plastic parts ultrasonic welding

Plastic Parts Assembly Technique- Plastic Parts Ultrasonic Welding

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We have introduced several plastic parts assembly techniques in the last few posts, plastic welding is one of the assembly methods. Among them, ultrasonic welding is one efficient method and revolutionizing the way plastics come together in precision and efficiency. Now let’s start reading the blog and learn what is plastic parts ultrasonic welding and learn the pros and cons of it.

What is Ultrasonic Welding?

Ultrasonic welding is a technique that uses high-frequency vibrations to fuse two plastic parts together seamlessly. Ultrasonic welding transforms high-frequency electrical energy (20-40Hz) into mechanical vibrations. The ultrasonic waves vibrate 10’s of thousands of times per second. These vibrations create frictional heat at the contact point between plastic parts, facilitating their fusion without altering their state—a characteristic termed “solid-state” welding. So, the ultrasonic welding process is also called the solid-state process. Thanks to the controlled heat application, the molecular bond formed retains the original material properties during the welding process. Ultrasonic plastic welding stands out for its efficiency, precision, strength, and preservation of the plastic’s intrinsic characteristics, making it a trusted solution in diverse manufacturing industries. This precision ensures a near-perfect bond, rivaling injection molding in material characteristics.

The Basic Steps of Ultrasonic Welding

1.Parts in Fixture:

Place the two plastic parts to be joined in a fixture, one on top of the other, ensuring accurate alignment.

2.Ultrasonic Horn Contact:

The ultrasonic horn, a vibrating component, makes direct contact with the targeted area on the plastic parts and starts the welding process.

3.Force Applied:

A controlled force is applied, clamping plastic parts together against the fixture.

4.Weld Time:

The welding action begins, with the ultrasonic horn transmitting high-frequency vibrations to the plastic parts. This generates localized heat at the joint, facilitating the fusion process. The ultrasonic horn is vibrated 20kHz or 40kHz times per second for a precise amount of time. this time is called the weld time.

5.Hold Time:

Post-welding, the clamping force is maintained for a designated hold time. This hold time allows the fused plastics to solidify and form a durable bond.

6.Horn Retracts:

At the end of the process, the ultrasonic horn retracts. That means the completion of the welding process. The newly joined plastic components remain securely bonded.

When and Why to Use Ultrasonic Welding?

Ultrasonic welding excels in situations where molding the plastic parts as a single product is impractical. This is common in complex designs or when parts need to be assembled around existing components, as seen in motor housings or enclosures.


Ultrasonic welding simplifies design considerations by negating the need for large flat areas or holes. This technique enables the creation of hermetically tight enclosures without relying on additional fasteners. So the piece count and weight are reduced. Then the time and cost savings.


Ultrasonic welding offers a cleaner alternative to adhesives. It eliminates challenges associated with mixing, storing, and dispensing adhesives, contributing to a more streamlined and environmentally friendly manufacturing process.

Advantages of Ultrasonic Welding

The Process is Fast:

Ultrasonic welding is a high-speed process, that ensures the assembly of plastic parts speed. Under precise pressure, the connection is sealed in less than 0.2 seconds.

Strong and Fully Sealed:

This method creates strong bonds between plastic parts, ensuring structural integrity. The fully sealed nature of the weld enhances the durability and reliability of the assembled components.

Free of Additional Material:

Ultrasonic welding eliminates the need for additional materials like adhesives or fasteners. This not only reduces production costs but also ensures a cleaner and environmentally friendly manufacturing process.

Versatile Plastic Compatibility:

Different types of plastic can be effectively welded together using ultrasonic welding. This versatility allows for the assembly of components with varying material characteristics.

Low Fault Rate and Easy to Operate:

Ultrasonic welding boasts a low fault rate, contributing to consistent and reliable manufacturing outcomes. Additionally, its ease of operation simplifies the overall production process, reducing the likelihood of errors.

Low Production Cost:

The combination of fast assembly, minimal material waste, and the absence of consumables leads to low production costs.

Disadvantages of Ultrasonic Welding

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Plastic Part's Thickness Limitations:

Ultrasonic welding is less suitable for very thick materials. Its effectiveness may diminish with increased thickness, limiting its application in certain scenarios.

High Initial Cost:

The ultrasonic welding equipment can be relatively expensive. This cost factor may be a consideration, especially for smaller-scale operations.

Plastic Parts Size Limitations:

Ultrasonic welding is most effective for smaller to medium-sized plastic parts. The parts’ length is usually less than 250mm.

Material Selection Limitations:

The success of ultrasonic welding depends on the chemical compatibility of the materials being joined.

Other Plastic Parts Assembly Techniques:

Except ultrasonic welding, there are other plastic parts assembly techniques.

Adhesive Bonding:

Using adhesives to bond plastic parts together. This method offers versatility and can join various types of plastics.

Heat Staking:

Heat staking involves localized heating of specific points on the plastic parts, creating a bond through thermal fusion.

Mechanical Fastening:

Traditional methods such as using nuts, bolts, or screws to mechanically fasten plastic components together.

Snap-Fit Assembly:

Designing plastic parts with interlocking features, allows them to snap together without the need for additional fasteners.

Hot Plate Welding:

Hot plate welding involves heating the joining surfaces of plastic parts and then pressing them together to create a bond.

Vibration Welding:

Similar to ultrasonic welding, vibration welding uses frictional heat generated by high-frequency vibrations to join plastic parts.

Spin Welding:

Spin welding involves rotating one of the plastic parts against the other, generating frictional heat and subsequently forming a bond.

RF Welding (Radio Frequency):

RF welding utilizes radio frequency energy to heat and fuse plastic parts through dielectric heating.

Solvent Bonding:

Solvent bonding involves using a chemical solvent to partially dissolve the mating surfaces of plastic parts, creating a molecular bond as the solvent evaporates.


This article presented an understanding of what ultrasonic plastic welding is, how it works, and how it is used in industry. Ultrasonic welding is a speed, precision, and cost-effective plastic parts assembly technique. For more information about manufacturing, consult our other guides or visit the Zhongde website.


Related Reading: plastic parts assembly techniques.

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