This article describes turning tools.
(This article is selected from Chapter 3, Section 3 Turning Tool of "Machining Characteristic Operations and Practical Cases")
(2) Use of indexable turning tools
Although practice at home and abroad has fully proved that the indexable tool is an advanced tool, but only by mastering its performance and using it correctly and rationally can we maximize its strengths and avoid weaknesses, and achieve good benefits. The promotion of indexable tools is to improve the quality of the tool on the one hand. The quality of design and manufacture and the expansion of varieties are the foundation. On the other hand, it must be used correctly and reasonably.
1. Cutting force clamping and mechanical clamping of the insert
The indexable insert is fastened in the tool groove with a clamping element, the purpose of which is to press the insert against each positioning surface - side and bottom surface, to ensure accurate position accuracy of the tool tip, it is not entirely dependent on the clamping element to bear the cutting force , The correct and good design should ensure that the total cutting reaction force always presses the insert against the positioning surface during the cutting process.
Figure 3-27 The force of the blade in the intersection plane. FO is the component force of the cutting reaction force in the orthogonal plane. The included angle with the cutting plane Ps is ψ, and the included angle between the bottom surface of the insert and Ps is ω. When the insert has no overhang Δa, the insert is not affected by the FO force. The condition for flipping away from the bottom surface is: αo<ψ<ω.
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Figure 3-27 The force of the blade on the orthogonal plane
In general, ψmin=20° will reach the maximum value (ψmax=65°) after the average thickness of the cutting layer is small (hD<0.03mm) and the cutting edge is passivated, that is, ψ=20°~65°. Obviously, The above-mentioned clamping condition formula of cutting force is easy to satisfy. Generally, the insert of indexable tool should protrude from the cutter body for a distance Δa (the value is generally about 0.5mm). The distance Δb from the cutter body should not be too large (Δb=1.4m or so is appropriate), so as to ensure the clamping force of the cutting force. Figure 3-28 shows the force on the insert in the base plane, and the angle θ between the thrust FD in the cutting layer dimension plane and the feed plane is determined by the formula tanθFp/Ff. The value of θ angle has the greatest relationship with the main declination angle kr, the larger kr is, the smaller θ is. In addition, the tool nose arc radius, secondary deflection angle and edge inclination angle are also greatly affected. The actual θ angle is always larger than the angle between the orthogonal plane po and pf. When kr is 90°, the θ angle is the smallest, but generally It is also above 12°, and the pressure center is not on the tip of the tool, but at the M point 1/2ap away from the tip of the tool. Therefore, the two commonly used typical structures shown in Figure 3-28, in the base plane The cutting force component still contributes to the clamping of the insert, clarifying the concept of cutting force clamping. Pay attention to two points during use: first, the clamping element is mainly to fix the blade on the positioning surface, so do not use too much force when tightening, so as not to damage the blade and the clamping element; Each positioning surface should be close to each other, without gaps, chips and other sundries. During use, the clamping components may become loose due to vibration and other reasons, and attention should be paid to timely inspection.
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Figure 3-28 The force of the blade in the base surface
2. Selection of tool nose arc radius rε and tool tip grinding
Due to the characteristics of the geometric angle of the indexable turning tool, the general secondary deflection angle k′r is relatively large, so the radius of the tool nose arc has an important influence on the feed rate and the roughness of the machined surface. In order to make the machined surface The roughness value should not be too large, the maximum value of the feed f should be less than 3/4 of the radius rε of the tool nose arc, and the rε of the indexable turning tool should take a larger value. On the one hand, a large feed rate can be selected to improve productivity, and on the other hand, the feed rate can be varied within a wide range to obtain a better chip breaking effect. If the rε value is small, the allowable value of the feed rate f is also small, especially when processing workpiece materials with better toughness, it is difficult to break chips. The arc radius of the tool nose also has a significant impact on the chip breaking area of the chip breaker. According to relevant information, when the same turning tool has the same geometric parameters, chip breaker parameters, cutting amount and workpiece material, only the tool nose arc radius There is a small change in rε, and the chip breaking area has a large change. It is an important technology to use indexable tools correctly to select or grind a reasonable tool nose arc radius according to the actual processing situation. The general principle is still to choose a larger one for rough machining. rε=0.5~2.0mm, smaller for finish machining, rε=0.2~0.5mm, in addition, the transitional edge, wiper edge and other cutting edge grinding techniques successfully applied to welding turning tools can be applied to turning On the turning tool, because these do not affect the positioning and clamping of the blade, it is feasible and allowed to sharpen the tip of the tool. The user should work hard on the grinding of the tip of the tool and make a fuss.
