基于Geomagic Qualify软件的冲压件回弹检测

快速准确获得回弹量是实现冲压件回弹控制的关键因素。针对冲压件的回弹检测,提出了基于Geomagic Qualify的检测方法。利用Geomagic Qualify的强大比较分析功能,对冲压件的点云数据和CAD模型进行3D比较、2D比较和边界比较,分别检测了冲压件的整体、重要截面以及边界的回弹情况,并将检测的结果以图文方式直观显示出来。该研究为冲压件的回弹检测提供了方便、快捷的方法。     

An Automated Inspection System

An automated inspection system for manufactured parts is proposed using a cloud of 3D measured points of a part provided by a range sensor, and its CAD model. In spite of the high precision attained by coordinate measuring machines (CMM), range sensors offer significant advantages for dimensional inspection: a high speed of digitisation and the capacity to take 3D measurements on the whole surfaces of a part without physical contact. The system first registers a cloud of 3D points with a CAD model of the part, then segments the 3D points in different surfaces by using the CAD model, and finally measures the control of the specified tolerances on the part. Results of the inspection are displayed in two ways: visually, using a colour map to display the level of discrepancy between the measured points and the CAD model, and a hardcopy report of the evaluation results of the tolerance specifications. Two range sensor technologies have been tested and inspection results are compared with the results obtained with a CMM.     

基于扩展高斯球的点云数据与CAD模型配准

针对点云数据和三维CAD模型坐标配准过程中初始对应位置无法定量确定及最临近点计算效率问题,提出基于扩展高斯球的快速模板匹配算法,通过点云数据扩展高斯球空间与笛卡尔空间的相互转换,使外特征配准算法中测量点云与三维CAD模型初始位置的确定得到定量解决.为提高配准算法中点云数据与三维CAD模型最临近点的计算效率,采用三维CAD模型引导点云对测量数据与三维CAD模型进行桥接,从而将测量点与自由曲面的数值迭代计算问题转化为三维空间中最临近点的空间搜索,使算法的效率得到提升,实例验证了算法的有效性.     

基于光学测量的发动机燃烧室容积反求研究

以汽车发动机缸盖燃烧室容积的测量为研究对象,复制了缸盖燃烧室的硅胶模型。应用三维光学测量技术对燃烧室硅胶模型进行扫描测量,以获取燃烧室模型的点云数据。利用反求工程技术进行燃烧室模型重构,获得燃烧室的CAD模型。运用UG软件的体积计算功能计算燃烧室CAD模型的体积,得到缸盖燃烧室体积(容积)数据。同时,可将燃烧室CAD模型存档备用,为燃烧室的再设计、再制造或再维修提供参考。     

牙颌模型的三维激光测量及模型重建

牙颌模型的数据测量是进行口腔修复CAD/CAM的基础。本文采用自制三维激光测量仪对牙颌表面数据进行三维测量,获得了单颗后磨牙缺失的牙颌模型多片三维点云数据。将各片数据在反求软件Surfacer平台上通过三点定位法进行数据拼合,准确地表示出缺失牙上下颌的咬合关系,重建牙颌的实体模型。     

A study of techniques in the evaluation of springback and residual stress in hydroforming

The increasing need for high strength complex hollow bodies for automotive application is pushing towards the use of sheet hydroforming techniques in conjunction with high strength steels. Unfortunately high strength steels are characterised by high springback levels. In this paper the springback and residual stresses have been analysed by means of laboratory trials carried out using the double sheet hydroforming technique. The attention has been focused on the upper blank of TRIP800 steel. The analysis has been performed using different approaches: i) characterisation of sample accuracy by means of a 3D coordinate measuring machine using a new proposed method based on the standard deviation calculation; ii) FE-analysis of both hydroforming and springback stages using an implicit FEM code; iii) residual stress evaluation by means of X-ray diffraction and laser cutting techniques. The effect of pressure, die insert geometry and friction at the blank holder on springback and residual stresses have been analysed and discussed in detail.     

