Vincent Thomson

Entropy as a measure of operational flexibility

As competition among firms is being based more and more on the level of service, there is a great interest in using a measure of flexibility to indicate a firms capability to respond to customer demands. Entropy is proposed as a measure of flexibility for manufacturing operations. The properties of entropy that make it a suitable measure of flexibility are outlined. A computer simulation of a job shop was used to test the measure through a number of different scenarios using a discrete-event stochastic simulator. Results showed that entropy succeeded in measuring flexibility when the relative demand for the fabrication of products changed. Entropy was also used to monitor process flexibility as time progressed.

A comparison of rapid prototyping techniques used for wind tunnel model fabrication

For faster new product introduction aerospace companies are interested in reducing the time it takes to make wind tunnel models. The increased capabilities of rapid prototyping technologies has made them attractive for this purpose. A study was done of rapid prototyping technologies and their ability to make components for wind tunnel models in a timely and cost effective manner. Components and corresponding fabrication technologies were put into three categories: non‐structurally loaded, lightly loaded and highly loaded according to the stress endured during wind tunnel tests. Rapid prototyping technologies were found capable for non‐structurally loaded parts, but numerically controlled machining was still best for any part enduring significant loads.

Ontology based interface design and control methodology for collaborative product development

Interfaces between subsystems in collaborative product development projects are presently defined by interface control documents. This paper presents a computer aided methodology for defining and controlling subsystem interfaces. Interfaces are considered as interconnections between subsystem ports. Ports are specified by using an ontology that ensures consistency of interface definitions among different design teams. Every port that is based on the ontology is eventually defined by a set of attributes that are derived from its form and function. Interfaces between ports are formed when ports are mated. The essence of port mating is described by logical information that is expressed in two forms. First, a set of requirements are defined for an individual port to ensure that it functions properly. Second, connectivity rules are expressed between ports to guarantee that they integrate correctly. A software architecture that operates on port information and controls the status of subsystem interfaces during collaboration is described. A piece of software is implemented based on the proposed architecture and its functionality is demonstrated by two examples. The examples show how the software can be used to replace interface control documents and support collaboration. The software allows designers to load subsystem descriptions from a shared repository and connect them together by defining connectivity rules. The software reports errors to designers when port requirements or connectivity rules are violated.

DESIGN PARAMETER ESTIMATION USING A MODIFIED QFD METHOD TO IMPROVE CUSTOMER PERCEPTION

This article presents an integrated approach to optimize cost while respecting the customer perception of a product using a modified Quality Function Deployment (QFD) method. This QFD method helps a design team to determine the effect of various design strategies for customer satisfaction. The new QFD method uses a two-phased approach for finding an optimum design strategy. During the first phase, the design team sets goals for customer perception for each customer attribute and relates them to those of its competitors (benchmarking); then, in the second phase, a goal-based model with a separated, mixed integer structure is used to minimize cost while respecting customer desires. The model defines fixed cost as a major improvement in design solutions such as changing parts, materials, or operational mechanisms. It also defines variable cost as a minor improvement in the current design solution. An illustrative example is given to demonstrate the use of the method, and a sensitivity analysis for budget limitation is shown. The method is applicable to a wide spectrum of design problems where, setting preferences over competitors’ products and respecting budget limitations are the major criteria in the design strategy.

Change prediction using interface data

Managing change can be challenging due to the high levels of interdependency in concurrent engineering processes. A key activity in engineering change management is propagation analysis, which can be supported using the change prediction method. In common with most other change prediction approaches, the change prediction method has three important limitations: L1: it depends on highly subjective input data; L2: it is capable of modelling ‘generalised cases’ only and cannot be; customised to assess specific changes; and L3: the input data are static, and thus, guidance does not reflect changes in the design. This article contributes to resolving these limitations by incorporating interface information into the change prediction method. The enhanced method is illustrated using an example based on a flight simulator.

