This article describes turning tools.
(This article is selected from Chapter 3, Section 3 Turning Tool of "Machining Characteristic Operations and Practical Cases")
2. Indexable turning tool
(1) Composition of indexable turning tools
The indexable turning tool is a machine-clamp turning tool using an indexable blade. Figure 3-20 shows the composition of the indexable turning tool. The tool shim 1 and the blade 2 are set on the clamping element 3 of the tool holder. The blade is pressed against the supporting surface to be fastened, and the front and rear angles of the turning tool are obtained after the blade is installed in the tool holder groove. After one cutting edge is blunt, it can be quickly shifted to an adjacent new cutting edge, and the work can continue until all the cutting edges on the blade are blunt, and the blade can be scrapped and recycled. After replacing the new blade, the turning tool can continue to work.
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Figure 3-20 Composition of indexable turning tools
1—Shim 2—Insert 3—Clamping element 4—Arbor
1. Advantages of indexable tools
Compared with welding turning tools, indexable turning tools have the following advantages:
(1) High tool life. Since the blade avoids defects caused by high temperature welding and sharpening, the geometric parameters of the tool are completely guaranteed by the blade and the groove of the tool holder, and the cutting performance is stable, thereby improving the tool life;
(2) High production efficiency. Since the machine tool operator no longer sharpens the tool, the auxiliary time such as stopping the machine and changing the tool can be greatly reduced;
(3) It is conducive to the promotion of new technologies and new processes. Indexable turning tools are conducive to the promotion of new tool materials such as coatings and ceramics;
(4) It is beneficial to reduce the tool cost, the tool bar has a long service life, and greatly reduces the consumption and inventory of the tool bar, simplifies the management of the tool, and reduces the cost of the tool.
Due to the above advantages, indexable cutting tools are listed as a national key promotion project, which is also the development direction of cutting tools.
2. Selection of indexable inserts
Indexable inserts are the most critical part of various indexable cutting tools. Correct selection and use of indexable inserts is an important part of rational design and use of indexable cutting tools. The selection of inserts includes material, shape and size, etc., insert material Choose to refer to the first section of this chapter.
(1) Shape selection. When selecting the shape of the blade, it is mainly based on factors such as the nature of the processing process, the shape of the part, the life of the tool, and the utilization rate of the blade. Among the most commonly used types of inserts, triangular inserts are used for 90° external circle, face turning tools, hole turning tools and 60° thread turning tools. Due to the small tool nose angle, its strength is poor, the tool life is low, but the radial force is small, it is suitable for 8° triangular and convex triangular inserts under the condition of poor rigidity of the process system. The sharp angles increase to 82° and 80°. When this kind of blade is used to manufacture 90° offset cutter, it not only improves the life of the cutter, but also reduces the residual area of the processed surface, which is beneficial to reduce the surface roughness value. Regular quadrilateral inserts are suitable for various outer turning tools, end face turning tools and hole turning tools with leading angles of 45°, 60°, and 75°. The strength of the blade and the life of the tool are improved. With the increase of the number of edges of the blade, the strength of the blade tip increases, and the utilization rate of the blade increases, but the back force Fp increases accordingly, and the position that the turning tool can reach when it is working is limited. The edge angle of the edge blade is 108°, and its strength and service life are good. However, it is only suitable for the case where the rigidity of the process system is good, and it cannot also be used as an outer circle and end face turning tool. Blades of other shapes, such as parallelograms and rhombuses, are used for profiling lathes and CNC lathes. Round blades can be used for turning curved surfaces and forming. noodles and fine car;
(2) Insert size selection, insert size selection, including insert inscribed circle diameter (or side length), thickness, tool tip arc radius, etc., side length selection is mainly determined according to the length of the main cutting edge (Lse), rough turning The side length L=(1.5~2) Lse is desirable for machining, and L=(3~4) Lse is desirable for finishing turning. The choice of blade thickness mainly considers the strength of the blade. Under the premise of satisfying the strength and smooth cutting, try to choose a small thickness The selection of the blade and the radius of the tool nose arc should consider factors such as the roughness of the machined surface and the rigidity of the process system;
3. Typical structure of blade clamping
The characteristics of indexable turning tools are reflected in the replacement of cutting edges by insert indexing, and the replacement of new inserts after all cutting edges are blunt. For this reason, the clamping of inserts must meet the following requirements:
(1) High positioning accuracy. After the blade is indexed or replaced with a new blade, the change of the position of the tool tip should be within the range allowed by the precision of the part;
(2) The blade is clamped reliably. The clamping element should press the blade to the positioning surface. It should ensure that the contact surface of the blade, tool shim, and tool holder are closely fitted to withstand shock and vibration. However, the clamping force should not be too large, and the stress distribution should be uniform to avoid crushing the blade. ;
(3) Chip removal is smooth. It is best to have no obstacles on the front of the blade to ensure smooth chip discharge and easy to observe. Especially for the hole cutter, it is best not to use the upward pressure type to prevent the chips from entanglement and scratching the processed surface;
(4) Easy to use. It is convenient and quick to change the cutting edge and replace the new blade. The structure of the small-sized tool should be compact. When the above requirements are met, the structure should be as simple as possible, and it is easy to manufacture and use.
