As every product developer knows, there are no hard and fast guidelines to determine the right welding or sealing process for a particular polymer or product design. Techniques such as hot air and hot wedge welding, radio frequency (RF) welding, and ultrasonic welding each offer specific advantages for different types of plastics sealing applications.
And the decision to use a particular welding method – or combination of methods – depends on many variables, from the product’s overall size, design, and functionality to the precise weld lengths and thicknesses.
The choice of welding method also depends heavily on the materials being joined. Carefully aligning the physical properties of a specific material with the appropriate welding technique is critical to achieving durable, high quality seals and successful finished products.
This is especially true when working with specialized thermoplastic materials, such as spunbond fabrics, breathable films, and glass-filled plastics. Increasingly popular in the medical, automotive, and personal care markets, these advanced materials can be easily damaged by excess heat or pressure during the welding process. They may also present unusual structural characteristics, such as air gaps, that make them incompatible with common welding methods.
Fortunately, impulse welding offers fabricators a simple but powerful option for joining challenging materials – as well as a wide range of conventional thermoplastics. Here’s a quick look at what makes impulse welding such a versatile sealing alternative.
1. It’s fast.
Impulse welding is a form of thermal contact welding that delivers momentary impulses of heat to thin layers of material, then allows them to cool quickly under pressure. Heating, fusion, and cooling occur in as little as 10 seconds, all under the same forming tool.
How it works. There are two key components to an impulse welder: an upper platen containing thin brass tooling and a lower bed constructed from heat resistant silicone. Electrical current is transmitted in short bursts through the bands which are mounted to the underside of the platen, generating enough heat to melt the layers of materials, which are cushioned from below by the flexible silicone bed. The thin bands of tooling heat and cool rapidly as the current is switched on and off. This eliminates the risk of overheating and prevents delicate materials from being damaged or deformed during the sealing process.
2. It’s flexible.
Versatility is one of the most valuable aspects of impulse welding. It is compatible with virtually all thin (0.5mm or less) thermoplastic polymers with a melt index below 680°F – a list that encompasses many common amorphous and crystalline polymers as well as specialty films and materials.
Materials Compatible with Impulse Welding
|Amorphous Polymers||Acetal, Acrylic, Acrylonitrile butadiene (ABS), ABS/polycarbonate alloy, Polycarbonate (PC), Polystyrene (PS), Polyvinyl chloride (PVC)|
|Semi-Crystalline Polymers||Acetal, Polyamide (PA), Polyester, Polyethylene (PE), Polyethylene terephthalate (PET), Polyphenyl sulfide (PPS), Polyphthalamide (PPA), Liquid crystal polymers (LCP)|
|Specialty Films||Spunbond nonwoven polymeric fabrics, breathable films, glass-filled polymers|
And unlike welding techniques that can only join identical or similar materials, impulse welding can be used to join two or more dissimilar layers. This is a significant advantage when fabricating products that combine layers that serve multiple functional roles, such as watertight seals and oxygen barriers.
Just as importantly, impulse welding can be used in multiple types of sealing operations, from long, straight welds to a variety of three-dimensional fitments and closures.
Seam welding. Depending on the type and specifications of the impulse welder, lengths from 5 cm to 730 cm can be joined in a single step.
Heat staking. Allows staking of plastic bosses of various sizes without excess heat or pressure that can damage sensitive electronics and other components.
Heat swaging. Provides precise application of heat and pressure to securely attach components in product assemblies.
3. It’s precise. Impulse welding provides remarkably accurate control when working with thin plastic materials and films. Unlike other forms of thermal sealing, the application of heat can be started and stopped instantly. The flow of energy is completely horizontal: with each pulse of electricity, heat moves quickly into and through the thin copper tooling bands, then dissipates immediately when the electricity is stopped. This allows heating and cooling cycles to be precisely controlled, and produces consistent, high quality welds. And because impulse sealing works without the need for heavy pressure during welding, there are no tooling marks or other imperfections on the finished surfaces of the parts being welded.
4. It’s efficient. Because it releases heat only during the actual welding process, impulse welding saves both production time and energy consumption. It eliminates warmup and waiting periods typical with other forms of contact welding. There is also no need to keep the heating bar on when the welder is not in use, which saves energy and reduces the risks of accidental injury. Specific cycle times and amounts of electrical current can be closely fine-tuned to meet the needs of the materials, product design, and production pace.
Naturally, there are some limitations to impulse welding. Product configurations with sharp 90-degree corners, for example, are difficult to achieve with impulse sealing and are more compatible with other techniques, such as RF welding. Thicker polymer sheets and films may also present challenges that are best addressed with more robust thermal contact methods – hot air or hot wedge welding, for example.
But for a surprisingly broad range of applications, impulse welding offers a unique combination of speed, accuracy, cost-efficiency, and consistency. It is already a familiar option for many types of sealing, pouch closing, web splicing, fitment attachments, and other polymer welding processes. And as the demand for specialized films and applications continues to grow, impulse welding is poised to take on an even more prominent role – as fabricators seek more precise, material-friendly sealing methods to meet the demands of today’s breathable, lightweight, and disposable product designs.