High efficiency machining hem optimize cutting eff

2022-06-21
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High speed machining (HSM) has become and will continue to be a good machining strategy for aerospace components. The combination of high spindle speed, fast feed rate and small cutting depth can produce the necessary surface finish and precision on the frame parts which often have fine thin wall and base. However, if the aerospace industry has the most important "speed" in the production of parts, then this speed is the speed at which parts are thoroughly processed and ready for assembly. Sandvik Coromant (felraun, New Jersey) believes that when a large amount of materials must be removed quickly, it can help the machining workshop change from HSM mode to a slower and more efficient cutting process. The company calls it efficient machining (HEM)

as the name suggests, the focus of hem is to optimize the cutting efficiency to obtain the maximum material removal rate. Unlike HSM, hem usually controls the spindle speed to a certain extent: it not only generates a large cutting torque and power, but also allows a large cutting depth. Hem is also different from the traditional large allowance cutting. In the large allowance cutting mode, the tool fully cuts into the material, while hem 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

in the production of aerospace components, hem may not replace HSM, and HSM's inherent rapid shallow cutting will still be necessary for semi finishing and finishing some key part features. However, if aluminum and titanium are to be roughened without causing part damage or premature tool wear, the potential benefits of hem are worth considering, especially in the case of processing some aerospace parts, each blank workpiece may have at most 95% final chips, and hem is particularly important

brian Davis, aerospace development manager of Sandvik Coromant, explained at the q&a annual meeting how the integration of hem technology and HSM technology can become the best way to produce aerospace components as soon as possible

1. What is the basic difference between HSM and hem

hsm depends on the machine tool in terms of the possible spindle speed and feed rate, and also depends on the tool for the geometric characteristics of machining with a very shallow cutting depth. Hem strategy focuses more on the whole process and parts, trying to minimize the cycle time

hem and HSM share one aspect, which is the lack of a common set of machining parameters. If you ask 10 mechanics about the definition of HSM's year-on-year growth of 49%, you are likely to get 10 different responses. Sandvik Coromant believes that the spindle speed involved in HSM is greater than 18000 r/min, and the cutting depth is generally within the range of 0.010 "(finish machining, 0.25mm) ~0.100" (rough machining, 2.5mm). On the contrary, the spindle speed of hem may be much lower than that of HSM, but the cutting depth of hem is many times that of HSM. These parameters are always very different depending on the artifact type

2. Which machine tool is most suitable for hem

the most suitable machine tool for hem is the 50n taper horizontal machining center. The horizontal machining center for hem must not only have a maximum spindle speed of 12000~15000r/min, but also provide very high available power and cutting torque

this simple curve shows the relationship between cutting power and spindle speed. In order to carry out efficient machining,

the maximum spindle speed with cutting power and cutting torque competent for the cutting process should be selected

in HSM mode, the main focus is the feed rate and spindle speed, but the cutting torque is as important as other indicators of hem to prevent oil leakage under high pressure, because it is the key to maximize the material removal rate. In order to determine the initial spindle speed of hem process, it is useful to understand the relationship between cutting torque and power within the spindle speed range of the machine tool. At the maximum spindle speed, the machine tool cannot provide the maximum torque; When the speed is too high, the torque begins to decrease. The objective of understanding the above relationship is to determine the maximum spindle speed at which the machine tool can simultaneously provide torque and power for the cutting process. This target speed varies by material and machine

for example, aluminum alloy is relatively soft, and high cutting speed can generally be adopted. However, because the cutting torque always decreases when the spindle speed is too high, a high-power machine tool may stop rotating in the process of cutting aluminum parts. Similarly, cutting titanium alloy requires high torque, but the spindle speed is often much lower than when cutting aluminum parts

hem cutting load is higher than HSM. In addition to providing a rigid and stable platform to control the cutting load, horizontal cutting enables a large number of cutting to fall off from the parts, so as to avoid the phenomenon of poor chip removal and chip being cut again, which is common in vertical cutting. Obviously, very long aerospace components, such as stiffeners, may require large vertical gantry machines. The cooling mode of coolant through the spindle is not only very important for prolonging the tool life, but also helpful for chip removal in the cutting area. In addition, it must be considered whether the machine tool has the ability to transport a large number of chips

3. What are the main differences between HSM and hem in terms of tools

monolithic cemented carbide tools are generally used in HSM, and these tools often have polycrystalline diamond (PCD) coating. Indexable inserts can also be used, However, their diameter is generally not greater than 2 "(50mm) 。 The HSM fast shallow cutting blade is very sharp, providing the possibility of smooth chip removal. These tools may not be suitable for hem because they are not suitable for deep cutting. In some cases, less expensive uncoated cemented carbide tools can provide better material removal rate, and their cutting depth and blade strength are larger, so they absorb larger chip load. Indexable inserts are more commonly used in hem

when hem involves rapid large allowance cutting of materials, do not confuse hem with traditional large allowance cutting or heavy cutting. The goal of traditional large surplus cutting is mostly to make the super thin 3104 can body material of the enterprise assisted by the China Aluminum Institute of cutting tools go through the acceptance of overseas customers, and finally cut into the material completely in terms of cutting length and width, which is generally carried out at a very low feed rate and spindle speed

high efficiency machining can be used to roughen the wall or partition of aluminum parts

one method is to use the overlapping and staggered (on both sides of the partition wall) "step support" cutting method to generate additional support force on the reverse side of the machined surface

many modern indexable insert milling cutters have the optimal cut depth ratio (usually 30~40% of the tool diameter). Feeding at a depth of only a fraction of the tool diameter can greatly increase the feed rate, which increases the material removal rate. This radial cutter not only provides the best feed angle, but also provides enough chip removal space and ensures that the coolant reaches the blade

it is appropriate to start from the optimal cutting depth ratio of the tool, as long as we know that the cutting process is stable. If a setting is weak or a part design is prone to deformation under cutting pressure, it is recommended to start with a half depth ratio

4. Can hem be used for thin wall machining

hsm is widely used in thin-walled parts. Because the cutting amount is very small, it is not easy to cause thin-walled deformation during the cutting process. Step supported milling enables some thin-walled aluminum parts to adopt hem, although the cutting depth is large. When this technique is adopted, the tool moves alternately from top to bottom on the two sides of the thin wall. The cutting depth of the first tool is far less than that of the later tool, so that the material on the back of the cutting point plays a supporting role

in these cases, titanium alloy is particularly easy to deform with low elastic modulus, which makes it rebound to its original position after cutting. Therefore, HSM should be used when machining titanium thin wall. At this time, the speed of the tool passing through the machined surface is very fast, making it impossible for the material to leave the tool

5. Is hem suitable for forgings

hem may be very useful in rough machining of large forgings. For example, a titanium landing gear support beam may be machined from a 2000 pound forging to a 600 pound part. These forgings have large draft angles and serrated fins, and the HSM process takes a particularly long time to remove these defects. The best method is to use hem for rough machining first, and then HSM for semi finishing and finishing, so as to control part deformation and provide good surface finish

participate as early as possible

davis pointed out that unlike other industries, the aerospace industry does not need to produce new aircraft or new important components every year. Aerospace technology is also an example in terms of safety regulations and requirements for process consistency and reliability. For these reasons, many manufacturing methods are locked in the early design stage of parts. The earlier the tool manufacturer participates in the design phase, the more likely it is to use the correct tool from the starting point of the part life cycle, and the greater the long-term return and benefit. (end)

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