I machine moulds for a local company which pours PVC into the mould (think a deep groove, open at the top). The finish on the top surface (open to the air) is very good, but maybe not quite as consistent over such a long length as you need, compared to injection moulding. The company do injection moulding too, but I have not made any of those. The challenge would be in machining such a large groove. I machine out of aluminium tooling plate, 450 x 450mm, or thicker blocks. The main cost is the mould. Once that is made, the cost of pouring the PVC is quite low. If I had to make any quantity of frames like yours, I would have them poured commercially. Tooling for injection moulding is much more expensive, and, as has already been pointed out, needs to be much stronger. Low quantity runs can get by with aluminium moulds, but higher quantities require steel moulds. Three other factors to bear in mind with poured PVC: the hardness of the PVC can be varied to suit the end product, but only up to around 70 Shore A; it is hand poured (at least in the factory doing the moulds I have made); pouring requires the mould to be heated, and the arrangement for doing that may impose a size limit on the moulds, in at least one dimension. Mine are all 450mm wide because they sit on fixed rails; undercuts are no problem in most moulds. Once the PVC has cooled and set, it is blown out of the mould using compressed air (usually injected from the top, in a poured mould). With the manual pouring and extraction, no CNC is involved.
Larger objects like car front scuttles, buckets etc, are moulded by using a male mould then heating a sheet of PVC and draping/vacuum sucking over the mould. Easy; but large moulds are expensive to make (3D CNC using large blocks of cast aluminium). Draping is not appropriate for your shape. Oh; poured PVC shrinks as it cools in a mould.. Marcus On 16 Oct 2016, at 07:10, linden wrote: > When I worked for a semi conductor tool manufacture we used to > plastic weld the drip trays out of PVC and Chemistry tanks out of other > plastics for HF, H2SO4 and other nastiness. > > The process is very similar to Tig welding metal. We used a hot air > gun and a filler rod to fuse and fill the seems. As with Tig welding > joint prep and weld temp is key. With a little practice it is not hard > to get sound joints and it is much easer than metal as you can see what > you are doing and work with out gloves. The only real issue are the > fumes released from the melting plastic. > > You probably already have a miter saw to cut with and a good table to > clamp your PVC to the cost of a welder filler rod and some scrap to > practice on would most certainly be less than building an injection > machine and certainly more versatile. Not as fun mind you;-) > > > n 2016-10-15 08:33 PM, Erik Christiansen wrote: >> On 15.10.16 22:44, Leonardo Marsaglia wrote: >>> Yes the idea is to machine the four strips and then joing them strongly. To >>> clamp the mold I was thinking about mechanical ways like eccentrics or may >>> be screw clamps. That way I can hold the mold together when the injection >>> takes place. I really don't worry about the time consumption on open the >>> mold and close it again. >> <2c> >> If joining by solvent is too weak or unsightly, have you considered "pvc >> welding"?. I haven't used the process, but google offers myriad hits. >> I've seen ΒΌ" thick PVC with a rippled joint looking much like a weld in >> steel. It may have been done on both sides, though, for complete >> penetration. (I don't recall.) >> >> OK, if molten plastic injection into the joint were a viable option, >> then the mould restraining force would be _much_ less than if moulding a >> large flat object from scratch, but just clamping four sheets for >> welding is orders of magnitude simpler & cheaper. I can't imagine that >> plastic welding gear is in the same ballpark as injection moulding, >> either. >> >> I suspect that molten filler material would need to be run straight from >> nozzle to every point of joining, i.e. run a nozzle along the joint. If >> injected at a central sprue, it would be too cold to melt the PVC strips >> for adequate fusing. (But that is speculation.) >> </2c> >> >> Erik >> >> ------------------------------------------------------------------------------ >> Check out the vibrant tech community on one of the world's most >> engaging tech sites, SlashDot.org! http://sdm.link/slashdot >> _______________________________________________ >> Emc-users mailing list >> Emc-users@lists.sourceforge.net >> https://lists.sourceforge.net/lists/listinfo/emc-users > > > ------------------------------------------------------------------------------ > Check out the vibrant tech community on one of the world's most > engaging tech sites, SlashDot.org! http://sdm.link/slashdot > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, SlashDot.org! http://sdm.link/slashdot _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
