A milling cutter is a rotary cutter with one or more teeth used for milling. When working, each cutter tooth intermittently cuts off the margin of the workpiece. Milling cutters are mainly used for processing planes, steps, grooves, forming surfaces and cutting off workpieces on milling machines. The author believes that when choosing a milling cutter, you should pay attention to the milling cutter body and tool holder: 1. Whether the milling cutter is used on a CNC machining center or an ordinary milling machine. 2. The material and hardness of the milling cutter. 3. The specifications of the milling cutter, such as: blade length, overall length, blade diameter, shank diameter, etc.
If it is used on a CNC machining center, solid carbide should be used. White steel can be used for ordinary milling machines.
The hardness of white steel milling cutter is softer than that of cemented carbide milling cutter. High-speed steel cutters are cheap, good toughness, but not high strength, easy to use, and relatively poor wear resistance, thermal hardness is relatively poor, high-speed steel milling cutters have a thermal hardness of about 600 degrees and a hardness of about 65HRC, which is obviously suitable for white steel milling. When the material is harder, if the coolant is not in place, it is easy to burn the knife. This is one of the reasons for the low thermal hardness.
Cemented carbide milling cutters have good thermal hardness and wear resistance, but have poor impact resistance. The blade will be broken if you drop it. Cemented carbide is a material made by powder metallurgy, and its hardness can reach about 90HRA. Up to about 900-1000 degrees. Therefore, white steel is suitable for ordinary milling machines and CNC machining centers for alloy milling cutters.
Selection of cutter diameter:
The choice of milling cutter diameter varies greatly depending on the product and production batch. The choice of cutter diameter mainly depends on the specifications of the equipment and the processing size of the workpiece.
①Plane milling cutter. When selecting the diameter of a face milling cutter, it is mainly necessary to consider that the required power of the tool should be within the power range of the machine tool, and the diameter of the machine tool spindle can also be used as the basis for selection. The diameter of the face milling cutter can be selected according to D=1.5d (d is the diameter of the spindle). In mass production, the tool diameter can also be selected as 1.6 times the workpiece cutting width.
②End mill. The choice of the diameter of the end mill should mainly consider the requirements of the workpiece processing size, and ensure that the power required by the tool is within the rated power range of the machine tool. For small diameter end mills, the main consideration should be whether the maximum number of revolutions of the machine tool can reach the minimum cutting speed (60m/min) of the tool.
③Slot milling cutter. The diameter and width of the slot milling cutter should be selected according to the size of the workpiece to be processed, and the cutting power should be within the allowable power range of the machine tool.
Choice of milling cutter blades:
1. For fine milling, it is best to choose a ground blade. This kind of blade has better dimensional accuracy, so the positioning accuracy of the cutting edge in milling is higher, and better machining accuracy and surface roughness can be obtained. In addition, the development trend of milling inserts used in finishing is to grind out the chip flutes to form a large positive cutting edge, allowing the insert to cut at a small feed and a small depth of cut. For carbide inserts without sharp rake angles, when using small feed and small deep cutting, the tool tip will rub against the workpiece and the tool life will be short.
2. It is more appropriate to choose pressed blades in some processing occasions, and sometimes it is necessary to choose ground blades. It is best to choose a pressed blade for roughing, which can reduce the processing cost. The dimensional accuracy and edge sharpness of the pressed blade are worse than that of the ground blade, but the pressed blade has better edge strength, impact resistance during rough machining, and can withstand greater depth of cut and feed. The pressed blade sometimes has a chip groove on the rake surface, which can reduce the cutting force, and at the same time can reduce the friction with the workpiece and chips, and reduce the power demand.
3. However, the surface of the pressed blade is not as tight as that of the ground blade, and the dimensional accuracy is poor. The height of the blades on the milling cutter body is quite different. Because the pressed blade is cheap, it is widely used in production.
4. The ground blade with large rake angle can be used to mill viscous materials (such as stainless steel). Through the shearing action of the sharp blade, the friction between the blade and the workpiece material is reduced, and the chips can quickly leave from the front of the blade.
5. As another combination, the pressing blade can be installed in the blade seat of most milling cutters, and a polished scraping blade can be configured. The squeegee blade removes rough machining knife marks, and can obtain better surface roughness than only the pressing blade. Moreover, the use of doctor blades can reduce cycle time and reduce costs. Scratching technology is an advanced technology that has been widely used in the fields of turning, grooving and cutting and drilling.
Choice of milling cutter body:
The price of milling cutters is relatively expensive. A face milling cutter body with a diameter of 100mm may cost more than $600, so it should be carefully selected to meet the specific processing needs.
1. First of all, when choosing a milling cutter, consider the number of teeth. For example, a coarse-tooth milling cutter with a diameter of 100mm has only 6 teeth, while a close-tooth milling cutter with a diameter of 100mm can have 8 teeth. The size of the tooth pitch will determine the number of cutter teeth involved in cutting at the same time during milling, and affect the smoothness of cutting and the requirements for machine tool cut rate. Each milling cutter manufacturer has its own series of coarse and dense tooth face milling cutters.
2. Coarse tooth milling cutters are mostly used for rough machining because they have larger chip pockets. If the chip pocket is not large enough, it will cause difficulty in chip coiling or increase the friction between chips and the tool body and workpiece. At the same feed rate, the cutting load per tooth of a coarse-tooth milling cutter is larger than that of a close-tooth milling cutter.
3. When finishing milling, the cutting depth is relatively shallow, generally 0.25-0.64mm, the cutting load per tooth is small (about 0.05-0.15mm), the required power is not large, you can choose a close-tooth milling cutter, and you can choose Large feed rate. Since the metal removal rate in fine milling is always limited, it does not matter if the chip pocket of the close-tooth milling cutter is smaller.
4. For spindles with larger tapered holes and better rigidity, a close-tooth milling cutter can also be used for rough milling. Since the close-tooth milling cutter has more teeth involved in cutting at the same time, when using a larger cutting depth (1.27-5mm), pay attention to whether the power and rigidity of the machine are sufficient, and whether the chip pocket of the milling cutter is large enough. The chip removal situation needs to be tested and verified. If there is a problem with chip removal, the cutting amount should be adjusted in time.
5. When carrying out heavy-duty rough milling, excessive cutting force can cause vibration of the machine with poor rigidity. This kind of chattering can cause the chipping of the carbide inserts, thereby shortening the tool life. The use of coarse-tooth milling cutters can reduce the power requirements of the machine tool. Therefore, when the spindle hole size is small (such as R-8, 30#, 40# taper hole), the rough tooth milling cutter can be effectively used for milling.