烧结金刚石钻头加工Kevlar纤维增强复合材料的试验研究

以正交铺设的Kevlar层合板为对象,采用烧结金刚石钻头对其孔加工进行试验研究.针对Kevlar复合材料的各种加工缺陷,设计了预压应力工艺装置,在此工艺条件下,可以采用水进行冷却,其加工质量良好.通过试验分析了钻头参数及加工工艺参数对加工效率的影响,为烧结金刚石钻头在该加工领域的应用提供了参考.研究成果为Kevlar复合材料的孔加工技术提供了一种新的方法.     

A study of abrasive waterjet cutting of metallic coated sheet steels

A study of Abrasive Waterjet (AWJ) cutting of metallic coated sheet steels is presented based on a statistically designed experiment. It shows that AWJ cutting is a viable technology for processing metallic coated sheet steels with good productivity and kerf quality. A scanning electron microscopy analysis indicates that micromachining and plastic deformation are the dominant cutting phenomena in sheet steel processing. Plausible trends and relationships between kerf characteristics and process parameters are discussed. It is found that an optimum water pressure together with small standoff distance between the nozzle and workpiece may be used, while the traverse speed should be selected as high as possible for through cuts in order to increase the cutting rate. Empirical models for kerf geometry and quality are finally established for the prediction and optimization of AWJ cutting performance.     

Prediction of forming limit in deep drawing of Fe/Al laminated composite sheets using ductile fracture criterion

Axisymmetric deep drawing processes of laminates composed of mild steel and various aluminium alloy sheets are simulated by FEM. From the calculated stress and strain histories of elements in each layer, the fracture initiation site and the forming limit are predicted by using the ductile fracture criterion. The predictions so obtained are compared with experimental observations. The results exhibit that various types of fracture initiations in deep drawing of the laminated composite sheets are successfully predicted. Furthermore it is found that the drawability is improved by setting the mild steel sheet on the punch side for the case of aluminium alloy sheet with comparatively high ductility, and by sandwiching the aluminium alloy sheet with the mild steel sheets for the case of low ductility.     

AN EXPERIMENTAL STUDY OF CO 2 LASER CUTTING OF METALLIC COATED SHEET STEELS

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Monitoring laser cut quality using acoustic emission

The paper presents results of an analysis of acoustic-emission (AE) signals obtained during laser cutting of a steel plates, which are frequently used in the production of automotive body components. In the course of laser cutting, continuous signals, which are related to the quality achieved of the laser cut, are measured. After laser cutting characteristic AE bursts in the specimen material, which are results of a thermal influence, can be detected. The presence of dross is an important indicator of poor quality of laser cutting. The investigation on laser cutting was conducted on an unalloyed steel DC04 sheet and on austenitic stainless steel X5CrNi18-10 sheet of 1.5 mm in thickness. The same physical mechanism in the cut formation at both steels, however, resulted in a considerable different cut quality, which was indicated by the AE signals captured after the cutting process.     

Production-based design of a hybrid load introduction element for thin-walled CFRP Structures

The project “Multi-Layer Inserts” (MLI) proposes a new design for inserts used in thin-walled CFRP structures. The proposed inserts consist of multiple thin metal sheets and is build up simultaneously with the laminate in an intrinsic hybridization process, eliminating time-consuming post-processing steps. Furthermore, at equal weight, such inserts greatly increase the bonding area between metal and CFRP in comparison to conventional inserts. This results in a significant increase of the loads that can be transmitted into the CFRP. The present work discusses how the shape of the metal sheets which the proposed inserts consist of influences the mechanical properties of the surrounding laminate. This influence is investigated by measuring the strain distribution during tensile tests by means of digital image correlation. The strain distributions around the following three different MLI design approaches are compared: An elliptical metal sheet, which is expected to be ideal in terms of mechanical performance of the overall structure; a cross-shape metal sheet representing a production-driven simplification which only requires the ability to perform cuts in individual tows perpendicular to the laying direction and can be performed by state-of-the-art AFP systems; and lastly, a compromise between manufacturability and achieved mechanical performance, a decagonal metal sheet design, which requires angled cuts of the fiber tows. It is shown, that the decagon is able to evenly spread the strain over a larger area and is therefore able to significantly reduce the maximum strain values compared to a cross-shape metal sheet, while still being automatable.     

