A case for trading risk in complex conceptual design trade studies

Complex conceptual system design trade studies traditionally consider risk after a conceptual design has been created. Further, one person is often tasked with collecting risk information and managing it from each subsystem. This paper proposes a method to explicitly consider and trade risk on the same level as other important system-level variables during the creation of conceptual designs in trade studies. The proposed risk trading method advocates putting each subsystem engineer in control of risk for each subsystem. A risk vector is proposed that organizes many different risk metrics for communication between subsystems. A method of coupling risk models to dynamic subsystem models is presented. Several risk visualization techniques are discussed. A trade study example is presented based upon a simplified spacecraft model. Results from introducing the risk trading methodology into a simulated Collaborative Design Center are presented. The risk trading method offers an approach to more thoroughly consider risk during the creation of conceptual designs in trade studies.     

A manufacturing system design framework for computer aided industrial engineering

This paper describes a framework that formalizes within a concurrent engineering approach the key steps in the process of manufacturing systems design. Many of the functions performed by industrial engineers, ergonomists and process planners are included in the framework and may be used iteratively as design detail is progressively added. The paper describes the framework and prototype software, indicates how the framework is evaluated and illustrates how a workplace may be designed. The emphasis of the work is the design of human centred manual assembly systems. The overall objective of the work is to improve the process of manufacturing systems design.     

An Examination of the Trade Study Process at NASA

Abstract:

Engineering managers increasingly rely on trade study processes to design optimum system architectures. Opinions on what constitutes a quality trade study differ, and this can hinder the engineering manager in determining what trade study processes to follow. This article contributes to the manager's body of knowledge by identifying trade study best practices through reviews of published research and interviews with engineers who conducted successful trade studies supporting the design of complex space systems.

A checklist of trade study best practices was developed. Three completed NASA trade studies were then evaluated against the checklist in conjunction with interviews of engineers involved in the studies. Through one-on-one interviews with engineers, assessments were made on the value, appropriateness, and effectiveness of each trade study. Key issues, taken from the checklist, were addressed and the lessons learned were identified. The goal of the study was to establish the groundwork for a more detailed analysis of trade study processes. The engineering manager can use these preliminary findings to ensure that their trade study processes are timely, set up properly, and contain needed checks and balances.     

CONDENSE: A concurrent design evaluation system for product design

In dealing with the issue of integrating design and manufacturing, concurrent design evaluation plays an important role. This paper presents a concurrent design evaluation system (CONDENSE) developed to help product designers in evaluating possible design solutions and design alternatives during the early stage of design. It consists of two important functions: a qualitative aspect evaluation applied during the stage of searching for combinations of solution principles to help determine the design specifications, and a quantitative aspect evaluation applied to provide information on performance, assemblability, manufacturability and costs to facilitate design selection. The framework of CONDENSE is based on a blackboard architecture that requires the classification of knowledge into appropriate knowledge sources. As design data are interrelated and may have uncertainty, a graph decomposition algorithm is used in constructing the knowledge sources, and a linguistic evaluation module is integrated with the qualitative aspect evaluation subsystem to deal with data uncertainty. The proposed system has been validated with respect to the design of golf club heads. The results, which have been validated by experienced designers, are promising and can contribute to the speed-up of design and development, improvement of design quality and facilitation of design selection.     

Features-based castability evaluation

A features-driven knowledge-based approach to the quantitative assessment of castings for ease of manufacture is presented. Geometric features such as undercuts, holes, sharp corners and hot spots are recognized from a solid model of the casting and analysed by a number of dimensionless criteria functions. The criteria have been developed through a detailed study of design heuristics used by practising engineers and are written as functions of geometric attributes of component and tool features. This is useful for identifying problem features in a casting at an early stage and for objective comparison of two or more design solutions for manufacturability. The proposed approach lends itself to computer implementation for automating the design of castings in a concurrent engineering environment.     

