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There are many reasons for processing deformation of aluminum parts, which are related to material, part shape, production conditions and so on. It mainly includes the following aspects: deformation caused by internal stress of blank, deformation caused by cutting force and cutting heat, and deformation caused by clamping force.
1 Process measures to reduce machining deformation 1. Reduce the internal stress of the blank. Natural or artificial aging and vibration treatment can partially eliminate the internal stress of the blank. Pre processing is also an effective process method. For the blank with fat head and big ears, due to the large allowance, the deformation after processing is also large. If the surplus part of the blank is processed in advance and the margin of each part is reduced, it can not only reduce the processing deformation of the subsequent process, but also release part of the internal stress after being placed for a period of time. 2. Improving the cutting ability of the tool, the material and geometric parameters of the tool have an important impact on the cutting force and cutting heat. The correct selection of the tool is very important to reduce the machining deformation of the part.
1) Reasonably select tool geometric parameters. Rake angle: under the condition of maintaining the strength of the blade, the rake angle should be appropriately larger. On the one hand, it can grind a sharp edge, and on the other hand, it can reduce the cutting deformation, make the chip removal smooth, and then reduce the cutting force and cutting temperature. Do not use negative rake tools. Back angle: the size of the back angle has a direct impact on the wear of the back cutter surface and the quality of the machined surface. Cutting thickness is an important condition for selecting back angle. During rough milling, due to large feed rate, heavy cutting load and large calorific value, it is required that the tool heat dissipation conditions are good. Therefore, the back angle should be smaller. During finish milling, the cutting edge shall be sharp to reduce the friction between the flank and the machined surface and reduce elastic deformation. Therefore, the back angle shall be larger. Helix angle: in order to make milling smooth and reduce milling force, the helix angle should be as large as possible. Main deflection angle: properly reducing the main deflection angle can improve the heat dissipation conditions and reduce the average temperature of the processing area.
2) Improve tool structure. Reduce the number of milling cutter teeth and increase the chip holding space. Due to the large plasticity of aluminum parts, large cutting deformation in machining and large chip holding space, it is better to have a large radius of chip holding groove bottom and a small number of milling cutter teeth. Fine grinding of cutter teeth. The roughness value of the cutting edge of the cutter tooth shall be less than RA = 0.4um. Before using a new knife, gently grind the front and back of the knife teeth with a fine oilstone to eliminate the residual burrs and slight serrations when grinding the knife teeth. In this way, not only the cutting heat can be reduced, but also the cutting deformation is relatively small. Strictly control the tool wear standard. After tool wear, the workpiece surface roughness increases, the cutting temperature increases, and the workpiece deformation increases. Therefore, in addition to the selection of tool materials with good wear resistance, the tool wear standard should not be greater than 0.2mm, otherwise it is easy to produce chip buildup. During cutting, the temperature of the workpiece shall not exceed 100 to prevent deformation.
3. Improve the clamping method of workpieces. For thin-walled aluminum workpieces with poor rigidity, the following clamping methods can be adopted to reduce deformation: for thin-walled bushing parts, if they are clamped radially with three claw self centering chuck or spring collet, once they are loosened after processing, the workpiece will inevitably deform. At this time, the axial end face compression method with good rigidity should be used. Locate with the inner hole of the part, make a self-made threaded mandrel, insert it into the inner hole of the part, press the end face with a cover plate, and then tighten it with a nut. When machining the outer circle, the clamping deformation can be avoided, so as to obtain satisfactory machining accuracy. When processing thin-walled sheet metal workpiece, it is best to select vacuum suction cup to obtain evenly distributed clamping force, and then process it with small cutting parameters, which can well prevent workpiece deformation. In addition, the packing method can also be used. In order to increase the process rigidity of thin-walled workpiece, medium can be filled in the workpiece to reduce the deformation of workpiece during clamping and cutting. For example, fill the workpiece with urea melt containing 3% 6% potassium nitrate. After processing, immerse the workpiece in water or alcohol to dissolve and pour out the filler.
