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Iknowyoulovereadingso..
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Discussion Starter · #1 ·
i've been curious as to how bumper covers are actually made. I know the process involves creating a mold and filling it with a substance and letting the substance cure while taking the shape of the mold.

1) how are molds made? what are they made from?

2) what substances are used to make the bumper? is it just plastic or something else?
 

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Banned
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5,364 Posts
Crash Course in Design, Manufacturing & Production - I do this for a living

Bumper covers are made using a process called injection molding, most likely. They can also be made with rotation molding or blow molding(very unlikely).

To injection mold there needs to be a two part mold (usually more than 2 parts) These two parts are closed together, and melted plastic is injected into the cavity. After about 3 or 4 seconds, the plastic is cool enough for the mold to be "knocked out"

If you look at a plastic part, say for example, the inside of a bumper cover or for simplicity's sake, look at the inside of a plastic lid (im looking at the choco nesquick lid) you will see that the panels of plastic have lines that run across them, and you will also see little circles and if you look hard enough you will find a "nipple"

The plastic lines are the seams where the molds connected. The circles are the knock out points. When the mold is opened The part will stick to the male part and an actuator mechanism will hit the part in several places at the same time and release the part from the mold. That is what leaves those circles there. This will usually occur on the non-cosmetic side.

Finally, if you can find a nipple, or several. That is the point where the injection of molten plastic ocurred. It leaves a nipple because of the retraction of material once it has poured the required amount.

Finally, high production molds like the ones used to make our bumpers are made out of metal. Preferably aluminum since it dissipates heat faster compared to steel.

How are molds made? Well, the designers at nissan drew up your Sentra on a piece of paper, then they made a 3D computer model. They probably did more than one and once the decided on a final shape, they created the entire vehicle in 3D space, with each part connecting to the other and all hardware in place. There are many programs they could have used but that's another thread. Once they had the FINAL look, they broke out the bumper onto a file by itself and sent it to a machine shop. Once at the machine shop (probably at Nissan also) they translated that 3D info into a 2D machining file. Then they carved out the shape of your bumper onto the mold. I dont know Exactly how many pieces our bumper was made out of.
(For this explanation, I have by-passed the whole auto clay modeling part of the car design that you sometimes see on tv because it has nothing to do on how to make a mold)

Once they carved out the shape of your mold, the plugged the molds into a huge injection molding machine and programmed the machine on how much juice to squeeze in the mold, how long to wait, which mold part to pull out first, how deep to push the knockers, etc etc etc.

After that is primed, painted and BAM on the car........ whew
 

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Own3d! by puddy-tats!
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501 Posts
My bumper cover is off and I am taking it to the shop for disposal tomorrow. Would you like some pictures of the inside for curiosity's sake? There's a hole in it, so you can kinda get a little peek at the styrofoam in the interior but not much.
 

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Iknowyoulovereadingso..
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Discussion Starter · #9 ·
^^buckswife, sure i would like to see. im trying to TRY and lean a little about how they are made. ive seen how models are made and am just curious as to if its kind athe same thing
 
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