What material properties must a CNC designer consider when it comes to precision CNC machining of metal and plastic parts?

In CNC precision machining of metal and plastic parts, CNC designers must consider the following material properties:

Metal material properties

Mechanical properties

Hardness: determines the material's ability to resist deformation and wear. Metals with high hardness, such as tungsten alloys and hardened tool steels, are difficult to process and require sharper, more wear-resistant tools, as well as greater cutting force and power.

Strength: includes tensile strength, compressive strength, etc. High-strength metals such as titanium alloys and high-strength alloy steels can withstand greater external forces, but the cutting force on the tool during machining is also large and easy to wear, so it is necessary to select cutting parameters reasonably.

Toughness: refers to the ability of a material to absorb energy and resist crack propagation before breaking. Metals with good toughness, such as copper alloys, are not easy to break during machining, but may produce large plastic deformation, affecting machining accuracy.

Physical properties

Electrical conductivity and thermal conductivity: Metals with good electrical conductivity and thermal conductivity, such as copper and aluminum, can quickly conduct cutting heat during machining, which can reduce tool temperature and increase tool life. However, in special processes such as EDM, electrical conductivity will affect the selection of machining parameters.

Thermal expansion coefficient: Metals with large thermal expansion coefficients, such as aluminum alloys, will experience large thermal deformation due to cutting heat during processing, which will affect the processing accuracy. Appropriate cooling measures and compensation strategies need to be taken.

Density: Metals with high density, such as tungsten alloys and lead, need to bear greater loads on the machine tool during processing, and the centrifugal force generated when rotating at high speed is large, which places high requirements on fixtures and tools; metals with low density, such as magnesium alloys, are light in texture, but have relatively low hardness and strength, and are easy to deform during processing.

Processing performance

Cutting performance: It is related to comprehensive factors such as the hardness, toughness, and strength of the material. Easy-to-cut metals, such as aluminum alloys and copper alloys, have small cutting forces, slow tool wear, and high processing efficiency; while high-hardness and high-strength metals, such as nickel-based alloys, are difficult to cut and require special tools and processing technology.

Forgeability and ductility: Metals with good forgeability and ductility, such as low-carbon steel and pure copper, are easy to pre-process through forging, stretching and other processes, which can reduce the margin of CNC processing and improve processing efficiency.

Plastic material characteristics

Mechanical properties

Hardness: The hardness of different plastics varies greatly. For example, polyoxymethylene (POM) has a higher hardness, while polyethylene (PE) has a lower hardness. Hardness affects the choice of tools and cutting parameters. Plastics with high hardness require harder tools and appropriate cutting speeds.

Toughness and brittleness: Plastics with good toughness, such as polycarbonate (PC), are not easy to break during processing, but may undergo elastic deformation; plastics with high brittleness, such as polystyrene (PS), are prone to cracks and edge collapse during processing, and require smaller cutting forces and feed rates.

Strength: Including tensile strength, bending strength, etc. High-strength plastics such as polyetheretherketone (PEEK) can be used to manufacture parts that withstand greater stress, but the processing difficulty is relatively large.

Physical properties

Thermal stability: Plastics with good thermal stability, such as PPS and PEEK, can maintain stable performance at higher temperatures, and can use higher cutting speeds and feed rates; while plastics with poor thermal stability, such as polyvinyl chloride (PVC), are prone to decomposition and deformation due to overheating during processing, and the processing temperature needs to be strictly controlled.

Shrinkage: The shrinkage of plastics is generally large and varies significantly between different types, such as polypropylene (PP) has a large shrinkage. When designing molds and CNC processing paths, it is necessary to consider the impact of shrinkage on dimensional accuracy and make appropriate compensation.

Transparency: For plastic parts that require transparency, such as polymethyl methacrylate (PMMA), surface scratches and internal stress should be avoided during processing to ensure transparency and optical properties.

Processing performance

Viscosity and fluidity: Plastics with high viscosity are prone to adhere to the tool during processing, affecting the quality of the processing surface. It is necessary to select appropriate tool coatings and cutting fluids; plastics with good fluidity may be deformed due to uneven internal stress during CNC processing after injection molding.

Wear resistance: Plastics with good wear resistance, such as POM and nylon, can be used to manufacture wear-resistant parts, but the wear on the tool is large during processing, and the tool needs to be replaced regularly.