内侧减薄拉深工艺的切块法分析

采用切块法对内侧减薄拉深工艺过程中坯料变形区的力学行为进行了分析推导,并利用推导结果对影响内侧减薄拉深工件质量的因素进行了分析讨论.最后给出了内侧减薄拉深力的计算公式.     

FINITE ELEMENT ANALYSIS AND EXPERIMENTAL STUDY OF THE METAL MULTIDIE IRONING PROCESS

ＦＩＮＩＴＥＥＬＥＭＥＮＴＡＮＡＬＹＳＩＳＡＮＤＥＸＰＥＲＩＭＥＮＴＡＬＳＴＵＤＹＯＦＴＨＥＭＥＴＡＬＭＵＬＴＩＤＩＥＩＲＯＮＩＮＧＰＲＯＣＥＳＳＦＩＮＩＴＥＥＬＥＭＥＮＴＡＮＡＬＹＳＩＳＡＮＤＥＸＰＥＲＩＭＥＮＴＡＬＳＴＵＤＹＯＦＴＨＥＭＥＴＡＬＭ...     

连杆机构在槽式熨平机上的应用

介绍一套连杆机构在槽式熨平机辊筒支撑结构上的应用,简述该连杆机构的工作原理和优点。通过采用该机构,槽式熨平机的辊筒可以对加热槽施加均衡压力,进而提高槽式熨平机的熨烫质量。     

高盒形件多道次变薄拉深工艺机理研究及数值模拟模型确立

盒形件有限元模拟通常采用壳单元进行建模,由于薄壳单元在计算中忽略了厚向应力,因此在多道次拉深成形及变薄拉深成形工况下的适用性存在质疑。以3003H14高盒形件多道次变薄拉深为研究对象,利用Dynaform并结合LS-DYNA有限元软件进行数值模拟,对比壳体单元与实体单元的模拟计算数据,通过分析外观模拟结果和Levy-Mises增量理论中瞬时本构关系系数的模拟数据,得到单元类型对薄板多道次变薄拉深成形模拟计算精度的影响规律。利用实际工程中的毛坯尺寸样本数据对建立的盒形件拉深毛坯尺寸计算程序进行训练,从而实现了盒形件拉深工艺毛坯尺寸预测软件的开发。此外,在明确建模方法后,结合实体单元有限元模拟结果研究板料在变薄拉深过程中材料的减薄与增厚的机理,揭示了材料流动规律。研究表明:实体单元模拟计算结果与实际更接近。若以坯料单元在工序前后的理论变形厚度的百分比差值作为变形程度衡量指标,当变形程度为0~11.1%时,两种单元计算差异为0.5%~27.8%;当变形程度为24.2%~34.9%时,两者计算差异为44.4%~79.3%。经多道次变薄拉深后,金属材料增厚区域多发生在凸缘及长边与短边交界处的圆角上;在模具的限制作用下,减薄区域多发生在底部圆角,长边与短边区域都有一定减薄;除工序1外,其他各个工序长边侧直壁平均厚度比工艺设计的理想值大1.00%~2.02%,短边侧直壁平均厚度比工艺设计的理想值小0.86%~12.90%。     

Experimental study on multi-stage deep drawing for rectangular cup with high aspect ratio

Multi-stage deep drawing process for rectangular cup using finite element method has been analyzed to understand the main process parameters, to modify the tool configurations for achieving sound intermediate blanks, and to obtain the rectangular deep-drawn cup in the prior study. As shown in the results of the numerical analysis, it has been ensured that the rectangular deep-drawn cup could be obtained. In this study, the tool fabrication and development considering the effects of the intake angle and the ironing operation are performed. The developed tool sets are applied to the multi-stage deep drawing process of this study, and a systematic experiment for the rectangular deep drawing process is carried out. From the first trial in the experiment, several failures are predicted. To solve these failures, the contact surface on the lower die is modified. As shown in the experimental results for the second trial by applying the modified lower die, it is investigated that the failures such as wrinkling and tearing phenomena are not observed, and the excessive deformation behavior due to thinning and thickening effects is decreased. Furthermore, the thickness distributions on the major axis and the minor axis of the intermediate blanks are investigated to be already satisfied by the target (ironing) thickness, respectively. By this systematic approach, it is confirmed that the experimental results show a good agreement with the designed and required configuration of the final product.     

An investigation on manufacturing process parameters of CNG pressure vessels

Mass production of CNG pressure vessels requires an accurate understanding of process effective parameters. In this paper, the finite-element method has been used to study the vessel manufacturing parameters. The FE model has been verified by experimental results. The entire manufacturing process, including deep drawing, redrawing and ironing, of an aluminum liner sample of CNG pressure vessels (without spinning) have been simulated. The deep drawing process has been modeled by using three types of dies: flat, conical and tractrix; then drawing force and wall thickness variations have been compared. In order to achieve the final diameter of the liner, the redrawing process has been implemented in a conical die. To obtain a uniform wall thickness, the ironing process has been simulated in two stages, and the required force and die angle for each process have been extracted. The result of this work presents an integrated perspective for decision-making on the manufacturing of CNG liners.     

