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February 23, 2021

How to choose better milling cutter body

Milling cutter is a kind of rotary cutter with one or more cutter teeth for milling. When working, the cutter teeth cut off the allowance of the workpiece intermittently in turn. Milling cutter is mainly used for machining plane, step, groove, forming surface and cutting workpiece on milling machine. In my opinion, we should pay attention to the body and carriage of milling cutter when we choose milling cutter: is milling cutter used on NC machining center or ordinary milling machine. And the material and hardness of milling cutter. Milling cutter specifications, such as: edge length, full length, edge diameter, shank diameter, etc.

If it is used on CNC machining center, it should choose the whole cemented carbide. Ordinary milling machine can use white steel.

The hardness of white steel milling cutter is softer than that of cemented carbide milling cutter. High speed steel cutter is cheap and has good toughness, but its strength is not high. It is easy to make the cutter, and its wear resistance and thermal hardness are relatively poor. The thermal hardness of high speed steel milling cutter is about 600 degrees, and its hardness is about 65hrc. Obviously, when milling hard materials with white steel, if the coolant is not in place, it is easy to burn the cutter. This is one of the reasons why the thermal hardness is not high.

Cemented carbide milling cutter has good thermal hardness and wear resistance, but its impact resistance is poor. It will be broken if the blade is dropped casually. Cemented carbide is made of powder metallurgy, with hardness of about 90hra and thermal property of about 900-1000 degrees. Therefore, white steel is suitable for ordinary milling machine, alloy milling cutter for CNC machining center.

Selection of milling insert:
1. For finish milling, it is better to choose grinding blade. This kind of blade has better dimensional accuracy, so the positioning accuracy of the blade in milling is higher, and better machining accuracy and surface roughness can be obtained. In addition, the development trend of milling insert used in finish machining is to grind out chip curling groove and form large positive rake cutting edge, which allows the blade to cut on small feed and small cutting depth. For cemented carbide inserts without sharp rake angle, when small feed and deep cutting are adopted, the tool tip will rub the workpiece and the tool life is short.
2. It is more appropriate to select the pressing blade in some processing occasions, and sometimes it is also necessary to select the grinding blade. It is better to choose the pressing blade for roughing, which can reduce the processing cost. The dimensional accuracy and sharpness of the pressing blade are worse than those of the grinding blade, but the strength of the pressing blade is better, and it is resistant to impact during rough machining, and can bear larger cutting depth and feed rate. Sometimes, there are chip curling grooves on the rake face of the pressed blade, which can reduce the cutting force, reduce the friction with the workpiece and chips, and reduce the power demand.
3. However, the surface of the pressed blade is not as close as that of the ground blade, the dimensional accuracy is poor, and there are many differences in the height of each tool tip on the milling cutter body. Because the pressing blade is cheap, it is widely used in production.
4. The sharpened large rake blade can be used for milling viscous materials (such as stainless steel). The friction between the blade and the workpiece material is reduced by the shearing action of the sharp blade, and the chip can leave the front of the blade quickly.
5. As another combination, the pressing blade can be installed in the blade seat of most milling cutters, and then equipped with a polished blade. The results show that the surface roughness of the blade is better than that of the blade. Moreover, the application of the scraping blade can reduce the cycle time and the cost. Scraping technology is an advanced technology, which has been widely used in turning, cutting and drilling.



Selection of milling cutter body:

The price of milling cutter is relatively expensive. The price of a surface milling cutter body with a diameter of 100 mm may exceed 600 US dollars, so it should be carefully selected to meet the actual processing needs.

1. First of all, when selecting a milling cutter, the number of teeth should be considered. For example, a coarse tooth milling cutter with a diameter of 100 mm has only 6 teeth, while a dense tooth milling cutter with a diameter of 100 mm can have 8 teeth. The size of the pitch will determine the number of cutter teeth involved in the milling at the same time, and affect the smoothness of the cutting and the requirements of the cutting rate of the machine tool. Each milling cutter manufacturer has its own series of coarse tooth and dense tooth face milling cutters.
2. Coarse tooth milling cutter is mostly used for rough machining, because it has a large chip holding groove. If the chip holding groove is not large enough, it will make it difficult to roll the chip, or the friction between the chip and the tool body or workpiece will increase. At the same feed rate, the cutting load of coarse tooth milling cutter is larger than that of dense tooth milling cutter.
3. In finish milling, the cutting depth is relatively shallow, generally 0.25-0.64mm, the cutting load of each tooth is small (about 0.05-0.15mm), and the power required is not large. The dense tooth milling cutter can be selected, and the larger feed rate can be selected. Because the metal removal rate is always limited in finish milling, it is no harm that the chip groove of dense tooth milling cutter is smaller.
4. For the spindle with larger taper hole size and better rigidity, the dense tooth milling cutter can also be used for rough milling. Because the dense tooth milling cutter has more teeth to cut at the same time, when using a larger cutting depth (1.27-5mm), we should pay attention to whether the power and rigidity of the machine tool are enough, and whether the chip groove of the milling cutter is large enough. The chip removal condition needs to be verified by experiment. If there is a problem in chip removal, the cutting parameters should be adjusted in time.
5. In heavy load rough milling, excessive cutting force can make the machine tool with poor rigidity vibrate. This kind of chatter will lead to the edge collapse of cemented carbide blade, thus shortening the tool life. The selection of coarse tooth milling cutter can reduce the requirement of machine power. Therefore, when the spindle hole size is small (such as R-8, 30 #, 40 #, taper hole), the coarse tooth milling cutter can be used for milling effectively.



Selection of milling cutter diameter:

The selection of milling cutter diameter depends on different products and production batches, and the selection of cutter diameter mainly depends on the specifications of the equipment and the processing size of the workpiece.

① Plane milling cutter. When selecting the diameter of the plane milling cutter, the power required by 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 plane milling cutter can be selected according to d = 1.5D (D is the diameter of spindle). In batch production, the tool diameter can also be selected according to 1.6 times of the cutting width of the workpiece.
② End mills. The selection of end mill diameter should mainly consider the requirements of 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, we should mainly consider whether the maximum revolution of the machine tool can reach the minimum cutting speed of the tool (60m / min).
③ Groove cutter. The diameter and width of the groove milling cutter should be selected according to the size of the workpiece to be machined, and the cutting power should be ensured within the allowable power range of the machine tool.
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