Bending of Titanium Sheet Using Laser Forming

Laser forming, a novel manufacturing method for bending sheet metal first reported in 1985, has been investigated as an alternative to hot brake forming (industry standard) of titanium sheet parts for the aircraft industry. Laser forming involves scanning a focused or partially defocused laser beam over the surface of a titanium workpiece to cause localized heating along the bend line and angular deflection toward the beam. The main advantage that laser forming has over conventional brake forming is increased process flexibility. An experimental investigation of this process (primarily designed experiments) met the following objectives: identified the response variables related to change in geometry (bend angle) and material microstructure; characterized the influence of process variables (scanning speed, beam diameter, laser power) on these response variables; determined the degree of controllability over the process variables; and evaluated the suitability of laser forming for the aircraft industry (most important), all with respect to titanium sheet. It has been determined that laser forming with an Nd:YAG laser is a controllable, flexible manufacturing process for titanium sheet bending. Unfortunately, these advantages over traditional hot brake forming are overshadowed by the fact that, with regard to forming with titanium, laser forming is significantly slower and more labor and energy intensive, and results in unacceptable material properties at the bend line according to aircraft industry standards. These findings cast doubt over the assertions of some researchers that laser forming may be a viable manufacturing process for parts made in small batches. Instead, it appears that it may be best suited for rapid prototyping of sheet metal parts.     

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.     

Optimal and Robust Design of the Laser Forming Process

The laser forming process of sheet metal has been extensively analyzed, but few attempts have been made in the area of process design. The task of the process design in the laser forming of sheet metal is to determine a set of parameters, including laser scanning paths, laser power, and scanning speed, given a prescribed shape. Response surface methodology is used as an optimization tool. The propagation of error technique is built into the design process as an additional response to be optimized via desirability function and hence make the design robust. Focusing on a class of shapes, the design scheme is applied progressively in four cases in which issues such as a large number of design variables are properly addressed.     

An Investigation of Selective Coloring with 3-D Laser Printing

This paper reports on preliminary results involving an experimental rapid prototyping process known as 3-D laser printing. The system builds parts by repeatedly laser printing thermoplastic cross-sectional “slice” images of a part one on top of the next. With each new layer, the total build thickness increases until the part is complete. An interesting extension to this system involves the use of a color print engine to produce selectively colored parts. Conventional rapid prototyping processes generally do not allow this sort of selective coloring. Initial results indicate that the system has considerable potential and warrants continued investigation.     

Nanosecond pulsed laser micromachining of PMMA-based microfluidic channels

This paper reports an investigation into the effects of nanosecond laser processing parameters on the geometry of microchannels fabricated from polymethylmethacrylate (PMMA). The Nd:YAG solid-state pulsed laser has a wavelength of 1064 nm and a measured maximum power of 4.15 W. The laser processing parameters are varied in a scanning speed range of 400–800 pulses/mm, a pulse frequency range of 5–11 Hz, a Q-switch delay time range of 170–180 μs. Main effects plots and microchannel images are utilized to identify the effects of the process parameters for improving material removal rate and surface quality simultaneously for laser micromachining of microchannels in PMMA polymer. It is observed that channel width and depth decreased linearly with increasing Q-switch delay time (hence average power) and increased non-linearly with higher scanning rates and not much affected by the increase in pulse frequency.     

Rotary ultrasonic machining of potassium dihydrogen phosphate (KDP) crystal: An experimental investigation on surface roughness

Potassium dihydrogen phosphate (KDP) crystal, widely used for important electro-optic parts, is a typical hard-to-machine material because of its soft, brittle, and anisotropic properties. High quality is usually required for machined surfaces on KDP parts. Reported machining methods for KDP crystal include diamond turning, grinding, magnetorheological finishing, and polishing. Each of these methods has its limitations. Therefore, it is desirable to develop new machining methods for KDP crystal. This paper presents an experimental investigation on surface roughness in rotary ultrasonic machining (RUM) of KDP. It was found that the surface roughness obtained when using a tool with a chamfered corner was lower than that obtained using tools with right-angle corners. Other process variables (spindle speed, feedrate, and ultrasonic power) also affected the surface roughness obtained.     

