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What Type of Plastic Molding is Best for Your Company?

The nature of plastic allows it to be molded into different shapes and sizes during its manufacturing process; so which is the best type of plastic molding for you?

Types of Plastic Molding - KB Delta

The processes involved vary greatly which could make it difficult to determine what type of plastic molding is best for your company and generally, the plastic molding machine that is required.

In line with that, questions like, “should the resulting product be large or small?,” “should it be spherical, square, or feature a unique shape?,” and “should it be flexible or stiff?” may arise.

But look at it this way:

If you’re manufacturing toys, beverage bottles, large containers, and a wide range of other products, then the plastic molding process employed in one will significantly differ from the other.

Nevertheless, the decision of which to settle for has been made easy through our review to the types of molding processes for plastic as well as the techniques applied in each.


What is Plastic Molding?

Plastic molding or moulding is the transfer of liquid or pliable raw material into a rigid, hollow frame called a mold or matrix in order for the cooled or set liquid to take its shape.

The same process can be carried out with the use of glass, ceramic, or metal raw materials in a bid to obtain the desired shape.

The matrix, on the other hand, which the raw material relies on can take advantage of two molds in a bi-valve molding process. It can also have multiple parts which are put together to form the final molding piece.


Types of Plastic Molding Processes

Different types of injection molding processes are employed in the creation of the resultant shape that is required and they include:

  1. Casting Molding
  2. Rotational Molding
  3. Injection Molding
  4. Blow Molding
  5. Compression Molding


1. Casting Molding

Casting also called foundering is the simplest molding process for plastic since complex technology is not required.

As one of the oldest plastic manufacturing process, its method of operation is to allow the plastic to be heated and transformed into liquid before it is poured into the mold or cavity whose shape is desired

The liquid is then left to cool or set before the mold is removed even though the plastic would’ve already adopted its shape.

In addition, casting requires low pressure in order to create intricate shapes from the plastic liquid and it is a method employed in plastic sheeting whose level of thickness starts at 0.5 inches.

Products That Can be Created Via Casting

The materials that can be formed as a result of casting include:

  • Liners
  • Pistons
  • Wheels
  • Mill rolls
  • Cylinder blocks
  • Machine tool beds

Advantages of Casting Molding

  • It is the cheapest manufacturing process
  • The size of the object is not a limitation during casting
  • Objects undergoing casting have a high compressive strength
  • Complex structures can be created economically via this process

Disadvantages of Casting Molding

  • Defects may be unavoidable
  • Some methods of casting such as sand casting can be labor intensive


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2. Rotational Molding

In the manufacturing process of shipping drums, toys, storage tanks, and other plastics with large hollow parts, rotational molding also known as rotomolding is used.

This method was first used in the production of plastics in the 1950s and it operates by pouring the molten plastic into the heated hollow mold and sealing it.

Next, two mechanical arms rotate the metal mold at the same level which allows the softened molten plastic to drip along the sides of the mold, stick to it, and adopt its crevices and patterns.

The constant slow rotation of the mold at all times produces a centrifugal force which gives the plastic an even wall while also preventing deformation or sagging in its cooling phase.

Furthermore, rotational molds can feature parts such as curves, inserts, contours, slots, and even logos. The slots, for instance, provide a place for the product to be placed after it has been molded.

Products That Can Be Created Using Rotational Molding

Some products that can be formed via rotational molding include:

  • Tanks
  • Coolers
  • Car parts
  • Pet houses
  • Road cones
  • Kayak hulls
  • Storage tanks
  • Marine buoys
  • Recycling bins
  • Bulk containers
  • Playground slides

Advantages of Plastic Rotational Molding

  • Plastic products produced can be small like ping pong balls or as large as 20,000-gallon tanks
  • It allows excess material to be reused thereby curbing wastage
  • The reuse of material makes it an environmental viable process
  • The molds are customizable to meet the requirements of a manufacturer
  • Tooling cost is lower than the injection or blow molding process since in-mold cooling or part ejection is not required

Disadvantages of Rotational Molding

  • High cycle times at eight rotations per minute
  • High labor cost in comparison with other manufacturing processes


3. Injection Molding

A plastic molding injection process allows three-dimensional objects such as butter tubs, yogurt cups, plastic toys, and bottle caps to be created.

