The Plastic Welding Process

PFI Plastic Welding Process, Plastic Welding Techniques and Methods

As the use and demand for plastics expands dramatically, the techniques in manufacturing products from this material are rapidly advancing as well. Plastic welding is a relatively new process that creates a molecular bond between two compatible substrates. The generation of heat is the essential component of the plastic welding process. The process itself consists of three parts; surface preparation, applying heat and pressure, and cooling.

Plastic welding offers an efficiency and versatility to create permanent bonds in a wide variety of plastic materials such as:

  • Polyvinyl chloride (PVC)
  • Acrylonitrile-butadiene-styrene (ABS)
  • Polycarbonate (PC)
  • Acrylic or polymethyl methacrylate (PMMA)
  • Polypropylene (PP)
  • Polyethylene (PE)
  • Polyethylene terephthalate (PETE or PET)

The equipment and techniques utilized to weld plastic will vary from the type of plastic used and its application. Contact the experts of PFI to help with your plastic welding project.

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Plastic Welding Techniques and Methods

Achieving a plastic weld can be completed through a variety of methods. Fusing plastic components together, at the molecular level, can be accomplished through a variety of plastic welding methods. The most common methods are:

  • Friction welding joins two pieces of plastic by generating heat through friction with both components in relative motion to one another.
  • Extruded bead sealing bonds two pieces of plastic together by applying a hot bead of plastic between the two parts and then pressing them together.
  • Solvent welding utilizes a chemical, such as Dichloromethane or Tetrahydrofuran, to soften the polymers to enable their polymer chains to merge. As the solvent evaporates and dries, the polymers harden and the bond (weld) is formed.
  • Laser welding connects two pieces of plastic together by using a laser beam to heat the joint between the two substrates to fuse them together.
  • Spin Welding uses pressure and friction created from both stationary and rotating plastics to melt and bond the two pieces.
  • Induction welding occurs when a piece of conductive metal placed between the two plastic parts is heated and transfers that heat to the plastic, once softened, the plastics are pressed together to form the weld.
  • High-frequency/ultrasonic welding bonds plastics by applying electromagnetic waves to the areas that are to be joined. The two pieces to be welded are placed on a table where pressure is applied directly following the exposure to the high-frequency waves to create the weld.
  • Hot-plate welding adjoins two pieces of plastic by applying a heated metal plate of the two components to be fused together. Once the correct temperature is reached, the two pieces are held in place until they are cool to bond them together.
  • Hot-gas welding is often referred to as hand welding. By using a specialized heat gun, the plastic is softened and bonded with a filler rod. This plastic welding technique is similar to extruded bead sealing, but often used on a smaller and more portable scale.

Hot-Plate Welding

Hot-plate welding has been one of the first methods used to bond plastic components. As its name implies, a heated plate is coated with PTFE (polytetrafluoroethylene) and is held above the two pieces of plastic that are to be adjoined. As the plastic softens via the heated plate, the two components are held together until cooled, thereby creating the weld. This method of welding plastic creates a bond between the two components that is nearly as strong as each of the actual components being welded. Polypropylene and Polyethylene are two excellent candidates for hot-plate welding applications.

Benefits of Hot-Plate Welding

Hot-plate welding has many advantages over other plastic welding techniques as it creates high-quality joints that are easily automated and efficient. It also can be utilized on large and complex components by providing conformed joints, all the while being a relatively flexible technique that can be adapted to weld items of various shape, dimension, and design. Hot-plate welds have great tolerance to warpage and dimensional changes that occur during the welding process.

Limitations of Plate Welding

Hot-plate welding does have some limitations in its application. The weld cycling for this technique can be long, depending on the size of the components being fused. It also emits a significant amount of flash. Hot-plate welding presents problems when a weld is desired between two different plastics. Manufacturing a plate to create a strong weld between two different substrates can be challenging and the accuracy of controlling these plates when welding can be cumbersome. This application also tends to limit the joint design options available for use on the product.

