Milling tool is a cutting tool used in metal processing, mainly used for milling operations on milling machines, machining centers and other machine tools. Milling is a process in which material is cut or removed from a workpiece by rotating a tool, often used to manufacture parts, molds, and other complex shaped workpieces.

Milling tools usually include the following types:

1. Face milling cutter: face milling cutter is mainly used for processing planes, which is characterized by: high production efficiency; Good rigidity, can use a larger feed; At the same time, there are multiple tool teeth involved in cutting, and the working stability is good; The structure of the insert teeth, the sharpening and replacement of the teeth are convenient, and the tool life is long. Face milling cutter is divided into two categories, one is to braze the cemented carbide blade fixed on the cutter teeth, and then the cutter teeth installed on the milling cutter body, which is called insert type face milling cutter; The second type is the carbide blade directly installed on the milling cutter body, and then fixed with screws, which is called indexable machine clamp milling cutter. The face milling cutter has two front angles of axial forward Angle and radial front Angle, and the direction of the two front angles is selected according to the material and cutting conditions of the object to be machined, that is, positive +, negative -, or zero.

 

2. Square shoulder milling cutter: The traditional design of square shoulder milling cutter is usually able to mill the "real" 90° shallow shoulder. Many square shoulder milling cutters are universal milling cutters that can be easily used for hole machining. They are an ideal alternative to face milling cutters when milling vertically or near the vertical.

3. Slot milling cutter: Slot milling cutter is a milling tool used to slot or cut grooves on the surface of the workpiece. Its design makes it particularly suitable for cutting straight or curved grooves for manufacturing grooves of various shapes, such as T-grooves, square grooves, V-grooves, etc. Slot milling cutters are usually used on milling machines, machining centers and other machine tools.

4. Copy milling cutter: It refers to the milling cutter that may be all with a round cutting edge or part with a round cutting edge, mainly the milling cutter with a round blade and the ball end milling cutter. The shape cutter uses a circular blade, and this change makes the shape cutter have a variety of advantages, most of which can be said to be a milling cutter with a small back cut and a large feed round blade.

When choosing a milling tool, it is necessary to consider the geometry of the workpiece, the material, the processing requirements, and the required surface quality. This helps to ensure that the right tool is selected for the best machining results.

So, how to choose the most suitable milling tool?

1. The choice of knife serrated saw

The pitch of the milling tool is the distance between a certain point on the blade and the same point on the next blade, according to the different tooth spacing, the milling tool can be divided into sparse (-L), dense (-M) and super dense (-H) three types.

1) Milling tools with loose teeth (-L) type: suitable for maximum productivity in the case of limited stability and power, by reducing the number of blades and using unequal pitch design. This tool is particularly suitable for large overhang tools and small machine tools, such as Morse taper 40. Under these conditions, the use of tooth thinning design can effectively balance the cutting performance to ensure the best machining results under limited stability and power conditions.

2) Dense tooth (-M) type milling tool: is a general purpose design, suitable for general purpose milling and a variety of mixed production. This tool design achieves a balance between stability and power, can be adapted to different machining needs, and is a common type of milling tool.

3) Ultra-dense tooth (-H) type milling tools: suitable for maximum productivity by using the maximum number of blades under stable conditions. This design is particularly suitable for handling short chips and heat resistant materials, and can perform well in demanding processing environments.

In the selection of milling tool spacing, according to the specific processing conditions and material characteristics, the reasonable selection of sparse, dense or ultra-dense tooth types will help improve production efficiency, ensure tool life, and ensure that the workpiece is machined to meet the requirements.

2. Choice of tool diameter

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

1) Surface milling cutter: When selecting the diameter of the surface 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 spindle can also be used as the basis for selection. The surface milling cutter diameter 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 of the workpiece cutting width.

2) End milling cutter: The choice of 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. If it is a small diameter end mill, the main consideration should be whether the highest revolution of the machine tool can reach the lowest 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 processed, and ensure that the cutting power is within the power range allowed by the machine tool.

According to convention, according to the size of the workpiece, mainly according to the width of the workpiece to choose the milling cutter diameter, of course, in the selection process, the machine power is the primary consideration. In order to obtain satisfactory results, other factors are also important, such as the position of the tool and the form of contact between the tool teeth and the workpiece.

 

3. Selection of the main deflection Angle of the tool

The principal declination Angle is the Angle between the cutting edge and the cutting plane. The main deflection Angle has great influence on the radial cutting force and cutting depth. The radial cutting force directly affects the cutting power and anti-vibration performance of the tool. The smaller the main deflection Angle of the milling cutter, the smaller the radial cutting force, the better the vibration resistance, but the cutting depth is also reduced.

When milling the square shoulder plane, select 90° lead Angle. The tool has good versatility and is suitable for single piece and small batch processing. Because the radial cutting force of this type of tool is equal to the cutting force, the feed resistance is large and easy to vibrate, so the machine tool is required to have a large power and sufficient rigidity.

