With the continuous development of the aviation manufacturing industry, the use of difficult-to-machine materials has increased rapidly, and the contradiction of processing has become more prominent. Aeroengine hard-to-machine materials are generally relatively low in processability. At the same time, the shape of aero-engine parts (such as disc shafts and casing parts) is complex, surface integrity and shape tolerance requirements are high, and the processing difficulty is increased. Therefore, it is important to choose a matching tool to ensure that a qualified part is machined. At present, each tool company is constantly researching new tool products suitable for its processing properties for difficult-to-machine materials.
The following are some examples of how we can solve the problem of cutting difficult parts of the engine by using new tool products in actual work:
Finishing of the inner hole of nickel-base superalloy An engine part is made of GH4169. The length of the machining is 109.5mm and the hole diameter is 166mm. Since the surface runout value of the inner hole is 0.02, the surface roughness is Ra0.8, the requirement is very high, and the material itself is poor in processability. It is difficult to ensure the use of the general blade for finishing, and the jitter value is generally 0.05, often Out of tolerance; and the processing efficiency is also low, the blade is easy to wear.
In order to solve this problem, we have selected the new blade product VNGP160408 S05F from Sandvik Coromant. The insert is a new technology designed to solve the cutting of nickel-base superalloys. The material has finer crystal grains and a 4μm thin coating of CVDTiCN-Al2O3-TiN. According to the product sample, the blade is especially suitable for the finishing of nickel-base superalloys. It has good wear resistance and is suitable for small depth of cut.
The parameters we used during the test were: n = 40 r / min, f = 0.18 mm / r, ap = 0.1 mm. However, the jitter value after machining is still 0.025, and the blade is also worn. Through analysis, we believe that the cutting parameters are too low. First of all, the depth of cut of 0.1 mm is cut on the hardened layer, strictly speaking not cutting but grinding. Moreover, the hardened layer is much harder than the substrate, and of course the blade wears fast; on the other hand, its line speed is too low, which is liable to cause cold welding, resulting in poor surface quality. And the blade is G tolerance, the speed is higher to show the superiority. Therefore, the parameters are increased: n=60r/min, f=0.18mm/r, ap=0.25mm. After machining a few knives, the blade has almost no wear and has a runout value of 0.01. Within the tolerance range, the surface is very good, reaching Ra0.8 or less. The cutting time was reduced by 7 min compared to the original. The use of this new type of blade solves the problem of out-of-tolerance, guarantees quality, and reduces the overall calculation cost.
Five-blade milling cutter for efficient machining of ring parts There is a strict ring piece, the material is GH4133B. The cutting parameters are very low with the general milling cutter, and the tool life is also low. The tool change is frequent and the machine takes a long time. To improve efficiency and reduce machine time, we have adopted Kennametal's new high performance solid carbide end mill VDDE1200 KC633M. This milling cutter has 5 cutting edges for higher metal removal rates. The angle between the blades is not equal and can reduce vibration. The milling cutter is characterized by high efficiency and sufficient chip space. The diameter of the proximal tooth core is small, the diameter of the core of the proximal shank is large, the section is parabolic, and the angle of the blade is not equal, which makes the cutting smooth and reduces vibration, and each groove type is also different.
After the test, we finally adopted the parameters: n=1000r/min, f=200mm/min, ap=4.5mm, ae=6.5mm, and one tool can process 3 pieces. The parameters of the original four-blade tool are only n=300r/min, f=70mm/min, and only one piece can be processed in one knife. In contrast, with this new type of tool, the efficiency is greatly improved.
Processing of large-diameter thin-walled parts Our company's processing of a sub-package part is a ring of 1m multi-diameter, with a wall thickness of 2mm, its beating value is very high, and it is a high-temperature alloy material, it is difficult to guarantee the shape tolerance. Due to the large diameter and thin wall, the blade processing is generally deformed. Moreover, after the deformation, the knife phenomenon occurs, the surface is hardened, and the tool is susceptible to wear.
