Sonic Welding

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Bonding Plastic Parts with Ultrasonic Welding

Many companies find they need to take two (or more) different injection molded plastic parts and join them together into a single assembly. Global Plastics offers a value-added assembly service to meet these customer client needs. One of the primary methods for bonding plastic parts together is the ultrasonic welding process (also called sonic welding). It uses carefully calibrated high-frequency sound vibration energy to create a strong bond between two plastic pieces of similar materials.
Sonic Welder

Parameters for Ultrasonic Welding

For ultrasonic welding to be a viable option to bond plastic parts together, both must be made from thermoplastic materials. They don’t have to be the exact same materials, but the key characteristic they need to share is having a similar melting point that falls within a tight range. The result of well-executed sonic welding is an incredibly strong bond between the two plastic parts. Many plastic injection molding service providers don’t offer ultrasonic welding. Those that do might also lack the deep expertise and state-of-the-art equipment Global Plastics utilizes to ensure the job is done right with this post-production assembly service.
Canister assemblies
Good Vibrations: How Ultrasonic Welding Works
The process of ultrasonic welding uses the energy generated by high-frequency sound vibration. The first all-plastic car was assembled using ultrasonic welding, and although plastic cars didn’t catch on, ultrasonic welding did. It can be used on both hard plastics and soft plastics. The “horn” (a sonotrode, often made of titanium) emits acoustic vibration energy ranging from 15 kHz to 70 kHz (depending on the materials being welded), sending the energy through the parts to focus on the precise desired melting location. At that location, the surfaces of the two plastic parts melt and fuse together, forming a solid bond. This mechanical process of the precision application of heat and pressure produces an especially strong bond between plastic parts. Interestingly, the horn only makes physical contact with one of the parts.
The Advantages of Ultrasonic Welding
With continual advances in ultrasonic welding techniques and equipment, it has never been easier or more economical to assemble two different plastic parts into one. The advantages include forming an incredibly strong bond without the use of bolts, nails, adhesive, soldering, or other kind of fastener for joining items together. Another advantage is the speed factor. Ultrasonic welding has much faster dry times than any conventional solvent or adhesive. With no long wait times for joints to cure or dry, along with automation of the process, greater efficiency saves both time and money over other conventional assembly methods. Ultrasonic welding is a very clean process, which makes it an especially good assembly technique for plastic parts in medical devices, medical equipment, and medical applications where a hermetic seal is needed.
Chemical Compatibility for Ultrasonic Welding
The goal of the sonic welding process is for the two plastic pieces to form a molecular bond for strength and durability. This can only be achieved if the two thermoplastic materials share chemical compatibility. For example, although polyethylene and polypropylene seem very similar, they are not chemically compatible and cannot be welded together. ABS to ABS parts will be compatible, ABS and acrylic parts are often compatible, and so on.

In addition to chemical compatibility, the two thermoplastic materials to be joined must have melting points within 40ºF (6ºC) of each other. They must also be of molecular structure. While similar amorphous polymers have a high probability for being welded together, most semi-crystalline materials are only compatible with themselves.

Additional factors beyond chemical compatibility that can affect weldability include hygroscopicity, mold release agents, lubricants, plasticizers, fillers, flame retardants, regrind, pigments, and resin grades. Global plastics is deeply familiar with all these compatibility and other factors related to ultrasonic welding.

Join Design for Ultrasonic Welding
In addition to material compatibility, joint design is critical for achieving the best assembly results. Factors here include the type of plastic, part geometry, and weld requirements. All kinds of joint designs are possible, but the basics that need to be covered by any joint design for ultrasonic welding are 1) a uniform contact area (mating surfaces in intimate contact around the entire join), 2) a small initial contact area (minimizing this area means less energy required, saving time and money), and 3) a means of alignment so the parts don’t become misaligned during welding (alignment is achieved by incorporating features such as pins, sockets, channels, and tongues into the part design, not by using the horn for alignment).
Global Plastics Ultrasonic Welding Equipment
sonic welding station with nest and horn 3

We’ve invested in state-of-the-art ultrasonic welding equipment to best serve your assembly needs. Our equipment is manufactured by the world’s leading plastic welding equipment manufacturer that has been innovating in the industry for many decades. A big part of what we appreciate about their ultrasonic assembly systems is how the tooling and/or application can be quickly changed, thereby offering flexibility and versatility other assembly processes or systems simply can’t match.

The ultrasonic welders also feature high reliability, long life, and consistent, repeatable performance, which helps keep production costs lower for customers. Ultrasonic assembly is now routinely used in a wide range of industries, including the automotive, medical, electrical and electronics, communications, appliance, consumer products, toys, textile, and packaging industries.

Value-Added Ultrasonic Welding for Assembly at Global Plastics

Because sonic welding is now such an economical process, our customer clients enjoy how it can significantly increase production while at the same time lowering assembly costs. Our Dukane ultrasonic welders can be easily integrated into our automation-driven manufacturing environment, and the equipment provides unprecedented repeatability, reliability, and accuracy to the process. If the ultrasonic welding capabilities at Global Plastics are of interest to your company, we invite you to get in touch through the contact us page of our website. We look forward to discussing your needs and offering the solutions you require.

In-house secondary operations at Global Plastics such as ultrasonic welding and hot plate welding to save you time and money.
Enhance your plastic parts as needed at Global Plastics with in-house laser etching, pad printing, hot stamping, and labeling.
Money-saving secondary operations offered in-house include post-shot machining, degating, leak testing, assembly, and kitting.