high spindle speed with light radial engagement and high feed per tooth. It is used for removing metal quickly from thin walled or difficult parts with low cutting force. This entry explains what it is, what the numbers on a data sheet mean, and what to put on a drawing.

It is written from the point of view of the buyer and the drawing office: the values that are realistic in production, the ones that cost money, and the way the result is verified. Where an industry sets the requirement, aerospace is used as the example: traceability and a first article before anything enters the batch.

In plain terms

High Speed Machining is milling at high spindle speed with light radial engagement and high feed per tooth. If you have not met the term before, the useful way to think about it is this: it is chosen when a part needs removing metal quickly from thin walled or difficult parts with low cutting force.

The terms you will hear

• Spindle speed – 20,000 to 40,000 rpm.
• Radial engagement – 5 to 10 per cent of diameter.
• Feed per tooth – 0.05 to 0.15 mm.

What it costs and how long it takes

Machine hour cost, because the spindle is expensive to run, and a realistic cycle is 20 to 90 minutes for a complex part. Those two numbers, not the headline hourly rate, decide the price of the part.

What to ask a supplier

• What tolerance will you hold in production, not just on the first part?
• What does the dimensional report cover, and which standard is it written to?
• What happens to the fixtures and programmes if we reorder in a year?

Applications

High Speed Machining is used for removing metal quickly from thin walled or difficult parts with low cutting force, and in practice it appears most often in thin walled enclosures, aluminium aerospace parts, mould finishing, graphite electrodes.

How it fits into a machining route

The route is fixed before the first part is cut, and it is the route rather than the individual setting that holds the result: machine hour cost, because the spindle is expensive to run. Where a drawing calls for something the route cannot hold economically, that is raised at quotation rather than after the parts are made.

Standards, documentation and what is issued

The documentation requirement is AS9100 where the customer requires it. Material is supplied against a certificate where the application calls for it, inspection results are recorded with the job, and the records are kept so that a repeat order can be compared with the first instead of being measured from scratch.

CMM and roughness gauge is the verification step. Where a customer format or a standard report is required, it is agreed before the batch starts, because a report written after the event is a report nobody can use.

Frequently asked questions

What tolerance should be specified for High Speed Machining?

±0.01 mm is realistic in production. Tightening it beyond the functional requirement increases cost without improving the part.

Which material is usually used?

7075-T6 aluminium is the usual choice, supplied against AS9100 where the customer requires it.

How is the result verified?

CMM and roughness gauge, with the results recorded so a repeat order can be compared with the first.

What is the most common mistake?

A toolpath with sharp direction changes, which the control cannot feed through smoothly.

How long does it take and what does it cost?

A realistic cycle is 20 to 90 minutes for a complex part, and the cost driver is machine hour cost, because the spindle is expensive to run.

Related capability

If you are specifying High Speed Machining on a drawing and want a second opinion on the route, send the model and the quantity. The first response is a manufacturability review with the likely risk points and a quotation, so the decision can be made on facts rather than on a price alone.

Machining, inspection and documentation are handled in one place, which is why the dimensional report and the material certificate arrive with the parts rather than after them.

Related entries

These entries sit next to High Speed Machining in the encyclopedia: Thread Milling, Deep Hole Drilling, Ti-6Al-4V Titanium. Reading them together gives a fuller picture of how the process, the material and the measurement affect each other.