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The difference between Injection Moulding and Blow Moulding

When it comes to the molding options for the production process, manufacturers use two common methods, namely Injection Molding and Blow Molding. Both play an integral role in the custom manufacturing of plastic parts that are used worldwide, especially in the toy industry.

While it is the personal choice of the manufacturer what process he wants to opt for, it’s good to know the key differences between the two to make the appropriate choice. Each method of molding uses a different process and comes with its specific set of advantages and disadvantages. Here’s a quick guide that will help you to differentiate.

A Complete Introduction to Injection Molding

Injection Molding is one of the effective ways of producing plastic parts in a large volume. It is typically used in mass productions where the identical part is being manufactured thousands of times in succession.

The principal benefit of using injection molding is its ability to scale production to a great extent. It has numerous applications in a wide variety of industries, be it the automotive, medical, or toy industry.

Injection Molding is a process to manufacture molded plastic products by pressing molten plastic materials into a mold. The process is further divided into six major steps, namely – Clamping, Injection, Swelling, Cooling, Mold Opening, and Removal of Products.

This molding process uses dedicated equipment which is further divided into two units – a clamping unit and an injection unit. Also, there are two types of clamping methods – the toggle type and the straight-hydraulic type.

How does Injection Molding Work?

The first stage of Injection Molding is to create a mold itself. It is made from any metal, like Aluminum or Steel, and uses the precious machined to match the features of the product they are to produce. Once the mold has been created, the material for manufacturing a part will be injected into a heated barrel and mixed with the help of a helical-shaped screw.

The molten plastic will be then injected into the mold cavity where it cools and hardens later on. Manufacturers can reduce the cooling time by using the cooling lines that circulate oil or water from an external temperature controller.

Mold tools are generally mounted on platens or plate molds, which open once the material has solidified so the part can be ejected from the mold. Depending on the part, molds can feature single or multiple cavities. While steel molds are extremely durable, they are quite expensive and may not be suitable for low-budget projects.

There are plenty of things that should be kept in mind before opting for an Injection Molding process. Check them out here.

    • Entry Cost
  • While Injection Molding is a cost-effective way of creating thousands of identical products, the entry cost of this molding process is a matter of consideration for manufacturers. The initial cost of Injection Molding includes the cost of machinery and the molds themselves, making it a bit higher.
    • Design Factors
  • Injection Molding works best with a minimum number of parts and simplified mold designs. Hence, manufacturers are required to keep the number of parts limited and easy the geometry of the items to carry out the process easily. Also, consider the design of the mold tool which is important to avoid defects during production.
    • Production Quantity
  • The next important thing is to check how many parts you wish to produce with the Injection Molding method as it will help you decide whether choosing this molding process is cost-effective or not.

The Pros and Cons of Injection Molding

Although Injection Molding has innumerable applications in a wide range of industries, it still isn’t the best choice for every project. Hence, before you decide whether or not to use injection molding, carefully consider its major advantages and disadvantages to make an informed choice.

Pros

    • Mass Production
  • Injection Molding is a perfect way to produce large volumes. However, you must pay attention to weld lines, corner transitions, vent and gate placement, and more to achieve precise parts.
    • It’s compatible with a wide range of materials.
  • The best thing about using Injection Molding is that it is compatible with over 25,000 engineered materials, including thermostats, silicones, resins, thermoplastics, and more. The commonly used materials include Polystyrene, Polyethylene, ABS, and Polypropylene.
    • It is cost-efficient in the long run
  • Since Injection Molding is an ideal choice for mass production, this technique is highly cost-efficient in the long run. Also, it generates less post-production material waste and allows you to reuse the material, which further lowers its cost.

Cons

    • Long Initial Lead Times

Injection Molding has a longer lead time as compared to other manufacturing processes. It often takes 5 to 7 weeks to manufacture parts and 2 to 4 weeks to produce and ship them.

    • High Entry Costs
  • Since customized molds are to be created for each project, initial costs for this process are high, making it unfit for low-volume and low-budget production runs.
    • Changes are expensive
  • The whole concept of Injection Molding is based on the molds, which are created at the beginning of the production process. Hence, making a design change during the production or post-production is not valid for Injection Molding.

What is Blow Molding?

Blow Molding is primarily introduced to manufacture high-volume, one-piece hollow objects. This process follows the basic steps found in glass blowing and is suitable for creating uniform, thin-walled containers.

It covers three main thermoplastic processes, namely Extrusion Blow Molding, Injection Blow Molding, and Stretch Blow Molding. Extrusion is the largest of all three, followed by Stretch and Injection.

The process of Blow Molding involves heating and inflating a plastic tube known as a parison or preform. Bottles and packaging are the two major applications of the Blow Molding process.

The parts included in this manufacturing process are

    • The feed from the Extruder
    • Molten Plastic
    • Extruder Head
    • Airtube
    • Parison
    • Mold
    • Air Pressure
    • End Product

How does Blow Molding Work?

