What is High Speed Machining (HSM)?
High speed machining (HSM)–also called trochoidal milling, adaptive clearing, volumill, and more–is a milling technique that can increase material removal rates, reduce cycle time, and increase Jasa Machining tool life.
This video from my CNC Chef series for Cutting Tool Engineering Magazine gives a quick What is High Speed Machining (HSM) intro:
For a quick into to High Speed Machining (HSM), try my CNC Chef video…
Note: This High Speed Machining article is Lesson 11 of our Free Email Feeds & Speeds Master Class. Click here to learn more about the Master Class.
There are many definitions for High Speed Machining (HSM). MMSOnline uses the tagline “Achieving high metal removal rates with quick milling passes” for the HSM zone on their site. Another very high tech definition of HSM is “Machining at the Resonant Frequency of the Machine,” which goes to HSM techniques for selecting spindle speeds that minimize chatter. You’d think that the “High Speed” part of HSM would emphasize faster spindle speeds (Sandvik says HSM begins at 18000 rpm), but that interpretation is not universal as various shops discovered HSM techniques can work well even on slower milling spindles. Others argue that HSM is all about high material removal rates and leaving a surface finish good enough to call finished in one pass.
One of the things that got people thinking about HSM was the discovery that after a certain point, increasing spindle speed actually reduces the heat in the cut:
This amazing chart is from Dr Herbert Schulz’s, “History of High Speed Machining.”
The dotted lines represent temperatures at various surface speeds measured in m/min. Here is the US, we’re more used to SFM. Want to understand Surface Speed, SFM, and how do we get from SFM to RPM on the spindle? Jasa Machining Medan If you’re not familiar, it’s simple stuff and the link will explain.
Note that all of the materials go steadily up and then eventually start dipping back down again as surface speed increases. Somehow, high speed machining causes temperatures decrease beyond a certain spindle rpm!
This chart is in meters/minute, so multiply the values by about 3 to get to SFM. For aluminum, we have a pretty good dip by the time we’re hitting 1000 SFM, for example. In fact, it’s temperature is more equivalent to less than 300 SFM on the other side of the aluminum curve–that’s nothing for aluminum. Heck, if we have a fast enough milling spindle, there’s even room to run HSS faster and get lower temperatures (you’ll note various cutter materials critical temperatures are also marked off–stay below the line for your cutter!).
Steel and cast iron taper down more gently than aluminum, but the effect is still alive and well. Yes Virginia, there surely is some strange behavior when you start in with that HSM stuff!
The same research showed that cutting forces also come down, and that’s at least one reason why the temperatures drop, and why for HSM machining in the right rpm ranges, you can achive high MRR’s with lower cutting forces.
Sidebar: Coating Activation Temperature, Shock Cooling, and Turning Off the Coolant
While we’re on the subject of temperature, sometimes a little heat is important. Certain coatings, such as TiAlN, require a minimum “activation” temperature. At that temperature, their chemical composition changes, the coating is “activated” and it is only then that the coating is doing its job of protecting the cutter.
The combination of a desire to activate the coating and the desire to avoid shock cooling delicate carbide (which causes it to crack and splinter) is why we may see a recommendation from the tooling manufacturer to turn of the coolant even when running at very high spindle speeds common for High Speed Machining.High Speed Machining Techniques
Datron’s M8 Cube uses a high speed spindle and high speed machining techniques to achieve maximum productivity…
Whatever your pet definition of HSM may be, I like to look at HSM machining as a collection of techniques that “grew up” together in various aerospace machining operations such as Boeing’s. It initially involved very high speed spindles but many of these techniques have since turned out to be applicable even for lower speed milling spindles.
These techniques are so useful that many CAM Programs include HSM Toolpaths that make it easy to employ HSM on any job.
Let’s list off some of these techniques:
– HSM prefers to combine roughing and finishing passes. This is really only possible with higher speed spindles, because lower speeds just don’t produce the surface finish. The potential to skip the finish pass will also vary with the CAM package. Some HSM algorithms are smoother than others. If you’re trying to get by with a slower spindle, you’ll have to split into the more traditional roughing and finishing passes. For the finishing pass, use tooling with as many flutes as possible. Finishing assumes all the inside corners have been roughed out, so there will be plenty of chip clearance available. The more flutes you have, the faster you can feed through the work for a given chip load. Hence, productivity goes up. The only reason to use fewer flutes is to improve chip clearance.
– HSM prefers smaller tooling that moves faster to very large slow moving tooling designed for “hogging”. The smaller tooling saves on tool changes and makes it easier to achieve the ideal of eliminating the need for separate roughing and finishing passes.
– To maximize tool life, take advantage of relatively low cut width: 10-15% of tool diameter down to as little as lima% depending on where the sweet spot is for your milling spindle’s max rpm and the SFM your tool can handle in the material. These low radial depths allow the tool better chip clearance and time to cool down in air, allowing for much higher productivity especially on harder materials. See the article on taking heat out of the cut for some idea of how this works. With low cut width, increase the cut depth. This allows more of the cutter’s flute to come into play instead of just wearing out the bottom of the endmill. Choosing the best cut width for optimum material removal is not an easy task. The rules of thumb available can be far off the mark. For best results, you want a Feeds and Speeds Calculator that’s capable of optimizing HSM cutting parameters like our G-Wizard Calculator.
– Higher MRR’s (and shorter cycle times) typically require a little more Cut Width. Think of Tool Life more in terms of how many cubic inches of material can be removed with the tool rather than how many minutes it can run and you will quickly see that These wider Cut Widths make better economic sense. Some testing is in order to find your balance.
– When spindle speed is a limiting factor, consider a high feed endmill. High feed endmills maximize axial chip thinning and allow much higher feedrates. Another popular roughing strategy when you don’t have as much spindle speed as you’d like are as much machine rigidity is plunge roughing.
– Use CAM toolpath strategies that avoid the “Tyranny of the Corner” (see below for more on cutters). Such strategies include constant tool engagement angle strategies such as Volumill or Adaptive Clearing, Trochoidal Milling, and Slicing or Peeling of Corners.
– Since true HSM spindles offer a much broader range of rpms than conventional spindles, HSM often emphasizes choosing spindle speeds that maximize stable milling zones were chatter is much less likely. The same anti-chatter principles can be applied to lower spindle speeds, you simply have less rpm territory in which to find a stable zone that maximizes productivity. See our article on chatter for more on stable milling zones and the role of spindle rpm in chatter.
– HSM is going to involve a lot more movement on your CNC machine to implement its swirling toolpaths. That Jasa Machining Medan puts greater demands on your machine’s controller. Many controllers require an extra cost HSM feature to be enabled before they can get the full benefit of HSM toolpaths.
So there you have a small arsenal of strategies to choose from for increasing your productivity using ideas learned in the HSM world. Let’s drill down a bit more on some of them.Radial Chip Thinning when High Speed Machining
One of the first issues you will encounter when attempting to practice HSM with its low width of cut (or stepover) is radial chip thinning. We’ve written a detailed article on the subject, but for a quick overview, consider the following diagram:
View down the axis of the cutter shows how radial chip thinning works…