Thanks, Tim! This is a great explanation. After looking around, I noticed that Design News had an article about this process last year which went into a little more detail. This site has a schematic which illustrates the process. And this site shows a similar process where the projectile is propelled by water instead of gas. What a neat process!
In typical projection injection molding, a projectile shaped like a bullet is loaded onto a hollow pin the molten material is molded over the projectile. It is usually loaded with some sort of automation or pick and place. When the skin has cooled enough, the projectile is forced through the part by high pressure gas (usually nitrogen). The projectile is usually lodged into the end of the part. The benefit of this process over gas assist injection molding is a uniform wall thickness that is similar to an extrusion interior.
sensor pro: Your explanation is very clear. However, I'm still confused by the use of the word "projectile" in the article, and I'd still love to see a video of the process.
From what I know, the molding is synchronizes in a way that first the main section is molded and then the temperature drops to cure the first set of parts. Then the second material is propelled via numerous tube guides to variaous points in the mold interface of main parts and spreads evenly. It is important to inject the material in many places to keep the thickness consistent.
sensorpro: Ok, so where does the projectile come in? Sorry if I am being dense, but maybe it is just the use of the word projectile which is confusing me.
Imagine you are molding two sections that have to be removed and then sealed together. In this process the mosl creates both parts in a proper position as they will be matched after molding and then while still in the mold specially positioned guides inject another sealing material that bonds both parts.
This way a complete assembly is removed from the mold.
I thought I understood the description of the process right up until I got the the sentence "a projectile then forces the majority of the still liquid elastomer out." I'm envisioning bullets shooting through the mold cavity, which I'm sure is not correct! Is there a video of this process, or something which would help me get a better idea of how this is done?
This is the kind of innovation that's plentiful in the auto industry, yet too often overlooked when we discuss technical advancements in vehicles. Most automotive engineers spent countless hours struggling to cut pennies from their bottom lines, knowing that those pennies mount up when they're building a couple million vehicles per year. Kudos to the engineers who developed this. Good story.
This is very interesting. Clearly a technique that saves time and possible weight, duw to part count. It remind me a molding method I used some years ago called "Two step injection", where would inject conductive sections with conductive polimer and then the shell using regular PPS. This gave us a nice looking part without any metal parts, which resulted in a lower part count, assembly time and reliability.
I see that this process may bring out numerous benefits.
Are there weight savings associated with integrating more previously separate components into a one-piece assembly? If so, I'm betting we'll see processes like this agressively adopted as automakers look for any and all weight reductions to help increase mileage (in gas and hybrids) and range (in EVs).
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