**2. Position of the MPW process today and its influences**

Joining processes technically and financially offer strong potentials and represent a significant global market. An overview of the added value brought by the joining activities is briefly presented to address the growing interest in this engineering field. This part of the chapter explains the technical-economic status of the welding technology including recent develop‐ ments in 2005–2007 about the added value with its increasing trend for the global market of the welding. Current status of the technical evolution marks a major technological transition with the emergence of the solid state welding method for the MPW. A brief review of the technical solutions developed by MPW is addressed. It also provides various representations of successful configurations, suitable combinations of materials and major advantages offered by the MPW process.

#### **2.1. Socio-economic influences of the joining and welding processes**

A recent survey focused on the European zone provides data related to the technical and financial consequences of the joining technology and the added value brought by the joining manufacturing activities [15]. In the case of Germany, the data gives a representative indication since this country is the leading manufacturer of joining machines which represent about onethird of the EU's production [15]. Available data inform that, for this country alone, the added value generated by the assembly industry is increased more than 22 billion euros by 2000s without any significant decrease [15], which corresponds to a proportion of 26% increase at European level. But contributions of other countries are also important; this includes Italy, France, Poland and United Kingdom which have respectively provided 18%, 10%, 9%, and 8% [15]. This assessment does not include either the worldwide data or the recent data, but represents an indication of the socio-economic influence of the joining technology.

rate plastic deformation. In general, the workpiece experiences a strain rate of up to 102

effect between electromagnetic phenomena with metal plasticity contributes towards the advantages of this process in comparison with conventional and other high speed welding techniques. However, this process has not been widely implemented until now, even though it is known since late 1960s [13, 14] and its booming advantages have been paid attention by automotive manufacturers in early 2000s. That is, large scale implementation of this technol‐ ogy has always been challenged by the existence of unique complex realities of this process. But, fortunately, recent technological advancements allow for thorough investigations to understand the physical phenomena of this multi-physics process and facilitate an effective utilization of the technology into modern engineering applications. Emerging scientific technology provides more room to explore such high speed manufacturing processes using sophisticated engineering tools such as high speed measurements, experimental observa‐

MPW is believed to bring innovative solutions in joining technology and the merits of the process are covered in this context. The objectives of this chapter are divided into five main sections including position of the MPW today and its potentials, description of the process, weld features and variance, identification of the weld nature by simulating the interface behaviour during the collision, and computation of the in-flight dynamics using coupled multi-

Joining processes technically and financially offer strong potentials and represent a significant global market. An overview of the added value brought by the joining activities is briefly presented to address the growing interest in this engineering field. This part of the chapter explains the technical-economic status of the welding technology including recent develop‐ ments in 2005–2007 about the added value with its increasing trend for the global market of the welding. Current status of the technical evolution marks a major technological transition with the emergence of the solid state welding method for the MPW. A brief review of the technical solutions developed by MPW is addressed. It also provides various representations of successful configurations, suitable combinations of materials and major advantages offered

A recent survey focused on the European zone provides data related to the technical and financial consequences of the joining technology and the added value brought by the joining manufacturing activities [15]. In the case of Germany, the data gives a representative indication since this country is the leading manufacturer of joining machines which represent about onethird of the EU's production [15]. Available data inform that, for this country alone, the added value generated by the assembly industry is increased more than 22 billion euros by 2000s

–107

[11] while this could reach an ultimate value of 106

244 Joining Technologies

tions, microscopic analyses and advance computing techniques.

**2. Position of the MPW process today and its influences**

**2.1. Socio-economic influences of the joining and welding processes**

physics numerical simulations.

by the MPW process.

–104 s-1

s-1 at an interface [12]. The synergetic

Welding activities generally cover a substantial part of the assembly industry. For reference purposes, they returned a total market turnover of 19.3 billion euros for Germany in 2003, providing 6% of the jobs linked to this industry, which represents 1.7% of increase in employ‐ ment opportunities including all sectors [16]. A comparative study carried out between 2001 and 2005 has shown an added value increased by 18% of job creation including 5% directly linked to the welding activities [16]. Such expansion highlights the socio-economic benefits brought by the welding technology. Furthermore, note that the welding represents a nonnegligible investment in several industrial branches including the most advanced sectors in transportations, energy and medicine.

In the specific case of metal joining, welding methods bring some useful flexibilities. It does not require intermediate joining component (bolt, rivet, adhesive layer, brazing material etc.) allowing thereby possibilities to produce structures with the benefits of cost and weight reduction. A weld can confer as a permanent joint which is suitable for many mechanical performances. In addition, the welding methods can be applied at varied length scales, from micrometric (micro welding) to several hundreds of millimetres. Furthermore, welding practices include several techniques and processes, making them robust, widely used and intrinsic to technological advances and innovations.

## **2.2. Innovative nature of the electromagnetic pulse technology (EMPT)**

Conventional welding processes show difficulties in joining new metal combinations. The current innovations increasingly introduce dissimilar assemblies that enable to meet new challenges such as light weight requirement, structural reinforcement, and other functional specifications. In this respect, innovative solutions have led to the consideration of complex functional material combinations including metallic assemblies with different melting temperatures, where the fusion welding processes fail when producing such joints at the interface. The discrepancy between the melting points of two dissimilar metals prevents a successful joint formation by solidification of a molten pool as usually achieved during a fusion welding process. The exploration of new methods have led to various welding principles among which high velocity impact welding (HVIW) methods enable bonding dissimilar metallic combinations. High pressure, short duration and low temperature bonding form the main particular characteristic of these methods [17]. The welding involves a strong interfacial collision in various high velocity impact methods using the explosive detonation (explosive welding), the laser shock impulse (laser spot welding), the magnetic impulse (MPW), or the vaporizing foil actuation (vaporizing foil actuation welding).

