【作者】 何耿煌；

【导师】 刘献礼；

【作者基本信息】 哈尔滨理工大学 ， 机械制造及其自动化， 2013， 博士

【摘要】 大型筒节毛坯为自由锻造而成,其直径最大可达7m以上,最大高度达6.4m,单件重达200多吨。大型筒节毛坯锻件表面加工条件非常恶劣,其荒加工过程中材料去除量高达50%,切削深度ap更是达到30mm,其材料采用高温高强度钢2.25Cr-1Mo-0.25V,切削过程中不同切削参数会产生刚度极高且形态各异的大型切屑,切屑的折断需要很大的机械载荷。因此,切屑的每次折断均会给刀片造成机械冲击。切削过程中由工件表面的锻造缺陷和大型切屑折断瞬间所引起的冲击载荷以及工件表面的金属硬化物等均会引起硬质合金车刀发生冲击破损(冲击断裂和疲劳断裂)以及高温力学性能失稳现象的发生。针对大型锯齿形切屑生成特点,通过应用有限元仿真及切削实验研究相结合的方法,深入分析重型切削特点及大型切屑形式与卷曲过程,借助扫描电镜观察,揭示大型切屑形成机理；通过应用有限元仿真分析大型切屑卷曲过程，明确其折断位置范围,建立大型切屑折断载荷力学模型,定量描述其折断载荷大小及分析影响模型精确度的相关因素,并通过切削实验验证模型的准确性及可靠性。针对重型切削过程中硬质合金车刀易产生冲击断裂的问题,应用机械冲击理论从冲击载荷角度分析重型硬质合金车刀冲击断裂产生的原因,并确立其产生冲击断裂的临界条件；采用数值描述结合有限元仿真的方法,分析研究重型硬质合金车刀冲击断裂产生机理及破损形式,并通过冲击实验揭示硬质合金抗冲击强度的尺度特性。针对重型硬质合金车刀发生疲劳失效现象。通过疲劳实验,提出动态载荷下硬质合金疲劳断裂产生机制；通过断续切削实验,研究分析导致硬质合金车刀疲劳行为产生的本质原因,提出预防硬质合金车刀过早出现疲劳的措施。针对重型切削过程中由高温引起的硬质合金车刀力学性能失稳问题。对重型车削过程中的切削热产生与影响进行研究。通过有限元仿真分析,揭示重型切削过程切削热产生机制；采用温升实验方法,对硬质合金硬度与温变的关系进行分析,研究硬质合金车刀硬度的温变规律：通过热冲击和热膨胀实验,研究热冲击对硬质合金车刀力学性能的影响,并明确重型切削最高温度范围。提出一种基于图像处理技术的大型筒节毛坯锻件荒加工：过程车刀切削行程计算和冲击寿命评价方法,并明确该方法的限定条件：综合分析筒节荒加工过程特点,提出实现大型筒节高效加工的技术措施。本文采用硬质合金车刀,以重型筒节材料高温高强度钢2.25Cr-1Mo-0.25V钢的切削过程为研究对象,通过理论分析、数值计算模拟以及高温性能实验、切削实验相结合的方法,在大型切屑折断力学、硬质合金车刀冲击断裂、疲劳断裂、高温力学特性以及车刀寿命评价等方面进行研究。研究可为重型切削加工的生产增效以及重型切削刀具开发技术的推广提供理论指导和技术支撑。更多还原

【Abstract】 The large shell blank is made by free forging, with the maximum diameter of above7m, the maximum height of6.4m and weight of over200tons. The processing condition of its forging surface is so worse. During its hogging machining, the material removal amount reaches50%and the cutting depth ap even reaches30mm. The high-temperature and high-strength steel2.25Cr-1Mo-0.25V is adopted as its material. During the cutting process, different cutting parameters will generate large chips with extremely high rigidity and various shapes. The fracture of the chips requires great mechanical load. Therefore, the fracture of the chips for each time will give rise to mechanical impact for the cutters. During the cutting process, the impact load (resulting from the forging defect and large chip fracture) and the hardened metal material of the work piece surface lead the hard alloy turning tool to generate impact breakage (impact fracture and fatigue fracture) and the occurrence of instability of mechanical properties under high temperature.Aiming at the generation feature of large saw-tooth chip, by the means of the integration of finite element simulation and cutting experiment study, it makes deep analysis on the features of heavy cutting, forms of large chip, and curling process, and reveals the generation mechanism of large chip by virtue of SEM observation; by the means of applying finite element simulation to analyze the curling process of large chip, it clarifies the scope of its fracture position, establishes a mechanical model of large chip fracture load, makes quantitative description towards its fracture load magnitude, analyzes the relevant factors influencing the accuracy of the model, and tests the accuracy and reliability of the model through cutting experiment.Aiming at the problem that the hard alloy turning tool easily generates impact fracture during the cutting, it applies mechanical impact theory, analyzes the causes of the impact fracture generation of the heavy hard alloy turning tool from the respective of impact load, and determines the critical condition for generating impact fracture; it adopts the method of integrating numeric description with the finite element simulation, analyzes and researches the generation mechanism and impact fracture form of the heavy hard alloy turning tool, and reveals the axial dimension rule of hard alloy shock strength through impact experiment.Aiming at the fatigue failure of heavy hard alloy turning tool, through fatigue experiment, it puts forward the generation mechanism of hard alloy fatigue fracture under dynamic load; through interrupted cutting experiment, it analyzes and researches the essential causes for the occurrence of fatigue behavior of hard alloy turning tool, and puts forward measures of preventing the early occurrence of fatigue.Aiming at the problem about the instability of mechanical properties of hard alloy turning tool resulting from high temperature during the heavy cutting process, it makes research on the generation and influence of the cutting heat. Through finite element simulative analysis, it reveals the generation mechanism of cutting heat during the heavy cutting process; through adopting temperature rise experiment, it analyzes the relation between the hard alloy hardness and the temperature variation, and makes research on the temperature variation effect of the hardness; through thermal shock and thermal expansion experiment, it makes research on the influence of thermal shock on the mechanical properties of hard alloy turning tool, and clarifies the maximum temperature range of the heavy cutting.It puts forward the cutting stroke calculation and impact lifespan evaluation method of the hogging machining procedure of large shell blank on the basis of image processing techniques, and clarifies the limit conditions of such method; it makes comprehensive analysis on the features of hogging machining of the shell, and puts forward the technological measures to realizing high-efficiency processing of the large shell.This paper adopts the hard alloy turning tool, and takes the cutting process of high-temperature and high-strength steel2.25Cr-1Mo-0.25V of heavy shell material as the research object. Through the methods of integrating theoretical analysis, numerical computational simulation with high-temperature performance test and cutting experiment, it makes research on the mechanics of large chip breaking, impact fracture, fatigue fracture, high-temperature mechanic features and lifespan evaluation of the hard alloy turning tool, etc. This research will provide theoretical guidance and technical support for the production synergy of the heavy cutting processing and the popularization of heavy turnin tool development technologies.更多还原