Milk Jug (HDPE) Vacuum Forming

Milk Jugs are made from a highly recyclable plastic (HDPE), which is excellent for Vac-Forming prototypes (rather than using virgin plastic)

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High Density PolyEthylene is one of the most recyclable plastics out there, (it can be repeatedly recycled with almost no loss in mechanical/chemical performance), yet most vacuum forming is done with virgin sheet plastics such as ABS.

Although for industrial applications, ABS is preferable to HDPE, (as the resulting mould is compatible with many adhesives), in many applications Vac-Forming is used to create a mould for casting, plaster, resins or even chocolate. In such instances, ABS is not only unnecessary, it's also more likely to have the mould stick, and is not food safe.

Even if working with ABS, it is wise to use Milk Jugs as a 'beta test' or prototype mould, that can be refined before committing virgin plastic stock. Given that 2500000 plastic bottles are consumed in the US per hour...should we not explore ways to reuse before we recycle?

The process of Vac Forming with HDPE was pretty straightforward - the slightly tricky part was getting it into a flat sheet! To do this I cut out a section of the milk jug as show, with the approximate dimension of the size used in my Mayku Formbox (~225mm square), and used a heatgun (or a hairdryer will work) to warm up the plastic gently. Given that thermoplastics have 'memory' they will naturally try to revert to their original form. Taking care not to create any hotspots by keeping the heatgun moving around, the plastic becomes warm enough to flatten out and even stretch slightly (wearing gloves) to the right form factor.

From this 'rough' square, it can be clamped into the Formbox (or any other Vac Former), and if given a little heat, it will 'level out'. You could actually stop here and create a 'ready to go' sheet for future moulds, or indeed, keep hearing up and form as you would in a Vac Forming process as usual. More images here.

One thing I did notice was that Vac Forming with HDPE is slightly at the limit of the max temp of the Formbox (though many industrial Vac Formers go higher, so this is not an issue), but to speed up the warming I simply made a small 'heat shield' from some metal from a biscuit tin, and this meant it warmed up faster. Indeed, Mayku were so impressed by this little trick that they now sell it in their shop

I hope you have great fun making this, and please share any results from this or other plastics. One safety note is to check what fumes might be given off when heating plastics - luckily HPDE is not toxic, (another great reason to work with it!), but do read the MSDS first!

Disclosure & Disclaimer: I was given a Formbox by Mayku to experiment with, but this project was done under my own initiative, and is not directly affiliated with them, so please know you do this at your own risk with Formbox or indeed any other Vac Former, and neither Mayku nor myself can accept responsibility for any damage or harm caused by attempting this 'hack'.

CC: Attribution-NonCommercial-ShareAlike 4.0 International (CC BY-NC-SA 4.0)

  • 1 × 4ltr Milk Jug

  • Mould Magic

    jude_pullen06/10/2022 at 10:05 0 comments

    An update on the moulding process!

  • The power of a beta test - Heat Shield

    jude_pullen06/10/2022 at 09:59 0 comments

    As mentioned in the main article on using Milk Jugs to Vac Form with, I realised that a little extra sheet was needed when using the Mayku Formbox. It's rather nice to see that some months after posting this and Makyu released their own version, for those who might not have the workshop or the DIY skills to realise it. Pretty nice when these little beta tests come full circle, and it's credit to the startup to consider doing small updates like this. 

View all 2 project logs

  • 1

    Overview of the project - and how I got started. Also shows how it works.

  • 2
    Tools & Materials

    You will need a Heat Gun (though a hairdryer will do also at a push).

    Scissors, a lollypop stick, and if you have it some 1" / 25mm metal strip (You can scavenge this from a biscuit tin if you don't have this in the workshop).

  • 3
    Cut out Section

    As shown, remove a 230x230mm (approx.) section as shown. If you're unsure about what size this is, I suggest getting a bit of paper, cutting to size (perhaps a little bigger, even), and then drawing around it. 

View all 17 instructions

Enjoy this project?



jude_pullen wrote 06/13/2022 at 09:59 point

Having had a look at your project, it would seem fine to form over something as small as a sweet... Perhaps the smallest (realistic) size would be like a 10x10x10mm cube? It's probably about 0.5mm thick, so keep that in mind also, and avoid sharp edges (even a 1mm radius helps). 

  Are you sure? yes | no

Alain d'Espaignet wrote 06/14/2022 at 20:09 point

Thanks for the response. Maybe it could still be used to seal the whole PCB as a means of minimizing cavity place material.

  Are you sure? yes | no

jude_pullen wrote 06/20/2022 at 07:59 point

You could potentially 'seal' two side of HDPE using a soldering iron, but I'd only say it's 'splash proof' not worth the risk submerging....for that's I'd using a proper resin to encase the PCB, or a IP-rated enclosure. 

  Are you sure? yes | no

Alain d'Espaignet wrote 06/13/2022 at 09:52 point

Interesting. How small can the things that you are vacuum forming over be? Take a look at my project could it be used in my context?

  Are you sure? yes | no

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