Well-controlled engineering change propagation via a dynamic inter-feature association map

Currently, engineering companies face the challenge of delivering complex engineering project in a compressed time frame, which warrants concurrent and collaborative engineering. Due to the tedious dependencies embedded in collaborative domains, engineering change propagation is commonly a challenge and the procedure is carried out by engineers manually without systematic consistency check. Design change impacts are difficult to predict. To address the above challenge, an explicit and comprehensive engineering constraint modeling method is investigated according to a feature-based engineering scheme. To represent the network of constraints, a dynamically generated feature parameter association map is developed to analyze the associations among those parameters. Then, a dynamic mechanism of identifying the locally admissible value ranges of those related constraint parameters has been proposed in order to quickly accept design changes or to identify potential design conflicts. This mechanism then determines the admissible domain for the variable arrays in the formulated constraint satisfaction problem (CSP). Consequently, a well-controlled and progressively expanded change propagation method is proposed. This progressively expanded CSP solving approach is dynamic and incremental based on the association map. This proposed method is demonstrated to be effective to assist engineers with a typical intelligent change propagation solution.     

CAE FOR THE MANUFACTURING ENGINEER: THE ROLE OF PROCESS SIMULATION IN CONCURRENT ENGINEERING

As America refocuses its attention on the factory, design and manufacturing engineers must work together closely to design the appropriate products, and matching production process in a team effort. By building off the designer's CAE tools that predict product performance, the manufacturing engineer is today able to simulate the proposed production process. Process simulations for the following manufacturing processes are available or being developed:

▪Forging, ▪Machining, ▪Injection Molding, ▪Die Casting, ▪Investment Casting, ▪Metal Forming, ▪Heat Treating, ▪Assembly Tolerancing

By utilizing the same 3-D solid model and finite element modeling tools used by the designer, coupled to powerful analysis simulation tools to predict the transient nonlinear heat transfer and plastic material flow found in many manufacturing processes, the manufacturing engineer is able to explore alternative processing plans, evaluate trade-offs and even influence the design to produce superior products.

Process simulation brings a science to support the manufacturing engineers experience for reduced lead time, lower cost, increase product quality and better understanding of the process. The next step will be to directly link the process simulation to an expert system.

This paper describes the current state of technology in the area of manufacturing process computer simulation for a number of manufacturing operations and suggests how these tools can be used “up-front” and lead to concurrent engineering.     

Incentive contract design in project management with serial tasks and uncertain completion times

This article investigates an incentive contract design problem for a project manager who operates a project consisting of multiple tasks performed sequentially by different subcontractors in which all task completion times are uncertain and described by fuzzy variables. On the basis of an expected value criterion and a critical value criterion, two classes of fuzzy bilevel programming models are developed. In the case where the uncertain task completion times are mutually independent, each model can first be decomposed into multiple equivalent sub-models by taking advantage of the structural characteristics, and then a two-step optimization method is employed to derive the optimal incentive contract in each sub-model. In a more general case where the uncertain task completion times are correlative, the approximation approach (AA) technique is adopted first in order to evaluate the objective functions involving fuzzy parameters, which are usually difficult to convert into their crisp equivalents. Then, an AA-based hybrid genetic algorithm integrated with the golden search method and variable neighbourhood search is designed to solve the proposed fuzzy bilevel programming models. Finally, a numerical example of a construction project is conducted to demonstrate the modelling idea and the effectiveness of the proposed methods.     

Optimum tolerance allocation in mechanical assemblies using an interval method

Tolerance allocation methods serve as effective tools for design engineers to reduce the overall manufacturing cost of products. In every mechanical design, it is the design engineer’s task to assign tolerances to all dimensions and clearances to all joints in an assembly. This paper presents an optimum allocation method, based on interval analysis, for finding the optimum values of tolerances and clearances in mechanical assemblies that will not only minimize a stated objective function, but also satisfy the required functional and design constraints. The design constraints include dimensional requirements that the related parts must match relative to each other with a specified precision. Given a set of trial values of component tolerances and joint clearances, the present method utilizes the sequential quadratic programming method, Broyden–Fletcher–Goldfarb–Shanno quasi-Newton method and line search approaches to find the optimum values of tolerances and clearances. The effects of different cost function models on the manufacturing cost are also compared and discussed. Numerical examples are presented to illustrate the application of the method.     

2003 ASEM Conference Call for Papers

Abstract:

Product management as an organizational design has been around for decades as companies continually strive for competitive advantage. The goal is to create a system whereby new products are developed, and existing products managed, by an individual (or team), whose primary responsibility is the business success of those products. The person with the title product manager is expected to understand the technical side of the business as it relates to product design and manufacture, as well as the business side as it relates to satisfying customer needs profitably. However, many people are hired into product manager positions without a clear understanding of the skills and abilities required to be successful. Five specific product manager competencies (along with 18 subcategories) are described in this article, with a final tool for developing a product manager scorecard. The intent of this article is to help engineers who are moving into product management positions better understand the requirements of the new job.     

