Journal of Mechanical Engineering 53 (2007) 7-8

Editorial

Computational Approaches to Critical Engineering Problems

James Maxwell, the famous physicist, said: "There is nothing more practical than a good theory". In this spirit, this thematic issue presents advanced theory-based computational solutions to some en­gineering problems. The included papers use knowl­edge-intensive computational models to address practical engineering issues. These issues range from machine design, through materials and prod­uct engineering, to information processing in the development process. What is common in the pro­posed solutions is that (i) critical engineering prob­lems have been identified by the authors (ii) they have been theoretically analysed and underpinned, and (iii) the robust theoretical basis has yielded use­ful computational solutions for the practice. The tar­get applications cover a wide range, likewise the used computational principles that were initially pro­posed in other fields of knowledge, such as natural language processing, artificial intelligence, and downstream product validation. The papers included in this issue integrate these computational solutions into the early phase of product design. This tells us that the application of computational tools is gradu­ally moving towards, and increasing in, the early stages of product design and development, where the most influential decisions are made. We believe that it is essential for researchers and developers at universities and research institutes to learn the pro­posed computer-oriented methods and tools, and we hope that they will prove to be useful and suffi­ciently intuitive for industrial end-users too.

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Improving Information Extraction Using a Probability-Based Approach

Corresponding author - Sanghee Kim

Authors - Saeema Ahmed - Ken Wallace

Abstract

Information plays a crucial role during the entire life-cycle of a product. It has been shown that engineers frequently consult colleagues to obtain the information they require to solve problems. However, the industrial world is now more transient and key personnel move to other companies or retire. It is becoming essential to retrieve vital information from archived product documents, if it is available. There is, therefore, great interest in ways of extracting relevant and sharable information from documents. A keyword-based search is commonly used, but studies have shown that these searches often prove unsuccessful. Searches can be improved if domain entities of interest, e.g., 'gas turbine', are explicitly associated with their types, i.e., gas turbine is a type of engine, thus reducing the ambiguity of referring to the entities using various different ways of expressing them. It would be helpful to compile a full list of entities associated with the relevant types before identifying them in texts. However, due to the various ways of referring entities in the texts, manually defined identification rules tend to produce high precision but with low recall. In order to increase the recall, while maintaining the high precision, a learning approach that makes identification decisions based on a probability model, rather than simply looking up the presence of the pre-defined variations, looks promising. This paper presents the results of developing such a probability-based entity-identification approach. Tests show that the proposed approach achieves improved recall, i.e., from 53% to 80%, with comparable precision.

Keywords - information searches, name entity identification, natural language processing, taxonomy, probability methods

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 53(2007)7-8, 429-441
UDC 025.4.03

Improving Information Extraction Using a Probability-Based Approach (pdf)

 

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Product Design Using a Contact-Optimization Technique

Corresponding author - Istvan Paczelt

Authors - Attila Baksa - Tamas Szabo

Abstract

It is well known that in engineering practice high stresses occur and that these stresses depend on the shapes and the loads of the bodies in unilateral contact. The stress distribution is often not smooth and has some singularities, thereby decreasing the lifetime of the machine elements. It is an important objective to obtain a smooth stress distribution when optimizing the shape of the elements. One of the goals of this paper is to present a method that resolves the above problem. By controlling the contact pressure a prescribed, smooth contact pressure distribution can be achieved. The optimization problems take into account the limit stress constraints of the material. In the present paper two types of contact problems are investigated. Firstly, contact optimization problems are analyzed assuming linear elasticity and small displacements, including steady-state wear process. Two numerical examples are presented on this topic for a rolling machine element: a punch optimization and a shape optimization. We also investigated which parameter values of the controlling function result in the maximum loadability. This can be useful in the design of brakes or bearings. In the second part of the paper the solution of the contact problem for large displacements and deformations is investigated where an air-spring is analyzed by calculating the nonlinear load-displacement curve and comparing it with measurements.

Keywords - finite element methods, product design, mechanical contacts, contact optimization, iterative methods

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 53(2007)7-8, 442-461
UDC 658.512.2

Product Design Using a Contact-Optimization Technique (pdf)

 

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A Constraint-Based Limits-Modelling Approach to Investigate Manufacturing‑Machine Design Capability

Corresponding author - Jason Matthews

Authors - Baljinder Singh - Glen Mullineux - Tony Medland

Abstract

Manufacturers purchase processing machinery, tailor made to handle a specific, limited product range. However, during the life span of the machines, these products are likely to change. The manufacturer often calls on the original equipment supplier to assess the ability of the machines to process either a variant of their existing range or even to consider the handling of a totally new product. In the UK such equipment manufacturers tend to be small concerns, employing 80 staff or less, and with such limited resources that there is not the expertise or time available to perform any in-depth analysis of how well the design operates or what constraints there are that may stop it reaching the new performance requirement. In the past this has led to the manufacturers purchasing new equipment, which puts a high financial burden on companies wishing to introduce new products into already highly competitive market sectors. This paper presents an approach to investigating the manufacturing capability of a machine. The methodology, based on limits modelling, utilizes the capability of a constraint environment to model multiple variations of a design and compare their performances against a range of failure modes. This process allows a variety of graphical visual representation techniques to be created to illustrate and compare the limiting conditions for all machines.

