Now let’s talk about the tools commonly used in cnc machining.
1.Application of milling cutter
Milling is the most widely used cutting method among various cutting methods. Therefore, whether it is slotted, concave cut, flat or even various shapes, it can be processed, and the surface brightness and precision can be obtained through milling. Milling cutter is a round tool with multiple cutting edges. The principle of milling is to apply the multi-blade rotation of the milling cutter to produce cutting effect. Therefore, although the tool cuts into the workpiece deeply, the cutting amount of each edge is not large. The cutting thickness of the blade can still be kept very thin, and the resulting machined surface is also good, and the tool life can be maintained for a long time. With good cutting efficiency and wide range of uses, milling cutters occupy a very high proportion in current metal machining.
Since milling cutters can almost replace most of the traditional cutting tools in the current cutting process, no matter in the design and manufacture of milling cutter materials, shapes, structures, etc., there are not only a great variety and complexity. Now only the types of milling cutters commonly used in general mold milling are described below.
2.Types of milling cutters
In mold milling, because the mold itself is a workpiece with a complex shape, considering factors such as cnc cutting efficiency, tool life, and workpiece shape, etc., it is necessary to use only a single shape of the milling cutter to complete the mold machining. impossible. Therefore, in mold machining, different shapes of milling cutters are often used to process molds. The most commonly used milling cutters for general mold machining are the following three types: A, end mills; B, ball cutters; C, round nose cutters.
2.1 Features of end mill
When milling a 2D-shaped workpiece, since the area in contact with the workpiece is the outer edge and the bottom surface, you can use extremely efficient values regardless of the tool pitch or cutting depth. Conversely, if you use it for milling 3D-shaped molds, you can find that the area in contact with the workpiece is almost near the sharp point, so you must reduce the tool spacing or cutting depth, so the machining efficiency is reduced.
The milling cutter has milling teeth on the outer edge and bottom surface to form the cutting edge, so it can be used to mill the vertical surface and vertical surface of the workpiece. The shape of the end mill is very complicated. It is suitable for various types of machining, such as milling planes, grooves or contour planes, etc. It can be said that it is the most widely used milling cutter. Generally speaking, end mills are very suitable for 2D shaped workpieces, but they are not so applicable when applied to 3D shaped mold machining. We explain the problems that occur when applying end mills to mold machining for the following reasons:
In mold machining, end mills are usually used to process 2D areas in the mold, such as vertical planes and horizontal planes or sharp corner areas in the mold. In traditional mold machining, end mills are also used for roughing.
The milling cutter with a ball shape at the bottom is a ball cutter. Ball cutters are used quite frequently in current mold machining, especially when milling 3D molds. Ball cutters are an indispensable tool.
Compared with the former-end mill, because the ball cutter does not have a sharp edge like the bottom of the end mill, but a blade with an R angle, the blade of the ball cutter is stronger and less prone to chipping; in other words, Ball cutter life is more stable than end mills. In addition, the contact area between the ball cutter and the workpiece is the R-angle cutting edge. Therefore, a larger value of the tool distance can be used during finishing, and the machining surface has an excellent effect.
So whether it is tool life or machining efficiency, the ball cutter is a good choice for mold machining! However, the ball cutter also encounters some problems in mold machining. When milling a 3D mold, although the area where the ball tool is in contact with the workpiece is the R-angle blade, the actual contact position will change with the shape of the workpiece. Such differences 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 cutting material. When the cutting edge material is harder than the cutting material and the cutting speed reaches, the area where the cutting material and the cutting edge contact will be removed. Therefore, the cutting speed is very important for the cutting effect of the tool. If the cutting speed is insufficient or too low, the cutting edge is not cutting the workpiece, but grinding the workpiece. In order to generate cutting speed, in turning, it is to rotate the workpiece to produce cutting speed; in milling, it is to rotate the tool to produce cutting speed.