4. When the process is reasonably arranged for high-speed cutting, due to the large machining allowance and intermittent cutting, the milling process often produces vibration, which affects the machining accuracy and surface roughness. Therefore, NC High-speed machining process can be generally divided into: rough machining - semi finishing - corner cleaning - finishing and so on. For parts with high precision requirements, it is sometimes necessary to carry out secondary and semi finishing, and then finish machining. After rough machining, the parts can be cooled naturally to eliminate the internal stress caused by rough machining and reduce deformation. The allowance left after rough machining shall be greater than the deformation, generally 1 2mm. During finish machining, the finished surface of parts shall maintain a uniform machining allowance, generally 0.2 0.5mm, so that the tool is in a stable state in the machining process, which can greatly reduce the cutting deformation, obtain good surface machining quality and ensure the accuracy of products. 2 In addition to the above reasons, the operation method is also very important in practical operation.
1. For parts with large machining allowance, in order to have better heat dissipation conditions during machining and avoid heat concentration, symmetrical machining should be adopted. If a 90mm thick plate needs to be processed to 60mm, if one side is milled immediately and the other side is milled to the final size at one time, the flatness will reach 5mm; If repeated feed symmetrical processing is adopted, each side is processed to the final size twice to ensure that the flatness reaches 0.3mm. 2. If there are multiple cavities on the plate parts, the sequential processing method of one cavity one cavity should not be adopted during processing, which is easy to cause uneven stress and deformation of the parts. It adopts multiple processing in layers, and each layer shall be processed to all cavities at the same time as far as possible, and then the next layer shall be processed to make the parts bear the force evenly and reduce the deformation. 3. Cutting force and cutting heat can be reduced by changing cutting parameters. Among the three elements of cutting parameters, the back draft has a great influence on the cutting force. If the machining allowance is too large and the cutting force of one-time tool walking is too large, it will not only deform the parts, but also affect the rigidity of the machine tool spindle and reduce the durability of the tool. If we reduce the amount of back knife, the production efficiency will be greatly reduced. However, in NC machining, high-speed milling can overcome this problem. While reducing the back draft, as long as the feed is increased accordingly and the rotating speed of the machine tool is increased, the cutting force can be reduced and the machining efficiency can be guaranteed.
4. Pay attention to the order of cutting. Rough machining emphasizes the improvement of machining efficiency and the pursuit of cutting rate per unit time. Generally, reverse milling can be used. That is to cut off the excess material on the surface of the blank at the fastest speed and in the shortest time to basically form the geometric contour required for finishing. The finishing emphasizes high precision and high quality, and forward milling should be adopted. Because the cutting thickness of the cutter teeth gradually decreases from the maximum to zero during forward milling, the work hardening degree is greatly reduced and the deformation degree of the parts is reduced at the same time. 5. The deformation of thin-walled workpiece during machining due to clamping is difficult to avoid even finish machining. In order to minimize the deformation of the workpiece, the pressing part can be loosened before the finish machining is about to reach the final size, so that the workpiece can be freely restored to the original state, and then slightly pressed, subject to the ability to clamp the workpiece (completely by hand feeling), so as to obtain the ideal machining effect. In short, the action point of the clamping force is best on the bearing surface. The clamping force should act in the direction of good rigidity of the workpiece. On the premise of ensuring that the workpiece is not loose, the smaller the clamping force, the better. 6. When machining parts with cavity, try not to let the milling cutter directly plunge into the parts like a drill bit, resulting in insufficient chip holding space of the milling cutter and unsmooth chip removal, resulting in overheating, expansion, tool collapse, tool breakage and other adverse phenomena of the parts. First drill the cutter hole with a drill of the same size or larger than the milling cutter, and then mill with a milling cutter. Alternatively, the spiral cutting program can be produced with CAM software. The main factor affecting the machining accuracy and surface quality of aluminum parts is that such parts are prone to deformation in the machining process, which requires operators to have certain operation experience and skills.
