Jun 29, 2020
Choice of diameter
The choice of face milling cutter diameter can be divided into three situations:
(1) The surface area is not large. When choosing a tool, pay attention to choose a tool or a 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 plane milling cutter reaches 1.3 to 1.6 times the width of the processing surface, it can effectively ensure the better formation and discharge of chips.
(2) When the processing plane area is large, it is necessary to select a milling cutter with an appropriate diameter and mill the plane 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 blade and tool;
(3) When the machining plane is small and the workpieces are scattered, an end mill with a small diameter needs to be selected for milling. In order to maximize the processing efficiency, the milling cutter should have a diameter of 2/3 in contact with the workpiece, that is, the diameter of the milling cutter is equal to 1.5 times the width of the milling. 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 at such a ratio, you can divide the axial cutting thickness two or more times to maintain the ratio of the milling cutter diameter to the cutting width as much as possible.
Selection of 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 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 density of the cutter teeth will affect the production efficiency and product quality. 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 inconvenience to discharge the chips. According to the diameter of the cutter teeth, it can be divided into sparse teeth, fine teeth and dense teeth.
Thinning is used for rough machining of workpieces. It uses 1 to 1.5 blades per 25.4mm diameter and 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 conducive to machining under stable conditions, and are generally used for rough machining of cast iron. They are also suitable for shallow cutting, narrow cutting of superalloys, and cutting without chip space. Dense teeth are used in fine milling. The axial depth of cut is 0.25 to 0.64mm. The cutting load per tooth is small and the required power is not large. For example, it is used in the processing of thin-walled materials. The size of the tooth pitch will determine the number of cutting teeth that are involved in cutting at the same time during milling. At least one blade should be cutting during cutting to avoid milling shocks, resulting in damage to the tool and overload of the machine tool.
In addition, the number of blade teeth must be selected so that the chips are properly curled and easily leave the cutting area. Improper chip accommodation space will lead to chip holding, damage to the cutting edge and possible damage to the workpiece. At the same time, the blade should have enough density to ensure that no less than one blade is cutting at any time during the cutting process. If this is not guaranteed, it will cause a violent impact, which will lead to the rupture of the blade, damage to the tool and the machine tool. Of overload.
Tool angle selection
The cutting angle of the tool can be positioned at a positive rake angle, a negative rake angle and a zero rake angle relative to the radial plane and the axial plane. Since 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 angle of the face milling cutter has an impact on the contact method of the plane milling. In order to minimize the impact of the tool, reduce the degree of tool damage, and avoid the surface contact method of the STUV, the geometry of the face milling cutter must be Consider it from a perspective. The combination of radial and axial rake angle determines the cutting angle. Commonly used basic combination methods include: radial negative rake angle and axial negative rake angle; radial positive rake angle and axial positive rake angle; radial negative rake angle and Axial positive rake angle; radial positive rake angle and axial negative 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 require high power and rigidity of the machine tool. "Double negative" inserts have high cutting edge strength and can withstand large cutting loads. Tools with negative double angles also require high rigidity of the machine tool, workpiece and fixture.
The cutters with positive axial and radial rake angles (hereinafter referred to as "double positive") increase the cutting angle, so the cutting is light and the chip removal is smooth, but the cutting edge strength is poor. This combination is suitable for processing soft materials and stainless steel, heat-resistant steel, ordinary steel and cast iron. This combination should be preferred when low-power machine tools, insufficient rigidity of the process system, and the occurrence of built-up edges.
The combination of a negative radial rake angle and an axial positive rake angle. The negative radial rake angle increases the strength of the cutting edge, while the positive axial rake angle produces a shearing force. This kind of combination method 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 allowance.
Radial positive rake angle and axial negative rake angle make the chip breaking direction below the center, so that the chip will scratch the processed surface, so the chip evacuation is not good.
Selection of milling inserts
The choice of milling insert preparation in face milling is also a consideration. In some processing occasions, it is more appropriate to choose a pressing blade, and sometimes it is necessary to choose a grinding blade.
For roughing, it is better to use pressed blades, which can reduce the processing cost. The dimensional accuracy and sharpness of the pressing blade are worse than the grinding blade, but the cutting blade has a better blade strength. For rough milling, it is impact resistant and can withstand a large amount of back-eaten knife and feed. The pressed blade has a chip flute on the front blade surface, which can reduce the cutting force, and at the same time reduce the friction with the workpiece and chips, reducing the power requirement. However, the surface of the pressed blade is not as tight as that of the grinding blade, and the dimensional accuracy is poor. The height of each tip on the cutter body of the milling cutter differs greatly. Because the pressing blade is cheap, it is widely used in production.
For fine milling, it is best to choose a grinding blade, which has better dimensional accuracy, so the positioning accuracy of the blade in milling is higher, and higher machining accuracy and lower surface roughness values can be obtained. In addition, the development trend of grinding milling inserts used in finishing is to grind out chip flutes and form large positive rake angle cutting edges, allowing the blade to cut at a small feed and small back. However, when the carbide blade without sharp rake angle is processed with a small feed and small back, the tool tip will rub the workpiece and reduce the tool life.