What is High Speed Machining?

High-speed machining, specifically milling, has the same variables as traditional milling. There are speeds and feeds to set and a depth of cut to be determined. However, in a high-speed machining operation, slow, heavy cuts are replaced by fast, lighter cuts.

While it may seem counterproductive to take lighter cuts when heavy cuts are possible, shops that can make this switch in thinking will produce accurate parts faster.

Defining high-speed machining is difficult because it can be one of many operations, or a combination of them. It can be defined as:

• Machining at a high cutting speed (vc).
• Machining with a high spindle speed (n).
• Machining with a high feed rate (vf).
• Machining with a high removal rate (Q).

High-speed machining is not defined, however, as machining with a high material removal rate using a large axial depth of cut (Ap) or large radial depth of cut (Ae).

High speed machining is usually associated with any spindle speed above 15k rpm, but it is much more than just a faster spindle. The whole machine must be considered when selecting a good candidate machine for HSM. Thermal compensation, overall machine rigidity and construction, positional feedback, the motion control system, tool retention, and many other characteristics must be looked at, in detail, before determining that a particular machine is suitable for the task.

Traditionally, finish machining of hardened materials was performed by the use of EDM technology; and although this process was very effective, shops were continuously looking for faster and more efficient ways to produce their products. Eventually, as CAD/CAM software technology evolved, and new and more productive toolpath generation became available, the use of these advanced CAM systems also began to grow. Although the use of this new technology was primarily focused on the die mold industry in the beginning, it has become much more prevalent today - and is present in all areas of the manufacturing arena. Subsequently, and in addition to efficiently removing large amounts of material very quickly, the technology has proven to be quite effective for machining thin walled features as well. Although the machine tool itself must be robust and well equipped enough for high speed machining, the real magic lies in the toolpath generated by today’s advanced CAM software packages. The ability to produce a cutter path with a consistent chip load and tool engagement - especially in the corners - is really the secret sauce to the whole process. The finite control of the toolpath, and the ability to consistently control the amount of material engagement the tool will encounter, allows for dramatic increases in the cutting parameters. Even small diameter tooling can be pushed far beyond traditional limits.

Conventional machining differs greatly from High Speed Milling in a lot of aspects. When using conventional machining techniques, the contact time between the tool and piece is much greater than it is with HSM. Conventional machining also involves a much greater cutting force.

Conventional Machining will typically lead to a less accurate workpiece and inferior surface finish than could be achieved through high-speed machining. Another major difference associated with high-speed machining is the material removal rate is much higher.

 Use Dedicated Tools

- It is important to have dedicated roughing and finishing tools in order to reduce tool wear between separate operations.

Keep Tooling Short

- Machine tools are pushed to their limits for HSM. In order to obtain high accuracy, repeatability, and surface finish, fixtures and tools must be absolutely rigid to withstand the high loads associated with the process.

Balanced Tooling

- Tool balance is important when running at high RPMs. Most common tool designs with tool holders will work without a noticeable problem at speeds less than 7,000 to 8,000 RPM. But, at higher speeds, you can start to see runout problems and decreased tool life. Shrink fit tooling is essential in order to maintain balance at high RPM.

A Clean Process

- High Speed Milling generates chips faster than conventional milling. Use oil mist/air blast, or coolant (when necessary) in order to clear chips away to an appropriate chip management solution.

Trochoidal Machining

Trochoidal milling is a method of machining used to create a slot wider than the cutting tool’s cutting diameter. This is accomplished using a series of circular cuts known as a trochoidal tool path. A form of High Efficiency Milling (HEM), trochoidal milling leverages high speeds while maintaining a low radial depth of cut (RDOC) and a high axial depth of cut (ADOC). Trochoidal milling is largely based on the theory surrounding chip thinning in machining. Conventional thinking suggests that cutting tools have an optimal chip load that determines the ideal width and size of the chips produced. The concept of combating chip thinning involves machining with a chip load that is larger than “optimal” in order to maintain a constant maximum chip thickness. Plunge Roughing CNC plunge milling, also called z-axis milling, is a CNC milling process. In this process, the feed is provided linearly along the tool axis while doing CNC processing. Plunge milling is effective for the rough machining process of complex shape or free form shapes like impeller parts.

Radial Chip Thinning

Radial chip thinning, which occurs whenever radial-cutter engagement falls below 50 percent of the cutter diameter, is just as relevant on CNC machining centers as it is on manually-operated knee mills. For example, a 1/2-inch, 4-flute end mill feeding at 0.01-inch per tooth (IPT) with a 1/4-inch or greater stepover (radial depth of cut) produces a chip thickness equal to the programmed IPT feedrate, or 0.010-inch. But decrease the stepover to 10-percent (0.050-inch) and the IPT value must be bumped up to 0.0167-inch to achieve comparable chip thickness.

Side Steps

Side steps are the connections that create effective transitions between adjacent tool paths when feed rates are particularly high. Parallel scan-line surface machining is the type of machining that has been used for the last ten years to finish machine multi-surface models. This type of machining tends to produce sharp stepover moves at the end of every pass. Using simple “looping” tool paths in place of sharper turns between scan passes is an appropriate solution at moderate feed rates (20-40 ipm). However, at higher feeds, these simple rounded moves are still too sharp. An alternative that has proven more effective in some cases is a “golf club” stepover between passes.

Cornering

To exactly execute a sharp corner in the toolpath, the feedrate of a CNC machine must instantaneously drop to zero at that point. This constraint is problematic in the context of high-speed machining, since it incurs very high deceleration/acceleration rates near sharp corners, which increase the total machining time, and may incur significant path deviations (contour errors) at these points. HSM Cornering Strategies utilize linear drives on all axes and high speed spindles in order to ensure high deceleration and acceleration in and out of corners

Smart Machining

Feedrate optimization is an important aspect of getting shorter machining time and increase the potential of efficient machining. Autonomous machining system and optimization strategies predict and improve the performance of milling operations. The machining process is simulated and analyzed in virtual machining framework to extract cutter-workpiece engagement conditions. Cutting force along the cutting segmentation is evaluated based on the laws of mechanics of milling. In simulation, constraint-based optimization scheme is used to maximize the cutting force by calculating acceptable feedrate levels as the optimizing strategy. The intelligent algorithm was integrated into autonomous machining system to modify NC program to accommodate these new feedrates values.

Knowledge of Stock Remaining

Go from rough to semi finish machining without intermediate cutting when your programming software accurately recognizes remaining stock from previous operations

Mikron MILL S

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