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Custom Plastic Molding Techniques to Know

For the ideal product, it’s helpful to know the different custom plastic molding techniques available. Every process is unique, which you can learn more about below.

Custom Plastic Molding Techniques to Know - KB Delta

Do you need a custom-made plastic product or spare part but don’t really know how to get one? The different kinds of molding techniques that will be highlighted in the following paragraphs will reveal the ideal processes for creating the custom product you need.


Plastic Molding: What is It?

Molding refers to the process of shaping pliable material or liquid via the use of an inflexible frame known as a mold.

To mold plastics, a liquid or powder polymer – such as polypropylene or polyethylene –  is poured into a hollow mold. The intent is to ensure the polymer takes the shape of the mold.

Then, several ranges of pressure and heat are applied, based primarily on the type of process used. At the end of the entire process, the finished product emerges.


A Brief History of Plastic Molding

Plastic molding processes began in the late 19th century and were developed in order to create plastic billiard balls. At the time, most billiard balls were made of ivory.

But by 1868, American inventor John Wesley Hyatt discovered a unique way to create billiard balls by ingeniously injecting celluloid into a mold. And just 4 years later, the inventor and his brother were able to invent and patent a molding machine that automates the entire molding process. This is regarded as the first plastic injection molding equipment in the world. It used a pretty basic plunger to adequately inject plastic into a mold via a heated cylinder.

However, by 1946, James Hendry invented the screw injection molding machine. This molding machine conveniently replaced the plunger injection equipment and is still in use to this day.


Types of Plastic Molding

As mentioned earlier, several plastic molding techniques exist today. And you can use any of them to get the custom plastic product you are looking for. Here they are in no particular order:


  • Injection Molding


This process of creating custom plastic parts involves injecting molten plastic material at incredibly high pressure right into a metal mold. The mold is then cooled and opened in order to reveal the solid plastic product.

Common Uses: Injection molding is generally used for making incredibly high volumes of custom plastic parts. The large versions can easily mold vehicle parts, while the smaller injection molding machines are used for producing highly specific plastic items for surgical procedures or applications.

The versatility of the resins and additives that can be used with the injection molding technique significantly boosts its flexibility for designers and engineers.


  • Rotational Molding


Also referred to as roto-molding, this is a manufacturing molding process for producing large products and hollow parts. This occurs by pouring a resin or powder into a metal mold. Then it is rotated in a heated oven until the resin coats the interior of the mold.

Constant rotation of the mold easily creates a centrifugal force that forms products with even walls. And as soon as the mold cools, the plastic hardens and is removed from the mold.

Rotational molding is a technique that wastes very little material during the entire process. Excess materials are re-used, thus making this technique environmentally and economically friendly.

Common Uses: This technique is generally used for creating hollow plastic products such as car parts, pet houses, storage tanks, marine buoys, road cones, playground slides, etc.

Moreover, rotational molds are cost-effective and highly customizable. For instance, it can be used for molding several products, including contours, curves, and inserts. This implies that you can use this technique to create the custom plastic product you are looking for.


  • Compression Molding


This type of molding is performed by heating a mold. An already heated plastic material – which generally comes in bulk or sheets – is placed into the hot mold and pressed into a pre-determined shape.

As soon as the heated plastic is compressed into the specific shape desired, the plastic retains its maximum strength, thanks to the heating process. Then the plastic is cooled, trimmed, and then removed from the mold.

Common Uses: Compression molding is the best option for replacing metal parts with plastic components. It is generally used for making small plastic components and parts in large volumes.

The automotive industry relies heavily on compression molding as a means to create durable and strong products.


  • Blow Molding


This molding technique is generally employed for making custom, thin-walled plastic products. It is chiefly used for making parts with wall thickness that need to be uniform. It is also the go-to technique to use where shape plays a crucial role in the customization of the product.

Blow molding equipment readily heats plastic materials by injecting air that blows up the hot plastic until it looks like a balloon. The plastic is eventually blown into a mold and presses against the walls of the mold as it expands.

After filling up the mold with the so-called plastic balloon, it is then cooled rapidly and hardened. Afterward, the finished product is ejected.

Common Uses: Most people that use bottles, fuel tanks, and plastic drums have zero knowledge about how they are made. But these products are all produced using the blow molding technique.

This technique is highly economical and fast as the mold itself generally costs far less than injection molding.


  • Extrusion Molding


This technique bears great similarity to injection molding; the only difference is that using this technique produces long continuous shapes. Another significant difference between extrusion molding and injection molding is that the former uses what is known as a ‘die’ and not a mold.

Extruded plastic parts are created by squeezing hot raw material via a custom die. Other forms of molding usually employ extrusion in order to get the resin into a mold. But extrusion molding technique involves extruding the melted plastic directly into the die. The shape of the die – not the mold – readily determines the overall shape of the final custom product.

Common Uses: Straws, hoses, PVC piping, etc., are just a few examples of plastic products created via the extrusion molding technique. If you are looking for a custom product that does not need to be round but must have the same shape from top to bottom, this is the molding technique to use.



As you can see, there is more than one way to skin a cat, i.e., different ways to create a custom plastic product. Every molding has its weaknesses and strengths. This is why engineers and designers make it a priority to fully understand the different molding techniques.

However, unless you are a specialist or technician, you should leave the production of custom plastic parts or components to experienced professionals.

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