A Study on Torch Path Planning in Laser Cutting Processes Part 1: Calculation of Heat Flow in Contour Laser Beam Cutting

Conductive heat transfer in contour laser beam cutting is analyzed by using a transient, two-dimensional finite difference model, and the result is combined with a simple analytic model. From the calculation results, the correlation is derived between workpiece temperature and opening angles at a corner in contour cutting. As a result, a modified analytic solution is developed to predict if excessive workpiece heating occurs for given cutting contours in a nested plate. The main objective is to use the computation results in the optimization of torch path planning to provide fully automated CNC programming software for laser cutting. To efficiently apply the analytic model in torch path planning, the critical temperature that should be avoided during the cutting sequence is considered. This leads to an improvement of the cutting quality in the automatic cutting process.     

计算机模拟显示数控线切割加工轨迹

介绍用Basic语言编制国内常见的数控电火花线切割 3B格式程序的计算机仿真程序。可实现在计算机上模拟显示线切割加工轨迹 ,从而可验证所编 3B程序的正确性等。     

Striation Formation and Melt Removal in the Laser Cutting Process

The mechanisms of melt ejection and striation formation in continuous wave laser cutting of mild steel are discussed. Melt ejection from the cutting front is shown to be a cyclic phenomenon. Striation formation is strongly affected by the oscillatory characteristic of the thin liquid film on the cutting front during melt ejection, together with the oxidation and heat transfer process. Cutting speed determines whether the liquid film will rupture or generate waves on the cutting front. Theoretical explanations are given according to the instability theory of a thin liquid film in a high-velocity gas jet and the diffusion-controlled oxidation theory. Striation frequency and depth are predicted according to the above theories. Experimental investigations were carried out and the results are consistent with the calculations. The better understanding has shed light on further investigations and optimal process development.     

Geometry Regulation of Material Deposition in Near-Net Shape Manufacturing by Thermally Scanned Welding

This paper introduces a thermally scanned material deposition control method for near-net shape manufacturing of metal parts by welding. To eliminate thermal distortion and the required intermediate-layer milling steps, and to control the material structure, plasma arc scan welding under infrared pyrometry sensing regulates the temperature field by providing in-process heat treatment of the part. In laboratory tests, the material is simultaneously deposited by a gas metal arc welding torch, with monitoring of the weld profile by two laser stripe profilometers. These sensors provide measurements of the bead width for its feedback control by modulation of the wire feed. To compensate for measurement delays, real-time prediction by a deposition model is employed, with its parameters identified during the process. Preview of the geometric surface irregularities in front of the deposition is used as feedforward to ensure the desired layer deposition patterns in adjacent beads. The performance of this bead-size control scheme is assessed experimentally on a robotic laboratory station, and applications of the thermally scanned material deposition technique are explored in rapid manufacturing of customized metal products.     

Systematic reallocation of aqueous resources using mass integration in a typical pulp mill

This work deals with the application of mass integration to the Kraft process in an effort to minimize the fresh water usage. Due to the recycle and reuse of various aqueous streams present in the given process, there is a build-up of non-process elements (or NPEs) which has to be addressed. The approach consists of gaining process insights from the flow sheet via a graphical solution strategy followed by mathematical optimization. A targeting approach is described. The source sink diagram and path diagram are included in the analysis. A rule based on the lever arm and material balance is used to determine the sequence of steps at fresh water minimization. The graphical approach is easy to apply and allows the user to determine initial solutions to the problem. This is followed by a detailed mathematical optimization formulation for the problem and the solution strategy to be used to converge on the final solution. A case study dealing with the Kraft process, and chloride being the targeted NPE, is considered to demonstrate the potential benefits of the approach. Significant reductions in fresh water demands and wastewater discharges are observed for the Kraft process along with the allocation of NPEs. Any build-up of NPEs due to the recycle and reuse of various aqueous effluent streams to replace fresh water is accounted for via the inclusion of path diagram equations in the mathematical optimization. The principles developed are generic in nature and can easily be extended to other pulp processes as well.     

