With the rapid development of modern manufacturing, the shapes of parts are becoming increasingly complex, which puts forward higher requirements for processing efficiency and accuracy. At present, the traditional processing methods have been difficult to meet the demand for efficient and high-precision processing of complex and irregular parts. ComputerNumericalControl (CNC) turning and milling compound machine tools integrate turning and milling functions. They have advantages such as multi-axis linkage and multi-process integration, and have unique advantages in processing complex and irregular parts.
1. Overview of CNC Turning and Milling Compound Machine Tools
The CNC turning and milling compound machine tool is a high-end CNC processing equipment integrating turning and milling functions, featuring multi-axis linkage and multi-process integration. Compared with the traditional single processing method, CNC turning and milling compound machine tools have obvious advantages in processing efficiency, accuracy and the manufacturing capacity of complex irregular parts. This type of machine tool is usually equipped with high-speed and high-precision spindles, which can achieve C-axis interpolation and milling functions, and is capable of processing complex curved surfaces, inclined surfaces, threads, splines and other special shapes. Meanwhile, advanced numerical control systems and programming software provide strong support for the process planning and optimization of CNC turning and milling compound machine tools [2]. Multi-axis linkage technology enables the cutting tool to move along complex spatial curves, achieving the processing of complex parts with a single clamping. This significantly reduces the number of clamping operations and processing time, and enhances processing efficiency and accuracy. In addition, CNC turning and milling compound machine tools integrate functions such as automatic tool changing, online measurement, and adaptive control, further enhancing the intelligent level of processing.
2. Characteristics of irregular-shaped parts
Special-shaped parts refer to components with complex geometric shapes, non-standard structures and high-precision requirements. Its processing is difficult and the technological requirements are high, which brings many challenges to the manufacturing industry. The characteristics of irregular-shaped parts are mainly reflected in three aspects. Firstly, the structure of irregular-shaped parts is complex, usually containing various geometric features such as freeform surfaces, deep cavities, thin walls, and small radii, and the processing of these features requires multi-axis linkage and precise control. Secondly, the dimensional accuracy and surface quality requirements for irregular-shaped parts are high. The shape and position tolerances, surface roughness and other indicators of irregular-shaped parts often reach the micrometer level, which poses extremely high requirements for processing equipment and technology. Finally, there are many types of materials for irregular-shaped parts, including common metal materials as well as difficult-to-machine high-temperature alloys, titanium alloys, etc.
3. High-efficiency processing technology for irregular parts based on CNC turning and milling compound machine tools
3.1 Process Planning and Programming
In the efficient processing technology of special-shaped parts based on CNC turning and milling compound machine tools, process planning and programming are crucial links. First, process personnel need to use Computer-aided Design (CAD) software to create three-dimensional solid models of irregular-shaped parts. Through 3D modeling, process personnel can comprehensively analyze the geometric features of the parts, optimize the design plan, and lay the foundation for the subsequent processing technology planning. Second, after completion of modeling, technology personnel need to use computer aided manufacture (ComputerAidedManufacturing, CAM) software, such as MasterCAM, PowerMILL, etc., for tool path planning and processing programming. CAM software can automatically identify the processing characteristics of parts, generate reasonable tool paths, and optimize cutting parameters, greatly improving programming efficiency and quality. Thirdly, for materials used in irregular-shaped parts, such as stainless steel, aluminum alloy, titanium alloy, etc., process personnel need to reasonably select cutting parameters in combination with the physical properties and processing characteristics of the materials, including cutting speed, feed rate and cutting depth, etc. Under normal circumstances: When processing stainless steel, the cutting speed is 30 to 50m·min -1 and the feed rate is 0.1 to 0.3mm·r-1. When processing aluminum alloys, the cutting speed is 200-500m·min-1 and the feed rate is 0.2-0.5mm·r-1. When processing titanium alloys, the cutting speed is 20-40m·min-1 and the feed rate is 0.05-0.20mm·r-1.
Fourth, while optimizing the cutting parameters, CAM software can achieve intelligent optimization of the tool path, such as adopting strategies like equidistant offset paths and equal-height Z-layer cutting, to reduce idle travel time and avoid frequent tool lifting and lowering, thereby significantly enhancing processing efficiency. Fifth, simulation and emulation technology is also playing an increasingly important role in process planning. By using simulation software, process personnel can conduct virtual simulation of the entire processing procedure before actual processing, comprehensively review issues such as tool movement trajectories, cutting parameter Settings, interference and collision, and thereby promptly identify and correct program errors.
