Types of Plastic Blow and Injection Molding - Microdyne (2023)

Types of Plastic Blow and Injection Molding - Microdyne (1)Each plastic part requires a specific manufacturing process which can be significantly different from one product to another. Injection molding is used to manufacture solid components while blow molding is used to make plastic products with hollow areas, such as bottles and containers

Injection stretch blow molding combines the injection molding and blow molding processes.The plastic is first molded into a solid preform, to create a threaded bottle neck. Once the preform cools it is fed into a stretch blow mold machine. The preform is then reheated using an infrared heater and blown into a plastic bottle with forced compressed air.

Injection molding and blow molding are two core processes in plastic manufacturing. Products made through these processes are used in a wide range of industries such as automotive, food service packaging, electronics, medical devices, irrigation, dental, firearms, energy and environmental industries.

To help you better understand the different manufacturing methods available for your project, we have compiled an overview of the main types of injection and blow molding methods used by plastics manufacturers.

The Injection Molding Process

Injection molding is used to manufacture higher volume quantities of plastic products ranging in size from large components to small components requiring micro-precision accuracy.

There are many types of manufacturing methods categorized under injection molding, such as thermoplastic injection molding, over molding, insert molding, cold runner molding and hot runner molding.

Thermoplastic Injection Molding
Thermoplastic injection molding uses thermoplastic polymer, meaning it changes to a liquid state when heated. Unlike thermoset plastics that cool into permanent solid, thermoplastics can be remitted into a liquidafter cooling into a solid.

Overmolding, or two shot molding, is a process that covers an injection mold over another substance, such as metal, to improve the performance or durability of a product. A rubber-like compound, called thermoplastic elastomer (TPE), is a commonly used overmold material. An example of a TPE overmold application is the handle grips on a toothbrush. Overmolds can also be used to seal products with parts made from several injection molds.

Insert Molding
Like overmolding, insert molding is an injection moldingprocess that combines two or more components into a single finished product. Insert injection molding inserts a component into the injection mold cavity and plastic material is filled around the insert. Inserts can add strength to a product and eliminate the need for additional parts to reduce the product weight.

Cold Runner Injection Molding
Cold runner molds use a sprue to fill the runners that inject plastic resin into the mold cavity. In 2 plate molds, the runner system and parts are attached, and an ejection system may be used to separate the pair from the mold.The cold runner can reduce waste by recycling and regrinding the material, but this can also increase the total cycle time. Cold runner systems can be used for a wide variety of polymers and can allow for easy color changes.

Hot Runner Molds
Hot runner molds use a manifold to heat melted plastic resin and then send the material through a gate to fill the mold cavity. The two main types of hot runner molds are externally heated and internally heated. The externally heated molds can be used with polymer that is less sensitive to thermal variations while internally heated hot runner molds allow for better control of material flow.

Because hot runner molding does not require the use of runners, potential waste material is reduced and the recycling and regrind and process of virgin plastic does not impact the total run cycle time.

The Blow Molding Process

During the blow molding process, the raw plastic material is shaped into a hollow tube with one open end called a parison. The parison is pressed into a cooled metal mold and compressed air is forced into the parison. When the formed plastic cools and hardens, the metal mold opens and expels the product.

There are three types of blow molding processes:

1. Injection Blow Molding
In injection blow molding, a blow or core rod is used throughout the process. First a parison is injected into a split mold cavity around the rod. The parison that is formed looks similar to a test tube. The core rod transfers the parison to the blow mold machine where forced air creates the final shape. The rod then transfers and extrudes the finished product from the machine.

2. Extrusion Blow Molding
Extrusion blow molding can be continuous or intermittent. In continuous extrusion blow molding, a parison will be constantly fed into the mold and each form will be cut off with a blade as it forms. Intermittent extrusion blow molding expels each new plastic from the metal mold when it is cooled and the parison is fed into the mold only after the preceding parison is expelled.

Extrusion blow molds are generally much less expensive than injection blow molds and can be produced in a much shorter period of time. Extrusion blow molding is appropriate for smaller runs. Advantages include cost savings on tooling and shorter production time while disadvantages usually include lesser control of wall thickness and greater amount of scrap material.

3. Injection Stretch Blow Molding
Injection stretch blow molding combines the injection molding and blow molding processes. The plastic is first molded into a solid preform, to create a threaded bottle neck.

Once the preform cools it is fed into a stretch blow mold machine. The preform is then reheated using an infrared heater and blown into a plastic bottle with forced compressed air.

What Molding Processes Does Your Product Require?
What type of manufacturing process is right for your next project? Our engineers have decades of experience and understand what type of material and mold is right for you. Contact us to discuss your new plastic design or product idea today and we will walk you through the manufacturing process that is best for your project needs.

