What causes the deformation of aluminum alloy processing

What causes the deformation of aluminum alloy processing

Aluminum alloy is a very commonly used hardware, but also a very important industrial raw material, widely used in various fields of industry. Most of the hardware in our home is made of aluminum alloy. However, in the processing of aluminum alloy, because the hardness of aluminum alloy is small, the coefficient of thermal expansion is large, so in the process of thin-walled parts, it is easy to deformation.

In addition to improving the performance of the tool and eliminating the internal stress of the material using aging treatment in advance, from the perspective of the processing technology, some means can also be taken to reduce the processing deformation of the material as much as possible.

For aluminum alloy parts with large processing allowance, in order to create better heat dissipation conditions and reduce thermal deformation, it is necessary to avoid too much heat concentration as far as possible, and the method that can be taken is symmetrical processing.

For example, there is a 90mm thick aluminum alloy plate, it needs to be milling to 60mm thick, if the milling side immediately turned over to milling the other side, because each face is a processing to the size, continuous processing allowance is large, it will cause the problem of heat concentration, so that the flatness of the milling aluminum alloy plate can only reach 5 mm. If the symmetric processing method with repeated feed on both sides is used, each surface is processed at least twice until the size is reached, which is conducive to heat dissipation, and the flatness can be controlled at 0.3mm.

First, layered multiple processing method

When there are multiple cavities on the aluminum alloy plate parts that need to be processed, if the method of processing one cavity one cavity in turn is used, it is easy to make the cavity wall entangled and deformed due to uneven force. The solution is to take layered multiple processing method, that is, to process all cavities at the same time, but not at one time, but in several levels, layer by layer processing to the required size. In this way, the force on the parts will be more uniform, and the probability of deformation is smaller.

Second, the appropriate choice of cutting parameters

Choosing the right cutting parameters can effectively reduce cutting force and cutting heat in the cutting process. In the machining process, the cutting amount is too large to lead to the cutting force of a cutting tool, which is easy to cause the deformation of parts, and will affect the rigidity of the machine tool spindle and the durability of the tool.

Among the various elements of cutting parameters, the impact on cutting force is the amount of back cutting tool. It is said that reducing the amount of back cutting is conducive to ensuring that the parts do not deform, but at the same time, it will reduce the processing efficiency. CNC machining high-speed milling can solve this problem, only need to reduce the amount of back cutting at the same time, increase the feed accordingly, and improve the speed of the machine can reduce the cutting force, but also to ensure the processing efficiency.

Third, improve the cutting ability of the tool

The material and geometric parameters of the tool have an important influence on the cutting force and cutting heat. The correct selection of the tool is very important to reduce the deformation of the parts.

1, reasonable selection of tool geometric parameters

Front Angle: under the condition of maintaining the strength of the blade, the front Angle is properly selected to be larger, on the one hand, you can grind out a sharp cutting edge, and you can reduce the cutting deformation, so that the chip removal is smooth, and then reduce the cutting force and cutting temperature. Do not use knives with negative front angles.

Back Angle: The size of the back Angle has a direct effect on the wear of the back tool surface and the quality of the machined surface. The cutting thickness is an important condition for selecting the back Angle. Rough milling, due to the large feed, heavy cutting load, large heat, requiring good tool heat dissipation conditions, therefore, the back Angle should be selected smaller. When finishing milling, the cutting edge is required to be sharp, reduce the friction between the back tool surface and the machining surface, and reduce the elastic deformation, so the back Angle should be selected larger.

Helix Angle: In order to make milling smooth and reduce milling force, the helix Angle should be selected as large as possible.

Main declination Angle: Properly reducing the main declination Angle can improve the heat dissipation conditions and reduce the average temperature of the processing area.

2, improve the tool structure

Reduce the number of cutter teeth and increase the chip space. Due to the large plasticity of aluminum alloy material, large cutting deformation during processing, and the need for a larger chip space, the bottom radius of the chip groove should be larger and the number of teeth of the milling cutter should be less.

For example, a milling cutter with Φ20mm or less uses two teeth; Φ30 ~ Φ60mm milling cutter with three cutter teeth is better to avoid the deformation of thin-walled aluminum alloy parts caused by chip blockage.

Fine grinding tool teeth: the roughness value of the cutting edge of the tool teeth is less than Ra=0.4um. Before using a new knife, a fine stone should be used to gently sharpen the teeth in front and behind the knife several times to eliminate residual burrs and slight serrated lines. In this way, not only can reduce the cutting heat and cutting deformation is relatively small.

Strict control of tool wear standards: After tool wear, the workpiece surface roughness value increases, the cutting temperature rises, 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 tumors. When cutting, the temperature of the workpiece is generally not more than 100 ° C to prevent deformation.

Four, the knife order is exquisite

Roughing and finishing should use different cutting sequences. Roughing requires the fastest cutting speed and the shortest time to cut off the excess material on the blank surface to form the geometric profile required for finishing. Therefore, the emphasis is on processing efficiency, and the pursuit of material removal rate per unit time should be used.

The finishing has higher requirements for processing accuracy and surface quality, and emphasizes processing quality, so it should be used. Because the cutting thickness of the cutter teeth gradually decreases to zero during down-milling, the work hardening phenomenon will be greatly reduced, and the deformation of the parts will also have a certain degree of inhibition.

Five, the thin-walled parts are pressed twice

In the processing of aluminum alloy thin-wall parts, the clamping force is also an important reason for deformation, which is difficult to avoid even if the processing accuracy is improved. In order to reduce the deformation of the workpiece due to clamping, the pressed part can be loosened before the finishing reaches the size, releasing the pressing force, so that the part can be freely restored to the original state, and then re-pressed slightly.

The application point of secondary compression is suggested on the support surface, the clamping force should act in the direction of the workpiece rigidity, and the size of the clamping force should be determined by the strength of the workpiece without loosening, which has higher requirements for the experience and feel of the operator. The compression deformation of the parts processed in this way is small.

Six, first drilling and then milling processing method

When machining parts with cavity, if the milling cutter is directly inserted into the part, the chip removal will be poor because of the lack of chip space of the milling cutter, which leads to the accumulation of a lot of cutting heat of the part, and the expansion deformation, and even may cause accidents such as breaking the knife and breaking the knife. It is recommended to drill before milling, that is, to drill out the cutter hole with a drill bit of a size not less than the milling cutter, and then use the milling cutter to reach into the cutter hole to start milling, which can effectively solve the problems mentioned above.

Through the above aluminum alloy processing methods, it can be a good solution to the deformation of aluminum alloy thin-wall products. The deformation of aluminum alloy products is affected by various factors, so as long as we do more to improve the processing method, we can better reduce the probability of deformation of aluminum alloy.