Application of the most efficient cutting technolo

2022-08-14
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The application of high-efficiency cutting technology in mold processing

mold has a unique and important position in the research and development, innovation and production of manufacturing products, which makes the mold manufacturing ability and level become an important symbol of national innovation ability. In the forming and manufacturing of modern dies, due to the increasingly complex shape design of dies, higher requirements are put forward for die processing technology, that is, to ensure high manufacturing accuracy and surface quality, and to pursue the beauty of the machined surface. On the other hand, with the process of globalization, the international competition in the manufacturing industry has become increasingly fierce. In order to remain invincible in the competition, many enterprises are committed to "reducing costs", "shortening delivery time" and so on. High precision and high efficiency machining of molds has become an important goal of mold industry. Efficiency is the most important contradiction among the many contradictions faced by the mold manufacturing industry in the world today. Practice has proved that only through the continuous pursuit of efficiency can we deal with other contradictions economically and effectively. Therefore, in the development of modern mold manufacturing technology, efficiency has been pushed to the most prominent position. High efficiency cutting technology has become the mainstream of modern mold manufacturing technology, which is an inevitable development trend

as a term in die application - "high speed cutting (HSC)" actually means two different aspects. First of all, it means that the finish machining at high spindle speed and ultra-high feed rate ensures that the surface finish after machining is good enough to significantly reduce, or even eliminate the auxiliary manual finish machining on the bench. In addition, the term also refers to heavy roughing at a high metal removal rate. Therefore, high-speed cutting is one of the means of efficient machining. More importantly, high-speed cutting can lead to process substitution, thereby simplifying the production process. Using high-speed hard milling instead of EDM in mold manufacturing is a typical example of ten potential suppliers to carry out scheme design and selection. Hardened workpieces can be processed into finished products by rough milling and high-speed fine milling under one clamping. This also reflects that the application of high-speed hard milling has created conditions for the integration of cad/cam/hpc in mold manufacturing. High speed hard milling technology has undoubtedly brought a major change to mold manufacturing technology

however, high efficiency cutting (HPC) is not only the increase of speed, HPC milling is described as a milling process that can meet the requirements of improving metal removal rate. Q=ae is available for material removal per unit time of milling × ap × vf/1000=ae × ap × fz × z × N/1000 (cm3/min). The material removal rate that the milling cutter can achieve has become an important index to measure the machining performance of the milling cutter. FZ is one of the important parameters, which is related to many factors, such as the chip thickness of the material being cut. In order to obtain the best chip thickness, different cutting parameters are needed when machining a specific kind of workpiece material. The feed rate per tooth that needs to be input when preparing CNC machining program can be calculated by the following formula: FZ = h/sin κ。 For a certain kind of workpiece material, the given value of H has a numerical range, in which the smaller value is the chip thickness at the starting point of cutting. When milling aluminum or non-ferrous alloys on a machining center with a machine power of 50HP, the recommended chip thickness range is h=0.051 ~ 0.076mm; When processing stainless steel, aluminum alloy and heat-resistant superalloy, the recommended chip thickness range is h=0.076 ~ 0.152mm; When processing steel, cast iron and ductile iron, the recommended chip thickness range is h=0.152 ~ 0.254mm. If the chip thickness is greater than the recommended value, there is a risk of blade overload and cutting edge collapse

a way to improve the bearing capacity of the blade is to increase the size of the blade, such as increasing the thickness to improve the strength of the cutter teeth. The vertical blade structure of the milling cutter changes the plane section of the blade that usually bears the load to the vertical section, without changing the size of the blade, but only changing the installation direction of the blade to increase the bearing capacity of the blade, such as helitang vertical spiral edge milling cutter

starting with the chip thickness h value to improve the cutting efficiency is an effective idea of efficient cutting in recent years

chip thickness h=fz × sin κ It is related to the main deflection angle of the tool. For straight edge milling cutter and end milling cutter, the main deflection angle is certain, and the chip thickness is also constant. With the exception of circular milling cutter, the main deflection angle of the circular cutting edge at each point is variable. When cutting with circular edge, for example, if the chip thickness is 1 at 90, it is 0.94 at 70, 0.87 at 60 and 0.71 at 45. The chip thickness cut by the round blade will increase with the increase of cutting depth. Therefore, the average chip thickness HM can be used to represent the cutting thickness of the round blade. For different types of workpiece materials, the typical HM value selection range is the same as the above H value selection range

compare the cutting condition of a round blade with that of a 90 blade. If the two blades use the same cutting depth and feed per tooth for cutting, the amount of chip they cut is also exactly the same. However, if the cutting depth is 1/2 of the inscribed circle of the round blade, the chip thickness of the round blade will be reduced by 29%, because the cutting edge of the round blade radially connected with the workpiece is longer. In other words, if the amount of chips cut by the round blade and the 90 blade is equal, and the chip length produced by the round blade cutting is about 50% longer than the 90 blade, the chip thickness cut by the round blade is bound to be significantly reduced. At this time, if the feed rate remains unchanged and the cutting depth is reduced to 25% of the circular blade of the milling cutter, the chip thickness cut by the circular blade milling cutter will be reduced by 50% when the chip amount is equal. In order to improve productivity by thinning the chip thickness, the maximum cutting is selected as 2 The measurement depth of static bending strength and elastic modulus shall be 20% - 25% of the inscribed circle of the circular blade

