The definition of difficult to machine materials has been changing with the development of processing technology. At this stage, it mainly refers to titanium alloy, super heat resistant alloy, carbon fiber and other materials. In recent years, the industrial manufacturing industry has greatly increased the requirements for high hardness, high toughness and high wear resistance of parts, and this kind of difficult to machine materials will be encountered more and more. In addition, some new difficult to process materials are constantly appearing in the list of machined materials. When cutting difficult materials, the tool life will be significantly reduced due to the large amount of cutting heat. Therefore, it is necessary to take corresponding technical measures for different cutting methods to improve machining efficiency and prolong tool life.
Requirements of cutting tool materials for cutting difficult machining materials
In terms of tool materials, cubic boron nitride tools have the best high-temperature hardness among the existing tool materials, and are the first choice for machining difficult materials. In addition, cubic boron nitride sintered body is also a good choice for processing high hardness steel and cast iron materials, and with the increase of cubic boron nitride content, the service life will also increase. At present, CBN sintered body without binder has been developed.
Titanium and titanium alloys in difficult to machine materials, due to their high chemical activity and low thermal conductivity, are suitable for cutting with diamond tools with sharp edges and high thermal conductivity. Because the cutting tool of this material has less heat retained at the tip, and its chemical properties are relatively stable, it can prolong the service life of the cutting tool. The diamond sintered tool is also suitable for cutting aluminum alloy, pure copper and other materials.
In addition to the above two materials, there is a new type of coated cemented carbide material, which uses ultra-fine grain alloy as the matrix and selects coating materials with good high temperature hardness for coating treatment. By using coatings with different properties, it can be almost suitable for cutting all kinds of difficult to machine materials. With the help of some coating materials with superior performance, this kind of tool has been applied to the field of high-speed machining.
Requirements of cutting tool shape for machining difficult materials
Let's take a look at the geometry of the tool, which is also a very important determinant, which directly affects the performance of the tool material. This mainly includes the front angle, back angle and cut in angle of the tool, as well as some treatment of the tool tip. In recent years, with the wide promotion and application of high-speed milling technology, small cut depth reverse milling has become the mainstream, which is conducive to reducing the load of cutter teeth and improving the feed speed. In order to adapt to this trend, the design idea of tool cutting edge shape is also undergoing an "evolution".
When drilling difficult to machine materials, in order to minimize torque and cutting heat, it is necessary to control the contact area between the cutting surfaces within a minimum range. The means that can be taken is to increase the sharp angle of the drill and carry out cross grinding. The difficulty of chip removal in drilling is a prominent problem. In order to facilitate the discharge of chips, a coolant spray outlet can be set at the back of the bit cutting edge, which is a very effective method to improve the cooling and chip removal effect.
Requirements for cutting conditions for machining difficult materials
When cutting difficult materials, only very low machining conditions are usually set. However, with the improvement of tool performance and the use of high-speed CNC machine tools and high-speed milling, the cutting conditions of difficult to machine materials have been greatly improved, and even entered the era of high-speed cutting.
At present, the requirements of cutting difficult to machine materials for cutting conditions are mainly focused on reducing the load on the cutting edge of the tool and reducing the cutting heat. Using small cutting depth can effectively reduce the cutting edge load of the tool, so as to improve the cutting speed and feed speed; Intermittent cutting can avoid a large amount of cutting heat staying on the cutting edge. For example, in the finishing of holes, the trend of using intermittent cutting method to replace the traditional continuous cutting method is more beneficial to increase the stability of cutting, improve chip removal performance and prolong the tool life. The same processing strategy is also applied to screw hole processing.
When rough machining difficult materials with ball end milling cutter, the tool shape and fixture should be well matched, which can improve the swing accuracy and clamping rigidity of the cutting part of the tool, so as to ensure that the feed rate per tooth is maximized under the condition of high-speed rotation, and at the same time, it can also extend the service life of the tool.