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Production level molding
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Soul Rider
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PostPosted: Apr 11, 2010 5:49 pm    Post subject: Production level molding Reply with quote

I'm embarking on a molding project that will duplicate a small scale production mold. We've all seen the molded boards, such as Inland Surfer or Placebo. For boards that are going to be mass produced this methodology offers many advantages:

1) Identical production
2) Parts (boards) come out of the mold nearly finished
3) Lower direct materials inventory needed
4) There is no shaping involved so less skilled labor is needed. The "press" can be run by less skilled labor.

Molding a board requires a multi-part mold. I plan on just using two parts a TOP and a BOTTOM. The two will mate during production to create the board that is INSIDE.

The process of creating a mold with fiberglass as opposed to metal, like bronze, use a plug. I will be duplicating an existing board so my plug, in effect IS a board.

In typical mold production the plug, in situations like this, is disposable, although, I'm hoping to save my plug. Also, I will be using tooling gelcoat to form the inner most layer of the mold's surface, subsequent layers will be chopped strand mat and polyester resin. The heat generated by the curing polyester resin can reach temperatures in excess of 300 degrees which is hot enough to create dimples in EPS foam. If the plug is a simple EPS structure, it can be ruined from the mold making process.

I have chosen a new board made specifically for this molding project. It has no fin boxes and has been highly polished. It also has tucked under rails. Negative relief angles are exceptionally hard to mold and require complex mold building, the tucked rails create a negative relief angle.. When building a mold you need to always rememer de-molding. A negative relief angle will prevent the board from popping out of the mold unless there are multiple pieces of the mold that can be removed, typically the part line is at the apex of a curve or angle - which is what I will do.

Some pictures of a prior molding test.

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PostPosted: Apr 11, 2010 6:15 pm    Post subject: Reply with quote

You can see the old delapidated frame has the rocker of a surfboard and the pictures that show the deck side of the mold, show the rocker and outline.

The first step, after acquiring the plug, is to build the framework to support the mold as it is made.

I use a 1/2" thick sheet of ply and attach some stiffeners underneath - stiffness somes from structure more than materials. The stiffeners are 2x2's, and I run three the 5 foot length of the bottom of the frame.

I start with a 4x8' sheet of 1/2" ply, marking out a 5' x 26" section. This will give me a 2" width around the entire board. The mold parts will have a 2 inch wide flange around the outside that I'll use for alingment and to limited the clamping when I start making a part. I cut the 5'x26" section with a circular saw.

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PostPosted: Apr 11, 2010 6:20 pm    Post subject: Reply with quote

I attach the 2x2 stiffeners such that I have 2 inches around the perimeter and one down the middle. I like to leave the gap around the edge so that I can attach clamps quick and easy. I use 2" wood screws from the top down into the 2x2's, making sure the head is flush or countersunk with the surface of the 1/2 thick plywood.
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PostPosted: Apr 11, 2010 6:27 pm    Post subject: Reply with quote

With the bottom part of the frame solid, I start working on the supports for the rocker. The rocker needs to be fairly close to that of the plug. I use a 2x4, 2x2 and a 1x2 to mimic the rocker of the board/plug. The green board in the picture isn't the plug, but at this st age, it's rough and I don't wish to risk scratching the plug. ANYTHING on or in the plug, will be duplicated in the mold's surface.
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PostPosted: Apr 11, 2010 6:36 pm    Post subject: Reply with quote

In the previous picture, I have trimmed the supports to length and then screwed them down through the bottom of the frame and into the stiffeners. No exposed screws and this three attachment points gives a solid/stiff frame work.

The top part of the frame must bend to the rocker, so I use a 1/8" ply. It has proven thick enough to support the plug and the layup for the deck mold.

I take a 4x8' sheet and trim it to the same 5'x26" size.

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PostPosted: Apr 11, 2010 6:40 pm    Post subject: Reply with quote

Now I bring out the plug (thanks Mike and Dennis!) while I affix the 1/8" plywood to mirror the rocker of the board. In this picture, I've already attached the 1/8" ply to the frame.
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PostPosted: Apr 11, 2010 6:50 pm    Post subject: Reply with quote

The next part gets tricky. The rails of the board are curved and as I mentioned earlier, the rails have a tucked under edge. The cross section of the rails are curved, the apex or high point of the rails is just slightly above the about an 1/8" or so. I could build up the surface of the rockered ply, but instead I make a utout of the frame and I will lay that over the board and attached it to the curved/rockered plywood that is already attached to the frame.

This cutout board will become the part line of the mold. That is, the top will separate at that point and then then bottom will mate to this section, as I move on.

I start by cutting down a 4x8' section of 1/8" ply to the 5'x26" section. I also mark the centerline at the nose and tail to use so that I can align the board/plug.

