Solid-state welding (SSW) is a process in which the materials are joined without fusion of the base metals. Bonding occurs by atomic diffusion caused by pressure, temperature, or both, typically below the melting point. It eliminates several defects inherent with fusion welding and has applications in dissimilar metals and precision requirements.

Capabilities

Advantages: No melting, minimal distortion, strong dissimilar metal bonding, no filler required.

Disadvantages: High equipment cost, complex setup, material and geometry limitations.

Applications: Aerospace panels, heat exchangers, battery terminals, dissimilar metal joints.

Process Cycle

• Surface cleaning and preparation
• Pressure application (mechanical or ultrasonic)
• Localized optional heating (below the melting point)
• Material plastic deformation and diffusion
• Inspection and cooling later

Equipment

• Friction welding equipment (linear or rotary)
• Ultrasonic welding equipment
• Diffusion bonding furnaces
• Roll bonding and explosive welding equipment
• Pressure regulators and force actuators

Tooling

Primary:

• Pressure anvils and dies
• Precision alignment fixtures

Secondary:

• Vibration horns (ultrasonic)
• Heat shields and backing plates
• Force/load monitoring sensors

Materials

Possible Defects

• Incomplete bonding or cold welds
• Flash formation (in friction welding)
• Material expulsion
• Inclusions in the joint interface

Design Rules

• Form parallel and clean joint surfaces
• Utilize symmetrical joints and constant cross-sections
• Utilize force-applying geometries for uniform pressure distribution
• Have thermal and mechanical compatibility in dissimilar joints
• Design fixtures for repeatability and uniform alignment

Cost Drivers

• Type of equipment (ultrasonic vs. friction stir)
• Geometry and complexity of joint geometry and alignment
• Size of workpiece and surface preparation
• Energy and cycle time per weld
• Number of setups and tool changeovers

Solid-state welding produces high joint integrity with minimal thermal distortion, thus becoming an attractive process for electronics, automotive, and aerospace industries' high-technology manufacturing.