Effect of material microstructure and tool geometry on surface generation in single point diamond turning

There is a strong desire in industry to improve surface finish when performing ultra-precision, single point diamond turning (SPDT) to reduce the amount of post process polishing required to meet final product specifications. However there are well known factors in SPDT which limit achievable surface finish. This paper focuses on the role of material microstructure, including grain boundary density and the presence of inclusions, as well as tool design on surface roughness using the concept of size effect. Size effect can be described as an interplay between the material microstructure dimension and the relative size of the uncut chip thickness with respect to the cutting edge radius. Since one of the controllable parameters in size effect is grain size and dislocation density, controlled studies were performed on samples whose microstructure was refined by mechanical strain hardening through rolling and a friction stir process (FSP). The use of the ultra-fine grained workpiece prepared using an FSP was observed to reduce side flow as well as grain boundary and inclusion induced roughness. The role of tool geometry on material induced roughness was investigated using a tool with a rounded primary cutting edge and a flat secondary edge. The use of the flat secondary edge was observed to improve surface finish when machining a flat surface. This improvement was primarily attributed to a reduction in side flow and material microstructural effects. By combining these approaches an average surface roughness R_a value of 0.685 nm was achieved when SPDT a flat surface. Furthermore the custom tool has the potential to significantly improve the productivity of SPDT by allowing for a much higher feed rate while still achieving a high quality surface finish.     

Lessons from the Lollipop: Biotribology,Tribocorrosion, and Irregular Surfaces

Biotribology and tribocorrosion are often not included in numerical or computational modeling efforts to predict wear because of the apparent complexity in the geometry, the variability in removal rates, and the challenge associated with mixing time-dependent removal processes such as corrosion with cyclic material removal from wear. The lollipop is an accessible bio-tribocorrosion problem that is well known but underexplored scientifically as a tribocorrosion process. Stress-assisted dissolution was found to be the dominant tribocorrosion process driving material removal in this system. A model of material removal was described and approached by lumping the intrinsically time-dependent process with a mechanically driven process into a single cyclic volumetric material removal rate. This required the collection of self-reported wear data from 58 participants that were used in conjunction with statistical analysis of actual lollipop cross-sectional information. Thousands of repeated numerical simulations of material removal and shape evolution were conducted using a simple Monte Carlo process that varied the input parameters and geometries to match the measured variability. The resulting computations were analyzed to calculate both the average number of licks required to reach the Tootsie Roll^® center of a Tootsie Roll^® pop, as well as the expected variation thereof.     

Mathematical model of micro turning process

In recent years, significant advances in turning process have been achieved greatly due to the emergent technologies for precision machining. Turning operations are common in the automotive and aerospace industries where large metal workpieces are reduced to a fraction of their original weight when creating complex thin structures. The analysis of forces plays an important role in characterizing the cutting process, as the tool wear and surface texture, depending on the forces. In this paper, the objective is to show how our understanding of the micro turning process can be utilized to predict turning behavior such as the real feed rate and the real cutting depth, as well as the cutting and feed forces. The machine cutting processes are studied with a different model compared to that recently introduced for grinding process by Malkin and Guo (2006). The developed two-degrees-of-freedom model includes the effects of the process kinematics and tool edge serration. In this model, the input feed is changing because of current forces during the turning process, and the feed rate will be reduced by elastic deflection of the work tool in the opposite direction to the feed. Besides this, using the forces and material removal during turning, we calculate the effective cross-sectional area of cut to model material removal. With this model, it is possible for a machine operator, using the aforementioned turning process parameters, to obtain a cutting model at very small depths of cut. Finally, the simulated and experimental results prove that the developed mathematical model predicts the real position of the tool tip and the cutting and feed forces of the micro turning process accurately enough for design and implementation of a cutting strategy for a real task.     

Developing a Computer-Aided Environment to Investigate the Influences of Design Schedule Changes on Material Requirement Planning

Recently, the concepts of concurrent engineering have been implemented in many manufacturing areas. However, very few efforts were addressed to linking design procedures and material requirement planning (MRP). In general, an engineering change (EC) might have an influence on the material requirements as well as on the inventory, and hence might affect the manufacturing process. Therefore, it is necessary to consider the material status during the EC stage. This concept has formed a new area for concurrent engineering, that is design for MRP (DFMRP). In this paper, a computer-aided environment that integrates a product data management (PDM) module and an MRP module, to support DFMRP has been proposed. The major function of this environment is to investigate the influence of EC schedule changes on MRP. In other words, this environment provides the information about the influence on MRP when the starting time or finishing time of certain EC tasks have been altered. A process model was developed to describe the relations between EC and production management tasks. In addition, an integration module was developed to extract the related information from PDM and MRP, and to analyse the possible influence on MRP based on the process model. The analysed results can be used as reference information for project management in PDM.     

