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Do you know the three principles of milling cutter selection?


Do you know the three principles of milling cutter selection?
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Milling cutters are rotary tools with one or more teeth for milling. During work, each cutter tooth intermittently cuts off the remainder of the workpiece. The milling cutter is mainly used for milling planes, steps, grooves, forming surfaces and cutting workpieces.

 

I think that when choosing a milling cutter, pay attention to the milling cutter body and tool holder:

  • The milling cutter is used on the CNC machining center or ordinary milling machine.
  • Material and hardness of milling cutter.
  • Milling cutter specifications, such as blade length, full length, blade diameter, shank diameter, etc.

 

If it is used on CNC machining centers, it should be solid carbide. White steel can be used for ordinary milling machines.

 

 

White steel milling cutters are softer than hard alloy milling cutters. High-speed steel cutters are cheap and have good toughness, but the strength is not high. They are easy to make, and the wear resistance and heat hardness are relatively poor. The high-speed steel milling cutter has a heat hardness of about 600 degrees and a hardness of about 65HRC. For harder materials, if the coolant is not in place, it is easy to burn the knife, which is one of the reasons why heat hardness is not high.

 

Cemented carbide milling cutters have good thermal rigidity and abrasion resistance but have poor impact resistance. The blade will break if they are dropped. Cemented carbide is a material made by powder metallurgy, with a hardness of about 90HRA and a thermal rigidity of About 900-1000 degrees. Therefore, white steel is suitable for ordinary milling machines, and alloy milling cutters are suitable for CNC machining centers.

 

A. Selection of milling cutters diameter

The choice of milling cutter diameter varies greatly depending on the product and production batch. The choice of cutter diameter depends mainly on the specifications of the equipment and the processing size of the workpiece.

1.Flat milling cutter

When selecting the diameter of a face milling cutter, it is mainly necessary to consider that the power required by 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 a basis for selection. The diameter of the face milling cutter can be selected according to D = 1.5d (d is the spindle diameter). In mass production, the tool diameter can also be selected according to 1.6 times the cutting width of the workpiece.

2.End mill

The choice of end mill diameter 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 maximum number of revolutions of the machine can reach the minimum cutting speed of the tool (60m / min).

3.Slot 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 its cutting power should be within the power range allowed by the machine tool.

 

B.Choice of milling cutters blades

1. For fine milling, it is best to use a grinding blade. This insert 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 grinding and milling inserts used for finishing is to grind out the chip flute to form a large positive rake angle 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 feeds and small cutting depths, the tooltip will rub the workpiece and the tool life will be short.

 

2. In some processing occasions, it is more appropriate to choose a pressed blade, and sometimes it is necessary to choose a ground blade. For rough, it is better to use a pressed blade, which can reduce the processing cost. The dimensional accuracy and sharpness of the pressed blade are worse than those of the ground blade, but the edge strength of the pressed blade is better, and it is resistant to impact during rough machining and can withstand large cutting depth and feed. Pressed blades sometimes have chip flutes on the rake face, which can reduce cutting forces, and at the same time reduce friction with the workpiece and chips, reducing power requirements.

 

3. However, the surface of the pressed blade is not as close as the ground blade, the dimensional accuracy is poor, and the heights of the tips on the milling cutter body are much different. Since press blades are cheap, they are widely used in production.

 

4. Ground large rake angle inserts can be used to mill viscous materials (such as stainless steel). Through the cutting 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 pressing blade can be installed in the blade seat of most milling cutters, and a grinding scraping blade can be configured. Scraping the blade to remove rough machining marks can achieve better surface roughness than using only a pressed blade. Moreover, the application of the scraping blade can reduce the cycle time and cost. The scraping technology is an advanced technology, which has been widely used in the fields of turning, grooving and drilling.

 

C.Selection of milling cutter body

The price of a milling cutter is relatively expensive. The face of a 100mm diameter milling cutter body may cost more than $ 600, so you should choose it carefully to meet the specific processing needs.

 

1. First of all, when choosing a milling cutter, the number of teeth must be considered. For example, a coarse-tooth milling cutter with a diameter of 100mm has only 6 teeth, while a dense-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 participating in the cutting at the same time during milling, which affects the smoothness of the cutting and the requirements on the cutting rate of the machine tool. Each milling cutter manufacturer has its own series of coarse and dense tooth milling cutters.

 

2. Coarse tooth milling cutters are mostly used for rough machining because it has a large chip flute. If the chip flute is not large enough, it will cause difficulty in chip curling or increase friction between the chip and the cutter body and workpiece. At the same feed rate, the cutting load per tooth of a coarse-toothed milling cutter is larger than that of a dense-toothed milling cutter.

 

3. The shallow cutting depth during fine milling is generally 0.25 to 0.64mm, the cutting load per tooth is small (about 0.05 to 0.15mm), and the required power is not large. You can choose a close-tooth milling cutter and use a larger Feed rate. Because the metal removal rate is always limited in fine milling, it is not a problem to have a smaller chip flute in the dense tooth milling cutter.

 

4. For spindles with larger taper hole specifications and better rigidity, rough milling can also be performed with close-tooth milling cutters. Since the dense-tooth milling cutter has more teeth to participate in cutting at the same time, when using a large cutting depth (1.27 ~ 5mm), pay attention to whether the machine tool’s power and rigidity are sufficient, and whether the milling cutter chip flute is large enough. Chip removal needs to be verified by tests. If there is a problem with chip removal, the cutting amount should be adjusted in time.

 

5. During heavy-duty rough milling, the excessive cutting force can cause the chattering of the machine with poor rigidity. This chattering can cause chipping of carbide inserts, reducing tool life. The use of coarse-tooth milling cutters can reduce the requirements for machine power. Therefore, when the size of the spindle hole is small (such as R-8, 30 #, 40 # taper hole), a coarse-tooth milling cutter can be used for effective milling.

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