A Beginner’s Guide to Plastic Molding Processes


What is Plastic Mold? A Beginner’s Guide to Plastic Molding Processes

Plastic molding is a manufacturing process used to create precise injection molding parts and products by shaping different types of thermosetting and thermoplastic polymers into custom designs. Plastic molds are commonly used to make a variety of everyday items, from plastic bottles and containers to automotive parts and medical devices. Understanding what plastic molds are and how they work provides important insight into modern manufacturing.

An Introduction to Plastic Molding Processes

Plastic molding utilizes specialized tooling and equipment to form plastic resin into net shapes or near-net shapes. The plastic molding process involves pouring molten plastic, compressing it under high pressure, and then cooling it to solidify the end product. The plastic mold gives shape to the liquefied plastic during the molding process.

There are several techniques used in plastic molding, each with advantages based on the type of plastic used and the properties desired in the end product. The four main types of plastic molding processes are:

Injection Molding

Injection molding is one of the most common methods of plastic molding. It is used to make a variety of everyday plastic items. The injection molding process forces molten plastic into a mold cavity under high pressure. The pressure packs the plastic tightly into the mold and allows for an accurate reproduction of intricate detail from the mold tool. Once the plastic cools and solidifies, the mold opens to eject the finished part.

Injection molding is highly suitable for producing high volumes of plastic parts efficiently and is thus widely used for mass production. Parts made by injection molding have tight tolerances and minimal scrap material. The process can use thermosets or thermoplastics and is used to make parts like bottle caps, containers, automotive dashboards, pocket combs, and parts for electronics.

Blow Molding

Blow molding is used to make hollow plastic parts like bottles and containers. In this technique, the plastic is molded by inflating it with compressed air. First, a molten plastic tube called a parison is created through extrusion or injection molding. The parison is then clamped into a hollow mold cavity and air is blown into it, forcing the plastic to expand until it conforms to the shape of the mold. Once cooled and hardened, the mold opens to reveal the finished hollow part.

The main advantage of blow molding is its ability to make hollow parts and shapes that are difficult to produce by other methods. It is commonly used to produce bottles, jars, and other containers in large quantities. Extrusion blow molding is the most common type used to make bottles for foods, cosmetics, pharmaceuticals, and household chemicals.

Rotational Molding

Also known as rotomolding, rotational molding is used to make seamless, hollow plastic items like tanks, containers, playground equipment, and kayaks. In this low-pressure, high-temperature process, plastic resin is added to a hollow mold that is then slowly rotated on both the vertical and horizontal axes.

As the mold rotates, the powdered plastic coats the inside cavity of the mold and melts to form the desired shape. The continual rotation allows the liquefied plastic to evenly coat the entire mold cavity and makes hollow parts with uniform wall thicknesses. Once cooled, the finished part is removed. This technique excels at making large, one-piece hollow products.


In thermoforming, plastic sheets are heated until soft and pliable, then formed over a mold using vacuum, air pressure, or mechanical means. The softened plastic sheet takes the shape of the mold as it is pressed against it by a thermoforming machine. After cooling and hardening, the finished part is removed from the mold.

Thermoforming is commonly used to manufacture packaging like blister packs and clamshell containers from recycled plastic sheets. It also produces parts for automotive and aircraft industries, construction materials, household appliances, and medical devices. The process can use thermoplastic materials like acrylic, PVC, PETG, and ABS.


Plastic molding with custom-engineered molds provides a versatile, cost-effective manufacturing method to mass produce intricately shaped plastic components. Understanding the different types of plastic molds and molding processes allows effective utilization of this technology across product design and production. From consumer packaging to automotive parts and medical products, plastic molding will continue innovating to build the components shaping our world.



Written by chengsteven

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