Explanation of commonly used tools in CNC machining(2)

2. Types of milling cutters

In the mold milling process, because the mold itself is a workpiece with a complex shape, considering the cutting efficiency, tool life and workpiece shape... etc., it is necessary to use a single shape milling cutter to complete the mold processing. impossible. Therefore, in mold processing, different shapes of milling cutters are often used to process molds. Generally, the most commonly used milling cutters for mold processing are as follows: A, end milling cutter; B, ball cutter; C, round nose cutter.

　　2.1 Features of end mills

　　When milling a 2D-shaped workpiece, since the contact area with the workpiece is the outer edge and the bottom surface, it is possible to use extremely efficient numerical values for both tool spacing and cutting depth. On the contrary, if it is used for milling 3D-shaped molds, you can find that the contact area with the workpiece is almost always close to the sharp point, so you have to reduce the tool spacing or cutting depth, so the processing efficiency is reduced.

　　The outer edge and bottom surface of the milling cutter have milling teeth to form the cutting edge, so it can be used to mill the vertical surface and the vertical surface of the workpiece. The shape change of the end mill is very complex, suitable for all kinds of processing, such as: milling plane, groove or contour surface... etc. It can be said to be the most widely used milling cutter. Generally speaking, end mills are very suitable for 2D-shaped workpieces, but when applied to 3D-shaped mold processing, they are not so suitable. We explain the problems that occur when end mills are used in mold processing for the following reasons:

　　 So in mold processing, end mills are generally used to process 2D areas in the mold, such as vertical and horizontal surfaces or sharp corners in the mold will be processed by end mills. In traditional mold processing, end mills are also used for roughing.

　　2.2

　　 ball knife

　　 The milling cutter whose bottom blade is a ball shape is a ball cutter. Ball cutters are used quite frequently in the current mold processing, especially when milling 3D molds, the ball cutter is an indispensable tool.

Compared with the former-end mill, because the ball cutter does not have a sharp edge at the bottom like an end mill, but a blade with an R angle, the blade of the ball cutter is stronger and not easy to break; in other words, The life of the ball cutter will be more stable than that of the end mill. In addition, the contact area of the ball knife with the workpiece is the edge of the R angle, so the knife spacing can be larger in the finishing process, and the machined surface also has an excellent effect.

　　 Therefore, whether it is tool life or processing efficiency, ball knives are a good choice for mold processing! But the same, ball knives will also encounter some problems in mold processing. When milling 3D molds, although the contact area of the ball cutter with the workpiece is the edge of the R angle, the actual contact position will change with the shape of the workpiece. This difference will have the following effects:

　　 2.2.1 Cutting speed

　　 The most basic concept of cutting is to give the cutting edge and the relative speed of the material to be cut. When the material of the edge is harder than the material to be cut and the cutting speed is reached, the contact area between the material and the cutting edge will be removed. Therefore, the cutting speed is very important for the cutting effect of the tool. If the cutting speed is not enough or too low, the cutting edge is not cutting the workpiece, but grinding the workpiece. In order to generate cutting speed, in turning, the workpiece is rotated to generate cutting speed; in milling, the rotating tool generates cutting speed.

　　 When rotating, the corresponding cutting speeds at points 1, 2, and 3 are all different, and even the cutting speed at point 2 is almost equal to zero. Therefore, the disadvantage of the ball knife is that the cutting speed is unstable.

　　You can see that when the ball cutter is milling a 3D workpiece, the contact position of the blade and the workpiece will constantly change, so the cutting speed has been changing. The cutting speed is stable at two points a and c, so this area is where the blade is cutting the workpiece, and a good machining surface can be obtained. At the two points b and d, the cutting speed will be too low or even no cutting speed will cause the cutting edge to rub the workpiece, and the quality of the machined surface will of course be greatly affected.

　　2.2.2 Tool loss

　　 When the ball cutter mills a flat area, it is as follows: At this time, most of the contact positions with the workpiece are a, b, and c. So in fact, the bottom of the ball cutter is used to mill the workpiece. When the area of the entire workpiece is very large, in addition to the low cutting speed at the bottom of the ball cutter, the blade at the bottom will also wear quickly. The blades on both sides are actually not used, so the quality of the processed surface is not only low, but also because of the tool The relationship between loss and the accuracy of the machined surface will also be affected.

　　 Ball cutters are most commonly used for milling in mold processing

　　Ball cutters are most commonly used to mill 3D molds in mold processing, especially in finishing and corner-clearing, but they are not suitable for milling flat areas. Because of the small contact area with the workpiece, the tool spacing cannot be increased.

　　2.3 round nose knife

The shape of the round nose cutter is similar to that of the end mill, and both have a flat bottom design. The difference is that the bottom of the round nose cutter is a blade with a R angle instead of a sharp point, so the strength of the blade is better than that of an end mill , It is not easy to collapse, so the life of the tool will be better than that of the end mill.

　　 In addition, round nose cutters have better machining efficiency than ball cutters and end mills, especially when roughing. Because the bottom of the round nose knife is flat, the horizontal knife spacing of the round nose knife can be larger than that of the ball knife. In the finishing process, it also has the same advantages as the ball knife, so the knife spacing can also be used with a larger value. Therefore, the round nose knife is a very suitable choice whether it is used for roughing or finishing.

　　 When milling 3D molds, another advantage of the round nose cutter is that it cannot be compared with a ball cutter. The cutting speed of the ball cutter itself varies greatly with the contact position of the workpiece, so the quality of the machined surface is unstable. Although the round nose knife also has this situation, its cutting speed does not change as much as the ball knife. Therefore, the quality of the workpiece processed with the round nose knife is of course stable. The reasons for the stable cutting speed of the round nose cutter are explained below.

　　 2.3.1 Cutting speed

　　You can see where the blade is in contact with the workpiece at four points a, b, c, and d. No matter how the blade is in contact with the workpiece, even the contact point of the round nose knife will continue to change like a ball knife, but the resulting cutting speed will not change as sharply as a ball knife, even at the two points b and d. The cutting speed of the ball knife will be almost 0, but the round nose knife can maintain a certain cutting speed. Therefore, when the round nose knife is used for machining, the cutting edge can of course be maintained, and the quality of the machined surface will of course be stable.　　The advantage of the round nose knife is that the cutting speed changes steadily, so you can see that the surface of the workpiece after finishing machining shows the brightness of the metal after being cut.