I. R. Pashby

Joining techniques for aluminium spaceframes used in automobiles: Part II — adhesive bonding and mechanical fasteners

Abstract Concerns regarding the environmental impact of motor vehicles are driving automotive manufacturers to develop lighter, more fuel-efficient vehicles. Such a task is further compounded by customer demands for greater performance and more luxury and safety features, all of which tend to increase vehicle weight. Aluminium spaceframe body structures substantially reduce weight relative to traditional steel monocoques, whilst maintaining essential strength and stiffness. Such structures also present a considerable challenge for fabrication in volume production. This paper considers adhesive bonding and mechanical fasteners as potential techniques for the joining of spaceframe components in volume production. Production issues pertinent to the automotive industry are discussed in conjunction with a consideration of the physical properties of the joint produced. Comparisons are also made with welding techniques discussed in Part I of this paper. Whilst the findings show that processing problems associated with each technique differ in nature, the overriding issues remain common to all. No one technique discussed was found to provide an ideal combination of low cost, process reliability, consistently good quality, good microstructural integrity, high strength, and excellent impact and durability performance. However, whilst a definitive solution is not evident, it is concluded that a combination of techniques could be utilised to great effect. Such an approach could capitalise on the benefits of certain techniques, whilst at the same time minimising or eliminating some of their more significant shortcomings.

Joining techniques for aluminium spaceframes used in automobiles: Part I — solid and liquid phase welding

Abstract Concerns regarding the environmental impact of motor vehicles are driving automotive manufactures to develop lighter, more fuel-efficient vehicles. Such a task is further compounded by customer demands for greater performance and more luxury and safety features, all of which tend to increase vehicle weight. Aluminium spaceframe body structures substantially reduce weight relative to traditional steel monocoques, whilst maintaining essential strength and stiffness. Such structures also present a considerable challenge for fabrication in volume production. In this two-part paper potential joining techniques are reviewed not only in terms of the physical properties of the joint produced, but also with due consideration to production issues pertinent to the automotive industry. This paper reviews solid and liquid-state welding techniques, including the conventional automotive method of spot-welding, in the context of their applicability to aluminium spaceframe structures. The capital cost of equipment, operator safety and work-place environmental issues are found to figure strongly among the many determinants governing the selection of an appropriate fabrication process. However, the ultimate success of spaceframe body structures will depend on how well the fabrication process can be shown to lend itself to volume production. The findings suggest that whichever technique(s) are eventually adopted, conventional vehicle manufacture will be considerably changed. Such change could however be minimised by retaining the traditional technique of spot-welding which, whilst no one technique emerges here as a definitive solution, remains a strong competitor.

Review: Various methods of machining advanced ceramic materials

Abstract A collaborative programme has been initiated recently under the title ‘Machining of Advanced Engineering Materials Using Traditional and Laser Techniques’. A first step of reviewing the ‘state-of-the-art’ of the various aspects of this venture has been undertaken, examining aspects of machining Ceramic Matrix Composites (CMCs) by a range of methods, these including grinding, ultrasonics, abrasive water jet, electrical discharge and laser techniques. This paper reports on each and considers the trade-off between the material removal rate and the level of near-surface damage that these process involve.

High speed milling of nickel-based superalloys

Abstract The use of the recently developed 70° bevel cutter with tangentially arranged positively raked carbide inserts (P40 grade) has led to the use of higher cutting conditions than those employed when milling the nickel-based nimonic 75 alloy with a 45° approach-angle cutter having negatively raked carbide inserts. This paper discusses the results obtained with different cutter/insert combinations when machining nickel alloys under various cutting conditions. The K20 grade of cemented-carbide tools out-performed the K40 grade when milling with a 45° approach-angle cutter due to their improved properties. Chipping and/or fracture of the tool edges were the dominant failure modes under most of the conditions tested, these being caused by a combination of high temperature and high thermal and mechanical stress, as well as adhesion of the work material on the tool rake-face during milling. Tool fracture can be caused also by attritional wear and thermal cracking mainly at the high temperatures usually generated under high cutting conditions. The positive cutter/insert combination results in a smooth cutting action, lesser power consumption and a very good surface finish.