Managing subsystem interfaces of complex products

An interface management model for multidisciplinary products is proposed with the aim of improving communication between design groups. The systematic methodology described in this paper captures the interaction of different systems in an object oriented model. This helps to define the connectivity of subsystems such that the effect of modifications is more visible to designers. With the use of common definitions and greater visibility of the impact of changes, the number of incompatible design decisions is reduced. This results in lower product development times and eases subsystem modifications. Interfaces are modelled using object oriented technology since this parallels the object nature of product data and since object technology provides a formalised way of integrating interfaces into product data management software.

Post-Certification Engineering Taxonomy and Task Value Optimization in the Aerospace Industry

Abstract: This article proposes a novel taxonomy of post-certification engineering activities as a first step toward true lean product development (PD). Relying on key notions developed in a novel lean engineering performance model, the authors compare the leanness of post-certification versus pre-certification tasks for the design of aerospace parts. Discrete event simulation and integer linear programming models are developed to help ascertain the influence of factors such as multitasking, concurrency, task size, task value, and post-certification budget decision making on lean engineering PD performance. The models developed provide the foundation for enhanced PD performance and the establishment of optimal PD process parameters.

Agent-based control of manufacturing processes

Modern manufacturing systems deal with highly dynamic and complex processes, and need to adapt to rapid changes in manufacturing environments. These requirements can be met by model-based control that greatly improves process adaptiveness by integrating process phenomena knowledge with advanced simulation tools. Intelligent agent-based technologies provide a flexible platform for the implementation of model-based control. Two model-based control systems were implemented using an agent-based architecture: a linear, tuneable model for the plastic thermoforming process, and a non-linear, mathematical and rule-based model for the metal powder grinding process. Resulting advantages and improvements in performance, adaptiveness and productivity are highlighted.

Appraisal of New Product Development Success Indicators in the Aerospace Industry

Assessing performance in developing new aerospace products is essential. However,choosing an accurate set of success indicators to measure the performance of complexproducts is a nontrivial task. Moreover, the most useful success indicators can changeover the life of the product; therefore, different metrics need to be used at different phasesof the product lifecycle (PLC). This paper describes the research undertaken to determinesuccess measurement metrics for new product development (NPD) processes. The goal ofthis research was to ascertain an appropriate set of metrics used by aerospace companiesfor assessing success during different phases of the PLC. Furthermore, an evaluation ofthe differences and similarities of NPD success measurement was carried out betweenaerospace companies and the nonaerospace companies practicing in the business-to-business (B2B) market. Practical case studies were carried out for 16 Canadian andDanish companies. Seven companies belong to the aerospace sector, while nine are non-aerospace companies that are in the B2B market. The data were gathered from relevantproduct managers at participating companies. The outcomes of this research indicatethat: (1) the measurement of success of aerospace NPD practices depends on thePLC phase being measured, (2) product and process management performance are themore important indicators of success in the early PLC phases with revenue and marketshare indicators being important during late phases, and (3) there are reasonablesimilarities in success measurement between aerospace and nonaerospace B2Bcompanies. Sets of metrics for measuring success during each PLC phase of aerospaceproducts are proposed, which can guide companies in determining their ideal practices.[DOI: 10.1115/1.4004974]Keywords: new product development (NPD), aerospace industry, business to business(B2B), success metrics, product lifecycle (PLC)

A study of overlapping and functional interaction mechanisms for concurrent engineering processes

This article reports the use of a stochastic computer model to study hybrid overlapping and functional interaction strategies, where, within a given process, different degrees of overlapping or gradually increasing or decreasing functional interaction were modeled. The study aims to understand the contribution of these strategies to process performance, that is, product development effort and span time. Simulation results of the hybrid models are discussed in comparison to a baseline model, where the baseline process was uniformly overlapped and functional interaction was constant throughout its execution. Research outcomes indicate that under high information uncertainty, sequential processes perform better than any model with overlap. When uncertainty is moderate or low, the baseline model outperforms the hybrid models. Under high sensitivity conditions, hybrid overlapping models perform equally well in comparison to the baseline model with complete overlap, and superiorly when information evolution is slow.