基于ANSYS概率设计系统的电弧切割参数敏感性分析

为研究切割电流、切割速度、工件厚度和有效加热半径对低合金钢电弧切割质量的影响,建立了基于ANSYS概率设计系统的电弧切割参数敏感性分析模型.以低合金钢2Cr13为研究对象,通过施加移动高斯热源模拟电弧切割过程,研究了工件温度场和应力场随各参数的变化规律.采用响应面概率设计方法分析了温度场和应力场对各切割参数的敏感性,结果表明,切割电流和切割速度对电弧切割质量影响较大,有效加热半径和工件厚度影响较小;切割电流和工件厚度对温度场为正影响,切割速度和有效加热半径对温度场为负影响;切割电流、工件厚度和有效加热半径对应力场是正影响,切割速度对应力场是负影响.文中模型对低合金钢电弧切割工艺设计具有重要的借鉴和指导意义.     

An investigation of workpiece temperature variation in end milling considering flank rubbing effect

Better prediction about the magnitude and distribution of workpiece temperatures has a great significance for improving performance of metal cutting process, especially in the aviation industry. A thermal model is presented to describe the cyclic temperature variation in the workpiece for end milling. Owing to rapid tool wear in the machining of aeronautical components, flank rubbing effect is considered. In the proposed heat source method for milling, both the cutting edge and time history of process are discretized into elements to tackle geometrical and kinematical complexities. Based on this concept, a technique to calculate the workpiece temperature in stable state, which supposes the tool makes reverse movement, is developed. And a practicable solution is provided by constructing a periodic temperature rise function series. This investigation indicates theoretically and experimentally the impact of different machining conditions, flank wear widths and cutter locations on the variation of workpiece temperature. The model results have been compared with the experimental data obtained by machining 300M steel under different flank wear widths and cutting conditions. The comparison indicates a good agreement both in trends and values. With the alternative method, an accurate simulation of workpiece temperature variation can be achieved and computational time of the algorithm is obviously shorter than that of finite element method. This work can be further employed to optimize cutting conditions for controlling the machined surface integrity.     

固定电弧等离子弧焊接热传导的数值计算

针对固定电弧等离子弧焊接过程建立了二维稳态热传导模型 ,在模型中考虑了工件表面与周围环境换热及辐射散热对整个焊接热过程的影响 ,并且将焊接电流在流经工件时产生的焦耳热作为热能方程的源项进行计算。针对所建立的模型 ,采用大型商业软件PHOENICS(Parabolichyperbolicorellipticnumericalintegrationcodeseries)对工件中的温度场以及电流密度的分布进行了计算。采用该软件对焊接热过程进行数值模拟 ,可以很方便地对求解变量和边界条件进行操作 ,显著提高了效率。比较结果显示 ,计算结果与实际测量结果吻合良好     

Heat partitioning in dry milling of steel

A predictive model for heat induced shape deviations would facilitate the optimization of dry milling strategies. Results from milling experiments aiming at a physically based regression model for the heat flux distribution along the contact arc are presented. The contact arc was discretised by varying the width of cut on four levels for each combination of cutting speed, feed speed, and depth of cut. Heat fluxes to the workpiece were iteratively determined in an inverse procedure. Heat partitioning not only depends on the thermal number as in orthogonal cutting but also on the feed speed and the depth of cut.     

整体硬质合金铣刀铣削热实验研究

本文通过建立一种整体硬质合金铣刀铣削热研究的实验方法,在相同的切削条件下,利用人工热电偶法和红外测温法对3种不同刃数的整体硬质合金铣刀的铣削温度进行了测量,并运用有限长移动线热源数学模型计算出不同刃数的铣刀在铣削过程中传入工件和切屑的热量值。研究结果表明:相同的切削条件下,刀刃数目越多,铣削温度越高,实验结果与实际加工一致。     

基于整体刀具的铣削加工温度有限元分析

在对金属切削的热力学以及热传导过程进行理论分析的基础上,基于整体刀具建立了铝合金薄壁件铣削加工的三维有限元模型。改变切削深度、切削速度以及进给率等工艺参数,分析了铣削工艺参数对温度的影响。仿真结果表明：切削深度对铣削温度影响最大,切削速度和进给率对铣削温度的影响相对较小。将仿真结果与试验测量结果进行对比分析,仿真结果温度值略高于试验结果,但总体变化趋势和规律基本一致。     

