Can you UV print onto materials before forming in the Multiplier?
We recommend inkjet printing specifically designed for pressure forming as the UV printed pattern on the plastic sheet will break after being formed in the Multiplier as it stretches during the forming process so UV printing might not be the best option. It’s also possible to pre-print the plastic.
The key is to use ink specifically designed for thermoforming. This ink should be solvent-based and adhere well to plastic, preventing it from breaking during the heating and stretching process. The most common printing method for this is inkjet printing. Some companies have even started selling UV inkjet printers for this purpose.
We haven’t tested inkjet printing yet, only UV printing, so we are unable to advise on the process at the moment. We recommend that any customers outsource to a professional printing company, where they have inks and the printing method designed for thermoforming, to ensure the best professional outcome.
What is webbing?
When plastic folds over itself in thermoforming, it's called "overdraw" or "overstretching." This happens when the plastic sheet is stretched too much during the forming process, causing it to create folds or wrinkles.
How does it occur?
Webbing occurs in areas of deep draws or sharp corners in the part. It happens when the plastic sheet is forced to conform to the tool shape, leading to excessive stretching and the formation of folds or wrinkles. It's considered a defect because it can weaken the plastic and make it look uneven.
How can I avoid it?
To reduce webbing follow the guidance of "Placement" and "Height vs Width". Optimal tool design, such as adding fillets to sharp corners, and using the right thickness of plastic also help prevent webbing.
EVA: How can I prevent the sheet from popping / breaking?
- Double check that there are no sharp undercuts; this may be caused by debris under the tool or a warped tool. Sharp undercuts can cause a break and therefore a loss of pressure.
- Female tools - avoid sharp corners as this causes corner thinning. This particularly applies to EVA sheets when stretched material can cause the sheet to pop.
- Tool cavity depth - do not draw the sheet material into a cavity that is deeper than it is wide. (The thicker the sheet material, the further it will be able to stretch). You can read more about design principles for tooling here.
Removing the tool from the formed sheet
PTFE - Apply before forming
- Use PTFE for easy demolding. Cover all surfaces of the tool that will touch the plastic sheeting with PTFE spray
- Wipe surfaces clean so that it is dry to the touch
- We recommend four coats of PTFE spray
Tips for demolding
Undercuts can appear from a degrading mold where the sharp edge degrades. Here are some tips for difficult tool removals:
- Safe removal. On a soft sponge surface, press down in the center of the formed object, this evenly applies pressure all around the edge and the piece should pop out.
- Riskier removal. On a hard surface, with one hand push down on the center of the printed part, with the other hand pull the material and work your way round in a circular motion.
- For tough thick material. Cut an offset around the part less than 10mm from the edge. The closer proximity to the edge enables more malleability of the wall, allowing air intake and demold.
Note: Do not hit the part against a hard object or pierce the skin unless you want to damage your master mold.