Guide to Manufacturing: How are Plastics Made?

Workers Operate Plastic Manufacturing Machine

Plastics are everywhere and are the most common material used for producing products, ranging from toys and household goods to precision parts in automotive and aerospace components. Plastics are versatile, with a wide range of materials that can be formed into parts that resemble rubber to products that are strong like steel, with complicated geometries that hold up under stress. Plastic materials come with varying specifications allowing a manufacturer to choose the best plastic raw material for the job with the properties required whether strong or bendable, UV or corrosion resistant, and in any color imaginable.

When it comes to how plastics are made, there are many options available with various manufacturing processes used to make plastic products. The most common types of plastic manufacturing processes include:

  • 3D Printing
  • CNC Machining
  • Polymer Casting
  • Rotational Molding
  • Blow Molding
  • Vacuum Forming
  • Extrusion
  • Injection Molding

For the purposes of this article, we will be addressing the most common plastic manufacturing types when the goal is high precision or high volume, specifically CNC machining and plastic injection molding.

Contact QT Manufacturing to Learn More

How to Choose the Right Plastic Manufacturing Process

When choosing the best manufacturing process for plastic products, the most important considerations include:

Volume: What is the volume of parts required? High-volume production may have higher up-front costs but lower costs per piece, whereas low-volume parts could have lower start-up costs but higher per piece costs. Volume plays an important role in choosing the best plastic manufacturing process.

Form: What is the shape of the part? Internal features, complex geometries or tight tolerance requirements can dictate the best plastic manufacturing method and requirements for part design.

Material: Plastic materials come in a wide range of properties and manufacturers must consider aesthetic and functional requirements when choosing the optimal material. Part specifications and application characteristics are a major consideration when choosing the best plastic manufacturing method.

Lead time: Lead time has a role in the plastic manufacturing process chosen, as some methods can produce a part rather quickly while others require tooling to be constructed before high-volume production can begin.

Types of Plastic Material

Plastic material comes in a wide variety of chemistries and formulations with countless types of additives to meet aesthetic and functional properties. There are basically two types of plastic materials, thermoplastics and thermosets.

Thermoplastics are the most widely used type of plastic material and usually come in raw plastic pellet form or plastic sheets. Thermoplastics have the ability to be reheated and melted down again, after molded into plastic parts, to possibly reuse the material.

Common types of thermoplastic resins include:

  • Polycarbonate (PC)
  • Polyethylene (PE)
  • Polypropylene (PP)
  • Polyvinyl Chloride (PVC)
  • Polyether ether ketone (PEEK)
  • Acrylic (PMMA)

Thermoset plastics differ from thermoplastic resins in that they do not have the ability to be melted down and formed again after curing into a solid state. Thermoset materials cross-link during curing which forms an irreversible chemical bond.

Common types of thermoset plastics include:

  • Epoxy
  • Silicone
  • Polyurethane
  • Polyester
  • Vulcanized rubber

CNC Production Machining

Computer Numerically Controlled, CNC, machining is a process typically used for machining metal parts although can also be used to machine plastic parts. CNC machining requires the job to be setup on a CNC machine, where the process of controlling the movements and speed of the cutting tools is set up with computer precision. Machining is ideal for lower volume plastic part requirements that require tight tolerances and complex geometries that may be difficult to mold. CNC machining can also be beneficial when producing prototype parts. Learn more about the Top 5 Advantages of CNC Production Machining

Plastic Injection Molding

Injection molding is the most common type of manufacturing process for thermoplastic resins, especially for high-volume production demands and can also provide very high precision for tight tolerance parts. Injection molding requires that a steel mold be constructed first, with cavities for the molten plastic to be ‘injected’ into to form and set prior to ejecting from the mold as a complete, molded part.

Injection molding is extremely beneficial for high-volume production as molds can be constructed with multiple cavities, to produce multiple parts at once such as 4,8,16, even 32 cavity molds for smaller parts. With quick cycle times usually measured in seconds, parts can be molded and ejected quickly, often producing thousands of parts during just one work shift, depending on the size of the part, mold cavitation and cycle time.

Thermoplastic resins are typically loaded into a hopper in pellet form, drawn into the injection molding press after heated up to a molten state and injected into the mold. The steel mold is typically made of hardened steel to produce upward of a million cycles, if a less-expensive material like aluminum is used it is typically for prototyping purposes and cannot support high-volume production.

Injection molding has higher up-front costs than some other plastic manufacturing methods as the cost of the mold, or tool as also referred to, can be thousands of dollars. The ability to produce very high-quality, high-precision parts, however, quickly and with repeatability for mass production is the best benefit of injection molding and comes out to be the most economical even with the cost of the tool. Learn more about Top 4 Advantages of Plastic Injection Molding

Custom Injection Molds

Constructing injection molds, the steel frame which houses the cavities to produce the plastic parts, requires experienced mold makers who are familiar with the injection molding process. Injection molds are now constructed with high precision computerized technology, although prior to the days of computer driven mold making equipment, journeymen moldmakers carved the steel with lathes and precision tools to form extremely complex geometries and shapes designed to meet plastic part specifications.

Journeymen moldmakers are still required to construct quality molds, which must be designed to meet part design requirements often with complex features to meet tolerances in the range of +/- .001 (a thousandth of an inch is thinner than that of a human hair).

QT Manufacturing Offers Plastic Manufacturing Solutions

QT Manufacturing offers CNC machining, injection molding and custom injection mold making to meet the needs of various industries including:

  • Aerospace
  • Fiber optics
  • Optoelectronics
  • Consumer goods
  • Medical
  • Defense
  • Firearms

We offer prototype solutions, low or high-volume production and custom, precision molds to support these industries and others. We follow a strict quality policy as part of our ISO9001 and AS9100 rev D certifications, with focus on continual improvement and total customer satisfaction.

Request a Quote Now

QT Manufacturing is a leading provider of plastic parts and complex plastic components with proven high-quality methods of plastic manufacturing. No matter the method chosen for how plastics are made for your requirements, you can have confidence in our ability to guide you with the most efficient, economical and quality process to meet your needs. Contact us at (972) 221-0537 to speak with an engineer and with any questions on how plastics are made to meet your custom requirements.