Robust generalized numerical inspection fixture for the metrology of compliant mechanical parts

Free-form non-rigid parts form the essence of today’s automotive and aerospace industries. These parts have different shapes in free state due to their dimensional and geometric variations, gravity and residual strains. For the geometric inspection of such compliant parts, special inspection fixtures are used in combination with coordinate measuring systems (CMM) and/or optical data acquisition devices (scanners). In our previous work, a general procedure was developed to eliminate the use of inspection fixtures. We measured the similarities between CAD model and scanned data by taking the advantage of the geodesic distance metric. Then, using finite element non-rigid registration, we deformed the CAD model into range data to find the geometric deviations. Here, we apply a new method to robustify the generalized numerical inspection fixture. We filter out points causing incoherent geodesic distances and demonstrate that our approach has several significant advantages, one being the ability to handle parts with missing range data. The other advantage of the method presented is its capacity to inspect parts with large deformations.     

Metal flow prediction during sheet-metal punching process using the finite element method

In this study, part springback and metal flow caused by punch penetration into a sheet was investigated by punching circular test specimens with concentric circular tools. Strain gauges were bonded on the upper surface of the specimens at radial distances varying from 2 mm to 10 mm from the cutting edge of the punch. The experiments were used to validate a finite element model (FEM) valid for numerical simulation of sheet-metal punching processes. Damage and crack propagation were taken into account by means of an elastoplastic constitutive law. The main difficulty encountered in simulating this operation is describing the behaviour of the sheet continuously from the beginning of the operation up to the total rupture. The choice of a behaviour law is crucial, since each successive step in the whole process has to be described accurately. In this investigation, an elastoplastic behaviour law coupled with damage was retained to describe the progressive damage accumulation in the workpieces. During the analysis, the initiation of a crack is assumed to occur at any point in the structure where the damage reaches its critical value D _c . The crack propagation is simulated by the propagation of a completely damaged area. This is taken into account in the FEM by a decrease in the stiffness of the broken elements. The numerical results obtained by the simulation were compared with the experimental ones in order to verify the validity of the proposed FEM.     

Springback prediction of high-strength sheet metal under air bending forming and tool design based on GA�CBPNN

Based on orthogonal test for air bending of high-strength steel sheets, 125 values of sheet thickness (t), tool gap (c), punch radius (r), ratio of yield strength to Young??s modulus (?? _y /E), and punch displacement (e) are used to model the springback for air bending of high-strength sheet metal using the genetic algorithm (GA) and back propagation neural network (BPNN) approach, where the positive model and reverse model of springback prediction are established, respectively, with GA and BPNN. Adopting the ??object-positive model?Creverse model?? learning method, air bending springback law is studied with positive model and punch radius is predicted by reverse model. Manifested by the experiment for air bending forming of a workpiece used as crane boom, the prediction method proposed yields satisfactory effect in sheet metal air bending forming and punch design.     

Path planning of multi-patched freeform surfaces for laser scanning

In this paper, a new method for scanning a complex surface model with multiple patches is proposed. In scanning of freeform-shaped models, it is difficult to generate a measuring plan by human intuition due to the complexity of the part. The developed method calculates the number of scans, scan direction, and scan path for a stripe-type laser scanner. The user can designate the surface patches that need to be scanned. In generating the scan plan, surface information is first extracted from the CAD model automatically. Other information such as, design knowledge, functionality and machine parameters are provided interactively. Based on this information, the original surface model is sampled in the u, v parameter domain and the sampled points are grouped using the view angle of the laser scanner. The scan direction is determined by calculating the global mean vector of the sampled points that belong to a group. The range of the view angle can be varied to enhance the quality of captured point data. The optical scan paths for each scan direction are calculated by projecting the sampled points onto a 2D plane. The optical constraints are also verified to guarantee the generated scan plan.     