Types of Plastic Blow and Injection Molding - Microdyne (2)


What are the 3 types of blow molding? ›

In general, there are three main types of blow molding: extrusion blow molding, injection blow molding (one stage), and injection stretch blow molding (two stages). In the extrusion blow molding process (EBM), plastic is melted and extruded into a hollow tube (a plastic parison).

What are the five 5 types of plastic processing moulding? ›

These plastic moulds can then be used for a wide range of purposed. There are 5 types of plastic moulding that is considered to be the most effective and most popular. These 5 types are extrusion moulding, compression moulding, blow moulding, injection moulding and rotational moulding.

What is the difference between blow molding and injection molding plastic? ›

In general, blow molding is used to make singular, hollow products like bottles and beakers. Injection molding makes solid parts, like plates and discs, or is used to produce solid parts or pieces for plastic products.

What type of plastic can be blow Moulded? ›

MATERIALS. The materials used for blow moulding include Polyethylene (High Density, Low Density and Linear Low Density), Polypropylene, Polyethylene-Terephthalate (PET), and PVC.

What are the 4 stages of blow molding? ›

Injecting of molten raw materials into the preform mold by the injection machine. Cooling of molten PET preform to room temperature. Processing of preform by a finishing machine. Transferring of the preform to reheating stretch blow molding machines.

What are the two types of blow moulding? ›

What are the three types of blow Moulding?
  • Extrusion Blow molding. The extrusion blow molding process is to extrude the parison. ...
  • Injection blow molding. The injection blow molding process is more suitable for the production of some large-batch, but small-volume products. ...
  • Stretch blow molding.
Nov 18, 2021

What are the four types of molding? ›

4 Types of Molding Processes: Applications and Advantages
  • 1) Compression Molding. The compression molding process is used to make rubber and plastic parts. ...
  • 2) Melt Molding. When applied to thermoplastic materials, compression molding is referred to as melt molding. ...
  • 3) Transfer Molding. ...
  • 4) Injection Molding.
Jul 22, 2021

How many types of plastic molding are there? ›

The most popular techniques in plastic molding are rotational molding, injection molding, blow molding, compression molding, extrusion molding, and thermoforming.

What are the 10 different species materials commonly used for moulding? ›

The Top 10 Plastic Injection Molding Materials
  • acrylic (PMMA)
  • acrylonitrile butadiene styrene (ABS)
  • nylon (polyamide, PA)
  • polycarbonate (PC)
  • polyethylene (PE)
  • polyoxymethylene (POM)
  • polypropylene (PP)
  • polystyrene (PS)

What is the strongest plastic for injection molding? ›

One of the strongest thermoplastic materials, polycarbonate is one of the most shatter-resistant plastic materials available for use in injection molding.

What plastic is best for injection moulding? ›

ABS plastic is one of the most commonly used plastics in injection molding due to its wide temperature range, good stability, and insulating properties. ABS is commonly found in plastic toys such as Lego bricks, but it's also often used in many types of electronics, tools, and home repair equipment.

What is an example of blow molding? ›

Everyday hollow plastic objects like milk cartons, shampoo bottles, storage drums and watering cans all have a specific manufacturing process in common – blow moulding.

What is the most commonly blow molded product? ›

Cooling system overflow containers, windshield washer fluid bottles, and even fuel tanks are commonly made with blow molding. Appliance components – Your major appliances at home include reservoirs that contain fluids and help to wash your clothes and dishes.

What is the difference between blow mold and injection mold? ›

Injection molding is used for complex solid components whereas blow molding is used for thin-walled hollow parts. Injection molding forces plastic into a mold under high pressure. Blow molding, on the other hand, expands a hollow tube of plastic into a mold using compressed air.

What grade is HDPE blow molding? ›

HDPE Blow Molding grade B52H06 shall meet the requirements stipulated in IS 10146:1982 on 'Specification of Polyethylene for safe use in contact with Foodstuff, Pharmaceutical & Drinking water'.

What is the difference between Roto mold and blow mold? ›

Rotational molding is the more versatile of the two, boasting great design flexibility and low startup costs. Blow molding, on the other hand, produces products on a shorter cycle time but is less flexible in terms of design. Initial setup costs are also very high.

What is the difference between continuous and intermittent blow molding? ›

In Continuous Extrusion Blow Molding the parison is extruded continuously and the individual parts are cut off by a suitable knife. In Intermittent blow molding there are two processes: straight intermittent is similar to injection molding whereby the screw turns, then stops and pushes the melt out.

What is the difference between blow molding and stretch blow molding? ›

Stretch blow molding is a manufacturing process that's well suited for different applications across a broad range of industry sectors. Blow molding is an engineering procedure in which hollow plastic forms such as water bottles and juice bottles are formed.

What is the difference between blow molding and extrusion blow molding? ›

Blow molding is a specialized type of plastic processing used to create hollow plastic parts. The extrusion form of blow molding is a manufacturing process whereby plastic is melted and extruded into a mold. This process is specific to producing a high volume of hollow, one-piece objects.

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