As is well known, aluminum alloy is a major raw material in industry. Due to the special properties of the material, after receiving small-batch CNC machining orders for aluminum alloy parts, how to achieve ideal CNC machining results is a key consideration in the batch CNC machining manufacturing process of aluminum alloy parts. To ensure good aluminum alloy machining quality, Kzron analyzed the technical characteristics of batch machining of aluminum alloy parts: How to solve the technical problems of batch machining of aluminum alloy parts for small-batch CNC machining orders? This analysis determined the selection of relevant tool materials, tool angle parameters, cutting parameters, and cutting fluids during the production process, thereby obtaining good surface quality. Aluminum alloy, as a major raw material in industrial production, is mainly composed of the alloying elements magnesium and silicon. It has moderate strength, a hardness of 85~95HB, good corrosion resistance and weldability, and good oxidation performance. It is widely used in various industrial structural components requiring certain strength and corrosion resistance, such as aerospace, drones, trucks, tower structures, ships, trams, railway vehicles, and furniture. Meanwhile, due to its good toughness and excellent cutting performance, the chips are continuous ribbons that easily entangle with each other, and if not cleaned in time, they can easily scratch the workpiece surface. Furthermore, it exhibits high viscosity and high machining friction during cutting, resulting in high cutting temperatures during CNC machining that are difficult to lower, potentially leading to built-up edge formation, which significantly impacts parts requiring high surface quality. This necessitates the selection of appropriate process parameters when producing 6061 aluminum alloy products.
We will analyze the technical characteristics of aluminum alloy parts by examining a small-batch order of aluminum alloy parts. Its dimensions are shown in Figure 1. We will analyze its processing characteristics based on its technical requirements: The raw material for this part is 6061 bar stock, with a production batch of approximately 500 pieces per month, classifying it as a small-batch production. Its technical requirements are as follows: Small-batch processing order requirements for aluminum alloy parts: (1) Chamfered edges; (2) No dents or scratches allowed on the surface; (3) Surface roughness of 3.2µm for all parts; (4) Unspecified tolerances are +0.1mm. First, based on its surface requirements: a surface roughness of 3.2µm, a CNC lathe will be used to ensure this.
Secondly, this part also has a 13mm groove to be machined. This dimension is a key consideration during machining for this highly viscous raw material. Tool parameters, lubrication methods, and timely cooling and lubrication must be taken into account to prevent surface burning during machining. Third, in addition to the 3.2µm roughness requirement, the surface must be free of any dents or scratches. This requires that chips be prevented from remaining on the machined surface and cleaned promptly. Fourth, there are holes to be machined and tapped in two mutually perpendicular directions. When machining on a drilling machine, a simple fixture can be used to ensure the relative positions of the holes. Cutting process parameters and cutting fluid selection: From the above analysis of the part’s process characteristics, it is clear that to ensure the part’s dimensional and surface quality requirements, it is essential to select appropriate tool materials, process parameters, and a suitable cutting fluid. The following sections will explain how to make these selections appropriately.
I. Tool Material:
Many tool materials can be chosen for cutting aluminum alloys, such as cemented carbide, ceramics, cermet, and polycrystalline diamond. Cemented carbide is the main and commonly used tool material for high-speed cutting of aluminum. In actual machining, uncoated cemented carbide tools are usually used because thick coatings can dull the tool tip radius, while thin coatings will wear out quickly during machining, neither of which can extend tool life. Furthermore, since P-series and M-series cemented carbide contain TiC, and TiC has a good affinity with aluminum, it is not conducive to cutting. Therefore, K-series cemented carbide tools are preferable. Polycrystalline diamond tools have a significantly longer service life than cemented carbide tools under the same cutting conditions, but due to small production volumes and their high price, they are not selected in this case. Therefore, cemented carbide tools can be used for cutting.
II. Tool Geometry Parameters
During the cutting of aluminum alloys, a large amount of heat is generated. If it is not dissipated in time, it can lead to surface burns on the part and the formation of built-up edge on the tool, affecting the surface finish. Therefore, the tool angle plays a crucial role in surface quality. The selection of tool geometry primarily depends on the tensile strength and Si content of the aluminum alloy material (see Table 1 for specific contents). Studies show that the rake angle and tip radius are the main factors affecting the machining quality of aluminum alloys. Increasing the rake angle can reduce chip deformation and frictional resistance, thereby reducing cutting force, cutting power, and heat generated during cutting. However, an excessively large rake angle will lead to reduced cutting edge strength and a smaller heat dissipation volume, resulting in reduced tool life. The selection of the clearance angle affects tool stiffness; increasing the clearance angle is beneficial for improving tool life but will reduce cutting edge stiffness. For workpieces with high strength and hardness, a smaller clearance angle should be used; for soft and sticky workpieces, a larger clearance angle should be used. Therefore, considering the machining characteristics of this part, a rake angle of 30°~35° and a clearance angle of 10°~12° are selected to ensure tool stiffness while increasing the clearance angle as much as possible.
III. Selection of Cutting Parameters
Due to the presence of the secondary cutting edge angle, regular tool marks are often left on the surface of the workpiece after machining. The area formed by these tool marks constitutes the geometric basis of the surface roughness. The height of the residual area is called the maximum profile height Ry, calculated by the formula Ry = fcotkr + cotkr’, where f is the feed rate; kr is the principal cutting edge angle; and kr’ is the secondary cutting edge angle. From the above formula, it can be seen that to reduce Ry, a smaller numerator and a larger denominator should be chosen. This requires a small feed rate and minimizing both the principal and secondary cutting edge angles of the tool. This allows for a smaller maximum profile height and thus a higher surface quality. Therefore, when conditions permit, cutting parameters with high speed, small depth of cut, and small periodic feed rate should be selected to ensure the surface finish of the workpiece.
IV. Selection of Cutting Fluid
The appropriate selection of cutting fluid is a necessary condition for ensuring the surface quality of the machined workpiece. This is because selecting a suitable cutting fluid can improve the friction coefficient between the workpiece and the tool, reduce cutting force and cutting temperature, thereby reducing tool wear and ensuring the machining quality of the workpiece. In the actual production process, it was found that if ordinary cutting fluid is used, the surface of the machined product will be dull and not smooth, and there will be obvious burn marks, making it difficult to guarantee the surface quality[5]. Therefore, kerosene or diesel oil was selected as the cutting fluid for cutting, and it was found that the surface finish of the machined product was very good, which could well guarantee the technical requirements of the parts. Moreover, diesel oil is not expensive, which can better guarantee the economy of the machining. Finally, through the comprehensive application of the above CNC machining conditions and machining parameters, the surface quality of the product can be well guaranteed in the production process, the surface finish requirements of the product can be met, and the production efficiency is relatively high. It can be produced at a rate of 100 pieces/day to achieve the expected results. Therefore, in the cutting process of aluminum alloy, the selection of tool material and tool geometry parameters as well as the selection of cutting fluid are particularly important. Only by comprehensively considering these factors can qualified products be produced more efficiently.
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