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CNC milling tool selection

Release time:May 13, 2019 Visits:

              Keywords: CNC milling, cutting tool  

    CNC milling is widely used in CNC machining of mechanical parts. The selection of milling tools and their parameters is an indispensable part of CNC machining. It directly affects the machining efficiency and machining quality of parts. In order to adapt to the high speed, high efficiency and high degree of automation of CNC machine tools, the tools used are moving towards standardization, generalization and modularization.
  First, the type of CNC milling tools
  Flat-bottom milling cutters, face milling cutters, ball-end milling cutters, and fillet milling cutters are the most commonly used tool types in CNC milling, as well as drum cutters, cone cutters, and disc cutters.
  1. Flat bottom milling cutter and end milling cutter
  The flat end mill is one of the main tools for milling, as shown in Figure 1(a). The flat-bottom end mill mainly cuts with the peripheral cutting edge. Due to factors such as the forming method and the shape of the tool, it is mainly suitable for the processing of curved surfaces with flat curvature changes. The flat end mill is easy to manufacture, has high cutting edge strength, good cutting performance and relatively low price.
  The end mill has a cutting edge on both the circumferential surface and the end surface, and the end cutting edge is a minor cutting edge. The end mills are mostly made of sleeve-type inserts, which are mainly used for large-area face milling and flatter three-dimensional contour milling, and the machining efficiency is high.
  The advantages of machining efficiency and quality of the flat-end milling cutter and the end-face cutter in the machining plane are obvious.
  2. Fillet milling cutter
  The rounded milling cutter combines the common point of the ball end mill and the flat bottom cutter, and is one of the commonly used tools for rough and fine milling, as shown in Figure 1(b). For insert-finished knives, since the insert mill only needs to index or replace worn blades after the tool wears, the shank can be reused, resulting in a much lower cost. In order to meet the requirements of CNC machine tools for durable, stable, easy to adjust, changeable, etc., in recent years, insert-type alloy blades have been more and more widely used.
  3. Ball end milling cutter
  The head of the ball-end milling cutter is spherical, also called R-knife. The structural feature of the ball-end milling cutter is that the ball is covered with a cutting edge, and the circumferential edge is connected with the arc of the ball, which can be fed radially and axially. As shown in Figure 1 (C). Ball end mills are most commonly used in CNC machining of freeform surfaces.
  The tool center trajectory during the ball-end milling cutter is formed by offsetting a tool radius along the outer normal direction of the part contour. Even in the case of three-coordinate machining, the ball-end knives can be processed except for the concave vignetting. Moreover, it is easy to program and use. The ball-end milling cutter has the characteristics of less surface processing interference and good surface quality, and is often used for milling various curved surfaces and circular grooves.
  The ball-end milling cutter is difficult to manufacture. Because the cutting edge has a spherical structure, the cutting conditions at different points on the cutting edge are different. The closer to the end of the ball, the worse the cutting performance is. The cutting speed is close to zero at the end of the ball, so To ensure the processing accuracy, the cutting line spacing is generally close.
  (a) Flat-bottom milling cutter (b) Fillet milling cutter (C) Ball-end milling cutter
  4. Drum knife
  The drum knife is shaped like a drum, as shown in Figure 2. Its cutting edge is distributed on a circular arc surface with a radius of R, and the end surface has no cutting edge. During the machining, the upper and lower positions of the tool are controlled, and the cutting position of the cutting edge is changed accordingly. Different oblique angles from negative to positive can be cut out from the workpiece, as shown in Fig. 3. The smaller the radius R of the arc, the wider the range of angles that the drum cutter can process, but the worse the surface quality obtained. This type of tool is characterized by difficult grinding, poor cutting conditions, and is not suitable for machining bottomed contoured surfaces. 
  5. Forming cutter
  Forming cutters are typically designed for specific shapes of workpieces or machining content. Such as involute tooth surface, dovetail groove and T-shaped groove processing, as shown in Figure 4.
  Second, CNC machine tool selection tool principle
  The spindle speed of CNC machine tools is much higher than that of ordinary machine tools, especially in machining centers, where the spindle speed is higher. The spindle speed has a great influence on the tool, so the CNC tool should fully consider the strength and durability of the tool. Generally speaking, the tool for CNC machine tools should have the following characteristics: strong durability, good rigidity, good material anti-brittle performance, strong chip breaking ability, convenient replacement and adjustment. Pay attention to the following issues when making tool selections:
  1. Planar milling is easy to use non-reground hard end mills or end mills. For roughing, end mills are generally used. The spacing of milling lines is smaller than that of end mills to avoid picking marks. The diameter of the tool during finishing is best to accommodate the entire width of the plane, and the continuous cutting is performed in one pass, and the machining effect is good.
  2. The peripheral profile of the milled planar part is generally an end mill. The tool can be selected according to the following principles:
  (1) The tool radius R should be less than the minimum radius of curvature of the inner contour of the part, generally taken.

(2) The machining height of the part to ensure sufficient rigidity.

(3) When roughing the inner profile, the tool diameter can be estimated by the following formula 2-4.

  3. The NC machining profile and the bevel profile profile often use ball-end knives, ring knives, drum knives, etc. The application of ball-end knives is most common when machining curved surfaces.

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