List of Tables
Chapter 1 Introduction, Literature Review, Significance and Objective of Work
1.3 Significance of work
A number of literature are available in the field of joining using end forming of tubes (e.g. a tube to a sheet, a tube to a tube or a tube to a disc etc.). Some novel methods of joining a tube to a sheet and a tube to a tube have been proposed by researchers in the past. Important process parameters influencing the joint quality have been determined and then range of parameters for successful joint formation is obtained. Strength evaluation of end formed joints has also been conducted. The following discussion highlights some of the important results related to end formed joints.
In the field of joining of a tube to a sheet, Alves et al. (2011b) joined sheet panels to tubular profiles using fundamental modes of tube end forming. They also demonstrated
Chapter 1 that how joining sheet panels to tubular profiles by tube end forming can be successfully
employed in industrial applications. They also concluded that joints made using tube end forming and welding performed identically under torsional loads. The major drawback of this work is that joining is completed in two stages. The first stage is compression beading, and the second stage is external inversion. Similarly, Alves et al. (2018a) joined a tube to a sheet in two stages. In the first stage, an annular flange is produced by partial compression of tube wall thickness along the longitudinal direction. In the second stage, the upsetting of free end of tube against a sheet with a beveled hole is done to lock the two parts. Alves and Martins (2013) proposed an innovative mechanical joining process for fixing sheet panels against tubular profiles with a single ram stroke. They also predicted the safe window of the operating variables. Strength of end formed joints and welded joints performed identically in their work. For joining of a tube to a tube, the work performed by Zhang et al. (2014), Alves et al. (2014), Alves et al. (2017c), Alves et al.
(2017d) and Silva et al. (2015) needs special attention. In Zhang et al. work a big experimental set-up is required as they used rotary swaging method to join two tubes which will not be resource intensive. Alves et al. (2014) and Alves at al. (2017c) used the same method to join two tubes at their ends. Though authors claim that joining is possible in single stroke, chamfering needs to be done at the ends of the tube before start of joining experiments. Same is the case with Silva et al. (2015) work. Similary, in Alves et al.
(2017d) work, the joining process consists of three stages. Strength of end formed joints has been conducted experimentally, as numerical prediction of strength of end formed joints is unavailable in literature. From these studies, it is found that there is scope to propose a new method of joining a tube to sheet and a tube to a tube. A simple one stroke joining solution for joining of a tube to a sheet or to a tube is the need of industry.
Further, a new method may be advantageous when compared to available methods in many ways including accuracy of joint formation, strength of joint, ease of conducting joining experiments, feasibility of joining processes for different materials and dimensions, shop floor production of joints etc.
Although plenty of literature are available in the field of FSW/FSP of flat plates and sheets, literature available in the field of FSW/FSP of tubes is limited (Lammlein et al., 2011), (Kang et al., 2016), (Chen et al., 2015) and (Yuan et al., 2012a,b). Further, literature available in the field of end forming of FSPed tubes is not much. Moreover the end forming of tubes after FSW/FSP is not studied at all. As mentioned earlier, despite
Chapter 1 challenges in FSW/FSP of tubes, few research groups such as Kang et al. (2016), Chen
et al. (2015), Lammlein et al. (2011), Maggiolini et al. (2016), Susmel et al. (2017) and Yuan et al. (2012a,b) have attempted FSW of tubes. In this, Chen et al. (2015), Lammlein et al. (2011), Maggiolini et al. (2016) and Susmel et al. (2017) have attempted butt welding of tubes. Yuan et al. (2012a) converted a rolled sheet into a pipe via roll forming and then FSWed for joining. Further, they conducted spinning operation on them. But none of them carried out FSP of tubes.
As it has already been stated that FSP has been developed on the basic principles of FSW. The basic purpose of FSP is microstructural modification and mechanical properties enhancement in the processed zone. FSW can also be used to fabricate Aluminium tubes from raw sheet after roll forming. Instead of this route to study the effect of FSW parameters on the forming behaviour after tube fabrication, one can follow FSP of Aluminium tubes to study the effect. Both the results are equivalent. Tailor welded tubes can also be fabricated via longitudinal FSW of tubes of different diameters and materials. The routes are schematically shown in Fig. 1.1.
Fig. 1.1 (a) FSW of rolled sheet into pipe form, (b) FSP of normal tube, and (c) fabrication of tailor made tubes through FSW
In this context, FSP of AA 6063-T6 tubes at different levels of parameters in defect free environment has been carried out in the present work with an aim of getting an
Chapter 1 optimum processing condition at which a processed tube can perform better than raw
tube. Some interesting results have also been obtained through FSP of tubes.