Cutting knife operation of the technical requirements

Cutting knife operation of the technical requirements

In modern metalworking, cutting can be performed on automation equipment with state-of-the-art bar feed mechanisms or state-of-the-art CNC machines. However, the wrong choice of cutting carbide inserts may result in downtime, damage to tools, scraping of workpieces and even damage to the machine.

In order to obtain the ideal cutting effect, it is necessary to understand the cutting mechanism in detail. Many of these variables must be considered: (1) the material and shape of the workpiece; (2) the machine tool; (3) the cutting edge associated with the central axis of the part; (4) the type of insert and chip breaker; (5) Grade and coating; (6) other cutting conditions affecting tool life. This article focuses on the first three variables.

1. Workpiece material and shape

To simplify the problem, the three most common shapes of workpieces are discussed here - solid, hollow, and irregular shapes that require intermittent cutting, such as square and hexagonal materials and hollow materials with inconsistent wall thicknesses.

Materials are generally divided into seven types, in order to simplify the problem, here is divided into three categories.

The first category is for materials that require the use of sharp positive rake cutting edges. It includes superalloys, titanium alloys, aluminum, plastics and other non-ferrous metals as well as austenitic stainless steels. Sharp cutting edges prevent work hardening of these materials. For example, a sharp cutting edge allows the use of high cutting speeds and feeds, and the ability to cut silicon-aluminum alloy neatly without leaving a curl. It is also suitable for most non-metallic materials (such as plastic, nylon and other soft, process-free materials).

The second category is for materials that require cutting with zero or negative cutting edges. It includes standard carbon steel, alloy steel and cast iron. Zero or negative rake angle can increase the strength of the cutting edge, and allows the use of a larger feed rate and to prevent cutting edge cutting intermittent damage. For most materials that produce long continuous chips, this zero or negative rake tool, which is also the type most commonly used in industrial production, should be used.

The third category includes those materials that require the use of a tool with a chip breaker that will be discussed later. These materials, at normal cutting speeds and feed rates, will produce long filaments, such as 52100 # steel used in the bearing industry and other high grade steels.

The machine usually requires the use of chip breaker when machining. When machining soft mild steel and alloy steels with low nominal feed rates, it usually produces unwanted long chips, requiring the operator to shut down frequently to clear chips. This will reduce productivity and endanger the operator because these chips are very sharp. The same problem can occur with some types of superalloys at very low cutting speeds.

When you choose to cut the blade, the geometry of the blade can be used with turning and milling the same angle blade. Normally, if a material is machined with a Tapping or Milling Insert, the same geometrical angle can be selected for the cutting operation.

2. machine tool

The key to effectively shutting down the operation is to be able to control the cutting speed and feedrate. The right combination of the two will extend the tool life, maintain the stability of the machining size and effectively control the chip. The type of machine used (its type and characteristics) determines to a large extent the extent to which the user can control the cutting parameters.

The machine is divided into two categories here: CNC and non-CNC machine tools. Automation equipment is the most commonly used form of mass production. This may create some important problems when using cutting tools.

When a tool to work with the lowest feed speed, then the machine can determine the maximum speed can be used. Due to the fact that some tools are simultaneously cut in several different positions in automated production, the cutting speed and the feed rate are hardly adjusted during machining. For example, when a HSS twist drill or forming tool is working in one of its locations, its optimum cutting speed will determine the cutting speed of all other tools, which is too low for most cemented carbide tools. New automation equipment allows the operator more control over the feed speed. Some CNC-type automation machines provide complete control of the entire cutting cycle.

The machine being used will determine the grade of the carbide insert, the chip breaker and the type of cutting edge. For traditional automation equipment, you need to choose the better toughness of the carbide grades. Carbide cutters below the normal cutting speed will be tested on these machines.

Ultrafine carbide grades have greatly improved the performance of cutting tools for automation equipment. They have the same strength as high-speed steel and have the same good wear resistance as cemented carbide.

Another type of machine that can be cut off is a CNC lathe. It is usually equipped with a bar feeder or similar device for high volume production. This type of machine has many advantages, the most important of which is the complete control of cutting speed and feed rate during the cutting cycle. This makes it possible to work efficiently with cemented carbide inserts with high cutting speeds. However, care must be taken that the cutting speed and feed rate are within the manufacturer's recommendations.

CNC machine tools are easy to program and change to suit the needs of machining different parts. Therefore, they are a preferred type of shorter stroke cut operation and their ability to adjust cutting speed and feed rate also helps to control swarf and increase tool life consistency.

3. Correct installation

When cutting with cemented carbide, it is important that the tool is correctly installed. If the cutting edge and workpiece contact position is not correct, the tool may collapse or damage the workpiece, and sometimes even damage the machine.

The two most common problems are that the cutting tool is not perpendicular to the workpiece or that the cutting edges are mounted too high or too low with respect to the central axis of the workpiece and that their effect on tool life, chip control, and the ability to maintain vertical and smooth cutting will result in larger Affect, will also result in the surface of the finished parts left convex, concave surface. If these problems are serious, the tool will fail.

