Plastic is the most common material used for producing final-use components and products, spanning everything from consumer goods, transportation, and engineering machinery, to medical equipment. Plastic is a highly versatile material, with thousands of polymers to choose from, each possessing its unique set of mechanical properties.
But how are plastic parts manufactured?
This article will help you understand the different plastic manufacturing processes that evolved to encompass a wide range of applications, part geometries, and types of plastics. help the designers and engineers engaged in product development, be familiar with the available manufacturing options today.
Types of Plastics
There are thousands of types of plastics, each with different basic chemical compositions, derivatives, and additives. Their formulations encompass a wide range of functionalities and aesthetic characteristics. The two main types of plastics commonly used are thermoplastics and thermosetting plastics:
The primary characteristic of thermoplastics is their ability to undergo multiple cycles of melting and solidification without significant degradation. Thermoplastics are typically supplied in the form of small granules or sheets, which are heated and processed using various manufacturing techniques to achieve the desired shapes. This process is entirely reversible and does not involve chemical bonds, making thermoplastics highly recyclable.
Common thermoplastic materials: Acrylic (PMMA), Acrylonitrile Butadiene Styrene (ABS), Polyamide (PA), Polylactic Acid (PLA), Polycarbonate (PC), Polyether Ether Ketone (PEEK), Polyethylene (PE), Polypropylene (PP), Polyvinyl Chloride (PVC).
Thermosetting plastics (also known as thermosets) remain in a permanent solid state after curing. The polymers in thermosetting materials undergo cross-linking during a curing process induced by heat, light, or appropriate radiation. This curing process forms irreversible chemical bonds. Thermosetting plastics decompose rather than melt when heated and do not deform upon cooling. Thermosetting materials cannot be recycled.
Common thermosetting materials: Cyanate Ester, Epoxy Resin, Polyester, Polyurethane, Silicone, Vulcanized Rubber.
Plastic Forming Characteristics
The ability of polymers to take on a shape under temperature and pressure is referred to as moldability. Using moldability, polymers can flow into mold cavities under the influence of temperature and pressure, and then solidify to form various components.
The deformation of polymers when stretched or compressed in one or two directions is referred to as extensibility.
The ability of polymers to take and retain a shape when subjected to extrusion deformation is called extrudability. Engineering plastics are often subjected to extrusion in the molding process, such as in the barrels and molds of extruders and injection molding machines.
Engineering plastics typically undergo useful deformation through extrusion only in a molten state. The extrudability of engineering plastics depends primarily on melt viscosity. For most engineering plastics, melt viscosity decreases with increasing shear or shear rate. If the melt viscosity of engineering plastics is low during extrusion, although flowability is excellent, the ability to retain shape is poor. Conversely, if the melt viscosity is high, it can lead to difficulties in flow and molding. The extrudability of engineering plastics is also influenced by the structure of the processing equipment. The flow of molten plastic in the extrusion process increases with increasing pressure.
Viscosity and Elasticity
Engineering plastics typically transition from a solid to a molten state and then from molten to solid, becoming a product during the molding process. This transition reflects both solid elasticity and melt viscosity. However, due to the gradual movement of long-chain polymer molecules, what is observed is not pure elasticity and viscosity but a combination of the two, known as viscoelasticity.
In addition to the above characteristics, the forming performance of plastics also includes thermodynamic properties, crystallinity, orientation, shrinkage, flowability, thermal sensitivity, moisture sensitivity, hygroscopicity, compatibility, and more.
Eight Common Plastic Manufacturing Processes
3D printing, also known as additive manufacturing, is a technology that constructs objects by using digital model files as a foundation and applying materials like powdered metal or plastic that can bond together, layer by layer. Unlike traditional subtractive manufacturing, 3D printing creates plastic solid models by digitally scanning and processing the model in three dimensions.
|Processing Method||Material Requirements|
|Fused Deposition Modeling (FDM)||Various thermoplastic plastics, primarily ABS and PLA|
|Stereolithography (SLA)||Thermosetting resin|
|Selective Laser Sintering (SLS)||Thermoplastic plastics, typically nylon and its composites|
CNC (Computer Numerical Control) machining is a subtractive manufacturing process used to create precise parts and components from various materials, including plastic. CNC machining involves the removal of material from a solid block or sheet of plastic to achieve the desired shape and dimensions.
CNC machining is known for its high precision, accuracy, and versatility in producing complex and custom-designed plastic parts. Several types of plastic materials are commonly used in CNC machining:
polyurethane casting, also known as Urethane casting, is a manufacturing process used to produce low to medium volumes of plastic parts or components using polyurethane materials. This process is particularly valuable when you need to create prototypes, functional parts, or products with specific material properties that are not easily achieved with traditional injection molding or CNC machining.
The plastics suitable for polymer casting processing include Polyurethane, Epoxy, Polyether, Polyesters, Acrylic, and Silicone.
Rotational molding (also known as roto-molding) is a process that involves heating a hollow mold filled with powdered thermoplastic plastic and rotating it around two axes to produce primarily large hollow objects. Rotomolding with thermosetting plastics is also available but less common.
Compared to other molding techniques, rotational molding uses centrifugal force rather than pressure to fill the mold, and molds are typically less expensive. Typical rotational molding products include tanks, buoys, large containers, toys, helmets, and canoe hulls.
The plastics suitable for rotational molding processing include Polyethylene, Polypropylene, Polyvinyl chloride, Nylon, and Polycarbonate.
