In the field of CNC machining, fixtures, as key technical devices, directly affect the stability and accuracy of machining precision. In this article, we will explore in depth the key influences of fixtures on machining accuracy, including fixture rigidity and stability, positioning accuracy, and the impact of uneven cutting force distribution on custom CNC machining. By dissecting these factors, we will focus on methods to optimize fixture design, aiming to improve the performance of fixtures in CNC machining.
Which Features of a Fixture Affect Machining Accuracy?
The influence of fixtures on machining accuracy is mainly reflected in the following aspects.
Fixture Rigidity and Stability
As a device for fixing the workpiece, the fixture carries the force and torque of the workpiece and maintains its position and attitude during the machining process. The rigidity and stability of the fixture directly affect the positioning accuracy, shape accuracy, surface accuracy, and other aspects of the machining process. The higher the rigidity of the fixture, the smaller the position change of the workpiece in the machining process, and the higher the positioning accuracy; poor stability of the fixture is likely to lead to changes in the attitude of the workpiece in the machining process, resulting in a decline in machining accuracy.
Fixture Positioning Accuracy
The positioning accuracy of the fixture has a direct impact on the machining accuracy. Positioning accuracy refers to the fixture for the position of the workpiece in the machining process control accuracy. Good positioning accuracy of the fixture can ensure that the workpiece is stably fixed in the correct position, to avoid displacement or deviation of the workpiece in the machining process, thus ensuring the stability and accuracy of machining precision.
Poor fixture positioning accuracy may lead to the following problems:
- Positional error: poor positioning accuracy of the fixture may lead to positional error of the workpiece during machining, which directly affects the accuracy of the machining results.
- Parallelism error: Poor positioning accuracy of the fixture may cause parallelism error of the workpiece during machining, which affects the flatness of the workpiece surface.
- Right angle error: poor positioning accuracy of the fixture may also cause right angle error of the workpiece in the machining process, affecting the shape accuracy of the workpiece.
In order to improve the fixture positioning accuracy, fixture positioning accuracy can be improved by reasonably designing the structure of the fixture, selecting the appropriate positioning method, and using auxiliary fixtures to ensure the reliability and accuracy of CNC machining.
Uneven Distribution of Fixture Cutting Force
The fixture fixes the workpiece in machining, but due to the limitations of the fixture’s own structure and the uneven distribution of force in the cutting process, it may have a negative impact on machining accuracy. When the cutting force is concentrated in a localized area of the workpiece, the stress concentration in that area increases, leading to a localized increase in deformation, which reduces machining accuracy.
Uneven deformation will make the geometry and size of the workpiece deviation, at the same time, uneven distribution of fixture cutting force will also cause small changes in the relative position of the workpiece and the tool, which in turn will have a negative impact on machining accuracy.
How to Improve Fixture Design for Machining Accuracy?
Optimize the Design of Fixture Rigidity and Stability
In order to improve the design of the fixture, the following aspects need to be considered:
- Rigidity design: select high-strength and high-rigidity alloy materials, such as steel and aluminum alloy, and adopt reinforcing bars and increase the support of the joints in order to improve the overall rigidity of the fixture.
- Stability design: Improve the stability of the fixture by increasing the positioning points and clamping force of the parts, reasonably distributing the clamping points, and using auxiliary devices such as springs and dampers.
- Consideration of cutting force and thermal deformation: In the design of fixtures, according to the size and direction of the cutting force, choose the appropriate support points and clamping methods, and at the same time, consider the problem of thermal deformation in the machining process, and take heat dissipation measures to ensure the stability of the fixtures.
These improvement measures can improve the rigidity and stability of the fixture to ensure that the parts can be stably and accurately positioned during machining, thus improving machining accuracy and efficiency.
Methods to Improve the Positioning Accuracy of the Fixture
In order to improve the positioning accuracy of the fixture, the following measures can be taken:
- Structural design: the fixture structure should be simple and compact to avoid loosening and deformation. Choose materials with high strength and good rigidity, and use adjustable positioning blocks and clamping devices so that they can be adjusted according to the dimensions of different parts to improve the accuracy of positioning.
- Positioning methods: Choose appropriate positioning methods, such as plane positioning, pin positioning, curved surface positioning, etc., and make reasonable choices according to the shape of the parts and processing requirements to ensure that the fixture can accurately position the parts.
- Auxiliary fixtures: Adopt auxiliary fixtures, such as setting auxiliary positioning blocks, clamping steel plates, etc., to increase the clamping force and stability and improve the accuracy of positioning.
Strategy of Balanced Fixture Cutting Force Distribution
In fixture design, balanced fixture cutting force distribution is an effective way to improve the accuracy and stability of parts machining. Adopt the following strategies:
- Consider the characteristics of the parts: according to the geometric shape of the parts and process requirements, choose different fixture positioning and fixing methods, combined with the direction and size of the cutting force to optimize the design.
- Material selection and machining process: Select materials with good rigidity and deformation resistance, such as high-strength alloy steel, while taking appropriate process measures during fixture machining to improve the hardness and accuracy of the material to ensure the stability of the fixture.
- Multi-point clamping: For parts with complex shapes, consider using multi-point clamping to increase the contact area between the fixture and the part, evenly distribute the cutting force, and reduce deformation and vibration.
- Compensating mechanism and adjusting device: add a compensating mechanism and adjusting device in the design of the fixture structure to realize the dynamic adjustment and balance of fixture cutting force and improve the stability and consistency of machining.
Conclusion
The design and optimization of fixtures is a key link to ensure machining accuracy and efficiency. By comprehensively considering the rigidity, stability, positioning accuracy, and cutting force distribution of the fixture, the quality of parts machining can be effectively improved to meet different process requirements and improve production efficiency.