The use of electromagnetic impulse to provide a significant Lorentz force makes the MPW as an attractive method with respect to other high speed collision welding processes. The EMPT is particularly different in terms of cost, reliability, ease of use, flexibility, rate of work, no

**Figure 1.** EMPT for industrial applications implemented by "PSTproducts" (a) Al/Cu electric bus bar [www.pstprod‐ ucts.com], (b) EMPT crimped gear box part [www.pstproducts.com] (c) EMPT welded Al pressure vessel for air condi‐ tioning system [28], (d) EMPT welded Al/steel crash box [www.pstproducts.com], (e) EMPT welded Al/Cu cooling plate [www.pstproducts.com] (f) EMPT crimped Al/steel tube instrumental panel beam [28], (g) EMPT for hemming of a Al pressure vessel [28], (h) EMPT crimped Al lid on a pharmaceutical glass bottle [29], (i) EMPT crimped drive shaft [28] and (j) EMPT crimped air suspension [28].

**Figure 2.** (a) Automated robotic arm used to implement EMPT during a Body in White (BIW) construction and (b) var‐

Magnetic Pulse Welding: An Innovative Joining Technology for Similar and Dissimilar Metal Pairs

http://dx.doi.org/10.5772/63525

247

In general, the MPW process is a user-friendly joining method. The working principle of the process is simple and the welding procedure is fast, easy, and viable. This section briefly explains the general principle of the process including the architecture of the welding machine and the welding parameters. Interactions between process and welding parameters are provided including the specifications of their controllable and measurable natures. This gives a holistic understanding of the process principle with different variables involved in the

**Figure 3** shows typical magnetic pulse welding architecture with overlap configuration used to weld a core clad combination. The MPW is sufficiently flexible to weld various shapes of components for different joint configurations such as half lap, overlap, cross lap and end lap (Section 2.2). Basically, a MPW setup consists of a pulse generator, a coil and an optional field shaper. The generator contains a transformer which transforms a low-voltage power supply into a high voltage charge in the range of kilo-Volts stored in a capacitor bank. This generator set, connected to an inductive coil through a control switch, delivers a high discharge current in the range of a few hundred kilo-Ampere. The electric discharge flowing through the coil generates a magnetic field which creates significantly large Lorentz force within the external tube (the flyer) in the case of a tubular assembly. Thus, the flyer tube undergoes a high strain rate plastic deformation and collides onto the fixed inner rod to produce a high velocity collision. The discharge pulse frequency depends on the parameters of the electromagnetic circuit (Equation 1) and which lies in between 10–200 kHz, but usual operational frequencies are in between 10–20 kHz during the applications. The inductive multi turn coil can be used

ious welded components produced using the robotic arm by "PSTproducts" [20].

**3. Description of the MPW process**

selection of the welding parameters.

**3.1. Magnetic pulse welding architecture**

requirement of being consumable and eco-efficiency [18]. This method simply uses a standard electrical source intermittently and a magnetic coil. The welding test does not require either a surface treatment or a long experimental preparation, and is performed in a very short period of time, i.e. it only takes less than a few hundred microseconds to produce a joint. This is a precise joining method that has been successfully applied on several similar and dissimilar metallic combinations for different configurations such as overlap, half lap, cross lap, end lap etc. This joining method is also suitable for various geometrical components including tubular assembly, plates or any specific shape. It is possible to generate a complex distribution of a magnetic pulse force due to the strong flexibility of electromagnetic welding tool design [19]. Current potentialities of the EMPT are depicted by Kapil et al. [18]. The authors addressed a comprehensive review of successful applications, where some are being industrialized, and the growing interest given to the process in several industrial sectors such as in automobile, aerospace, nuclear, electrical and microelectromechanical systems (MEMS), ordinance and packaging [18]. Although the pragmatic results are numerous, concisely its applications are well suited to any tubular assembly, regular or irregular shapes, as well as to any flat shape connections (**Figure 1**). EMPT is successfully implemented to perform various manufacturing tasks using semi and fully automated lines by "PSTproducts GmbH" that also offers engi‐ neering and industrial solutions including a robotic arms to effectively handle the portability of the unit in industrial welding cases (**Figure 2**) [20]. In addition, the process covers a broad range of material combinations including Cu/Zr-based metallic glass [21], Al/metallic glass [22], Cu/Manganin [23], flexible circuit boards [24], Cu/Brass, Cu/steel, Cu/Al, Al/steel, Al/Mg, Al/Ni, Al/Fe, Al/Ti and Ti/Ni [25–27]. With all these aforementioned benefits, the EMPT is continuously explored and progressively optimized to bring new potential advancements for effective industrial implementation.

**Figure 2.** (a) Automated robotic arm used to implement EMPT during a Body in White (BIW) construction and (b) var‐ ious welded components produced using the robotic arm by "PSTproducts" [20].