Original title: process measures and operation skills to reduce aluminum processing deformation! Machining super practical knowledge!The source of the article: WeChat official account: world advanced manufacturing technology forum, welcome to add attention! Please indicate the source of the article.
"I just thought, 'Really?' We have 22 years in this. Do we really want to start another business now?" Christine recalls.
But the hesitation didn't last long. In October of last year, the Benders opened KW Anodizing Ltd., located next door to their RJB Machining business in Waterloo.
They realized the anodizing facility was the best way to protect the viability of their machining business, which makes parts for cameras, lasers and other electronics products for high-tech companies in the area.
The new facility has the capacity to do medium-sized anodizing jobs for RJB's customers, as well subcontracted work from other machine shops in the area. It can do black and clear anodizing, as well as yellow and clear chromate coatings on metal.
Anodizing is a process that involves putting aluminum parts into a bath of electrolyte solution and passing an electrical current through it in order to penetrate the metal with a tough, resistant film.
Unlike paint, the film seeps into the metal and gives it a finished look. It's the sleek black metal look you see around the lens of a camera or on smartphones and music players, for example. Parts for the aircraft industry also are anodized because the process gives the metal more durability under stress.
Of course, anodizing is an entirely different kind of business from machining precision parts. It involves chemical solutions, detergents and dyes and big tanks of boiling water. "It was a bit scary because this was a whole different world for us," Ron says.
It was also risky from a business point of view because setting up an anodizing line required an investment of nearly $1 million. And anodizing represents only a fraction, perhaps a tenth, of what the Benders get for a part, which explains why it made sense for them to contract out that work for so many years.
But the stringent requirements of their customers forced them to act. Small anodizing subcontractors might not have the latest technology to satisfy high-tech customers who are extremely picky about the final look and function of their parts.
"This is our niche," says Ron. "Our attention to detail is so high." If even a little bit of oil gets stuck in a tiny hole or corner because a metal part wasn't cleaned properly, the anodized coating might not be uniform, which could mean scrapping a very expensive part, he says.
"A lot of the parts we make, like the camera parts, have very high cosmetic specifications," Christine says.
There are big specialized anodizing plants with the newer equipment in Ontario, but those facilities want high volume, fast production jobs, she says. "They didn't want to have to baby our parts in the way that our parts needed to be babied." The Benders, who employ 66 people at RJB, added almost 8,000 square foot to their main plant on Colby Drive to move some machining equipment from the building they leased next door. The anodizing equipment, including 18 tanks for the water and electrolyte solutions and racks and filtration equipment, were then installed next door.
The anodizing facility was built with the latest in clean air and water filtration equipment. "We were able to take advantage of the latest technologies," Ron says.
One of RJB's employees, Emil Spatar, was promoted as general manager of KW Anodizing. Originally from Romania, Spatar had already proven himself as a hard working employee, with a sharp eye for detail.
Although anodizing was a big learning curve for him, "he knew more about it than most people here and understands the quality behind it and what it has to look like," Ron says. Three people run the anodizing facility.
It took until March to get everything working to the satisfaction of the Benders. "But now we are getting quality that is actually a little better than expected," Ron says. "We are getting the nice, rich colours." The Benders hope to fill the capacity of the 3,300-square-foot facility by getting contracts from other machine shops. "We think there is enough of a market here," Ron says.
Christine, who handles the books for RJB, says the scrap ratio in the machining business is going down because the company does anodizing in-house, "and that helps in saving costs all along the line." Their machines are not making as many parts over again, which frees them up do more. "We have a faster throughput," Ron says.
Manufacturing was in a deep recession in 2009 when the Benders began making the investment in anodizing. "But sometimes, a recession is the best time to start a business," Ron says.
"We really couldn't afford not to do it," Christine now says. "Even after 22 years in business, we are obviously not done, and to keep a business viable, you have to keep moving forward.