Modelling of cutting induced workpiece temperatures for dry milling

A thermal model has been developed that predicts machining induced workpiece temperatures for peripheral milling. The model was developed to determine the magnitude and distribution of workpiece temperatures for dry milling of aerospace aluminium alloys. The analytical model incorporates elements of the physical nature of the metal cutting process with analytical approaches developed for grinding to produce a peripheral milling thermal model that is directly applicable to industry. Test and model results show that cutting induced workpiece heating reduces significantly as cutting speed and feedrates are increased. The research suggests that dry machining of aluminium should be carried out at high cutting speeds and feeds to minimise temperature rise in the workpiece.     

Analytical modeling and experimental investigation of tool and workpiece temperatures for interrupted cutting 1045 steel by inverse heat conduction method

Cutting temperature is a key factor which directly affects tool wear, workpiece integrity, and machining precision in high speed machining process. The interrupted cutting process consists of several periodical characteristics, such as cutting force and time varying heat source. Induced cutting temperature models with time varying heat flux are developed in this paper to predict temperature distribution at tool inserts and workpiece during interrupted cutting process. A set of interrupted cutting experimental installation is designed to verify the proposed models. The comparison of predicted and measured results for 1045 steel in interrupted cutting processes shows reasonable agreement. The measured temperature of both the tool inserts and workpiece increase firstly and then decrease as the cutting speed increases. The peak temperature of the workpiece appears at 1500 m/min, while the peak tool inserts temperature appears at 1250 m/min approximately. Heat flux is calculated by the inverse heat conduction method. The applicability of Salomon's hypothesis to the temperature of tool inserts and workpiece is discussed during the interrupted cutting process. The dropped temperature at high cutting speed is mainly caused by that heat flux into tool inserts decreases and heat transfer time is not enough after the critical cutting speed.     

小孔等离子弧焊接热场的有限元分析

根据小孔等离子弧焊接的工艺特点，建立了相应的热源模型和焊接热场的分析模型。数值模拟结果表明，一般的双椭球体热源和三维锥体热源不能准确描述小孔等离子弧焊接热过程。提出了改进型的三维锥体热源模型，可以较准确地计算焊缝的正面和背面熔宽，但熔合线走向的计算精度仍较低。在此基础上，考虑等离子弧对熔池的热-力作用，建立了符合小孔形态的热源模型，对小孔等离子弧焊接热场进行了有限元分析，计算出的小孔等离子弧焊缝形状与试验结果吻合良好。     

航空薄壁件铣削加工铣削力预测方法研究

铣削加工中铣削力是导致加工变形的直接原因,而航空薄壁件加工中,加工变形是加工误差产生的主要因素.本文以航空薄壁件铣削加工过程的铣削力为研究对象,通过确定铣削力模型和切削系数参数,建立了刚性和考虑刀具工件变形耦合的柔性预测两种模型.在柔性模型中,采用预扭Timoshenko梁单元的刀具/工件独立建模的方法建立有限元模型,利用Python语言在通用有限元软件Abaqus下迭代求解.实验验证表明预测模型具有很高的准确性和有效性.     

Mechanics and dynamics of general milling cutters.: Part I: helical end mills

A variety of helical end mill geometry is used in the industry. Helical cylindrical, helical ball, taper helical ball, bull nosed and special purpose end mills are widely used in aerospace, automotive and die machining industry. While the geometry of each cutter may be different, the mechanics and dynamics of the milling process at each cutting edge point are common. This paper presents a generalized mathematical model of most helical end mills used in the industry. The end mill geometry is modeled by helical flutes wrapped around a parametric envelope. The coordinates of a cutting edge point along the parametric helical flute are mathematically expressed. The chip thickness at each cutting point is evaluated by using the true kinematics of milling including the structural vibrations of both cutter and workpiece. By integrating the process along each cutting edge, which is in contact with the workpiece, the cutting forces, vibrations, dimensional surface finish and chatter stability lobes for an arbitrary end mill can be predicted. The predicted and measured cutting forces, surface roughness and stability lobes for ball, helical tapered ball, and bull nosed end mills are provided to illustrate the viability of the proposed generalized end mill analysis.     