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PostPosted: Apr 11, 2010 6:54 pm    Post subject: Reply with quote

In the preceeding picture, I've used Irwin clamps to get the parting line board to match the rockered play and then I lay the plug down and trace the outline.
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PostPosted: Apr 11, 2010 6:57 pm    Post subject: Reply with quote

After tracing the outline, I use a jigsaw to cut the interior out. This will allow the part line to over lay the board.
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PostPosted: Apr 11, 2010 7:01 pm    Post subject: Reply with quote

It's really hard to see, but this parting line is even with the apex on the rails. One other thing to note, this parting line board will only be attached to the rockered board underneath with screws. When I go to release the top mold, I can pull the parting line board/plug/top half of mold fairly easily, making releasing the board/plug from the top mold easier.
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PostPosted: Apr 12, 2010 3:28 am    Post subject: Reply with quote

Very interesting. Look forward to following this!
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PostPosted: Apr 12, 2010 12:24 pm    Post subject: Reply with quote

Wrong picture! Oh well, I'll look for the correct image this evening.

Thanks Nooga, molding offers quite a few options in board construction, the key, though, is to move away from the injection molded methodology which typically uses scrap plastic salvaged from other products, or the super heavy boards that are mostly resin. I'd also like to avoid the use of staples to hold the fabric in place while the mold is closed. Hopefully, I'll be able to explore making a lightweight performance board that "could" be used by a manufacturer here in the US to compete with Asian imports.

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PostPosted: Apr 12, 2010 12:26 pm    Post subject: Reply with quote

A cross-sectional view/drawing of what the mold making process will look like:
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PostPosted: Apr 12, 2010 12:57 pm    Post subject: Reply with quote

So...I will never be an artist! Smile In the picture, that is an attempt to show what the mold/frame/plug will look like if I cut the whole project in half - width-wise. If you look at the curved area on the rail, everything below the part line is a negative relief angle. Molds can't bee too rigid and my intent will be to make it as rigid as my patience will allow. You can imagine that if the deck side of the mold went over the apex and continued down towads the bottom, such that the mold was cupped around the curve in the rails, the plug, nor the final part, won't release from the mold.

So the part line, needs to be at the apex or high point of the curve on the rail. In this way, the plug and/or final part won't get stuck in the mold.

The area marked as "clay" is exaggerated, but I will use a non-hardening clay to fill the gap between the parting board and plug. In this way, none of the polyester resin / Gelcoat gets into the frame or structure supporting the mold and plug.

Now, the last thing to note about the picture is the layers of the mold itself. I'll start with tooling gelcoat. It's a slight tougher gelcoat than what you'd find on your boat, plus it will be black. The black will give a visual cue if any of the fabric, laid into the mold, is dry or wrinkled.

The second layer, which will be ontop of the gelcoat, will be a leightwieght fabric, no doubt I'll use 4 oz eglass. The eglass will drape easily and conform to the complex shape of the mold's surface.

The third layers - plural because I'll build that up substantially with multiple layers - will be chopped strand mat. The CSM adds bulk and a ton of fiber with just a few layers.

I have the clay and fiberglassing materials on order, so it may be a few days before I can continue.

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PostPosted: Apr 12, 2010 5:15 pm    Post subject: Reply with quote

So do you pour foam into the mold and then glass what pops out, or is there away to glass it in the mold, so what comes out is ready to use.
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PostPosted: Apr 12, 2010 5:55 pm    Post subject: Reply with quote

You have just described the basis of injection molding, where the cavity in a mold is injected with "something". Typically the something is melted scrap plastic from other products. Injection molding is cheap and rugged, because it's using old waste product for the core.

The process that I intend to go through, will be to wet out the fabric, lay that into each side of the mold, then lay up a piece of high density sheet foam, followed by another layer of wet out glass. Finally, I'll lay in the core and put the two mold halves together. With that done, I'll slide the mold into a vacuum bag, applying pressure until it's cured. This is basically the concept of compression molding. The internal core will be slightly larger than the finished board, so that when the mold is compressed, the core is finished shaped and it forces the exterior glass up against the mold surface - that then creates a gloss finish.

Thanks for following along Nooga.

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PostPosted: Apr 12, 2010 7:21 pm    Post subject: Reply with quote

The parting board needs some release agent. The gelcoat will stick to the porous wood, so it needs to be waxed a bazillion times. I like to wax the underside just in case any of the resins seep through. I don't wax the center, as I still need to tack glue the plug.

The process of waxing, especially later on the mold surface, entails applying, letting it dry and then buffing it off. The wax fills all the microsopic holes, preventing the gelcoat and resins from sticking.