Conceptual design of an integrated heating system at LKAB Malmberget with consideration of social-environmental damage costs

LKAB Malmberget is a Swedish mining site located at Malmberget, Sweden. Seven boiler centers are located in the north part of Malmberget. There are no connections in between these boiler centers, meaning that it is a decentralized heating system. The heat generated is used to heat up buildings and for mine ventilation air mainly during the cold periods. The heat is mainly provided from electric and oil boilers. However, most boilers under use are over 20 years old, and it is time to retrofit the boiler system and infrastructure. The purpose of this work is to design and optimize the heating system by introducing an integrated concept to minimize the heat production cost.An optimization model based on the mixed integer linear programming (MILP) has been developed. Several technical options have been considered in a new centralized heating system. The optimization principle is based on two kinds of perspectives: current price and external costs. With consideration of environmental and health damage from society concerns point of view, instead of environmental taxes in the current price perspective, the monetary values of externalities due to pollutants such as CO₂, NO_x, SO₂ and particulates emitted from the heating system are included. On the basis of data input and assumptions, modeling results indicate that a lower cost could be achieved when a waste heat recovery boiler is installed at the older pelletization plant to recover sensible heat from flue gas. This technical option is the best solution or at least contributes to the best solution in all optimization results. Including the externality cost is useful for making fair evaluation of the social-environmental impacts of the alternatives.     

城市生活垃圾收运路线优化的数学模型与算法

给出了城市生活垃圾收运路线优化问题的一般描述,考虑时间窗、车容量等约束,以收运路线总行程最短为目标。建立了该优化问题的数学模型。设计了求解谊问题的单一组合邻域搜索算法。随机邻域搜索算法和变邻域搜索算法三种类型的邻域搜索算法。通过对多组算例的求解实验,结果表明变邻域搜索算法的优化效果明显优于其余类型的邻域搜索算法。     

新型长时热流测量装置的研制及应用

目的设计一种新型热流测量装置,使传感器满足长时间热流测量的需求,且传感器外表面可以适量打磨,与飞行器的气动外型面完好随型。方法采用铜和钢作为备选材料,施加相同的表面热流边界,对比敏感端内外壁温差情况。优化热流辨识传感器传热路径、敏感端厚度,通过有限元模型分析打磨对热流辨识结果的影响。基于优化结果,研制出热流测量装置,并通过地面试验验证该装置的有效性。结果从热响应获取时间延迟角度来看,Cu比钢具有较大的优势。综合考虑敏感端外表面需要与飞行器外表面随型打磨,选用5 mm的厚度具有一定的安全可靠性。敏感端的适度打磨基本不影响温度测量结果。辨识获得的热流数据与实际控制热流吻合较好,最大偏差约15%。结论成功研制了热流测量装置,并通过地面热试验证明了热流测量的有效性。     

Cutting tool temperatures in interrupted cutting—The effect of feed-direction modulation

Transient tool temperatures in interrupted machining processes were investigated. The initial focus was feed-direction modulated turning. Here, the instantaneous uncut chip thickness (IUCT) was modeled including the regenerative effect introduced by the modulation. Treating the tool as a one-eighth semi-infinite body, for a rectangular heat patch governed by the IUCT at the corner, the tool heat conduction problem was solved. The Green’s function solution procedure included heat convection from exterior surfaces. The results indicated that modulation lowered the cutting temperature, more significantly at a higher modulation frequency. However, heat conduction into the tool dominated over convection to the ambient. The IUCT was found to lag the peak temperature, indicating that modulation can possibly alter the thermal softening of the cutting tool in continuous cutting without a concomitant decrease in material removal rate. The same tool temperature model applied to face-milling indicated that the peak temperature occurred only at cut exit. Carefully planned interrupted hard-facing experiments were performed varying the frequency and duration of interruption. Tool-life data confirmed the beneficial effects of lower cutting temperatures due to slight interruption.     

Performance-Based Predictive Models and Optimization Methods for Turning Operations and Applications: Part 3—Optimum Cutting Conditions and Selection of Cutting Tools

This paper presents a summary of recent developments in developing performance-based machining optimization methodologies for turning operations. Four major machining performance measures (cutting force, tool wear/tool life, chip form/chip breakability, and surface roughness) are considered in the present work, which involves the development and integration of hybrid models for single and multi-pass turning operations with and without the effects of progressive tool wear. Nonlinear programming techniques were used for single-pass operations, while a genetic algorithms approach was adopted for multi-pass operations. This methodology offers the selection of optimum cutting conditions and cutting tools for turning with complex grooved tools.     

