Design of forging process variables under uncertainties

Forging is a complex nonlinear process that is vulnerable to various manufacturing anomalies, such as variations in billet geometry, billet/die temperatures, material properties, and workpiece and forging equipment positional errors. A combination of these uncertainties could induce heavy manufacturing losses through premature die failure, final part geometric distortion, and reduced productivity. Identifying, quantifying, and controlling the uncertainties will reduce variability risk in a manufacturing environment, which will minimize the overall production cost. In this article, various uncertainties that affect the forging process are identified, and their cumulative effect on the forging tool life is evaluated. Because the forging process simulation is time-consuming, a response surface model is used to reduce computation time by establishing a relationship between the process performance and the critical process variables. A robust design methodology is developed by incorporating reliability-based optimization techniques to obtain sound forging components. A case study of an automotive-component forging-process design is presented to demonstrate the applicability of the method.     

A New Approach for Robust Design of Mechanical Systems

Robust product design aims to develop a product that satisfies design requirements while ensuring minimal effects of environmental variability on product performance. Environmental variations may come from raw materials, manufacturing processes, and/or operational environments, which can cause deviations of product functions. This research can verify that the independence axiom can lead to a robust design, while robust designs do not necessarily require functional independence. Thus, designs can be divided into three categories - feasible designs, robust designs and ideal designs. In the first level of the design process, the designers should generate a feasible design, then seek to acquire robustness, and finally determine the possibility of independence. Axiomatic design aims to achieve the independent design; the traditional robust design is an experimental method that may not reach design independence. The proposed approach introduces the integration of the independent analysis that is based on axiomatic design, with the robust analysis that is based on the traditional robust technique. It can help the designer to seek an ideal design or a robust design in respect to the specific design conditions.     

Concurrent optimization of design and machining tolerances using the genetic algorithms method

The allocation of design and machining tolerances has a significant effect on both manufacturing cost and quality. This paper presents a procedure to concurrently allocate both design and machining tolerances based on optimum total machining cost. The non-linear multi-variable optimization problem formulated is solved using the genetic algorithms method. Two design examples involving concurrent allocation of both design and machining tolerances are presented to demonstrate the effectiveness of the method.     

Design improvement using process capability data

Historical process capability data (PCD) is commonly used during product design. Such data can be stored in a formal database known as a process capability database (PCDB). PCD is primarily used during product design to allocate tolerances or forecast and manage manufacturing variation. However using a PCDB for these purposes alone does not exploit its full potential. This paper describes a method by which PCD can be applied to predict product performance variation early in the design process, thus saving time and reducing subsequent redesign costs. More specifically it describes the use of PCD during the initial design stage to predict how the product will operate, in terms of functional reliability, after it has been manufactured. An illustrative example based on the design of an electrical connector is provided. In this case connector beam normal force is a strong indicator of connector reliability and the example shows how the variation of this normal force can be predicted during initial connector design.     

Parametric process optimization to improve the accuracy of rapid prototyped stereolithography parts

The functional requirements of a rapid prototyping system are speed and accuracy, and they are both functions of vendor defaulted and user selected manufacturing parameters. Accuracy is evaluated by dimensional errors, form errors and surface roughness of manufactured parts. A specially designed specimen with 20 dimensional, geometrical, and surface roughness features has been used in the inspection of RP manufacturing processes. In terms of Taguchi experimental design techniques, an orthogonal array of experiments has been developed which has the least number of experimental runs and desired process parameter settings. Using a 3-D coordinate measuring machine and surface profilometer, a series of measurements in evaluating the SLA parts quality has been conducted to find the functional relationships between the output part quality and input manufacturing process parameters. Two analysis tools, response surface methodology and Analysis of Variance (ANOVA), have been used to evaluate the SLA RP process and to perform the product optimization. The optimal setups of SLA manufacturing parameters for both individual features and a general part with various features have been concluded from this study.     

Optimization method for stamping tools under reliability constraints using genetic algorithms and finite element simulations

Controlling variability and process optimization are major issues of manufacturing processes which should be tackled together since optimal processes must be robust. There is a lack of numerical tool combining optimization and robustness. In this paper, a complete approach starting from modelling and leading to the selection of robust optimal process parameters is proposed. A model of stamping part is developed through Finite Element simulation codes and validated by experimental methods. The search for optimal tool configurations is performed by optimizing a desirability function and by means of a genetic algorithm based optimization code. Several tool configurations are selected from the resulting solutions and are observed through robustness analysis. Noise parameters relating to friction and material mechanical properties are taken into consideration during this analysis. A quadratic response surface developed with design of experiments (DOE) links noise parameters to geometrical variations of parts. For every optimal configuration, the rate of non-conform parts which do not satisfy the design requirements is assessed and the more robust tool configuration is selected. Finally, a sensitivity analysis is performed on this ultimate configuration to observe the respective influence of noise parameters on the process scattering. The method has been applied on a U-shape part.     

