Because injection molded and blow-molded products are found everywhere in today’s world, many people assume the processes are interchangeable. However, the reality is that these two methods of producing high-quality plastic parts and products serve distinct markets and create different products. For this reason, it’s important to understand the differences between these processes so that you can choose the right one for your application. Here is an overview of the top three differences between injection and blow molding.
Differences in Molds
For injection molding, the hardest part is creating an error-free mold. There must be a high precision match between the two halves of the mold; otherwise, the material flow cannot be adequately controlled, and a manufacturer will be left with imprecise plastic parts or products. Depending on your application and the required quality of the final product, it may be worth investing in the slightly more expensive injection molding process over blow molding.
Blow molds have a bit more leniency in design because each mold part forms its own wall shape. However, this doesn’t mean blow molding is without its challenges. With this process, you’ll need to factor in variables like wall thickness, air leaks, flash, and streaks. For this reason, you’ll need a team of experts who can evaluate the effectiveness of the mold and make improvements to the mold and the molded components.
Differences in Process
While both injection molding and blow molding use molds to produce cost-effective plastic parts, the way these molds are used differs between the two processes.
During the injection molding process, melted resin is poured into the hollow parts of a mold until the mold is completely filled. The injection mold is then placed under extreme pressure so that the plastic resin touches every part of the mold, effectively taking the shape of the mold.
With blow molding, a plastic tube is warmed up until it is malleable, and then it is filled with air. This pocket (or balloon) of hot plastic is called a parison. A mold is placed around this bubble of plastic while air is still sent into the parison. Eventually, the parison will take the shape of the mold.
Differences in Products Produced
As you’ve seen, injection molding and blow molding vary greatly in mold construction and process steps. For this reason, it makes sense that the products they produce also differ from each other. Injection molding creates solid parts, while blow molding produces hollow products.
Injection molding is well suited for products that require rigid parts, such as automotive components, medical devices, or housings for computers. If you need a plastic piece that is flexible, structural, or can hold fluid, blow molding is the better, more economical choice. Blow molding is often used for products such as plastic bottles, toys, and stadium seating.
Choosing a Plastic Molding Method
Injection molding and blow molding each have their place in various industries. However, blow molding is more suited for low-tech products, while injection molding is best for parts or products that are complex and require a certain degree of accuracy and quality. Before deciding on a molding method, it’s best to perform thorough research.
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