- April 29, 2020
- Posted by: Plastic Injection Molding
- Category: plastic injection molding
A little late to add something about the difference between extrusion and injection molding, blow molding, but I want to add a practical insight into the market that includes the factors of how much the molds cost and how many items are desired.
Extrusion is a continuous process that is used to make sheets, tubes and profiles, films and coatings, wire, filament and fiber coatings, blow mold feeding and pellet mixing / manufacturing for other processes, including injection molding. Continuous extrusion dominates these markets: There are ways to extrude in a closed mold, perhaps useful for low volume applications.
Almost all injection molding actually does this too, using a screw to melt the material, and then as a piston to force the melt into the mold. However, these processes are always called “injection” and the use of the phrase “extrusion molding” is confusing without further explanation.
Basically, FILLS injection molds, blow molding (and sheet thermoforming) drag material to the mold surfaces. As a result, injection molds need to take much more pressure and are therefore much more expensive.
Injection blow molding is a process that has always existed for small containers, but has grown due to PET beverage containers; In this process, the preforms are injected, then reheated, stretched for added strength, and molded into molds. Most of these preforms are manufactured by straight injection molding in very large and very expensive multi-cavity molds, which become economical due to the huge volumes of these products on the market.
Preforms can also be made using a combination of partial injection and compression (first seen as Dynaplast Co-Blow in the 1978 K show), which allows for lower melting temperatures and corresponding benefits for PET food / beverage packaging. It can also allow for lower mold costs and thus be preferable in low volume applications that do not run 24/7 for weeks or months at a time with the same product.
All of the above is related to thermoplastics. Thermosets (phenolics, epoxies, some urethanes, certain polyesters) are another world, they can be compression molded, transfer molded, injected, even continuously processed (pultrusion). They use different materials and generally serve different markets, they rarely compete with thermoplastics.
And which is better?
Well depending on what we are looking for. From a mass production point of view, plastic injection molding ends up being the best of both processes.
Injection molding of parts is a popular practice in the thermoplastic industry, and facilitates the manufacture of countless objects that we use in our daily lives.
From components of the cars we use every day, to many toys that children have fun with, this technique has proven to be very efficient and, in addition, has led to the replacement of plastics with other dangerous materials or that deteriorated much earlier, like wood, glass or some metals.
Massive chain production becomes much easier using plastic injection molding. The pieces will remain with the highest quality as long as the machine is properly adjusted, and also allows certain variants without having to make much effort.