CNC cutting  plays an important role in the modern manufacturing industry, and its high efficiency and precision machining capabilities make it widely used in aerospace, automotive manufacturing, mold processing and other fields. However, despite the high degree of automation and precision control of CNC technology, dimensional instability problems still occur from time to time during the actual processing. These instabilities not only affect the quality of the product, but also may lead to a decrease in productivity and an increase in cost. In this article, we will delve into the causes of dimensional instability in CNC cutting and propose targeted solutions to help practitioners improve machining accuracy and stability.

Causes

1. The impact of the workpiece material

• Material heterogeneity: different materials in the machining process shows different mechanical properties, especially the hardness and toughness of the changes will affect the stability of the cutting force, resulting in inconsistent size.
• Thermal expansion effect: in the cutting process, the workpiece may expand due to heat, and different materials have different coefficients of thermal expansion, which may also lead to dimensional deviations.

2. Effect of tooling

• Tool wear: the tool will gradually wear in the process of use, after the wear of the tool can not maintain stable cutting performance, resulting in increased dimensional error.
• Tool geometry angle: tool geometry angle design is not reasonable, will also affect the cutting process of the force situation, thus causing dimensional instability.

3. The impact of the machine tool

• Insufficient rigidity of the machine tool: the rigidity of the machine tool directly affects the stability of processing, rigidity of the machine tool in the cutting process is prone to vibration, resulting in dimensional errors.
• Temperature changes in the machine tool: machine tool in the process of heat generated by the operation of the machine tool structure will cause small deformation, this thermal deformation if not effectively controlled, will lead to the processing of dimensional instability.

4. The influence of process parameters

• Cutting speed, feed rate and depth of cut: unreasonable process parameter settings may lead to uneven tool force, thus triggering fluctuations in machining size.
• Improper use of coolant: the use of coolant not only affects the temperature of the cutting area, but may also affect the stability of the cutting force. If cooling is not appropriate, it may lead to the concentration of thermal stresses, thus causing dimensional changes.

5. Influence of the machining environment

• Temperature and humidity changes: changes in the temperature and humidity of the machining environment can lead to thermal expansion or contraction of the machine tool, cutting tool and workpiece, thus causing fluctuations in machining dimensions.
• Vibration interference: Mechanical vibration from the surrounding environment may be transmitted to the machine tool, affecting machining accuracy.

Strategies

1. Material Selection and Pre-treatment

• Material Selection: Before machining, select suitable materials according to the specific requirements of the workpiece, especially in the coefficient of thermal expansion and mechanical properties should be fully considered.
• Material pre-treatment: For materials that are susceptible to thermal deformation, heat treatment or natural aging can be used to reduce their internal stress and improve machining stability.

2. Tool optimization

• Tool material and coating selection: selecting the right tool material and coating can reduce tool wear, extend tool life and ensure machining stability.
• Optimization of tool geometry parameters: According to the machining requirements, optimize the geometric angle of the tool, such as the main offset angle, front angle and back angle, in order to reduce the cutting force and reduce the dimensional error.

3. Machine tool maintenance and adjustment

• Regular maintenance: carry out regular inspection and maintenance of the machine tool, especially the calibration of key components such as machine guides and screws, in order to ensure the machining accuracy of the machine tool.
• Thermal deformation control: For machine tools that are more sensitive to thermal deformation, constant temperature control, cooling system optimization and other means can be taken to reduce the impact of thermal deformation on dimensional accuracy.

4. Optimization of process parameters

• Reasonable setting of cutting parameters: According to the material of the workpiece and processing requirements, reasonably set the cutting speed, feed rate and depth of cut to ensure the stability of the machining process.
• Coolant management: optimize the use and flow of coolant to ensure that the temperature of the cutting area is controlled within a reasonable range and reduce the impact of thermal stress on the dimensions.

5. Environmental control

• Temperature and humidity control: In the machining environment, constant temperature and humidity equipment is used to reduce the impact of environmental temperature and humidity changes on the machine tool and workpiece.
• Vibration isolation: Reduce the influence of environmental vibration on machining accuracy by installing vibration-damping devices on the foundation of the machine tool or taking other vibration isolation measures.

Applications

1. Online measurement and feedback control

• Online measurement technology: By installing high-precision online measurement equipment, real-time monitoring of dimensional changes in the machining process, timely adjustment of process parameters to ensure machining accuracy.
• Closed-loop control system: Apply closed-loop control technology to feedback the online measurement results to the CNC system, automatically adjust the machining parameters and improve the machining stability.

2. Intelligent tool management system

• Tool life prediction: Through the intelligent tool management system, real-time monitoring of tool use conditions, predicting tool life, timely replacement of tools to avoid dimensional errors caused by tool wear.
• Adaptive tool parameters: According to the actual state of the tool in the machining process, adaptively adjust the geometric parameters and cutting parameters of the tool to optimize the machining quality.

3. Advanced machine tool structure design

• High-rigidity machine tools: develop high-rigidity, vibration-resistant machine tool structures to reduce vibration during machining and ensure dimensional stability.
• Thermal compensation technology: Introduce thermal compensation technology in machine tool design, automatically adjusting the position compensation of the machine tool by real-time detection of temperature changes in various parts of the machine tool to reduce the impact of thermal deformation.

Case

In the CNC machining of an aerospace part, because the workpiece is made of high-strength alloy, serious dimensional instability occurred during the cutting process.

Through a comprehensive analysis of the machining process, it was found that the problem mainly originated from tool wear and insufficient machine rigidity. In response to this problem, the technical team took the following measures:

(1) replace the tool with better wear resistance and optimize the tool geometry to reduce the cutting force.

(2) strengthen the rigidity of the machine tool and install vibration-damping devices in key areas. 3. apply on-line measurement technology for real-time measurement.

(3) apply on-line measurement technology to monitor the dimensional changes in real time, and adjust the parameters through the closed-loop control system.

After these optimization measures, the final machining dimensional stability of the part has been significantly improved, and the pass rate has increased from 85% to 98%.

Summarize

The problem of dimensional instability in CNC cutting machining is a complex, multi-factor influence of the problem. Through the comprehensive consideration of materials, tools, machine tools, process parameters and environmental factors, and the introduction of advanced measurement and control technology, the problem of dimensional instability can be effectively reduced to improve machining quality and productivity.

In the future, with the development of intelligent manufacturing technology, the accuracy and stability of CNC cutting machining will be further improved to provide stronger support for the manufacturing industry.

This blog post not only provides theoretical analysis, but also combines practical cases to provide practical solutions for practitioners in the CNC machining industry. We hope that this article will contribute to the improvement of CNC machining accuracy and stability.