What Is Face Milling?

Face milling cutters have cutting edges that are perpendicular to the shank and the outer circle, and are mainly used for milling planes. The cutting edge of the outer circle is the main cutting edge, and the cutting edge on the end face plays the same role as the scraper. Face milling cutters have shorter cutting edges than sleeve end mills.

Face milling cutters are mainly used for machining planes, which are characterized by: high production efficiency; good rigidity, can use larger

The structure of hard alloy face milling cutter can be divided into three types: integral welding type, machine welding type and indexable type.

The figure below shows a solid welded face mill. The knife has a compact structure and is easier to manufacture. However, the entire milling cutter will be scrapped after the teeth are broken, so it has been used less.

(1) Diameter and number of teeth Diameter and number of teeth are the two main structural parameters of a face milling cutter. In order to meet the different cutting requirements of the factory, the national standard stipulates that the number of teeth of the face milling cutter of the same diameter is divided into three types: coarse, medium and fine. Taking a diameter of 100 mm as an example, the number of coarse, medium, and fine teeth is 5 teeth, 6 teeth, and 8 teeth, respectively.

(2) Geometric angle indexable surface milling cutter The main geometric angles are principal deflection angle _r , back rake angle _p , and side rake angle _f . There are four main declination angles: 45 °, 60 °, 75 °, and 90 °. 75 ° is the most commonly used. When processing flat or thin-walled workpieces with shoulders, 90 ° should be selected.

Dorsal rake angle _p and lateral rake angle _f can be combined into three types: positive rake angle type, negative rake angle type, and positive and negative rake angle type. Positive rake type is used to process general materials, such as _p = 7 °, _f = 0 ° when milling ordinary steel and cast iron parts, and _p = 18 °, _f = 11 ° when milling aluminum alloys. Negative rake angle type is used for processing cast steel and hard materials. _p = -7 ° and _f = -6 ° are generally used. Positive and negative rake angle type have good impact resistance and chip removal performance. It is suitable for milling general steel and cast iron , Mostly used for machining center machine tools, the common values are _p = 12 ° and _f = -8 °. ^[1]

Face milling cutters have cutting edges on the circumferential surface and end surface, and the end cutting edge is a secondary cutting edge. Because the diameter of the face milling cutter is generally larger, 50 500 mm, it is often made into a sleeve-type insert structure Coming Tooth and

The tools for machining flat workpieces are mainly face milling cutters, whose cutting edges cover the circumference and end faces. The cutting edge on the end face is a secondary cutting edge. The face milling cutter has a large diameter, so when the cutter is selected, the cutter teeth and the cutter body are usually separated to achieve the purpose of long-term use.

Choice of face milling cutter diameter

The choice of face milling cutter diameter is mainly divided into three cases:

(1) The area of the surface is not large. When selecting a tool, pay attention to selecting a tool or milling cutter with a diameter larger than the width of the plane, so that a single plane milling can be achieved. When the width of the face milling cutter reaches 1.3 to 1.6 times the width of the working surface, it can effectively ensure the better formation and discharge of chips.

(2) When the area of the machining plane is large, a milling cutter with an appropriate diameter needs to be selected to mill the plane in multiple times. Among them, the diameter of the milling cutter will be limited due to the limitations of the machine tool, the depth and width of the cutting, and the size of the insert and the tool;

(3) When the machining plane is small and the workpiece is scattered, an end mill with a smaller diameter needs to be used for milling. In order to maximize the processing efficiency, the milling cutter should have 2/3 of the diameter in contact with the workpiece, that is, the milling cutter diameter is equal to 1.5 times the milling width. In down milling, the reasonable use of the ratio of the tool diameter to the cutting width will ensure that the milling cutter has a very suitable angle when cutting the workpiece. If you are not sure whether the machine tool has enough power to maintain the milling cutter cutting at such a ratio, the axial cutting thickness can be divided into two or more times to maintain the ratio of the milling cutter diameter to the cutting width as much as possible. ^[1]

Choice of face milling cutter teeth

When selecting a milling cutter for processing, the number of teeth of the milling cutter needs to be considered. For example, a sparse milling cutter with a diameter of 100mm has only 6 teeth, while a dense milling cutter with a diameter of 100mm can have 8 teeth. Whether the teeth are dense or not will affect the level of production efficiency and the quality of the product. If the cutter teeth are dense, the production efficiency will be improved, and the quality of the processed workpiece will be better, but the dense cutter teeth will also cause the inconvenience of chip discharge. According to the diameter of the cutter teeth, it can be divided into sparse teeth, fine teeth, and dense teeth.