Selection of an optimum sample size for flatness error estimation while using coordinate measuring machine

In the present day manufacturing environments it is becoming increasingly important to be able to deliver quality products at the right time to the market at competitive costs. The quality, cost and time to market depend not only on the design and manufacturing but also on the inspection process adopted. Design specifications rely on extensive usage of form tolerances to ensure that the functionality of surfaces and features of the product are maximized. The use of the coordinate measuring machines (CMM) has greatly improved the efficacy of form tolerance measurement and is also used as the key device in this work. The focus of this work is to deal with the method and strategies for measurement of flatness error so as to be able to predict the flatness error accurately at reduced sample sizes in batch and mass production setups. Accurate evaluation of flatness will require large sample sizes which increase the cost and time of inspection and hence a need to reduce the sample sizes without compromising on the accuracy. In the absence of robust models that can predict the errors due to manufacturing processes, an alternative technique has been devised to arrive at a reduced sample size. The procedure involves using large sample data inspected on the first component as the basis for evolving smaller sample sizes for subsequent components.Experimental verification of the developed algorithm shows that flatness error can be predicted with sufficient accuracy at small sample sizes.     

Change of datum of the dimensions on engineering design drawings

Frequently the datums chosen for dimensions on engineering drawings are unsuitable for manufacturing and inspection purposes and it is necessary to redimension the design from new datums. A theory is presented for performing this change of datum and a procedure is discussed for allocating tolerances to the new dimensions. This procedure enables the relative difficulty of producing each dimension to be included in the calculations for the new tolerances. Finally, the procedure of change of datum is presented as part of a computer aided design or drafting system.     

基于成组技术的模具敏捷设计技术研究

模具已公认为是一种低成本生产高精度复杂形面零件最有效的方法。而成组技术已在制造业的很多领域得以应用。据此本文阐述了一种运用成组技术的核心思想来指导模具设计的方法 ,以期实现模具敏捷设计 ;并针对模具的特点提出了一套新的模具零件分类编码系统 ,为进一步的软件开发奠定了理论基础     

基于仿真分析的BT40主轴系统公差设计与优化

公差设计质量直接影响产品的性能和制造成本。为提高主轴系统公差设计的质量和效率,提出了一种基于建模仿真的公差设计与优化方法。模拟BT40主轴系统的结构和装配过程,首先在CETOL6σ软件中建立主轴系统的数字化公差模型,利用该模型分析各主要公差对系统输出精度的贡献度和敏感度。然后以类比法公差设计作为原始方案,仿真检验其设计效果。最后以公差贡献度和敏感度为依据,对原有公差设计方案进行修正及优化。结果表明:优化后的方案显著提高了主轴系统的输出精度。     

排辊成形工艺参数化设计系统集成开发技术

排辊成形是利用若干组小排辊将带钢续弯卷成管筒的一种辊式成形工艺,是制造焊管的重要加工技术。现代的排辊成形工艺设计涉及到CAD,CAE和知识管理等多个方面的技术,技术平台的集成至关重要。本文以Visual Basic为开发平台,利用Visual Basic与ACCESS数据库、MATLAB与ANSYS的接口技术,将参数设计、有限元模拟和知识管理集成,开发了直缝焊管排辊成形工艺设计系统。通过该系统可以实现直缝焊管排辊成形过程的工艺参数管理、机组的轧辊设计、花型设计、工艺参数设计以及CAD/CAE建模仿真。该平台可以为工程人员进行直缝焊管工艺设计提供重要参考。     

永磁环形力矩电机期望补偿自适应鲁棒控制

针对复合A/C轴直接驱动永磁环形力矩电机伺服系统易受外部扰动、参数不确定性以及齿槽转矩的影响,为实现高性能控制和准确参数估计,设计了根据期望轨迹构造自适应律的期望补偿自适应鲁棒位置控制器。该期望补偿自适应律只需根据期望轨迹,采用不连续参数投影算法对系统不确定性进行离线估计。与常规自适应鲁棒控制器相比,该控制器降低了测量噪声对系统的影响,实现参数估计过程更快且参数估计值更加精确。仿真结果表明该方法不仅使伺服系统具有较好的暂态性能,而且提高了系统的最终跟踪精度。     

An approach to selection of material and manufacturing processes for rocket motor cases using weighted performance index

Material selection is a very critical design decision, which has a profound influence on the entire development program for rocket motor cases. In the selection process, the main performance parameters and the most appropriate fabrication technology with proven processes must be considered. Many years of practical experience in material selection process with a thorough understanding of materials behavior under various loading environments and hands-on experiences with various available manufacturing processes are of immense help to the design and development engineer for successful completion of the development program. In this paper, an attempt has been made to present an approach for selecting appropriate material and manufacturing process for rocket motor case based on method of Weighted Performance Index (WPI) with the hope that this approach will also provide additional aid to the design engineer for the selection of material and manufacturing process for rocket motor cases. In this method, different properties are assigned a certain weight depending upon their importance to the service requirements. Different properties are normalized using a scaling factor, and finally a weighted property index is computed. The material that scored the maximum numerical value is chosen as the material for fabrication. This approach closely matches with the actual performance. Maraging steel and D6AC are found to be the preferred materials for rocket motor cases for critical missions. HSLA steels are appropriate for less-critical applications, in which rocket motor cases are required in very large numbers (e.g., flow-formed AISI 4130 motor cases^[8]). For the selection of an appropriate manufacturing method, the major parameters considered are dimensional accuracy, cost of production, minimum material waste, and flexibility in design. Again, these properties are given a relative grading, which is then converted into a scaled property. Finally, the weighted performance indices are estimated. The flow-forming method has emerged as the manufacturing method of choice for motor tubes.     

