Ultrasonic Welding: Types and Applications Explored

Ultrasonic Welding Types and Applications Explored

Types of Ultrasonic Welding

Ultrasonic welding can be classified into two types based on the direction of the transmission of the ultrasonic elastic vibration energy to the workpiece. One type involves the transmission of vibration energy tangentially to the surface of the workpiece, causing relative friction between the welding interfaces as shown in Figure 6-4a, suitable for welding metal materials.

Figure 6-4 Two Types of Ultrasonic Welding
  • a) Tangential Transmission
  • b) Direct Transmission
  • 1 – Concentrator
  • 2 – Upper Sound Pole
  • 3 – Workpiece
  • 4 – Lower Sound Pole
  • F – Direction of Vibration
  • v- Static Pressure

The other type involves the transmission of vibration energy perpendicular to the surface of the workpiece, as shown in Figure 6-4b, primarily used for welding plastic.

Figure 6-5 Schematic Diagram of Ultrasonic Spot Welding
  • 1 – Static Pressure
  • 2 – Upper Sound Pole
  • 3 – Workpiece
  • 4 – Lower Sound Pole
  • V – Direction of Vibration

The joint in ultrasonic welding must be a lap joint. Based on the form of the joint weld, metal ultrasonic welding can be divided into spot welding, seam welding, ring welding, and line welding. In recent years, dual vibration system welding and ultrasonic opposition welding have also been used.

(1) Spot Welding

Spot welding is the most widely used form of ultrasonic welding. During welding, the workpiece is welded under pressure from the cylindrical upper and lower sound poles, completing one weld point at a time.

As per the energy transfer method, spot welding can be divided into single-sided and double-sided types, as shown in Figure 6-5. When ultrasonic vibration energy is transmitted through the upper sound pole only, it is single-sided spot welding.

When ultrasonic energy is transmitted through both the upper and lower sound poles, it is double-sided spot welding. Currently, the most widely used is single-sided spot welding.

Based on the vibration system, spot welding can use the longitudinal vibration system, bending vibration system, or a lightweight bending vibration system in between. Small power spot welding machines under 500W often use a lightweight longitudinal vibration structure, while large power machines over a kilowatt often use a heavy-duty bending vibration system.

The lightweight bending vibration system is suitable for medium and small power welding machines, combining the advantages of the above two vibration systems.

(2) Ring Welding

The ring welding method, as shown in Figure 6-6, is primarily used for one-time forming of sealed welds, with the energy transmission using a torsional vibration system. This type of weld is generally ring-shaped but can also be square, rectangular, or elliptical. The surface of the upper sound pole is made according to the required weld shape.

Figure 6-6 Schematic Diagram of Ultrasonic Ring Welding
  • 1 – Transducer
  • 2 & 3 – Concentrator
  • 4 – Coupling Rod
  • 5 – Upper Sound Pole
  • 6 – Workpiece
  • 7 – Lower Sound Pole
  • F – Static Pressure
  • V – Direction of Vibration

During welding, coupling rod 4 drives the upper sound pole 5 to make a torsional vibration, with the amplitude symmetrically distributed relative to the axis of the sound pole. The amplitude is zero in the core area and maximum at the edges.

This type of welding method is most suitable for the packaging process of microelectronic devices and is sometimes used for linear welds with particularly high air-tightness requirements, replacing seam welding. Because the area of a single ring weld is large and requires a large power input, it is common to use multiple transducers for reverse synchronous driving.

(3) Seam Welding

The workpiece is clamped between the disc-shaped upper and lower sound poles, continuously welded to form partially overlapping weld points, thus forming a continuous seam, as shown in Figure 6-7. Depending on the vibration state of the disc-shaped sound poles, ultrasonic seam welding can be divided into longitudinal vibration, bending vibration, and torsional vibration.

Figure 6-7 Schematic Diagram of Ultrasonic Seam Welding
  • 1 – Disk-shaped Upper Sound Pole
  • 2 – Concentrator
  • 3 – Transducer
  • 4 – Workpiece
  • 5 – Disk-shaped Lower Sound Pole
  • V – Direction of Vibration
  • N – Direction of Rotation
  • I – Ultrasonic Oscillation Current

The most commonly used are longitudinal and bending vibrations, with the direction of the pole vibration perpendicular to the weld direction. In actual production, the bending vibration system, which has better process performance, is most widely used.

(4) Line Welding

Figure 6-8 illustrates the schematic diagram of ultrasonic line welding. Line welding uses a linear upper sound pole or multiple spot-welding sound poles stacked together to form a straight seam within one welding cycle, which can be seen as an extension of spot welding.

Now, using the ultrasonic line welding method, it is possible to obtain a linear seam approximately 150mm long with a single linear upper sound pole, which is suitable for linear sealing of metal foils.

Figure 6-8 Schematic Diagram of Ultrasonic Line Welding
  • 1 – Transducer
  • 2 – Concentrator
  • 3 – Welding Sound Pole Head (Length 125mm)
  • 4 – Center Axis
  • V – Direction of Vibration
  • F – Static Pressure

In addition to the above four common metal ultrasonic welding methods, a plastic ultrasonic welding method has been developed in recent years. The working principle is different from that of metal ultrasonic welding, as the vibration direction of the sound pole during plastic ultrasonic welding is perpendicular to the workpiece surface and consistent with the direction of the static pressure.

