Posted by Nancy Grossbart
5 ways products manufactured by injection molded foam differ from compression molded foam, not counting the obvious...Injection molded foam products are made by a pellet to product process, injecting a melted pellet into a closed mold foaming the formula into a multi-dimensional design. Compression molding foam can't come close to creating the same complex designs. However, when injection molding produces the same, or similar, product to compression molding here's how they differ.
Aesthetic Quality. When it comes to a finished look, the overall appearance of a compression molded (vacuform/thermoform) foam part cannot compare with that of an injection molded foam part. The increased density, and perfect "mold" finish of an injection mold, produces a part with far superior aesthetics. Because the foam used for compression molded parts is outsourced, the quality of the foam is also likely to be variable, affecting the final aesthetics of the part. On the other hand, because the injection molded foam is manufactured in-house with the foam and part made simultaneously, the quality is always consistent.
Specific variables that affect quality in compression parts, but not injection parts, are:
- inconsistent cell count within the foam, variable pigmentation and density in the raw materials causing color variation
- inconsisent part to part processing time, temperature and degree of compression causing variation in part definition.
Dimension Quality: The ability to produce a consistent dimensional part is based on how well the molding process can be controlled. The pellet to product process means that the manufacturing of the foam, and final part, are one and the same. Most processing conditions can be controlled and duplicated, resulting in minimal part to part variation. Compression molding, however, starts with a bun or sheet of foam that is heated and molded into a different shape, subject to far more variable processing conditions. In addition, the need for final trimming of the compression molded part can also be a major contributor to a low quality image.
Thickness Variation: If the final product has varying height profiles, a compression molded part must start with a sheet (bun) of foam that is the height of the tallest dimension of the part. If the foam chosen for the compression molding process does not come in a thick enough bun, laminating sheets together is required to form thicker buns. This can result in that some parts have a lamination line which can delaminate with time. Injection molded foam parts, however, can be made to any height, not limited by the process, without need for lamination.
Post Mold Stability: Another area where the two processes differ significantly is what happens to the part after it is processed. Injection molded parts are extremely soft and malleable when they finish their molding cycle. During the post molding phase, a cooling fixture may be required to help the part maintain its shape. Unless the part is subjected to external forces that causes it to change shape, the final cooled part will be exactly what was expect. On the other hand, compression molded foam parts can suffer post molding shrinkage and warp, even if cooling fixtures are utilized.
Cost and Value: Compression molded foam parts will almost always cost less than injection molded foam parts. Not only is the tooling and manufacturing equipment less expensive but the parts as well. Because compression molding uses bun stock, low density (inexpensive) foams are often chosen. This results in lower quality products that are great for a give-away or other temporary product. Injection molded foam products, while more expensive, are attractive, with long lasting value.
Both compression molded foam and injection molded foam have their place in the world of manufacturing. Choose the foam process that is best for your product.
Posted by Nancy Grossbart
It's amazing how much you can learn about subjects that you thought you had no interest in.
I majored in anthropology in college and never used any of it after I was graduated. My career had been exclusively in the marketing, advertising and graphic design area until 1999, when we came up with the idea to manufacture Injection Molded Foam parts with this incredibly unique process.
In the past 10 years on the job, I have gained a deep understanding of 3D geometry, production, quality, testing and standards, distribution/shipping and foaming materials.
Gaining this kind of knowledge is good for business because it allows you to walk and talk the talk. And if you are the least bit verbally adept, you will find potential customers asking you questions about your background that can shock you.
I have been asked more times than I can count if I am an engineer. This question has always made me laugh. Me? An engineer? Obviously, the answer is no but I must be doing and saying something right or why would people ask.
My favorite, however, is when Ron Snyder (Croc's CEO) asked me if I was a Polymer Chemist. OMG. That one really made me roar with laughter (on the inside). We were sitting on a boat in a Miami harbor beginning our relationship with Crocs. I was trying to remain professional so I didn't laugh out loud. At this point, I guess I had learned a lot about foaming materials, enough to "convince" a highly experienced and intelligent person to believe that I knew what I was talking about.
It's a perfect example that, if you want to, you can always step out of your comfort zone to learn the most complicated things.
I'd love to hear about the job you have that you were not qualified for when you started!