Guide to Thermoplastic Welding

Over the past several decades, thermoplastics have become increasingly popular across industries. Thermoplastic welding allows manufacturers to create complex, intricate joints in thermoplastic components with durable molecular bonds that are more reliable and effective than more traditional mechanical fasteners and adhesives. Welded components can be joined into a single product quickly and efficiently, creating a long-lived weld that is both strong and dependable.

At Plastic Design, Inc., we provide reliable, innovative plastic material solutions for our customers in various critical industries, including medical and biomedical devices, pharmaceutical process equipment, microelectronics, and photonics. Using only the latest in automated technology, we design and manufacture complex and specialty components and products that meet even the most stringent industry standards. We have the knowledge and equipment necessary to complete projects in a timely and highly cost-effective manner.

What are Thermoplastics?

Thermoplastics are synthetic plastics that can be melted, shaped, and cooled to form specific design shapes. Thermoplastics can undergo repeated melting and cooling processes, whereas thermoset plastics only set once and burn when exposed to heat after setting. Many thermoplastics are available on the market, each with unique features that make it useful for particular products and applications. Some of the most popular thermoplastics include:

Polyethylene (PE)

A lightweight ethylene polymer resin, polyethylene has a variable crystalline structure that makes it highly versatile. It is inexpensive, chemical resistant, and available in high- and low-density formulations for use in everything from medical implements to plastic bags.

Polypropylene (PP)

Multiple propylene monomers combine to create polypropylene, a rigid and inflexible semicrystalline thermoplastic that is ideal for packaging, medical implements, and low-friction components.

Polyvinyl chloride (PVC)

Designers and manufacturers value PVC for its chemical resistance and toughness. This polymerized synthetic resin made from vinyl chloride sees frequent use in pipes and fixtures, construction supplies, medical devices, electronics, and automotive components.

Polystyrene (PS)

Polystyrene is a synthetic polymer composed of styrene monomers and available in foam and solid forms. Solid polystyrene is transparent and hard, often used in food and pharmaceutical packaging, medical equipment, and laboratory equipment.


Acrylic is a lightweight, highly transparent thermoplastic often used as a more durable alternative to glass in industrial, medical, retail, and other applications.


Nylon is a smooth thermoplastic composed of synthetic polyamide polymers. This highly versatile material creates threads, fabrics, ropes, and solid shapes.

Plastic Welding Techniques

Thermoplastics feature compatibility with various heat treatments, and a variety of plastic welding techniques harness this quality. Some of the most common thermoplastic welding techniques include:

Friction welding

Friction welding generates heat by rubbing two parts together at a specific speed. Friction-generated heat melts both parts’ edges, and pressure holds them together until they solidify into a single joined part.

Extruded-bead seal welding (extrusion welding)

Extrusion welding is ideal for large and thick components that require a longer weld. A welding rod softens the plastic in an extruder. The extruder forces the softened plastic onto the parts being joined, which have also been softened using hot air jets. The extruded plastic bonds to the softened surfaces, creating a strong bond.

High-frequency welding

High-frequency welding uses high-frequency electromagnetic waves to generate heat within specific polymers. The process is highly localized and facilitates long, continuous welds between parts without added material.

Hot plate welding

Hot plate welding — also known as hot tool welding — incorporates heated tools shaped to match the joints of the component parts. The heated plates (tools) are applied to the ends of the parts to be welded. Once melted, the ends get pressed together until the joint cools and creates a bond.

Hot gas welding

Hot gas welding – also called hot air welding — features a welder with a plastic filler rod. The welder emits a hot jet of air or gas to soften both the filler material and the surfaces being joined together. The plastic filler material must be similar to or the same as the component material to create a sufficient bond.

Laser welding

Laser welding uses a laser to heat the material between the components, causing them to melt and join along the welding line. For this method to be effective, one component must be transmissive and the other absorptive so the laser can pass through the transmissive component and reach the absorptive part at the desired joining point.

Induction welding

Injunction welding uses an electromagnetic current to heat and melt plastics with embedded carbon fiber, metal, or other conductive materials. This process is particularly useful for reinforced materials used in the aerospace industry.

Solvent welding

Solvent welding uses specialized solvent chemicals to dissolve the thermoplastic material, allowing the polymer chains from both components to combine with each other and create a solid bond.

Ultrasonic welding

Ultrasonic welding uses high-frequency vibrations to generate friction heat between the component parts. This extremely fast welding technique can be used with almost any thermoplastic.

Spin welding

Similar to friction welding, spin welding uses friction generated by one component spinning against a stationary component. Once the material between the two has melted, the spinning component is stopped and held against the stationary component until the plastic has cooled, forming a solid bond.

Benefits of Plastic Welding

Plastic welding offers numerous benefits over other bonding techniques, including:

  • Cost-effective. Plastic welding does not require extra solvents, uses very little energy, and cycles quickly for increased productivity and lower overhead costs per unit.
  • Fast and clean. Plastic welding does not present a weld flash, making it an extremely safe, quick, and easy process. The end product presents a clean appearance, with nearly invisible or seamless lines.
  • Highly versatile. Plastic welding can be used on components of almost any size, shape, and configuration, and completes high- or low-volume orders with speed and precision.
  • Permanent. Plastic welding creates a permanent molecular bond between the welded components for a highly dependable joint.
  • Works with almost all thermoplastics. Plastic welding can be used on almost any thermoplastic polymer, even most thermally-sensitive plastics.