Dissimilar metal deposition with a stainless steel and nickel-based alloy using wire and arc-based additive manufacturing

The wire and arc-based additive manufacturing process applies arc welding technology; the wire material is melted by the arc discharge, and is then accumulated successively in this process. The wire and arc-based additive manufacturing process directly and locally adds material to the molten pool. By changing the material locally during the process, more than one kind of material can be used simultaneously in a single manufactured component. In this study, two kinds of dissimilar metal deposition were conducted. A combination used was a stainless steel and Ni-based alloy. Mechanical properties near the interface such as hardness and bond strength were investigated. As a result, it was found that the mechanical properties of the manufactured alloy were comparable to those of a bulk material. In addition, an additive manufacturing system and a torch path planning method for using more than two kinds of material were proposed. By using this method, highly functional shapes whose surfaces and inner structures are made of different material could be made.     

Study on process parameters and its analytic application for nonaxisymmetric rectangular cup of multistage deep drawing process using low carbon thin steel sheet

Multistage deep drawing process is widely used to obtain various nonaxisymmetric rectangular cups. This deep drawing scheme including drawing and ironing processes consists of several tool sets to carry out a continuous production within one progressive press. To achieve the successive production, design and fabrication of the necessary tools such as punch, die, and other auxiliary devices are critical, therefore, a series of process parameters play an important role in performing the process design. This study focuses on the tool design and modification for developing the rectangular cup with an aspect ratio of 5.7, using cold-rolled low carbon thin steel sheet with the initial thickness of 0.4 mm. Based on the design results for the process and the tools, finite element analysis for the multistage deep drawing process is performed with thickness control of the side wall in intermediate blanks as the first approach. From the results of the first approach, it is shown that the intermediate blanks could experience failures such as tearing, wrinkling, and earing by excessive thinning and thickening. To solve these failures, the modifications for the deep drawing punches are carried out, and the modified punches are applied to the same process. The simulation results for the multistage rectangular deep drawing process are compared with the thickness distributions before and after the punch shape modifications, and with the deformed shape in each intermediate blank, respectively. The results of finite element reanalysis using the modified punches show significant improvement compared with those by using the original designed punch shapes.     

Novel methods for high-speed observation of material removal and molten pool movement in EDM

This paper proposes two new methods to observe discharge phenomena without interference from the plasma in electrical discharge machining. The first method uses a bandpass filter with a bandwidth of 800–820 nm and laser illumination with a wavelength of 800–820 nm. The second method also uses a bandpass filter with a bandwidth of 800–820 nm; however, in this method, the tungsten material is used not only as the tool electrode but also as the illumination source. First, the discharge process was observed using traditional methods to investigate the influence of the plasma on the observation of the discharge process. Then, the process of removing molten material from both the tool electrode and workpiece, as well as molten pool movement, was observed using the first method proposed in this paper. The material removed from the tool electrode was scattered upward along the end profile of the tool electrode, while the material removed from the workpiece was distributed along the horizontal direction. To explain these phenomena, the flow distribution in the gap was qualitatively analyzed using a fluid simulation. Finally, the discharge process was also observed using the second method proposed in this paper. A tungsten tool electrode can emit light with a wavelength of 800–820 nm, which shines on the observed region during the discharge process. The observation results verified the phenomenon of multiple explosions of the molten pool during the discharge process. Moreover, it was found that the material removed by the explosion of the molten pool was scattered in different directions and hardly influenced by the flow distribution in the gap.     

X射线异物检测的图像屏蔽算法

X射线异物检测系统检测包装食品过程中,由于产品某些包装区域的材质以及厚度特征,此区域对X射线的吸收率与异物对X射线的吸收率十分相似,导致系统在异物识别时将这些区域误判为异物,造成误检。针对此类问题,结合X射线异物检测原理和图像分割理论,提出了4种图像屏蔽方法。Matlab仿真结果表明,针对不同检测产品采用相应的屏蔽算法,均可有效屏蔽该检测产品中被误判为异物的区域,大大提高了X射线异物检测系统的灵敏度,具有较好的商业使用价值。     

轴对称多模变薄拉深的上限分析与试验研究

给出一种以非线性流线（除边界流线）描述的轴承对称变薄拉深初始流动模型,通过总功率的极小化确定最佳动许可速度场。建立多模变薄拉深任一凹模出口拉应力的一般上限解。提出摩擦因子的试验测试方法并给出其计算公式。凹模出口拉应力和变薄拉深力的理论解与试验结果良好吻合。     

