One of the factors that determines HSM’s effectiveness is the machine itself. Today’s machine tools designed specifically for HSM often are extremely robust.

What exactly is HSM? A general misconception is that high-speed machining and high-performance machining (HPM) are the same. But they are not the same. HPM provides a high chip removal rate, using trochoidal toolpaths with long tool engagement. However, HSM uses specific techniques and factors in a number of different aspects.

“It wasn’t until the 90s that the machine design really started to change,” said Meekma. “Conventional machines often used a boxway system, but with the rise of HSM, linear guideways were introduced to enable faster feeding and to perform HSM.”

When you think of machining at high speeds, you might immediately think high heat. But that is not the case. Though it may sound counterintuitive, it is possible to run at a high surface speed, heat generation often can be overcome. This is mainly because the cutting tool spends less time engaged with the workpiece.

With HSM, there is a balancing act of the parameters involving the tool capabilities, machine capabilities, workholding conditions, toolholding options, and part material to ensure high-quality surface finish.GF Machining Solutions

HSM allows you to save time, better utilize the machine, and get the part closer to the net shape with the roughing pass. This part, made out of Polmax with a hardness of 52 HRC, has an Ra 0.018-µm mirror finish on a 3D surface. MC Machinery Systems

“One of the primary advantages of HSM is heat dissipation,” said Meekma. “Using conventional techniques of cutting metal, heat is developed by forcing the cutting tool through it. When you go faster, by increasing the surface speed or RPM, you will get a certain peak before the temperature falls. The heat never really gets a chance to develop into the workpiece and is dissipated by the chip much better.”

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“If you were to take a tool and run it at a very low speed, no matter what the feed rate or stepover, you won’t achieve as good of a finish like you would if you turn up the spindle and go really fast,” said Meekma. “The reason you don't do that in most scenarios is because the tool won't be able to handle the surface feed under the same conditions. But with all proper parameters dialed into HSM, you can. The faster RPM you get, the shinier the material will appear after cutting.”

“With HSM, there is a balancing act of the parameters involving the tool capabilities, machine capabilities, workholding conditions, toolholding options, and part material,” said Christian Meekma, milling project manager, GF Machining Solutions, Lincolnshire, Ill. “When it comes to the milling world, there is no perfect formula, it’s all about understanding how various aspects influence the process and then adapting to that. And that is especially true when it comes to ensuring a good surface finish.”

Cone-shaped pins that support a workpiece by one or two ends during machining. The centers fit into holes drilled in the workpiece ends. Centers that turn with the workpiece are called “live” centers; those that do not are called “dead” centers.

Working with HSM means that the machine should have a strong frame to withstand the high forces and vibration generated. Choosing a machine with a polymer granite base, for example, provides significant absorption of vibration as well.

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“Cutting tool and workpiece stability all play a role,” said Gillcrist. “You should use a well-balanced tool with limited runout. Also, a rigid spindle with a quality toolholder will limit chatter. If you have a thin holder with the tool sticking way out and run it at a high RPM, it’s going to deflect and reduce surface finish quality.”

“This is not true in all materials,” said Meekma. “For example, aluminum doesn’t act the same way as hardened steel. Obviously, the material will then dictate what you can actually do, and ultimately there is only so fast you can go on certain things, and that will affect surface finish.”

When working with HSM, you must consider the feed rate, especially as it relates to chip load. A larger feed per tooth will leave a rough surface finish compared to a smaller feed per tooth, which will result in a smooth surface finish. However, feeding too slow may cause burnishing, leaving a poor surface finish.

When machining hardened steels, chips that are blue or purple indicate that the heat is reaching the chip away from the part.

Thread milling techniques, in many respects, offer greater advantages over tapping with reduced cutting loads for higher reliability. Solid carbide taps pose higher risk of tool breakage, while HSS taps offer shorter tool life. In addition, insert screws are designed not to detach from the cutter body when completely loosened during insert setup so operators will have no concern dropping or losing the tiny screws in the machine.

Additionally, cutting tool attributes will play a role in surface finish. A quality cutting tool will be able to perform at high spindle speeds while the cutting edge cuts uniformly on the surface. This is also dependant on a good, rigid spindle that can hold the tool concentrically to the workpiece.

The HSM process needs to be well though out, especially when working with hard materials like this medical mold insert made out of H13 steel with 52 HRC. MC Machinery Systems

Available in two major types: tungsten high-speed steels (designated by letter T having tungsten as the principal alloying element) and molybdenum high-speed steels (designated by letter M having molybdenum as the principal alloying element). The type T high-speed steels containing cobalt have higher wear resistance and greater red (hot) hardness, withstanding cutting temperature up to 1,100º F (590º C). The type T steels are used to fabricate metalcutting tools (milling cutters, drills, reamers and taps), woodworking tools, various types of punches and dies, ball and roller bearings. The type M steels are used for cutting tools and various types of dies.

Tungaloy introduces an indexable thread milling solution for tapered pipe threads to its ThreadMilling series. The indexable thread milling system of ThreadMilling allows various types of threading insert(s) to be fitted on a single cutter body, making the operations extremely economical. With the new multipoint threading inserts and cutter bodies, thread milling for NPT and NPTF threads as well as BSPT thread are now possible on machining centers, using its spiral interpolation feature.

