CNC aluminum processing deformation "big battle" - practical skills to help you accurate processing

In the process of CNC aluminum machining, accidental deformation is a common and thorny problem. Deformation will not only affect the dimensional accuracy and appearance quality of aluminum products, but also may lead to the product can not meet the design requirements, or even scrap. This has brought huge economic losses to the production enterprises, and also affected the production efficiency and the market competitiveness of the products.

For example, in the manufacture of some precision instruments and electronic products, the dimensional accuracy of aluminum components is very high. If unexpected deformation occurs during processing, it may cause parts to fail to assemble normally, affecting the performance and reliability of the entire product. In addition, deformation may also cause the surface of aluminum products to appear uneven, distorted and other problems, reducing the appearance of the product quality, affecting consumers' willingness to buy.

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Blank residual stress

The blank residual stress is mainly formed by the superposition of stress caused by the non-uniform deformation during the quenching process and extrusion of profiles. During the quenching process, the aluminum alloy will form a large residual thermal stress and structure stress. At the same time, in the extrusion process, due to the uneven stress of each part, it will also produce stress. These stresses are superimposed together to form the blank residual stress.

The residual stress of blank has great influence on machining. Due to the stress inside the blank, during the machining process, when the material is removed by cutting, the stress will be redistributed, resulting in the deformation of the workpiece. This deformation may affect the dimensional accuracy and surface quality of the parts, and may even make the parts unable to meet the design requirements.

Processing stress

The main reasons for the processing stress are as follows:

1. Asymmetry in cutting process: Asymmetry in cutting process will lead to uneven cutting force, resulting in deformation of the workpiece. For example, when the cutting allowance is large, the material removal rate is high, and there is a large processing stress. Moreover, the processing interval is short, so that the residual stress is not released, the residual stress is out of balance on the overall profile, and then cause the workpiece deformation.
2. Poor workpiece rigidity: poor workpiece rigidity will cause uneven cutting and clamping force, resulting in deformation. For some parts with thin walls and poor rigidity, such as aluminum thin-walled shell parts, deformation is more likely to occur during the cutting process.
3. Different processing sequence: different processing sequence will cause residual stress to be released asymmetrically, resulting in workpiece deformation. For example, machining one part first and then another part may lead to uneven stress distribution, which in turn causes deformation.

Tool optimization

In CNC aluminum machining, parts deformation can be effectively reduced by selecting the correct tool parameters and controlling tool wear. Specifically, it can be optimized from the following aspects:

1. Spiral Angle: The spiral Angle should be as large as possible, which can improve milling stability and reduce milling force. For example, in actual processing, the larger spiral Angle can make the cutting process more stable and reduce the deformation of parts caused by excessive cutting force.
2. Front Angle: The reasonable configuration of the front Angle can maintain the strength of the blade, reduce the wear of the sharp edge, ensure smooth chip removal, thereby reducing the cutting force. It is generally not recommended to use a negative front Angle tool, because a negative front Angle will increase the cutting force and increase the risk of part deformation.
3. Back Angle: The size of the back Angle has an important impact on the machining quality and back tool surface wear. In rough milling, the back Angle should be selected smaller, because the cutting speed is large, the cutting load is heavy, and better tool heat dissipation conditions are required. For precision milling, the back Angle should be selected to be larger to make the edge sharp, reduce the friction between the tool and the machining surface, and reduce elastic deformation.
4. Deflection Angle: Reducing the deflection Angle can enhance heat dissipation and reduce the average processing temperature. Proper deflection Angle can improve the heat distribution during processing and reduce the deformation of parts caused by heat accumulation.
5. Tool wear control: With the tool wear, the workpiece surface roughness increases, which will lead to the workpiece temperature rise, and then cause parts deformation. Therefore, tools with good wear resistance should be used, and the degree of tool wear should not exceed 0.2 mm to avoid the formation of nodules. At the same time, before using the new tool, the burr and serration pattern of the knife teeth can be gently sharpened with a fine stone, so that the roughness of the cutting edge of the tool can reach Ra=0.4μm, minimizing the possibility of cutting deformation.

