10 Valuable Tips for CNC Machining

CNC machining, also known as numerical control machining, refers to machining performed with numerically controlled machining tools. It has the advantages of stable machining quality, high machining accuracy, high repeatability, the ability to process complex shapes, and high machining efficiency. In the actual machining process, human factors and operating experience, to a large extent, will affect the final machining quality. Below are 10 valuable tips for CNC machining.

1. How to divide CNC machining processes?

The division of CNC machining processes can generally be done by the following methods:

a. Concentrated Tool Division Method:

Dividing processes based on the tools used, with the same tool completing all feasible parts on the workpiece. The  subsequent tools will be used to complete additional portions, reducing tool changeovers, minimising non-cutting time, and decreasing unnecessary positioning errors.

b. Part-Based Division Method:

For parts with complex CNC machining requirements, sections can be divided based on structural features, such as internal features, external features, surfaces, or planes. Usually, flat surfaces and positioning surfaces are machined first, followed by hole machining. Simple geometric shapes are machined before complex ones, and lower precision areas are machined before high-precision areas.

c. Rough and Finish CNC Machining Division Method:

Parts that are prone to deformation during CNC machining often require separate procedures for roughing and finishing, due to the need for shaping after roughing.

When dividing processes, it's essential to consider the part’s structure and manufacturing feasibility, machine functionality, the extent of CNC machining content, installation frequencies, and the organisation's production conditions. The principle of centralised or dispersed processes should be determined based on specific conditions, with a focus on rationality.

2. What principles should be followed in arranging the CNC machining sequence?

The sequencing of processes should be based on the part's structure, the condition of the raw material, and the requirements for positioning and clamping, with a priority on preserving the part's rigidity. The sequence should generally follow these principles:

a. The previous machining operation should not affect the positioning and clamping for subsequent operations, and any interposed conventional machine tool operations need to be comprehensively considered.

b. Internal cavity processes should precede external feature machining.

c. Processes with the same positioning and clamping method or using the same tool should be connected to minimise repeated positioning, tool changes, and workpiece relocation.

For multiple operations performed in a single setup, priority should be given to those that cause the least rigidity damage to the part.

3. What aspects should be considered when determining workpiece clamping methods?

When determining positioning references and clamping schemes, attention should be paid to the following three points:

a. Seek unified references for design, process, and programming calculations.

b. Minimise the number of clamping instances and attempt to complete all required surfaces in a single setup.

c. Avoid using manual adjustments.

For situations where the fixture obstructs tool movement, methods such as using vise jaws or adding a base plate for clamping should be considered.

4. How to determine the tool setting points reasonably? What is the relationship between the workpiece coordinate system and the programming coordinate system?

Tool setting points can be set directly on the workpiece, but they must align with established reference points with a known fixed distance. The relative tool setting position is generally located on the machine table or fixture and should be easy to find, convenient to program, have minimal tool setting errors, and be easily verifiable during machining.

The workpiece coordinate system’s origin is set by the operator after workpiece clamping and tool setting, reflecting the distance and position relationship between the workpiece and the machine tool zero point. The workpiece coordinate system is typically fixed once established and should be consistent with the programming coordinate system during machining.

5. How to choose the tool path?

The tool path refers to the trajectory and direction of the tool relative to the workpiece during CNC machining. Proper selection of the tool path is crucial as it directly impacts the machining accuracy and surface quality. Considerations for selecting the tool path involve:

a. Ensuring the precision requirements of the workpiece.

b. Easy numerical calculation and reduced programming workload.

c. Seeking the shortest machining path to minimise non-cutting time and improve machining efficiency.

d. Minimising the number of program segments.

Ensuring the workpiece's final contour is machined last and using the appropriate cutting strategies for entry and exit points to avoid sudden changes in cutting forces and potential workpiece damage.

6. How to monitor and adjust during CNC machining?

After workpiece setup and program verification, production proceeds to the automatic machining stage. During this phase, operators should monitor the cutting process to prevent quality issues and accidents. Monitoring is primarily focused on:

a. Monitoring the cutting process during roughing, focusing on efficient material removal and load distribution.

b. Monitoring cutting sounds for their stability and identifying deviations that indicate tool wear or workpiece abnormalities.

c. Paying attention to chip control and surface quality during finishing, adjusting cutting parameters as needed to maintain consistent quality.

Direct Tool monitoring is essential and can help prevent the occurrence of processing quality problems caused by untimely tool modifications.

7. How to select cutting tools reasonably?

The choice of cutting tools depends on the type of machining operation and the workpiece material, with considerations for tool material, geometry, and coatings. It’s important to understand the significant elements of cutting parameters and the types of cutting tool materials, in addition to carefully determining the tool's rotational speed, cutting speed, and cutting width.

8. What is the role of a machining program sheet? What should it include?

The machining program sheet is an essential part of CNC machining process design and serves as a guideline for operators, containing detailed instructions related to programming, workpiece clamping, tool usage, and machining characteristics.

The program sheet should include information on the drawing and programming file names, workpiece details, fixture sketches, program names, tooling details, maximum cutting depths, machining characteristics, theoretical machining time, and any special considerations.

9. What is necessary before CNC programming starts?

Before CNC programming begins, it’s crucial to understand the workpiece clamping method, the size of the workpiece stock to determine the extent of machining, the material of the workpiece to choose appropriate tools, and a review of available to avoid programming adjustments due to the absence of specific tools required for the job.

10. What are the principles of setting a safe height during programming?

The safe height should generally be set above the highest surface of the workpiece to avoid tool collisions. Alternatively, setting the programming zero point at the highest surface of the workpiece can effectively prevent tool collisions.

The above are 10 valuable experiences that can be referenced during CNC machining. JLC3DP focuses on 3D printing and CNC processing. It now has advanced 3D printing equipment, large-scale precision CNC machine tools, and is equipped with complete testing equipment and an after-sales service system. For customization needs of processed products, join and get an instant quote!