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2.3 round nose knife

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

In addition, the round nose cutter has better processing efficiency than ball cutter and end mill, especially in rough machining. Because the bottom of the round nose knife is flat, the horizontal knife spacing of the round nose knife can be used larger than the ball knife. In finishing, it also has the same advantages as the ball knife, so the knife spacing can also be used in larger values. Therefore, the round nose cutter is a very suitable choice for roughing and finishing.

When milling 3D molds, the round nose cutter has another advantage that is not comparable to the use of ball cutters. The ball cutter itself will vary greatly with the position of contact with the workpiece, and the cutting speed will vary greatly, so the quality of the machined surface is unstable. Although the round nose knife also has such a situation, but its cutting speed does not change as much as the ball knife. Therefore, the quality of the workpiece processed by the round nose cutter is of course stable. The reason why the cutting speed of the round nose cutter is stable is explained below.

2.3.1 Cutting speed

The following figure is to simulate the contact between the round nose cutter and the workpiece when the round nose cutter is milling 3D workpiece,

You can see the position of the blade in contact with the workpiece at four points a, B, c and d. No matter how the blade contacts the workpiece, the contact area of the blade will fall in the two areas I and II shown in the lower left figure. It can be clearly understood from this figure that even if the contact point of the round nose knife is constantly changing like a ball knife, the resulting cutting speed change will not be as drastic as the ball knife, even at the position of 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 using a round nose cutter, of course, the cutting edge can be maintained in the cutting state, and the quality of the machined surface will of course be stable. The following figure on the left shows roughing with a round nose knife. The advantage of roughing with a round nose knife is that the horizontal knife spacing can be used very large, so the roughing efficiency is far better than that of a ball knife. The following

The figure is finished with a round nose cutter. The advantage of a round nose cutter is that the cutting speed changes stably, so you can see that the surface of the workpiece after finishing presents the brightness of the metal after being cut.

3. Distinguish by tool device

The use of general milling cutter can be divided into the following two forms of milling cutter:

1. Discard cutter

2. Integral cutter

3.1 discard tool

This type of tool, as the name implies, that is, the cutting edge of the milling cutter is a replaceable design. Usually in the design is divided into two parts: the cutter seat and the blade. The blade is the cutting edge of the milling cutter used to cut the workpiece, while the cutter seat is used as a fixed or supporting 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 blades. The blade part has many shapes, materials... and other changes. The user can replace the appropriate blade according to different processing conditions. After all the cutting edges on the blade are worn out, the blade is abandoned without re-grinding, and only a new blade needs to be replaced. So the tool cost, the use of elasticity for its advantages. The following illustration shows a discard tool.

3.2 integral tool

The integral cutter is designed to integrate the blade and the cutter body. The blade and the milling cutter body on the milling cutter are made of the same material. Therefore, the integral cutter is higher than the discarded cutter in terms of precision and strength of the blade. However, the relative material cost of making the cutter will increase, and the blade needs to be reground before it can be used. In addition, considering the strength of the cutting edge and the difficulty in manufacturing, it is extremely difficult to produce discarded tools below 10mm, so generally milling cutters below 10mm are integral tools. The following illustration shows an integral tool.