本文選題：高速切削 + 鋸齒狀切屑��； 參考：《山東大學(xué)》2016年博士論文

【摘要】：隨著高速切削機(jī)床和先進(jìn)刀具的迅速發(fā)展,高速切削加工技術(shù)已在汽車制造、航空航天和國(guó)防工業(yè)等領(lǐng)域開始獲得應(yīng)用。相比于普通切削速度加工,高速切削條件下的高應(yīng)變率特性導(dǎo)致工件材料動(dòng)態(tài)力學(xué)性能發(fā)生劇烈變化,進(jìn)而導(dǎo)致切屑形成機(jī)理和切屑形態(tài)的轉(zhuǎn)變。隨切削速度提高時(shí),塑性金屬材料的切屑形態(tài)演化規(guī)律為帶狀切屑、連續(xù)型鋸齒狀切屑、完全分離的鋸齒單元分節(jié)切屑,并最終形成類似于脆性材料切削時(shí)的碎斷切屑。以往研究主要針對(duì)高速切削切屑鋸齒化臨界條件以及鋸齒狀切屑的幾何表征等問(wèn)題,關(guān)于材料動(dòng)態(tài)力學(xué)性能對(duì)鋸齒狀切屑和碎斷切屑形成時(shí)材料變形及斷裂行為的控制機(jī)理研究較少,目前尚缺乏深入的理解和認(rèn)識(shí)。金屬切削可認(rèn)為是切屑與工件材料之間產(chǎn)生目的性斷裂的過(guò)程,揭示鋸齒狀切屑和碎斷切屑形成時(shí)的材料變形和失效機(jī)理,不僅能夠指導(dǎo)優(yōu)化切削工藝參數(shù),有助于實(shí)現(xiàn)高效率低能耗加工,而且可以為高速機(jī)床設(shè)計(jì)、刀具設(shè)計(jì)等提供理論基礎(chǔ)。本文以Ti6Al4V、Inconel 718和7050-T7451等三種工件材料為研究對(duì)象,通過(guò)材料力學(xué)和切削理論分析、有限元仿真、切削實(shí)驗(yàn)及顯微觀測(cè)等手段對(duì)鋸齒狀切屑和碎斷切屑的形成機(jī)理進(jìn)行研究,重點(diǎn)分析在高切削速度下工件材料的動(dòng)態(tài)力學(xué)性能變化——特別是塑性金屬材料的塑脆性能轉(zhuǎn)變——對(duì)切屑變形和失效行為的影響規(guī)律。主要研究?jī)?nèi)容包括：不同形態(tài)切屑的形成過(guò)程;碎斷切屑形成的臨界切削條件；材料性能對(duì)鋸齒狀切屑剪切局部化的敏感性分析；應(yīng)力狀態(tài)對(duì)鋸齒狀切屑斷裂行為的控制機(jī)理；以及高速切削切屑形成過(guò)程的能量耗散特性分析等。通過(guò)該文研究,以期在高應(yīng)變率下材料動(dòng)態(tài)力學(xué)性能與高速切削工藝之間建立起研究橋梁,為高速切削機(jī)理的揭示和高速加工技術(shù)的推廣奠定理論基礎(chǔ)。首先,針對(duì)高速切削切屑形成過(guò)程進(jìn)行研究,分析切削速度提高時(shí)工件材料的切屑形態(tài)演化規(guī)律,揭示不同切削速度下切屑的變形和斷裂機(jī)理,建立鋸齒狀切屑和碎斷切屑的形成模型。對(duì)獲得切屑的不同部位(包括切屑橫截面和自由表面、切屑斷口等)進(jìn)行顯微觀察,探索三種工件材料的切屑變形和失效機(jī)理,根據(jù)鋸齒狀切屑形成特點(diǎn)提出絕熱剪切-韌性斷裂復(fù)合型切屑形成模型,而碎斷切屑的形成是由脆性斷裂所致。針對(duì)金屬材料在高應(yīng)變加載下的塑脆轉(zhuǎn)變機(jī)制,應(yīng)用應(yīng)力波傳播理論,建立超高切削速度下碎斷切屑形成的臨界判據(jù),獲得碎斷切屑形成的臨界切削條件。根據(jù)切屑形態(tài)特點(diǎn)及其變形機(jī)理,將切削范圍劃分為普通速度切削、高速切削和超高速切削。然后,建立高速直角切削鋸齒狀切屑形成的有限元仿真模型,探索材料性能對(duì)鋸齒狀切屑剪切局部化影響的敏感性,揭示工件材料內(nèi)廩變量(包括材料力學(xué)性能和損傷特性參數(shù))對(duì)高速切削切屑形態(tài)的影響規(guī)律和控制機(jī)理。仿真獲得不同切削速度下切屑形態(tài)的演化規(guī)律,以切屑鋸齒化程度和鋸齒化頻率等幾何參數(shù)為指標(biāo),利用高速直角切削實(shí)驗(yàn)對(duì)有限元仿真模型的有效性進(jìn)行驗(yàn)證。通過(guò)調(diào)控工件材料的本構(gòu)模型參數(shù)和損傷模型參數(shù),研究不同材料性能參數(shù)變化時(shí)切屑形態(tài)的變化特性,并提出切屑鋸齒化敏感性參數(shù)和切屑曲率變化敏感性參數(shù)兩個(gè)評(píng)價(jià)指標(biāo),定量表征材料性能對(duì)切屑剪切局部化的影響規(guī)律。研究結(jié)果表明,本構(gòu)模型參數(shù)中初始屈服強(qiáng)度與熱軟化系數(shù)對(duì)切屑剪切局部化的影響最大,損傷模型參數(shù)中初始失效應(yīng)變和指數(shù)因子對(duì)切屑剪切局部化的影響最大。其次,建立高速切削鋸齒狀切屑形成時(shí)第一變形區(qū)的法向應(yīng)力分布模型,揭示切削第一變形區(qū)的應(yīng)力三軸度分布規(guī)律。將鋸齒狀切屑第一變形區(qū)的材料變形抽象為常剪切梯度拉伸／壓縮復(fù)合加載下的材料變形與失效問(wèn)題,建立綜合考慮應(yīng)變率和溫度影響的Bao-Wierzbicki斷裂應(yīng)變修正模型,通過(guò)對(duì)比分析切屑變形時(shí)的等效塑性應(yīng)變與材料斷裂應(yīng)變,獲得鋸齒狀切屑的斷裂軌跡,并討論不同切削速度下鋸齒狀切屑斷裂軌跡的演化規(guī)律。研究結(jié)果表明,第一變形區(qū)內(nèi)法向應(yīng)力呈不均勻分布,其中靠近切屑自由表面處為拉伸應(yīng)力區(qū),應(yīng)力三軸度為正值且服從線性分布：而靠近刀尖區(qū)域?yàn)閴嚎s應(yīng)力區(qū),應(yīng)力三軸度為負(fù)值且服從冪函數(shù)分布。在靠近切屑自由表面處為剪切、拉伸復(fù)合加載,切屑斷裂面呈現(xiàn)拉伸應(yīng)力引起的韌性斷裂模式；在靠近刀尖處為壓縮、剪切復(fù)合加載,切屑發(fā)生剪切斷裂并在斷裂面處分布有剪切型韌窩。切削速度提高時(shí)拉伸應(yīng)力區(qū)的擴(kuò)大是導(dǎo)致鋸齒狀切屑內(nèi)絕熱剪切帶裂紋擴(kuò)展加劇和切屑鋸齒化程度提高的本質(zhì)控制因素。最后,針對(duì)高速切削形成的鋸齒狀切屑與超高速切削形成的碎斷切屑,建立不同形態(tài)切屑形成時(shí)的能量耗散模型,探索不同切削參數(shù)下由于切屑變形行為差異引起的能量耗散變化規(guī)律,并綜合利用切削力和聲發(fā)射信號(hào)驗(yàn)證不同形態(tài)切屑的能量耗散模型。研究結(jié)果表明,鋸齒狀切屑形成時(shí)能量耗散主要包括第一變形區(qū)的塑性變形能、切屑與刀具前刀面之間的摩擦能和切屑動(dòng)能；而碎斷切屑形成時(shí)的能量耗散主要包括切屑的斷裂能和局部動(dòng)能。在高速切削階段,選擇大前角刀具和較大的未變形切屑厚度有利于減小切削過(guò)程的能量耗散。碎斷切屑的形成實(shí)現(xiàn)了塑性材料的脆性域加工,使得切削能量耗散大幅降低,表明超高速加工具有高效率和低能耗的優(yōu)點(diǎn)。切削過(guò)程中的聲發(fā)射信號(hào)強(qiáng)度受切削能量的耗散所影響,而切削能量的耗散由工件材料的力學(xué)性能和加工參數(shù)共同決定。
