Torgeir Welo

Cross-sectional deformations of rectangular hollow sections in bending: Part II - analytical models

In this part, analytical models to predict the deflection of cross-sectional members such as flanges and webs are developed. The models are based on the deformation theory of plasticity along with the energy method, using appropriate shape functions capable of including the restraining effect of adjacent members. The present method provides explicit solutions of cross-sectional deformations prior to buckling, onset of buckling, as well as post-buckling deformations at different stages of bending. The predictions show that the suck-in of the tensile flange is closely related to geometry parameters, particularly the flange width. Plastic anisotropy appears to be the most significant material parameter. The width-to-thickness ratio tends to be the governing parameter with respect to buckling of the inner (compressive) flange. Also, the strain hardening of the material has a major effect on onset of buckling as well as post buckling deformations. Upon continued bending after buckling, the wavy deformation of the inner flange develops more rapidly than the more uniform deformation of the outer (tensile) flange. For relatively compact sections, however, the deformation mode of the compressive flange resembles that of the tensile flange without any typical buckling waves. There are also obvious interactions between deformations of different members. Comparing the theoretical predictions with the experimental results presented in Part I, a reasonably good agreement was found.

On the application of lean principles in Product Development: a commentary on models and practices

Over the past decade, attempts have been made to apply lean principles to improve capabilities in Product Development (PD). However, methodologies from lean production are not directly applicable to PD. It is, therefore, desirable to establish a deeper understanding of lean PD as a basis for development of a generic framework. This paper gives an overview of lean PD followed by a discussion on its key component: defining (customer) value. Findings from prior art have been systemised into a framework that includes six key components, along with an assessment tool that has been used with select companies to identify areas where lean PD would provide the greater potential for payback. Examples of results from these analyses are given.

Cross-sectional deformations of rectangular hollow sections in bending: Part I — experiments

Abstract This investigation deals with deformations of individual cross-sectional members as flanges and webs in bending of rectangular hollow sections. Part I describes the experimental work, while analytical models developed to predict pre- and post-buckling deformations are presented in a paper to follow (Part II). The experimental program involved rectangular single- and double-chamber aluminium alloy AA6060 extrusions with three different wall thicknesses. The profiles were given two distinct heat treatments to obtain different hardening characteristics. Multiaxial tests were performed to determine the mechanical properties of the materials. The profiles were then bent into a number of different bend radii. Measurements of strains, curvatures, deflections and bending forces were taken. The results show that cross-sectional distortions take place from the very beginning of bending; at first in the form of a uniform sagging-like deformation along the entire length of both sides of the bend until the inner (compressive) flange buckles into several half-waves, superimposing the pre-deformation modes. The instant at which buckling occurs is found to be mainly associated with the width-to-thickness ratio of the flange and the strain hardening characteristic of the material. The magnitude of pre- and post-deformations, however, appears to be more directly related to the actual width of the flange than to its slenderness. The material stress–strain curve is shown to have an increasingly effect on the distortions of members directly sustained to buckling as bending proceeds beyond the onset of buckling, leading to severely concentrated deformations for sections made of low hardening materials. The material has less impact on sagging of the outer (tensile) flange.

Redefining customer value in lean product development design projects

Purpose – The aim of this paper is to suggest a redefinition of the functional product value calculation in lean product development (LPD). The proposed method integrates emotional customer value into the traditional model, which is based on minimizing operating costs and reducing time‐to‐market.Design/methodology/approach – Perceptions of customer value among employees at a Norwegian boat manufacturer, customers, and competitors are investigated through a case study. Results are compared with principles for promoting value and minimizing waste in LPD.Findings – Findings from the case study suggest that a less‐than‐perfect match between customer needs and product offerings sometimes improves customer satisfaction. Furthermore, how customers perceive product value depends on experience that may be at variance with current needs. It is also suggested that deep understanding of customer‐defined value does not imply an ability to satisfy that value.Research limitations/implications – Understanding the positio...

Maximizing Product Innovation through Adaptive Application of User-Centered Methods for Defining Customer Value

Establishing deep understanding of customers is a prerequisite to improve success rates of innovations under today’s transient business conditions. This paper summarizes methods and tools to increase customer understanding in new product development. A case study of developing an office chair was conducted, utilizing four such methods (web based survey, interview, observation and workshops) to provide directions for later application. Results indicate that methods revealing emotionally-related customer information (workshops and observation) are resource-intensive and provide less amount of information directly applicable to the product development team. The opposite is the case for methods providing more functionally-related information (web based survey and interview). The overall conclusion is that the latter methods are more suitable for product improvements, while the former may provide valuable information for creating more differentiated products.