Quality Plastic Welding by Plastic Design, Inc.

At Plastic Design, Inc., we are dedicated to providing our customers with the highest quality thermoplastic welding services in the industry. With more than 40 years of experience in the design and fabrication of specialty plastic components for critical industries, we understand that every project has unique requirements. Whether you need plastic prototypes for a new medical device or a full production run for a custom automotive component, Plastic Design, Inc., has the knowledge, skills, and equipment necessary to produce components quickly and efficiently within your budget. In addition to state-of-the-art welding services, our 30,000-square-foot IPCA 620 and ISO 9001:2015-certified facility features CNC machining that allows us to provide a variety of milling, drilling, and boring services.

To learn more about our comprehensive thermoplastic welding and fabrication services, contact our experts today or request a quote.

Plastic Design, Inc. COVID-19 Efforts Highlighted by Bentley University

Daryl Flynn, President of Plastic Design, Inc., was recently highlighted in an article by his alma mater, Bentley University, for the company’s efforts in supplying medical frontline workers with personal protective equipment (PPE). Read an excerpt below:

Unlike other alumni who are running into production roadblocks due to a lack of materials amid the pandemic, Daryl Flynn ’93, co-president of Plastic Design, Inc. is lacking people. Namely, workers at his custom plastic fabrications company in Chelmsford, Mass. When we spoke, Flynn was overseeing a limited staff of 13 — far lower than the usual 40 on the factory floor.

“It’s fear,” he says. Pick a crisis: fear of the virus, fear of spreading the virus. “You can’t manage fear,” he adds. “That’s something they really don’t teach you.” However, Flynn himself isn’t afraid. “I’m a realist,” he explains. “I look at the numbers. I wash my hands. It’s contagious, but I’ll take my chances.”

Because what’s on the line are nine-inch face shields — thousands of them. A plastic line of defense far surpassing any cloth mask an essential worker can find on Etsy.

Flynn’s parents bought Plastic Design, Inc. in the mid-’80s. At 19, Flynn started working at the company, and joined up full-time after graduating from Bentley in 1993, as did his brother Kurt ’95, two years later. Since then, the duo has kept the family business in stride with the times, evolving from custom display cabinets to biomedical products and even casino tables. If you’re playing roulette at Foxwoods, chances are you’re sitting at a table made by the Flynn brothers.

When COVID-19 struck, Flynn answered the call of a friend: an anesthesiologist looking for safety glasses. “I had some extra material lying around, so I asked him if I could make a face shield instead,” Flynn says. He went into work the next day and mocked up a design using existing materials from a project he had done for the U.S. Navy — plastic shields used to encase wires on the ships. “He said it was great.”

To read the rest of article, go to Bentley University.

Plastic Machining Guide

Machining is an umbrella term for the controlled, subtractive manufacturing techniques used to produce parts made from a wide range of materials. Today, many companies employ computer numerical control (CNC) machining to achieve greater precision and accuracy in their end products.

When deciding on a machining method for a part, it is essential to keep in mind the design and construction material as these factors significantly impact the production process and final result. For plastic machining projects, these considerations are especially important due to the greater susceptibility of plastic materials to warping, cracking, and deformation when improperly handled. Further exacerbating the problem is the broad selection of plastics and plastic composites available, with each type exhibiting its own properties and best use cases. Altogether, these challenges necessitate partnering with a supplier who demonstrates a deep understanding of your chosen material.

With over 40 years of experience in plastic fabrication, Plastic Design, Inc. has the knowledge and skills necessary to take on any plastic machining challenge. Equipped with state-of-the-art CNC machining equipment, our expert team has the means to perform several different types of machining processes on a variety of industrial plastics to execute the optimal manufacturing plan for every product.


An Overview of Plastic Machining Services

plastic machiningLike all machining processes, plastic machining is a subtractive method that removes layers of material to shape and form the end part or product. Some of the most common machining operations employed for plastic materials are:


Generally, cutting operations generate some amount of heat, which can damage the plastic material. When cutting plastics, operators must take care to avoid causing thermal warping. With proper precautions, sawing is completely appropriate for cutting plastic sheets to a desired size and shape.


Plastic turning operations occur on a lathe, which rotates and manipulates the workpiece to allow the stationary cutting tool to cut and remove excess material as per the intended design.


While turning operations involve the rotation of the plastic workpiece, milling operations require the rotation of the cutting tool to remove chips of plastic from the stationary workpiece. Some milling techniques work better with plastics than others (such as down-milling), but the ideal choice depends on a number of factors.


Drilling plastics can be risky, resulting in overheating or shearing if the proper drill isn’t selected. However, given the proper preparation and tools, a skilled technician can create both small and large diameter holes in a plastic product without damaging its structure.


