**3. Different parameters affecting the explosive welded products**

There are various parameters which influence the final product of the explosive welding process. Therefore, careful control of welding parameters is very critical. The criteria for selection of the welding parameters depends upon the mechanical properties of the matting surfaces [32, 33]. Many researchers change the magnitude of these parameters by playing with the different parameters such as detonation velocity, stand-off distance, explosive type etc. The various process parameters are discussed below.

**Explosive:** In explosive welding, controlled energy of explosive is used to accelerate the flyer plate and help to impact on to the base plate, to produce a strong metallurgical bond. Explosive is generally characterized by their velocity of detonation (VoD) and density. In most of the engineering materials, the velocity of sound is between 4.5–6 km/s and most of the common explosives have VoD ranging between 6 and 7 km/s. Therefore, high VoD in explosive welding is not preferable as in case of joining the weld will get dismantle or in some cases it will destroy the material. In explosive welding, VoD is mostly applied in the range of 2–3 km/s to obtain a uniform detonation across the joining metal plates [32–34]. Many researchers have worked with different explosives to obtain a sound weld. A. Loureiro et al. have studied the effect of explosive mixture i.e. emulsion explosive with two different sensitizers i.e. hollow glass microspheres (HGMS) and expanded polystyrene spheres (EPS) on the weld interface of copper-aluminum. They observed improved surface using HGMS and higher wave amplitude was witnessed by employing EPS [35]. Similarly, many works related to explosive optimization have been done in the past in explosive welding [36, 37]. Recently Sherpa et al. have developed a low velocity of detonation (VoD) explosive welding process (LVEW)

**29**

**Table 1.**

*Explosive Welding Process to Clad Materials with Dissimilar Metallurgical Properties*

explosives used for explosive welding process are shown in **Table 1**.

interface which lead to the increase in corrosion rate [49].

defined limit it will cause entrapment of jet [33, 52].

melt pockets across the weld interface [20].

*Different explosives used in the explosive welding process.*

**3.1 Weldability window**

ANFO (ammonium nitrate

with fuel oil)

flyer plate [50, 51].

in which VoD was less than 2 km/s and obtained a sound joint [38]. Some of the

**Stand-off distance:** Stand-off distance is normally selected based on the thickness of the flyer plate and the explosive parameters. It is one of the critical parameters which influence the bond quality. Stand-off distance is selected basically to provide necessary dynamic bend angle and the impact velocity for proper bond to form. Durgutlu et al. studied the effect of stand-off distance on copper and stainless steel bond. They observed an increase in wavelength and amplitude of the wave with an increase in stand-off distance. As well as hardness value across the weld interface also increased with increasing stand-off distance [48]. M.R. Jandaghi et al. studied the effect of stand-off distance on the copper and aluminum interface. They observed that with an increase in stand-off distance, plastic deformation, kinetic energy at the collision point and as well as the melting increases at the weld

**Flyer plate velocity:** It is the velocity at which the flyer plate strike into the base plate after the detonation has started. To obtain good bonding, the flyer plate velocity should be in the described limits i.e. between the minimum and maximum flyer velocity. Experimenting with flyer plate velocity above defined range can lead to certain defects such as melting zone, cracks, brittle phases, bend and damage of

**Collision angle (β):** It is the angle formed between the flyer plate and the base plate during the collision process. Collision angle should be selected very carefully to meet the requirement of the bonding parameters. If the angle is selected below the critical collision angle, a jet-less phenomenon will occur and if β is chosen above

**Collision velocity (Vc):** It is the velocity with which collision point moves along the area being welded. For proper welding to occur there should be some plastic flow ahead of the collision point. Hence, the collision point velocity should be less than the sonic velocity in the metals. The smooth interface is observed at lower collision velocity while the wavy interface is observed at higher collision velocity at the weld interface. Increasing the collision velocity may also increase the chances of

The condition that should satisfy for proper bonding to take place is defined by weldability window. Detailed view with the description of weldability window is shown in **Figure 3**. It is plotted between collision angle (β) and collision velocity (Vp), where it is well defined by four different lines [50, 51]. The first limit is placed at the rightmost side in which formation of the jet at the collision point

