Basic of Solid State Welding & Its Types

Solid state welding stands as a revolutionary group of welding processes, representing an innovative technique of coalescence at temperatures below the melting point of the base materials. It doesn’t require the addition of filler metal to join the metals. 

Unlike traditional welding methods that rely on melting and solidifying metals, solid state welding achieves bonding through mechanical pressure, heat, or a combination of both. 

This groundbreaking approach not only preserves the structural integrity of the base materials but also minimizes thermal distortion and metallurgical changes. Solid state welding is not merely a welding technique; it’s a transformative process that redefines the possibilities of metal fabrication.

Solid state welding
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  • This transformative process ensures a joint which is free from microstructural defects,
  • It eliminates pores, non-metallic inclusions, and segregation of alloying elements that can damage the weld
  • What sets it apart is the seamless integration of mechanical properties, mirroring those of the parent metals with striking precision. 
  • No consumable materials such as filler materials, fluxes, or shielding gasses are required. This not only streamlines the welding procedure but also contributes to a cleaner, more efficient workflow.


  • The process demands a series of meticulous steps, including degreasing and the removal of oxides, coupled with precise brushing and sanding techniques. 
  • The requirement for expensive equipment adds a layer of complexity to the undertaking. 
  • Thorough surface preparation becomes not just a procedural requirement but a hallmark of dedication to excellence in the intricate world of metal fabrication.

Solid state welding can be divided into 8 categories. They are

  • Cold welding
  • Forge welding
  • Diffusion welding
  • Friction welding
  • Explosion welding
  • Hot pressure welding
  • Roll welding
  • Ultrasonic welding

Let’s discuss them briefly-

Cold Welding

Cold welding, a fascinating solid-state welding process, redefines the conventional understanding of joining metals. This innovative technique harnesses the power of pressure at room temperature to achieve coalescence, accompanied by substantial deformation at the weld.

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The magic unfolds as extremely high pressures are applied to impeccably clean interfacing materials, ensuring a flawless bond. Astonishingly, even simple hand tools can generate sufficient pressure when uniting extremely thin materials, showcasing the versatility of cold welding.

However, when dealing with heavier sections, the process calls for the assistance of a press to exert the necessary pressure for a successful weld.

Indentations strategically made in the parts undergoing cold welding add another layer of precision to the process, making it remarkably adaptable for joining ductile metals.

Notably, aluminum and copper, metals that are often considered challenging to weld, find compatibility and synergy through the transformative art of cold welding.

Forge Welding

Forge welding, an ancient solid-state welding technique, unveils the art of joining metals through a harmonious dance of heat and force. Executed within the confines of a forge, metals are heated to a point where they yield to the touch, then pressure or blows are applied with precision, inducing permanent deformation at the interface and birthing a seamless coalescence.

In its historical context, forge welding, often dubbed hammer welding, was a revered practice among blacksmiths. In this bygone era, blacksmiths would skillfully heat metal parts to a red glow, below the molten temperature, employing flux to enhance the process.

The blacksmith’s deft use of a hammer and anvil became the orchestrator of pressure, delicately fusing the materials. While this method holds a rich heritage, it occupies a minor role in contemporary industrial welding, serving as a testament to the evolution of metallurgical practices over time.

Diffusion Welding

Enter the realm of diffusion welding, a solid-state welding marvel that orchestrates the seamless union of faying surfaces through the alchemy of pressure and elevated temperatures.

In this intricate process, microscopic deformation, melting, or relative motion of the parts is eschewed, providing a unique avenue for coalescence. Filler metal, with the option of electroplated surfaces, may or may not be employed, adding a layer of versatility to the technique.

Diffusion welding finds its niche in the delicate realm of refractory metals, ensuring their metallurgical properties remain unscathed even as they bond. Induction, resistance, or furnace heating sets the stage, with atmosphere and vacuum furnaces playing pivotal roles, often necessitating a protective inert atmosphere for most refractory metals.

The precision of diffusion welding shines when joining dissimilar metals, making it a linchpin for the aircraft and aerospace industries. For instances where a layer of filler material enhances the bond, it transitions into diffusion brazing, further expanding its applications and solidifying its significance in the intricate world of metal fabrication.

Explosion Welding 

Unlocking the marvels of metal bonding, explosion welding emerges as a dynamic solid-state welding process, reshaping the very essence of joining metals. Here, coalescence is orchestrated by the controlled detonation’s high-velocity movement, rendering the need for applied heat obsolete. Despite the absence of direct heat, an illusion of molten metal at the interface during welding adds an intriguing layer to the process.

The sources of heat are diverse, arising from the shock wave impact, collision energy, and the plastic deformation accompanying jetting and ripple formation at the interface. This plastic interaction, especially pronounced during surface jetting, facilitates the necessary metal flow for a high-quality weld. Explosion welding proves its mettle by seamlessly uniting almost all metals, bridging the gap for dissimilar metals that eluded conventional arc processes.