双金属温度补偿片的精整加工技术

航空用双金属温度补偿片要求能够可靠地起到温度补偿作用,对内、外形的形位公差及断面粗糙度要求较高,从分析双金属温度补偿片结构特点和冲压工艺性入手,结合生产需求,提出了小余量切削的精整加工工艺方案。详细解析了精整工艺参数设计方法,并对倒装及正装复合精整模具结构进行优劣对比分析,最终选用正装式复合精整模具结构,其能够在足够小的余量切削条件下一次完成整修加工,保证断面粗糙度要求;同时,巧妙地将3面定位改为6点定位,解决了废料挤压在定位板与工件之间而造成的操作困难以及定位板变形问题。生产实践证明,采用该工艺方法及模具结构取得的效果良好,不仅大大提高了生产效率,产品合格率也得到显著提升。     

Scaling laws for the laser-oxygen cutting of thick-sheet mild steel

The laws of scaling the laser-oxygen cutting of mild steel based on experimental optimization are proposed. The sheets from 5 to 25 mm are cut with the aid of CO₂ laser.It has been established that the minimal surface roughness is reached within the whole thickness range if the laser energy value per unit of the removed material and the power per sheet thickness unit are held constant. The results permit to determine the laser power and cutting speed values optimal for a certain sheet thickness. Within the range of large thicknesses, the conditions of cutting with minimal roughness are written as ratios between dimensionless variables. Evaluation of the maximum thickness of the sheet, at which the high-quality cutting is realizable, has been made.     

Prediction of cutting forces in helical end milling fiber reinforced polymers

Machining of fiber reinforced composites is an important activity in the integration of these advanced materials into engineering applications. Machining damage due to excessive cutting forces may result in rejecting the composite components at the last stages of their production cycle. Therefore, the ability to predict the cutting forces is essential for selecting process parameters that would result in minimum machining damage. This work utilizes mechanistic modeling techniques for simulating the cutting of carbon fiber-reinforced polymers (CFRP) with a helical end mill. A methodology is developed for predicting the cutting forces by transforming specific cutting energies from orthogonal cutting to oblique cutting. It is shown that the method developed is capable of predicting the cutting forces in helical end milling of unidirectional and multidirectional composites and over the entire range of fiber orientations from 0° to 180°. This is a significant improvement over previous models that were only capable of addressing orthogonal cutting and/or a limited range of fiber orientations. Model predictions were compared with experimental data and were found to be in good agreement in cutting unidirectional laminate, but with lesser agreement in the case of a multidirectional laminate.     

Use of zinc selenide and germanium lenses in the SM400/K701 laser cutting system

Abstract

Appreciably higher cutting speeds, narrower cuts and heat affected zones were obtained on laser cutting of thin sheet steel with an SM400/CO₂ high performance laser system in which ZnSe focusing lenses were substituted for the Ge lenses fitted as standard equipment.     

Modelling and experimental analysis of the effects of tool wear on form errors in stainless steel blanking

The main defects that characterize the quality and accuracy of blanked parts are the form errors which can be found on the blanked surface. These defects are basically related to tool wear and process parameters. This work presents theoretical modelling of the effects of tool wear on the shearing mechanism and resulting form errors. To this end, a new parameter denominated effective clearance, which characterizes the distance between a punch and the die cutting edge when a tool is worn, is defined. An experimental analysis of form errors as a function of this new parameter is made, using 6 and 8 mm AISI A2 steel punches and 1 mm thick AISI 304 stainless steel sheet. Finally, design criteria are proposed for the process parameters to fulfil the quality requirements of blanked parts.     

基于高强度钢切削加工的切削力和扭矩对比试验

本文对高强度钢的切削加工性能进行了分析，通过试验总结了普通麻花钻切削高强度钢时的磨损、破损特点，并对普通麻花钻和基本型群钻进行了切削对比试验，证明群钻可使切削力和扭矩减小，使刀具耐用度提高。从而为高强度钢的切削加工提供了理论依据。     

爆炸焊接可焊性窗口下限药量试验研究

在T10／Q235复合板的爆炸焊接试验中发现,成功爆炸焊接所需的实际最少药量比传统可焊性窗口下限动态参数确定的药量还减少了15％－20％左右,由此给出爆炸焊接药量系数修正式。依据修正式对3Cr13/Q235、1Cr18Ni9Ti／铸钢和62硬质黄铜／Q235复合板进行实际爆炸焊接生产检验,不仅大大减少了焊接药量和减轻了爆炸效应对环境的危害,而且复合板的焊接质量也完全满足工程的使用要求。因此,将修正式定义为对复合板爆炸焊接生产具有重要实际指导意义“最佳焊接药量窗口”。     

焊接吊耳锯切质量评定指标及影响因素

焊接吊耳是钢结构制造过程中用于吊装的重要零件。结合传统的锯切原理,从结构上分析焊接吊耳的锯切,为减小留根量,在利用带锯条锯切焊接吊耳时需要采用水平锯切方式,同时不能使用传统的带锯条扭转装置,而应该增大张紧力保证锯切质量。并将切口表面粗糙度Ra和留根斜度的正切值ρ作为锯切焊接吊耳质量的评定指标。采用正交实验法研究张紧力、锯切速度以及进给速度对焊接吊耳锯切质量的影响。研究表明:张紧力和进给速度对Ra和ρ的影响最大,锯切速度对粗糙度影响较小;张紧力越大,进给速度越小,则锯切质量越好。     

Effect of Gas-Laser Cutting on Formation of Texture, Structure, and Chemical Composition of Cut Surfaces of Titanium Preforms

The effect of gas-laser cutting of sheet titanium preforms in a medium of technical nitrogen on the quality of the cuts is studied. The influence of the cutting rate is considered as a factor most strongly affecting the quality of the cut, which is evaluated according to the appearance and according to the chemical composition of the surface of the cut. It is shown that observation of optimum cutting conditions ensures good quality of the cut as well as the permissible content of gas admixtures, including nitrogen in the surface layer of titanium preforms.__________Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 2, pp. 22 – 25, February, 2005.     

