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What is Ultrasonic Plastic Welding?

Ultrasonic plastic welding is a fast and efficient technique used to seal hermetic seals fast without compromising quality, ideal for packaging, medical devices and other specialized applications requiring high quality seals. It has become increasingly popular as more manufacturing operations use ultrasonic welding for production without sacrificing quality seals.

Ultrasonic welding machines and equipment offer manufacturers fully automated solutions that create reliable seals without consumables, meeting environmental goals while increasing recyclability, decreasing packaging material use and eliminating chemicals adhesives and solvents.

How Does Ultrasonic Plastic Welding Work?

Ultrasonic Plastic Welding Components

Below is a brief listing of components commonly found in ultrasonic plastic welders:

Power Supply Unit - The power supply unit (PSU) supplies electricity to welding machines at a predetermined voltage; typically between 110-240 V. This voltage may differ depending on your application, however.

Pneumatic Piston/Press - The pneumatic piston/press pushes down on a stack consisting of transducer/converter, booster and horn to ensure plastic parts mate together properly and reach temperatures suitable for welding. While similar to traditional pneumatic presses, this component only exerts enough pressure for welding to occur successfully.

Transducer/Converter - Although sometimes split into two separate parts, the transducer/converter is responsible for turning electrical energy into mechanical vibrations. Inside it lie several piezoelectric plates that respond to electrical signals by expanding or contracting in response to piezoelectricity signals from sinusoidal AC current; when sinusoidal AC current is applied to it, these piezoelectric plates expand or contract at high frequencies producing mechanical vibrations necessary for ultrasonic welders (typical output frequency 15-40kHz though exact details vary based on materials being utilised).

Booster - While welding signals generated are of high frequency, output vibrations from transducer must be amplified for welding to take place--hence the need for a booster. Like its name suggests, this component resonates at specific frequencies to amp up signals to the horn in order to cause sufficient welding activity. Furthermore, this part serves as the connector between stack subassembly and welding press.

Horn - Welding horns are tuned components designed to add mechanical gain to vibration signals, creating mechanical gain for vibration machines. Being one of the most stressed components, welding horns must be constructed of durable materials like titanium or aluminum and designed so they transfer vibrations effectively without cracking - this may include features like axial slotting, hardened tips or contoured tips that contour to each part for maximum energy transfer.

Anvil - An anvil is part of the support tooling used for welding operations, to keep parts fitting together properly during welds. Like its counterpart the horn, an anvil often features low tolerance contours which prevent movement during operation and serve to keep parts secure against movement during welding operations.

Application for Ultrasonic Welding

This technology has many applications across industries, particularly for components that are small, delicate, or complex:

Electrical and Computer Components: microcircuits, computer disks, flash drives, wired connections, field coils, capacitors.

Automotive and Aerospace: instrument panels, steering wheels, air ducts, interior door panels, engine components.

Medical: blood/gas filters, dialysis tubing, cardiometry reservoirs, IV catheters and filters, heart sensors for bypass patients, even textiles such as hospital gowns, face masks, and other sterile garments

Packaging: blister packs, wrappers for items such as candy bars, frozen food packages, containers for beverages such as milk or juice, containers for hazardous or heat-sensitive materials such as ammunition or fireworks

Consumer Goods: toys, tools, butane lighters

Ultrasonic Welding Part Design

When employing ultrasonic welding in assembly plastic parts, they must be designed appropriately - taking into account both materials and joint designs.

Explore common materials and their effectiveness across ultrasonic welding applications with this free guide.

Material Considerations

Ultrasonic welding works best on thermoplastic materials that soften gradually over a wide temperature range. These include thermoplastic amorphous structures with melting behavior characterized by their "glass transition temperature", or Tg.

Polyphenylene oxide (PPO) and acrylonitrile butadiene styrene (ABS) plastics are some of the easiest materials to weld ultrasonically, while polyvinyl chloride (PVC), cellulose acetate (CA/B/P), and polyolefin materials can prove more difficult due to their semi-crystalline structures.

Dissimilar Plastics 

Joining plastic parts together is usually easier when they come from one material, while assemblies utilizing parts made of different properties of plastic may present unique challenges. While semi-crystalline plastics may only be joined directly together during assembly.

Assessing the weldability of disparate thermoplastic materials requires taking into account three key criteria - Tg, chemical compatibility and melt flow index (MFI).

As a general guideline, Tg of two dissimilar plastics should fall within 40degF in order to fuse effectively.

Chemical compatibility is a complex topic, with values similar among materials being indicators of compatibility.

Melt Flow Index (MFI) measures how easily plastic flows as it transitions from its solid state into liquid state. You can find an MFI value for any material in its manufacturer literature; in order to achieve maximum effectiveness when joining plastics together they should all possess similar MFI's.

Ultrasonic Weld Joint Design

When performing ultrasonic welding, it's crucial that energy be focused in as few areas as possible - this means including an "energy director" into your plastic design for ultrasonic welding.

