The hottest dry cutting tool and its design

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Dry cutting tool and its design

1 Overview

with more and more stringent environmental protection laws and regulations, dry cutting is more and more widely used in automobile and small and medium-sized manufacturing industries abroad. At present, nearly half of enterprises in Western Europe have adopted dry cutting, especially in Germany. Japan's "production equipment market" magazine selected the top ten domestic large and medium-sized enterprises in Japan's factory automation industry in 1997, including "the concretization of processing technology for environmental protection". It can be seen that dry cutting technology will become one of the development directions of machining technology in the future

dry cutting can not be realized simply by eliminating cutting fluid. Meaningful and economically feasible dry cutting requires careful analysis of specific boundary conditions and mastering the complex factors of dry cutting, and provides the required technical data for the design of dry cutting process system. The working conditions of dry cutting tools are poor and their service life is shortened. Therefore, it is necessary to reasonably select the tool material and coating, and design reasonable tool geometric parameters. This paper analyzes the characteristics of dry cutting, puts forward the specific requirements of dry cutting for cutting tools, and discusses the design points of dry cutting tools

2. Requirements of dry cutting on cutting tools

dry cutting is to create the same or similar cutting conditions as wet cutting by pressing the "OK" key without cutting fluid. Therefore, higher requirements are put forward for cutting tools

tools should have excellent high temperature resistance

current tool materials, such as new performance cemented carbide, polycrystalline ceramics and CBN, have sufficient high temperature wear resistance and can be used under dry cutting conditions. In addition, the most effective method is to coat the tool. The function of the coating in the cutting process is like adding a force and heat isolation layer between the tool and the chip, which can prevent the heat from being transferred to the tool matrix, so as to ensure that the cutting edge of the tool is sharp, so that the hardness of the tool head will not decline quickly, and its high temperature resistance can be greatly improved. Production practice has proved that although the heat generated in the cutting area can not be completely discharged with the chips in dry cutting, as long as the tool geometry and cutting parameters are reasonably selected, most of the cutting heat can be discharged with the chips and good machining results can be achieved

the friction coefficient between the chip and the tool should be as small as possible

during dry cutting, the high temperature in the cutting area will produce chemical instability, the friction between the tool and the chip will increase, and the chip removal speed will slow down, which is very easy to produce chip buildup and aggravate tool wear. Therefore, it is necessary to reduce the friction coefficient between the chip and the tool. The most effective method is to coat the tool surface and design the tool structure with good chip removal. For example, TiAlN coated taps with large helix angle are dry cutting tools with this performance

the structure of the tool should be able to remove chips quickly

in dry cutting, in order to ensure the processing quality of the workpiece and the service life of the tool, the tool is required to discharge chips quickly, so that the heat transferred into the workpiece and the tool is greatly reduced

tools should have higher strength and impact toughness

select tool materials suitable for dry cutting, such as ultra-fine grain cemented carbide, ceramic and Cermet Tool Materials, diamond and CBN, and also apply appropriate coatings on high-speed steel and cemented carbide substrates, such as TiAlN coating, TiCN coating, tialn+mos2 coating, diamond-like carbon (DLC) coating, etc. Diamond and CBN can be used for dry cutting cast iron, hypereutectic aluminum alloy, various steels and titanium alloys

3. Design points and application of dry cutting tools

3.1 design points of dry turning (milling) tools

the main failure reason of dry cutting tools is usually crescent wear, which is caused by the temperature rise in the contact area between the tool and the chip during machining. Therefore, the cutter should usually have a large rake angle and blade inclination. However, when the rake angle increases, the strength of the cutting edge will be affected. At this time, appropriate negative chamfering or rake face strengthening units should be used to make the tool tip and edge have sufficient materials and a more reasonable way to bear the cutting heat and cutting force, slow down the impact and crater expansion, so that the tool tip and edge can maintain sufficient strength in a long cutting time. In addition, with large nose rake angle and nose rake angle, the wedge angle of the tool edge can be increased, the contact length between the tool and the machined surface can be reduced, and the wear and damage probability of the flank can be effectively reduced

using the geometric blade as shown in Figure 1 can greatly reduce the contact area between the tool and the chip, so that the chip can take away a lot of heat. Figure 2 shows the processing process of dry cutting and ordinary turning and milling. It can be seen from the figure that when the chips flow through the rake face of the ordinary blade, due to the large contact area, more heat is transferred into the tool, resulting in crescent depression wear and reducing the tool life; With the blade shown in Figure 1, there are reinforcing edges on the front face of the tool, the contact area between the tool and the chip is also greatly reduced, most of the heat is taken away by the chip, and the cutting temperature can be reduced by about 400 ℃ compared with the ordinary blade. At the same time, the shear angle is also increased, which significantly improves the service life of the tool, and a higher 3 Measuring the cutting speed of the beam displacement improves the production efficiency. If the normal cutting speed is maintained, the tool life can be increased by 3 ~ 4 times

Fig. 1 geometry of dry milling insert

Fig. 2 Comparison of processing process between dry cutting and ordinary cutting

for ceramic tools, due to their great brittleness, T-shaped or double T-shaped edges can be selected, or grinding, or a combination of several methods. As recommended by American valenite company, 0.5 × The 30 ° T-shaped edge surface is used for al2o3+tic blade, dry processing hardened steel, and try to use large residual deflection angle. According to different blade geometries, the tool offset angle during semi precision turning is -5 ~ 30 °, and the commonly used blade geometries are square, triangle and 80 ° diamond. Tensile test and tensile behavior of polymers for CBN tools, the chamfer is too large. When machining hardened steel, high temperature will be generated at the contact between the tool and the workpiece, causing rapid wear of the cutting edge. Therefore, generally, large chamfering is not adopted, and the cutting edge can adopt inclined plane or rounding and negative rake angle to maximize the residual deflection angle. The recommended value range is: (15 ° ~ 25 °) × 0.25mm T-shaped chamfer, and then 0.01 ~ 0.03mm grinding

3.2 key points of dry thread machining tool design

at present, when tapping with a tap, the emulsion containing organic chloride to resist extreme pressure has the best effect. However, organic chlorides cause great environmental pollution. In order to reduce environmental pollution, Germany emuge thread tool factory has developed an ecologically beneficial tap, which can be tapped on a wide range of materials without cutting fluid. In order to complete dry tapping, it must be considered in the tap parameter design:

there is a small friction resistance to obtain threads with accurate size and small surface roughness value

the groove design shall make the chip curl easily and leave the screw hole freely

coat the tap surface to obtain an ideal surface state, reduce cutting stress and protect the tap

there are two sizes of this tap, namely, M5 ~ M10 reinforcing handle size series and M12 ~ M20 size series

the groove type of screw tap for dry cutting steel thread is usually spiral groove, and the spiral angle is different when machining through-hole thread and blind hole. For example, when machining blind hole threads, the large helix angle of 35 ° is often used; When the hole depth is greater than 2 times the tap diameter, a small helix angle can be used, usually 5 °. At this time, the tap cutting length is c/2 ~ 3 teeth. When dry cutting cast iron thread, the tap groove type is straight, whether it is through hole or blind hole, and its cutting cone length is c/2 ~ 3 teeth. For small-diameter taps, in order to improve the strength and stiffness, the groove can also be designed into special shapes, such as slottless extrusion Taps. Slottless extrusion taps are very effective for machining small diameter threads or threads on materials with large plasticity. Dry cutting taps usually need coating treatment, and the commonly used coating is tin or TiCN

Fig. 3 Comparison between dry and wet processing

processing conditions: M6 × 1-g7p, through hole thread, workpiece material: zinc steel plate,

thread length: 3.2mm, bottom hole diameter: f5.55mm, cutting speed: 15m/min

test condition: M5 × 0.8 tap, workpiece material: pure aluminum Ly-2, thread hole shape: blind hole,

thread length: 11mm, bottom hole diameter: 4.2mm (cutting), 4.5mm (extrusion)

cutting speed: 15m/min (cutting), 10m/min (extrusion), machine tool: ag-32

in addition, the author has discussed the process of machining threads on A3, 45 steel and other sheet parts (thickness less than 2mm), and adopted a new bottom hole forming process, The dry cutting and thread extrusion processes have been successfully applied. The specially designed and manufactured bottom hole forming tools and coating extrusion taps can be used to complete the processing of bottom hole and thread at the same time, avoiding the trouble of welding nuts or designing and manufacturing special die punching in the original process, and solving the thread processing process of sheet metal parts that has plagued the automobile, sheet metal and other industries for a long time, with excellent processing results

4. Conclusion

on the one hand, it is necessary to select reasonable tool materials and carry out appropriate surface coating for tool dry cutting; On the other hand, it must have reasonable tool structure parameters. According to the successful application examples abroad and the research of the author, it is shown that as long as the conditions are properly selected, its dry cutting can be realized under the existing technical conditions in China

dry cutting is an ideal green manufacturing process. Although the application scope of dry cutting is not very wide at present, its research has become one of the current hot spots. The application research abroad is quite extensive, mainly because of the strict requirements of relevant laws and regulations and the optimistic prospect of dry cutting, some successful application demonstrations have promoted the development of dry cutting technology. At present, there are still different views on dry cutting for 209 door closer in China, but from the perspective of development, the application of dry cutting is an inevitable trend

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