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Ultrasonic Welding

Ultrasonic welding has been a staple in the welding industry for years. In this process the two components to be fused are held together and are then subjected to high frequency vibrations that heats and softens the material to be conjoined. Ultrasonic welding uses the process of hysteretic heating to create the weld. The critical component in this technique is the horn or sonotrode that comes within a quarter inch of the area to be welded which also gives it the name of “near field” welding.

Benefits of Ultrasonic Welding

Ultrasonic welding is quite popular and presents great benefits to the industry by expediting the welding process. Ultrasonic welds are very fast and efficient; most are completed in just seconds and require minimal materials and energy to produce high-quality bonds between components. Only small amounts of flash is created by this technique and is much safer as the need for highly heated components is not necessary. Ultrasonic welding is also efficient in requiring little manual labor and is easily adapted for automation.

Limitations of Ultrasonic Welding

Two significant limitations of ultrasonic welding exist: the expense of custom tooling for the welder components (horns) and the thickness of the substrates that can be effectively welded. For smaller manufacturers, the high investment for the welding equipment and the lead time for the precise tooling setup can be prohibitive. Joint sizes also pose a significant limitation for ultrasonic welding. Large joints often can be welded in a single run and will require multiple applications to achieve the proper bond.

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Hand Welding

Hand welding is often referred to as stick welding, hot-gas welding or manual welding. It is completed by utilizing a specialized heat gun that will heat the surfaces to be welded and also the welding rod or stick used to create the bond. The results of using the stick welding method provides results with welds that are comparable to extrude bead sealing. Hand welders are available in straight or pistol-gripped configurations.

Benefits of Hand Welding

Hand welding possesses numerous distinct advantages when contrasted with alternative methods. Its inherent portability and versatility make it an exceptional option for tasks involving repairs or smaller-scale projects. In terms of cost-efficiency, hand welding stands out favorably against other techniques, offering a rapid and highly efficient route to achieving top-notch welds. Because the plastic welder exercises complete control throughout the process, hand welding consistently yields some of the industry’s finest joints.

Limitations of Hand Welding

The greatest limitation on hand welding is its inability to create airtight or hermetic seals. For such applications such as lengthy joint requirements, hand welding does not enable such efficient production methods for larger quantities. There is also a greater chance of inaccuracies and a lack of precision as they require human operation rather than various technological means.

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Plastic Welding vs. Metal Welding

Although both welding of plastic and metal materials share a common underlying process, their method differs. Metal welding uses an electrical arc to bind surfaces together, whereas its plastic counterpart utilizes gas and hot air to create the bond. Plastic welding has a significant advantage over metal welding as it is more efficient and does put welders at a higher risk due in part to the sparks and fumes that are released through metal welding. At PFI Advanced Equipment Manufacturing we have the technology and the know-how to safely and accurately perform both metal and plastic welding to meet all your fabrication needs.

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Plastic Welding Applications

At PFI, our mission is to fabricate the highest quality components of the utmost precision for a variety of industries. Our plastic welding applications are used to manufacture some of the industry’s finest and most reliable products such as battery trays, drip pans, and utility boxes for microelectronics, pharmaceutical, photonics and biomedical fields. Our plastic welding capabilities can be completely customized for acid containment and underground tanks, vaults, and tubs.

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With the ability to utilize a plethora of materials such as plastic, metal and foam, PFI is equipped with the latest manufacturing technology and equipment to provide you with the quality product you deserve. We have the capabilities to customize products to your specifications and pride ourselves on our quick turn-around time. For your next custom plastic fabrication project, contact PFI’s highly skilled fabricators to put the expertise and precision of over 40 years of plastic fabrication to work for you.

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Brian Schubel

Brian Schubel is an accomplished Shop Manager and Machinist who began his career in 1985 with Albert Seisler Machine Corp. In January 2006, PFI acquired the Seisler business, and Brian became a PFI employee. In his 38+ years tenure in the shop he has be known as “the Mayor,” Brian has always been the go-to guy for all issues related to machining, fabrication and assembly. Other employees have relied on Brian’s knowledge and experience to guide them in their daily activities.