Through analysis, we believe that preventing deformation during the processing of this part is the main task, which requires the tool to be sharp and cannot produce work hardening. We have boldly used large-angle polishing blades for processing aluminum alloys. This type of blade is made of aluminum. It is also used in the processing of thin-walled parts of high-temperature alloys. We have tested the Sandvik Coromant Blade VBGT160408-W-25 and Seco's VCGT160408F-AL KX. In the process of processing a large surface of the blade, the knife must be changed, and there is a knife mark and the deformation amount is above 0.05, which needs to be processed. There is no need to change the tool in the middle of the polishing blade with large rake angle. Because the sharpness of the tool tip is sharp, the deformation amount is greatly reduced, and the deformation amount is controlled within 0.02, which ensures the geometrical tolerance requirement. In the use of tools, expand your thinking, you can bring good results.
High-precision machining of the face groove has a part made of GH4133. This piece has a face groove, a width of about 10mm, a depth of 28mm, and the groove surface jump value is 0.015, it is difficult to guarantee with the original blade, often out of tolerance, because the general manufacturer's groove cutter positioning method is V-shaped arc surface positioning, side There is a slight turbulence in the edge machining. Although these small turbulences are only in the micrometer range, if the cutting edge is repeated, the cutting edge is in an inappropriate position, which will affect the guarantee of 0.015 pulsation accuracy.
We checked the information and selected Sandvik Coromant new material insert N123H2-0400-0004-TF 1105, cutter bar RE123H25-25B-132BM. The blade and the shank match are T-rail positioning. This T-rail design accurately holds the blade on the body and maintains the position of the cutting edge with high stability without turbulence. We use the slotted knife positioning of the T-rail to effectively solve the problem of over-jumping of the groove surface and ensure the beating accuracy of 0.015. The positioning of this structure is also well applied in the machining of the end face groove of the annular thin-walled member.
Ceramic blade processing cobalt-based superalloy The one-turn package of our company is made of cobalt-based superalloy. There are problems in processing: the processing efficiency is extremely low, the tool wear is serious, and the dimensional accuracy and surface quality cannot be guaranteed. Based on the worn-out blades, we conclude that the tool material used does not match the material being machined. The material to be processed is a cobalt-based superalloy, which is much more difficult to machine than a nickel-based superalloy, with greater cutting resistance and higher cutting temperatures. It is necessary to select a tool that matches the physical, chemical, and especially mechanical properties of the material being processed to ensure processing.
Based on the experience of using ceramic cutting tools to cut the intermediate machine, we use Kennametal Sailong ceramic cutter RNGN120700KY2100 and Sandvik Coromant aluminum oxide vanadium ceramic blade RNGN120700 6065. The effect is very good, not only high efficiency, dimensional accuracy, surface The quality is not bad. When using a ceramic insert for high-speed cutting, the chip shape also changes: from strip crumbs to unit chips. The friction between the chip and the rake face is no longer the main source of cutting force and cutting heat; the elastic deformation of the workpiece material at the flank face is also reduced because the deformation speed can not keep up with the cutting speed, so the friction of the flank face also The reduction is beneficial to reduce the cutting force and cutting heat.
Compared with cemented carbide inserts, the efficiency of machining cobalt-based superalloys with this insert is greatly improved, which is more than 16 times that of the original tool. The dimensional accuracy and surface quality are good, and there is no knife. The original tool is seriously worn and the quality is difficult to guarantee. Sai Aron ceramic tools are more suitable for processing cobalt-based superalloys.
Since we have selected new products and new tools, we have provided reasonable cutting parameters, which not only solves the problem of over-difference of difficult-to-machine parts of the engine, but also guarantees the quality, reduces the wear of the blades, and greatly improves the efficiency. In the future, we will also pay attention to the new tool products developed by various tool companies for the aerospace engine difficult-to-machine materials to solve the cutting problems of our hard-to-machine parts.