Basic knowledge of metal cutting tools

When choosing the tool angle, we need to consider the influence of many factors, such as workpiece material, tool material, processing properties (rough, finishing) and so on, we must choose reasonably according to specific conditions. Generally speaking, the tool angle refers to the marking angle used in manufacturing and measuring. In practical work, the actual working angle and the marking angle are different, but the difference is usually very small, because of the different installation position of the tool and the change of cutting direction.

Tool materials must be of high temperature hardness and wear resistance, necessary bending strength, impact toughness and chemical inertia, good workmanship (cutting, forging and heat treatment, etc.) and not easily deformed.

Usually, when the material is of high hardness, the wear resistance is also high, and the impact toughness is high when the bending strength is high. However, the higher the hardness, the lower the flexural strength and impact toughness. Because of its high bending strength, impact toughness and good machinability, high speed steel is still the most widely used tool material in modern times, followed by cemented carbide.

Polycrystalline cubic boron nitride is suitable for cutting hardened steel and hard cast iron with high hardness; polycrystalline diamond is suitable for cutting iron-free metals, and alloys, plastics and FRP, etc. Carbon tool steel and alloy tool steel are now used only for tools such as files, plate teeth and taps.

The cemented carbide indexable inserts have been coated with TiC, TiN, Alumina or composite hard layers by chemical vapor deposition (CVD). The developing physical vapor deposition method can be used not only for cemented carbide tools, but also for high speed steel tools, such as drills, hobs, taps and milling cutters. Hard coatings act as barriers to chemical diffusion and heat conduction, slowing down tool wear during cutting, and prolonging the life of coated inserts by more than 1-3 times compared with uncoated inserts.

Due to the high temperature, high pressure, high speed, and working in corrosive fluid medium, more and more difficult-to-machine materials are used, the level of automation in cutting and the requirement of machining accuracy are higher and higher. In order to adapt to this situation, the direction of tool development will be the development and application of new tool materials; further development of tool vapor deposition coating technology, deposition of higher hardness coatings on high toughness and high strength substrate, better solve the contradiction between tool material hardness and strength; further development of indexable tool junction. Improve the manufacturing precision of the cutter, reduce the difference of product quality, and optimize the use of the cutter.

According to the cutting motion mode and the corresponding blade shape, the cutting tool can be divided into three types. General-purpose cutting tools, such as turning tools, planers, milling cutters (excluding formed turning tools, forming planers and forming milling cutters), boring tools, drills, reamers and saws; forming tools, such as cutting edges with the same or close to the section of the workpiece being processed, such as forming lathes, forming planers, forming milling cutters, drawing cutters, etc. Cutters, bevel reamers and various thread cutting tools, etc. Generating cutters are used to process the tooth surface of gears or similar workpieces by generating methods, such as hobs, shapers, shavers, bevel gear planers and bevel gear cutters.

The structure of various knives is made up of clamping part and working part. The clamping part and working part of the integral structure cutter are all made on the cutter body; the working part of the toothed structure cutter (cutter tooth or blade) is mounted on the cutter body.

The clamping part of the cutter has two kinds: the hole and the handle. The tool with hole is mounted on the spindle or mandrel of the machine tool by the inner hole, and the torque is transmitted by the axial key or the end face key, such as cylindrical milling cutter, sleeve face milling cutter, etc.

The tool with handle usually has three kinds: rectangular handle, cylindrical handle and conical handle. Turning tool, planer, etc. are generally rectangular shank; taper shank * bears axial thrust and transfers torque with the aid of friction; cylindrical shank is generally suitable for smaller twist drills, end milling cutters and other cutters, cutting with the aid of friction generated by clamping torque transmission. Many tool shanks with shanks are made of low alloy steel, while the working parts are butt welded with high speed steel.

The working part of the cutter is the part that produces and processes chips, including the knife edge, the structure that breaks or curls the chips, the space for discharging or storing the chips, the channel of cutting fluid and other structural elements.

Some cutting tools work part is the cutting part, such as turning tool, planer, boring and milling cutter, etc. Some cutting tools work part includes cutting part and calibration part, such as drill, reamer, inner surface broach and tap. The function of the cutting part is to cut the chip with the cutting edge, and the function of the calibration part is to trim the machined surface and guide the cutting tool.

The working parts of the cutting tool are of three types: the integral type, the welding type and the mechanical clamping type. The overall structure is to make cutting edges on the blade body; the welding structure is to braze the blade to the steel blade body; the mechanical clamping structure has two kinds, one is to clamp the blade on the blade body, the other is to clamp the brazed blade on the blade body. Cemented carbide tools are generally made of welding structure or mechanical clamping structure; porcelain tools are mechanical clamping structure.