The Blow Molding process simply begins with the Extruder machine, consisting of a cylinder and barrels where the plastic is to be heated up. The feed from the Extruder is given as input into the Blow Molding machine.

Melted plastic will then act as a medium for the creation of plastic hollow components and has to be sent to the Extruder Head so that it can be passed through multiple other channels. The air tube is used to pressurize the air when the molten plastic injects into the mold cavity and is about to bulge. At this stage, the Parison, or thermoplastic molten tube, comes into the role. It has a hole at one end through which compressed air can pass.

Blow Molding includes a mold cavity, which further consists of patterns where molten plastic is to be deposited and solidification takes place. When the molten plastic transfers to the mold cavity from the parison, air pressure is added into the cavity and the molten plastic touches the mold corners, and then solidification takes place. Once the solidification is done, manufacturers can then obtain the final product.

The Pros and Cons of Blow Molding

Here, we have outlined the major advantages and disadvantages of the Blow Molding process, that make it different from Injection Molding.

Pros

  • It can produce variable products

The best thing about Blow Molding is that it can help create variable products, making it an integral part of several applications and industries. The products created using this technology are the seat support for vehicles, toy wheels, fuel tanks, flower pots, and more.

  • Low Cost

Since Extrusion Blow Molding uses a lower level of pressure, it means that machinery costs are low, making it a cost-efficient choice for low-budget production projects. Besides that, this technology helps reduce labor costs.

  • It promotes productivity.

Since it helps create a variety of products, this process has now been adopted universally. It significantly increases production capabilities and helps manufacturers produce greater quantities in just a short time.

Cons

  • Its dependency on Petroleum might bother some.

Identical to the gas industry, the Blow Molding sector is based on petroleum to produce plastic products. Owing to this, it has become an ongoing threat to the diminishing oil supply and impacts the environment greatly.

  • It comes with limited uses.

Since it requires air pressure to complete the process, Blow Molding is quite limited to hollow forms, like bottles, toy wheels, etc.

  • It may need the accuracy of material creating waste.

As this technology is mainly adopted to manufacture hollow products, examining the wall thickness should be precise; otherwise, it restricts the wasted material from processing products with particular dimensions.

The Major Differences Between Injection and Blow Molding

Since you are now well aware of the Injection and Blow Molding process, let’s move on to key differences that will help you pick the most appropriate method that suits your production project.

  • Molding Procedure

The major difference between Injection and Blow Molding lies in their production procedure. When it comes to Injection Molding, the plastic is sealed in the injection chamber, and the mold throughout the process.

However, in Blow Molding, the blow mold begins when the mold is removed from the plastic, which gives some more freedom for the blowing to expand the product to attain the necessary, final size.

  • Usage of Air

The second most important difference between Injection and Blow Molding is the usage of air. While air is totally unacceptable in Injection Molding, it is the major component in the Blow Molding process.

If air is present during the Injection Molding manufacturing process, it can create air pockets and bubbles, which further create weak spots in the final product.

On the other hand, Air is extremely important when it comes to the Blow Molding method as this technique revolves around the air pressure, which is required to push and expand the product. All in all, without air, blow molding is not even possible to perform.

  • Different Molds

While both methods require a specific mold design to carry out the process, the mold design is completely different, which further differentiates these two techniques from each other.

Injection Molds must feature great precision between mold halves so the flow of a material can be controlled. Creating the mold is 90% of the battle when it comes to the Injection Molding process.

However, the concept of molds in the Blow Molding method is somewhat different. Blow Molds give more design freedom between mold halves; hence, creating a mold is only half the work done as several other factors must be monitored to obtain the final product.

  • Cost matters the most

Yet another difference between Injection and Blow Molding is their initial or set-up cost. Since injection molding mainly depends on mold precision, its initial cost is way too higher than any other plastic production method.

Blow Molding, on the other hand, isn’t fully dependent on mold preciseness and accuracy; hence, it is less expensive than Injection molding.

  • Range of applications and products

Perhaps the most noticeable difference between these two molding processes is their products and applications. Injection Molding is mainly used to create solid parts, while blow molding is suitable for manufacturing hollow parts.

In other words, Injection Molding is an ideal approach for uniform, rigid products, while you need to choose Blow Molding if you are looking to create flexible and structural parts, like toy wheels.

  • The ease of making design changes

The next major difference lies in the ease of making post-production changes. Since Injection molding solely depends on the molds, it is quite challenging to make any post-production change in the products created using this technique.

However, Blow Molding equally values other factors, like air pressure, wall thickness, etc., along with mold; hence, making post-production changes in the products manufactured using this method is possible and less expensive.

That’s all about the differences between Injection and Blow Molding. Both methods are popular and play a critical role in the manufacturing process of plastic parts and products. Hence, manufacturers are suggested to pick the option that goes well with their production project, product requirements, and budget.

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