Notably, this self-contained and portable technique thrives in speed and efficiency, delivering weld joints with strength surpassing the weaker of the metals involved. While explosion welding hasn’t saturated all welding domains, its prowess shines in specific applications like cladding, tube-to-tube sheet joins in heat exchangers, and as a repair tool for leaking joints.

A promising frontier emerges with its application in socket joint pipe joining, hinting at an expanding role in the welding landscape of the future.

Friction Welding

Step into the dynamic world of friction welding, a solid-state welding marvel that orchestrates coalescence through the heat generated by mechanically-induced sliding motion. In this intricate dance, work parts unite under pressure, often involving the rotation of one piece against another to produce frictional heat at the junction. When the optimal temperature is attained, rotational motion halts, additional pressure is applied, and coalescence becomes reality.

Two variations, the original process and inertia welding, showcase the adaptability of friction welding. The former, where one part remains stationary and the other rotates, claims precise control with regulated speed, pressure, and time. Inertia welding, propelled by a flywheel, reduces rotational speed, providing a slightly different approach.

Friction welding’s prowess lies in its ability to yield high-quality welds swiftly, sans filler metal or flux. It accommodates diverse metal combinations and is well-suited for dissimilar metal unions. However, its demand for relatively expensive apparatus, akin to a machine tool, stands as a notable factor.

The success of a friction weld pivots on three critical factors: rotational speed, pressure, and welding time, all meticulously controlled by an automatic sequence controller. Visual inspection post-weld hinges on the flash shape, a crucial indicator of the welding parameters’ precision. Between extremes lies the realm of correct flash shape, offering a visual cue to the weld’s integrity.

As a final touch, the flash is typically removed, leaving behind a testament to the seamless fusion achieved through the intricate ballet of friction welding.

Hot Pressure Welding

Embark on the transformative journey into hot pressure welding, a formidable solid-state welding technique weaving coalescence through the orchestration of heat and applied pressure. Here, the magic unfolds as materials come together, subjected to pressure sufficient to induce macro-deformation in the base metal. Coalescence, at the heart of this process, materializes at the interface, a dance between pressure, heat, and noticeable deformation.

This intricate ballet, conducted in closed chambers with the aid of vacuum or a shielding medium, cracks surface oxide films, exposing clean metal surfaces. The diffusion across interfaces becomes the silent architect, seamlessly welding clean metal to the abutting part.

Hot pressure welding finds its niche in aerospace weldment production, epitomizing precision and quality. A variant, the hot isostatic pressure welding method, introduces a twist where pressure, applied by a hot inert gas in a pressure vessel, adds a nuanced layer to this dynamic process.

Roll Welding

Delve into the nuanced world of roll welding, a solid-state welding technique that masterfully orchestrates coalescence through a dance of heat and pressure, all under the guiding touch of rolls.

The essence of this process parallels that of forge welding, with a notable distinction—pressure finds expression through rolls rather than the resounding blows of a hammer. As the rolls assert their influence, coalescence unfolds at the interface, driven by the intricate dance of diffusion at the faying surfaces.

Roll welding’s prowess finds a distinctive calling in the cladding domain, where it excels in marrying mild or low-alloy steel with high-alloy materials, such as stainless steel. This process, a silent artisan in the welding repertoire, also carves a niche in crafting bimetallic materials tailored for the intricate needs of the instrument industry.

Roll welding, with its finesse in metal fusion, stands as a testament to the versatility and precision achievable through the dynamic interplay of heat, pressure, and rolls.

Ultrasonic Welding

Embark on a journey into the realm of ultrasonic welding, a solid-state welding marvel that breathes life into coalescence through the deft application of high-frequency vibratory energy. In this intricate ballet, work parts are embraced under pressure while the ultrasonic tip or electrode, a masterful energy coupling device, oscillates parallel to the weld interface, setting the stage for fusion.

Dynamic stresses, introduced by the combined clamping pressure and oscillating forces, weave minute deformations into the base metal. This delicate dance generates a moderate temperature rise in the weld zone, fostering coalescence without reaching the melting point. Ultrasonic energy, a silent artisan, aids in cleansing the weld area, breaking up and carrying away oxide films.

The vibratory energy, harnessed by a transducer, converts high-frequency electrical energy into mechanical energy. Ductile metals find unity through this process, enabling the welding of various dissimilar metal combinations. While the weld strength equals the base metal strength, the process is ideal for relatively thin materials, making its mark in the electronics, aerospace, and instrument industries.

Additionally, it weaves its magic in crafting packages, containers, and sealing them with precision and finesse.


Solid state welding is one the many basic types of welding techniques available. Among different welding techniques, solid state is an easier, stronger and less costly technique. I have covered the basics of solid state welding here for beginners. If you have any questions feel free to comment.

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