Size effects in manufacturing of metallic components

doi:10.1016/j.cirp.2009.09.002

CIRP Annals

Volume 58, Issue 2, 2009, Pages 566-587

https://doi.org/10.1016/j.cirp.2009.09.002 Get rights and content

Abstract

In manufacturing of metallic components, the size of the part plays an important role for the process behaviour. This is due to so called size effects, which lead to changes in the process behaviour even if the relationship between the main geometrical features is kept constant. The aim of this paper is to give a systematic review on such effects and their potential use or remedy. First, the typology of size effects will be explained, followed by a description of size effects on strength and tribology. The last three sections describe size effects on formability, forming processes and cutting processes.

Introduction

Rules for up- or down-scaling are extensively used in fluid dynamics, enabling experiments with smaller samples, which are cheaper and much easier to conduct than real size experiments. The theory of similarity describes the conditions which must be satisfied for a successful up- or down-scaling for that purpose. Pioneering work in this area was done by Pawelski [1], [2], who worked on the rules of similarity with respect to metal forming, reportedly the earliest [3], [4]. It was shown that the rules of similarity can help to design proper experiments, for example, for compression testing with lubrication [5]. But, due to the complex nature of processes such as metal forming, Pawelski comes to the conclusion that it is often not possible to obey all necessary rules of similarity when up- or down-scaling a process [6], while the results of those limitations lead to so called size effects. A recent research work illustrates such effects in solid metal processing through simulation [7].

Microtechnology is very prominent field where size effects play an important role. Reviews on micro forming highlight the importance of size effects in this field [8], [9], where long-term basic research is required to realise industrial applications [10]. Also in the assembly of micro systems, size effects are one of the problems to be solved [11]. Also, it is evident from the recent review on micro machining [12] that no major effort has been made relating size effects, and no recent interdisciplinary review on size effects was reported since then. The aim of this paper is to comprehensively review the work done with respect to size effects.

Section snippets

Definition

In order to establish the contents of this paper, size effects need to be defined first. This is done as proposed in [13] as follows.

Size effects are deviations from intensive or proportional extrapolated extensive values of process characteristics which occur, when scaling the geometrical dimensions.

Size effects occur due to the fact that the ratio among all decisive features cannot be kept constant according to the process requirements [13].

Intensive variables are those which do not change

Methods for scaled strength determination

The measurement of the flow stress in scaled experiments, for example, when the sheet thickness or rod diameter is reduced, can become very difficult in the micro range, as the handling of the small samples tends to introduce distortion and therefore uniaxial stress conditions are difficult to guarantee. Furthermore, machines are necessary which allow the adaptation of the loading parameters (e.g., speed) to the sample size. One solution for such a machine, which can be used for different types

Scalable friction tests

From the large variety of tests for the determination of the coefficient of friction (COF), only a few were used in scaling experiments. This is obviously due to the fact that many tests demand the use of special equipment such as the Duncan–Shabel test or the draw beam simulator, which cannot be directly used for scaled experiments, but would demand a large number of scaled devices. Therefore, the high costs for the equipment prevent the application of many friction tests. Nearly all tests

Sheet formability in tension

Through tensile and bending tests it is found that: for T/D > 1 (T: thickness, D: average grain diameter), the yield strength and tensile strength decrease with the decrease in T/D ratio; for T/D < 1, the yield strength and tensile strength increase with the decrease in T/D ratio. The lower the T/D ratio, the worse is the formability [30].

Scaled tensile tests were performed to investigate the size effects on flow curves and fracture strain for Cu foils [90], Al 99.0–99.5% [29] and for CuZn36 [91].

Forming

Forming operations cover bulk and sheet metal forming both in cold conditions and at elevated temperatures. In [8], a comprehensive description of the state-of-the-art in micro forming is given. Table 2 indicates the types of micro forming processes that have been investigated with respect to size effects. In the following sections size effects related to forming forces and stresses, processing windows and accuracy will be described. It is clear that specific experimental work will be related

General

Generally, in literature the term size effect in metal cutting is understood as the non-linear increase of the specific cutting energy with decreasing the undeformed chip thickness. Backer et al. [139] were among the first to determine the energy consumed in deforming a unit volume of a ductile material (SAE 1112 steel), and develop a relationship between the shear energy per cubic volume and the specimen size. They showed the decreasing trend in shear energy per unit volume for three major

Conclusions

It is shown by this review that size effects have a strong influence on production processes. The knowledge about size effects is essential for a proper process control. The main features of size effects, which can be divided into three groups of density, shape and structure effects, are:

1.
The flow stress of material is influenced by different types of size effects, which are dominant in different size scales. Both an increase and decrease in strength can be observed with increasing size, while

Acknowledgements

The authors like to thank the following scientists for contributing actively to this paper.

M. Arentoft and N. Bay (Denmark); E. Brinksmeier; U. Engel, M. Geiger, P. Groche, G. Hirt, H. Hoffmann, F. Klocke, K. Lange, L.W. Meyer, R. Kopp, V. Schulze, and K. Weinert (Germany); P. Jenssen (The Nederlands); J. Cao, D.A. Lucca, S. Melkote, and A.K. Balaji (USA).

Furthermore, special thanks are devoted to the Deutsche Forschungsgemeinschaft for financial support of many of the reported work, especially

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Size effects in manufacturing of metallic components

Abstract

Introduction

Section snippets

Definition

Methods for scaled strength determination

Scalable friction tests

Sheet formability in tension

Forming

General

Conclusions

Acknowledgements

Ähnlichkeitstheorie in der Umformtechnik

Technische Plastomechanik

Beitrag zur Ähnlichkeitstheorie der Umformtechnik

Archiv für das Eisenhüttenwesen

Einführung in die Umformtechnik

The Effect of Specimen Size on Stress–Strain Behaviour in Compression

Transactions of the ASME

Ways and Limits of the Theory of Similarity in Application to Problems of Physics and Metal Forming

Journal of Materials Processing Technology