碳纤维/树脂基复合材料铣削表面粗糙度及表面形貌研究

目的研究了CFRP材料铣削加工过程中,部分主要工艺对CFRP材料加工表面质量的影响规律,为工艺参数优化,提高此类零件的表面质量提供依据。方法设计了CFRP材料铣削中的切削参数、刀具结构、加工方法与加工表面粗糙度及表面形貌之间的单因素试验。通过单调改变一个切削参数而其余切削参数不变,得到了工件表面粗糙度和表面形貌随切削参数、刀具结构、加工方法的变化规律。结果当铣削速度增大时,工件的表面粗糙度变化不大,表面微坑缺陷的数量却有所增加,但变小、变浅。当进给速度增大时,工件表面粗糙度呈上升趋势,表面缺陷也随之增加。无涂层多齿刀具铣削后的工件表面粗糙度最大,其次是金刚石涂层多齿刀具铣削的工件,最小的是金刚石涂层交错齿刀具铣削的工件。多齿刀具加工后的表面有较多的微坑缺陷,但普遍深度较浅且面积较小。交错齿刀具对分层缺陷的抑制作用最明显,但在左旋和右旋刀齿交错处容易出现较严重的加工缺陷。与普通机械加工方法相比,超声振动加工方法得到的工件表面质量较好,可以有效减少表面微坑缺陷,改善CFRP铣削加工表面质量。结论 CFRP材料铣削加工时,为了获得较好的加工表面质量,切削参数应选用较高的切削速度和较低的进给速度,切削刀具宜选用多齿带涂层刀具。和普通机械加工方法相比,超声振动铣削加工方法更为有利于获得好的表面质量。     

Temperatures in deep grinding of finite workpieces

This paper investigates the diverse thermal effects generated in high efficiency deep grinding (HEDG). Using a new thermal model of circular arc contact with transient analysis, the transient behaviour of the maximum contact temperature has been analysed for various grinding conditions. It is found that steady state conditions can be achieved for the conditions of sufficient workpiece length and high workspeeds. The effect is important for the understanding of the deep grinding process and for the prediction of satisfactory grinding conditions. HEDG conditions also have very apparent effects on the depth of heat penetration to the workpiece. The parameters investigated include mean contact angle, Peclet number and the heat source distribution. Experimental results are presented for specific energy, energy partition and mean temperature for high efficiency deep grinding.     

Prediction of tool and chip temperature in continuous and interrupted machining

In this paper, a numerical model based on the finite difference method is presented to predict tool and chip temperature fields in continuous machining and time varying milling processes. Continuous or steady state machining operations like orthogonal cutting are studied by modeling the heat transfer between the tool and chip at the tool—rake face contact zone. The shear energy created in the primary zone, the friction energy produced at the rake face—chip contact zone and the heat balance between the moving chip and stationary tool are considered. The temperature distribution is solved using the finite difference method. Later, the model is extended to milling where the cutting is interrupted and the chip thickness varies with time. The time varying chip is digitized into small elements with differential cutter rotation angles which are defined by the product of spindle speed and discrete time intervals. The temperature field in each differential element is modeled as a first-order dynamic system, whose time constant is identified based on the thermal properties of the tool and work material, and the initial temperature at the previous chip segment. The transient temperature variation is evaluated by recursively solving the first order heat transfer problem at successive chip elements. The proposed model combines the steady-state temperature prediction in continuous machining with transient temperature evaluation in interrupted cutting operations where the chip and the process change in a discontinuous manner. The mathematical models and simulation results are in satisfactory agreement with experimental temperature measurements reported in the literature.     

Heat flux distribution model by sequential algorithm of inverse heat transfer for determining workpiece temperature in creep feed grinding

The purpose of this study is to determine the heat flux distribution and to estimate the workpiece temperature in creep feed grinding. The sequential algorithm of the inverse heat transfer was used for determining the heat flux distribution. The amount of heat flux to the workpiece, the energy partition and the convective heat transfer coefficients both at the front and at the back of the heat flux were determined. Three heat source models using the determined amount of heat flux were applied to estimate the workpiece temperature. The workpiece temperatures estimated by the heat source models were compared with that measured by the embedded thermocouple. The scalene triangle model correlated best with measured and theoretical temperature profiles obtained for creep feed grinding.     

