A strategy for efficient and quality cutting of materials with abrasive waterjets considering the variation in orifice and focusing nozzle diameter

In Abrasive Waterjet (AWJ) cutting, orifice and focusing nozzle diameter undergo continuous change in their dimensions due to erosive nature of high velocity abrasive waterjet. This particular phenomenon can affect the efficiency and quality of the process. To achieve maximum efficiency and desired quality with this process, the parameters need to be optimally selected from time to time considering the changes in the dimensions of orifice and focusing nozzle. In an effort to develop strategies for this purpose and to build the knowledge base for adaptive control of the process, the present work aims to study the influence of orifice and focusing nozzle diameter variation on the performance of abrasive waterjets in cutting 6063-T6 aluminum alloy. The performance was assessed in terms of different parameters such as depth of cut, material removal rate, cutting efficiency, kerf geometry and cut surface topography. In order to maintain the desired performance, it is essential to monitor the condition of nozzles and suitably adjust the process parameters with a view to control the process. Towards the latter, the present work attempts to suggest a strategy that can aid in replacing the nozzles at an appropriate time for maintaining the performance of process within certain limits so as to maintain the precision in machining with abrasive waterjets.     

Experimental analysis of irregularities of metallic surfaces generated by abrasive waterjet

Experimental study of the surface quality produced by abrasive waterjet (AWJ) on metallic materials has been performed. The surface roughness/waviness was quantitatively evaluated by using the contactless optical measurement. In order to characterize the cut surface qualities, a single-parameter criterion has been proposed. Based on root mean square (RMS) roughness evaluation of the worst cut surface zone, the dimensionless statistical parameter C can be calculated as a basic quantity for AWJ surface cut characterization. As it was approved, besides its dependency on depth of AWJ trace, the value of C-parameter for the specific material is noticeably related also to the traverse speed of the cutting head. Such a relationship can be potentially used for adjusting the cutting speed of the machining process.     

A study on surface roughness in abrasive waterjet machining process using artificial neural networks and regression analysis method

In the present study, artificial neural network (ANN) and regression model were developed to predict surface roughness in abrasive waterjet machining (AWJ) process. In the development of predictive models, machining parameters of traverse speed, waterjet pressure, standoff distance, abrasive grit size and abrasive flow rate were considered as model variables. For this purpose, Taguchi's design of experiments was carried out in order to collect surface roughness values. A feed forward neural network based on back propagation was made up of 13 input neurons, 22 hidden neurons and one output neuron. The 13 sets of data were randomly selected from orthogonal array for training and residuals were used to check the performance. Analysis of variance (ANOVA) and F-test were used to check the validity of regression model and to determine the significant parameter affecting the surface roughness. The statistical analysis showed that the waterjet pressure was an utmost parameter on surface roughness. The microstructures of machined surfaces were also studied by scanning electron microscopy (SEM). The SEM investigations revealed that AWJ machining produced three distinct zones along the cut surface of AA 7075 aluminium alloy and surface striations and waviness were increased significantly with jet pressure.     

Enhancement of bending formability of brittle sheet metal in multilayer metallic sheets

The formability of multilayer metallic sheets is evaluated by tensile, V-bending, hat bending and hemming tests. A monolithic type-420J2 stainless steel sheet cannot be formed because of poor elongation as small as 1.7%. Marked enhancement of the bending formability was observed in the bending of type-420J2 stainless steel sheets when they are layered by type-304 stainless steel sheets and composed into a multilayer metallic sheet. The mechanism of the enhancement of the formability of type-420J2 stainless steel in a multilayer metallic sheet is investigated analytically by focusing on the delay of the initiation of necking, and by performing stress analysis by finite element method (FEM).     