Isogeometric analysis based on geometric reconstruction models

In isogeometric analysis (IGA), the boundary representation of computer-aided design (CAD) and the tensor-product non-uniform rational B-spline structure make the analysis of three-dimensional (3D) problems with irregular geometries difficult. In this paper, an IGA method for complex models is presented by reconstructing analysis-suitable models. The CAD model is represented by boundary polygons or point cloud and is embedded into a regular background grid, and a model reconstruction method is proposed to obtain the level set function of the approximate model, which can be directly used in IGA. Three 3D examples are used to test the proposed method, and the results demonstrate that the proposed method can deal with complex engineering parts reconstructed by boundary polygons or point clouds.     

Virtual binocular vision systems to solid model reconstruction

The geometry of a solid model can be determined in an effective manner if sufficient spatial information of its shape and corresponding edges can be obtained. The binocular vision system, in which images are obtained from calibrated cameras, has traditionally been the most popular method. In this paper, a virtual binocular vision system, which is composed of one CCD camera and a rotary platform, is proposed as an alternative for measuring three-dimensional objects. The fundamental matrix of the virtual binocular vision system is proposed such that the coordinates of feature points can be determined through an efficient searching and matching procedure. Subsequently, point clouds of the object can be obtained to construct a solid model by utilizing CAD software, such as CATIA and Pro-E. This model can in turn serve as a basis for further analysis and extended applications.     

基于逆向工程的车灯罩壳模具的快速设计与制造

逆向工程技术已成为模具CAD/CAM的制造技术之一,以车灯罩壳模为例,首先利用三维激光测量仪对零件进行测量,获取三维点云数据,然后利用UG软件将得到的轮廓数据三维重构,得到实物原型的三维数字模型,最后进行模具CAD/CAM。采用逆向工程技术可以快速实现模具的设计与制造,同时大大缩短了整个产品的开发周期。     

Numerical simulation and experimental investigation of multistage incremental sheet forming

Multistage forming is usually adopted to form those parts which have steep angles or even vertical walls during incremental sheet forming (ISF) process. In order to study the multistage incremental forming further, based on a finite element method model which was experimentally verified, different forming strategies were adopted to form a frustum of cone with a wall angle of 30° to research the influence of the number of forming stages (n) and the incremental wall angle between the two adjacent stages (?α) on the formability of ISF. The simulation results including the thickness distribution, the equivalent plastic strain, and the magnitude of springback were analyzed in detail. It was found that with the growth of n, the minimum thickness increases largely, and more uniform thickness distribution is achieved, but the quantity of springback becomes larger in contrast with a single-pass process because of the accumulation of springback during each forming stage. Furthermore, an expression to figure out the appropriate value of n was given. In addition, the maximum thickness reduction decreases initially and then increases as the value of ?α grows. Meanwhile, it indicates that there is no relation between ?α and the quantity of springback.     

Theoretical and experimental research on error analysis and optimization of tool path in fabricating aspheric compound eyes by precision micro milling

Structure design and fabricating methods of three-dimensional （3D） artificial spherical compound eyes have been researched by many scholars. Micro-nano optical manufacturing is mostly used to process 3D artificial compound eyes. However, spherical optical compound eyes are less at optical performance than the eyes of insects, and it is difficult to further improve the imaging quality of compound eyes by means of micro-nano optical manufacturing. In this research, nonhomogeneous aspheric compound eyes （ACEs） are designed and fabricated. The nonhomogeneous aspheric structure is applied to calibrate the spherical aberration. Micro milling with advantages in processing three-dimensional micro structures is adopted to manufacture ACEs. In order to obtain ACEs with high imaging quality, the tool paths are optimized by analyzing the influence factors consisting of interpolation allowable error, scallop height and tool path pattern. In the experiments, two kinds of ACEs are manufactured by micro-milling with different too path patterns and cutting parameter on the miniature precision five-axis milling machine tool. The experimental results indicate that the ACEs of high surface quality can be achieved by circularly milling small micro-lens individually with changeable cutting depth. A prototype of the aspheric compound eye （ACE） with surface roughness （Ra） below 0.12 p.m is obtained with good imaging performance. This research ameliorates the imaging quality of 3D artificial compound eyes, and the proposed method of micro-milling can improve surface processing quality of compound eyes.     