基于改进NSGA-Ⅱ算法的危险品运输路径优化研究

危险品运输路径的选择对于降低危险品运输事故危害有着重要的影响。首先通过构建时空矩阵存储道路信息用以模拟危险品运输事故率和事故后果,并结合成本因素建立综合、动态、多目标的危险品运输路径优化模型;然后改进了NSGA-Ⅱ算法,即在其算法模块中利用基于优先级的编码方式代替传统二进制编码方式,自定义问题模块中加入判断跨时间段的条件语句及调用不同时间段数据的语句,实现对上述模型的求解;最后以进出天津港的主干线为研究区域进行实证研究,通过收集道路相应数据并结合危险品运输事故情景建模计算事故威胁区域,利用上述建立的模型及改进的算法,选出了一条最优的危险品运输路径。     

Path creation for sustainable consumption: promoting alternative heating systems in Finland

There are many cost-effective technologies to reduce resource use and carbon dioxide emissions in space heating, yet they are adopted very slowly, and inefficient heating systems persist. In this article, we examine path dependence and path creation in home heating systems. Path dependence refers to the self-sustaining characteristics of existing systems such as the dominant energy system. Path creation is a related concept that highlights entrepreneurship in ‘mindfully deviating’ from existing paths and creating new ones by engaging various stakeholders and generating momentum. Research on path creation in energy systems has focused on energy production systems, whereas end-use technologies have gained less attention. We explore the role of path creation in end-use technologies through four attempts to change heating systems for detached houses in Finland via the promotion of heat pump technologies. Within the path creation process, we focus on how the initiators of new paths try to counter the forces maintaining the dominant system. In particular, we pay attention to how small organizations make use of co-operation to challenge the existing path. The aim is to identify the conditions for successful path creation by entrepreneurs and energy end-users under adverse conditions.     

Tool Path Planning for Avoiding Exit Burrs

Milling exit burrs usually form along the edges of a workpiece when the tool leaves the part while removing stock material. One of the most efficient methods for minimizing exit burrs is to prevent the tool from exiting the workpiece during material removal. This paper describes a systematic framework to generate tool paths that always enter a part, which is not a thin structure, in a planar milling operation. Three distinct tool exit conditions are analyzed for polygonal parts. A test criterion is then proposed to examine the occurrence of tool exits. For each condition, a tool path planning scheme is developed to avoid tool exits. These schemes are proved to be effective using the test criterion. This work is integrated into a networked manufacturing environment as a burr agent. Test parts are cut to demonstrate that this framework enhances edge quality by minimizing tool exits.     

Analytical model of metalworking fluid penetration into the flank contact zone in orthogonal cutting

Metalworking fluids (MWFs) are used widely in machining process to dissipate heat, lubricate moving surfaces, and clear chips. They have also been linked to a number of environmental and worker health problems. To reduce these impacts, minimum quantity lubrication (MQL) sprays of MWF delivered in air or CO₂ have been proposed. MQL sprays can achieve performance comparable with conventional water-based or straight oil MWFs while only delivering a small fraction of the fluid. This performance advantage could be explained by the enhanced penetration into the cutting zone that results from delivering MWF in high pressure and precise sprays. To explore this hypothesis, an analytical model of MWF penetration into the flank face of the cutting zone is developed and validated using experimental data. The model is based on a derivation of the Navier–Stokes equation and the Reynolds equation for lubrication and applied to an orthogonal cutting geometry under steady-state conditions. A solution to the model is obtained using a numerical strategy of discretizing the analytical scheme with two-dimensional centered finite difference method. Penetration into the cutting zone is estimated for MQL sprays delivered in air, CO₂ and N₂ as well as two conventional MWFs, straight oil and semi-synthetic emulsion. The model suggests that conventional MWFs, do not penetrate the cutting zone fully and fail to provide direct cooling to the flank zone where wear is most likely to occur. MQL sprays do penetrate the cutting zone completely. Using convective heat transfer coefficients from a previous study, a finite element heat balance is carried out on the tool to understand how each fluid impacts temperature near the flank tip of the tool. The results of the modeling effort are consistent with experimental measurements of tool temperature during turning of titanium (6AL4V) using a K313 carbide tool. The prediction of temperature near the flank indicates that MQL sprays do suppress temperatures near the flank effectively. These results help explain the low levels of tool wear observed for some MQL sprays, particularly those based on high pressure CO₂. This modeling framework provides valuable insight into how lubricant delivery characteristics such as speed, viscosity, and cutting zone geometry can impact lubricant penetration.     