Proper processing methods

To reduce the risk of part deformation, the following processing techniques can be used:

1. Symmetrical processing: symmetrical processing can effectively dissipate heat during CNC processing of aluminum alloy, preventing excessive heat accumulation around parts, thereby reducing the chance of thermal deformation. For parts with large processing allowance, symmetrical processing can make them have better heat dissipation conditions during processing and avoid heat concentration. For example, a 90 mm thick plate needs to be processed to 60 mm, if the use of repeated feeding symmetrical processing, processing twice on each side to the final size, can ensure that the flatness reaches a higher precision, compared with a one-time processing to the final size, can effectively reduce deformation.
2. Layered technology processing: for parts with multiple cavities, due to the uneven force of the plate is easy to distort, layered technology can be used for processing. The parts are first divided into several layers, and then processed layer by layer into the required size. In this way, the force applied in the CNC machining process of aluminum alloy is more uniform, and the risk of deformation is less than that of directly processing the part.
3. Pre-drilling and milling: Parts with cavities may have problems in the milling stage, such as uneven chips, heat generation leading to component expansion deformation or tool fracture. These problems can be solved by pre-drilling and then milling. Drill holes with a tool slightly larger than the milling cutter to provide space for the cutting material, so that the chips are evenly removed from the blank aluminum, and finally milling.
4. Use different milling methods: aluminum alloy CNC machining has two methods of roughing and finishing. Roughing cuts blanks in the shortest time with the fastest cutting speed, focusing on material removal rate and processing efficiency; Finishing requires more precise machining and surface quality, with an emphasis on milling quality. Reasonable operation of these two methods can significantly change the deformation rate of parts.

Reasonable cutting parameters

Choosing the right cutting parameters can reduce the cutting force and cutting heat, and avoid the deformation of parts due to excessive cutting force and excessive heat. Among the three elements of cutting parameters, the amount of back cutting tool has a great influence on the cutting force. When the machining allowance is too large, the cutting force of the tool is too large, which will not only deform the parts, but also affect the rigidity of the machine tool spindle and reduce the durability of the tool. Therefore, the method of high-speed milling can be used to reduce the amount of back cutting tools at the same time, improve the feed rate and machine speed, thereby reducing the cutting force and ensuring the processing efficiency. For example, the cutting speed can be controlled at 250 ~ 300m/min, the feed speed is 300 ~ 400mm/min, the rough milling back cutting amount ap=0.5mm, and the fine milling ap=0.1 ~ 0.2mm.

The clamping method is suitable

When machining thin-walled aluminum parts, improper clamping method is easy to cause wall deformation. To reduce this risk, the pressed part can be loosened before the final feature is completed, releasing the pressure, allowing the part to return to its original shape, and then re-applying the pressure. The second applied pressure should act on the supporting surface, and the direction should be the most rigid direction, and the force should be enough to maintain the stability of the workpiece during the processing. For thin-wall shaft sleeve parts, the radial inner hole clamping method can be used to locate the part's internal thread, make a threaded shaft journal, insert the part's internal thread, press the inner hole with the cover plate and then tighten it with the nut to avoid clamping deformation when machining the outer circle. For the thin-wall sheet workpiece, the vacuum suction cup can be used to obtain a uniform adsorption of the clamping force, processing with a small cutting amount, or the filling method is used to inject urea melt containing 3% ~ 6% potassium nitrate into the workpiece to improve the processing stiffness of the workpiece, and the workpiece is immersed in water or alcohol after processing to dissolve the filler.

In the process of CNC aluminum machining, accidental deformation is a problem that needs great attention. By analyzing the causes of deformation and taking corresponding preventive measures, the accidental deformation in aluminum processing can be effectively avoided.

First of all, the blank residual stress and processing stress are the main causes of aluminum processing deformation. The blank residual stress is mainly formed by the superposition of stress caused by the non-uniform deformation during quenching and extrusion. Machining stress may be caused by factors such as asymmetric cutting, poor workpiece rigidity and different machining sequence. Understanding these causes will help us to take targeted preventive measures.

Secondly, the risk of aluminum deformation can be effectively reduced from the aspects of tool optimization, proper processing methods, reasonable cutting parameters and appropriate clamping methods. In terms of tool optimization, choosing the right spiral Angle, front Angle, back Angle, deflection Angle and controlling tool wear can reduce cutting force and cutting heat and reduce part deformation. In terms of processing methods, symmetric processing, layered technology processing, pre-drilling and milling, and the use of different milling methods and other skills can make the processing more stable and reduce the occurrence of deformation. Reasonable selection of cutting parameters, reduce cutting force and cutting heat, avoid parts due to excessive cutting force and heat deformation. In terms of clamping methods, for thin-walled aluminum parts, the risk of wall deformation can be reduced by adopting appropriate clamping methods.

In short, avoiding accidental deformation in CNC aluminum processing has important practical application value for improving product quality, reducing production costs and enhancing enterprise competitiveness. In actual production, we should comprehensively use these methods according to the specific situation, and constantly explore and innovate to ensure the stability and reliability of aluminum processing.