Neural computing-based design of components for cellular manufacturing

In this paper, a neuro computing approach for integrating design and manufacturing engineering is developed. Products and components have been traditionally designed without considering constraints imposed by a manufacturing system. With the introduction of concurrent engineering, design and manufacturing engineering are viewed as an integrated area. A three layer neural network that integrates several manufacturing functions is constructed for designing a cellular manufacturing system. The neuro computing system proposed provides a designer with the desired features that meet the current manufacturing constraints for design of a new component. The proposed methodology overcomes the typical limitations of neutral networks such as the internal representation and training problem, and proves to be appropriate for concurrent engineering.     

Enhanced probabilistic analytical target cascading with application to multi-scale design

Probabilistic analytical target cascading (PATC) is an approach for multi-level multi-disciplinary design optimization under uncertainty. In the original PATC approach, only the mean and variance of each interrelated response and linking variable are matched in a multi-level hierarchy. The ignorance of response correlation introduces difficulties in finding optimal solutions especially when the covariance of interrelated responses has a significant impact. In this article, an enhanced PATC (EPATC) approach is proposed. In addition to matching the first two statistical moments, the covariance between the interrelated responses is also considered by applying a modified updating strategy for estimating the statistical performance of an upper-level subsystem. A mathematical example and a multi-scale design problem are used to demonstrate the effectiveness and efficiency of the proposed EPATC approach. This study shows that the EPATC approach outperforms the original PATC by providing more accurate optimal solutions.     

Hydrogel Bioink Reinforcement for Additive Manufacturing: A Focused Review of Emerging Strategies

Bioprinting is an emerging approach for fabricating cell-laden 3D scaffolds via robotic deposition of cells and biomaterials into custom shapes and patterns to replicate complex tissue architectures. Bioprinting uses hydrogel solutions called bioinks as both cell carriers and structural components, requiring bioinks to be highly printable while providing a robust and cell-friendly microenvironment. Unfortunately, conventional hydrogel bioinks have not been able to meet these requirements and are mechanically weak due to their heterogeneously crosslinked networks and lack of energy dissipation mechanisms. Advanced bioink designs using various methods of dissipating mechanical energy are aimed at developing next-generation cellularized 3D scaffolds to mimic anatomical size, tissue architecture, and tissue-specific functions. These next-generation bioinks need to have high print fidelity and should provide a biocompatible microenvironment along with improved mechanical properties. To design these advanced bioink formulations, it is important to understand the structure–property–function relationships of hydrogel networks. By specifically leveraging biophysical and biochemical characteristics of hydrogel networks, high performance bioinks can be designed to control and direct cell functions. In this review article, current and emerging approaches in hydrogel design and bioink reinforcement techniques are critically evaluated. This bottom-up perspective provides a materials-centric approach to bioink design for 3D bioprinting.     

Concurrent optimization of assembly tolerances for quality with position control using scatter search approach

Tolerance allocation to individual parts in any assembly should be a vital design function with which both the design and manufacturing engineers are concerned. Generally design engineers prefer to have tighter tolerances to ensure the quality of their design, whereas manufacturing engineers prefer loose tolerances for ease of production and the need to be economical. This paper introduces a concurrent tolerance approach, which determines optimal product tolerances and minimizes combined manufacturing and quality related costs in the early stages of design. A non-linear multivariable optimization model is formulated here for assembly. A combinatorial optimization problem by treating cost minimization as the objective function and stack-up conditions as the constraints are solved using scatter search algorithm. In order to further explore the influence of geometric tolerances in quality as well as in the manufacturing cost, position control is included in the model. The results show how position control enhances quality and reduces cost.     

A distributed multi-agent environment for product design and manufacturing planning

This paper describes a multi-agent approach to the integration of product design, manufacturability analysis, and process planning in a distributed manner. The objective is to develop a distributed concurrent engineering system to allow geographically dispersed entities to work cooperatively towards overall system goals. In the paper, an agent-based concurrent engineering system concerning product design and manufacturing planning, and its fundamental framework and functions are presented. The proposed model considers constraints and requirements from the different product development cycles in the early development phases and fully supports the concept of design-for-manufacturability. This methodology uses conflict resolution (CR) techniques and design-improvement suggestions to refine the initial product design. The model comprises a facilitator agent, a console agent and six service agents. Each service agent is used to model different product development phases, and the console agent acts as an interacting interface between designers and the system, while the facilitator is responsible for the decomposition and dispatch of tasks, and resolving conflicts of poor designs. A prototype system for part design, manufacturability analysis, and process planning has been implemented. The performance of the prototype system shows that it could be extended to include other service agents, such as assemblability analysis, to become a comprehensive distributed concurrent engineering system for geographically dispersed customers and suppliers.     