[Abstract]:With the rapid development of high speed cutting machine tools and advanced cutting tools, high speed machining technology has been applied in the fields of automobile manufacturing, aerospace and national defense industry. Compared to ordinary cutting speed machining, high strain rate characteristics under high speed cutting lead to dramatic changes in the dynamic mechanical properties of the workpiece material, and then lead to cutting. When the cutting speed increases, the chip shape evolution of the plastic metal material is banded chip, continuous sawtooth chip, completely separated sawtooth chip, and eventually forming broken chips similar to brittle material cutting. The previous research was mainly aimed at high-speed cutting sawsaw. The critical conditions for the dentation and the geometric characterization of the sawtooth chips are not studied. There is little understanding and understanding of the control mechanism of the material deformation and fracture behavior of the material when the sawtooth and broken chips are formed. Metal cutting can be recognized as the purpose between the chip and the workpiece material. The process of fracture reveals the deformation and failure mechanism of the sawtooth and broken chips, which not only guides the optimization of the cutting process parameters, but also helps to achieve high efficiency and low energy consumption, and provides a theoretical basis for the design of high speed machine tools and tool design. This paper is based on three kinds of work pieces, such as Ti6Al4V, Inconel 718 and 7050-T7451. As the research object, the formation mechanism of sawtooth chip and broken chip is studied by means of material mechanics and cutting theory, finite element simulation, cutting experiment and microscopic observation. The change of dynamic mechanical properties of the workpiece material at high cutting speed, especially the plastic brittle properties of the plastic metal material, is emphatically analyzed. Change - the law of influence on chip deformation and failure behavior. The main contents include the formation of different forms of chip, the critical cutting conditions of broken chip formation, sensitivity analysis of the shear localization of the sawtooth chip, the control mechanism of the serrated chip fracture behavior of the stress state, and the high speed cutting. The energy dissipation characteristics of chipper forming process are analyzed. Through this study, a study bridge is established between the dynamic mechanical properties of the material and the high speed cutting process at high strain rate, which lays a theoretical foundation for the discovery of the mechanism of high speed cutting and the popularization of high speed machining technology. First, the research on the formation process of high speed cutting chips is carried out. After analyzing the evolution law of chip shape of the workpiece material when cutting speed is raised, the deformation and fracture mechanism of chip in different cutting