Pinch analysis approach to carbon-constrained planningfor sustainable power generation

A graphical pinch-based methodology for planning retrofits for carbon capture and storage (CCS) in the power generation sector is presented in this work. CCS is widely seen as one of the essential interim technologies to mitigate greenhouse gas emissions, while still being able to utilize fossil fuels, which are relatively inexpensive and reliable in comparison to inherently low-carbon renewable resources. However, retrofitting power plants for CCS entails major capital costs as well as a reduction of thermal efficiency and power output. Thus, it is essential for planning purposes to implement the minimal extent of CCS retrofit that meets the sectoral carbon footprint targets. At the same time, it is necessary to plan for additional power generation capacity or efficiency enhancements to compensate for energy losses resulting from CCS retrofits. The simple graphical approach used in this paper is designed to determine such targets, and shares the same intuitive, insight-driven characteristics of pinch analysis techniques. A case study is shown to illustrate the methodology.     

A case study on raw material blending for the recycling of ferrous wastes in a blast furnace

The utilisation of ferrous wastes in a blast furnace is a well established recycling process to cope with the enormous amounts of ferrous residues in the iron and steel industry. The further input flows of this process, that is especially coke and fluxes, as well as its output flows, that is pig iron and by-products, are highly dependent on the blending of the ferrous wastes while they differ highly in the revenues gained for the treatment and their chemical composition. So far, no planning approach exists for the blending of the residues on the operational planning level that models the dependency of the costs and revenues on the raw material blend and the thermodynamic reactions in the recycling processes adequately. Therefore we present an approach for this operational production planning problem focusing on an integration of such a sufficiently detailed modelling of the underlying metallurgical processes into the planning model. The basis of our approach is a thermodynamic simulation of the processes. From this simulation we derive linear input-output functions for the relevant material and energy flows by using multiple linear regression. These input–output functions form the core of our blending model developed for the planning task. The model is implemented as an integrated decision support system. Exemplary application results are given. These results validate the approach and show that ecological the economic optimisation leads also to results which are advantageous in terms of resource efficiency and emission reduction. Though developed for a specific recycling process, the methodology can be transferred to other metallurgical (recycling) processes, as well as other parts of the process industries, and is therefore of high relevance.     

Pulsed laser micro polishing: Surface prediction model

The objective of this work is to predict the final roughness of metal surfaces that have undergone pulsed laser micro polishing. The motivation for pulsed laser micro polishing is to reduce the surface roughness of parts whose surface texture can approach the feature size. Being able to predict the magnitude of the polishing and frequency (wavelength) content of the surface will assist in the design of optimal processing parameters with minimal experiments. Laser pulses are used to create shallow melt pools with a controlled size (e.g., depth) and duration in order to allow surface tension forces to “pull down” asperities with small radius of curvature. There is no ablation occurring in the process being modeled. The melt depth and duration are predicted with a transient, two-dimensional axisymmetric heat transfer model with temperature-dependent material properties. The surface of the melt pool is analytically modeled as oscillations of stationary capillary waves with damping resulting from the forces of surface tension and viscosity. Above a critical spatial frequency, f_cr, a significant reduction in the amplitude of the spatial Fourier components is expected. The work described in this paper extends the concept of critical frequency to a physics-based prediction methodology for predicting the spatial frequency content and surface roughness after polishing, given the features of the original surface, the material properties, and laser parameters. The proposed prediction methodology was validated using line polishing data for stainless steel 316L and area polishing results for pure nickel, Ti6Al4V, and Al-6061-T6. The predicted average surface roughnesses were within 12% of the values measured on the polished surfaces.     