Multidisciplinary Design Optimization with Quasiseparable Subsystems

Numerous hierarchical and nonhierarchical decomposition strategies for the optimization of large scale systems, comprised of interacting subsystems, have been proposed. With a few exceptions, all of these strategies lack a rigorous theoretical justification. This paper focuses on a class of quasiseparable optimization problems narrow enough for a rigorous decomposition theory, yet general enough to encompass many large scale engineering design problems. The subsystems for these problems involve local design variables and global system variables, but no variables from other subsystems. The objective function is a sum of a global system criterion and the subsystems' criteria. The essential idea is to give each subsystem a budget and global system variable values, and then ask the subsystems to independently maximize their constraint margins. Using these constraint margins, a system optimization then adjusts the values of the system variables and subsystem budgets. The subsystem margin problems are totally independent, always feasible, and could even be done asynchronously in a parallel computing context. An important detail is that the subsystem tasks, in practice, would be to construct response surface approximations to the constraint margin functions, and the system level optimization would use these margin surrogate functions. The purpose of the present paper is to present a decomposition strategy in a general context, provide rigorous theory justifying the decomposition, and give some simple illustrative examples.     

Teaching Concurrent Engineering at the University of Central Florida

U.S. manufacturing has discovered that the serial, over-the-wall approach to product development has to give way to a concurrent engineering approach. This customer-centered, multi-disciplinary team approach is being more widely used and today's graduating engineer must be prepared to understand and function in this environment. This paper describes an approach used to teach concurrent engineering at the University of Central Florida.     

基于组件智能元的开放CAD系统

采用基于组件的方法和智能元技术提出了一种开放的协同设计CAD系统框架。在该系统中,产品的零部件被设计成独立的、可重用的组件智能元。组件智能元作为系统的基本模块,由基于Web的接口管理器管理。装配车间通过组合不同的组件智能元完成产品的开发。产品的开发过程由基于Web的设计会话管理器管理。     

Influential Structural Engineers: A Project in a Third-year Structural Analysis Course

A study of structural analysis is enhanced by an exposure to the pioneers in the field. Students can more fully appreciate the tools and techniques of structural analysis when given life through a study of those engineers who developed and used them. Of special significance in this age of powerful computer capabilities is the technological context within which many of the important engineers lived and made their contributions. This paper describes a special project undertaken in the second of a two course sequence in structural analysis during the Spring quarter, 1992, in the Department of Civil Engineering and Construction at North Dakota State University. The class of 65 students was divided into 13 groups of five students each. With some guidance, each group chose an engineer who made a significant contribution to modern structural engineering theory and/or practice. Each group was required to research the life and work of the chosen engineer and present an oral, in-class demonstration, experiment, or other visual illustration of a theoretical or applied concept that characterized a major contribution of the selected individual. In addition, each student was required to submit an independently written paper addressing one of a set of standard questions posed to all groups. The project encouraged the students to discover the unique engineering skills demonstrated by some of the great engineers who made important contributions to modern structural engineering practice. By integrating the stories of influential engineers and their achievements into a quantitative analysis course, the students experienced the technical material within a broader context, helping them to appreciate the practice of engineering as a living, human endeavor.     

Interfacing sensor assemblies with windowless cockpit displays

An interface for converting aircraft instrument information into a video display was created. Due to the limited development time available, the interface was divided into two subsystems. The goal of the division was to allow concurrent work on two major system components. The division used greatly aided the development, test, and calibration tasks. The key to being able to develop and test them simultaneously was attributable to two factors. Both subsystems had local intelligence in the form of microprocessors, and their interconnection was kept physically simple. Testing of each subsystem was accomplished by simulating the other subsystem on a general-purpose computer. It is concluded that the testing went as expected. The only surprise when the instrument interface was eventually connected to the PC was the lock-up problem. The author describes system specifications and design, the instrument-to-PC interface, the PC-resident software, and subsystem test and calibration