Keywords - machine designs, product variations, modeling limits, constraints

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 53(2007)7-8, 462-477
UDC 658.512.2

A Constraint-Based Limits-Modelling Approach to Investigate Manufacturing‑Machine Design Capability (pdf)

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Constraints Influencing the Design of Forming Shoulders and the Use of Exact Geometry

Corresponding author - G. Mullineux

Authors - C. J. McPherson - B. J. Hicks - C. Berry - A. J. Medland

Abstract

This paper considers the design of the forming shoulder, which is a crucial part of a vertical form, fill and seal machine used for packing small discrete items. As with other forms of packaging machine, the basic design has evolved over a number of fears and is based on a number of empirical design rules, whose application can be time consuming and costly. To address this issue, the aim of this paper is to investigate the effects of machine-material interaction and the parameters of the design that influence these effects. In particular, the geometry of the shoulder is considered and means for defining its complex form discussed, together with the design issues related to the performance of the machine in terms of web tension and its ability to track correctly. In industrial practice, a modified form of the geometry is used to encourage better tracking, even though this increases web tension. An experimental investigation with exact shoulders has shown that they have better tracking properties than conventional ones and that they can deal successfully with a wider range of materials. It has also been found that a different approach to the design of the shoulder is possible, concentrating initially on web tension rather than tracking. As an exact shoulder can handle a wider range of materials, it is also found that it is possible to design machines in which fewer change parts are required.

Keywords - computer aided design, product modeling, form-fill-seal machines, forming shoulders

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 53(2007)7-8, 478-490
UDC 677.057.78

Constraints Influencing the Design of Forming Shoulders and the Use of Exact Geometry (pdf)

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Cavity-Pressure Estimation for a Piston-Moulding Life-Cycle Cost Model

Corresponding author - Charl L. Goussard

Authors - Anton H. Basson

Abstract

In this paper we propose and evaluate an approach for quickly estimating the cavity pressures during the piston moulding of thermoplastics. The approach applies analytical solutions in a small number of control volumes. The resulting semi-analytical model is intended for use when optimising the design of piston moulding machines, leading to a life-cycle cost optimisation. The model is also applicable to similar injection-moulding cases. Some advantages and disadvantages of piston moulding, compared to injection moulding, are discussed. The main contribution of the semi-analytical model is the speed with which a reasonably accurate estimate of the cavity injection pressure is calculated. This approach is useful in cases when numerical simulations would be too cumbersome and time consuming, e.g., in optimisation studies where the independent variables could vary over a wide range. Different analytical flow models found in the literature and their applicability to injection moulding are discussed. This is followed by a discussion of the derived semi-analytical model, with its underlying simplifications. The results from the semi-analytical model are compared to numerical solutions for three case studies. These case studies show that the model is sufficiently accurate for machine-layout design purposes and for investigating life-cycle cost trends.

Keywords - injection moulding, piston moulding, cavity pressure, cost modelling

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 53(2007)7-8, 491-502
UDC 678.056:678.7

Cavity-Pressure Estimation for a Piston-Moulding Life-Cycle Cost Model (pdf)

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Minimizing the Thicknesses of Injection-Molded Plastic Parts Based on a Moldflow Simulation

Corresponding author - Yimin Deng
Authors - Di Zheng

Abstract

Determining the thickness of parts is an important task in injection-molded plastic part design. In general, the thicknesses of parts should be minimized so that less material is used and at the same time the relevant quality requirements are also met. There are already a number of methods for thickness optimization in the area of structural optimization, where strength, stability, deformation, etc., are the primary concerns. In contrast to this, very little work has been done on thickness optimization that is oriented to part moldability and other molding-quality requirements. Without molding-quality-oriented thickness optimization, the plastic-part design will result in either a waste of material or poor molding qualities. As a first step to tackle this problem, this paper attempts to seek minimized part thicknesses by employing a Moldflow® simulation-based method. Briefly, it consists of an automated, iterative process of changing the part thicknesses, conducting a Moldflow simulation, retrieving the simulation results to assess the specified molding-quality criteria, until the design objectives are met. A route for part-thickness change is proposed, which is governed by the respective methods under several different situations. Three convergence criteria are proposed. A software prototype implementing the methodology was developed and presented. To illustrate the methodology as well as the software, a design case is also studied. The paper shows that the proposed methods are applicable to the molding-quality-oriented part-thickness minimization.

Keywords - injection moulding, thickness optimization, simulations, software packages, MOLDFLOW

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 53(2007)7-8, 503-518
UDC 678.056:678.7

Continuous Improvements in Die-Casting Using a Six Sigma Approach (pdf)

  

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