When rotating, the cutting speeds corresponding to the positions of 1, 2, and 3 are different, and the cutting speed of 2 is almost equal to 0. Therefore, the disadvantage of the ball cutter is that the cutting speed is unstable.
You can see that when the ball cutter is milling a 3D workpiece, the position where the blade touches the workpiece will continuously change, so the cutting speed is always changing. The cutting speed is stable at two points a and c, so this area is the cutting edge of the cutting workpiece, and a good machining surface can be obtained. At the two points b and d, the cutting edge is rubbing the workpiece because the cutting speed is too low or there is no cutting speed. Of course, the quality of the working surface will be greatly affected.
2.2.2 Tool loss
When a ball cutter is milling a relatively flat area, it is as follows: At this time, most of the positions in contact with the workpiece are a, b, and c. So in fact, the bottom of the ball cutter is milling the workpiece. When the area of the entire workpiece is very large, in addition to the low cutting speed of the bottom of the ball cutter, the blade at the bottom will wear quickly. The blades on both sides are not actually used, so the machining surface is not only of low quality but also because of the tool The relationship between losses also affects the accuracy of the machined surface.
Ball cutters are most commonly used for milling in mold machining
Ball cutters are most commonly used for milling 3D molds in mold cnc machining, especially in precision machining and clear-angle machining, but they are not suitable for milling flat areas. Because the contact area with the workpiece is small, the tool spacing cannot be increased.
2.3 Round nose knife
The shape of the round-nose knife is similar to that of the end mill, with a flat bottom design, except that the bottom of the round-nose knife is an R-shaped blade rather than a sharp point, so the blade is stronger than the end-mill It is not easy to break, 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 during roughing. Because the bottom of the round-nose knife is flat, the horizontal distance between the round-nose knife can be larger than the ball knife. In finishing, it also has the same advantages as a ball cutter, so a larger value can be used for the tool distance. Therefore, round nose cutters are very suitable choices for roughing and finishing.
When milling 3D molds, round nose cutters have another advantage that is not comparable to the use of ball cutters. The ball cutter itself has a very large change in cutting speed depending on the contact position with the workpiece, so the quality of the machined surface is unstable. Although the round nose knife has such a situation, the change of its cutting speed is not as great as the ball knife. Therefore, the quality of the workpiece processed with the round nose knife is of course stable. The reason why the round nose cutter’s cutting speed is stable is explained below.
2.3.1 Cutting speed
You can see the position where the blade touches the workpiece at four points a, b, c, and d. No matter how the blade touches 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 cutter will be almost 0, but the round nose cutter can maintain a certain cutting speed. Therefore, of course, when using a round-nose knife, the cutting edge can be maintained in the cutting state, and the quality of the machined surface is of course 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.
3.Classification by tool device
In general, the milling cutter can be divided into the following two types of milling cutters:
3.1 Disposable cutter
This type of cutter, as its name implies, is that the cutting edge of the milling cutter is replaceable. Generally speaking, the design is divided into two parts: the tool holder and the blade. The blade is the cutting edge of the milling cutter to cut the workpiece, and the tool holder is used to fix or support the blade. The diameter of the tool holder determines the size of the milling cutter. In addition, the tool holder can also be designed with multiple edges. The blade part has many shapes, materials, etc … The user can replace the appropriate blade according to different machining conditions. After all the cutting edges on the blade are worn, the blade is discarded without resharpening, and only a new blade needs to be replaced. Therefore, the tool cost and flexibility are its advantages.
3.2 Integral Tool
The integrated cutter is designed with the blade and the body as a whole. The blade and the cutter body on the milling cutter are made of the same material, so the integral cutter will be higher than the discarded cutter in accuracy and strength of the blade. However, the relative material cost of making the tool will increase, and the blade needs to be reground after being worn before it can be reused. In addition, considering the strength of the cutting edge and the difficulty in manufacturing, it is extremely difficult to produce disposable tools below 10 mm, so milling cutters below 10 mm are generally integrated tools.