Process of both external (e.g., thread milling) and internal (e.g., tapping, thread milling) cutting, turning and rolling of threads into particular material. Standardized specifications are available to determine the desired results of the threading process. Numerous thread-series designations are written for specific applications. Threading often is performed on a lathe. Specifications such as thread height are critical in determining the strength of the threads. The material used is taken into consideration in determining the expected results of any particular application for that threaded piece. In external threading, a calculated depth is required as well as a particular angle to the cut. To perform internal threading, the exact diameter to bore the hole is critical before threading. The threads are distinguished from one another by the amount of tolerance and/or allowance that is specified. See turning.

“When you take away any of one of those individual elements, that's where the surface finish starts to degrade,” said Meekma.

As a concept, high-speed machining (HSM) was conceived by Dr. Carl J. Salomon during a series of experiments he undertook in 1924. Fast forward 100 years, and high-speed machining is not just a theoretical concept but one that, if done correctly, can provide exceptional surface finish and increased productivity.

Effective HSM depends on a number of different elements and features. Any one aspect of the process can be a limiting factor to success.

“HSM requires the right combination of a number of factors,” said Gillcrist. “The sharper the cutting tool, the better. A sharper cutting tool will get that shearing action, moving the chip away from the cutting zone to remove the heat. But that’s not always the case. For example, machining carbide, a sharp tool will not work, so it really does depend on the application.”

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HSM emphasizes high speeds and feeds to increase productivity and improve surface quality. It requires a higher spindle RPM, uses smaller tools, and makes lighter cuts than traditional milling operations. It often is associated with a spindle speed above 15,000 RPM. But that’s not all that goes into HSM.

Vibration in any capacity hampers the ability to achieve high-quality surface finish. For example, when the cutting tool vibrates, it can leave marks on the workpiece, which may require additional passes to reach the desired finish.

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Stepover, a term to describe how far the tool moves over between each pass, also plays a big role in surface finish quality and productivity. One of the advantages of HSM is the time savings it takes to produce a part. However, if the stepover is too big, there will be a cusp between the toolpath that becomes visible. To get that visibly shiny surface, lighter cuts and smaller stepovers are required, and this can be effectively achieved through high spindle speeds.

Lindsay Luminoso, sr. editor/digital editor, contributes to both Canadian Metalworking and Canadian Fabricating & Welding. She worked as an associate editor/web editor, at Canadian Metalworking from 2014-2016 and was most recently an associate editor at Design Engineering.

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Machining operation in which a tap, with teeth on its periphery, cuts internal threads in a predrilled hole having a smaller diameter than the tap diameter. Threads are formed by a combined rotary and axial-relative motion between tap and workpiece. See tap.

Process of generating a sufficient number of positioning commands for the servomotors driving the machine tool so the path of the tool closely approximates the ideal path. See CNC, computer numerical control; NC, numerical control.

Luminoso has a bachelor of arts from Carleton University, a bachelor of education from Ottawa University, and a graduate certificate in book, magazine, and digital publishing from Centennial College.

“Spindle speed, feed rates, stepovers, step downs, cutting tool geometry, toolholder, runout, tool length-to-diameter ratio will all come into play, and this is especially true when HSM hard materials,” said Gillcrist. “The process itself needs to be well thought out.”

“With HSM, it enables a reduced depth of cut and uses faster speeds and feeds,” said William Gillcrist, national product and applications manager - machining division, MC Machinery Systems, Elk Grove Village, Ill. “Because you are able to go faster, you get better material removal rates even though you are taking smaller passes. This can result in the elimination of a semi-finish pass. HSM allows you to save time, better utilize the machine, and get the part closer to the net shape with the roughing pass.”

The goal of the process is to get the heat and chips away from the part as quickly as possible. Chip shape and colour are good indicators of a successful operation.

3 types of tapered threads are available: NPT (for 11.5 and 14 TPIs) and NPTF (for 14 TPI) of the U.S. standard, as well as BSPT (for 11 and 14 TPIs), which is common in Asian markets

There is a balance that needs be struck, especially because the tool engagement during HSM is reduced compared to conventional techniques, but generally speaking, if you can get past that peak heat threshold, you can anticipate reduced heat.

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Running at a higher RPM means that the chip load is reduced, and the chips that are produced tend to be smaller, resulting in a smoother surface finish.

For example, when roughing a 3D shape, there can be big steps, known as stair-stepping, in the part geometry. When working with HSM, the depth of cut can be reduced and the speed increased, meaning that you are taking smaller passes, leading to less visible stepovers.

Machining operation in which metal or other material is removed by applying power to a rotating cutter. In vertical milling, the cutting tool is mounted vertically on the spindle. In horizontal milling, the cutting tool is mounted horizontally, either directly on the spindle or on an arbor. Horizontal milling is further broken down into conventional milling, where the cutter rotates opposite the direction of feed, or “up” into the workpiece; and climb milling, where the cutter rotates in the direction of feed, or “down” into the workpiece. Milling operations include plane or surface milling, endmilling, facemilling, angle milling, form milling and profiling.