An energy director is a raised region with a triangular cross-section. When applied with ultrasonic energy, its triangle tip presses against mating plastic parts while friction causes local temperature rise quickly; eventually reaching Tg melting temperature for plastic components to join together.

Energy director designs are employed in most ultrasonic welding plastic part designs, except when dealing with semi-crystalline plastics that feature narrow glass transition temperatures and tend to move rapidly into liquid form compared to their amorphous counterparts. To address this, parts designed using semi-crystalline materials feature shear joints - formed when opposing parts are pushed together side walls colliding - in order to address this.

Common Types of Energy Director Designs 

The main types of energy director designs are as follows:

1. Butt Joint: This joint features one flat surface while another has an irregular triangle shape, with as sharp of an edge as possible to maximize energy transfer and transference.

2. Step Joint: Its This mating surface features a stepped design to restrict lateral movement while the triangle point presses against a flat surface (this simplifies part location during assembly). 

3 Tongue and Groove Joint: Energy directors feature raised tongues that fit snugly into grooves in the mating part for accurate alignment and reduced flash.

4. Criss-Cross: Both surfaces feature energy directors aligned perpendicularly to one another for stronger welds but may create too much flash. For an airtight seal, configure crossing energy directors as sawtooths.

5. Textured Surface: Texturing non-energy-director surfaces is an effective way of increasing weld strength.

6. Perpendicular: In this design, energy directors run perpendicular to joint faces rather than in parallel - this reduces flashback.

7. Interrupted: Here energy directors are kept short to reduce energy requirements for weld production. 

8. Chisel: A variation on a step joint that involves placing the energy director along a wall to enable welding of thinner sections.

Additional Considerations

There are other considerations when using materials, particularly polyamide (nylon) and to a lesser extent polycarbonate, that are hygroscopic; meaning they will absorb moisture from the air. Since water can easily change phase transition energy to steam at 100C with considerable phase change energy and polyamide and polycarbonate melt at higher temperatures, any heat energy produced in joint details containing trapped water may absorb all available heat until it can escape through flash to steam, often leaving behind a joint detail pounded down by clamp force but never warm enough for melting or welding. If a joint does heat up enough to flash water into steam, there will be an explosion within it due to steam taking up significantly more volume than water (this is how steam locomotives work). Such joints typically appear foamy and fragile, lacking strength or any hermetic seal to provide strength or seal protection. Assuming a part dry enough for molding is also dry enough for welding, in moderate- to high-humidity environments parts should either be immediately welded while still warm, or sealed into bags with desiccant packs and not opened until ready to enter the welder.

There are various combinations of dissimilar materials that can be ultrasonically welded together successfully using ultrasonic welding technology, but for this to occur they must possess chemical affinity with one another. Imagine an ultrasonically welding frozen motor oil to frozen ice - an impossibility in itself, since most semi-crystalline materials only can be joined via ultrasonic welding processes. Few amorphous materials possess chemical affinity with multiple materials; only few materials meet this criteria. Furthermore, both materials must possess similar melt index numbers and melt temperatures for successful ultrasonic welding to occur. It's best to consult an expert and conduct exhaustive experiments before committing to products requiring ultrasonic welding of dissimilar materials.

What Ultrasonic Welding Can Provide That Other Processes Can't

Ultrasonic welding offers several key advantages over other forms of welding:

1. It saves time. Ultrasonic welding is significantly quicker than traditional methods, with virtually no drying or curing time necessary compared to conventional ones. Furthermore, being highly automated reduces manpower costs while getting you parts sooner.

2. It reduces production costs. This process joins materials without needing glue, adhesives or fasteners such as screws. In addition, its low energy consumption ensures lower costs for your business and reduced production costs are the result.

3. It creates high-quality bonds and tight seals without using filler materials or excessive heat, eliminating potential for the introduction of contaminants or thermal distortion, creating no visible seams where parts were joined, creating a visually pleasing finish, producing durable bonds superior to many other methods for joining components, with its reliable sealing making ultrasonic welding particularly ideal for food packaging and medical products.

Why choose Dizo?

We specialize in plastic welding technology and customer-centric solutions tailored specifically to each application of each customer. Customers who know exactly what they require can count on us to listen, understand, and deliver quality products that fulfill those specifications. Customers looking to start from the ground up benefit from our consulting relationship; drawing upon 15 years of experience to craft cutting-edge solutions to even the most demanding welding needs. We have provided time tested technological breakthroughs in several industries; taking each project as an opportunity to develop our sense of innovation while keeping customer relationships at the core of everything we do.

Top-notch Ultrasonic Welding Machine at Affordable Price

At our organization, we specialize in manufacturing, exporting and supplying top-grade Ultrasonic Welding Machine at competitive prices. These units are made of top quality raw material in accordance with international quality standards for optimal results and durability. Furthermore, each piece undergoes stringent quality assurance checks by our quality inspectors for additional assurance of quality and longevity before being made available at highly affordable prices.

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