cost of injection molding? 1

[oaky]

I'm trying to figure out the cost of manufacture a small plastic part, from begining to end. It's a very simple design, basically just a cover, about 2 inches cubed with hollow inside. Can anyone help me find pricing for this. For example, initial costs, small prodition run costs. Any help would be very appreciated.

oaky

 

[insideman]

Your description is a bit hazy, but seems to be a 5 sided cube, two inches on a side. You do not specify material or wall thickness.

Assuming high impact styrene at $0.60/lb and wall = 0.06 inches:

Part weight is about .05 pounds. Material cost=$0.033

Cycle time is about 20 seconds or 180 shots per hour. At $35 per hour, cost to mold is $0.19. If you have multiple cavities, divide this cost by the number of cavities.

Add more for packaging, shipping, profit.

This is a simple mold. For a single cavity it should cost about $9000. This should include a sample run of several hundred parts. For future runs a setup charge of $250 to $750 per run would apply.

Does this help?

 

[airkidd]

dont forget about the cost of tooling

 

[insideman]

Airkid: I DID include tooling!

 

[oaky]

Insideman,

You're the Man! That helped so much.

Yes, my discription of the part is "a bit hazy", but your assumptions were right on. Let me try to discribe it a little better, and see if you can find any hidden costs.

It has to be durable, able to withstand say a 200 lb. person stepping on it, dropping it on cement, things to that degree. With that, would the high impact styrene and .06 in. walls be sufficient?

As for disign, to be more discriptive, the basic shape is a 5 sided cube, but with a rounded top. So it's kind of a cross between a cube and a cylinder. The base being a square, rising up to the shape of a cylider at the top.

It also has to have a small opening at the base, on one side, shaped like a bell or a hat, so a small rope can slide through it.

One last thing, the part will fasten to a piece of thin metal to close the bottom side. I was thinking this could be done with screws running throu holes in the metal and into the plastic. So for this the part would need some sort of studs to screw into. Can you estimate the amount of additional material this would require? Or any other suggestions on how to connect the metal and plastic, and still be able to access the inside?

Anymore information you can give me would be great.

Thanks,
oaky

One last thing, can you explain why multiple cavities would reduce the mold cost?

 

[insideman]

Last question first: Multiple caviies does not reduce the mold cost. Quite the contrary!
It does reduce the cost to mold the parts since multople parts are molded in each shot, saving press time.

Other questions/comments: Rounded end is no problem, will reduce amount of material used slightly. Hole in end is no problem. Not sure whether this is what you have in mind...

Strength should be OK.

Bosses for screw attachment of a sheet metal coveer COULD be troublesome. I need to think about this for a while, maybe come up with a good design. This will add to mold cost, material cost, and may effect cycle time. I will prepare a rough drawing of this and get back to you later.

 

[insideman]

I will attempt to attach a sketch of a design that should work well. The bevels on the outside serve to eliminate long core pins for the screw bosses and blobs of plastic in the corners (which would bring on troubles with warps and loooong mold cycles.)

I guess I don't know how to attach something here. I can Email it to you if you give me your Email address.

 

[patprimmer]

Snap fits might work to attach the metal part Regards
pat

 

[Soupcat]

Correct me if I'm wrong Insideman but at a cost to mold of $0.19, I'd suggest that dividing this cost by the number of cavities for a multiple cavity scenario is a dangerous comment to make? I know if I were charging 20p for a single imp unit cost, I'd expect a 4 imp tool to cost that same part at 13.5p. Just an observation.
Oaky, also bear in mind the enviroment that the part will be in, chemical & temperature exposure etc as this will affect the material selection process as well as loading.

Kieran

http://www.moulddesigner.com

Patprimmer, did u get my email last week?

 

[patprimmer]

Yes Kieran, I did recieve your e-mail and the image was perfect, and enlightening.
I havn't managed to dig out my info yet, but I haven't forgoten.
When I look at the image, and the draft angle, a 250 Kg load(from memory) will generate considerable side force. The shape of the bottom edge of the ribs will be critical. If they can roll over the top edge, and form a bit of a hook to hold the sides of the lower tray in, I am sure that would help considerably.
It does look like a very nice design.
I would expect that there could be some problems with filling the cavity inthe centres of the grid area. with weld line and gas burns a potential problem.
I like the rib around the bottom, as it will partly counteractthe tendency of the sides to shrink in. It also appears to have good radii between the base and sides. This will help reduce the extent of the hot sopt on the inside rad, and reduce the tendency to pull in Regards
pat

 

[patprimmer]

I also agree, multiple cavities do reduce part costs, but it is not a simple linear relationship. The more the cavities, the slower the mould runs, and the greater the chance that not all cavities are working, hence, 4 cavities might be a 60% or even 70% saving in a good example, but not a 75% saving. Also, often a larger machine is required, which has a higher hourly rate. Regards
pat

 

[Soupcat]

Pat,
I agree with you that the 250 Kg load will generate considerable side force especially on the bottom few of the stacked trays. I have created an interlocking form to counter any tendancy to splay. I've also had an analysis carried to confirm that it will perform under all conditions stated and incorporated a few land areas within the grid section for ejectors which should eliminate gassing. My only concern I quess is that Acetal is the correct material for this application and that it will perform as required over the products lifetime.

Kieran

http://www.moulddesigner.com

 

[patprimmer]

I have found reams of data on Acetal and hydrolysis, I am now deciding just how much to scan and send Regards
pat

 

[Soupcat]

Thanks Pat, don't be spending too much of your time sending the info now in fairness. Enough to point me in the right direction,

Cheers

Kieran

http://www.moulddesigner.com

 

[prototypeman]

If you should decide to go ahead with a prototype go to

http://www.prototypemold.com

Kevin can help you without breaking the bank!

 

[einzats]

Hi, this is einzat. The question I have is; I need to make hundreds of thousands of polymer-wax parts that are small-about 3"x1/4" at the largest. My plan is to re-create 20 or so parts using a soft epoxy compound [like putty] in my soft silicone[reinforced] molds, then cradle them in a plaster plate, representing the positive half of a injectin-mold. I then plan to use chemicals similiar to those used in printing industry to create a "conductive" surface[basiclly a silver nitrate film] take this to an electro-plater and have this side nickle plated to 1/8th inch thick. Next I would gently break away the plaster, clean it up, and bring it back to the electro-guy and have him put a release on it[graphite powder?] and plate the other half. I would then go to an aluminum foundry and make the plates geometrical for clamping. I have a bench-top injection mold device that can do the rest. Is this feasible? Do you know the price of basic electro-plating [nickle sulfamate watts bath] has this technique worked for this apllication before? These parts are highly detailed and are designed to articulate in various ways [joints etc.]