Aluminum has good ductility and adequate tensile strength. They also benefit from low hardness and good thermal conductivity, making them suitable for high-speed machining. However, aluminum has a high coefficient of thermal expansion, which makes it prone to deformation during turning. Therefore, it is often advisable to use heat or cold treatment before the cutting.
Aluminum Performances in Turning
The physical properties of aluminum alloys primarily influence cutting problems in three areas: tool adhesion, cutting-induced deformation, and vibration.
- Tool adhesion: Friction and heat will soften aluminum material, and in severe cases, even melt it. Due to aluminum’s excellent ductility, chips cannot be expelled quickly enough. The heated chips then adhere to the cutting edge, leading to tool adhesion or built-up edge (BUE).
- Cutting deformation: Aluminum is relatively soft and has poor resistance to plastic deformation. During turning, the combined effect of heat and stress can cause the workpiece to deform, negatively impacting the final part’s usability.
- Vibration issues in cutting: When turning aluminum alloys, elastic recovery often occurs. This is triggered by the aluminum alloy’s low modulus of elasticity, which induces vibrations in the cutting tool and the feed system.
How to CNC Turn Aluminum Parts
Taking a thin-walled aluminum roller part as an example, we can analyze the turning process for aluminum walls. The main structure of the roller typically includes three parts: the roller body, an aluminum sleeve, and a PC plastic support ring. The outer layer material is aluminum alloy with a wall thickness of only 1.5mm, qualifying it as a standard thin-walled aluminum part.
Therefore, manufacturers must follow the specialized procedures for processing thin-walled aluminum parts. The internal bore is processed as a separate operation, while the outer ring is assembled by press-fitting method. Given the sleeve-type structure of this roller, it is critical to ensure that the inner bore and the outer ring share the same spindle axis and that the corresponding mating clearance/distance is precisely controlled. This prevents excessive shaking and friction between the inner bore and the outer ring during operation. To maintain a high-quality finish, special attention must be paid to friction-induced heating and measures must be taken to control it. Measures typically focus on workpiece clamping, tool parameters, and tool material.
The key requirements for turning thin-walled aluminum parts include workpiece clamping, solving Rigidity issues during turning, tool parameters, and process parameters. Only by controlling these critical steps and utilizing advanced equipment and technologies can the quality of the manufactured parts be improved.
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Clamping
Clamping aims to secure the part during machining while minimizing the influence of extrusion or clamping forces on the part. A common method is the two-center clamping technique. This involves installing two prefabricated end plugs into the workpiece before lathe processing. The design of these plugs is crucial and must be based on the structure and dimensions of the thin-walled part, ensuring parameters such as the center hole and inner bore diameter match the part perfectly.
The specific operational steps are:
- Outer diameter referencing and centering: Use the lathe’s clamping and locating function to establish the outer diameter reference and drill the center hole.
- Parting/cutting off: Perform the parting operation to achieve the highest possible machining accuracy while minimizing error.
A precise fit between the end plugs and the part’s internal dimensions significantly improves the machining accuracy. Therefore, the design and manufacture must be highly prioritized in this step.
Solving Rigidity Issues During Turning
Due to the inherent material properties, addressing the rigidity issue during turning is a major challenge. Aluminum alloy has inherently poor resistance to plastic deformation, a characteristic that is even more pronounced in the machining of thin-walled components. When processing such low-rigidity material, it is highly susceptible to cutting forces, which can induce vibrations in the workpiece and the tool, leading to workpiece deformation. This deformation is typically most pronounced in the central section of the part. Excessive deformation can prevent subsequent finishing operations, ultimately failing to meet requirements and resulting in material waste.
To solve this problem, a quantity of elastic filler material can be placed inside the part’s inner bore during machining to enhance the thin-walled part’s resistance to deformation. The filler material’s specifications should be selected based on the inner bore’s dimensions. As an auxiliary tool, the filler must ensure the part remains intact before machining. By installing the end plugs after placing the filler material, the part’s overall rigidity can be effectively increased, providing the necessary conditions for precision finishing.
Tool Parameters
When turning aluminum parts, the selection and setup of the cutting tool can improve part accuracy and quality. The general requirements for lathe tools include a sharp cutting edge and a design that enhances heat dissipation from the cutting edge. In high-speed turning, friction between the tool and the part generates significant heat, which can affect the stability of thin-walled aluminum parts. Thus, heat dissipation is very important. The use of coolant helps achieve this.
Furthermore, the tool’s geometric angles must be adjusted based on the specific part being machined. To ensure prompt chip evacuation and prevent chips from adhering to the cutting edge, the rake face should be polished beforehand, often used in conjunction with an oil-based lubricant.
Process Parameters
Process parameters are factors that critically influence workpiece quality during turning. Control of these parameters primarily involves the cutting speed, feed rate, and depth of cut. These parameters must be reasonably adjusted during the actual machining process.
Strict control over the machining allowance and depth of cut is essential, as improper control of these two parameters can lead to severe workpiece deformation. These parameters should be pre-set before part machining. Additionally, reducing the feed rate and increasing the cutting speed can improve the surface finish of the workpiece. Continuous optimization and scientific control of process parameters are key to elevating the overall machining level of the workpiece.
Specialized Vacuum Clamping Fixture
When turning aluminum parts, using traditional clamp plates and pads to secure the material often makes it difficult to guarantee the quality of the finish machining due to the applied clamping force. The ideal state for finish machining is to preserve the material’s original mechanical properties—that is, achieving precision machining with zero or negligible clamping force.
The use of a vacuum clamping system can approach this ideal machining environment. This system is composed of a thermal-conducting frame, a specialized vacuum adsorption fixture for finish machining, and a vacuum pump. By reserving machining allowance on the inner frame face and both sides of a deep groove after rough machining and then ensuring the adsorption surface of the fixture maintains close contact with the installed fixture base during finishing, a deformation-free clamping environment can be achieved through fine-tuning with nuts.
