High speed milling (HSM) is a metal processing method used in CNC machine tools. The tool speed and feed rate are much faster than traditional cutting, which makes the cutting thickness smaller, so the chip will be thinner than traditional cutting. According to the Solomon curve, if the cutting speed is high to a certain level (for example, ten times the traditional cutting speed), the cutting temperature will be lower than that of traditional cutting.
Advantages
- The feed rate of the high speed milling machine is 5 to 10 times that of traditional cutting, which can save about 30% of the processing time.
- The cutting force requires less force, so it can be processed for thin-walled workpieces, such as aluminum parts with a wall thickness of 0.5mm.
- The accuracy of the machined surface is improved, which can save traditional roughing (because of the high material removal rate of high-speed cutting) and finishing (because of the high surface accuracy of high-speed cutting).
- The cutting speed is faster than the heat conduction speed. Most of the heat is left on the chips and cannot be transferred to the workpiece. It can also avoid the warpage of the workpiece due to heat.
- Hard materials can also be used for high-speed cutting, even materials with a hardness of 60HRC (such as alloy steel parts after heat treatment). So that no additional hardening process is required after machining, and the risk of hardening process is also eliminated.
Disadvantages
- The ultra high speed of high speed milling requires equipment to improve its safety protection in the workplace. The small chips at high speeds will have a fairly high flying speed, which may even be faster than the projectile motion of a gun bullet.
- The tool is easier to wear, which will reduce the tool’s life. But the time required for material processing is also shortened.
- High-speed cutting also has high requirements on the balance of the tools. The imbalance may produce great force to damage the tool and strongly affect the position of the spindle.
- Due to the extremely high speed and load of high speed cutting, the consumption rate of components is high. The machine maintenance and spindle and tool replacement are frequently required on a regular basis.
To give full play to the performance of high speed milling, each link of machining must be closely coordinated. If one of the links is not well matched, the performance of high speed milling will not good or successful. The 5 essential factors are following you must know:
1. High-speed tool holders and tools
Since the actual cutting action is by the tool rather than the machine, the choice of the tool is very important. For instance, the factors as below will affect the quality of tools:
- Shape (such as ball end mill, toroidal cutter, reamer)
- Material (like high-speed steel, carbide, cermet, cubic boron nitride CBN)
- Tool coating (such as TiN, TiCN, TiAlN)
- Quality (like radial runout, shape accuracy, dynamic balance, rigidity)
The milling machine tools for high speed cutting are generally made of fine-grained and extremely fine-grained cemented carbide. Polycrystalline cubic boron nitride (PCBN) and polycrystalline diamond (PKD) are often used as tool materials.
Most of them will be matched with hard coatings, and they will also have special tool shape designs.
2. High-speed spindle
Bearings: with high torque
Bearingless (air driven): low torque, but very fast speed. There is air as the medium between the spindle and the bearing, the spindle runs almost without friction, so that high-speed and high-precision movement can be achieved.
3. Highly dynamic XYZ axis
Traditional hard rails can be adjusted on the machine to obtain better accuracy, but it cannot achieve the high-speed machining that linear slide rails can achieve. The high-power and high-speed XYZ axis can reduce the time waste of each axis. It can make the cutting surface better and reduce tool wear.
4. High-speed CNC controller
With sensitivity and rapid response capabilities.
5. High-speed programming strategy
Analyze the material, surface, and processing path to set the most efficient process.
High speed milling processing is a new technology and application method. It can overcome and improve processing quality that cannot be achieved by traditional CNC machining. Some of complex procedures also can be simplified during high speed milling processing.
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