@Lafras_Henning oh! So the chamber is expelled of air, and then sealed so no more air can get in? I’m not understanding what resistance the piston is meeting in injecting the melted plastic into the empty space of the mould. Maybe it is similar to the reason why is takes a strong force to open an evacuated chamber?
Depends on mold layout, channels, etc, some air might be exposed, other air will be trapped in pockets as the viscous plastic is injected. The force of the injection ‘crushes’ any trapped bubbles into non-existence. Works the same way as pressure casting resin.
@Ted_Huntington Sorry I am not explaining it well, from the start…
The pellets (a.k.a resin) is hopped into a chamber where it melts and forms a liquid , the rest of the chamber has air above it. As the piston closes the air expels through the SPRU which is located at the highest point in the piston. When the liquid rises to the top it starts being forced through the SPRU (nozzle) which is 1 to 3 mm dia, this requires pressure and causes “back pressure”.
In a FDM 3d printer this is the point when the plastic comes out the nozzle of 0.4mm x 10mm long or so.
However in Injection Moulding the melt (molten resin) is now forced into the shape of the mould which is a complex set of geometries which may be approximated to series of diameters and lengths.
The pressure require to perform this operation is relative to the cube of the aria * the length of the channel.
So the piston has to push really hard to overcome this back pressure generated by the many long thin channels.
After all this a few small bubble may be in the melt - they will be crushed… air in the mould cavity will be pushed out at the seam or special vents if needed.
Hope this helps.
@Lafras_Henning Yes, thanks for that detailed explanation. So it can be compared to the force a 3D printer extruder needs to push melted filament through the small nozzle opening.
Where would one source a mold? From everything I have read the injection machine is the cheapest part. Getting molds made that last are the most expensive
@Phillip_Ramirez on the campaign page it shows how you can cast a mould from a 3d print for only a few $. The machine comes with everything you need to get started.
yea lost pla casting. then allot of polishing. ill have to look more into it. the last time though it still came down to quality molds that last.
Lost PLA casting is an option, but the danger puts it out side the comfort zone of most makers. Many-maker uses Hard Silicone or Resin cast moulds (or other options listed on the campaign), they last only a few hundred shots, but are very cheap,easy and quick to remake. This is in contrast to the traditional “quality molds that last” approach. I am sure traditionalist will criticize the new approach but time will tell if it is becomes popular. It is not there to take the place of traditional high speed, high volume injection moulding, it is a compromise to create a intermediary between 3D printing and mass production.
Great to hear about this exciting design- please keep us updated on your progress. You are following in a great line of inventors that include Gutenberg and many other great science workers/makers.
@Lafras_Henning that is information I wasn’t aware of. Any links to making these silicone molds?
Jewelry making silicone slabs are affordable and should work well.