The Effect of Adhesion and Tensile Properties on the Formability of Laminated Steels

Laminated steel has been implemented in vehicle structures by several automotive manufacturers to reduce in-cabin noise. This study provides an understanding of how the adhesion between the steel skin and the viscoelastic polymer core affects laminate formability. Material properties, including peel strength, shear strength, and tensile strength were determined. The presence of the viscoelastic core was found to slightly reduce tensile properties of the laminate compared to the skin sheet. Forming limit diagrams were also determined. These indicated that the viscoelastic core properties can significantly affect formability of laminated steel compared to that of solid steel sheet. In general, the formability of laminated steel was found to be similar to or less than that of the much thinner skin sheet material, which indicates that its formability should be less than that of solid steel of the same gauge. This article was presented at Materials Science & Technology 2007, Automotive and Ground Vehicles symposium held September 16-20, 2007, in Detroit, MI.     

Investigation into thermal characteristics of linear hotwire cutting system for variable lamination manufacturing (VLM) process by using expandable polystyrene foam

The dimensional accuracy and efficiency of VLM-S, which is a new rapid prototyping process using hotwire cutter and expandable polystyrene (EPS) foam sheet, depends significantly on the thermal fields of EPS foam sheet when the hotwire cuts the sheet. The objective of this study is to investigate thermal effects of the hotwire cutting on the sheets and to find relationships between process parameters in order to obtain optimal conditions for hotwire cutting and improve dimensional accuracy of the process. Several experiments were performed to find the relationships between maximum cutting speed and heat input, and between cutting offset and heat input. Numerical analyses were carried out to investigate the influence of the cutting parameters on temperature distribution around the hotwire and to estimate the amount of the sheet melted away. Moreover, the size of the thermal front as the hotwire is about to lose its stiffness was predicted to propose the optimal cutting conditions. Based on the results, the optimal cutting conditions of the hotwire cutting system for cutting of an EPS foam sheet were found. In addition, the outcomes of the present study were reflected on the fabrication of a spanner shape and a clover punch shape.     

Application of an optimized SA-ANN hybrid model for parametric modeling and optimization of LASOX cutting of mild steel

Laser assisted oxygen cutting (LASOX) process is an efficient method for cutting thick mild steel plates compared to conventional laser cutting process. However, scanty information is available as to modeling of the process. The paper presents an optimized SA-ANN model of artificial neural network (ANN) and simulated annealing (SA) to predict and optimize cutting quality of LASOX cutting process of mild steel plates. Optimization of SA-ANN parameters is carried out first where the ANN architecture and initial temperature for SA are optimized. The optimized ANN architecture is further trained using single hidden layer back propagation neural network (BPNN) with Bayesian regularization (BR). The trained ANN is then used to evaluate the objective function during optimization with SA. Experimental dataset employed for the purpose consists of input cutting parameters comprising laser power, cutting speed, gas pressure and stand-off distance while the resulting cutting quality is represented by heat affected zone (HAZ) width, kerf width and surface roughness. Results indicate that the SA-ANN model can predict the optimized output with reasonably good accuracy (around 3%). The proposed approach can be extended for prediction and optimization of operational parameters with reasonable accuracy for any experimental dataset.     

复合电热餐具铝/不锈钢接触反应钎焊新技术

采用接触反应钎焊实现了复合电热餐具铝热管与铝板以及铝板与不锈钢板结构的高致密连接. 通过选择接触反应钎焊的中间层成分, 采用Si为中间层介质进行钎焊工艺试验. 对接头组织的显微分析表明, Si中间层介质与铝基体之间发生共晶反应所产生的Al-Si共晶液相, 能够将铝加热管与铝板以及铝板与不锈钢板大面积结构致密地连接在一起.     

钎焊过程原位合成高强度银钎料

AgCuZnSn合金具备高强度、成分无害化的优势,在绿色制造中应用前景广阔,但Sn元素的加入导致的成形性能下降,限制了其使用. 为克服该不足,设计了一种使用AgCuZn/ZnCuAgSn/AgCuZn复合焊片在钎焊过程中原位合成AgCuZnSn高强钎料的方法,采用的复合钎焊片外层为AgCuZn低熔合金,内层为ZnCuAgSn合金,二者熔点接近且内层合金低于合成后钎料熔点,复合钎料的加工性优于同成分的AgCuZnSn钎料. 使用复合钎焊片进行了感应钎焊不锈钢试验. 结果表明,钎焊过程中两种合金几乎同时熔化,经瞬间保温后可充分熔合,获得高强度钎缝,采用该工艺获得的接头强度高于常规钎焊连接强度.