When machining a flat surface with square shoulders, a milling cutter with 88° main declination can also be selected. Compared with 90° main deflection Angle milling cutter, its cutting performance has been improved to some extent. Surface milling with 90° square shoulder milling cutter is also very common. If the shape of the workpiece is irregular, or the surface of the casting will cause the depth of cut to change, the square shoulder mill may be the best choice. In other cases, however, you may benefit more from using a standard 45° face mill.

 

When the cutting Angle of the cutter is less than 90°, due to the thinning of the chips, the axial chip thickness will be less than the feed rate of the cutter, and the cutting Angle of the cutter will have a great influence on the feed rate per tooth applied to it.

In the face milling process, the face milling cutter with a cutting Angle of 45° will make the chips thinner. As the cutting Angle decreases, the chip thickness will be less than the feed per tooth, which in turn can increase the feed rate to 1.4 times the original. The radial cutting force of 45° main deflection Angle milling cutter is greatly reduced, about equal to the axial cutting force, and the cutting load is distributed on the longer cutting edge, which has good vibration resistance, and is suitable for the boring and milling machine spindle overhanging longer processing occasions. The blade breakage rate is low and the durability is high when this type of tool is used to process the plane. When machining cast iron, the edge of the workpiece is not easy to crack.

 

4. Choose the right milling method

Another way to improve the milling process is to optimize the milling strategy of the face milling cutter. When programming a surface milling program, the user must first consider the way the tool cuts into the workpiece. Usually, the milling cutter just cuts directly into the workpiece. This cutting method is usually accompanied by a larger impact noise, because the milling cutter produces the thickest chip when the blade is pulled out. Because the blade forms a large impact on the workpiece material, it often causes vibration and produces tensile stress, which shortens the life of the tool.

Figure. 1 Cutting a face mill directly into the workpiece will cause vibration and create tensile stress

The better way to feed is to use the rolling cutting method, that is, without reducing the feed speed and cutting speed, the milling cutter rolls into the workpiece. This means that the milling cutter must be turned clockwise to ensure machining in a milling manner. The chip formed in this way is from thick to thin, which can reduce the vibration and tensile stress on the tool, and transfer more cutting heat to the chip. By changing the way, the milling cutter can cut into the workpiece every time, and the tool life can be extended by 1-2 times. In order to achieve this feed method, the programming radius of the tool path should be 1/2 the diameter of the milling cutter and increase the offset distance of the tool to the workpiece.

FIG. 2 The rolling cutting method can reduce the vibration and the tension stress acting on the tool

Although the rolling cutting method is mainly used to improve the way the tool cuts into the workpiece, the same machining principle can be applied to other stages of milling. For large area surface milling, the common method is to have the tool pass through the entire length of the workpiece one by one, and then complete the next cut in the opposite direction. In order to maintain a constant radial feed amount and eliminate vibration, a combination of helical downcutters and rolling milling workpiece angles usually achieves better results.

Hobbing workpiece corners can eliminate noise and extend tool life. Under normal circumstances, the angular radius of the workpiece should be 75%-100% of the diameter of the milling cutter, which can shorten the arc length of the milling cutter, reduce vibration, and allow the use of higher feed speeds.

In order to extend the life of the tool, in the face milling process, the tool should be avoided from the hole or break part on the workpiece. When the face milling cutter passes through the middle of a hole on the workpiece, the tool is up-milling on one side of the hole, and the other side of the hole is up-milling, which will have a great impact on the blade. This can be avoided by bypassing the holes and cavities when programming the tool path.

5. Choice of up-milling and up-milling

There are two ways relative to the feed direction of the workpiece and the rotation direction of the milling cutter:

1) Down milling: the rotation direction of the milling cutter and the feed direction of the cutting are the same, and the milling cutter bites the workpiece and cuts the final chips at the beginning of the cutting.

2) Inverse milling: the rotation direction of the milling cutter and the feed direction of the cutting are opposite, the milling cutter must slip a section on the workpiece before starting to cut, starting with zero cutting thickness, and reaching the maximum cutting thickness at the end of the cutting.

Due to the best cutting effect of down-milling, down-milling is usually generally selected, and only when the machine has a thread clearance problem or a problem that can not be solved by down-milling, the inverse milling is considered. Because during the inverse milling, the blade produces strong friction before cutting, causing the machining surface to harden, making it difficult to cut the next blade tooth.

When downmilling, the milling width should be approximately equal to 2/3 of the diameter of the milling cutter, which ensures that the blade can be cut into the workpiece immediately from the beginning, with almost no friction. If the cutter diameter is less than 1/2, the blade begins to "rub" the workpiece again, because the cutting thickness becomes smaller when cutting, and the feed per tooth will also be reduced by the narrowing of the radial cutting width. The result of "friction" shortens the tool life, and it is more favorable to increase the feed per tooth and reduce the cutting depth for cemented carbide tools.

FIG. 3 Comparison table between up-milling and up-milling

For each tool, the most important thing is to be able to meet the requirements of the equipment you use and the actual working requirements, therefore, I hope that the several contents we introduce here can help you choose a more suitable tool.