summary:
[Objectif]Aiming at the defects of special milling machines for screw processing, such as low degree of automation, poor functional integration, long production process cycle, old machine tool structure and poor stability of mechanical structure .
[Méthode]The research team started from the research on the structural stability design of the CNC milling machine system. According to the design goals of the machine tool and various performance index requirements, the research team studied the layout of the functional mechanism compatible with the processing technology. , designed the overall structure plan of the machine tool and focused on studying the loading and unloading of the mechanism, rotary milling system, transmission system and machine bed.
[Résultats]High-end motor shaft screw milling and turning equipment with excellent performance and complete functions has been designed to realize automatic processing of motor shaft screws, reduce labor production costs enterprise work, improve production efficiency and increase the economic benefits of the enterprise.
[Conclusion]The overall structure design of this CNC milling machine is stable and compact, with a small footprint and high integration.
Keywords: CNC milling machine; mechanical structure; optimized design;
0. Introduction
In recent years, the performance of my country’s motor shaft and screw rotary milling equipment has been greatly improved, but compared with foreign high-end rotary milling equipment, it is still in a low-level repetitive state. The specific manifestations are as follows: 1) The degree of equipment integration is low. The functional structure of existing machine tools cannot meet the optimal strategy of the production process. The parts circulation cycle is long, the production efficiency is low, and the floor space is large. 2) The structure of the machine tool is old. Existing motor shaft screw whirling milling machines are mainly based on flat bed bodies, which have lower cutting rigidity than foreign inclined guide rail and stepped guide rail machine tools, and the exposed surface of the guide rail is prone to wear and thermal deformation due to the impact of a large number of chips. 3) The cyclone milling head has insufficient stability.
The power configuration of domestic cyclone milling heads is mainly rear-mounted, and the belt type is combined narrow V-belt. Transmission efficiency is low and torsional vibration is likely to occur. and the rear end bearings of the cutting shaft, and the wear of the rear bearings increases. The cutter shaft of the milling head is long, and the inner hole is mainly a straight cylinder, which seriously limits the processing range of the helix angle of the screw. In order to prevent chips and liquids, most milling heads are sealed. Increasing the friction temperature of bearings during operation can easily cause thermal deformation of the cutter shaft. There are many reasons that affect the performance of rotary milling equipment. In addition to factors such as material properties, manufacturing processes and installation techniques, the design of mechanical structure stability is also one of the important factors. In order to develop rotary milling equipment with stable, safe and reliable structure, researchers started from the forming mechanism of rotary milling and explored the effects of process path, cutting parameters, tool number , tool material, workpiece properties and other factors on chip morphology. distribution, forming precision. Based on the influence of equipment processing efficiency, we constructed a time-varying cutting force model and a time-varying heat source model, optimized the number and arrangement of tools and provided significant technical support for the dynamics of the rotary milling system. analysis, design and optimization of equipment structure and improvement of equipment performance.
The thermal characteristics and dynamic and static performance of the rotary milling system are the focus of research on the stability of the rotary milling system. Son et al. evaluated the stability of the rotary milling head from the thermal, dynamic and static characteristics of the key components performing whirl milling. The research results show that the increase in friction temperature of the milling head bearing is the main influencing factor of the thermal deformation and vibration of the rotating milling component and is one of the research contents important in the design and manufacture of the cyclonic milling machine. In addition, the researchers also carried out dynamic performance analysis of the bed and milling head of the screw whirling milling machine and turbine whirling milling machine, and carried out modal tests, which provided guidance for the design of CNC rotary milling equipment. Tan Lixin studied the deformation and vibration error of the workpiece at different rotation speeds of the multi-axis rotary milling device and proposed a method to control the rotation speed to change the vibration error value. Zhang Chunjian et al. conducted dynamic simulation analysis on the main transmission system and milling system of a large whirl milling machine and proposed using multi-point supports and silicone oil dampers to suppress vibration of the rotary milling system . Yin Huijun et al. carried out a test and analysis on the vibration of the cyclone milling machine when processing the external thread of a large anchor, and adopted a method of thickening the base of the milling head to reduce the vibration. Although researchers have carried out in-depth research on rotary milling mechanism and system structure stability design, the above-mentioned research objects mainly focus on screw, thread, screw, screw large modulus, impeller, etc., aimed at motor design. Rotary shaft screw milling equipment. Structural optimization design is rarely reported. Therefore, it is necessary to formulate a fully automatic machining process plan for the motor shaft screw based on existing research, reasonably plan the structural layout of the machine tool, carry out research on the milling mechanism of the motor shaft screw parts, clarify the number and arrangement of tools, and use advanced technology on this basis. The design method rationally constructs a system structure that matches, optimizes and improves the processing technology plan.
In summary, this paper takes the research on structural stability design of CNC milling machine systems as a starting point. According to the design goals of the machine tool and various performance index requirements, the layout of the functional mechanism suitable for the processing technology is studied. and the overall structural plan of the machine tool is designed, focusing on the upper and lower parts. The design of hardware mechanism, rotary milling system, transmission system and machine frame. Significantly improve the rigidity of the process system to achieve reduction and suppression of vibration of the screw processing system and ensure the precision of workpiece processing.