A design method for prediction of dimensions of rectangular hollow sections formed in stretch bending

Abstract Local deformation of individual cross-sectional members is of great interest in bending of aluminium alloy extrusions for tight tolerance production such as automotive components. The primary concern is the impact of such distortions on manufacturability as well as the dimensional tolerances of the component. This paper presents analytical models for the determination of local post-buckling and suck-in deformations in stretch bending. The models are based on the deformation theory of plasticity combined with an energy method using appropriate shape functions. The analytical predictions are being verified with experimental results. Based on the present findings, a simplified design method for evaluation of bendability of sections in industrial forming operations is being proposed. The results show that the slenderness (b/t) and the width of the flange are the main parameters related to the bending radius at the onset of plastic buckling and the magnitude of local deformations, respectively. Material parameters have proven to be relatively more important to the former than to the latter. Although there is some discrepancy at tight nominal bend radii, the overall correlation between the experimental and theoretical results is surprisingly good. It is therefore concluded that the present method provides to be an efficient means to the evaluation of bendability of rectangular hollow sections.

A design method for rectangular hollow sections in bending

Abstract Local deformation of individual cross-sectional members is of great interest in the bending of aluminium alloy extrusions for automotive applications. The primary concern is the impact of such distortions on the manufacturability of components as well as the dimensional tolerances of the final build. This paper presents analytical models for the determination of local post-buckling and suck-in deformations in bending. The models are based on the deformation theory of plasticity combined with an energy method using appropriate shape functions. The analytical predictions are verified with experimental results. Based on the present findings, an approximate design method for evaluation of the bendability of sections in industrial forming operations is proposed. The results show that the slenderness ratio (b/t) and the width of the flange are the main parameters related to the bending radius at the onset of plastic buckling and the magnitude of local deformations, respectively. Material parameters have proven to be relatively more important to buckling radius than to deformation of individual cross-sectional members. Although there is some discrepancy between the experimental and theoretical results at tight nominal bend radii, the overall correlation is surprisingly good. It is, therefore, concluded that the present approach provides an efficient method for the evaluation of the bendability of rectangular hollow sections.

Conditions for Sticking Friction between Aluminium Alloy AA6060 and Tool Steel in Hot Forming

The frictional conditions between an aluminium AA6060 alloy and tool steel in hot bulk forming have been investigated. The compressive-rotational method for frictional measurements, presented herein, represents an innovative approach for defining the thermo-mechanical conditions required for sticking friction at the interface between the two metals. Aluminium disks with inserted contrast material were subjected to a variety of pressures and rotated at one end at temperatures ranging from 250 °C to 500 °C. Visual inspection of the surfaces in combination with sectioning of the deformed disks formed a method for studying how different factors affect a stick-slip criterion in metal forming. It was found that the normal contact pressure required for sticking to occur was strongly dependent on the instantaneous temperature. When comparing the normal contact pressure q with the characteristic shear strength k of the aluminium alloy, q/k > 0.6 yielded sticking friction for temperatures above 300 °C, while a ratio of 0.7 was required for the lower temperatures.

Sheet Metal Forming

Sheet metal forming represents an extensive research area involving numerous topics such as finite element techniques and modeling, material models, material characterization, formability, component and full-scale test methods as well as a variety of industrial processes and technologies. In the present overview, however, attempts have been made to mainly concentrate on recent technology development and innovative sheet metal forming methods, representing a summary of works presented at ESAFORM conferences during the past decade. The first objective is to demonstrate advances in sheet metal forming by specific examples with different degree of industrial readiness—from new process ideas to fully industrialized processes. The second objective is to give a brief discussion on marked and industrial trends, forming the basis and direction for future technology development and associated research within more basic fields in sheet metal forming.

ENHANCING PRODUCT INNOVATION THROUGH A CUSTOMER-CENTERED, LEAN FRAMEWORK

For companies to survive and thrive in todays market, a key strategy is to leverage innovation capability through an effective process of converting unmet customer needs into successful products, creating value for customers, the company and other stakeholders. This work demonstrates how Lean becomes a pre-competitive factor in product innovation through customer value focus. The goal is to determine the applicability of user-centered methodologies in generating input that ultimately leads to differentiated products. An office chair case study implies that although user-focus is necessary, this will not inevitably lead to novel products, since users are engrossed with past and present.