When you think of attaching two or more components together, the first thing that may come to mind is a simple screw or a nut and bolt combination. While that can easily work, that is also a way to add cost to a manufacturing process and complexity that may not be needed. There may be a simpler solution available with ultrasonic welding that will reduce complexity and cost while meeting or exceed the durability requirement of the assembly.
What is Ultrasonic Welding?
Ultrasonic welding is an assembly process or technique that uses high-frequency ultrasonic acoustic vibrations in a localized area to create a solid-state weld. The components are held together under pressure in a fixture while the vibrations melt the substrate to create the localized weld area. Ultrasonic welding is commonly used for plastics, and a great option for joining dissimilar materials. For ultrasonic welding there are no fasteners such as bolts or nails, soldering materials, or adhesives necessary to connect the materials together. Other uses for this manner of welding include electronic assemblies, medical devices, and automotive parts.
How Does It Work?
Ultrasonic welding uses frictional heat generated from high-frequency mechanical motion to melt plastics. The motion is generated from electrical energy being converted by an ultrasonic mechanical horn that applies the generated heat and a pressure to melt the plastics and create a molecular mechanical bond between the associated parts.
What is the Process to Do It?
Ultrasonic welding is a simple and quick process. These are the six common steps involved:
Step 1 – Parts nested together and are laid in a fixture that supports the components in their soon to be attached configuration.
Step 2 – The ultrasonic horn made from titanium or aluminum is brought into contact with the top plastic part that will be melted for the connection.
Step 3 – A slight pressure is applied by the horn and the ultrasonic welding is started.
Step 4 – The ultrasonic welding occurs for the set amount of time required by the design. The horn is vibrated vertically between 20,000 (20 kHz) and 40,000 (40 kHz) times per second keeping a slight contact to the plastic being melted. The mechanical motion crates a friction heat high enough to melt the plastic material and the plastic begins to flow in a semi-liquid state. When the functional plastic joint is created molecularly, the welding is stopped to allow the plastic to cool.
Step 5 – While the melted plastic cools to form a mechanical connection between the pieces, the clamping force is kept for a determined amount of time. This ensures the components don’t move during cooling. This time is known as ‘hold time’, and the clamping force can be the same as the force applied during the welding portion of the process or increased as required by the process design.
Step 6 – When the melted plastic has completely cooled and solidified, the clamping force is removed and the horn retracted away from the welded assembly. The assembly can be removed from the fixture and the process started over for the next set of parts.
What Are the Benefits of Ultrasonic Welding?
- This type of welding offers good reliability and durability in the finished assemblies. There’s no need to worry of fasteners being stripped, corrosion, or long-term issues associated with other fastening methods
- There are no consumable items used in the process. No solvents, adhesives, or mechanical fasteners are used, which reduces set-up time, process costs, and cleanliness of your work areas.
- The welding process does not contaminate the final product and leaves a clean assembly that doesn’t require additional work before moving to the next step or the finished product area.
- The welding process is fast and efficient. It’s done in seconds, not minutes, and is easy to maintain.
- The welding process is very repeatable day over day and will allow you to focus on other areas of quality without constantly maintaining unreliable equipment and processes.
- It can be used extensively to add threaded inserts into components which make it flexible for many applications.
Is it Always the Best Process to Use?
While ultrasonic welding has many great applications, one area that it doesn’t do well in is for assemblies that may require disassembly in the future. A process using mechanical fasteners like screws may need to be disassembled. As with other welding, it is meant to be a permanent attachment method. If your product needs to be disassembled for any reason, welding may not be the best choice for mechanical attachment.
If you have questions about what attaching method would be best to use for your product, contact us. We use many fastening methods during assembly, including ultrasonic welding. Our customer and in-house designed and assembled products range from military grade assemblies to the outdoor industry. Our experts can advise you on what may be the best option for your new product idea or how to change your current product to reduce cost, increase productivity, and also increase quality. Just keep in mind that ultrasonic welding should be designed in as the process for maximum durability. Adding it later may require design changes to the parts to make it an efficient and effective attachment method.