because the chip thickness decreases with the shallower cutting depth, in order to obtain high machining productivity, it is necessary to compensate for the smaller cutting depth by increasing the feed rate. Whether using a round blade or a milling cutter with a small main deflection angle, the chip thinning effect can be used to achieve high feed rate milling

therefore, when determining the feed rate per tooth entered into the CNC machining program, the variables average chip thickness HM and the main deflection angle are κχ Substitute into the calculation formula fz=hm/sin κ The feed rate can be greatly improved

an example of using axial thinning technology: this task involves rough machining of P20 die steel with width of 1500mm, length of 1500mm, thickness of 430mm and hardness of hrc36 ~ 40. In the design of the die, more than 2000kg of material needs to be removed during rough machining. In order to complete this heavy-duty rough machining task, it requires a lot of time and resources. At first, a round blade milling cutter with a diameter of 4in (1in=25.4mm, the same below) is used for rough machining. Each cutting edge of the blade can only be processed continuously for about 15min. For hardened P20 tool steel, the processing parameters are cutting depth of 1mm and feed speed of about 1000mm/min. Moreover, this rough machining tool has a large tip arc radius, which means that the finishing tool will eventually encounter more processing volume. The solution is to use D100 profiling milling cutter. Using the D12 blade of ic908 brand, the feed speed of 1650mm/m was obtained at the speed of 450r/min and the cutting depth of 1.5mm. When using this milling cutter, the blade life of each cutting edge is 1H, which is 4 times of the original. But this is still unsatisfactory. Later, iscar's feedmill UFO milling cutter was used. This series of cutters used a triangular blade with a special shape, which can withstand a feed of up to 3.5mm per tooth. The triangular blade uses a large arc radius, and the shape of the cutting edge makes the tool run at a high feed speed, with a large amount of cutting per tooth. In addition, the blade is designed with a boss at the bottom, which can be installed in the matching hole on the blade base. This enables the blade to withstand higher cutting forces and operate at a higher feed rate than normal. With this design, the blade is clamped more firmly, and therefore most of the stress normally acting on the clamping screw can be released. Therefore, the cutting force acts on the spindle along the axial direction, which helps to provide stability even if there is a long overhang during machining. When machining, the overhang on the spindle exceeds 203mm, use d63mm feedmill, the cutting depth is 1mm, and operate at the speed of 800r/min and the feed speed of 6350mm/min. Thin cutting with small main deflection angle enables each tooth to withstand higher feed

the thin cutting technology with small main deflection angle can also be used in other milling cutters for mold processing, such as octagonal milling cutter with a feed of 3.0mm per tooth, transformer milling cutter with a feed of 1.0mm per tooth and bull nose cutter with a feed of 1.5mm per tooth

this high feed technology is not only used in special feedmills, but also in the most conventional indexable end mills. For example, iscar can be installed on the high feed milling inserts of apkt10 and adkt15 of conventional end mills. The design concept of this multi edge large feed fillet cutter is to reduce the cutting edge size within the limited tool outer diameter according to the previous edge number design method, but will not reduce the edge strength. Set the main cutting edge radius of the blade of the large feed fillet end mill to R8. Compared with the round blade with the same radius of R8, it has the same edge strength, but it minimizes the blade area. For example, adkt1505r8t-ff can feed 1.5mm per tooth, which is 5 ~ 10 times that of ordinary milling cutter adkt1505pdr

changing the chip cross section can also reduce the cutting force. The deep cavity processing of the mold is often troubled by vibration problems. The tool uses a large overhang to process the deep part, and its rigidity is inversely proportional to the fourth power of the overhang length. The main constraint of the processing efficiency is the processing vibration, so the tool walking speed must be reduced. By changing the shape of the chip, the cutting speed can be increased with the chip cross-section unchanged, or the cutting resistance and power consumption can be reduced by 15% - 30% with the same metal removal rate

the wavy edge of the circular blade of iscar air fire wheel milling cutter divides the long chips into chips, reducing the cutting force, so that milling has a huge impact on the plastic and plastic waste recycling industry at the same time. The cutter can also cut stably and reliably under the condition of 10 times the length diameter ratio. At the same time, the broken chips are easier to be discharged in the deep cavity, avoiding the entanglement of long chips to processing and the possibility of being cut again. Specially designed for mold industry, serrated blade is used for deep cavity machining, with high tool stability, smooth chip removal and small cutting force

it can be seen from the above that the focus of HPC is to optimize the cutting efficiency to obtain the maximum material removal rate. Unlike HSC, HPC usually controls the spindle speed to a certain extent, which not only produces a large cutting torque and power, but also allows a large feed and a certain cutting depth. HPC is also different from the traditional Dayu, which can produce parts with high gloss surface in the one-step production cycle. Under the large allowance cutting mode, the tool fully cuts into the material, while HPC only uses a small part of the effective diameter of the tool to cut, leaving room for improving the feed rate and material removal rate. Therefore, HPC is the key technology value that determines the performance potential of a processing process, which can be increased by 200% - 500% compared with traditional processing technology. A broader explanation is that the term HPC also means optimizing the whole processing process chain, with the goal of reducing production costs by 10% - 30%. (end)

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