To ensure that the tool is perpendicular to the workpiece, the operator should follow a simple installation procedure. First carefully clean the locking area and install the cutting tool on the hexagonal turret. Then an indicator is used to measure tool offsets over a 100 mm stroke, which should not exceed 1 mm.

One common way to check if the tool is vertical is to check the resulting chips. If the chips generated by the workpiece flow to one side in a filament, this may be incorrect tool installation. Another phenomenon is the premature wear at the cutting blade fillet, which indicates that one side of the blade is under more pressure than the other.

If the performance of the tool or the quality of the part produced during machining changes, follow the above mentioned installation procedure. Sometimes a slight collision tool can cause bias. Therefore, it is a good idea to check the cutting conditions of the cutting tool as soon as possible after installation, which can help to identify and prevent serious tool failure.

Another major consideration in cutting tool installation is the position of the cutting edge relative to the workpiece axis. Inaccurate blade mounting raises a number of issues, the most common of which are premature tool wear and sudden failure, poor chip formation, poor side roughness and vibration. These problems are further exacerbated by the sometimes difficult to pinpoint the actual location of the cutting edge. These phenomena occur more often on older manual and automatic machines.

Most manufacturers of carbide inserts designed to be mounted slightly higher than the central axis of the workpiece. This location facilitates the use of welding chip breakers and ensures that the blades are securely clamped to the arbor.

When the blade is mounted slightly above the center, the tangential force can act on a larger blade area. This increases the strength of the tool and firmly positions the blade in the sipe.

In addition, when the angle between the cutting edge and the workpiece is determined, cemented carbide cutting inserts are often designed to maximize their strength and robustness. If the blade is above the centerline too much, the blade clearance will decrease. Resulting in the upper part of the flank friction with the workpiece, so the cutting area will produce a lot of heat. This, in turn, can cause premature blade wear and cold work hardening. The most common sign of this is that the blade has excessive flank wear after short-term cutting.

Lower than the center of the blade will have more problems. When the blade is below the centerline, the relief angle will increase. This allows a small tip portion to withstand the full cutting forces, shortening tool life and increasing the chances of a sudden tool failure.

Another problem with lower centerline blades is the irregular blade offset. As most of the cutting forces act on the tip, it tends to vibrate and bounce, and this irregular movement will have an effect on tool life, usually in the form of chip breaking at the front of the cutting edge. It will produce vibration marks and poor surface roughness on the bottom and sides of the part groove.

One of the most serious consequences of using a lower centerline blade is that the blade is being pulled out. Rotation of the part actually pulls the blade out of the slot when the blade touches the entire bar; residual burrs on the part center accumulate on the cutting edge and as the part continues to rotate it pulls the blade out of the slot.

If this is not the case, the toolholder will be damaged during the machining of the next part and may cause damage to the machine tool and the part being machined. This means wasting time. Even if the blade is not pulled out of the holder, burrs that rotate through the top of the cutting edge can cause damage to the tool.

For these reasons, it is necessary to prevent the cutting tool from cutting beyond the center of the workpiece. After the center point, the actual direction of rotation is reversed and the resulting cutting force may pull the blade out of the holder. At the same time, this rotation will rub the blade flank, causing the blade to wear out prematurely. 

To overcome the problem of blade pullout, many cutting tool manufacturers are adopting the concept of automatic clamping developed by ISCAR in the early 1970s. This method does not require screws and levers to position and clamp the blade, it relies on rotation and tool pressure to position the blade within the wedge-shaped sipe. In this way, the cutting depth of the tool can be almost unlimited without the pressing device, and the type of the tool holder and the blade is another factor in mounting the tool in a centered high position. - The most common types of cutting tools are the body and blade system. It consists of a locking body mounted in the chuck of the machine and a replaceable double-sided blade for mounting of the alloy blade, with a self-locking sipe on the blade.

T-type cutting knife is - a combination of two kinds of blades and blade, using a simple wedge lock. On the top and bottom of the blade there is a bevel matching the blade. The blade is wedged by the spring force generated by the blade and held in the sipe. Under some conditions, the blade may be pushed further into the sipe, changing the cutting edge position below the center. Large feed rate cutting, intermittent cutting and wear of the groove may cause this phenomenon.

In the F-type cutting tool, the blade and the knife have - fixed positioning groove. A positioning block is welded to the blade in contact with the top surface of the support blade. Once the blade is installed in the sipe, it will remain in a fixed position.

Any combination of a blade and a blade should allow the chips to drain smoothly from the cutting zone. If the chips accumulate and invade the grooves before the parts are cut, the blades are likely to cut the chips again and suddenly fail. If the swarf violently rubs the blade, it will generate a lot of heat, which can also cause fatigue and accelerate the failure.

All manufacturers of carbide cutting tools offer high center of their products. Therefore, the manufacturer's recommendations should be strictly observed.

The geometry of the insert and the type of insert have an impact on the center height. Often blade widths greater than 0.5 mm, the following formula is useful for determining the maximum center height: Center height = 0.8 mm × width + 0.025 mm.

In the cutting process, we must remember that the cutting edge installed in the center of the high or slightly higher than the center of the high. Operators and installers who use HSS cutters or similar tools often think that these tools work better well below center height. However, for modern carbide inserts, working below center height will make cutting operations more difficult.