Several typical structures are introduced below:
(1) Lever-type clamping, as shown in Figure 3-21a, is a straight-rod structure. When the screw 6 is screwed in, the lower end of the lever 2 is pressed, and the lever tilts with the drum-shaped cylinder in the middle as the fulcrum. The shaped cylinder presses the blade to the two positioning sides of the knife groove and is fastened, and the knife pad 3 is positioned with the spring sleeve 1. When the blade is released, the knife pad maintains the original position by the tension of the spring sleeve and will not loosen. Figure 3-21b is also a straight rod structure, the difference is that the lower end of the lever 2 is pushed by the screw cone, and the curved rod structure is shown in Figure 3-21c, the blade 4 is clamped by the curved rod 2 through the screw 6, and the curved rod 2 The rod swings with its corner convex part as the fulcrum, and the spring 7 rebounds the curved rod to release the blade after the screw 6 is loosened. Among them, there is a large gap between the inner wall of the spring sleeve and the curved rod, which is convenient for the curved rod to swing therein.
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Figure 3-21 Lever type clamping
This kind of curved rod clamping mechanism is easy to realize the positioning of the two sides of the blade, because of its high positioning accuracy, reasonable force direction of the blade, reliable clamping, small size of the cutter head, flexible loading and unloading of the blade, and convenient use. better clamping form. The disadvantage is that the structure is complex and difficult to manufacture.
(2) Wedge pin clamping, as shown in Figure 3-22, the blade 2 is positioned in the hole by the pin shaft 3, when the wedge 4 is pressed down, the blade is pushed against the pin shaft 3, and when the screw 5 is loosened, The spring washer 6 automatically lifts the wedge. This structure has a large clamping force and is simple and convenient, but the positioning accuracy is low, and the force on the blade is uneven during clamping.
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Figure 3-22 Wedge Pin Clamping
1—shim 2—blade 3—pin 4—wedge 5—screw 6—spring washer
(3) Eccentric screw clamping, as shown in Figure 3-23, is an eccentric screw pin clamping structure. It uses an eccentric screw as a rotating shaft, and the upper end of the screw is an eccentric cylindrical pin. The eccentricity is e. When the eccentric screw 1 is turned, The eccentric screw clamps or loosens the blade. It is also possible to replace the screw with a cylindrical shaft, but the eccentric screw pin utilizes the thread self-locking performance to increase the anti-loosening ability. This kind of clamping structure is simple and easy to use. Its main disadvantage is that it is difficult to ensure the balance of the clamping force on both sides. When it is required to use the two sides of the sipe to position and clamp the blade, the rotation angle tolerance of the rotating shaft is required to be extremely small, which is difficult to achieve under the general manufacturing precision, so in fact, it is often clamped on one side, and the blade under impact and vibration Easy to loosen, this structure is suitable for continuous and smooth cutting.
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Figure 3-23 Eccentric screw clamping
1—eccentric screw 2—knife shim 3—blade 4—knife rod
(4) Push-up clamping. The above three clamping structures are only suitable for blades with holes. For blades without holes, especially blades with back angles, the push-up clamping structure is required (see figure 3-24), this structure has large clamping force, stable and reliable, convenient clamping, and easy manufacture. For the blade with holes, the combination of pin positioning and upward pressure clamping can also be used. The main disadvantage is the larger size of the cutter head.
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Figure 3-24 Push-up clamping
1—pin shaft 2—knife shim 3—blade 4—pressure plate 5—tapered hole pressure plate 6—screw 7—support nail 8—spring
(5) Pad-pull clamping. The principle of pad-pull clamping is to generate a component force on the inclined surface of the tapered hole of the pad through the conical head screw, forcing the pad to drive the blade to press against the positioning surfaces on both sides. The pad is clamped The element is the tool shim, which is dual-purpose. This structure is simple and compact, with firm clamping, high positioning accuracy, large adjustment range, and unobstructed chip removal. The disadvantage is that the moving groove of the pull pad should not be too long, generally 3~5mm, otherwise the strength and rigidity of the positioning side will be reduced. In addition, the rigidity of the cutter head is weak, so it is not suitable for rough machining, as shown in Figure 3-25.
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Figure 3-25 Pull Pad Clamping
1—Pull pad 2—Blade 3—Pin shaft 4—Taper end screw
(6) Press-hole clamping, as shown in Figure 3-26, directly fastens the blade with countersunk head screws. This structure is compact, the manufacturing process is simple, the clamping is reliable, and the size of the cutter head can be made smaller. Its positioning accuracy is guaranteed by the positioning surface of the cutter body, which is suitable for the case where there are requirements for the chip space and the size of the cutter head, such as the hole cutter often adopts this structure.
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