SEP 7000 1300 [41, 42] Emulsion explosive 2200 1150 [43] Elbar-5 3000–3800 700–800 [44–46] PAVEX 2000–3000 530 [37, 47]

**) Ref.**

2300–2800 650–700 [39, 40]

**Explosive Velocity of detonation (m/s) Density (kg/m3**

*DOI: http://dx.doi.org/10.5772/intechopen.94448*

#### *Explosive Welding Process to Clad Materials with Dissimilar Metallurgical Properties DOI: http://dx.doi.org/10.5772/intechopen.94448*

in which VoD was less than 2 km/s and obtained a sound joint [38]. Some of the explosives used for explosive welding process are shown in **Table 1**.

**Stand-off distance:** Stand-off distance is normally selected based on the thickness of the flyer plate and the explosive parameters. It is one of the critical parameters which influence the bond quality. Stand-off distance is selected basically to provide necessary dynamic bend angle and the impact velocity for proper bond to form. Durgutlu et al. studied the effect of stand-off distance on copper and stainless steel bond. They observed an increase in wavelength and amplitude of the wave with an increase in stand-off distance. As well as hardness value across the weld interface also increased with increasing stand-off distance [48]. M.R. Jandaghi et al. studied the effect of stand-off distance on the copper and aluminum interface. They observed that with an increase in stand-off distance, plastic deformation, kinetic energy at the collision point and as well as the melting increases at the weld interface which lead to the increase in corrosion rate [49].

**Flyer plate velocity:** It is the velocity at which the flyer plate strike into the base plate after the detonation has started. To obtain good bonding, the flyer plate velocity should be in the described limits i.e. between the minimum and maximum flyer velocity. Experimenting with flyer plate velocity above defined range can lead to certain defects such as melting zone, cracks, brittle phases, bend and damage of flyer plate [50, 51].

**Collision angle (β):** It is the angle formed between the flyer plate and the base plate during the collision process. Collision angle should be selected very carefully to meet the requirement of the bonding parameters. If the angle is selected below the critical collision angle, a jet-less phenomenon will occur and if β is chosen above defined limit it will cause entrapment of jet [33, 52].

**Collision velocity (Vc):** It is the velocity with which collision point moves along the area being welded. For proper welding to occur there should be some plastic flow ahead of the collision point. Hence, the collision point velocity should be less than the sonic velocity in the metals. The smooth interface is observed at lower collision velocity while the wavy interface is observed at higher collision velocity at the weld interface. Increasing the collision velocity may also increase the chances of melt pockets across the weld interface [20].

## **3.1 Weldability window**

*Material Flow Analysis*

ness of flyer plate.

uniformly.

discussed below.

**2.3 Terminology used in explosive welding**

occur during collision due to explosion effects.

**Base plate:** It is the one which is placed at the open ground or at the anvil. This is kept stationary and is the one on which the cladding is performed. Both the base plate and the flyer plate are cleaned thoroughly and polished gently before welding. **Flyer plate:** It is the one which is placed above the base plate and during collision this plate hits onto the base plate. The selection of flyer plate and base plate is done on the basis of mass per unit area, whoever is less is placed as flyer plate. As com-

**Stand-off distance:** It is the one which maintains the distance between the flyer plate and the base plate. Stand-off distance helps the flyer plate to accelerate and acquire the required impact velocity to generate jetting. Apart from this, it also provides the exit path to the jet and the air formed between the flyer and base plate during the collision. In general stand-off distance is kept half or equal to the thick-

**Buffer sheet:** This sheet is placed over the flyer plate. It is made up of rubber or PVC. The main role of this sheet is to protect the flyer plate from damage which can

**Explosive box:** It is placed over the metal plates to be welded. This acts as a source of energy which provides the required forces to weld the materials. Explosive can be used as powder, slurry or sheet form which is spread over the buffer sheet

**Detonator:** This is placed at the top of the explosive box. The main function of the detonator is to help in initiating the main explosive. The detonator is detonated