Design and fabrication of a laminated thermoforming tool with enhanced features

Thermoforming is a popular manufacturing process for creating useful shapes out of heated thermoplastic sheets using a porous tool under differential pressure. For large, heavy-gauge parts, thermoforming tools are typically made by CNC machining a billet of material or sand casting from an inexpensive master pattern. Although these tooling methods are well established, it is difficult to incorporate enhanced tool functionality such as conformal cooling channels, embedded sensors, unimpeded vacuum channel placement, and customized thermal mass. Profiled Edge Laminas (PEL), a rapid tooling method based on profiling, assembling, and clamping an array of thick layers, is ideally suited for tools used for thermoforming large, heavy-gauge parts and requiring enhanced features. This paper describes how the PEL tooling method can be applied to the design and fabrication of a thermoforming tool and demonstrates the entire process through a case study. Tooling design guidelines and analytical models for predicting conformal channel and vacuum line performance are included. The ease with which multiple-zone conformal cooling/heating channels, vacuum lines, and temperature sensors are incorporated into the tool is also highlighted. Specifically, a 46-layer aluminum PEL tool clamped together with bolts is successfully designed, fabricated, and demonstrated for thermoforming a 0.3×0.4×0.4 m part made from a PVC/Acrylic blend based on the outlined method. The tool incorporates three independent cooling zones sealed by a polymer sealant, three embedded temperature sensors, and an elaborate matrix of vacuum channels. All tool features and the basic geometry were machined into each individual lamina in the same set-up by 2D abrasive waterjet machining, and the final tool surface was CNC-machined. The PEL tooling method is successfully applied to the manufacture of a large, heavy-gauge thermoformed part intended for production.     

复杂河流系统水污染的计算机图形模拟

讨论在河流系统水污染规划中应用交互式计算机图形技术。通过对复杂河流系统水污染的图形模拟,提出建立图模型的一般理论和方法,并就浑太流域河流水污染案例给出实际模拟结果。     

基于激光烧结升温特性分析的月壤原位成型技术研究

目的分析利用激光烧结技术实施月壤原位成型的特点及方案,为月壤原位成型工程化设计和分析提供借鉴。方法基于国内外月壤原位成型技术路径,对比分析激光烧结成型技术方案的优势。通过激光照射条件下多层月壤颗粒升温模型,分析加热温度随激光器输出功率、月壤粒径、聚焦光斑直径及激光扫描速度的变化规律。基于“纪念碑”成型任务,提出一种基于封闭烧结腔和补给移动机构的激光烧结方案。结果激光烧结成型技术方案的优势是成型体性能及精度较高,无需添加辅料,非接触式,便于操作和控制,能耗及体积可接受。月壤颗粒能达到的温度取决于能够接受到的辐射能量,无论是提升激光器输出功率,还是缩小光斑直径,都能提升颗粒接受到的辐射能量密度。降低扫描速度,则颗粒接收辐射能量的时间增长,而月壤颗粒粒径变小,由于颗粒质量与粒径是三次方的关系,也能够提高单个颗粒接收到的辐照能量。激光烧结成型系统由控制装置、激光光源、补给装置、移动装置及电源组成,基于初步的分析计算,建议的系统耗能约为300 W,光斑直径为50μm,成型效率约为38 g/h。结论基于激光烧结技术路径的月壤原位成型技术具有一定的优势,建议采用低功率、小光斑、低扫描速度的技术策略,初步估算的技术指标具有工程可实现性。     

The development of a novel process planning algorithm for an unconstrained hybrid manufacturing process

The application of state of the art manufacturing processes has always been constrained by the capabilities either from technical limitations such as limited materials and complex part geometries or production costs. As a result, hybrid manufacturing processes – where varied manufacturing operations are carried out – are emerging as a potential evolution for current manufacturing technologies. However, process planning methods capable of effectively utilising manufacturing resources for hybrid processes are currently limited. In this paper, a hybrid process, entitled iAtractive, combining additive, subtractive and inspection processes, along with part specific process planning is proposed. The iAtractive process aims to accurately manufacture complex geometries without being constrained by the capability of individual additive and subtractive processes. This process planning algorithm enables a part to be manufactured taking into consideration, process capabilities, production time and material consumption. This approach is also adapted for the remanufacture of existing parts. Four test parts have been manufactured from zero and existing parts, demonstrating the efficacy of the proposed hybrid process and the process planning algorithm.     

Geometric variability and surface finish of weld zones in Yb:YAG laser welded advanced high strength steels

Laser welding is used for joining advanced high strength steels (AHSS) to improve formability and performance. In this paper, the geometric variability observed in the fusion zones and heat affected zones of several combinations of AHSS (different types, coatings and thicknesses), which were butt welded using a Trumpf TRUDISK 6000^® Yb:YAG laser beam, is presented. The surface texture parameters such as roughness and waviness of laser welds were also measured and correlated with geometric variability. Results indicate that although high quality welds with minimal defects can be obtained using the Yb:YAG laser welding process, there is considerable variation in both the shape and the dimensions of weld zones. The variability increased with an increase in thickness differentials between the sheets being welded. Analysis of the top of the weld surfaces also suggested that aluminum coating on USIBOR samples contributes significantly to increased roughness. An increase in laser power coupled with corresponding increase in welding speed did not impact variability. A fair correlation between the surface roughness and weld region variability exists, although this needs further study.     

