How to make a complex mold

[Jtultra]

Hi, I'm new to composites and I'm planning on duplicating a complex piece from a dash in a car. I can't think of a way to duplicate it, I may use a 2 piece silicone mold but the way it is shaped it seems almost impossible. The whole piece is curved back at an angle, w/ many clips and crevices in the back. Anyone have any ideas? I'm gonna post a link to pictures of it shortly.

 

[patprimmer]

It is probably an injection moulded part, from a mould that cost many tens of thousands of dollars to make, and possibly over $100,000. If so it will not be easy to reproduce it precisely in detail without spending a considerable amount of money.

Even if you digitise the part and cut a mould in a CNC mill or machine centre, details like snap fits of components and spacing of mounting holes etc will be the most problematic due to undercuts and mould shrinkage.



Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Jtultra]

here are the pics

http://jdmdash.mypicgallery.com/mpg/Route.asp

 

[MikeHalloran]

The guy who made the original part probably spent upwards of $20,000 just for the blocks of metal from which the mold was cut, and another $80,000 to generate and polish and finish the actual cavity.

How good a duplicate do you need, and how many?

A silicone mold can do a nice job on the front face, and probably survive making quite a few acrylic castings.

The rear face is more difficult. A silicone mold won't survive many casting sessions before tearing. Precise features like locating surfaces won't come out right. Snap fits won't work in acrylic resin, and silicone molds won't work on stuff like ABS or polyolefin, which is probably what the original is made from.

For quick and cheap, the best you can do is replicate the front face by slush casting a veneer of acrylic on a silicone mold, and glue the resulting faux part in place.

Realy long shot: Find and acquire the original mold.

Less long shot: Find the original replacement parts in warehouses and dealer stock, and buy them.



Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[Jtultra]

what is i fill in those cavaties to make those parts solid? and how do you slush cast a veneer of acrylic on a silicone mold

 

[MikeHalloran]

First, you make a negative of the exposed face with the silcone. Then, you put some release agent on it.

Then, you mix up a batch of acrylic casting resin, spoon it on to the coated silicone, and keep moving the silicone around underneath it until the silicone is fully coated and the acrylic 'kicks'. You might want to preinstall some dams around the edges of the silicone to keep the acrylic from running off the negative's face.

When the acrylic has cured, peel away the silicone and you have a replica of the exposed face of the plastic part, with an irregular wall thickness, and nothing behind it.

Next, instead of trying to reproduce the back face of the plastic parts, I'd make a replica of the part of the car that faces the back face of the plastic parts, make an acrylic negative of that, and bond the two acrylic pieces to each other back to back, maybe with some urethane insulation foam between them to stiffen and bond them.

The resulting extra- thick laminated assembly could be stuck to the car with a little rubber cement on the back.




Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[Jtultra]

since the front is curved, do you guys have any ideas to how to make a proper mold of the front. I don't want to make a flat container of silicone and dip it in because it would leak to the back due to its shape

 

[davidinindy]

It doesn't seem like you have enough experience or knowledge to understand what the others have explained to you. I would highly suggest finding someone in your area with experience, and having them help you out. If I knew your location, i might be able to recomend someone.

 

[Jtultra]

yea, I don't have much experience. but I'm trying to learn. I live in Marietta GA, north of atlanta, GA

 

[Pud]

If you only need a few it might be worth geting them scanned (reverse engineered) and made as rapid prototype parts (SLA/SLS etc) - modern (SLA) materials are available to reproduce most properties. You will then have all the clips etc on the part.

Rgds

Harry

 

[CAddison]

the part is the top piece of the center dash that belongs to the japanese domestic market (jdm) toyota celicas. the u.s. versions offer a 'sunglass holder'. it's in high demand in the 'automotive tuner' market and it's used to house a tv/navigation lcd screen.

as already stated, it's pretty easy to make a mold for the face. u.s. composites sells many mold-making materials (

http://www.shopmaninc.com/moldmaking.html

) and i highly recommend them as a source for non-commercial fabrication. even though there are many companies that buy products from them in bulk, they also sell in small enough quantities so that personal projects can be done..such as in your case, jltura.

as for the back clips, i can't offer much help. it is an injection molded piece..as with the rest of the center console so duplicate fabrication would be a huge hassle...and maybe impossible without pouring a lot of cash into the project.

i assume you are trying to duplicate this piece to sell to others for a profit (they are usually sold for about $130..but the cost of materials is probably only around $50 or less..as a rough estimate). in this case, i would suggest you only fabricate an 'attachment piece' that you would bind to a cut-out original u.s. spec console. (you would have to get people to send you their piece, then you would cut it out and fit your attachment duplicate). this way you would not need to worry about the clips..and you can still leave a very professional, original look.