Reasons for deformation of aluminum alloy parts and blackening of workpiece surface Factory Suppliers Manufacturers Quotes

Reasons for deformation of aluminum alloy parts and blackening of workpiece surface

1. Reasons for processing deformation

There are many reasons for the deformation of aluminum alloy parts, which are related to the material, the shape of the part, the production conditions, and the performance of the cutting fluid. There are mainly the following aspects: deformation caused by internal stress of the blank, deformation caused by cutting force, cutting heat, and deformation caused by clamping force.

2. Process measures to reduce processing deformation

(1) reduce the internal stress of the blank
The natural stress of the blank can be partially eliminated by natural or artificial aging and vibration treatment.

(2) Improve the cutting ability of the tool
1. Reasonable selection of tool geometry parameters
Front angle: The front angle is appropriately selected under the condition of maintaining the strength of the cutting edge. On the one hand, the sharp edge can be sharpened, the cutting deformation can be reduced, the chip removal can be smoothed, and the cutting force and cutting temperature can be reduced. Never use a negative rake cutter.
Back angle: The size of the back angle has a direct impact on the flank wear and the quality of the machined surface. Cutting thickness is an important condition for selecting the back angle.
Helix angle: In order to make the milling smooth and reduce the milling force, the helix angle should be as large as possible.
Leading angle: Properly reducing the lead angle improves the heat dissipation conditions and reduces the average temperature of the processing zone.

2 improve the tool structure
Reduce the number of teeth of the milling cutter and increase the space of the chip: Since the aluminum alloy material has large plasticity, the cutting deformation during processing is large, and a large chip space is required. Therefore, the bottom radius of the chip groove should be large, and the number of teeth of the milling cutter is small. .

Fine grinding teeth: The roughness value of the cutting edge of the cutter is less than Ra=0.4um. Before using a new knife, you should use a fine stone to grind gently in front of and behind the teeth to eliminate burrs and slight zigzag remaining when sharpening the teeth.

Strictly control the wear standard of the tool: After the tool wears, the surface roughness value of the workpiece increases, the cutting temperature rises, and the workpiece deformation increases. Therefore, in addition to the selection of high-abrasion tool materials, the tool wear standard should not be greater than 0.2mm, otherwise it will easily lead to built-up edge.

3 improved workpiece clamping method
For thin-walled aluminum alloy workpieces with poor rigidity, the following clamping methods can be used to reduce distortion:

For thin-walled bushing parts, if the three-claw self-centering chuck or the collet chuck is used to clamp from the radial direction, once the workpiece is loosened after machining, the workpiece is inevitably deformed. At this time, a method of pressing the axial end face with good rigidity should be utilized. To position the inner hole of the part, a threaded threading mandrel is made and inserted into the inner hole of the part, and a cover plate is pressed against the end surface and then tightened with a nut. When the outer circle is machined, the clamping deformation can be avoided, and satisfactory machining accuracy can be obtained.
 
When processing thin-walled thin-plate workpieces, it is best to use vacuum suction cups to obtain a uniform distribution of clamping force, and then to process with a small amount of cutting, which can prevent deformation of the workpiece well.

In addition, the filling method can also be used. In order to increase the process rigidity of the thin-walled workpiece, the medium can be filled inside the workpiece to reduce the deformation of the workpiece during the clamping and cutting process. For example, a urea melt containing 3% to 6% potassium nitrate is poured into the workpiece, and after the processing, the workpiece is immersed in water or alcohol, and the filler is dissolved and poured out.

4 reasonable arrangement of procedures
During high-speed cutting, due to large machining allowances and intermittent cutting, the milling process often produces vibrations that affect machining accuracy and surface roughness. Therefore, the numerical control high-speed machining process can be generally divided into: roughing-semi-finishing-clearing-finishing-finishing. For parts with high precision requirements, it is sometimes necessary to perform secondary semi-finishing before finishing. After roughing, the parts can be naturally cooled, eliminating internal stresses caused by roughing and reducing distortion. The margin left after roughing should be greater than the amount of deformation, typically 1-2 mm. During finishing, the finished surface of the part should maintain a uniform machining allowance, generally 0.2-0.5mm, so that the tool is in a stable state during the machining process, which can greatly reduce the cutting deformation and obtain a good surface processing quality. Product accuracy.

3, operation skills

The parts of the aluminum alloy material are deformed during the processing, and in addition to the above reasons, the operation method is also very important in actual operation.

For parts with large machining allowance, in order to make them have better heat dissipation conditions during processing, and avoid heat concentration, symmetric processing should be adopted during processing.

If a piece of 90mm thick material needs to be machined to 60mm, if the other side is milled, the other side will be milled, and the flatness will be 5mm once. If it is processed by repeated infeed, each side will be processed twice. The final size guarantees a flatness of 0.3mm. If there are multiple cavities on the plate parts, it is not advisable to use a cavity and a cavity order processing method during processing, which is easy to cause deformation of the parts due to uneven force. Multi-layer processing is used, each layer is processed into all the cavities at the same time, and then the next layer is processed to make the parts evenly stressed and reduce the deformation.

The order of the knife must also pay attention to it. Roughing emphasizes the improvement of processing efficiency and the pursuit of resection rate per unit time. Generally, up-cut milling can be used. That is to remove the excess material on the surface of the blank at the fastest speed and the shortest time, basically forming the geometric contour required for finishing. The finishing work emphasizes high precision and high quality, and it is recommended to use down milling. Because the cutting thickness of the cutters gradually decreases from the maximum to zero during the milling, the degree of work hardening is greatly reduced, and the degree of deformation of the parts is alleviated.

4, the surface of the workpiece becomes black

Aluminum oxidation processing Aluminum alloy casting is generally cast in metal form, metal aluminum and aluminum alloy have good fluidity and plasticity, but it is easy to blacken during use due to:

Unreasonable process design
Aluminum alloy die-casting parts are improperly treated after cleaning or pressure inspection, which creates conditions for mildew and blackening of aluminum alloy die-casting parts, and accelerates the formation of mildew.
Warehouse management is not in place
The aluminum alloy die-casting parts are stored at different heights in the warehouse, and the mildew conditions are also different.
Aluminum alloy internal factors
Many aluminum alloy die-casting parts manufacturers do not do any cleaning treatment after die-casting and machining processes, or simply flush with water, and cannot be thoroughly cleaned. Corrosion of mold release agent, cutting fluid, saponification liquid, etc. remains on the die-cast aluminum surface. Substances and other stains that accelerate the blackening of the mold-extruding parts of aluminum alloy die-casting parts.
Aluminum external environmental factors
Aluminum is a reactive metal that is easily oxidized, blackened or moldy under certain conditions of temperature and humidity, which is determined by the properties of aluminum itself.
Do not use cleaning agents

The cleaning agent selected is highly corrosive, causing corrosion corrosion of die-cast aluminum.

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