With the development of modern manufacturing technologies, CNC (Computer Numerical Control) technology has become an essential core technology in the manufacturing industry. The 3-axis CNC milling machine, as one of the most commonly used CNC machines, is widely applied in precision machining, aerospace, automotive manufacturing, and mold processing. Through the integration of CNC technology, 3-axis milling machines can efficiently and precisely process complex geometric parts. This article will discuss the part design and practical machining processes on a 3-axis CNC milling machine, incorporating relevant professional terminology to help students fully understand this technology.

I. Part Design Course

In the process of designing parts for a 3-axis CNC milling machine, the first step is to clarify the functional requirements and design goals of the part. The part design must meet the mechanical properties, operational conditions, and machining accuracy requirements, all of which directly influence the subsequent machining process planning and CNC program development.

1.1 Part Design Requirements and Analysis

Before beginning the part design, it is essential to analyze the part's functional requirements, operating environment, and its role within the entire mechanical system. Part design needs to consider not only functional performance but also the feasibility of the machining process. The designer must ensure that the part meets design requirements while also being easy to machine. For example, when designing an aluminum alloy part, the designer should consider the material’s high rigidity and low deformation characteristics to ensure high precision during machining.

In addition to material selection, factors such as dimensions, tolerances, and surface roughness should be carefully considered. Dimensional tolerances must be set according to practical application requirements to ensure proper fitting during assembly. Surface roughness directly affects the part's performance and appearance quality.

1.2 CAD Modeling and Machining Features

Once the part design is complete, 3D modeling is typically performed using CAD (Computer-Aided Design) software. Common CAD software includes SolidWorks, AutoCAD, and CATIA, which helps designers to represent the part's geometry intuitively. During modeling, designers must pay particular attention to machining features such as hole locations, slots, and inclined surfaces, as these features will directly affect the choice of machining process.

For example, in the design of a part with multiple holes, the designer needs to consider the arrangement, diameter, and positional accuracy of the holes. These design factors not only affect the part's functionality but also the difficulty and time required for machining.

1.3 Process Planning Analysis

When designing parts, process planning must also be taken into account. Process planning refers to the selection of machining steps based on the part's shape, material properties, and required precision. For a 3-axis CNC milling machine, a typical approach would be to establish a reasonable sequence of rough and finish machining steps.

• Rough Machining: In the rough machining phase, larger tools and higher cutting parameters are used to remove excess material. The goal is to achieve the approximate part shape. The selection of tool paths during this phase is crucial to avoid excessive cutting, which can reduce tool wear.

• Finish Machining: After rough machining, finish machining is performed using smaller tools and lower cutting parameters to achieve the final dimensions and surface quality. Tool paths need to be planned more precisely to avoid issues such as tool interference.

1.4 CNC Program Development

Once part design and process analysis are complete, the next step is to develop a CNC program. The CNC program (typically in G-code) is the core instruction that controls the 3-axis CNC milling machine to perform the machining operations. When writing a CNC program, factors such as the part's datum, coordinate system, and the rationality of the machining path must be considered.

Common G-codes include:

• G00: Rapid positioning

• G01: Linear interpolation

• G02/G03: Circular interpolation

• M03: Spindle clockwise rotation

In addition to the G-codes mentioned above, M-codes are used to control auxiliary functions of the machine tool, such as spindle speed and coolant on/off. When writing a CNC program, optimizing the tool path is key, as efficient tool paths reduce machining time and improve precision.

II. Practical Machining Course

After part design, the next step is to translate the design into actual machining. The process of machining a part on a 3-axis CNC milling machine involves multiple steps, from machine preparation to actual machining, and each step requires precise control.

2.1 Machine Preparation and Workpiece Clamping

Before starting the machining process, it is essential to check the CNC milling machine. The checklist includes:

• Verifying that the worktable is flat;

• Ensuring the spindle is in normal working condition;

• Checking if the tools are suitable for the current machining task;

• Confirming that the control system is functioning properly and can accurately execute the program.

Next, the workpiece must be securely clamped and positioned. Proper clamping is critical for maintaining machining accuracy. Common clamping methods include using three-jaw chucks or flat fixtures. During clamping, it is essential to ensure the workpiece is held securely to prevent movement, which could lead to machining errors.

2.2 CNC Program Input and Dry Run

Once the machine and workpiece are prepared, the CNC program is input into the CNC milling machine's control system. After input, a dry run should be performed, where the program is run without the workpiece. This dry run helps check that the program follows the intended path without any issues. It can also help detect problems such as tool interference with the workpiece or fixture.

2.3 Machining Process and Tool Path Control

The machining process on a 3-axis CNC milling machine is generally divided into rough machining and finish machining. In the rough machining phase, larger tools and higher cutting parameters are used to efficiently remove material. During this phase, tool path planning must be reasonable to minimize idle time and avoid unnecessary movements.

In the finish machining phase, precision becomes more critical. Smaller tools and lower cutting parameters are used to ensure the part reaches the required dimensions and surface finish. Tool paths during this phase need to be precise to avoid tool interference and errors.

2.4 Quality Control and Inspection

During the machining process, constant quality checks are required to ensure the part's accuracy meets the design requirements. Common measurement tools include calipers, micrometers, and internal/external diameter gauges. In the finish machining stage, careful attention to dimensional accuracy is essential.

In addition, surface roughness measurements should be conducted to verify that the part's finish meets the design specifications.

2.5 Post-Processing and Assembly

After machining, the part may have burrs that need to be removed. Deburring can be done manually or with deburring tools. For certain parts, post-processing treatments such as plating, spray coating, or heat treatment may be required to enhance wear resistance, corrosion resistance, or appearance.

III. Conclusion and Reflection

The part design and practical machining processes on a 3-axis CNC milling machine involve both challenges and attention to detail. In this entire process, students not only need to master the fundamental theory of part design but also learn how to convert the design into actual machining steps. Through CNC program development, tool path planning, and quality control, students can deepen their understanding of CNC machining and enhance their practical skills.

As CNC technology continues to advance, 3-axis CNC milling machines will be increasingly applied to more complex machining tasks. Therefore, mastering modern CNC technologies and machining processes will lay a solid foundation for students in their future engineering careers.