With the rapid development of the automobile industry, the lightweight design of the automobile has been a wide concern. In order to reduce the weight of the automobile body, lightweight materials such as aluminum alloy has been widely used, which has set a higher standard for the joining technology of similar and dissimilar metal plates [1
]. In most cases, fusion welding, adhesive bonding and mechanical fastening are used to join metal sheets. Although fusion welding is widely used, the high temperatures required may reduce the quality, accuracy, and reliability of joined parts [2
]. Moreover, it is difficult to weld dissimilar metal sheets, because the melting points of dissimilar materials are very different [3
]. Adhesive bonding and mechanical fastening are available for joining dissimilar metal sheets [4
]. However, adhesive bonding is time-consuming due to the curing process. In addition, adhesive bonding requires the cleaning and roughening of the surfaces to be bonded. The mechanical fastening technology needs pre-drilled holes on the surface of the metal plates, which may destroy the air tightness and water tightness of the joints [5
]. To solve these problems, mechanical clinching (with or without cutting) and self-pierce riveting have been developed [6
]. In mechanical clinching, metal sheets are joined by local cold forming between a punch and a die without the use of additional elements [7
]. In self-pierce riveting, metal sheets are joined by forcing a rivet directly between two sheets without the use of a pre-drilled hole, thus saving much running time (which is almost one second) [8
]. The metal sheets are joined by plastic deformation in these two processes, during which the coating layer will not be destroyed and the heat affected zone will not be produced [9
]. Furthermore, plastic joining processes without melting are attractive for joining dissimilar metal sheets [10
]. Compared with the conventional joining technology, mechanical clinching and self-pierce riveting have additional advantages, such as process cleanliness, absence of surface pre-treatments and post-treatments, low cost per joint, ease, and robustness of the processes [11
]. Besides, Varis [12
] compared the joining costs of mechanical clinching and self-pierce riveting. The results showed that mechanical clinching without any additional joining elements has lower running costs than self-pierce riveting. An exhaustive literature research has been produced on mechanical clinching of metal sheets driven by the increasing interest from automotive industries. Lambiase and Di Ilio [13
] proposed a numerical model which can accurately predict the fracture paths produced during the clinch joining of thin aluminum AA6086-T6 sheets. Jiang et al. [14
] investigated the effect of pre-straining on the mechanical behavior and joint strength of the clinched aluminum-to-steel joint. Because of the advantages mentioned above, the employment of mechanical clinching has been extended to a wide range of materials. Lambiase and Di Ilio [15
] verified the suitability of mechanical clinching for the production of hybrid metal-polymer joints and evaluated the influence of main process parameters (pre-heating conditions, forming pressure, and die geometry) on the joinability and mechanical behaviors of clinched connections. Lee et al. [16
] developed a new mechanical clinching process, namely hole-clinching, which can join aluminum alloys to high-strength/low ductility materials including carbon fiber reinforced plastics. Lambiase [17
] investigated the mechanical behavior of polymer-metal hybrid connections produced by clinching process using different types of tool.
However, there are two main problems while joining similar and dissimilar materials by mechanical clinching process. Firstly, the poor formability of materials limits the application scope of mechanical clinching. To this end, two possible solutions are available: increasing the material formability by pre-heating and improving the material flow by optimizing the geometry of the clinching tools [13
]. Based on these two solutions, low-ductility materials can be joined by mechanical clinching. Lambiase [18
] investigated mechanical clinching of heat-treatable aluminum alloy sheets (AA6082-T6) with low ductility and analyzed how to control the material flow during the clinching process by the employment of tool variation and different pre-heating schemes. Abe et al. [19
] studied the suitability of mechanical clinching for joining ultra-high strength steel sheets with a low ductility and modified the diameter and depth of the die to control the metal flow. Secondly, the joint strength of clinched connections produced by mechanical clinching is lower than those obtained by the other joining methods. Mori et al. [20
] reported that the static strength for the mechanical clinching was about half for the resistance spot welding. The joint strength is determined by the undercut and neck thickness, therefore the strength of mechanically clinched joints can be improved by maximizing the undercut and reducing the neck thinning. Lee et al. [1
] proposed a design method of clinching tools with analytical models which can inversely calculate the required undercut and neck-thickness based on the desired joint strength.
The miniaturization of products is an important growing trend in precision mechanics and the electronic industry, which brings increased demands on joining processes in micro scale [21
]. Nevertheless, the mature processing theory and technology for joining of macro scale metal plates cannot be directly transplanted into the field of micro scale joining owing to the size effects [22
]. There are some limitations when mechanical clinching and self-pierce riveting are used in micro scale joining (where the thickness of metal foils is less than 100 microns). First of all, the fabrication of micro punch and micro rivet is very difficult and expensive. What is more, the extremely small clearance between micro punch and micro mold makes it difficult to control the alignment accuracy, which will reduce the service life of the tools and affect the quality of joints. Therefore, non-contact processes are very suitable for joining metal foils in micro scale. Daehn and Lippold [23
] found that laser impact spot welding can be used to weld similar and dissimilar metal foils in the micro/nano scale. A further approach for joining metal foils is given by laser shock forming. With this non-contact process, undercuts of micrometer-foils can be produced [2
]. Afterwards, Veenaas et al. [21
] improved this technology and verified the feasibility of using a TEA-CO2 laser to join aluminum foil (50 μm) and stainless steel (100 μm) which was pre-drilled with a hole having a diameter of 4 mm. They measured the pressure distribution in open and closed environments and analyzed the forming behavior during the joining process by laser induced shock waves to gain a better understanding of this process [26
]. This is considered as a potential, but still immature, technology to join metal foils, however, the process is very complicated and influenced by many experimental variables. Since the use of different metal foils with different thicknesses would lead to differences in the performances of joining, a lot of further research is required.
The purpose of the current study was to experimentally verify the feasibility of a novel micro clinching with cutting process for joining similar and dissimilar metal foils. Many important process parameters were determined by studying the deformation behavior of single layer metal foil in the mold. The process window of the 1060 pure aluminum foils and annealed copper foils (Al/Cu) was given through a series of experiments. The effect of laser energy on the interlock and the minimum thickness of upper foils were studied. Moreover, the connection strength of different joints was measured by the single lap shearing tests.