3.2 Fixture Selection
When processing irregular parts with CNC turning and milling compound machine tools, the selection of fixtures is of vital importance. To ensure that the workpiece has a high degree of stability and repeatability during the processing, it is necessary to select special fixtures with higher precision according to the characteristics of the irregular parts. First of all, a comprehensive analysis of the geometric shape, dimensional tolerance, material properties, etc. of the irregular parts is required. On this basis, the basic type of the fixture should be determined. For complex-shaped parts with high dimensional accuracy requirements, precision fixtures such as chucks, three-jaw chucks, and pneumatic chucks are usually selected, combined with custom-made jaw shapes, to achieve rapid clamping and precise positioning of workpieces. For small and medium-sized irregular-shaped parts, general fixtures such as hydraulic fixtures and combined fixtures can be selected. Reliable clamping can be achieved by means of hydraulic pressure or combined positioning. For thin-walled parts, vacuum adsorption fixtures or magnetic fixtures should be given priority. Vacuum suction or magnetic force is utilized to achieve stable clamping of the workpiece while avoiding local deformation. Secondly, the machining accuracy of the fixture is a key factor to be considered when making a selection. To ensure the high repeatability of workpiece clamping, the manufacturing accuracy of the fixture should be at least one grade higher than that of the workpiece, and the geometric error of the positioning reference plane should be controlled within 5μm. Finally, in the case of multi-angle and multi-side processing, it is necessary to evaluate whether the fixture has good repositioning performance and sufficient rigidity to ensure the consistency of the workpiece position during multiple clamping processes.
3.3 Processing Execution and Monitoring
In the execution stage of processing irregular parts, it is crucial to give full play to the technical advantages of CNC turning and milling compound machine tools. Firstly, the CNC turning and milling compound machine tool is equipped with an advanced automatic tool changing system, with a tool magazine capacity of over 60 tools, capable of accommodating various turning tools, milling tools and drilling tools. The numerical control system automatically selects the required tools from the tool magazine according to the processing technology requirements and quickly installs them on the tool rest. The entire tool changing process is automatically completed through mechanisms such as mechanical arms or tool turrets, and the tool changing time is generally controlled within 2 to 3 seconds. Secondly, real-time monitoring and adaptive control during the processing cannot be ignored. Through various sensors built into the machine tool, such as temperature sensors and vibration sensors, key parameters like the spindle temperature rise, cutting force and tool vibration are collected in real time. When the monitoring data exceeds the preset threshold, the numerical control system automatically adjusts the cutting parameters such as the spindle speed and feed rate based on the feedback of the monitoring data, or promptly interrupts the processing and issues an alarm. This effectively avoids problems such as tool wear and workpiece damage caused by abnormal processing conditions, ensuring the stability of processing quality. For example: When the temperature of the main shaft rises to 80℃, the system can automatically reduce the main shaft speed by 20% and activate the cooling system to lower the temperature to 60℃ or below. When the cutting force exceeds 800N, the system can appropriately reduce the feed rate and cutting depth, and issue an alarm signal to remind the operator to check the tool status or optimize the cutting parameters. Finally, the online detection and compensation of processing accuracy is the key to ensuring the high precision of parts. CNC turning and milling compound machine tools are usually equipped with online measurement devices such as probes and line scanners to measure key quality characteristics such as dimensions and shape and position tolerances in real time during the processing. Among them, the repeat positioning accuracy of the probe can reach 1μm, and the measurement accuracy of the line scanner can reach 0.1mm. The measurement data is compared with the design model in real time, the processing error is automatically calculated, the point cloud map is generated and stored in the database. Then, the measurement data is analyzed and processed through the proprietary algorithm, the compensation parameters are automatically generated and sent to the tool path generation module and the displacement command unit, thereby adjusting the virtual position of the tool relative to the workpiece and achieving dynamic compensation of the processing error. Eliminate the cumulative effect of processing errors to the greatest extent.
4 Conclusion
This article explores the efficient processing technology of special-shaped parts based on CNC turning and milling compound machine tools. Through means such as process planning and programming optimization, innovative fixture design, real-time monitoring and compensation, the processing efficiency and accuracy of special-shaped parts have been significantly improved. The experimental results show that, compared with the traditional step-by-step processing technology, this method has achieved significant improvements in aspects such as processing time, accuracy control, surface quality and tool life. Future research can further explore directions such as intelligent process planning, multi-physical field coupling analysis, and advanced material processing technology to address the increasingly complex processing demands of irregular-shaped parts.
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