冲压稳健设计方法及其应用

利用冲压成形仿真技术 ,采用复合设计的方法 ,得到冲压件质量评价指标及其影响因素的回归公式 ,从而实现了冲压成形过程的稳健设计 ,并通过实际冲压实验证明了回归公式的正确性和冲压稳健设计方法的可行性。     

Solid modeling based servo system design for a high speed micro grinding machine

The flourishing hi-tech industry development has prompted the need to carry out high performance servo design and testing without actually having to construct a prototype system. However, the complicated mechanical structure and the nonlinear effects in many of the high performance systems have made it very difficult to carry out the design without a suitable model. In recent years, the software advances has achieved very accurate dynamic simulation result. It is also possible to integrate the control synthesis with the dynamic simulation. This study examines the possibility of performing the servo design within the system design environment and then applies the result to a realistic platform model. The robust sliding mode controller is employed to deal with the nonlinear characteristics in the grinding machine. The dynamic model included the multi-degree of freedom behavior and the friction effects. The simulation results also show that the sliding mode controller is able to suppress the structure resonances and achieve high accuracy control under plant uncertainties.     

基于现值质量损失的并行公差技术研究

在并行设计环境中,用多变量质量损失函数在连续复利条件下把产品质量特征的退化作为一个连续的现金流量函数进行建模,从而建立了多重质量特征产品的质量损失现值与其相关工序参数的函数关系。在此基础上,把质量损失的现值和产品随时间退化的影响集成到总的装配成本模型中,建立了并行公差设计的优化模型。产品的并行优化设计与工序公差,通过使总的装配成本最小化获得。一个圆锥齿轮装配的并行优化分配设计与工序公差实例验证了该模型在实践中的有效性。     

Tolerancing for manufacturing via cost minimization

The purpose of dimensioning and tolerancing for process planning is to determine the dimensions and tolerances that are to be produced at each stage in the manufacture of a component in order that the design dimensions and tolerances specified on the engineering drawing of the component are satisfied. Three proposed objective functions for cost minimization are developed in this paper according to various situations. When cost information is available average cost per acceptable unit produced in minimized, otherwise ratio of number of components to be machined to output is minimized. If residual tolerances exist sum of manufactured tolerances are maximized by assigning weights according to their process capabilities. Combining these objective functions a computerized optimization program has been developed which determines the optimum set of dimensions and tolerances which satisfies the specified design dimensions and tolerances and the permissible machining allowances, with the cost of producing all dimensions to the respective tolerances to be minimal.

This system takes into account machining cost, scrap and where in the production process it occurs, manufactured dimensions and their distributions, allocated tolerances and process capabilities.     

Application of detonation coatings to design a new metal cutting tool

This paper presents the results of a research and development study of a new metal-working tool using detonation spray hard alloy coating. The influence of a heat-insulating sublayer on thermal flows occurring at flow drilling has been studied. New design and technology to manufacture punches for plastic drilling with heat-insulating ceramic sublayer aimed at decreasing a parasitic thermal flow through the tool to the lathe’s spindle have been developed. In addition, a new design and manufacturing technology for replaceable cutting plates for lathe working involving the use of detonation spray hard alloy coating have been created. The proposed application of the new tool allows reduction of its conversion cost and improving of performance characteristics.     

水下焊接机器人磁块单元的优化设计

磁路设计是爬壁机器人的关键技术之一,针对一种新型水下移动焊接机器人的柔性履带吸附与张紧问题,提出一种既可增加机器人负载能力,又能实现履带非接触式张紧的新型双磁路磁块单元结构。运用有限元方法,建立了该磁块单元的数值计算模型,研究了永磁体、轭铁及铝块等因素对磁块单元吸附力的影响,分析了磁块单元周围的磁场分布,对其关键结构参数进行了分析和优化设计,使磁块单元能够为机器人提供较强的吸附力与合适的张紧力。通过试验表明,仿真计算结果与实际测试结果基本相符。     

Decoupling Executions in Navigating Manufacturing Processes for Shortening Lead Time and Its Implementation to an Unmanned Machine Shop

A new navigation method that decouples manufacturing processes of tailor-made products has been developed for shortening lead time. Axiomatic Design expresses manufacturing processes with two design equations; one with functional requirement (FR) of “defining process” and design parameter (DP) of “decisions in process,” and the other with FR of “predicting completion time of product” and DP of “priority of product.” Once formulated, decoupling the system with the rules of “No feedback” and “No moving up” effectively shortens lead time. Applying the navigation methodology to a real unmanned machine shop of molds, eventually shortened it from 44 to 7.7 days.