There are various parameters which influence the final product of the explosive welding process. Therefore, careful control of welding parameters is very critical. The criteria for selection of the welding parameters depends upon the mechanical properties of the matting surfaces [32, 33]. Many researchers change the magnitude of these parameters by playing with the different parameters such as detonation velocity, stand-off distance, explosive type etc. The various process parameters are

**Explosive:** In explosive welding, controlled energy of explosive is used to accelerate the flyer plate and help to impact on to the base plate, to produce a strong metallurgical bond. Explosive is generally characterized by their velocity of detonation (VoD) and density. In most of the engineering materials, the velocity of sound is between 4.5–6 km/s and most of the common explosives have VoD ranging between 6 and 7 km/s. Therefore, high VoD in explosive welding is not preferable as in case of joining the weld will get dismantle or in some cases it will destroy the material. In explosive welding, VoD is mostly applied in the range of 2–3 km/s to obtain a uniform detonation across the joining metal plates [32–34]. Many researchers have worked with different explosives to obtain a sound weld. A. Loureiro et al. have studied the effect of explosive mixture i.e. emulsion explosive with two different sensitizers i.e. hollow glass microspheres (HGMS) and expanded polystyrene spheres (EPS) on the weld interface of copper-aluminum. They observed improved surface using HGMS and higher wave amplitude was witnessed by employing EPS [35]. Similarly, many works related to explosive optimization have been done in the past in explosive welding [36, 37]. Recently Sherpa et al. have developed a low velocity of detonation (VoD) explosive welding process (LVEW)

pared to base plate it has the lowest density as well as tensile strength.

with the help of dynamo placed at some distance from the trial site.

**3. Different parameters affecting the explosive welded products**

**28**

The condition that should satisfy for proper bonding to take place is defined by weldability window. Detailed view with the description of weldability window is shown in **Figure 3**. It is plotted between collision angle (β) and collision velocity (Vp), where it is well defined by four different lines [50, 51]. The first limit is placed at the rightmost side in which formation of the jet at the collision point


**Table 1.**

*Different explosives used in the explosive welding process.*

**Figure 3.** *Weldability window concepts for explosive welding process.*

is considered. As jetting is one of the important criteria in explosive welding. Abrahamson [53] linked welding velocity with the collision angle β as shown in Eq. 1 for the first limit. The second limit is placed at the left side of the weldability window which is related to the formation of wavy morphology at the weld interface. Cowan et al. introduced Reynolds number for describing the laminar and turbulent flow [20] as shown in Eq. 2. The third limit is related to the minimum flyer plate velocity (Vpmin) which ensure that the impact pressure developed at the collision point exceeds the yield strength of the materials. Lower boundary equation was developed for third limit as shown in Eq. 3. While the fourth limit corresponds to the maximum flyer plate velocity (Vpmax) which maintains the required impact pressure below the value so that the melting does not occur at the weld interface. To avoid melting Eq. 4 was developed by Wittman [50]. Therefore, in order to obtain good bond, selection of welding parameters should be with in the described limits of weldability window [20, 34, 50, 54].

$$V\_{\epsilon} = \frac{\beta}{10} + 5.5\tag{1}$$

$$R\_t = \frac{\left(\rho\_a + \rho\_b\right)V\_\epsilon^2}{2\left(\mathbf{H}\_a + \mathbf{H}\_b\right)}\tag{2}$$

**31**

**Table 2.**

*Explosive Welding Process to Clad Materials with Dissimilar Metallurgical Properties*

<sup>H</sup> sin <sup>=</sup>

1.2: Imperfectly cleaned plate surface

22 V

( )

Explosive welding process is capable of joining similar and dissimilar material combinations irrespective of the difference in physical and chemical properties.