In this case, heat is not conducted through the workpiece surface, but is directly converted from mechanical vibration into thermal energy at the contact surface of the workpiece, resulting in a melting weld. Therefore, this method is only suitable for welding thermoplastic plastics and cannot be used for welding thermosetting plastics.

Scope of Application of Ultrasonic Welding

Due to its unique technical advantages, ultrasonic welding is now widely used in the following fields:

(1) Electronics Industry

It is mainly used for the welding of microelectronic devices, integrated circuit components, and transistor cores. For example, on a 1mm2 silicon chip, hundreds of aluminum or gold wires with diameters of 25~50μm are interconnected at the weld point via ultrasonic welding. The quality of the interconnection is key in the manufacturing process of integrated circuits.

Microcircuits and other electronic components can effectively be sealed using ultrasonic ring welding, such as the sturdy welding of transistor and diode casings, without contaminating the clean internal parts.

In the manufacture of lithium batteries, the connection between the metal lithium sheet and the stainless steel base has always relied on the fit between the wire mesh and the lithium sheet. The joint quality is unreliable and the resistance is large. Using ultrasonic welding, the lithium sheet can be directly welded to the stainless steel base, not only improving the joint quality but also greatly enhancing productivity.

(2) Electrical Industry

Ultrasonic waves can effectively weld low-resistance joints without contaminating or thermally deforming the parts. Both single and multi-strand wires can be interconnected or welded to terminals using ultrasonic welding, such as the commutator and coils in micro motors, the ground screens in ultra-high voltage transformer shielding components, and the welding of various capacitor leads.

Thermocouple joints made from many different metals also often use ultrasonic welding for connection. Ultrasonic adhesive spot welding has been successfully applied in the shielding components of 500,000V ultra-high voltage transformers manufactured in our country. This technology combines the many advantages of ultrasonic solid-phase connections and the high strength of metal adhesion.

Characterized by “adhesive first, welding second,” this method offers high conductivity, reliability, and corrosion resistance, effectively preventing the risk of tip discharge. It has replaced the internationally common brazing and riveting processes in the manufacture of 500,000V ultra-high voltage transformers.

The welding of various thermocouples in automotive electrical systems is an important application achievement in recent years. In the production of tantalum or aluminum electrolytic capacitors, the ultrasonic spot welding method is used to weld the leads. The welding yield rate has increased from the original 75% to nearly 100%.

(3) Packaging Industry

Ultrasonic welding is widely used in the packaging industry, from small foil packages to sealed cans. Ultrasonic ring welding, seam welding, and line welding can realize airtight structural packaging. Such as the sealed packaging of aluminum cans and extrusion cans, sterile packaging of food, drugs, and medical devices, as well as packaging of precision instrument components and detonators.

(4) Aerospace and Nuclear Industries

The components of aluminum and stainless steel in the nuclear power conversion devices of spacecraft, the grounding wires of missiles, and the glass windows on satellites all use ultrasonic welding. Ultrasonic welding technology is also used in the repair of helicopter channels and the manufacturing of solar cells for satellites.

(5) Plastics Industry

A large number of engineering plastics are widely used in the manufacture of instrument frames, panels, connectors, relays, switches, and plastic housings in the mechanical and electronic industries. These components all need to use ultrasonic plastic welding processes. In addition, ultrasonic welding can also be used for the connection of metal and plastic and the “sewing” of polyester fabrics.

(6) Other Applications

Ultrasonic welding can weld two materials with vastly different physical properties and make many bimetallic joints, such as connecting metal foils and wires to the thermal spray surfaces of glass, ceramics, or silicon chips; connections between superconducting materials and conductive materials can also use ultrasonic welding.

In the 1990s, with new breakthroughs in the tube industry, ultrasonic welding has been widely used in aluminum-plastic composite pipes in water pipes, gas pipes, and electricity. Ultrasonic welding, as the main welding method for aluminum-plastic composite pipes, is widely used in production.

Using the ultrasonic welding method, two materials with vastly different physical properties can be welded and many bimetallic joints can be made. Some bimetallic welding joints suitable for industry are shown in Table 6-1.

Table 6-1 Bimetallic (A+B) joints suitable for ultrasonic welding

Material AMaterial B
Aluminum and certain aluminum alloysCopper, Germanium, Gold, Nickel-Diamond Alloy, Molybdenum, Nickel, Platinum, Steel, Zirconium, Beryllium, Iron, Stainless Steel, Nickel-Chrome Alloy
CopperGold, Nickel Alloy, Nickel-Diamond Alloy, Nickel, Platinum, Steel, Zirconium
GoldGermanium, Nickel Alloy, Nickel-Diamond Alloy, Nickel, Platinum, Silicon
SteelAluminum, Zirconium
NickelNickel Alloy, Nickel-Diamond Alloy, Molybdenum

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