Super practical knowledge of CNC — Technological measures and operational techniques to reduce distortion in aluminum machining
There are many reasons for the deformation of aluminum parts machining, which are related to the materials, shapes of the parts, production conditionsand more.
There are several main factors that can cause deformation: internal stress in the blank, cutting force, cutting heat and clamping force.
Technological measures to reduce machining distortion
1. Reduction of internal stresses in blanks
The use of natural or artificial aging and vibration treatment can eliminate some of the internal stresses in the blank. Pre-machining is also an effective method. Blanks with large allowances also have large deformations after machining. If the extra part of the blank is machined away in advance to reduce the allowance of each part, it can not only reduce the machining deformation of the later machining process, but also release part of the internal stress after placing it for a while.
2. Improvement of cutting ability of cutters
The material and geometric parameters of the cutter have an important influence on the cutting forces and cutting heat,the correct selection of the cutter is essential to minimize the deformation of the part to be machined.
1) Proper selection of cutter geometry parameters.
Rake angle: Under the condition of maintaining the strength of the cutting edge, choosing a larger rake angle can sharpen the edge, reduce the cutting deformation, make the chip removal smooth, and then reduce the cutting force and cutting temperature. Attention: NO negative rake angle cutters are used.
Clearance angle: The size of the clearance angle has a direct effect on the wear of the back face and the quality of the machined surface. Cutting thickness is an important condition for selecting the clearance angle. During rough machining, the large feed rate leads to heavy cutting loads and increased heat generation, which requires good heat dissipation performance of the cutter. In this case, the clearance angle should be a smaller option. However, precision machining requires sharp edges to minimize elastic deformation by reducing the friction between the back face and the machined surface. At this point, the clearance angle should be larger.
Helical angle: The helical angle should be selected as large as possible in order to make the milling smoother and to reduce the milling force.
Tool major cutting edge angle: Appropriately reducing the tool major cutting edge angle improves heat dissipation and reduces the average temperature in the machining zone.
2) Improvement of cutter structure.
Reduce the number of teeth of the milling cutter and increase the chip space. Due to the large plasticity of the aluminum material, the cutting deformation in machining is larger, so a larger chip space is needed.
Fine grinding of cutter teeth. The roughness value of the cutting edge of the cutter teeth should be less than Ra=0.4um. Before using a new cutter, gently sharpen the front and the back of the teeth with a fine oil stone to eliminate burrs and slight serrations left from sharpening.
Control the wear standard of the cutter strictly. The surface roughness value of the workpiece increases after cutter wear, and both the cutting temperature and workpiece deformation will increase. Besides choosing a cutter material with favorable wear resistance, the cutter wear standard should not be greater than 0.2mm. The temperature during cutting should not exceed 100°C in general.
3. Improvement of workpiece clamping methods
For thin-wall aluminum workpieces with low rigidity, the following clamping methods can be used to reduce deformation:
When machining thin-wall and thin-plate workpieces, it is best to use vacuum suction pads to obtain an evenly distributed clamping force. At the same time, a smaller cutting amount is used for machining, which can prevent deformation of the workpiece very well.
Alternatively, the plugging method can be used. To increase the rigidity of the thin wall workpiece, the inside of the workpiece can be filled with a medium to minimize the deformation of the workpiece during clamping and cutting.
4. Reasonable arrangements of work processes
At high cutting speeds, the milling process tends to vibrate due to the large machining allowance and intermittent cutting, which affects machining accuracy and surface roughness. Therefore, CNC high-speed cutting machining can generally be divided into: rough machining, semi-precision machining, clear angle machining, precision machining and other processes.
For parts with high accuracy requirements, it is sometimes necessary to carry out secondary semi-precision machining before precision machining. After rough machining, the part can be cooled naturally to remove the internal stresses caused by rough machining, which also reduces distortion.
Operational tips to minimize machining distortion
The method of operation is also very important in order to prevent deformation of aluminum parts in practice.
1. For parts with large machining allowances, symmetrical machining is preferred to avoid heat concentration.
2. If there are multiple cavities in the plate parts, machining should be done in layers with multiple times. Machining all mold cavities at the same time for each layer can make the part uniformly stressed and reduce the deformation.
3. By changing the cutting amount to reduce the cutting force and cutting heat.
4. Roughing emphasizes the improvement of machining efficiency and the pursuit of the removal rate, which can generally be used in up milling. While precision machining emphasizes high accuracy and quality, it is better to use down milling.
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The main factor affecting the machining accuracy and surface quality of aluminum parts is that deformation is easy to occur during the machining process of this kind of parts, which requires the operator has some operating experience and skills.
Summary
Although aluminum parts are easily deformed, CYCO, with more than twenty years of experience in CNC machining, is still trustworthy. We have extensive experience in CNC machining and specialized staff with excellent machining skills. We will make every effort to provide CNC machined aluminum parts that meet your requirements and expectations.
In order to avoid wasting your valuable time, you can choose CYCO as your partner without any hesitation!
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