A Comprehensive Guide to Explosive Welding: Types and Uses

A Comprehensive Guide to Explosive Welding Types and Uses

1. Types of Explosive Welding

(1) Classified by Joint Form

Surface welding, line welding, and spot welding are different types, with line welding and spot welding being less common in actual production. Surface welding is the primary application type of explosive welding.

(2) Classified by Assembly Method

This can be divided into parallel and angular methods. The parallel method involves placing two test pieces parallel to each other, leaving a certain gap. During explosive welding, the test pieces successively connect as the explosive advances, leading to similar conditions at every point of the joint.

The angular method involves creating an angle between the two test pieces, starting the weld from the smaller gap, and progressing to the larger one. Due to the gap limitations, the size of the test pieces cannot be too large.

(3) Classified by Preheating of the Test Piece

This can be divided into hot explosive welding and cold explosive welding. Hot explosive welding involves heating metal materials with a lower brittleness value at room temperature to above their toughness transition temperature and immediately performing explosive welding.

For example, molybdenum, which is brittle at room temperature, is prone to fracturing after explosive welding. However, if heated to above 400°C (its toughness transition temperature), molybdenum no longer fractures and can be welded with other metals.

Cold explosive welding involves placing highly plastic metals in liquid nitrogen, removing them after they harden, and immediately performing explosive welding.

In addition, explosive welding can be categorized by product shape into plate-plate, tube-tube, tube-plate, tube-rod, and metal powder-plate explosive welding;

by the number of explosions into single, double, or multiple explosive welding, leading to distinctions of double-layer and multi-layer explosive welding; by explosive features into single-sided and double-sided explosive welding; and by location into ground, underground, underwater, airborne, and vacuum explosive welding.

Currently, explosive welding can be combined with standard metal pressure processing and mechanical processing methods to produce larger, longer, thinner, coarser, finer, and uniquely shaped or extreme shape composite metal materials, parts, and equipment. This combined process is an extension and development trend of explosive welding technology.

2. Application Range of Explosive Welding

Explosive welding is mainly used to manufacture metal composite plates, giving their surfaces or layers specific properties. It can also be used for welding transition joints of dissimilar materials (different metals, ceramics, and metals, etc.), providing them with good mechanical properties, electrical conductivity, and corrosion resistance.

For example, platinum-plated titanium used as the anode of an external current corrosion prevention device has been applied in large ships and marine engineering.

The platinum layer of platinum-plated titanium made by electroplating is not firmly bonded to the titanium substrate, and there are many microscopic cracks, looseness, and pores at the platinum/titanium interface, leading to the “platinum peeling” phenomenon.

However, platinum/titanium composite material obtained by explosive welding remains intact under the same test conditions.

Rapid life test results show that platinum-plated samples peel off after boiling once in water and concentrated hydrochloric acid, fall off after twice, and completely fall off after three times. However, explosive welding samples still did not fall off after boiling 30 times.

(1) Weldable Metal Materials

Explosive welding is primarily used for welding of the same metal materials, different metal materials, and metals and ceramics, especially for metals (such as aluminum and steel, aluminum and tantalum, etc.) with large differences in material properties that are difficult to reliably weld by other methods, materials with large differences in thermal expansion coefficients (such as titanium and steel, ceramics and metals, etc.), and highly reactive metals (such as tantalum, zirconium, molybdenum, etc.).

In fact, any metal with sufficient strength and plasticity and can withstand the rapid deformation required by the process can undergo explosive welding. Table 8-1 lists successful applications of explosive welding for different combinations of metals and alloys in engineering.

Table 8-1 Common Combinations of Metals and Alloys for Explosive Welding in Engineering

ZirconiumMagnesiumTungsten-Chromium-Cobalt AlloysPlatinumGoldSilverNiobiumTantalumCorrosion-resistant AlloysTitaniumNickel AlloysCopper AlloysAluminumStainless SteelAlloy SteelNon-alloy Steel
Non-alloy Steel
Alloy Steel
Stainless Steel
Aluminum
Copper Alloys
Nickel Alloys
Titanium
Corrosion-resistant Alloys
Tantalum
Niobium
Silver
Gold
Platinum
Tungsten-Chromium-Cobalt Alloys
Magnesium
Zirconium

Note: “√” indicates good weldability; blank indicates poor weldability or no reported data.

(2) Weldable Product Structures

Most products of explosive welding have simple structures with flat or cylindrical bonding surfaces.

1) Composite Flat Plates

The primary industrial application of explosive welding is the production of bimetallic composite plates, which can be double-layered or multi-layered. For example, welding stainless steel plates, copper plates, titanium plates, aluminum plates, etc., onto ordinary steel plates.

Typically, the base plate is fixed during welding, and its thickness is generally not restricted. However, the overlay, accelerated by the explosive shockwave, has a thickness limitation.

Composite plates are usually supplied in a post-weld state. As some distortion deformation typically occurs during the production of composite plates using explosive welding, leveling is required after welding. If the hardening occurring at the bonding interface has affected the engineering application, post-weld heat treatment is necessary.

When using the composite plate to fabricate pressure vessel heads, the possible formation of brittle intermetallic compounds at the bonding surface due to temperature effects during hot pressing should be considered. For example, titanium-steel composites should not be heated above 760°C, while this requirement does not apply to stainless steel and non-alloy steel composites.

2) Inner or Outer Cladding of Cylinders (Cones)

Outer cladding can be applied to round rods or solid cones. For products like pipes or tubes, inner or outer cladding can be applied as needed to obtain a cladding surface with special properties (such as corrosion resistance, high-temperature resistance, wear resistance, etc.). This explosive welding process can produce bimetallic weldments and can also be used to repair easily damaged components.

3) Production of Transition Joints

Explosive welding provides a good method for achieving high-strength metallurgical bonding between dissimilar metals with poor fusion welding weldability or metals that are not compatible metallurgically. During welding, two immiscible metals are first welded together using the explosive welding method to form a transition joint.

Then, this transition joint is welded to the same metal or metal with similar weldability on the product using conventional fusion welding methods. Figure 8-4 shows a schematic diagram of transition joints and welding methods for some dissimilar metals.

4) Tube-to-Tube Plate Welding

The welding between tubes and tube plates in heat exchangers can be produced using the inner cylindrical surface cladding explosive welding process, as shown in Figure 8-5. This includes welding of steel tubes to titanium tubes, titanium tubes to pure copper tubes, hard aluminum tubes to soft aluminum tubes, and aluminum tubes to steel tubes, etc.

Figure 8-4 Schematic diagram of transition joints and connection methods for some dissimilar metals.

A – Explosive welding seam in the transition joint
B – Fusion welding seam

Figure 8-5 Explosive welding of tube to tube plate


a) Pre-welding installation b) Welding process c) Completed welding
1 – Tube 2 – Tube plate 3 – Lead-in wire 4 – Explosive 5 – Positioning frame 6 – Explosive welding seam

5) Utilizing explosive welding to join complex curved surface structures. In such cases, explosive welding and explosive forming are often completed simultaneously. Figure 8-6 shows a schematic diagram of the explosive welding-explosive forming process. In the process shown in Figure 8-6a, the base layer (weldment) itself serves as the forming mold.

Figure 8-6 Schematic diagram of explosive welding-explosive forming process

1 – Detonator
2 – Explosive
3 – Overlay
4 – Base layer (weldment)
5 – Vacuum rubber ring
6 – Pressure transmission medium (water)

The process shown in Figure 8-6b requires the use of molds. The former is formed before welding, while the latter is formed after welding.

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