Tool is the part of machining equipment that directly participates in cutting. Whether the tool selection is appropriate directly affects the machining quality. When selecting cutting tools, it is necessary to comprehensively consider the workpiece materials, cutting tool materials, processing properties and other factors, so as to select the most appropriate cutting tools and achieve the best processing quality and efficiency.
General requirements and development direction of cutting tools
For the materials used in manufacturing tools, the most basic requirements are their high-temperature hardness and wear resistance. In addition, they also need to have good bending strength, impact toughness and chemical inertia, as well as the processability of machining methods such as cutting, forging and heat treatment. Generally, if the hardness of the material is high, the wear resistance will be high, but the bending strength and impact toughness will decline. When the material has high strength, its impact toughness will be higher.
Under normal working conditions, cutting tools will experience the test of high temperature, high pressure and high speed, and face many difficult to machine materials; In some abnormal working environments, corrosive fluid media will be encountered; In addition, in recent years, with the continuous development of processing equipment, the level of automation and the requirements for accuracy are constantly improving, which have put forward new topics for the tool industry.
In order to meet the above requirements, the tool industry must continue to develop and innovate, from the application of new tool materials to vapor deposition coating technology, and then to indexable tool structure, all of which are effective means to improve tool performance, and also an important reference for the machining industry to select tools.
Tool material classification and functional characteristics
Among the cutting tool materials, the most commonly used are high-speed steel and cemented carbide. High speed steel is the most popular tool material because of its high bending strength, impact toughness and good machinability. Cemented carbide is slightly less widely used than high-speed steel.
Cubic boron nitride is a new tool material rising in recent years. It is suitable for cutting metal materials such as high hardness hardened steel and hard cast iron; Polycrystalline diamond is suitable for cutting iron free metals, alloys, plastics and glass fiber reinforced plastics; There are also carbon tool steel and alloy tool steel, which are only used to make files, dies, taps and other tools at this stage.
Vapor deposition coating technology is an effective means to improve the function and durability of tools. The coated tools can greatly reduce the wear in cutting and significantly prolong the service life of tools. Among them, chemical deposition is often used to coat titanium carbide, titanium nitride, aluminum oxide hard layer or composite hard layer on cemented carbide tools. Physical deposition can be used to coat cemented carbide and high-speed steel tools.
Working part of the tool
The cutter is composed of working parts and clamping parts. The working part refers to the part of the tool used to generate and process chips, which usually includes the blade, chip breaking or chip curling groove, chip removal or chip holding space, cutting fluid channel and other structures. Some cutting tools only include the cutting part, whose function is to use the cutting edge to cut chips, such as turning tools, planers, boring tools and milling tools; In addition to the cutting part, some tool working parts also include the calibration part, whose function is to polish the machined surface that has been cut and guide the tool.
The working part of the cutter has three different structures, namely, integral type, welding type and mechanical clamping type. The overall structure is to make cutting edges on the tool body; The welding structure is to braze the blade to the steel cutter body; The mechanical clamping structure clamps the brazed cutter head of the blade on the cutter body.
Clamping part of tool
The clamping part of the tool has two different structural types, namely, with holes and with handles. The tool with hole is sleeved on the spindle or spindle of the machine tool by means of the inner hole, and the torsional torque can be transmitted by means of the axial key or the end key. Cylindrical milling cutter and sleeve face milling cutter all belong to this type.
The shape of the handle of a tool with a handle usually includes rectangle, cylinder and cone. The cutting tool used in turning and planing is generally rectangular handle; Conical handle bears axial thrust by its taper and transmits torque by means of friction; In most cases, cylindrical shanks are used in smaller tools such as fried dough twist drills and end mills to transmit torsional torque with the help of the friction generated during clamping. Many tool shanks with shanks are made of low alloy steel, while the working part is made of high-speed steel. The two parts are butt welded to form a defective knife.