These products generally have high quality and they can also be commercially reproduced. There is also a need to massively produce them in large volumes with the same quality.

The method employed in this process involves the melting of the plastic in the hopper before it is injected into a tightly sealed mold. It is then passed under high temperature and pressure into the mold’s cavity directly through the runner.

Within the mold, the plastic is able to adapt its shape and when it is cool after a few seconds, the mold is opened slowly in order to allow air to break the vacuum within the injection mold.

The solid plastic is then removed from the mold with the use of ejector pins and the leftover materials can be ground and reused for other plastic products.

It is also worthy to note that the mold, in question, can be reused a number of times before there is a need to get a replacement.

Products That Can Be Created Using Injection Molding

The plastic injection molding applications include:

  • Toys
  • Butter tubs
  • Bottle caps
  • Yogurt Pots

The injection molding machine can also be used to mold car parts in the case of large machines and to create plastic parts for surgical equipment when it comes to small machines.

Advantages of Injection Molding

  • It adds an extra value to the resulting product
  • High production output allows mass production of plastics
  • Complex products can be created in various shapes and designs

Disadvantages of Injection Molding

  • The high cost of the injection molding machine
  • Custom design has to be created before starting the manufacturing process


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4. Blow Molding Plastic Manufacturing

Blow molding plastic manufacturing process is used in the production of hollow objects with thin or uniform walls including milk bottles.

The method used here is one where the plastic is heated to a molten state before it is injected into a cold mold.

Unlike other mold patterns, the one used in this case has a tube in its enclosure and when inflated, it takes a particular shape.

Air is then blown into the tube to form a balloon which allows the plastic to press against the mold’s wall and adapt its shape. When the plastic is cool, it is removed from the mold.

Products That Can Be Created Using Blow Molding

The plastic blow molding applications include:

  • Bottles
  • Fuel tanks
  • Plastic drums

Advantages of Blow Molding Process

  • The process of generating the products is fast
  • It can produce a variety of products
  • Economical and allows high-volume bottles to be created
  • Tooling cost is less expensive than injection molding

Disadvantages of Blow Molding Process

  •  The process depends highly on petroleum
  • A lot of production methods are required
  • Process and material precision are needed which creates waste


5. Compression Molding of Plastic

Compression molding is seen as a plastic injection molding alternative and it has found use cases in the mass production of bottles despite the complicated and labor-intensive processes involved in this method.

It can be used to create high strength compounds such as car tires, fiberglass, boat hulls, and other reinforced plastics on a large scale instead of small bottles that are prevalent in other molding methods.

When it comes to its method of operation, compression molding uses a second mold to compress the heated plastic liquid that has already been transferred to the cavity of a heated mold.

The force exerted by the second mold squeezes the plastic into the cavity of the mold and creates the desired shape before it is left to be cured via a heating process in order to maintain its integrity and strength.

The plastic resin is also allowed to cool and transferred from the mold. Likewise, the products which are produced with excess plastic or flashing as a result of the compression is trimmed off.

Products That Can Be Created Using Compression Molding

Compression molding is used to create thermoplastic materials such as:

  • Polyesters
  • Phenolics
  • Melamines
  • Polyethylene
  • Polypropylene
  • Polyvinyl chloride


  • Low cost due to its simplicity nature
  • Cost-effective in comparison with other processes


  • The flask may need to be trimmed
  • Cycle times may be slow thereby affecting the production of larger volume orders



Now that you know the types of plastic molding processes, you can make the decision on which is the best for your company.

The feature of each process and their area of application also answers your question as to which is the best in terms of being economical and offering the plastics of the best quality.

Accordingly, you can opt for the casting process if you’re bent on reducing the production cost and the products to be created are simple.

On the other hand, you can use injection if you want to produce a large number of bottles or even the blow molding method that comes with the perk of allowing large machine parts to be created.

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