Integrated Synthesis of Assembly and Fixture Scheme for Properly Constrained Assembly

This paper presents an integrated approach to design an assembly, fixture schemes and an assembly sequence, such that the dimensional integrity of the assembly is insensitive to the dimensional variations of individual parts. The adjustability of critical dimensions and the proper constraining of parts during assembly process are the keys in achieving the dimensional integrity of the final assembly. A top down design method is developed which recursively decomposes a lump of initial product geometry and fixture elements matching critical dimensions, into parts and fixtures. At each recursion, joints are assigned to the interfaces between two subassemblies to ensure parts and fixtures are properly constrained at every assembly step. A case study on a simple frame structure is presented to demonstrate the method.

Using Ecosystem Landscape Models to Investigate Industrial Environmental Impacts

This article explores the use of ecosystem landscape models to estimate the environmental impacts of industrial activities at the regional / local scale. Integrated ecosystem and industrial modeling is first introduced within the context of life cycle assessment. Then, the use of integrated modeling to overcome problems stemming from the lumped parameter, static, site non-specific nature of life cycle assessment is discussed. Finally, the results of linking a handful of industrially relevant material and information flows demonstrate the ability of current ecosystem landscape models to respond to industrial burdens and estimate some environmental impacts.

Design for End-of-Life: Repair, Recondition, Remanufacture or Recycle?

Between 1980 and 1997, municipal waste in OECD (Organisation for Economic Co-operation and Development) countries increased by around 40%. The European Union has responded by introducing legislation on extended producer responsibility (EPR). This paper further explains the context of this new legislation and describes, compares and then contrasts the four alternative strategies to reducing end-of-life waste: namely repairing, reconditioning, remanufacturing or recycling. It also introduces a more robust definition of remanufacturing, validated by earlier research, which differentiates it from repair and reconditioning. From a consideration of the different factors involved, it concludes that remanufacturing may often be a strong strategy. This is based on the fact that it preserves both the embodied energy of virgin production (thus reducing the environmental impact) and the intrinsic “value adding” process of the producer (thus increasing the manufacturer’s profitability). As a result, this new environmental policy is likely to lead to significant increases in remanufacturing as an end-of-life strategy in the European Union. However, effective end-of life strategies are dictated by product characteristics and therefore vary from product to product (Rose et al, 1998). Thus further research is required to compare and contrast the effectiveness of remanufacturing and alternative end-of-life strategy for particular product types.

Manufacturing Feature Based Dynamic Cost Estimation for Design

Due to the ever-increasing competition in today’s global markets, the cost of the product is rapidly emerging as one of the most crucial factors in deciding the success of the product. Decisions made during the design stage affect as much as 70–80% of the final product cost. Hence, a manufacturing cost estimation tool that can be used by the designer concurrently during the design phase will be of maximum benefit. A literature study of the available cost estimation tools suggests that a majority of these tools are meant for use in the later stages of the product development lifecycle. In the early stages of a product lifecycle, the only information that is available to the designer is related to geometry and material. Hence, the cost estimation methods that have been developed with the intent of being used in the early stages of design make use of the geometric information available at that stage of the design. Most of the earlier models that use parametric cost estimation and features technology consider the design features in their implementation. However, such models fail to consider “manufacturing based features” such as cores and undercuts. These manufacturing based features are very important in deciding the manufacturability and the cost of the part. The Engineering Cost Advisory System (ECAS) is a knowledge-based system that presents cost advice to the designer at the design stage after considering various design parameters and user requirements. Some of these design parameters can be extracted via standard Application Programming Interfaces (APIs). Moreover, ECAS uses innovative techniques of geometric reasoning and the hybrid B-rep-voxel model approach to extract manufacturing feature-based geometric information directly from the CAD input. By considering the manufacturing based features along with the design parameters, the ECAS architecture is applicable to a much wider variety of manufacturing processes. The complexity of the part, which is derived from the geometric parameters (manufacturing based and design based) and other non-geometric user requirements (e.g. quantity, material), is used to estimate the manufacturing effort involved in process specific activities. The final cost is then estimated based on this manufacturing effort and considering the hourly rates of labor and other contextual resources as well as material rates.

Exploration of Local Blade Motions During Blade Shaping for Thick Layered Foam Cutting

The FF-TLOM (Free Form Thick Layered Object Manufacturing) technology is a Rapid Prototyping process based on flexible blade cutting of polystyrene foam. The heated blade is shaped by three parameters, which allows an infinite amount of minimum strain energy blade shapes with none, one or two inflexions. In the shaping domain stable and unstable blade shapes can exist. Stable shapes are defined as curves with none and one-inflexion and are applied for operational cutting of foam layers with the FF-TLOM technology. The tool motions are generated from the static tool poses and are calculated for a linear change of the flexible blade, when the cutting tool moves from one tool position to the next. The cutting blade is positioned to the foam slab with help of a point relative positioned on the flexible blade. The tool frame is positioned with a point fixed relatively to the tool frame. During the tool motions the blade curvature is changed and will introduce a shift of the half way point fixed on the blade (especially in the case of asymmetrical support inclinations and high curvature). Next the local displacement of the blade points in the bending plane of the blade due to blade shaping and tool pitching are quantified during the tool motions. These displacements induce an angle of attack of the blade in cutting direction, and will influence cutting speed and cutting accuracy. The quantification software is developed and will be used in the future for an overall prediction of the total tool curve displacements due to blade shaping, such as roll, pitch, yaw and linear positioning motions of the tool. A general rule for FF-TLOM cutting is minimization of all tool motions, which are not related to the forward cutting motion.

A Methodology for Integrating Welding in DFA

A design for assembly worksheet is introduced that enables flexible accounting of assembly activities, especially welding. Welding activity is broken down into a variety of pre- and post-welding activities and the time penalty is estimated. This weld estimate is included into the traditional worksheet. This approach is especially useful for large complex products that are produced in small volumes where a significant portion of the assembly activity is through welding. These types of products often pose challenges for employing DFMA techniques cost effectively because of the increased engineering cost, divided among relatively few products, outweighs the potential benefits.

Structured Approach to Dimensioning and Tolerancing: A Comprehensive Solution Strategy

This paper is the second of two in which a methodology is presented that provides a structured way of solving Dimensioning and Tolerancing (D&T) problems on new product design. In the previous paper, a methodology was developed for representing the D&T problems of a product in a matrix form known as a Dimensional Requirements/Dimensions (DR/D) matrix. In this paper a comprehensive strategy is presented for determining the values of dimensions and tolerances by satisfying all the relationships represented in DR/D matrix. The comprehensive strategy presented here includes: strategy for separating D&T problems into groups, for determining an optimum solution order for coupled functional equations and tolerance allocation strategies for solving different types of D&T problems. A number of commonly used cost minimization strategies such as the use of standard parts, preferred sizes, preferred fits, and preferred tolerances have also been incorporated into the proposed methodology. The methodology is interactive and suitable for use in a Concurrent Engineering environment.