End mill is a rotary tool used for milling, which has one or more cutting teeth. During the milling process, the milling cutter cuts the surface of the workpiece in sequence through rotational motion, gradually removing the excess material on the workpiece. This processing method uses milling machines as the main equipment and is widely used in the processing of planes, steps, grooves and various formed surfaces. In addition, the milling cutter can also be used to cut off the workpiece. Each tooth will intermittently contact the workpiece during operation, cutting according to the set path and depth to complete the predetermined processing task.
When choosing the type of end mill, pay attention to the milling cutter body and tool holder.
- Is the end mill used on a CNC machining center or on an ordinary milling machine.
- The material and hardness processed by the end mill.
- The specifications of the milling cutter, such as blade length, full length, blade diameter, shank diameter, etc.
If it is used on a CNC machining center, it should be made of solid carbide, and if it is used on an ordinary milling machine, it can be made of high-speed steel.
High-speed steel end mills are softer than carbide end mills. High-speed steel milling cutters are cheap and tough, but they are not strong and easy to break. In addition, they have relatively poor wear resistance and thermal hardness. The thermal hardness of high-speed steel milling cutters is about 600 degrees and the hardness is about 65HRC. Obviously, when white steel is used to mill harder materials, if the coolant is not in place, it is easy to burn the cutter. This is one of the reasons for the low thermal hardness.
Carbide milling cutters have good thermal hardness and wear resistance, but poor impact resistance. The blade will break if it is dropped casually. Carbide is a material made by powder metallurgy. The hardness can reach about 90HRA and the thermal resistance can reach about 900-1000 degrees. Therefore, white steel is suitable for ordinary milling machines, and alloy end mills are used in CNC machining centers.
Selection of End Mill Diameter
The selection of milling cutter diameter varies greatly depending on the product and production batch. The selection of cutting tool diameter mainly depends on the specifications of the equipment and the processing size of the workpiece.
Face milling cutter. When selecting the diameter of the plane 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. The spindle diameter of the machine tool can also be used as the basis for selection. The diameter of the plane milling cutter can be selected according to D=1.5d (d is the spindle diameter). In batch production, the tool diameter can also be selected according to 1.6 times the cutting width of the workpiece.
End milling cutter. The selection of the end milling cutter 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 milling cutter, the main consideration should be whether the maximum speed of the machine tool can reach the minimum cutting speed of the tool (60m/min).
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 ensure that its cutting power is within the power range allowed by the machine tool.
Selection of End Mill Inserts
For fine milling, it is best to use ground inserts. This type of insert has good dimensional accuracy, so the positioning accuracy of the blade in milling is high, and good processing accuracy and surface roughness can be obtained. In addition, the development trend of ground milling inserts used for fine processing is to grind out chip grooves to form a large positive rake angle cutting edge, allowing the insert to cut at small feeds and small cutting depths. However, for carbide inserts without sharp rake angles, when small feeds and small cutting depths are used for processing, the tip of the tool will rub against the workpiece, and the tool life is short.
It is more appropriate to use pressed inserts in some processing occasions, and sometimes it is necessary to choose ground inserts. It is best to use pressed inserts for rough processing, which can reduce processing costs. The dimensional accuracy and edge sharpness of pressed inserts are worse than those of ground inserts, but the edge strength of pressed inserts is better, and they are impact-resistant during rough processing and can withstand larger cutting depths and feeds. Pressed inserts sometimes have chip grooves on the front cutting edge, which can reduce cutting forces, and at the same time reduce friction with workpieces and chips, reducing power requirements.
However, the surface of the pressed insert is not as tight as that of the ground insert, the dimensional accuracy is poor, and the height of each cutting edge on the milling cutter body varies greatly. Since pressed inserts are cheap, they are widely used in production.
The ground large rake angle insert can be used to mill sticky materials (such as stainless steel). The shearing action of the sharp blade reduces the friction between the insert and the workpiece material, and the chips can leave the front of the insert faster.
As another combination, the pressed insert can be installed in the insert seat of most milling cutters, and then equipped with a ground scraped insert. The scraped insert removes the rough machining marks and can obtain better surface roughness than using only the pressed insert. In addition, the use of scraped inserts can reduce cycle time and reduce costs. Scraping technology is an advanced process that has been widely used in turning, grooving and drilling.
Selection of End Mill Cutter Body
Imported end mills are relatively expensive. A face mill body with a diameter of 100mm may cost more than $600, so you should choose carefully to meet your specific processing needs.
First, when choosing a milling cutter, you should consider its 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 teeth involved in cutting at the same time during milling, affecting the smoothness of cutting and the requirements for the cutting rate of the machine tool. Each milling cutter manufacturer has its own series of coarse-tooth and close-tooth face milling cutters.
Coarse-tooth milling cutters are mostly used for rough processing because they have larger chip grooves. If the chip groove is not large enough, it will cause difficulty in chip curling or increase the friction between the chips and the cutter body and the workpiece. At the same feed speed, the cutting load per tooth of a coarse-tooth milling cutter is greater than that of a close-tooth milling cutter.
The cutting depth is shallow during fine milling, generally 0.25-0.64mm, the cutting load per tooth is small (about 0.05-0.15mm), the required power is not large, and a dense-tooth milling cutter can be selected, and a larger feed rate can be selected. Since the metal removal rate in fine milling is always limited, it is okay for the dense-tooth milling cutter to have a smaller chip groove.
For spindles with larger taper hole specifications and better rigidity, a dense-tooth milling cutter can also be used for rough milling. Since dense-tooth milling cutters have more teeth involved in cutting at the same time, when using a larger cutting depth (1.27-5mm), pay attention to whether the machine tool power and rigidity are sufficient, and whether the milling cutter chip groove is large enough. The chip removal situation needs to be verified by test. If there is a problem with chip removal, the cutting amount should be adjusted in time.
When performing heavy-load rough milling, excessive cutting force can cause vibration in machines with poor rigidity. This vibration will cause the carbide insert to break, thereby shortening the tool life. The use of a coarse-tooth milling cutter can reduce the requirements for machine tool power. Therefore, when the spindle hole specifications are small (such as R-8, 30#, 40# tapered holes), coarse-tooth milling cutters can be used to perform milling effectively.
Which Milling Cutter to Choose: Left-hand or Right-hand
If end mills can be easily distinguished, they can be divided into two categories: left-hand and right-hand. Many people still have no idea about left-hand and right-hand.
Right-hand End Mill
First, the following methods can be used to determine whether the tool is left-hand or right-hand. Facing a vertical milling cutter, if the blade groove rises from the lower left to the upper right, it is right-hand. If the blade groove rises from the lower right to the upper left, it is left-hand. Right-hand rotation can also be determined by the right-hand rule, with the bent four fingers as the rotation direction and the pried thumb as the rising direction, which is right-hand. The spiral blade groove plays a role in chip storage and is also the part that constitutes the front angle and front of the milling cutter.
Left-hand End Mill
Left-hand milling cutters are generally selected under the demand for high-precision processing. Left-hand milling cutters are generally used for mobile phone button processing, membrane switch panels, LCD panels, acrylic lenses and other precision processing. But there are some with high requirements, especially the production and processing of some mobile phone buttons or electrical panels, which require high precision and smoothness. You should choose the lower row cutting and left turn, so as to avoid the whitening of the blade and the edge jumping of the workpiece.
In the entire manufacturing industry, the tools used for processing are usually right-handed tools. For milling cutters, the grooves of the blade determine the direction of the chips cut during milling.
If you make precision parts, it is recommended to use left-handed tools. Left-handed tools have certain advantages in processing precision parts.
