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Basic knowledge of woodworking knife tools (b)
- Jul 19, 2018 -

The tool can be divided into five categories according to the form of the workpiece surface. Tools for machining various external surfaces, including turning tools, planing knives, milling cutters, outer surface broaches and boring tools, etc.; hole machining tools, including drills, reaming drills, boring tools, reamers and internal surface broaches; thread processing Tools, including taps, dies, automatic opening and closing thread cutting heads, thread turning tools and thread milling cutters; gear processing tools, including hobs, shaper knives, shaving cutters, bevel gear machining tools, etc.; cutting tools, including inlays Tooth circular saw blades, band saws, hacksaws, cutting tools and saw blade milling cutters, etc. In addition, there are combination tools.


According to the cutting motion mode and the corresponding blade shape, the tools can be divided into three categories. General-purpose tools such as turning tools, planing knives, milling cutters (excluding formed turning tools, forming planers and forming cutters), boring tools, drill bits, reaming drills, reamers and saws; forming tools, cutting edges for such tools Having the same or nearly the same shape as the workpiece to be machined, such as forming turning tools, forming planers, forming cutters, broaches, conical reamers, and various threading tools; etc.; forming tools are used to process gears. Tooth surface or similar workpieces such as hobs, pinion cutters, shaving cutters, bevel gear planers and bevel gear milling cutters.


The structure of each tool consists of a clamping part and a working part. The clamping part and the working part of the integral structural tool are made on the body; the working part (knife or blade) of the inserting tool is mounted on the body.

The clamping part of the tool has two types of holes and handles. The perforated tool is placed on the spindle or mandrel of the machine tool by means of the inner hole, and the torsional moment is transmitted by means of the axial key or the end key, such as a cylindrical milling cutter, a sleeve face milling cutter and the like.


Tooles with handles usually have three types: rectangular handle, cylindrical handle and tapered handle. Turning tools, planing knives, etc. are generally rectangular shanks; taper shanks are tapered to withstand axial thrust and transmit torque by friction; cylindrical shanks are generally suitable for smaller twist drills, end mills, etc. The resulting frictional force transmits the torsional moment. Many of the shank-handled shanks are made of low-alloy steel, while the working part is made of high-speed steel to butt weld the two parts.


The working part of the tool is the part that produces and processes the chip, including the blade, the structure that breaks or rolls the chip, the space for chip removal or chip storage, and the passage of the cutting fluid. Some working parts of the tool are cutting parts, such as turning tools, planing tools, boring tools and milling cutters; some working parts of the tool include cutting parts and calibration parts, such as drill bits, reaming drills, reamers, and internal surfaces. Knives and taps, etc. The function of the cutting part is to cut the chips with a cutting edge. The calibration part is used to polish the machined surface and guide the tool.


The working part of the tool has three types: integral, welded and mechanically clamped. The overall structure is to make a cutting edge on the cutter body; the welded structure is to braze the blade to the steel body; the mechanical clamping structure has two kinds, one is to clamp the blade on the cutter body, and the other is to clamp the blade to the cutter body, and the other The brazed bit is clamped to the body. Carbide tools are generally made of welded structures or mechanically clamped structures; ceramic tools are mechanically clamped.


The geometric parameters of the cutting part of the tool have a great influence on the cutting efficiency and the quality of the machining. Increasing the rake angle reduces the plastic deformation of the rake face when the cutting layer is pressed, and reduces the frictional resistance of the chip flowing through the front, thereby reducing the cutting force and the cutting heat. However, increasing the rake angle will reduce the strength of the cutting edge and reduce the heat dissipation volume of the cutter head.


When selecting the angle of the tool, it is necessary to consider the influence of various factors, such as workpiece material, tool material, processing properties (rough, finishing), etc., which must be reasonably selected according to the specific situation. Generally speaking, the tool angle refers to the angle of labeling for manufacturing and measurement. In actual work, the actual working angle and the angle of the marking are different due to the different mounting positions of the tool and the change of the cutting motion direction, but usually the difference is small. 


The material used to make the tool must have high high temperature hardness and wear resistance, necessary bending strength, impact toughness and chemical inertness, good processability (cutting, forging and heat treatment, etc.) and not easily deformed.


Generally, when the hardness of the material is high, the wear resistance is also high; when the bending strength is high, the impact toughness is also high. However, the higher the hardness of the material, the lower the bending strength and impact toughness. High-speed steel is still the most widely used tool material due to its high flexural strength and impact toughness, as well as good processability, followed by hard alloys.


Polycrystalline cubic boron nitride is suitable for cutting high hardness hardened steel and hard cast iron; polycrystalline diamond is suitable for cutting iron-free metals, and alloys, plastics and glass steel; carbon tool steel and alloy tool steel are now only used Tools such as trowels, dies and taps.


Carbide indexable inserts have now been coated with titanium carbide, titanium nitride, alumina hard or composite hard layers by chemical vapor deposition. The growing 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. As a barrier to chemical diffusion and heat conduction, the hard coating slows the wear of the tool during cutting, and the life of the coated blade is about 1 to 3 times higher than that of the uncoated one.


Due to the high temperature, high pressure, high speed, and parts working in corrosive fluid media, more and more difficult materials are applied, and the automation level of cutting and the processing precision are getting higher and higher. In order to adapt to this situation, the development direction of the tool will be to develop and apply new tool materials; further develop the vapor deposition coating technology of the tool, and deposit a higher hardness coating on the high toughness and high strength substrate to better solve The contradiction between the hardness and strength of the tool material; further develop the structure of the indexable tool; improve the manufacturing precision of the tool, reduce the difference in product quality, and optimize the use of the tool.