July 14, 2022

Extrusion vs. Injection Molding, blow molding

blog aco mold

A little late to add anything about the difference between extrusion and injection molding, blow molding, but I want to add a practical market view including the factors of how much the molds cost and how many items are wanted.

Extrusion is a continuous process used to make sheet, pipe and profiles, film and coating, wire covering, filaments and fibers, feeding blow molders, and mixing/making pellets for other processes, including injection molding. Continuous extrusion dominates these markets — there are ways to extrude into a closed mold, perhaps useful for low-volume applications. Almost all injection molding really 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, injection FILLS molds, blow molding (and sheet thermoforming) draws 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 always existed for small containers but has grown because of PET beverage containers; in this process, preforms are injected, then usually reheated, stretched for greater strength, and blown out into molds. Most of these preforms are made by straight injection molding in very large and very expensive multiple-cavity molds, which become economical because of the huge volumes of these products on the market. Preforms can also be made by a combination of partial injection and compression (first seen as Dynaplast Co-Blow at the 1978 K show), which allows lower melt temperatures and corresponding advantages for PET food/beverage packaging. It also may allow lower mold costs, and thus be preferable in low-volume applications which don’t run 24/7 for weeks or months at a time with the same product.

All the above relate to thermoplastics. Thermosets (phenolics, epoxies, some urethanes, certain polyesters) are another world, may be compression molded, transfer molded, injected, even processed continuously (pultrusion). They use different materials and usually serve different markets, seldom competitive with thermoplastics.

Related Blogs

blog aco mold
Injection molding gears, consulting a qualified gear engineer

Gears are classified by their AGMA (American Gear Mfg Ass.) rating, AGMA 9 are easily achieved with injection molding and I have done AGMA 12 with injection molding. The AGMA …

blog aco mold
Molding sink marks determining

The two biggest determining factors of molding sink marks are product design and processing with the assumption that the tool is functioning correctly. With that being said there is a …

blog aco mold
How to calculate Weight tolerance of a molded part?

We understand that with plastic parts, weight is the best method of controlling the process capability. Is there a guideline or standard for defining the tolerance? The most common method …

blog aco mold
Difference Between Plastic Injection Molding and 3D Printing

The fees for a set of plastic molds may cost thousands or even hundreds of thousands of dollars. What if the products have many styles but with a small quantity? …

Tell us your request right now and contact us today about getting started on your next project together!

Email:
sales@acomold.com

Or Fill Out The Contact Form Below:

Support Your Business with Better Molding Solution

Contact Info
Copyright © 2023, ACO Mold. Terms of Service and Privacy Policy. All rights reserved.  Powered by ACO MOLD.
1 1.png

Join Our Network

Please email to sales@acomold.com
or fill out the contact form below: