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Hardware knowledge: high speed machining skills of hardened molds

high speed machining of hardened molds: high speed machining process of hardened molds. Some people have not mastered this technology, but as long as they follow some basic guidelines, they can apply this technology well, give full play to its advantages and receive good results. The author of this paper comprehensively introduces the main technological factors: machine tools, cutting tools, tool holders and programming

there are three main processes for mold processing: soft processing, hard processing and electrical processing. According to the structure and hardness of the mold, which method or combination of them is used is decided

when the mold is large and deep, soft machining is used for rough machining and semi finishing before quenching, and hard machining is used for finishing after quenching; Small and shallow moulds can be milled at one time after quenching. If the mold wall is very thin and the mold cavity is very deep, EDM is adopted. 1、 Selection of cutting tools: When Machining Hardened molds, it is important to select milling cutters correctly. There are three basic types of milling cutters: ball end milling cutter, fillet flat end milling cutter and sharp angle flat end milling cutter. Usually, the preferred tool is ball end mills. The large arc shape of the ball head can disperse the cutting force and cutting heat acting on the blade when machining hardened metal at high speed, and the machined surface is closer to the desired shape

if the die cavity has a large and flat bottom, then after rough machining with a ball end mill, a fillet flat end mill should be used, which has a worse dispersion effect on force and heat than a ball end mill. The flat end milling cutter with smooth angle is used to process the parts requiring back chipping. The back chipping is carried out after the ball end milling cutter or fillet flat end milling cutter has cut as much allowance as possible. The smooth angle of this kind of cutter is easy to collapse

the rigidity of the cutter is very important. In order to increase the rigidity of the small-diameter milling cutter, the diameter of the shank is much larger than the diameter of the cutter, so as to improve the machining finish and prolong the service life of the cutter; The overhang length of tool clamping should be as short as possible

secondly, the shape of the tool handle should adapt to the structure of the mold. Generally, there should be a half degree gap between the milling cutter and the side of the workpiece. For example, if the side of the workpiece is a 3 ° inclined plane, the shape of the tool handle should be made into 5/2 ° to obtain the maximum rigidity. If the side of the workpiece is a 90 ° straight face, the tool handle should adopt a thin neck structure. 2、 Reduce cutting heat: too much cutting heat will deform the workpiece and reduce the machining accuracy. One way to reduce the heat is to control the spacing of each tool

for rough machining, the tool spacing s should be equal to 25% - 40% of the diameter of the milling cutter. For finish machining, the tool spacing can be calculated according to the given tool mark height H

the size of the cutting distance determines the length of time that each cutting edge participates in cutting in each revolution, or the length of cooling time that does not participate in cutting, so it determines the amount of heat accumulated in the tool. The large distance between the tools, the cutting time of the blade in each revolution is more and the cooling time is less, which makes the heat accumulate continuously and the tool temperature rise; On the contrary, a small distance between knives can limit the generation and accumulation of heat. Therefore, by adjusting the distance between the cutting tools, the heat and the temperature of the tool can be controlled, and the cutting speed can be further increased so that the cutting temperature is still lower than the maximum temperature that the coating can withstand

on the other hand, you can also choose a new coating, so that the tool can withstand higher cutting temperature, that is, use higher cutting speed. For example, the maximum workpiece temperature of TiCN coating is 400 ℃ (720f), while TiAIN is 800 ℃ (1 exclusion method: take out the damping pin 470f). Because of its good heat resistance, TiAIN coating is more suitable for high-speed machining of hardened molds

cutting speed and feed rate are also the key factors to control heat. Thick chips take away more heat and leave less heat to the workpiece. If the chip is too thin, the pressing and friction of the tool on the workpiece will cause the workpiece to heat up. In addition, the large cutting section can prolong the tool life and improve the production efficiency. 3、 Tool durability and clamping: blunt tools must be replaced in time, so how to judge tool wear? Generally, it can be observed with the naked eye: when the tool is blunt, the tool head will turn red during cutting, indicating that the force and temperature have been overloaded. At the beginning, this burning red color only appears at the tip of the knife and where the amount of material removed is large, and it is not available at present. When it is blunt, it can be seen that the part of the knife head continues to be red. In order to make it easy to see this red color, turn off the lighting of the machine tool during observation

the correct clamping of milling cutters is very important for (4) the maximum load elongation and failure elongation in the processing of hardened dies, which involves the tolerance of the tool handle, the fit between the tool handle and the tool holder, the diameter jump after installation and other factors. The proper fit tolerance between the tool handle and the tool holder can ensure the rigidity, accuracy and consistency of the clamping. For this reason, the manufacturing tolerance of the tool handle should be - 0.0025mm to - 0.005mm, and the structure should be suitable for heat shrinkable clamping; The tolerance specified in the standard is as high as -0.0125mm, which will lead to excessive radial runout. In addition, the roundness of the tool handle should be kept at least ± 0.00625mm

the radial runout after clamping causes uneven cutting load. Some blades have a large load, while others have a small load when the blade body is separated from the dynamometer. The latter is the most taboo in hardening die processing. The vibration caused by the radial jump will cause the chatter of the machine tool and the edge collapse of the tool. Therefore, the radial jump of the tool should be strictly controlled, and attention should be paid not to polish the handle, because the polishing of the handle will reduce the reliability of clamping. 4、 High performance machine tools: when processing hardened molds efficiently, the requirements for machine tools should not be ignored. Although hardened workpieces can also be processed on a backward low-speed machine tool, the efficiency is very low. If the spindle speed of the machine tool is low, its feed speed is correspondingly low. Therefore, good results can be achieved by using a machine tool with good rigidity and high precision

the CNC system of mold processing machine tools needs to process a large amount of data. When considering purchasing new machine tools, we should pay attention to the performance of the CNC system. At high feed speed, the system should have high acceleration and deceleration compensation ability. The machining efficiency of the machine tool is also related to the speed of data processing, the response speed of the servo system, the speed of interpolation, the resolution of the feedback system and the quality of moving parts. 5、 Key points of programming: when machining the mold, the way of cutting in the tool, that is, the force condition of the tool, depends on NC programming. Therefore, programming is one of the keys to efficiently machining hardened steel. Spiral interpolation should be adopted for the path of cutting tool into the mold, so the cutting process is more stable. When cutting from the side or spiral is not allowed, oblique wave cutting should be adopted to avoid axial cutting. The programming also determines the size and cutting depth of the radial tool path

in a word, in order to realize the efficient processing of hardened steel, we need to reasonably apply the machine tools, cutters, tool holders and programming technology that have been used for a long time, and take every factor into consideration to achieve the desired effect

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