The sparse tooth is used for rough machining of the workpiece. It uses 1 to 1.5 blades per 25.4mm diameter, which has a large chip space. This tool is used for cutting soft materials that can produce continuous chips. Long blades and large widths are used. Dense teeth are favorable for machining under stable conditions, and are generally used for rough machining of cast iron. They are also suitable for shallow cutting, narrow cutting of high-temperature alloys, and cutting when no chip space is required. Dense teeth are used for precision milling. Its axial depth of cut is 0.25 to 0.64mm. The cutting load per tooth is small and the required power is not large, such as for thin-walled materials. The size of the tooth pitch will determine the number of teeth that are involved in cutting at the same time during milling. At least one blade should be cutting during cutting to avoid milling impact, resulting in damage to the tool and overload of the machine.

In addition, the number of blade teeth must be selected so that the chip is properly curled and easily leaves the cutting area. Improper chip space will cause chipping, damage the cutting edge and possibly damage the workpiece. At the same time, the insert should have sufficient density to ensure that at least one insert is cutting at any time during the cutting process. If this cannot be guaranteed, it will cause a severe impact, which will cause the cutting edge to break, the tool to be damaged, and the machine tool. Overload.

Choice of face milling cutter angle

The cutting angle of the tool can be positioned as a positive rake angle, a negative rake angle and a zero rake angle relative to the radial plane and the axial plane. Because the zero rake angle will cause the entire cutting edge to impact the workpiece at the same time, it is generally not used. The choice of the face milling cutter angle has an impact on the contact method of face milling. In order to minimize the impact of the tool, reduce the degree of tool damage, and avoid the surface contact method of STUV, the geometry of the face milling cutter must be considered while considering the angle of the cutter. Think about it. The combination of the radial and axial rake angles determines the cutting angle. Common basic combinations include: radial negative rake angle and axial negative rake angle; radial positive rake angle and axial positive rake angle; radial negative rake angle and Positive axial rake angle; positive radial rake angle and negative axial rake angle.

Tools with negative axial and radial rake angles (hereinafter referred to as "double negative") are mostly used for rough machining of cast iron and cast steel, but they require high machine power and sufficient rigidity. "Double negative" inserts have high cutting edge strength and can withstand large cutting loads. Double-angle negative tools also require high rigidity of machine tools, workpieces, and fixtures.

Positive axial and radial rake angle (hereinafter referred to as "double positive") tools increase cutting angles, so cutting is quick and chip removal is smooth, but the cutting edge strength is poor. This combination method is suitable for processing soft materials and stainless steel, heat-resistant steel, ordinary steel and cast iron. This type of combination should be preferred when low-power machine tools, inadequate rigidity of the process system, and the occurrence of built-up edge.
The combination of a negative radial rake angle and an axial positive rake angle increases the strength of the cutting edge, while the positive axial rake angle generates a shear force. The cutting edge has stronger impact resistance and sharper cutting edge during machining, so it is suitable for milling of steel, cast steel and cast iron with large allowances.
The positive radial rake angle and the negative axial rake angle make the chip breaking to the direction below the center, so that the chip will scratch the processed surface, so the chip discharge is not good. ^[3]

Choice of face milling cutter and milling insert

The choice of milling insert preparation for face milling is also a consideration. In some processing occasions, the use of pressed blades is more appropriate, and sometimes it is necessary to choose ground blades.

For roughing, it is better to use a pressed blade, which can reduce the processing cost. The dimensional accuracy and sharpness of the pressing blade are worse than those of the ground blade, but the cutting edge strength of the pressing blade is better. For rough milling, it is impact resistant and can withstand large backfeed and feed. There is a chip flute on the rake face of the pressed blade, which can reduce the cutting force, at the same time, it can reduce the friction with the workpiece and the chip, and reduce the power demand. However, the surface of the pressed blade is not as tight as the ground blade, the dimensional accuracy is poor, and the heights of the tips on the milling cutter body differ greatly. Since press blades are cheap, they are widely used in production.

For fine milling, it is best to use a grinding insert. This insert has better dimensional accuracy, so the positioning accuracy of the blade during milling is higher, and higher machining accuracy and lower 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 and form a large positive rake angle cutting edge, allowing the insert to cut at a small feed and a small back. For carbide inserts without sharp rake angles, when using small feeds and small backs, the tool tip will rub the workpiece and reduce the tool life. ^[3]