speed are revealed, and the formation model of sawtooth and broken chip is established. The microscopic observation on the different parts of the chip (including the chip cross section, free surface surface, chip fracture, etc.) is observed, and three kinds of work are explored. According to the formation characteristics of sawtooth chip, the adiabatic shear ductile fracture complex type of chip formation model is put forward, and the formation of broken chip is caused by brittle fracture. In view of the mechanism of brittle transition of metal material under high strain loading, the stress wave propagation theory is applied to establish the ultra high cutting speed. Critical cutting conditions for the formation of broken chips are obtained, and the critical cutting conditions for the formation of broken chips are obtained. According to the characteristics and deformation mechanism of the chip, the cutting range is divided into ordinary speed cutting, high speed cutting and ultra high speed cutting. Then, a finite element simulation model of high speed right angle cutting sawtooth shape is established to explore the material properties to the saw. The sensitivity of the shear localization of the toothed chip, which reveals the influence law and the control mechanism of the grain storage variables (including material mechanical properties and damage parameters) on the cutting chip shape in high speed cutting. The evolution of chip morphology under different cutting speeds is obtained, and the geometric parameters, such as the degree of sawtooth serration and the serrated frequency, are obtained. For the index, the validity of the finite element simulation model is verified by the high speed right angle cutting experiment. By adjusting the parameters of the constitutive model and the damage model of the workpiece material, the change characteristics of the chip shape when the performance parameters of different materials are changed, and the sensitivity parameters of the chip sawtooth sensitivity and the change of the chip curvature are proposed. The results show that the initial yield strength and the thermal softening coefficient have the greatest influence on the chip shear localization, and the initial failure strain and the exponential factor have the greatest influence on the chip shear localization in the parameters of the damage model. Secondly, the results show that the influence of initial failure strain and index factor on the chip shear localization is the largest in the parameters of the constitutive model. Secondly, the effect of the initial failure strain and index factor on the chip shear localization is the most. Secondly, the influence of the initial failure strain and the index factor on the chip shear localization is the most. Secondly, the effect of the initial failure model parameters on the chip shear localization is the most. To establish the normal stress distribution model of the first deformation zone in the formation of the high speed cutting sawtooth chip, the distribution of the stress three axis in the first deformation zone is revealed. The material deformation of the first