**Material combination Welding configuration Explosive used Ref.** Al alloy -Al alloy Tube PETN [55] Steel-steel plates Parallel set-up Elbar-5 [56–58]

Copper-copper \_\_ \_\_ [59]

**Material combination Welding configuration Interlayer used Ref.**

Inclined set-up (Under

Aluminum to stainless steel Parallel set-up Cu, Ti & Ta [16]

Titanium and aluminum Parallel set-up Not used [61, 62] Aluminum and copper Parallel set-up Al5052, Cu & SS304 [63]

Al and Mg alloy Parallel set-up Not used [64, 65]

Aluminum and copper Parallel set-up Not used [67–69] Aluminum and steel Parallel set-up Not used [70–73]

Steel-steel Cylindrical Emulsion explosive/

Copper-copper alloy Parallel set-up Powder emulsion

water)

water)

Sn and Cu Inclined set-up (Under

*Material combinations joined using explosive welding process.*

<sup>=</sup>

2 c

*T Cm o KC Cp b N h*

β

*k*

V 2

*V*

ρ

*C*

1/2 1/4

ρ

ANFO

explosive

Parallel set-up Not used [17]

Parallel set-up Aluminum AA1050 [66]

Thin AZ31 [60]

Not used [41]

(3)

(4)

[36]

[43]

*DOI: http://dx.doi.org/10.5772/intechopen.94448*

Where HV : Vickers hardness no.

K: Constant value

Where Tm: Melting temperature,

**Similar materials combinations**

**Dissimilar materials combinations**

Titanium and magnesium alloy

C103 niobium alloy and C263

Aluminum and carbon steel and Aluminum-stainless steel

AZ31

nimonic alloy

Cp: Specific heat capacity, K: Thermal conductivity, h: Thickness of flyer plate, Cb: Bulk sound speed

Ρ: Density of the material

Take value 0.6: Plate surface is very clean

<sup>1</sup> sin

**3.2 Different materials combination joined by explosive welding**

β

Where ρ ρ *a b* & : ρ Density of flyer plate and base plate

H &H *a b* : Hardness value of flyer plate and base plate

: *Rt* Reynolds number

*Explosive Welding Process to Clad Materials with Dissimilar Metallurgical Properties DOI: http://dx.doi.org/10.5772/intechopen.94448*

$$k\sin\beta = k\sqrt{\frac{\mathcal{H}\_\mathcal{V}}{\rho V\_\mathcal{C}^2}}\tag{3}$$

Where HV : Vickers hardness no.

*Material Flow Analysis*

is considered. As jetting is one of the important criteria in explosive welding. Abrahamson [53] linked welding velocity with the collision angle β as shown in Eq. 1 for the first limit. The second limit is placed at the left side of the weldability window which is related to the formation of wavy morphology at the weld interface. Cowan et al. introduced Reynolds number for describing the laminar and turbulent flow [20] as shown in Eq. 2. The third limit is related to the minimum flyer plate velocity (Vpmin) which ensure that the impact pressure developed at the collision point exceeds the yield strength of the materials. Lower boundary equation was developed for third limit as shown in Eq. 3. While the fourth limit corresponds to the maximum flyer plate velocity (Vpmax) which maintains the required impact pressure below the value so that the melting does not occur at the weld interface. To avoid melting Eq. 4 was developed by Wittman [50]. Therefore, in order to obtain good bond, selection of welding parameters should be with in the described limits

5.5

2

*V*

(1)

(2)

10 *Vc* = + β

*<sup>R</sup>* ρ +ρ <sup>=</sup> <sup>+</sup>

H &H *a b* : Hardness value of flyer plate and base plate

*t*

Where ρ ρ *a b* & : ρ Density of flyer plate and base plate

: *Rt* Reynolds number

( ) ( )

2H H *a bc*

*a b*

**30**

**Figure 3.**

of weldability window [20, 34, 50, 54].

*Weldability window concepts for explosive welding process.*

Ρ: Density of the material K: Constant value Take value 0.6: Plate surface is very clean 1.2: Imperfectly cleaned plate surface

$$\sin\left(\frac{\beta}{2}\right) = \frac{1}{2N} \frac{\left(T\_m \mathbf{C}\_o\right)^{1/2}}{\mathbf{V}\_c^2} \left(\frac{\mathbf{K} \mathbf{C}\_p \mathbf{C}\_b}{\rho h}\right)^{1/4} \tag{4}$$

Where Tm: Melting temperature,

Cp: Specific heat capacity, K: Thermal conductivity, h: Thickness of flyer plate, Cb: Bulk sound speed
