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Three principles for selecting milling cutters

Views: 4     Author: Site Editor     Publish Time: 2021-06-08      Origin: Site


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. When choosing a milling cutter, pay attention to the cutter body and tool holder: 1. Whether the milling cutter is used for CNC machining or on ordinary milling machines. 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 for CNC machining, solid carbide should be used. For ordinary milling machines, white steel can be used.

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 and thermal hardness. High-speed steel milling cutters have a thermal hardness of about 600 degrees and a hardness of about 65HRC. It is obvious that they should be milled with white steel. In the case of harder materials, it is easy to burn the knife if the coolant is not in place. This is one of the reasons why the thermal hardness is not high.

Cemented carbide milling cutters have good thermal hardness, wear resistance, but poor impact resistance, and the blade will break if you drop it. Cemented carbide is a material made by powder metallurgy, and its hardness can reach about 90HRA. Up to about 900-000 degrees. Therefore, white steel is suitable for ordinary milling machines, and alloy milling cutters are used for CNC machining.

Selection of milling cutter diameter:

The selection of milling cutter diameter varies greatly depending on the product and production batch. The selection 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 cutter 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=.5d (d is the diameter of the spindle). In mass production, the tool diameter can also be selected according to 6 times the cutting width of the workpiece.

②End milling cutter. The selection 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. If it is a small diameter end mill, the main consideration should be whether the high speed of the machine tool can reach the low 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 better 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. However, for carbide inserts without sharp rake angles, when small feed and small depth of cut are used, the tool tip will rub against the workpiece and the tool life will be short.

2. It is more appropriate to choose pressed blades for certain processing occasions, and sometimes it is necessary to choose ground blades. For rough machining, a pressed blade is used, 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 face, which can reduce the cutting force, and at the same time, it can reduce the friction with the workpiece and the chip, and reduce the power demand.

3. However, the surface of the pressed blade is not as tight as that of the polished blade, and the dimensional accuracy is poor. The height of each tool tip 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 for milling 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 leave the front of the blade faster.

5. As another combination, the pressed blade can be installed in the blade seat of most milling cutters, and then a polished scraper 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 a process that has been widely used in the fields of turning, grooving and cutting and drilling.

Choice of milling cutter body:

1. The price of milling cutters is relatively expensive. The price of a face milling cutter body with a diameter of 00mm may exceed $600, so it should be carefully selected to meet the specific processing needs.

First of all, when choosing a milling cutter, consider the number of teeth. For example, a coarse-tooth milling cutter with a diameter of 00mm has only 6 teeth, while a dense-tooth milling cutter with a diameter of 00mm 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-tooth 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 rolling or increase the friction between the chips and the cutter 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 shallow, generally 0.25-0.64mm, the cutting load per tooth is small (about 0.05-0.5mm), the required power is not large, you can choose a close-tooth milling cutter, and you can choose a Large feed rate. Since the metal removal rate in fine milling is always limited, it does not matter if the chip pockets of the close-tooth milling cutter are 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 (.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 performing heavy-duty rough milling, excessive cutting force can cause vibration of the machine with poor rigidity. This chattering can cause the chipping of the carbide inserts, thereby shortening 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.

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