XavierA practical guide to CNC machining aluminum
There are many noteworthy aspects of CNC machining aluminum, because aluminum is an important industrial raw material, but due to its relatively low hardness and large thermal expansion coefficient, it is easy to deform when machining thin-walled and thin-plate parts.
In addition to improving tool performance and eliminating material internal stress in advance, several steps can be taken to minimize material deformation.
1.Symmetrical processing
For aluminum parts with large machining allowances, in order to better dissipate heat and reduce thermal deformation, it is necessary to avoid excessive heat concentration. The method that can be taken is called symmetrical processing.
Imagine that a 90mm thick aluminum plate needs to be milled to 60mm thick. If one side is milled and then turned over to the other side immediately, since each side must be machined to the final size, the continuous machining allowance is large, which will cause heat concentration problems, and the flatness of the alloy plate can only reach 5mm.
However, if the method of repeated symmetrical processing on both sides is adopted, each side must be processed at least twice to reach the final size, which is conducive to heat dissipation, and the flatness can be controlled below 0.3mm.
2.Layered and multiple processing when CNC machining aluminum
When there are multiple cavities on an aluminum alloy plate, it is easy to cause the cavity wall to be distorted due to uneven force. The best way to solve this problem is to adopt the method of layered and multiple processing, that is, to process all cavities at the same time.
However, the processing of parts is not completed in one go, but is divided into several layers, and processed layer by layer to the required size, so that the force on the parts will be more uniform and the probability of deformation will be smaller.
3.Choose the right cutting parameters
Choosing the right cutting amount can reduce the cutting force and the resulting cutting heat. During the machining process, if the cutting amount is too large and the cutting force is too large, it is easy to cause deformation of the parts, and it will also affect the rigidity of the spindle and the durability of the tool.
Among all the cutting parameter factors, the biggest influence on the cutting force is the amount of back cutting. Although reducing the number of tools is conducive to ensuring that the parts are not deformed, it will also reduce the processing efficiency.
High-speed milling in CNC machining can solve this problem. By reducing the amount of back cutting, increasing the feed rate, and increasing the machine tool speed, the cutting force can be reduced during processing to ensure processing efficiency.
4.Optimize the capabilities of cutting tools
The material and geometric parameters of cutting tools have an important influence on cutting force and cutting heat, so the correct selection of cutting tools and cutting parameters is very important to reduce the machining deformation of parts.
Tool geometric parameters that may affect performance:
- Rake angle
The rake angle must be set appropriately to maintain the blade strength, otherwise the sharp blade will be worn. Correctly setting the rake angle can also reduce cutting deformation, ensure smooth chip discharge, and reduce cutting force and cutting temperature. Do not use negative rake angle tools. - Back angle
The size of the back angle has a direct impact on the wear of the back tool face and the quality of the machined surface. The cutting thickness is an important parameter to consider when configuring the back angle. When rough milling, the feed rate is large, the cutting load is heavy, and the heat generation is large. The tool must consider the heat dissipation problem, so the back angle should be small. When fine milling, the cutting edge is required to be sharp to reduce the friction between the back tool face and the machined surface and reduce elastic deformation. At this time, the back angle should be large. - Helix angle
In order to make milling stable and reduce milling force, the helix angle should be as large as possible. - Main deflection angle
Appropriately reducing the main deflection angle can improve the heat dissipation effect and reduce the average temperature of the processing area. - Improve the physical condition of the cutting tool
Reducing the number of milling cutter teeth can improve the processing capacity, which is very useful when processing aluminum alloys. Due to the characteristics of aluminum alloys, the cutting deformation is large and a larger chip space is required. The groove bottom radius should be large and the number of milling cutter teeth should be small. For example, milling cutters below 20mm use 2 cutter teeth, and milling cutters of 30-60mm use 3 cutter teeth to avoid chip blockage and deformation of thin-walled aluminum alloy parts. - Precision grinding of cutter teeth
The roughness of the cutter edge should be less than Ra=0.4um. Before using a new cutter, use a fine oil stone to gently grind the front and rear edges of the cutter teeth to eliminate burrs and slight serrations. This can not only reduce cutting heat, but also minimize cutting deformation. - Strictly control tool wear
After the tool is worn, the surface roughness of the workpiece increases, the cutting temperature increases, and the deformation of the workpiece increases. Therefore, in addition to selecting tool materials with good wear resistance, the tool wear standard should not be greater than 0.2mm, otherwise built-up edge will be generated. When cutting, the workpiece temperature should not exceed 100 degrees to prevent deformation.
5.Different CNC machining aluminum methods
The methods of roughing and finishing are different. Roughing requires the fastest cutting speed to remove excess material on the surface of the blank in the shortest time to form the geometric profile required for finishing. Here, the emphasis is on processing efficiency and material removal rate.
Finishing has high requirements for processing accuracy and surface quality, and attention should be paid to milling quality. As the cutting thickness of the cutter teeth decreases from the maximum to zero, the work hardening phenomenon will be greatly reduced, and the deformation of the parts can be suppressed to a certain extent.
6.Secondary compression of thin-walled parts
When processing thin-walled aluminum alloy parts, the clamping force will cause the workpiece to deform. In order to reduce the deformation of the workpiece caused by clamping, the clamped workpiece should be loosened before processing to the final size, the pressure should be released, and the workpiece should be restored to its original state before the second pressurization.
The second clamping point is best on the support surface, and the clamping force should be in the direction of maximum stiffness. If everything is done correctly, the compression force should be able to clamp the workpiece without loosening. This method requires an experienced operator, but it can ensure that the processing deformation of the machined part is minimized.
7.Drilling and milling
Machining parts with cavities also has its own problems. If the milling cutter is directly applied to the part, the milling cutter has insufficient chip space and poor cutting, resulting in a large amount of cutting heat accumulation, expansion and deformation of the part, and even possible breakage of the part or the tool.
The best way to deal with this problem is to drill first and then mill. That is, first drill the hole with a tool that is not smaller than the milling cutter, and then put the milling cutter into the hole to start milling.