Rapid laminated tooling

Abstract Rapid laminating methods predates rapid prototyping by several years, indeed the first work on laminated tooling by Professor Nakagawa was initially published in the late 1980s. Since then, Nakagawa’s team has been joined by a number of other research groups, with interest being boosted by the advent of rapid prototyping. This paper presents some of the finding of a 3 years study undertaken to investigate the use of laminated steel tooling for a range of automotive and aerospace production processes. The results of the programme are illustrated using production tooling for injection moulding of automotive components. The benefits of laminated tooling are shown, not just in terms of reduced cost and lead-times but perhaps more importantly, through reduced cycle times and improved part quality by the use of conformal cooling.

The Effect of Workpiece Temperature on the Machinability of an Aluminum/SiC MMC

Metal matrix composites (MMCs) are becoming an increasingly important class of engineering material which are finding applications both in the automotive and aerospace industries. However, their machinability is regarded as poor due to the severe abrasive tool wear observed during machining. Prior to an investigation into the laser-assisted turning of an aluminium/silicon carbide MMC, the machining behaviour of the material after pre-heating to 200, 300, and 400 degrees C was investigated. The results indicated that at cutting speeds from 20-90 m/min the wear rate increased with increasing workpiece temperature although the wear mechanism remained one of abrasion. The presence of a built-up edge (BUE) was noted and a strong correlation found between its presence and the amount of wear produced. The results of this work show that within the range of parameters investigated, the pre-heating of the MMC had a detrimental effect on its machinability.

Machining of advanced engineering materials using traditional and laser techniques

Abstract Lightweight structures are increasingly using polymeric materials in their construction. They are low density materials which inherently lack stiffness, reinforcements of various types being employed in order to redress this shortcoming. Unfortunately, the reinforcements used are invariably hard and abrasive, which transform the materials from being easy to machine into materials posing serious problems for conventional machining operations. In addition to traditional machining, a number of technologies have been developed to perform the cutting and drilling operations that are necessary even with modern near-net-shape processing. Water jet, abrasive water jet and lasers have all been employed to perform this function. This paper presents an overview of the state-of-the-art in these emerging technologies when applied to a wide range of matrix reinforcement systems.

A study of the effect of average preset voltage on hardness during electrolytic surface-hardening in aqueous solution

Abstract The electrolytic surface-hardening method in aqueous solution, especially using pulse current, has been found to be a new development in the area of surface-hardening technologies. Conventional surface heat-treatment processes are carried out at high temperature, hence both the equipment and the operational costs are high. A review of the literature available on heat treatment using direct-current electrolysis was attempted by the authors in a previous publication. This paper briefly introduces the development of this advanced surface heat-treatment technique that can be operated at room temperature, with low cost and easy control, which hence improves its competitiveness. In the investigation reported, a test-piece made of AISI 1050 steel has been surface hardened successfully by electrolysis in aqueous solution. Experimental work and analysis have been carried out in order to study the effect of the average preset voltage on the hardness of the test-piece under both direct-current and pulse-current conditions. Compared with direct current, the test-piece can be surface hardened at a lower average preset voltage and with a shorter heating time. A US patent application on this new technology has been submitted in order to protect the intellectual property rights.

Development of electrolytic heat-treatment in aqueous solution

Abstract Conventional surface heat-treatment processes are carried out at high temperature, hence both the equipment and the operation costs are high. A review of literature available on electrolytic heat-treatment has been attempted. This paper introduces the development of an advanced surface heat-treatment technique that can be operated at room temperature, with low cost and easy control, thereby improving its competitiveness. This is an electrolytic heat-treatment method in aqueous solution, especially using pulse current as a new aspect in the area of surface-hardening technologies. The results obtained under this surface heat-treatment using pulse current are presented briefly in this paper, and the advantages and disadvantages of the technology are also discussed.

The processing of SiC/SiC ceramic matrix composites using a pulsed Nd-YAG laser: Part II The effect of process variables

The machining of a composite material consisting of silicon carbide (SiC) fibres in a chemical- vapour-infiltrated SiC matrix has been investigated using a 400 W pulsed Nd-doped yttrium aluminium garnet laser. Part I of this work reported the findings of investigating the influence of the laser pulse parameters, principally with respect to the material removal rate. In this, the analysis concentrates on the quality of the processed surface and considers the effect of processing variables such as the choice and pressure of assist gas and the point of focus of the incident laser beam. Scanning electron microscopy is used to assess the extent of the heat-affected zone and its impact on the structural integrity of the composite.Throughout this study, comparison is made with related ceramic matrix composites (CMCs) that have been investigated. The intention is that, by determining the influential factors in each of the specific cases, observations may be made concerning the laser processing of CMC material systems in general.