I. Compare Machine Specifications
1.Number of Axes
The number of axes determines the machine’s ability to handle complex geometries. For example, a 5-axis machine can handle more complex parts than a 3-axis machine. A 5-axis CNC milling machine allows for flexible tool movement in multiple directions, enabling the machining of complex spatial surfaces and polyhedral parts, such as complex mechanical components and aerospace parts. In contrast, a 3-axis CNC milling machine is mainly used for machining simpler parts, such as flat surfaces, simple curved surfaces, and linear profiles.
2.Spindle Power
Higher spindle power enables the machining of harder materials and achieves higher precision. For example, when machining hard materials like high-strength steel and titanium alloys, higher spindle power is required to provide sufficient cutting force to ensure machining efficiency and quality. Additionally, higher spindle power helps improve machining accuracy by allowing higher cutting speeds and feed rates.
3.Worktable Size
Ensure that the machine’s worktable size can accommodate the size of the workpiece. If the workpiece is too large for the worktable, machining cannot be performed. For example, for the machining of large molds, a CNC milling machine with a larger worktable size is necessary.
4.Feed Rate and Speed
Higher feed rates and speeds can increase efficiency and reduce machining time. When machining simple-shaped parts made of softer materials, higher feed rates and speeds can significantly improve production efficiency. For example, when machining molds for plastic products, higher feed speeds can be used to complete the machining quickly.
5.Tool Capacity
A machine with a larger tool capacity can handle more complex operations without frequent tool changes. For example, when machining complex parts that require multiple tools for different machining processes, a larger tool capacity can reduce the number of tool changes and improve machining efficiency.
II. Choose Based on the Characteristics of the Parts to be Machined
1.Choose Based on the Size of the Parts to be Machined
A smaller vertical milling machine with a worktable width of less than 400 millimeters is best suited for machining small and medium-sized parts and complex contour milling tasks. This type of milling machine is compact and easy to operate, making it suitable for machining in limited spaces, especially for small molds and small mechanical components.
Larger machines, such as gantry milling machines, have a worktable width of more than 500 – 600 millimeters and are used for machining large and complex parts. For example, large ship components and large mechanical frames require the high load capacity and extensive machining range of gantry milling machines to meet the processing requirements of large parts.
2.Choose Based on the Precision Requirements of the Parts to be Machined
China has established precision standards for CNC milling machines, including specific standards for vertical milling machines. The standard specifies that the positioning accuracy of the linear motion coordinates should be 0.04/300 millimeters, the repeat positioning accuracy should be 0.025 millimeters, and the milling accuracy should be 0.035 millimeters. In practice, the precision of the machine tool at the time of leaving the factory has a certain margin, which is about 20% lower than the error value allowed by the national standard. Therefore, from the perspective of precision selection, ordinary CNC milling machines can meet the processing requirements of most parts, such as general mechanical processing parts and ordinary molds.
For parts with higher precision requirements, such as high-precision molds and aerospace components, precision CNC milling machines should be considered. Precision CNC milling machines offer higher precision, ensuring that the dimensional accuracy and surface quality of the parts meet higher standards.
3.Choose Based on the Machining Characteristics of the Parts
For machining frame planes or stepped parts with unequal heights, a point-to-point linear system CNC milling machine can be used. This system can precisely control the movement and machining of the tool between various points, making it suitable for machining simple planes and stepped structures.
If the part to be machined has a curved contour, a two-coordinate or three-coordinate联动system should be chosen based on the geometric shape of the curved surface. For more complex curved surfaces, such as molds for car body panels and complex sculptures, a three-coordinate联动system can better meet the machining requirements of the curved surface.
Depending on the machining requirements of the parts, a CNC indexing head or a CNC rotary table can be added to a conventional CNC milling machine. In this case, the machine system becomes a four-coordinate CNC system, which can machine spiral grooves, blade parts, etc. For example, when machining molds for spiral springs or aircraft engine blades, a four-coordinate CNC system can achieve the machining of complex spatial curved surfaces.
4.Choose Based on Batch Size or Other Requirements
For mass production, users can opt for special-purpose milling machines. Special-purpose milling machines are designed for specific machining requirements of certain parts, offering high production efficiency to meet the needs of large-scale production.
For medium and small batch parts that are frequently and regularly produced, CNC milling machines are very suitable. This is because multiple fixtures, programs, and other preparations can be made for batch production, and they can be stored and reused. In the long run, the replacement of conventional milling machines with highly automated milling machines is inevitable, which can reduce manual labor and improve production efficiency.