304不锈钢水下药芯割丝电弧切割机理

药芯割丝电弧切割(flux-cored wire arc cutting,FCAC)作为一种高效、低成本、安全的水下切割方法,具有广阔的应用前景. 由于水下复杂环境的干扰,该方法的不锈钢切割机理仍不明确,采用工艺试验、水下观测和数值模拟相结合的方法对水下割口成形机理进行研究. 首先通过工艺试验确定水下切割相关特征参数;其次采用半椭球体热源模拟切割热源,并根据试验观测设置热源的运动和切换方式;最后对工件进行网格划分和水下边界条件设置,使用生死单元法动态模拟切割中熔融金属的去除;对工件上特定点的模拟和实际温度以及切割后的模拟割口与实际割口形貌进行了研究对比,验证该方法数值模拟的准确性. 结果表明,水下电弧切割不锈钢割口主要分为“/ \”型、“| |”型和“\ /”型3种形貌. 通过高速摄像观察得出,水下不锈钢切割过程由多个周期型连续穿孔过程组成,通过模拟进行验证,对割口成形过程进行有效预测,有助于进一步优化工艺并进行有效控制.     

基于FLUENT的TIG焊瞬态熔池三维形态的数值模拟

根据流体力学和传热学原理,建立了 TIG 焊瞬态熔池三维数值分析模型.电弧热源模型采用典型的高斯热源分布模型,模型考虑熔池液态金属对流传热、熔池外工件的固态导热、焊接过程中的相变潜热、熔池流体的紊流特性、材料的热物理性能参数随温度变化等因素.用 enthalpy-porosity 方法处理工件熔化/凝固过程中的问题,FLUENT RNG k-ε湍流模型对 TIG 焊熔池模型进行求解.给出了熔池形状的可视化图形结果,熔池形状特征参数随时间的动态变化.结果表明,计算值与实测值吻合良好.

Abstract：

Based on theories of fluid dynamics and heat zransfer, a transient three-dimensional model of TIG weld pools is established, in which Gaussian distribution is used to describe the heat flux source of arc. Many factors are considered in the model including the convective heat transfer of liquid metal and the heat conduction of solid metal, latent heat in welding process, the turbulence characteristics of welding pool fluid, material thermo physical properties as the function of temperature and so on. The enthalpy-porosity technology is adopted to solve the problem with workpiece phase transformation. The graphics results of weld pools and the variation of shape parameters with time are given by using FLUENT RNG k-ε model to calculate the TIG wielding pool. The experiments show that the calculated results agree well with measured value.     

基于SYSWELD的穿孔等离子弧焊接温度场有限元分析

K－PAW焊接时形成具有“倒喇叭”状的焊缝．根据K－PAW的焊缝形状特点,通过比较多种热源作用模式,得到了适合于K—PAW焊接的组合式体积热源作用模式,即,沿板厚方向,工件的上部采用双椭球体热源,下部为中心轴热流峰值线性递增的圆柱体热源．将“双椭球体＋峰值递增圆柱体”组合式热源应用于SYSWELD软件与K—PAW焊接热...     

Tool temperatures and crack development in milling cutters

This paper presents a theoretical and experimental study of the dynamic temperature field on a milling cutter tooth. A finite element model is developed to simulate the heat cycle of the cutting tooth by a time-varying heat flux. Forced convection effect has been investigated at exit. Experiments on simulating thermal process of face milling by heating cemented carbide teeth with laser pulses have also been conducted; the dynamic temperature field on a cutting tooth was measured. It has been shown that when the tooth is disengaged its temperature does not decrease to a level which will induce tensile stresses on the rake face. Thus, thermal cracks are not initiated during this stage of cutting. In this paper the authors propose that thermal cracks develop cyclically with increases in the temperature gradient at each entry of the cutter into the workpiece.     

激光-等离子弧复合焊温度场的数值模拟

利用峰值热流随深度衰减的高斯体热源与高斯面热源相结合的方法,建立了激光等离子弧复合焊三维运动热源模型,重点考虑了由热源间距引起的激光束与等离子弧之间相互作用对热源模型的影响.基于所建立的热源模型对2 mm厚1420铝锂合金板的激光等离子弧复合焊接温度场进行了有限元分析,得到了不同热源间距条件下焊接区域的温度场分布.结果表明,仿真结果与试验结果相符合,证明了该热源模型是反映了客观实际的.此工作对于激光电弧复合焊接传热及工艺研究具有指导意义.