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The development of today's manufacturing industry requires short delivery times and low processing costs. Traditional production methods have been difficult to adapt. Therefore, intensive machine tools of the CNC compound turning center category have attracted much attention. Parts have tended to be a composite of a variety of composite shapes, consisting of a cylindrical surface and a flat surface, with holes on different sides, and so on. In order to machine such parts, in addition to turning, other cutting capabilities must be available. If the CNC composite turning center is used, multiple machining operations can be completed on one machine to achieve intensive machining. With this trend, turning tools for CNC compound turning centers have emerged.
In addition, with the advent of high-speed milling, cutting speeds and feed rates are increasingly becoming faster. Although the cutting speed and feed speed of turning are also improved, there is no large change in milling. The reason is that turning (continuous cutting) and milling (interrupted cutting) are different, mainly in the following aspects:
(1) Since the turning is performed by the rotation of the workpiece, it is difficult to maintain the clamping rigidity of the workpiece, reduce the amount of unbalance, and increase the cutting speed.
(2) Compared to interrupted cutting, turning with continuous cutting has a more adverse effect on tool life.
Therefore, it is difficult to achieve high precision and high efficiency machining when cutting with small depth of cut, high cutting speed, and fast feed cutting conditions. However, turning machining is also seeking new developments, and development of technologies required for intensive processing, rapid production, simplification of production equipment, short-term processing cycles, and low cost are being carried out. CNC compound cutting is a trend that requires turning and turning tools and can process a wide range of shapes.
This article provides an introduction to the latest developments in turning operations and the latest developments in high value-added processing tools.
2 Latest trends in turning tools
The blades used for turning are always coated with hard alloys, which require long blade life, high reliability and high speed cutting. Due to the development of the net forming technology of the workpiece blank, the machining allowance is gradually reduced and the cutting is more stable, so the tool life becomes the key to selecting the tool. The method of improving tool life does not improve the shape of the cutting edge like an end mill. Instead, it develops countermeasures against the tool material to improve the wear resistance of the carbide coating to extend tool life. In addition, a few years ago, an indexable insert having a special tip shape (a shape having a milling cutter effect) that improves the feed amount without lowering the surface roughness of the cutting surface has appeared.
2.1 The tool material for turning the indexable insert is mainly coated with cemented carbide. However, in recent years, the development of new coatings and matrix materials for high-speed cutting and tool life improvement has made great progress. Coated cemented carbides have also developed in recent years, such as cermets with high adhesion resistance, high-speed cutting in the finishing of steel below HRC40, and low surface roughness; but it is cutting Heat resistance and impact resistance are poor, so the scope of application is limited. If a cermet (smooth PVD TiAlN coating) coating is used, it is possible to ensure a low surface roughness and an increase in wear resistance for extended tool life. Previously, CBN tools were used to process high-hardness steels with hardnesses up to HRC50. Now, due to the improved performance of coated carbide inserts, it is also fully capable of cutting high hardness steels, thus increasing the application range of coated carbide inserts. .
The indexable inserts for turning mainly use CVD coating technology to improve the bonding strength and reliability of the coating. The wear resistance and chipping resistance have been greatly improved compared with the past. The following is a detailed introduction:
(1) Improvement of wear resistance In practical applications, the adhesion strength of the cemented carbide substrate and the coating can be improved by thick filming of the fine particle Al2O3 smooth coating, thereby improving the wear resistance; and also by increasing the TiAlN coating The proportion of Al in the layer enhances the wear resistance.
The indexable insert for turning cast iron can meet high-speed cutting conditions and extend tool life by removing the TiN layer of the rake face and adding special coatings (increasing the bond strength and the wear resistance of the rake face). The Si-based composite film (a coating of an amorphous Si-N nanocomposite structure) is characterized by oxidation resistance (an initial oxidation temperature of 1100 ° C or higher, a general TiAlN coating of 900 ° C or higher) and high hardness, and is capable of cutting cast iron at high speed. (300m/min or more).
(2) Anti-cracking improvement The surface strengthening and toughening treatment of the cemented carbide substrate (ultrafine particle alloy) can prevent chipping and breakage of the blade edge during cutting, so the tool manufacturer improves the coating substrate. Never stopped. At the same time, the improvement of the bonding strength between the substrate and the coating is adopted as a key measure for improving the reliability and life of the tool in the coated cemented carbide. For example, experimental reports have shown that if the surface roughness of the cemented carbide substrate is increased, the bonding strength of the coating is increased. Therefore, research results on the surface characteristics of the cemented carbide substrate are just around the corner.
(3) Reduction of bonding phenomenon In the turning process of SCM-based steel with high softness and high toughness, the blade cutting edge is prone to material adhesion, causing peeling and chipping of the coating. Blades that use a special Ti compound to smooth the surface of the coating can inhibit chipping and sticking.
(4) The blade edge is sharper to prevent the coating of the coated carbide blade from peeling off. The general method is to make the cutting edge into an R shape. The blades used for cutting small parts and grooves are sharp, so PVD coating thickness is best controlled at 3μm.
2.2 The shape of the blade is the closest, which can reduce the positive rake angle of the cutting resistance. The three-dimensional complex curved shape has more chipbreaking grooves, which are mainly divided into double-sided chip breaking groove and single-sided chip breaking groove. The former is suitable for light cutting with small depth of cut. Suitable for heavy cutting with deep cut depth.
Since the shape of the blade is a three-dimensional CAD design method, the development capability is remarkably improved, and as the forming technology advances, the shape of the free-form surface can be accurately displayed. For example, the precise formation of fine portions such as the chamfered shape of the blade edge portion is more advantageous for the improvement of the cutting performance.
The unique blade shape of the four-corner blade with 45° angles can meet the cutting conditions of high-speed and fast feed in medium and coarse cutting, inhibiting the occurrence of boundary wear, and is expected to improve the machining efficiency in the turning of heat-resistant alloys and titanium alloys. Extend tool life and improve chip handling.
In order to pursue the high efficiency and high precision of turning machining, in the past few years, various cutting tool manufacturers have developed a blade shape with a wiper function, that is, the blade edge R and the straight blade edge have a similar blade milling light. The edge of the blade. When finishing with a wiper blade and an R-shaped tip blade, the feed rate can be increased without lowering the finish, and high-efficiency and high-precision machining can be realized.
When cutting with a blade with a light-removing function, it needs to be corrected during programming because it has a different cutting edge position than a conventional rounded blade.
For the grooving and cutting blades, the shape of the independent chipbreaker that is press-formed and the concave shape that can withstand the cutting force are used. This high-performance grooving and cutting blade with complex shape made by molding technology has been produced by professional cutting tool manufacturers.
1 Introduction