Methods of Plastic Fabrication

February 17, 2022
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There are many methods of plastic fabrication.

According to Thomas Net:

Plastic fabrication is the design, manufacture, or assembly of plastic products through several methods, ranging from compounding to machining to welding to molding. Some manufacturers prefer plastic fabrication over other materials (such as metal or glass) due to the process’s advantages in specific applications. In this guide, we’ll be covering the most major plastic fabrication methods, as well as some factors to consider in choosing which plastic fabrication processes are best for your application.

Plastic Fabrication Methods

Plastic’s malleability and cost-effectiveness can make it a versatile and durable material for a range of different products. There is a wide range of plastic manufacturing processes, from injection molding to foaming to rotational molding. At a glance, we’ll be covering the following plastic fabrication processes here:

  • Plastic Welding
  • Compounding (Blending) Plastic
  • Plastic Molding, Including RIM, Rotational, Injection, Compression, and Blow Molding
  • Plastic Thermoforming
  • Plastic Extrusion
  • Plastic Foaming
  • Plastic Machining
  • Plastic 3D Printing
  • Plastic Lamination

Plastic Welding

Like metal welding, plastic welding involves using heat to melt two or more workpieces together. This process is effective when handling thermoplastics that are unsuitable for adhesive binding. Individual pieces are often fused with a filler material between them, especially if the plastics have dramatically different melting points. Welding can be accomplished through several different methods, including hot gas emissions, high-frequency vibration, spinning, or contact welding. The equipment used in plastic welding depends on the selected process and type of plastic involved.

Compounding (or Blending) Plastic

Compounding is a type of custom plastic fabrication that combines two or more plastics into an amalgam before forming them into a single part. It involves mixing molten plastics to exact specifications and forming them with a mold, die, or other shaping tools.

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Compounding is often used to either improve the ease of processing a given material or to enhance product performance. By combining the advantages and disadvantages of several types of plastic, the process can result in a unique material complementary to a specific application. Some common types of plastic compounds include:

  • Polymer fillers (which are added to plastic to reduce costs and add certain properties)
  • Base resins (pure plastic which is mixed with fillers and other additives)
  • Pigment masterbatches (plastic with concentrated pigment, to be used instead of straight pigment)
  • Blowing agents (used to create plastic foam)
  • Flame retardants
  • Purge compounds (which clean molding machines of leftover resin and dye)

Plastic Molding, Including RIM, Rotational, Blow, Compression, and Injection Molding

In plastic molding, plastic is formed into a specified shape by allowing the heated, pliable workpiece to cool and harden around or within a mold. There are numerous plastic molding processes, many of which are commonly used. These include:

  • Injection molding. Custom Injection molding is helpful in applications requiring a higher melt index, like dishware production. It involves the injection of melted plastic resin into a mold, which allows for inexpensive mass production. Overmolding, insert molding, and two-shot molding are variations on injection molding that involve injecting melted plastic around another part.

  • Blow molding. Blow molding is often used to create containers, such as bottles or fuel tanks. Instead of simply injecting liquid plastic into a mold, this process features the added step of pushing air into the mold in an expanding plastic bubble to create a hollow center and a more accurate impression. The plastic solidifies into the desired form as it hits the cool mold.

  • Rotational molding. Rotational molding results in hollow plastic products, such as canoes, toys, buoys, and automotive parts. However, in this process, unmelted plastic is sealed inside a mold which is then heated and rotated to ensure plastic thoroughly covers the inside in an even layer. This isn’t as precise as other methods, but it’s suitable for making larger complex products with uniform walls.

  • Reaction Injection Molding (RIM). RIM involves using thermoset plastics like polyurethane, which can only be melted once. Two different polymers are combined inside a mold, where a chemical reaction then hardens them into the final product. RIM can be used for large parts, insert molding, and varying wall thickness in a single piece. It also allows for cheaper tooling costs.

  • Compression molding. During this process, plastic powder or pellets are heated and compressed into the desired form. Often the powder or pellets are heated and compressed slightly beforehand into a “biscuit.” Plastic thermoforming, discussed below, is related to this.

Plastic Thermoforming

There are two types of plastic thermoforming: vacuum and pressure. Both processes involve heating and stretching plastic sheets over a male or female mold, pressing it into the mold, then trimming off the excess plastic. However, while vacuum thermoforming involves sucking all the air out of the gap between softened plastic and the mold, pressure thermoforming involves applying pressure (often air) to the top side of the plastic and letting that push the air out of the gap to create the desired shape. Pressure forming is better for capturing detail and texture since it’s more accurate.