Prediction of debris flake thickness

Earlier work has shown that plateaux of very fine-grained material can develop on the surface of a sliding test specimen. In the same tests, flake debris particles had the same chemical composition and structure as the plateau material, and it seems likely that the debris were generated from the plateaux. In this paper we describe a calculation which can yield a prediction of debris flake thickness. The work is based on an energy-based model of friction for coated systems. The basic idea is simple: one compares the friction coefficient μ₁ defined when plateaux are firmly attached to the base material, with the friction coefficient μ₂, defined when sliding occurs between the plateaux and the base material. Delamination occurs when μ₂<μ₁ and this in turn occurs when the plateaux exceed a critical thickness. The plateaux then delaminate by a local shear process and flake debris can be generated. Predictions are consistent with observed flake thicknesses.     

Hydrodynamic lubrication of the ironing process

A theoretical model is presented to calculate the lubricant film thickness in an unsteady hydrodynamic lubrication of cup-shaped products to be formed by the ironing process. The model covers the development of hydrodynamic lubrication in various phases of the ironing process. The model provides equations for estimating the lubricant film thickness for each phase. Experiments were conducted to study the effect of lubricant viscosity on die expansion and punch force in making cup-shaped products by the ironing process. It was found that the die expansion varied between unlubricated and lubricated cups and depended on the lubricant viscosity. The film thickness was estimated from the difference between the increased die/punch clearance, which was calculated from the expansion, and the lubricated cup wall thickness. The theoretical film thickness was compared with the estimated film thickness based on the die expansion measurement.     

Improving formability to develop miniature stamping technologies

In contrast to traditional manufacturing applications, small-scale manufacturing processes usually require sophisticated equipment, which generally involves high cost and low productivity. On the other hand, miniature stamping processes of thin materials can yield high productivity with relatively inexpensive equipment. However, it is well known that the formability of thin material using this type of process is not very good, and the possible shapes that can be produced via miniature stamping have, until now, been relatively simple. This study was motivated by the presumption that, if the problems related to formability can be solved, then miniature-scale stamping of complicated shapes can be realized. This research was carried out to demonstrate the feasibility of miniature stamping, and mainly focused on formability aspects. To improve formability, annealing was chosen as a means of improving the material properties, and the use of optimal blank shapes was chosen as a means of addressing process issues. Optimal annealing conditions were identified by examining the microstructures of the annealed material, and the optimal shape of the blanks was determined using the radius vector method. The combination of the annealing improvements and the use of optimal blanks improved the formability considerably. Therefore, both the annealing process and the blank shape are key technologies in the development of more effective miniature stamping processes.     

Process monitoring in precision cylindrical traverse grinding of slender bar using acoustic emission technology

The precision cylindrical traverse grinding process of slender bar is very complex for the strongly time dependent properties of the wheel. Therefore, it is very difficult for operators to properly judge the grinding state using naked eyes and ears. This calls for automatic monitoring technology that can monitor the process in precision cylindrical traverse grinding to guarantee machining quality and productivity as well as reduction in cost. This study developed an automatic monitoring system for precision cylindrical traverse grinding of slender bar using Acoustic emission (AE) technology. Grinding tests on molybdenum were conducted under traverse conditions in a conventional cylindrical grinder. It was found that larger radial material removal depth results in larger root mean square value of Acoustic emission signals (AE_RMS). Based on this, the AE_RMS was analyzed and used to determine the finishing of spark-out process and the pre-processing of tool alignment. The variation tendency of AE_RMS in one spark-out process was applied to determine when a wheel wears out and has to be dressed. The experimental results showed that the AE system was effective to monitor the pre-processing of tool alignment, spark-out and wheel wear in precision cylindrical traverse grinding of slender bar.

     

The Workpiece Material in Machining

In machining operations, much attention is paid to the improvement of the lifetime of tools by increasing the hardness of the tool whether or not it is combined with an optimised hard coating. Another method is to change the geometry of the tool by chip breakers and thus shorten the contact time and decrease the friction between chip and tool. Up to now, little attention has been paid to gaining an understanding of the influence of the workpiece material in machining. From forming operations, it is known that the fracture strain under different stress conditions can be predicted by using ductility curves. These curves can be determined easily by two simple material tests. It will be shown that these curves can also be used to understand chip breaking. The work clarifies a part of the role of the cooling liquid, and also the phenomenon that the tool life can sometimes be increased by using a harder workpiece material. A lower friction between chip and tool can be more effective than a harder tool material. Application of this idea teaches us the effect of Molybdenum sulphide (MoS2 ) as a tool coating and the fine cutting of steel with diamond tools. Another workpiece material property that influences the life-time of tools is its strain rate dependency on the flow stress. Its prediction is not easy and strongly depends on the material.