I guess my first question would be, why RIM molding? The tooling required is just as expensive as any other sort of injection molding, possibly more so, and I can’t imagine it would be cost effective for such a short run.
For something of that size, my first instinct would be to go for a vacuum or pressure-formed part – you can work some very thick sheet materials these days, that may address whatever structural concerns you’ve got, and the tooling is way cheaper.
I considered thermoforming…but stalled on it considering the structural and mounting strength I need from it.
I have never done a RIM program. I was under the (wrong?) impression that the tooling isn’t nearly as expensive as other conventional tooling. I always thought that because of the low pressure, softer materials than steel or aluminum could be used.
I haven’t designed for RIM before, but as I understand it, the pressures are similar to standard injection molding, and hence the tooling has to be of similar material and complexity.
Regardless of material, an injection tool base of the size you’re describing is going to be awfully expensive – which is why the only parts of that size I’ve ever done have been thermoformed (or rotomolded, depending on surface finish requirements).
Why not modify the design a little and use square metal tubing and bend it?
RIM tooling costs are significantly less than that of an injection mold. Because the RIM process incorporates low temperatures and low mold temperatures and pressure, the tool can me made out of less expensive mold materials such as cast aluminum. The choice depends on such factors as the number of parts to be made; dimensions, shapes, and tolerances; the quality and texture of the surface; mold life; required mold cost; and part performance
I think RIM molding could be a viable way to go but still expensive for 30 parts. I would imagine the mold would still be 5 - 6 k. That’s about 200 per part for the tooling. I think you could get this part fabricated from aluminum or ABS.
If I’m not mistaken rim tooling is low pressure and could be done with silicone RTV similar to prototypes. I recently made a small aluminum cavity to try to rim mold a few parts. It was a huge disaster. The urethane was very uncooperative in coming out of the mold even with a lot of release. It looks like on this part you may have some draft issues.
Internal draft has not been implemented yet. It is a work in progress. Draft will not be an issue.
5K - 6K for tooling is not such an issue for this part (the final cost for the product is ~$30K). Getting it CNC’d would be in the thousands per which is cost prohibitive. Amortizing tooling costs, as long as they aren’t astronomical, is less an issue than high part costs. Bent tubing doesn’t work either, as the outside A surface cross-section is effectively an ogee curve. Well, unless there’s some kind of process I am not familiar with.
If you are only going to do 30 pieces you can either use a fabricated frame – tubing or angle in aluminum or steel with a thermoformed skin or do the whole door in sheet metal, notch, form and weld the corners.
Low pressure injection. The material and catalyst are very low viscosity. The tool is usually on a bed that the RIM machine lifts up into the air to achieve gravity feed. It’s still a hot process as the reaction is exothermic. Tools are either epoxy or aluminum and approximate 20% - 30% of injection mold tools. RIM tools can produce tens of thousands of parts. Any number and complexity of sliders and removable cores can be included at minimal cost as they are hand extracted. Constant wall section is irrelevent, thin, thick, super thick to attach metal frame etc. Parts always have flash, sometimes a lot and consequently are sanded or grinder finished. RIM parts are always painted.
What about creep? I have been told that RIM may not be the way to go due to part creep. The guy I was talking to I trust, but he is still a salesman. He is pointing me in the direction of Structural Foam.
shrinkage is not as big a problem with rim as with thermo, but does exist. Sgructrual foam, same problems as rim. In the end wet lay up on open top molds and glue togeather or a extrusion die and then just weld em up.