1. Design method
1.1 Optimal design analysis of loading and unloading mechanism
According to the shape, weight and position of the blank at the end of the feeding mechanism, the dimensional parameters of the machine tool spindle and hydraulic clamp of the workpiece are comprehensively considered to determine the installation location and stroke range of the feed mechanism. Design a clamping mechanism that matches the shape of the blank, calculate the required clamping force, and match the appropriate force source mechanism. Based on the functional purposes of the feeding mechanism (clamping the blank and direct feeding into the workpiece clamping mechanism), transmission efficiency and speed of execution, the type of kinematic pair should be reasonably selected and the component parameters should be clarified. Based on the size of the load, calculate and determine the performance index parameters of the main motor of the feeding mechanism. Analyze the influencing factors such as shape, weight, workstation conditions of the castings, layout and stroke range of the cyclone milling head, and study and determine the functions of the return (receiving) mechanism , material clamping and cutting). It is planned to use the superposition mechanism design method to analyze each functional mechanism, clarify the type, quantity and performance parameters of kinematic pairs, and complete the component size and structural design to meet the functional requirements. . Based on the technical parameters such as mechanism running speed, rated load and moment of inertia, determine the power type, calculate and select the appropriate main motor specifications. Based on multi-body dynamics, simulate and analyze the running speed, stress state and motion interference of the feedback mechanism to optimize the design plan.
1.2 Dynamic design analysis of cyclone milling machine transmission system
In order to meet the process flow of the integrated cyclone milling machine and realize the construction of a compact integrated manufacturing unit, a dynamic design of the transmission system is planned by comprehensively considering the functional requirements such as the range of machine tool speed, transmission efficiency, transmission. precision, transmission stability and service life. Based on the execution functions and technical requirements of the integrated rotary milling machine, the design goals of each transmission system are proposed, and the configuration of each transmission system is optimized. 1) Design of the workpiece spindle transmission system. Based on the load characteristics of rotary milling, speed change range, transmission efficiency and other conditions, the output power of the workpiece spindle motor is calculated and selected. Under the conditions to meet the processing range of parts and not weaken the rigidity, based on the motor output power and spindle design principles, the amount of overhang, the size of the support span and the size of the pin opening are initially determined. Study the load distribution characteristics of the system, rationally select the types of bearings and check their service life. According to the transmission configuration mode and transmission ratio requirements, consult relevant design manuals, determine various working condition coefficients, comprehensively consider the limitations of installation space, rationally design the dimensions of the transmission components and complete the verification. ANSYS finite element analysis software is used to analyze the static and dynamic characteristics of the spindle transmission system. It mainly studies the regular changes between the strength, stiffness, vibration shape and structural parameters of the spindle, and optimizes the design plan of the spindle. transmission system. 2) Design of the axial and radial transmission system. According to the technical requirements of the cyclone milling machine processing precision, processing stroke, feeding speed, load size, etc., determine the operating parameters of the ball screw pair, Preliminary calculations determine the screw pitch, accuracy and dynamic load rating, and estimate the maximum allowable axial strain, lower thread diameter, determine the secondary specification code of the ball screw, and perform various performance checks. Calculate and analyze the total moment of inertia of the screw, total load torque of the screw, no-load acceleration and deceleration torque, etc., and then rationally select the motor model and check it. The maximum axial load of the bearing pair is determined based on the maximum load force of the system and the sum of the axial pretension force of the screw. Based on this value, the preload force of the bearing pair and the rated dynamic load of the bearing pair. , together with the equivalent load and other basic information, determine the bearing model and verify. According to the selection criteria of rolling guide rails and the actual working conditions of the pair of guide rails, determine the rail width, rail length, slider type, precision level, height type of combination, preload level, etc. Perform dynamic analysis of axial and radial transmission systems respectively to optimize the transmission system design.
1.3 Lathe bench optimization design based on sensitivity analysis
The bed is the most important supporting element of a cyclone milling machine. Its structural rationality and performance will directly affect the machining precision of the machine tool and the manufacturing cost of the equipment. The bed structure of the existing cyclone milling machine is analyzed from aspects such as layout form, load distribution, rigidity and overall stability. The project plans to use local corrugated ribs and high-rigidity ladder-type ribs reinforced with ribs with good vibration reduction. effects. Bed structure. Perform static and dynamic characteristic analysis according to its actual working conditions, comprehensively consider the importance of each mode, initially determine the size change range of design variables, and use BoxBehnken test method and sensitivity analysis to determine the impact of each design variable. on the output parameters (mass, displacement, inherent frequency), select design parameters with higher sensitivity and establish a response surface model. Taking the minimum mass, minimum displacement and highest natural frequency as objective functions, the screening method is used to perform multi-objective parameter optimization to obtain the optimal structural parameters. The optimization analysis diagram of the machine tool bed structure is shown in Figure 1.
Figure 1 Optimization analysis diagram of lathe bed structure
2. Conclusion
The research team proposed the optimization design theory of screw-specific CNC milling machine mechanical structure system and support system structure design are the deciding factors to realize fully automatic processing of milling machine integrated rotary. directly affect the processing performance of rotary milling equipment. Production efficiency and processing precision are the keys to solving the problems of long production process cycle, poor processing stability and poor integration of existing screw and motor shaft rotary milling equipment. The research team developed a new continuous-feed automatic processing technology, and designed and optimized the key functional structure which perfectly matches the process strategy. Designed to realize fully automated processing of motor shaft screws, it is expected to shorten the production cycle of the process and improve production efficiency. The overall machine structure design is stable and compact, with a small footprint and high integration.
source:
Authors: Chen Cong1, Wang Yicheng3, Zheng Xuefei1, Shao Sicheng2, Chen Jianxin1, Wang Sheng2, Zhu Qin1
(1. Zhejiang Heco Intelligent Equipment Co., Ltd. 2. Quzhou Vocational and Technical College 3. Quzhou Futeng Technology Co., Ltd.)
Daguang focuses on providing solutions such as precision CNC machining services (3-axis, 4-axis, 5-axis machining), CNC milling, 3D printing and rapid prototyping services.
