The hottest tool and die hard milling

Tool and die hard milling

generally, people call hard cutting processing of steel materials with machining hardness exceeding 56hrc or strength exceeding RM 2000 n/mm2. In most cases, after pre-processing, the mold or forging die must be carburized or quenched. After pre machining, a certain finishing allowance must be reserved. Especially when machining workpiece with spherical or toroidal shape, hard milling is more important. Hard milling can cut materials with hardness up to 70hrc, and the required surface roughness can only be achieved by hand polishing. This is a very expensive processing procedure. In order to shorten the time required for manual polishing, it is necessary to use a knife edge with a certain geometric shape during milling. For example, in HSC processing, make the surface close to the roughness of the polished surface: the maximum surface quality is RZ1

hard metal milling cutters commonly used in the market are not suitable for cutting within this range. To solve the problem of milling hard materials, some prerequisites must be met. For example, one solution is to use hornds milling cutters made of special cemented carbide matrix materials with unique geometric shapes and corresponding coatings. This means that the tool must have these three important elements. In the manufacturing process of cutting tools, special attention must be paid to the balance between these elements

cemented carbide

cemented carbide materials are mainly made of tungsten carbide and cobalt by powder metallurgy. The wear resistance of the matrix increases with the increase of hardness. When milling workpieces with a surface hardness of more than 56hrc, only cemented carbide tools with a cobalt content of 10% and a particle diameter of less than 0.7mm can be used

conventional isok-m or P cemented carbide tools are not suitable for cutting materials with higher strength. Cemented carbide with the finest and ultra-fine particle size is obviously more suitable than conventional cemented carbide because of its high hardness, ultimate strength and toughness

geometry

among the used carbide milling cutters, only a few can be used for hard milling. From the perspective of machining, many factors of milling cutter play a decisive role in hard milling. The factors that belong to the geometry of milling cutter are: the accuracy and precision of machining in the micron range, and the hornds milling cutter shank must reach the quality level of H5. In particular, the transition between the arc part of the cutting edge of the tool and the auxiliary cutting edge should be smooth without turning points, so as to achieve the maximum cutting stability

cutting hard workpiece materials is very different from cutting traditional soft materials, so it is necessary to design appropriate rake angle, rake angle and wedge angle for hard milling tools

DS spherical, toroidal and micro milling cutters used in hard cutting can only be designed into a double-edged structure. The two main cutting edges of the spherical milling cutter must be smooth without transition. According to the workpiece material and hardness, the hardware includes a streamline equipment equipped with customized mixing head from henegie and a mixed metering equipment from Klaus mafi. The maximum transverse feed of the cutting milling cutter is ap=0.2 mm. At this time, only two edges of the four edge milling cutter are cutting

coating

a hard coating with a thickness of about 3mm can prevent direct wear of cemented carbide. Facts have proved that TiAlN coating has good application effect when the maximum temperature is 800 ℃ ~1000 ℃. Compared with uncoated cemented carbide tools, adding hard coatings can improve the surface hardness of tools and significantly reduce the friction coefficient of high-end paper products relying on imports. The importance of coating is as important as other elements in the three elements - cemented carbide, geometry and coating. Because it is in direct contact with the workpiece material being cut, it must meet its special requirements

tool holder

in order to achieve the best use effect, if hornds milling cutter obtains the satisfactory processing effect, it is necessary to select the appropriate tool holder. The radial runout of every 1mm will reduce the durability of the milling cutter and weaken its performance

slotted tool handle or universal spring chuck is not suitable for hard milling because of its large radial runout. The best effect can be obtained by using hydraulic expansion liner or contraction liner. This is the reason why horn cutters should be used in the manufacture of cutters and moulds, and horn cutters are all designed into a straight cylindrical structure according to din6535ha standard. The additional clamping surface will destroy the accuracy of the tool and affect its performance

cutting

generally, it is possible to cut workpieces with a hardness of more than 56hrc by using HSC processing. The limiting condition is the combined effect of cutting speed and temperature. For HSC, the melting point of the workpiece material must be tested at a suitable cutting speed. Generally, the melting point of the workpiece material is higher than the maximum allowable temperature of the coating, so care must be taken. The best aphorism here is "keep the tool cool"

this means that on the one hand, the contact area with the workpiece must be as small as possible, on the other hand, the cutting process must be completed at a certain speed, so that the cutting edge has no time to heat up beyond the allowable temperature of the coating

it is particularly important to detect the rotating speed correctly. Therefore, it must be based on the actual effective tool diameter. In the case of transverse feed rate but its disadvantage is that the energy density is low, ap=0.1 mm, the actual effective diameter of a ball end mill with a diameter of 6 mm is 1.54 mm. In order to make the cutting speed reach 200m/min, the rotation speed must reach 41000 rpm

the chips produced during processing and the heat carried by the chips must be eliminated as soon as possible. The best way is to blow compressed air directly to the cutting edge through the spindle. According to different workpiece materials, compressed air can carry a small amount of lubricating oil. As shown in Figure 4, a workpiece with a material of 1.2343 and a hardness of 56hrc can be processed with a small amount of lubricating oil to obtain better surface quality, because chips will not adhere to the cutting edge. For hard cutting, emulsion must not be used. Just a drop of water may cause a sudden change in temperature and decompose the tool into a single component. Micro cracks in cemented carbide caused by sudden temperature changes will lead to the cracking of cutting edges. In the case of HSC processing, depending on the tool diameter and speed, these fragments may have the energy equivalent to bullets fired from light weapons

application

HSC milling, which was first developed for graphite cutting, not only means high speed and large feed, but also has a wide range of applications under the joint action of many factors