deformation zone of the sawtooth chip is abstracted into the deformation and failure of the material under the constant shear gradient tensile / compression composite loading, and the comprehensive consideration should be established. The Bao-Wierzbicki fracture strain correction model affected by the variable rate and the temperature is obtained by comparing and analyzing the equivalent plastic strain and the fracture strain of the material in the chip deformation. The fracture trajectory of the sawtooth chip is obtained, and the evolution law of the serrated chip fracture trajectory under different cutting speeds is discussed. The results show that the normal stress in the first deformation zone is in the first deformation zone. There is an uneven distribution, in which the free surface near the chip is a tensile stress zone, and the stress three axis is positive and obeys the linear distribution: while the area near the tip area is the compressive stress area, the stress three axis is negative and obeys the power function distribution. The shear, tensile composite loading near the free surface of the chip and the tensile stress of the chip fracture surface are presented. The ductile fracture mode caused by force is compressed at the tip of the knife, shear composite loading, shear fracture of the chip and the shear type dimple at the fracture surface. The expansion of the tensile stress zone is the essential control of the expansion of the crack expansion in the sawtooth chip and the increase of the serration degree of the chip when the cutting speed is raised. Finally, in view of the broken chips formed by the sawtooth chip and the ultra high speed cutting formed by high speed cutting, the energy dissipation model of different forms of chip formation is established, and the energy dissipation changes caused by the difference of chip deformation behavior under different cutting parameters are explored, and the different shapes of the cutting force and acoustic emission signal are used to verify the different shapes. The energy dissipation model of the state chip shows that the energy dissipation mainly includes the plastic deformation energy in the first deformation zone, the friction energy and the chip kinetic energy between the chip and the tool front surface, while the energy dissipation of the broken chip formation mainly includes the chip fracture energy and the local kinetic energy. In the high speed cutting stage, The selection of the large front angle tool and the larger undeformed chip thickness is beneficial to reduce the energy dissipation in the cutting process. The formation of broken chip has realized the brittle domain processing of the plastic material, making the energy dissipation of the cutting greatly reduced, indicating the high efficiency and low energy consumption. The dissipation of cutting energy is affected, and the dissipation of cutting energy is determined by the mechanical properties and machining parameters of workpiece materials.
【學(xué)位授予單位】：山東大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2016
【分類號(hào)】：TG506.1

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