Thermoforming allows someone to produce large numbers of an object at a low cost while maintaining a certain level of detail down to surface texture. However, it’s limited to thin-walled products, and there are limits to how complex parts can be. Additionally, pieces require trimming afterward, though this does allow for less waste as the trim can be recycled. Commonly ABS, HDPE, TPO, HIPS, and mixtures of PVC/Acrylic and PC/ABS are used in thermoforming. It’s a technique used for multiple industries, including the aviation, mass transit, medical, and industrial equipment sectors, with applications ranging from medical device and ATM enclosures to wastewater management components.

Plastic Extrusion

Plastic extrusion can be used to create tubing, piping, or sheeting components. It is also applied to enhance the effectiveness of further forming or processing stages. For example, plastic extrusion is often a precursor to adhesion or lamination procedures.

Profile extrusion and sheet extrusion are the most common forms of the process. To briefly describe the plastic extrusion process: profile extrusion uses a single screw extruder to melt plastic pellets, move the molten plastic through a pressurized screw mechanism, and force it into an annular die. The plastic then solidifies around a calibration sleeve to create a pipe or tube component of a specific diameter. Sheet extrusion, unsurprisingly, uses a similar technique to create thin plastic sheeting.

Plastic Foaming

Foam products can be formed into a variety of different shapes, including those for egg cartons or packaging cushioning. Standard foaming configurations include round, sheet, film, solid plank, rod, and bun stock. To achieve the desired characteristics, polymer composites are typically shaped through physical or chemical blowing. As in compounding, additives such as pigments, antioxidants, and fire-retardants can be included in the base material to optimize product performance for the user. Materials that can be foamed include polystyrene, polyethylene, polypropylene, polyamides, and plasticized PVC. Thermosets can also be foamed through chemical reactions into foam cushioning for furniture or other applications.

Plastic Machining

Machining encompasses several subtractive processes to shape a plastic workpiece, including milling, turning (also known as lathe work), drilling, cutting, grinding, and other services. While milling uses rotating cutters to remove material from a stationary workpiece, turning involves rotating the workpiece and moving the cutting tools along it. Drilling creates holes in the plastic using a drill bit, cutting slices off parts of the workpiece, and grinding files down edges or spots that protrude too far. You can find out more about how each machining process works in our guide on the subject.

Nylon, acrylic, ABS, PVC, PTFE, polyethylene, and polypropylene are commonly used in machining. Because plastic melts more easily than metal, any machining must include efficient heat removal, and the material’s tendency to grow or shrink with temperature must also be taken into account. Plastic machining is a common process; it’s used to create products across a range of industries from biomedical devices to microelectronics to food handling equipment.

Plastic 3D Printing

3D printing is executed through a variety of methods: curing liquid plastic into a solid by UV light, melting filaments and extruding them, and powder fusion are among the techniques used. Common plastics used in this manufacturing process include PLA, PVA, ABS, ASA, PETG, nylon, and polycarbonate. 3D printing is most often used for prototyping, research, tooling, spare parts, and production.

Plastic Lamination

Plastic lamination creates a barrier along the surface of another material. This process is most often used to improve durability, styling, or aesthetic quality. It can also be a cost-effective measure by shielding a sensitive or deterioration-prone material and reducing its potential need for maintenance.

Film and resin are the two most common types of lamination. In both processes, heat and pressure are applied to a fabricated film to enable its adhesion to a moving substrate. Film lamination is more effective for forming a plastic barrier on the exterior of a product, while resin lamination is more frequently used to create an adhesive layer between two substrates. Paper, fabrics, metal sheeting, and flexible foam are common lamination base materials.

Choosing a Plastic Fabrication Process

Product functionality and ease of manufacturing are essential to consider when choosing a plastic fabrication process. Some methods are inefficient for fabricating certain types of plastic, and therefore may not be helpful for your particular project. Some other issues to keep in mind include:

  • The need for single plastics versus plastic compounds
  • The intended proportion of plastic to non-plastic material in the product
  • The role of plastic in your fabrication process (as adhesion, lamination or base product)
  • The dimensions and use of the final product.

Conclusion

Now that we’ve covered the basics around the most common type of plastic manufacturing services, we hope this will better enable you to source effectively for the plastic manufacturing process you need.

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