3. Grinding of the edge area
It is as important to choose the section type and parameters of the edge area of the tool reasonably as to choose the material of the tool correctly. As the saying goes, "one line is worth a thousand gold". At present, some blades sold on the market have not been well passivated. Moreover, the type and parameters of the section of the cutting edge area vary depending on the cutting tool material, workpiece material and actual processing conditions. Therefore, grinding the edge area according to the actual processing conditions is another important technology in the popularization and application of indexable tools. When observing the edge with a microscope, it is often found that there are tiny cracks, which will become cemented carbide, etc. The starting point of chipping and cracking of brittle tool materials, which can be carefully ground and passivated to eliminate cracks can greatly improve tool life. The basic principle of reconditioning is that the harder and more brittle the tool material or the higher the hardness and strength of the part material, the greater the grinding parameters (bγ1, γ01, rn) of the tool. Brittle materials such as cemented carbide do not require high-speed Steel knives have sharp blades, and well-pressed blades can be used directly. In some cases, good results have been achieved for this reason. In addition, the larger the feed rate, the larger the grinding parameters should be. The chamfering width bγ1=(1-2)f has also achieved good results. During the cutting process, the profile parameters of the edge area will change due to wear, so it is very necessary to pay attention to grinding and grinding during use.
4. Blunting standard VB for indexable tools
If the blade needs to be reground after use, it is generally advisable to take VB=0.3mm, which can make the life of the blade the longest. If the blade is used for one time without regrinding, the value of VB can be larger or VB≤Δh (see Figure 3-29), Δh is the height of the blade relative to the sipe, because the back is the side positioning surface of the blade, and it is not a surface contact with the side of the sipe but a line contact (or a small area near the line). When VB>Δh, it will affect the accurate positioning and clamping of the insert in the tool groove after indexing.
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Figure 3-29 Insert contact with the side of the flute
At present, the general design takes Δh=0.5mm. In fact, for larger-sized indexable turning tools, Δh should be larger, so the VB value can also be larger.
The rational use of indexable inserts is an important issue in the promotion of indexable cutting tools. The first reason is to formulate reasonable blunting standards and life spans. It is uneconomical to transpose at the right time, too early or too late. The second is the regrinding and utilization of indexable blades. According to the situation in our country, it is economically cost-effective to regrind and utilize blunt blades. This needs to be solved: ①Recycling and management of blades, ②Regrinding technology and equipment, ③Knife The body is serialized to adapt to the use of large blades after changing to small blades.
5. Cutting amount and chip breaking of indexable turning tools
The maximum value of the feed rate f of the indexable turning tool should not exceed 3/4 of the radius rε of the tool nose arc, and at the same time, f should also be greater than three times the radius rn of the blunt circle of the cutting edge and the negative chamfer width bγ1 (0.3~ 1.2) times, the choice of the amount of back engagement ap should make the length of the main cutting edge (L= ap /sinkrcosλs) not greater than the length of the edge of the blade (1/2~2/3), due to the change of the indexable tool The auxiliary time of the cutting tool is shorter than that of the welding turning tool, and the wear resistance is slightly better than that of the welding turning tool. Therefore, the cutting speed vc of the indexable tool should be slightly higher than that of the welding tool (generally about 10% higher). This is beneficial for improving productivity and reducing costs. Unlike welding tools, the chip breaker of the indexable turning tool is pre-processed, and the chip breaker shape and parameters are certain. When processing a specific part material, the chip breaking range is certain, and the appropriate chip breaking groove shape formula and parameters can be selected according to the part material and the specific processing conditions. After the chip breaking groove and parameters are determined, it mainly depends on the feed rate. The change of the control chip breaking, when vc increases and ap increases, the feed rate corresponding to the reasonable chip breaking range increases.