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PostPosted: Apr 14, 2010 6:56 pm    Post subject: Reply with quote

My supplies arrived today, so I need to get a move on. I attach the plug/board to the rocker board using silicon seal. This will allow me to remove the plug/board easily and it cleans up easily.
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PostPosted: Apr 16, 2010 7:05 pm    Post subject: Reply with quote

Back to work! I use Roma Plastilina #1 to fill the gap and fill the transition between the parting line board and the plug.
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PostPosted: Apr 16, 2010 7:10 pm    Post subject: Reply with quote

I use a "bunch" to fill the gap and then trim it and smooth it into final shape.
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PostPosted: Apr 16, 2010 7:12 pm    Post subject: Reply with quote

A close up of the transition after smoothing. The best tool for this is your finger. Smile
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PostPosted: Apr 19, 2010 7:06 pm    Post subject: Reply with quote

The next step is to apply a bunch of coats of wax. My plan is for 8 coats. The wax does a few things. First is that it fills the small imperfections in the plugs surface - scrathes and sanding swirl marks. Second, is that it builds up a layer wax that the gelcoat won't penetrate and therefore prevents the gelcoat from sticking to the plug.
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PostPosted: Apr 19, 2010 7:14 pm    Post subject: Reply with quote

I like to apply the wax over a period of a few days. This allows the wax to fully dry and settle. I keep a sheet that quickl reminds me how many coats of wax I've put down. The key is to write it down! Smile
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PostPosted: Apr 19, 2010 7:21 pm    Post subject: Reply with quote

I like to cover the project with the towel I use to buff with. This keeps crap from sticking to the plug/wax...especially along the clay darker debris like hair is almost impossible to see AND get out once it's in there.
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PostPosted: Apr 20, 2010 7:02 pm    Post subject: Reply with quote

Two more coats.
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PostPosted: Apr 20, 2010 7:10 pm    Post subject: Reply with quote

Normally, after the wax has been applied and polished off, a coating of PVA is sprayed on. PVA - Polyvinyl Alcohol is a water soluble polymer. When sprayed on, it forms a very thin film that is resitant to gelcoat, but when the mold is all done, water cleans it up. I don't have the equipment available to me to spray the PVA, so I'll be using a substitute.
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PostPosted: Apr 21, 2010 7:32 pm    Post subject: Reply with quote

Last application of wax, when the weather warms up, I'll start applying the gelcoat.
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PostPosted: Apr 22, 2010 7:13 pm    Post subject: Reply with quote

PVA is a liquid polymer that solidifies and when cured is water soluble. So is hair spray Smile That's my alternative to the expensive PVA and related equioment. Polished, waxed and hairsprayed. Smile
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PostPosted: Apr 22, 2010 7:17 pm    Post subject: Reply with quote

400 CC os Black Tooling Gelcoat. I use the black so that the mold surface will show any unwetted fabric shows up clearly.
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PostPosted: Apr 22, 2010 7:19 pm    Post subject: Reply with quote

It's a little cool, so I mixed up 2% MEKP with the gelcoat.
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PostPosted: Apr 22, 2010 7:22 pm    Post subject: Reply with quote

And the first coat of gelcoat over the plug.
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PostPosted: Apr 23, 2010 2:52 am    Post subject: Reply with quote

I am going to be making a mold that allows me to put fin box tabs on homemade wooden fins. The directions on a swaylocks thread call for PVA mold release as well. The mold will be made out of 100% silicone, so could I use hairspray as well. I know in rifle bedding people also use shoe polish and cooking spray as release agents.

To make the mold, I will first create a jig from wood to fill with the silicone. Are there any other shortcut household products to get the silicone to release from the wood without having to buy special wax.

Here is the thread I was getting the directions from (about 9 post down):
http://www2.swaylocks.com/forums/yet-another-fin-thread
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PostPosted: Apr 23, 2010 4:20 am    Post subject: Reply with quote

Typically Silcone doesn't need a release agent, as it literally doesn't stick to anything. The exception being porous surfaces like wood and plaster. I would just wax the crap out of the inside of the wooden box before pouring the RTV Silicone in. The wax will fill the pores and release at the same time. I wouldn't pour without waxing either, it's the surface irregularities that will give you grief. An alternative would be to paint the interior with spray paint and then after that has cured, spray with something like PAM from the kitchen, but rattle can enamel takes MONTHS to fully cure. If it were me, I'd break out some paste wax and go to it.
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PostPosted: Apr 23, 2010 6:44 pm    Post subject: Reply with quote

I'm brushing the gelcoat rather than spraying - again I don't have a dump gun. You can see the glossy surface of the gelcoat - that's what I'll have on the inside up against the plug when I remove it - except it will be smooth and clean.
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PostPosted: Apr 23, 2010 6:51 pm    Post subject: Reply with quote

I did 400 cc's yesterday and today.
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