镀层金属板冲压成形断裂失效的有限元模拟

镀层金属板在加工过程中,由于工艺参数、模具几何参数的影响,经常会出现裂纹,并最终导致板材的断裂。以双面电沉积镍的低碳钢板为研究对象,采用基于连续介质损伤有限元模拟以及冲压成形实验相结合的方法对镀层金属板在冲压过程中的失效问题进行了研究。结果表明:随着冲压深度的增加,杯形件中的等效塑性应变与损伤值均增加,当冲压深度达到10mm时,在杯形件冲头圆角处出现断裂现象。通过冲力冲程曲线与成形件形状的比较和损伤变量分布、等效塑性应变分布以及厚度减薄的分析发现,有限元模拟结果与冲压成形的试验结果符合得较好,证明了有限元模拟的正确性。     

彩涂板技术发展及我国生产概况

简要介绍了彩涂板的生产工艺、性能特点、应用范围 ,以及彩涂板生产技术的发展趋势 ;同时介绍了我国彩涂板的生产概况、发展特点及今后应注意的问题。     

基于B/S模式的钣金展开/切割CAD/CAM系统研发

建立了基于B／S模式的钣金展开CAD／CAM系统。论述了基于ASP理念钣金展开／切割CAD／CAM系统的计算模型和编程原理、用户身份认证机制、零件信息输入与处理，NC指令生成及浏览器端的动态加工模拟、系统管理机制等关键技术及实现方法。     

板料直壁零件数控渐进成形

板料直壁零件成形是渐进成形的难点之一。为了成形直壁零件,一般采用多次成形的方法。文章对直壁零件多次成形法从理论上进行了分析,并且通过实验,验证了这种方法的正确性。     

单一尺寸矩形毛坯下料问题的一种确定性算法

针对单一尺寸矩形毛坯下料问题,讨论了如何用最少的库存板材切割出一定数量的单一尺寸矩形毛坯。提出1种切割工艺简单的5块排样方式,该排样方式将板材划分成5块区域,每块区域中矩形毛坯按照相同方向排列。设计了1种确定性算法求解下料方案,首先构造1种基于隐式枚举思想的算法确定整张板上的最优5块排样方式;然后对该算法进行扩展,使其能够求解部分板上的最优5块排样方式。采用算例将文中下料算法和文献中递归下料算法、拼合下料算法进行比较,数值模拟分析结果表明,文中的下料算法在切割工艺和板材利用率两方面均较为有效。     

A study of the tool-chip interface contact problem under low cutting velocity with an elastic cutting tool

To understand the effects of elastic deformation of the tool and the crater phenomenon generated by the cutting force and high pressure during metal cutting processing on the cutting process, an iterative mathematical model for calculating the tool-chip contact is developed in this paper under the assumption of elastic cutting tools. In this model, the finite-element method is used to simulate the cutting of mild steel by a cutting tool of three different materials. The results obtained in the simulation are found to match experimental data reported by related studies. The simulation results also indicate that tools with a smaller stiffness produce greater elastic deformation. Further, decrease of the rake angle due to elastic deformation of the tool can result in greater difficulty in internal deformation of the material and an increase in cutting force. The micro-crater phenomenon on the tool face generated by high pressure at the tool-chip interface is the preliminary symptom of crater wear on the tool face. Therefore, under some machining conditions, such as in precision machining or in automation processing where tool compensation is required, the phenomenon of elastic deformation of the tool must be considered carefully to ensure product precision.     

板料零件数控渐进成形工艺研究

板料零件数控渐进成形工艺是一种通过数字控制设备 ,采用预先编制好的控制程序逐点成形板料零件的柔性加工工艺。本文就板料零件数控渐进成形工艺的成形过程、变形机理、极限半顶角等方面进行了探讨。认为 ,板料零件数控渐进成形是使板料的厚度减薄 ,表面积增大 ,靠逐次的变形累积产生整体的变形。变形区厚度的变化与成形半顶角有关 ,其中 ,成形极限半顶角是数控渐进成形能否成功的关键 ,它不仅与材料有关 ,而且与板料厚度有关。