Rapid tooling aided by reverse engineering to manufacture EDM electrodes

The present work deals with the application of indirect rapid tooling (RT) technology to manufacture electrical discharge machining (EDM) copper electrodes from investment casting, with wax prototypes made by ThermoJet 3D printing, a rapid prototyping (RP) technique. The reverse engineering (RE) method is utilised to transform the point cloud data of an object surface, obtained from 3D digitising, in a 3D CAD surface model dataset. The methodology presented is fundamental to verify the prototype’s geometry for tooling so as to assure its metrological accuracy and to optimise foundry process parameters using finite element analysis (FEA). Based on a case study, some functional conclusions are presented for the application of RT in manufacturing EDM electrodes aided by 3D digitising and RE, validating the accomplishment by the integration of these technologies and methodologies in EDM manufacturing processes.     

Dynamic stiffness deterioration of a machining center based on relative excitation method

The tool point frequency response function(FRF) is commonly obtained by impacting test or semi-analytical techniques.Regardless of the approach,it is assumed that the workpiece system is rigid.The assumption is valid in common machining,but it doesn’t work well in the cutting processes of thin-wall products.In order to solve the problem,a multi-degree-of-freedom dynamic model is employed to obtain the relative dynamic stiffness between the cutting tool and the workpiece system.The relative direct and cross FRFs between the cutting tool and workpiece system are achieved by relative excitation experiment,and compared with the tool point FRFs at x and y axial direction.The comparison results indicate that the relative excitation method could be used to obtain the relative dynamic compliance of machine-tool-workpiece system more actually and precisely.Based on the more precise relative FRFs,four evaluation criterions of dynamic stiffness are proposed,and the variation trend curves of these criterions during the last six months are achieved and analyzed.The analysis results show that the lowest natural frequency,the maximum and the average dynamic compliances at x axial direction deteriorate more quickly than that at y axial direction.Therefore,the main cutting direction and the large-size direction of workpieces should be arranged at y axial direction to slow down the deterioration of the dynamic stiffness of machining centers.The compliance of workpiece system is considered,which can help master the deterioration rules of the dynamic stiffness of machining centers,and enhance the reliability of machine centers and the consistency of machining processes.     

基于逆向工程的产品快速制造的研究

以吸尘器为例,详细阐述了逆向工程技术和快速成型技术在产品设计中的应用和实现。采用三坐标测量机测得吸尘器表面若干空间点数据,利用U G N X 6.0对其点云数据进行处理并完成三维C A D模型的重建,最后基于3D P技术实现对吸尘器原型的快速成型制造,从而为后续对新产品进行快速评价、结构优化验证和性能测试等方面打下坚实的基础。结果表明,逆向工程与快速成型技术相结合,为新产品尤其是复杂型面产品的设计与制造提供了更为广阔的平台,并且缩短产品开发周期、降低试制成本、避免产品研发失败的风险,可以极大地提高企业的竞争力和经济效益。     

基于点云数据的复杂型面数字化检测技术研究

针对设计制造流程中复杂型面检测难的问题,建立了由数据获取、点云与计算机辅助设计模型匹配及偏差分析组成的数字化测量系统。采用格雷码加相移技术的三维非接触式光学测量技术,获取了待测零件的表面数据。为满足光学三角法要求,在测量机构中采用了定制光栅,提出了具有小扰动的改进最邻近点迭代算法进行点云与计算机辅助设计模型的准确匹配。在偏差分析中采用多分辨率层次分析法对测量点云与计算机辅助设计模型进行比较,为设计人员及时提供了精度分析数据,使设计制造检测成为一个反馈系统。以某型号轿车车灯配光镜为例,验证了该系统的可行性。     

板料成形中的回弹计算和模具修正

利用动力显式有限元计算程序MSC／DYTRAN,采用动力松弛法模拟了板料成形及回弹过程,计算出板料成形后的回弹量：提出“位移描述－结点修正”法,以回弹量为依据通过反向位移补偿和插值算法,编制程序自动对模具网格结点进行修正,通过反复迭代计算,最终可获得生成理想形状制件所必需的凸,凹模尺寸。