Larry Ludwig wrote: He uses what we call a squish mold, as in postitive and negative and you wetout the material and then pressure the two molds together and sandwich the material in between. It drives out the excess resin and leaves a finished surface on both sides of the hull.
Larry, Over in General Discussion, you mention this and I get the gist of it but will you elaborate?
Pressure obviously, but how, press, clamps?
Is squeezing out the resin (weight) the biggest advantage?
Any resulting hull strength?
Anyone reading this using this process?
Or has this been discussed previously?
I have not used, nor even heard of this method before, however, i would imagine, that, while probably not quite as efficient as a vacuum-bagged mould, this would probably work pretty well, (depending on the amount of pressure used) and would most definitely be rather less expensive in the short term than a vacuum unit…
I too would be interested to hear if anyone who has used this method would be willing to elaborate on the procedure, and if it does lend any extra strength to the part…
I would think you would need CNC milled molds or you would have thick and thin spots. Unless you just wax up the plug again and use it for the male part but that would leave the bottom thinner than the gunwales, I think.
the squish method. is actualy a very good way to make a hull. i know d @E subs make thier hulls that way. dave merriman is an artist doing it this was. the idea is basicly you make a male and female with a gap of 1/16 inch ( or what ever. then when you lay up al you have to do is wax the female mold. wet down the glass and then before the resin has kicked off. you put the male plug in. and tighten up the molds. the male mold would push the resin though the cloth and up the sides. giving you a even resin to cloth mix. i am not total sure how it works techicnicly. ( boy my spelling has gotten bad). this is his website. the man know alot about fibreglass
Yes, for ultimate quality in a composite part, “Compression-molding” is the best! The final product comes out with the desired finish on both sides, and consistently the same on each part made.
The important part when making this type of mold, is to be sure that the space between the male and female molds is of the right thickness, to allow proper “de-bulking” of the lay-up. This is so the extra resin is squeezed out, leaving the targetted resin content in the part, as well as “squishing” out all bubbles.
Pictured is molds for a micro servo mount, and a structural member belonging to one of my production hull kits (the smaller one)
Both mold surfaces are prepped, wet lay-up or prepeg put between molds, and whole assembly goes into a vac-bag, to compress the molds EVENLY.
I’m slowly in the process of converting all my molds to this method. I beleive it’s the best. It is harder to do, but long-term cost reductions from not have to use consumables such as, peelply, flow media, bleeder cloth etc. are the benefit to user.
Roto-molding and Infusion molding are also viable ways to keep resin and matrix at the correct ratios. Unfortunately both methods are best left to high production big boat designs where saving in resin equals profit!
NACRA’s current F-18 catamaran is of the Infusion process and they are able to hold weights of different boats much closer than hand lay-ups. Not nearly as time/labor consuming as “bagging” either.
In Larry Ludwig’s original quote, “… squish mold, as in postitive and negative and you wetout the material and then pressure the two molds together…”
Then I found this in a search after Dick Lemke’s post…
(Not Squish yet interesting)
Closed molding uses a two-part mold and is suitable for almost any shape that is conventionally “hulled” or open-molded. This process includes vacuum molding, infusion molding, resin transfer molding (RTM), and/or Seemann Composite Resin Infusion Molding Process (SCRIMP). Typical process steps:
* Prepare mold, including mold release agents
* Apply gel coat and allow to cure
Spray fibers onto gel coat layer, or manually place reinforcing media in mold (typically continuous strand glass fiber mats)
Close the mold and draw a vacuum to seal contact areas
Inject catalyzed resin (and other additives) to coat the perimeter then apply vacuum near part center to draw resin through entire part
Cure at varying time and temperature, depending on the workpiece size and shape, throughput rates, and resin cure requirements
So, in big boat production, they inject/pull the resin through the “dry” cloth that’s already in the mold. I bet this could (is already?) be done with our small molds.
Later: In thinking about it, injecting the resin is obvious since handling large sheets of wet glass when building a big boat would be kinda tough.
My simple method of making matched moulds.
Make the male mould in the normal way.make the female mould from it in the normal fashion.
Layup your first part in the female mould as you normally would.fill and fair the inside of your moulded part and build another mould on top of it…result…matched moulds.
Don: How do you do this accurately without CNC, or can you? There is no way that I could build a plug and a mold that were exactly(or even close) to “X” inches apart.
Would building a male plug, stretching thick latex over it ala German Rubber Molding (discussed in Forum but link bad - link/boatbuilding/boatbuilding tips), then casting a female mold over it work? The rubber would “represent” the thickness of the hull.
to make a mold i imagine that you could make a female mold from a plug made like described here: (so you start with correct external dimensions) http://www.dsv-modellsegeln.de/content/view/61/239/
then cover the mold with wax(thickness based on hull thickness) and lay up a male mold
That sounds doable. You could use multiple layers of rubber to build up the thickness and it would not require as much finishing as Brett’s. Using Bretts method you could still end up with thin or thick spots depending on your sanding abilities. That kind of mold is for production work anyway, I’ll probably never use it. I’m not that fussy about the inside of the hull;).