A R Mileham

A formal design for changeover methodology. Part 1: theory and background

Abstract A rapid changeover capability is central to todays thinking in respect of responsive, small batch manufacturing. Mass customization and other modern manufacturing paradigms have prompted companies to adapt swiftly to market turbulence and at the same time avoid the traditionally high unit costs associated with custom-made or small-volume products. Historically, an operation-focused approach has been adopted in reducing changeover times; however, it is argued that there is a significant benefit if there is a focus on equipment design. There is a considerable challenge to design and build cost-effective changeover-capable equipment. This challenge would be greatly assisted by the availability of a coherent design for changeover (DFC) methodology. The authors have been researching the changeover area for many years and present their latest thinking in two parts. In the first part of this paper the basic concepts for a formal DFC methodology are introduced. Drawing lessons from various existing DFX methodologies, including design for assembly and design for variety, these concepts set out the basics for a novel DFC methodology. The debated DFC methodology is presented in the second part alongside an illustrative case study [1].

On-screen real-time cost estimating

In the early phase of design the product detail is usually limited, offering general details such as overall size, basic shape and estimated volume. However, it is at this stage that a large proportion of the avoidable costs are typically created, normally between 50 and 70% of the final cost. Due to this the ability of designers to estimate product costs at this stage with more accuracy provides competitive advantage and can avoid some of these in-built costs. This paper describes a methodology of an on-line automated computer system for injection mouldings that enables more accurate cost estimating. The approach adopted enables designers to make informed choices during the design process, not only in terms of functionality, but cost implications in terms of design, materials and, in the case of injection mouldings, complexity. The proposed approach uses a CAD package, in this case IDEAS solid modeling, in which a special set of injection moulding features has been configured for product development. In the proposed approach the designer builds up the product stage by stage (sub-part by sub-part) and, at each addition to the design, parametrics are used to estimate costs using a small number of parameters derived from specific component features and other conceptual design data. This is the Injection Moulding Cost estimating Program. This process will be described in detail within this paper, illustrating the method of product build-up and how avoidable cost increases are identified easily during this process. The approach described provides a concurrent on-screen cost estimate as the product is developed that has been validated to within 20% of the actual cost employing the processing parameters likely to be used.

The impact of run-up in ensuring Rapid Changeover

Rapid changeover is a key pre-requisite for responsive manufacture. A changeover is typically composed of three phases, run-down, set-up and run-up. Other research has focused almost exclusively on set-up with little being done to address the run-up phase, although it has been shown that doing a set-up fast can often result in a disproportionate increase in run-up. This paper investigates run-up within processing lines for which a rich database of changeover information was collected from several companies. Data mining techniques were then used to identify the factors that had a direct influence on the extent of run-up for a particular line.

Incremental Sheet Metal Forming: A Die-Less Rapid Prototyping Process for Sheetmetal

This paper presents an account of some investigations into a new die-less rapid prototyping process for sheetmetal forming, namely Incremental Sheetmetal Forming (ISF). The process involves the use of a single smooth tool to carry out local sheet metal deformation progressively on a CNC milling machine. The controlled movement of the tool enables a 3-Dimensional profile to be made. The process can offer rapid prototyping advantages for sheetmetal parts to be made directly from a 3D CAD model to the finished product without the traditional intermediate stage of tool design and manufacture. The paper describes an investigation into the capabilities of the ISF process by using experimental data to develop a tool-path generation methodology for generic materials and shapes. This is achieved by looking at a number of process variables, such as tool rotational speed and tool feed rates, on surface finish, as well as dimensional accuracy. The ISF process can offer the advantages of short lead times, high flexibility and low cost for volume applications.

Design for Changeover (DFC)

A rapid changeover capability is central for today’s thinking concerning responsive, small batch manufacturing. The customer-driven mass customization paradigm places emphasis on satisfying market demands, particularly in terms of product individualization and ready delivery. Changeover capability is prominent in such a time-based manufacturing environment, where successful companies have to be able to adapt swiftly to market turbulence and at the same time avoid the traditionally high unit costs associated with custom made or small volume products.