基于多目标优化的装备群备件保障决策研究

针对装备群备件保障决策问题,从装备群-装备两个层次进行分析建模和优化。首先,根据可靠性分配方法将装备群系统可靠性分配给各装备子系统,在此基础上,考虑总费用和保障概率的要求,利用pareto多目标优化方法对各子系统装备所需携(运)行的备件进行合理优化,建立一个多目标优化决策模型。最后结合应用实例展开应用研究,可为装备群系统决策从定性到定量提供一种新的思路。     

Laser tempering based turning process for efficient machining of hardened AISI 52100 steel

Cost-effective machining of hardened steel components such as a large wind turbine bearing has traditionally posed a significant challenge. This paper presents an approach to machine hardened steel parts efficiently at higher material removal rates and lower tooling cost. The approach involves a two-step process consisting of laser tempering of the hardened workpiece surface followed by conventional machining at higher material removal rates with lower cost ceramic tools to efficiently remove the tempered material. The laser scanning parameters that yield the highest depth of tempered layer are obtained from a kinetic phase change model. Machining experiments are performed to demonstrate the possibility of higher material removal rates and improved tool wear behavior compared to the conventional hard turning process. Tool wear performance, cutting forces, and surface finish of Cubic Boron Nitride (CBN) tools as well as low cost ceramic tools are compared in machining of hardened AISI 52100 steel (~63 HRC). In addition, cutting forces and surface finish are compared for the laser tempering based turning and conventional hard turning processes. Experimental results show the potential benefits of the laser tempering based turning process over the conventional hard turning process.     

A simultaneous optimization approach for the design of wastewater and heat exchange networks based on cost estimation

A new systematic methodology for designing wastewater and heat exchange networks for process industries involving effluent streams containing multiple contaminants is proposed. A simultaneous optimization approach mathematically combines the problems of wastewater and heat exchanger network optimization into a single step. This process includes two global iterations of a similar two-stage approach and optimizes networks for water and heat exchange simultaneously based on cost estimation. The objective function is to minimize the total annual cost of the wastewater and heat exchange network design which is subject to the mass and energy balance constraints on all the pertinent flows and to constraints related to the concentrations of contaminants. The proposed method employs a strategy to address a mixed integer non-linear programming (MINLP) formulation. Cost estimates for optimized wastewater and heat exchange networks for an oil refinery process are generated, illustrating the effectiveness of the proposed methodology.     

基于理想点法的加筋板屈曲承载力优化

目的针对加筋板在使用工况中易发生屈曲和结构失稳,提出一种基于理想点法的屈曲承载力优化设计方法。方法以加筋板的屈曲承载力最大和结构质量最小为目标,以加筋板的屈曲、最大vonMises应力和筋条压损等为约束条件,并利用理想点法将多目标优化问题转化为单目标优化问题。基于ANSYS参数化建模技术,构建屈曲分析、优化设计一体化分析与设计模型,并采用单目标优化算法——DOWNHILL SIMPLEX算法实施了优化分析。结果优化后结构质量从0.195 kg增加到0.24 kg,增加了23%,结构承载力从129.4 k N提升到235.84 kN,提高了82%。结论通过优化能够获得结构性能折中的方案,可为加筋板结构设计应用提供参考。     

Numerical and experimental investigations on laser melting of stainless steel 316L metal powders

This paper presents numerical and experimental investigations on laser melting of SS grade 316L powder on top of AISI 316L substrate using a pulsed Nd:YAG laser. The objectives of the present study are to understand the effect of process parameters such as laser power, scanning speed and beam size on geometry characteristics of the melt zone and ball formation. We formulated a moving heat source problem and obtained transient temperature solutions using commercial finite element solver. The geometry characteristics of the melt zone are evaluated from the temperature solutions and compared with experimental results. The effect of laser parameters on the geometry, morphology and homogeneity of single track realization was methodically analyzed by utilizing characterization tools such as laser particle size analyzer, macro and microscopic inspection, Scanning Electron Microscope (SEM), X-Ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR). The results presented in this paper are beneficial to realize homogenous layer formation in additive manufacturing processes involving powder melting by laser beam.     

Machining Performance and Health Effects of Cutting Fluid Application in Drilling of A390.0 Cast Aluminum Alloy

Environmental issues in machining have led to a push to curtail the use of cutting fluids. However, cutting fluid effects on part quality, process planning, and operator exposure to aerosols need to be first studied. The effects of cutting fluid application on hole accuracy and mist generation have been studied for blind-hole drilling of A390.0 aluminum alloy. Different cutting fluid types and application modes were tested under varying conditions of cutting speed, feed, and hole depth. The cooling and chip-transporting ability of cutting fluids was found to have the maximum effect on dimensional accuracy. Dry cutting yielded holes with the least accuracy, while mist lubrication was found to give superior dimensional accuracy to dry cutting but had the worst aerosol concentration. Flooding with synthetic cutting fluid gave the best overall results.