How to: 3D Printing Vacuum Forming Tooling with PLA and HTPLA
Monday, 26 November 2018 11:13

How to: 3D Printing Vacuum Forming Tooling with PLA and HTPLA

Invent! Robotics kit with messy cables

In preparation for the Kickstarter of our Invent! Robotics Kit, we have been busy here at Tech Camp HQ designing some fancy new packaging to give a premium quality kit.

We have never been particularly happy with the way the cables are stored in the box - most of the parts are held in with a layer of laser cut foam, but there is a lot of empty space left in the box so the cables (and other parts) end up going everywhere!

The plan to solve this was a simple vacuum formed tray, to drop into the top of the box. Not only would this hold all of the cables and batteries still for shipping, but also fill up any spare space in the box so all of the modules underneath cannot come out of the foam.

We currently produce all of the packaging ourselves, which makes it really easy to change and modify things if we need to. It is generally also cheaper than getting a company in the UK to make things like foam cutouts for you, and certainly easier than having to order 1000 at a time from China and wait a month for them to arrive on a boat!

Step 1 - Get some new toys

We have a lot of weird and wonderful machines here at Tech Camp - but sadly a vacuum former wasn't one of them! A quick trip to eBay later and we had Clarke 725 forming machine. If you don't know much about vacuum forming, it is a really useful process for making thin plastic 'shell' type products from very simple moulds. Its great for things like prop making - you can make a large foam model and then make many plastic replicas, or thin items such as plastic packaging, pots and complex plastic pieces for things like vehicle trim. Check out the video below if you want to learn more.

We also needed some 3D printers - we do have a lot of those already, however for the new 3D Printing Course we were looking at using the fantastic Creality Ender 3, so it seamed like a good chance to test them out. You can print moulds very quickly with 3 printers running 24/7.....

3x Creality Ender 3 3D printersClarke 725 Vacuum Forming Machine

Step 2 - Design the Tooling

The most important thing for getting a good end result with vacuum forming is having a good mould, or tool. For making thousands (or tens of thousands!) of parts, these are usually made from machined aluminium or resin. Predictably these take a long time to make, not to mention the cost - a tool the size of an A4 piece of paper can be £1500 or more! Even for simple parts, the tooling can be quite complicated - vacuum forming tools (and parts) have a very important feature called the draft angle. This basically just means all of the vertical sides have a slight taper to them of around 3-5 degrees, depending on how complex the design is. This allows you to take the part off of the tool after it has been formed - without this angle you could never remove it and your tool and part would be useless! The tools also need lots of small holes in them to allow the air to be sucked out from the inside or parts, further complicating the design.

This is where our secret weapon comes in - 3D printing. Creating the tapers (draft angles) on the sides of the tool takes a very long time with a milling machine, but a 3D printer can produce them just as easily and quickly as straight sides, as everything is built up in layers. It can even build the holes in for sucking the air out just as easily - perfect for producing lots of tools quickly to try out different designs.

Fusion 360 model of vacuum forming tray tooling

To design the tooling itself we opted for Autodesk Fusion 360 - a fantastic piece of 3D design software, which we also teach in our 3D Printing Course to create models for 3D printing. It has all sorts of inbuilt tools to make creating complex things like draft angles easy - you can even analyse your design automatically to see if there are any sides that don't have a draft angle yet!

Step 3 - Print the Tooling

Cura slicing tooling model for 3D printing

Now we have a 3D design file, we can load it into Cura - this software slices the model into layers, and creates a file that can be used by the 3D printer to actually create the design. It pays to print in good quality here - the final part will take on every detail of the tool, so be prepared to wait a bit longer to get a really good print with very small layers. Our design ended up being almost a day to print the tooling for just one tray!

Step 4 - Prepare the Tooling and Test

Again - its is very tempting to get the tooling on the vacuum former straight away, but spending some time cleaning the mould and removing any pieces of stray plastic is critical here. Any extra pieces left by the printer will be imprinted on the final part - we also got some sandpaper and smoothed out any rough surfaces and edges before trying it for the first time.

Another thing to think about is how you are going to trim your part. There is always excess plastic around the edge of a vacuum formed part (this is called the flash), which needs to be trimmed to get the final part. In a factory they will often make specialised stamping tools to do this - also adding to the cost! Hobbyists often just trim with a Dremel or similar - but this can be messy and time consuming. As we had our large laser cutter to hand, we opted to try and trim it by laser - this ended up giving a really clean edge and being very quick to do! One slight issue of course is that laser cutters are really, really good at melting plastic and our tooling is also made of plastic..... A solution to this is some very carefully applied aluminium tape around the edges of the tool where the laser will cut. This reflects the beam and stops the laser cutting the part and the tool at the same time.

Check out our first two prototypes below - the laser trimming worked perfectly and we were then ready to produce the final tool.

Prototype tooling and parts for Invent! packaging tray alt=Prototype packaging tray in product box

Step 5 - Full Size Tooling

6 impression tooling for vacuum formed 3D printed trays

Every time you vacuum form something, you have to use the entire sheet of plastic - so getting as many parts as you can out of each sheet is a must to keep costs (and waste) down. We had designed our tray with this in mind - we could just fit 6 of them onto one sheet, but we needed a tool 6x bigger!

We couldn't do this in one piece, so we made 6 individual tools and fixed them together - 6 days worth of printing later, we had the final tool you can see in the picture. After adding the aluminium tape for the laser trimming, we tried it on the machine and it worked perfectly - 6 trays ready to be trimmed by the laser in one piece.

Step 6 - HTPLA Tooling

Protopasta HTPLA v3 Filament

PLA is a great plastic for 3D printing as it has a low glass transition temperature of 60-65 degrees Celsius - this is the temperature at which the plastic becomes flexible and easy to bend. However, you can probably guess the problems that you get when you suck a sheet of hot (~150 degrees) plastic on top of it! Without being left to cool completely between mouldings, a normal PLA vacuum forming tool wouldn't last very long for creating lots of vacuum formed parts.

This is where High Temperature PLA, or HTPLA comes in. This is a special type of PLA made by Protopasta (https://www.proto-pasta.com/), which you can 'cook' in the oven after printing to make it not only much stronger, but also up to 3x more heat resistant than normal PLA - much better for vacuum forming tooling!

We haven't printed these up yet but they are on the way - the aim is to have at least 2 tools for 6 parts on each, so one can be in the vacuum former whilst the other is in the laser cutter for high speed production!

To help us we have another 3 printers on the way, which have in fact just arrived as I am writing this - with 6 printers we can then produce an entire 6 part tool overnight. Stay tuned for an update once we have finished building them all.....

3x Ender 3 3D printers in boxes