Grinding is similar to milling in that the process removes chips of plastic from the workpiece to alter its shape. The main difference is that milling uses intermittent cuts, whereas grinding continuously shears plastic from the product to achieve a smoother shape and surface finish.

Common Materials Used in Plastic Machining

Plastics present some challenges for machining operations. For example, some plastic materials can have:

  • plastic tanksLower thermal resistance than metals, resulting in a higher risk of thermal expansion, overheating, and thermal damage
  • Higher material costs
  • Greater machining restrictions

Despite these limitations, plastic remains a common construction material for machined parts and products. In general, plastics offer several manufacturing advantages, such as:

  • Superior strength-to-weight ratios
  • Broader insulating properties (including electric, thermal, and vibration)
  • Greater resistance to corrosion and chemicals

Specific plastics also maintain their own unique benefits. For example, the following are some of the most commonly used plastics in machining operations:

  • Ultra-high molecular polyethylene (UHMW), due to its high machinability
  • Nylon, due to its affordability, strength, durability, and corrosion and chemical resistance
  • Acrylic, due to its formability, high tensile strength, and resistance to cracking and abrasion
  • Polyether ether ketone (PEEK), due to its chemical and wear resistance and ability to withstand high temperatures

Considerations for Plastic Machining

Ensuring the success of a plastic machining project requires choosing construction materials and machining operations that are well-suited for each other. When planning a plastic machining project, some of the factors to consider are:

Plastic type

Different chemical compositions yield different physical characteristics, impacting everything from strength and chemical resistance to the cost of the material. When choosing a plastic material for a machined part, it is important to keep these properties in mind as they will influence how well the material withstands the stresses of manufacturing and the end product withstands the stresses of the intended application.

Thermal regulation

In general, plastics melt at substantially lower temperatures than metals. As such, proper heat regulation, including the use of coolants, is essential if a polymer is to withstand machining.

Process support

As plastics are less rigid than metals, the vibrations generated by the machining operations can more easily cause burrs, cracks, and chatter marks. Incorporating additional support structures during machining operations reduces the risk of damage to the end product.

Finishing options

Many companies employ finishing services to enhance the functional and aesthetic properties of a machined product. Some of the typical finishing processes are annealing, polishing, and coating.

Applications of Plastic Machining

Biomedical Storage CabinetConsidering the benefits and limitations in sum, plastic machining is still one of the best options for producing a variety of industrial parts and products, such as:

Plastic Machining Services From Plastic Design, Inc.

At Plastic Design, Inc., we have the tools and knowledge required to machine nearly any plastic product. Our expert team takes projects from initial design to delivery of a turnkey product or system.

Our Plastic Machining Capabilities

We use cutting-edge CNC machines to craft precise plastic parts and components to tight tolerances. Our machining capabilities are as follows:

Machining Operations
  • Milling
  • Drilling
  • Boring
Plastic Forms
  • Sheets
  • Rods
  • Specialty shapes
Plastic Materials
  • ABS
  • Acetal (including Delrin®)
  • Acrylic
  • Flametec® (fire-safe plastics)
  • Kel-F®
  • Polycarbonate (including Kynar®)
  • Polyethylene
  • Polypropylene
  • PVC
  • PVDF
  • PTFE (including FEP, PFA, and TFE)
  • Length: up to 12 feet
  • Width: up to 5 feet
Production Volumes
  • Prototype
  • Production

Additional Capabilities

In addition to our plastic machining capabilities, we also offer:

Original Equipment Manufacturing

Over our years serving customers in the biomedical, pharmaceutical research, and semiconductor industries, we’ve garnered significant knowledge about the requirements expected for the equipment and systems used in the industries. This expertise allows us to serve as an original equipment manufacturer (OEM) of custom-built parts and equipment. With our OEM services, we provide technical guidance to take products from concept to completion.

Specialty Product Manufacturing

Outside of our OEM partnerships, we also manufacture a full catalog of specialty products for customers across a wide range of industries. Some of these past projects have included:

  • Automated wet process systems
  • Desiccators
  • Fume hoods
  • Hazardous waste systems
  • Tank lines

What Makes Us Different?

At Plastic Design, we are an ISO 9001:2015 certified fabricator. By partnering with us for their plastic machining needs, our customers benefit from our:

  • Over 40 years of experience in plastic manufacturing
  • Knowledge of specialized fields, including the biomedical, pharmaceutical, and semiconductor industries
  • 30,000-square-foot fabrication facility
  • OEM manufacturing capabilities

These characteristics allow us to meet some of the most difficult design challenges out there while forming lasting relationships with our industry clients.

Plastic Machining Solutions From Plastic Design, Inc.

Choosing a knowledgeable manufacturer for a plastic machining operation is the key to successful completion of the project. Plastics require specialized expertise to prevent expensive defects or product failures during production, and only a dedicated plastics provider can guide you through the complex material selection and testing process.

At Plastic Design, Inc., we have the technical capabilities and industry knowledge necessary to produce high-quality and cost-effective parts and products from a wide range of plastics. Whether you’re seeking a one-off prototype or a high-volume production run, we’ll work with you to turn your design into a reality.

To learn more about our plastic machining capabilities, contact us or request a quote today.