Environmental comparison of MESO-CLAD® process and conventional machining implementing life cycle assessment

CLAD^® process (Direct additive laser manufacturing, Construction Laser Additive Directe in French) allows the direct manufacturing of small parts, and especially in case of complex shapes, giving equivalent properties with traditional processes such as conventional machining or casting techniques. Present environmental considerations are very important for updates in legislation or in order to make economic allowances. A specified mechanical Ti₆Al₄V part is used as a support and SimaPro software allows to perform Life Cycle Assessment. This study suggests that the absence of chips production, which represents up to 80% of the titanium consumption, provides to CLAD^® process an unquestionable advantage. This process requires longer times of execution, which increase additional energy consumptions, and the comparison of this process with conventional machining demonstrates that damages to resources and to human health are highly reduced. In both cases a large part of the environmental impacts are due to the powder elaboration. Finally, CLAD^® process can add shapes on machined/casted parts and it is possible to consider the manufacture of a mechanical part via a hybrid process.     

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.     

Environmentally conscious long-range planning and design of supply chain networks

In this paper, a mathematical programming-based methodology is presented for the explicit inclusion of life cycle assessment (LCA) criteria as part of the strategic investment decisions related to the design and planning of supply chain networks. By considering the multiple environmental concerns together with the traditional economic criteria, the planning task is formulated as a multi-objective optimization problem. Over a long-range planning horizon, the methodology utilizes mixed integer modelling techniques to address strategic decisions involving the selection, allocation and capacity expansion of processing technologies and assignment of transportation links required to satisfy the demands at the markets. At the operational level, optimal production profiles and flows of material between various components within the supply chain are determined. As such, the formulation presented here combines the elements of the classical plant location and capacity expansion problems with the principles of LCA to develop a quantitative decision-support tool for environmentally conscious strategic investment planning.     

Software as a bridge between theory and practice in life cycle assessment

Three mutually dependent elements are required for the application of life cycle assessment: methodology, data and software. Obviously, the design of software is determined by the methodology and the type of data available. Conversely, the development of software dictates the way in which data should be collected and recorded, and improves the theoretical framework, as it forces one to state the principles clearly and unambiguously. The influence of the development of software on both data and methodology is addressed and illustrated by examples, with reference to two key terms: transparency and explicitness. Three types of influence are distinguished: the design of a protocol, the formulation in terms of recipes, and the presentation of data.     

An approach to scenario analysis of the sustainability of an industrial sector applied to clothing and textiles in the UK

Companies aiming to be ‘sustainability leaders’ in their sector and governments wanting to support their ambitions need a means to assess the changes required to make a significant difference in the impact of their whole sector. Previous work on scenario analysis/scenario planning demonstrates extensive developments and applications, but as yet few attempts to integrate the ‘triple bottom line’ concerns of sustainability into scenario planning exercises. This paper, therefore, presents a methodology for scenario analysis of large change to an entire sector. The approach includes calculation of a ‘triple bottom line graphic equaliser’ to allow exploration and evaluation of the trade-offs between economic, environmental and social impacts. The methodology is applied to the UK's clothing and textiles sector, and results from the study of the sector are summarised. In reflecting on the specific study, some suggestions are made about future application of a similar methodology, including a template of candidate solutions that may lead to significant reduction in impacts.     

3D finite element modeling and analysis of radial forging processes

This paper presents a novel 3D finite element model for the radial forging process with consideration of mandrel. As different with the previous works, the proposed model captures more accurately the features of the radial forging process. The proposed model is validated. With the proposed model, a comprehensive analysis of the deformation for the tube is presented. The contributions of the present work are: (1) a full 3D finite element model which captures more features of the radial forging process than the models in literature, (2) a proof that a full 3D finite element model is needed, (3) a proof of the effectiveness of the spring bar in stabilizing the contact between the hammer die and work-piece, and (4) the spindle speed has little effect on forging load. Finally, this model can be well used for the analysis and comprehensive understanding of the radial forging process and optimization of the process in future.