High-speed machining technology: principles, tool path optimization, and industrial applications
abstract
High Speed Machining (HSM) is not a simple spindle speed increase, but a complete technical system including machine tool dynamics, tool materials, cutting strategies and CAM path planning. Its core goal is to greatly improve material removal rate (MRR) and reduce cutting force through small depth of cut, high speed and large feed under the premise of ensuring machining accuracy. Starting from the physical essence of high-speed cutting, this paper explains the theoretical basis of "chip thinning effect" and "constant cutting angle" principle in depth, and systematically analyzes the technical requirements of tool materials (nano-coating, PVD-coated cemented carbide) and shank system (HSK heat shrinkable shank) suitable for high-speed machining. At the CAM level, the tool path strategies for high-speed machine tools such as cycloid milling, helical cutting, and smooth transition path are discussed, and the technology implementation of automatic feed rate adjustment and acceleration forward control is given. Taking the high-speed machining of automobile cover molds as an example, the comparative data of machining efficiency and surface quality are provided. Finally, the best practices of high-speed cutting in the machining of thin-walled parts, non-ferrous metals and hardened steel are discussed, and the operable parameter window is provided for technicians.
First, high-speed cutting: Definition and physical nature
The concept of high-speed cutting was first proposed by German scholar Carl Salomon, whose theoretical hypothesis holds that when the cutting speed exceeds a certain critical value, the cutting temperature decreases instead. Although this specific turning point has not been fully confirmed in many materials, high-speed cutting has indeed brought revolutionary changes in industry: reduced cutting force, smoother chip formation, and a lower proportion of heat entering the workpiece.
In fact, high-speed cutting is defined as a cutting speed of 1000-7000 m/min for aluminium alloys; 300-800 m/min for steel parts; and 150-300 m/min for hardened steel (above HRC 50). The distinguishing features of high-speed cutting are: a small radial depth of cut (usually 3% -10% of the tool diameter), a medium axial depth of cut, but an extremely high feed rate (up to 20 m/min or more). This "layer-stripping" cutting allows the cutting force to be mainly applied in the axial direction, reducing lateral deformation, and is especially suitable for thin-walled structures.
Chip thinning effect and constant cutting angle path
To understand high-speed cutting, it is necessary to master the "chip thinning effect". When using a small radial depth of cut (e.g. tool diameter 10mm, radial depth of cut 0.5mm), the maximum thickness of the chips is less than the feed per tooth. To maintain the desired chip thickness (to avoid overheating of the tool), the feed rate must be increased. The formula is: actual maximum chip thickness = feed per tooth sin (angle of cut). The angle of cut depends on the ratio of radial depth of cut/tool diameter. This effect allows for a significant increase in feed rate while maintaining the thermal load constant.
Based on this, a core principle of the high-speed cutting CAM path is to maintain a constant radial depth of cut, that is, a constant cutting angle. To this end, a cycloidal milling strategy was developed: the tool moves along an arc trajectory, and the radial depth of cut remains constant, even in groove milling or narrow cavity machining. This strategy makes the tool heat shock uniform and significantly extends the life.
Three, high-speed machining tool system and machine tool requirements
High-speed cutting places extremely high demands on tools and tool holders. Centrifugal expansion of conventional BT tool holders above 20,000 rpm can lead to tool drop. HSK tool holders (hollow short cones) are more suitable for high-speed spindles due to their double-sided contact structure. Heat-shrinkable or hydraulic tool holders provide better beating accuracy (
In terms of machine tools, high-rigidity beds (e.g. polymer concrete), linear roller guides, high-power electric spindles (≥30kW, above 30,000 rpm), and fast-responding servo drives are required. Of particular importance is acceleration and jerk control - there are a large number of tiny line segments in the high-speed machining path, and the control system needs to have a high-speed limit function to avoid machine vibration.
IV. CAM high-speed machining strategy and path smoothing
The traditional "serrated" equidistant offset tool path will produce sudden load changes and sharp direction turns, which is not suitable for high-speed cutting. Modern CAM has developed the following technologies specifically for HSM:
Constant-height spiral machining: spiral down layer by layer along the Z-plane, with smooth and continuous feed and exit.
Cycloidal groove milling: As mentioned earlier, it effectively solves the difficulty of deep groove chip removal.
Constant Load Connection: Automatic arc or S-shaped transitions are used at area connections instead of sharp right angles.
Automatic feed rate adjustment: adjust the feed rate in real time based on the change of cutting volume to maintain the spindle power constant.
Path smoothing filter: Small line segments are simulated into NURBS curves, and the controller performs direct interpolation to reduce acceleration impact.
Siemens NX's "Adaptive Milling" and Mastercam's "Dynamic Milling" are both representative strategies based on the concept of constant cutting angles.
Case: High-speed machining of automobile door panel molds
A large automobile door panel injection mold (material P20, hardness HRC32, cavity size 800500200mm). Traditional process: Ø 20mm ball head knife, S8000, F1500, radial depth of cut 6mm, roughing cycle 32 hours. High-speed process: use Ø 12mm super hard coated flat-bottom knife, S18000, F6000, radial depth of cut 0.8mm, cycloidal dynamic milling. Roughing only takes 9.5 hours, the tool life is increased by 3 times, and the subsequent semi-finishing allowance is uniform, no manual polishing is required. The final machined surface roughness is reduced from Ra1.8μm to Ra0.6μm.
VI. Conclusion
High-speed cutting requires an overall shift in programming thinking: from "heavy cutting depth and low speed" to "light cutting high and ultra-high speed". Successful implementation of HSM requires collaborative optimization of tools, machine tools, CAM and controls, especially with constant cutting angles at the core. For molds, thin-walled parts and difficult-to-machine materials, high-speed cutting has become a standard practice for enhancing competitiveness.
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