Vacuum forming or thermoforming is a manufacturing method where plastic is heated and shaped, typically using molds. Vacuum-forming machines come in various sizes and complexities, ranging from low-cost tabletop equipment to automated industrial machinery. Compared to other molding techniques, vacuum forming has lower mold costs.
This process is used to produce parts with relatively thin walls and simple geometries, making it an ideal choice for a wide range of applications, from custom products or prototypes to large-scale production. Typical components produced through vacuum forming include product packaging, shower trays, door liners, boat hulls, and custom products like dental braces.
Plastics suitable for vacuum forming processing include Acrylic (PMMA), Acrylonitrile butadiene styrene (ABS), Polyethylene terephthalate glycol (PETG), Polystyrene (PS), Polycarbonate (PC), Polypropylene (PP), Polyethylene (PE), Polyvinyl chloride (PVC).
The working principle of Injection Molding (IM) involves injecting molten thermoplastic plastic into molds. It is the most widely used process for batch production of plastic parts. Injection molding can produce highly complex parts, with production cycle times lasting only a few seconds, and it can produce millions of high-quality parts at a fraction of the cost of other manufacturing processes. Injection molding is extensively used in industries such as automotive interiors and exteriors, construction machinery, transportation, aerospace, instrumentation, and more.
Plastics suitable for injection molding processing include Acrylic (PMMA), Acrylonitrile butadiene styrene (ABS), Polyamide (PA), Polyethylene terephthalate glycol (PETG), Polystyrene (PS), Polycarbonate (PC), Polypropylene (PP), Polyethylene (PE), Polyvinyl chloride (PVC).
the working principle of Extrusion Molding is to push plastic material through a mold, with the mold’s shape determining the cross-section of the final part. Compared to other molding processes, extrusion is relatively inexpensive due to its simple shapes.
The cost of molds is only a small fraction of that of injection molding molds. Extrusion molding is similar to injection molding and is an almost continuous process, resulting in very low part costs. It is suitable for manufacturing products with continuously profiled cross-sections, including items like pipes, hoses, straws, and window frames.
Plastics suitable for extrusion molding include Acrylic (PMMA), Acrylonitrile butadiene styrene (ABS), Polyamide (PA), Polyethylene terephthalate glycol (PETG), Polystyrene (PS), Polycarbonate (PC), Polypropylene (PP), Polyethylene (PE), Polyvinyl chloride (PVC).
Blow molding is a manufacturing technique that involves heating a plastic tube inside a mold and inflating it until it takes on the desired shape, typically used for producing hollow plastic components. The molding pressure in blow molding is much lower than in injection molding, which helps reduce mold costs.
Similar to injection molding and extrusion molding, blow molding is a continuous process that can be fully automated, resulting in high productivity and low costs. Blow molding is the most common process for mass-producing hollow plastic products.
Typical applications include bottles, toys, automotive parts, industrial components, and packaging.
Plastics suitable for blow molding include Polyethylene terephthalate (PET), Polypropylene (PP), Polyvinyl chloride (PVC), Polystyrene (PS), Polycarbonate (PC), Acrylonitrile butadiene styrene (ABS).
How to choose the best plastic manufacturing process
When selecting a suitable plastic manufacturing process for your product, please consider the following factors:
- Complexity and geometry of the product: Does the part have complex features or strict tolerance requirements?
- Production volume/cost: What is the total quantity or annual production volume planned for the parts?
- Lead time: How quickly do you need the parts or finished products to be produced?
- Materials: What are the product’s use cases, and what kind of pressure and strain does it need to withstand?
Reference table for process selection
|Manufacture Process||Form||Lead time||Cycle time||Setup cost||Cost per part||Volume|
|3D Printing||Moderate to a high degree of freedom||Less than 24 hours||< 1 hour to multiple hours, depending on part size and volume||☆||☆☆☆||Low to mid-volume applications (~1-1000 parts)|
|CNC Machining||Medium degree of freedom||Less than 24 hours||< 1 hour to multiple hours, depending on part size, design, and complexity||☆☆||☆☆☆☆||Low to high-volume applications (~1-5000 parts)|
|Polymer Casting||Low-volume applications (~1-1000 parts)||Less than 24 hours to a few days||The high degree of freedom||☆||☆☆||The high degree of freedom|
|Rotational Molding||Medium degree of freedom, ideal for large hollow parts||Days to a few weeks||Typically < 1 hour||☆☆☆||☆☆||Medium volume applications (~200-5000 parts)|
|Vacuum Forming||Limited freedom, only thin-walled parts, no complex geometries||Less than 24 hours to weeks||Seconds to minutes, depending on the machinery||☆-☆☆☆☆||☆-☆☆☆||Any volume|
|Injection Molding||High-volume applications (5000+ parts)||2-4 months||Seconds||☆☆☆☆☆||☆||High-volume applications (5000+ parts)|
|Extrusion||Limited, only long continuous shapes||Weeks||Seconds (or continuous)||☆☆☆||☆||Medium to high volume applications (1000+ parts)|
|Blow Molding||Limited freedom, only hollow, thin-walled shapes, no complex geometries||Weeks||Seconds||☆☆☆☆☆||☆||High-volume applications (5000+ parts)|
Plastic manufacturing processes are constantly evolving and the inflection points where it makes sense to move from one technique to another are shifting due to improvements in equipment, materials, and economies of scale. Kusla Prototype provides various plastic manufacturing services for your projects, contact us today to find out which is the best for you.