As a developer of a very successful line of speed and feed calculators I sometimes get questions like : "I calculated speeds and feeds for a conventional toolpath. Got 5.5 cubic inches MRR(Material Removal Rate). And then I calculated S&F for the same endmill with HSM parameters turned on and got almost the same amount of  MRR! What is even the point in using HSM parameters?" -they ask.

I would like to clear some things up for my friends.
In this article I will explain exactly WHY HSM machining is better and HOW to achieve better productivity and tool life.

For starters here are the main features of a HSM-capable cutter:

As usual there are several components of HSM that need to be present in order for it to work to its fullest. These are:

a) Machine
b) Tool
c) Workpiece geometry
d) Workpiece material

I intentionally did not number these as each one of those is equally important.

a) Machine. You need to use a very rigid machine that is designed by the manufacturer to operate at high feed rates and cutting forces. If your machine is not up to the task, however, it does not mean that HSM machining will fail, but simply that you may not be able to utilize the spindle time to its fullest. There still are ways to successfully use HSM on older machines. And we will talk about it later.

b) Tool. Your tool should be designed for HSM. Tools, that are capable of performing conventional operations sure CAN, but are not the best at it by a wide margin.
Tools designed for HSM have thicker core to sustain high cutting forces. They have a lot more flutes stuffed into the same tip diameter than their conventional brothers. IE. a 1/2" HSM Endmill can have 7-10 flutes versus 4-5 for a standard endmill.
A cutter with so many flutes on such a small diameter simply can not effectively do any conventional milling at all.

Thus any attempt to compare "apples to apples" fails miserably. You just have to start comparing apples to oranges.

HSM cutters often have corner radius to prevent chipping. And some models even have a geometry of a feed mill on the end to allow for high speed ramping (where with of cut will be equal to the diameter of the cutter) into the material.

c) Workpiece geometry.
HSM machining with an end mills requires large depths of cut. Simple as that.
You part needs to have deep cavities and tall walls. At low radial engagement HSM cutters can take full flute depths of cut with almost no additional tool deflection. Your depths of cut should be more than x2 of the tip diameter. And they can be as large as x4 of the tip dia. without the need to compensate for that.

d) Workpiece Material.
Should be hard or tough material. Such as Stainless steel, titanium, tool steel, hardened steels. Maybe Mild steel. But not aluminum. aluminum is easy enough to machine the conventional way. With fluffy soft materials it may simply be impossible to compensate the lost air time with higher feed rate.

Lets compare performance of two 1/2" endmills in machining a 1.5" deep pocket in D2 Tool steel.

One is 1/2" 4 Flute TiAlN coated High Performance Endmill.
Because we will machine a 1.5" deep pocket the conventional way.
Our DOC (Depth of Cut) will be just 0.226"
MRR for this operation will be: 2.49 in^3:

Another tool is 1/2" 6 Flute TiAlN coated High Performance Endmill designed for HSM machining
Our DOC (Depth of Cut) will be 1.5" with 0.05" radial stepover
MRR for this operation will be: 5.96 in^3

Almost 6 cubic inches of metal removal versus 2.49 is more than twice the productivity!
And that was calculated with very conservative settings.

In addition to that You can also see that estimated Tool Life has increased to 149%.

This is basically it.

Let me know if something else needs more clarification and i will explain this article.

You may also like to learn about:

• A new Help article on HSM

• Ways in which High Speed Machining (HSM ) works

• Reasons why High Speed Machining works