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About Precious Plastic
Precious Plastic is an international, open-source community of DIY makers that was started in the Netherlands by Dave Hakkens, a creator and sustainability advocate. As part of his equivalent of the senior design project, he came up with 3 small-scale recycling machines -- a shredder, an extruder and an injection -- to democratize the industrial mass manufacturing methods for small scale makers. This led to the creation of local “workspaces” where communities can work together to convert waste plastic into usable products using the shredder and the injector. To date there are 80,000 participants representing over 1,000 workspaces. This network is supported by blogs, videos, mold-makers and open-source files for modifying and improving the process.
Project Overview
Figure 1: Precious Plastics Injection Machine
Our senior project, commissioned by US-based sustainability group Impact Mill, focused on functional improvements to the existing Precious Plastics Injection machine. The existing machine works by taking it plastic pellets at the hopper, heating the barrel and plastic up with heating bands, screwing in the mold at the nozzle, and pulling on the lever to inject molten plastic into the mold.
As a function of its open-source nature, the machine is simple to build but rudimentary in its design. Among other issues, it suffers from a slow cycle time from heating to part removal, necessitates the use of expensive machined molds, and requires a large amount of force on the lever to inject. As such, we focused our improvements to the machine in those key areas, while also taking into account the open-source nature of the improvements we could propose.
Project Objectives
Through this project, we seek to research, design, implement, test and scale improvements to the small-scale injection molding machine -- the Injector -- and the processes surrounding its use. The goals of this project are fourfold:
Physical improvements to the injection nozzle and control system to increase the output part quality
Decrease the cycle reset time (injecting a part and resetting the machine for next injection) through barrel analysis and quick release mechanisms on the mold
Research and create 3D printed molds to decrease the cost of creating molds and encourage design iteration
Create design files and user instructions that can be shared digitally to the Precious Plastic open-source community via Github or similar
Final Design
Our final design consists of 6 major improvements to the existing injection machine and its workflow:
A linear actuator, used in combination with a ratchet wheel mechanism, to decrease the force requirement on the user to pull on the lever
An aluminum barrel, replacing the existing steel barrel, to decrease the heat-up time
A transient thermal simulation of the barrel's heat up time and melting of the plastic pellets
A green light melt indicator, to inform the user when the plastic has fully melted
A quick release "mold cage" to house a 3D printed mold
List of 3D-printable filament compatible with injection molding
Figure 2: Injection Machine Final Design
As seen in the image above, we've added 5 parts to the physical machine. Of these 5 parts, the 3D printed mold & mold cage combo and the linear actuator are with our project sponsor, Mark Hansen, for testing because we do not have physical access to the machine. Because we needed our own data sets for the simulation, barrel testing and green light indicator, we designed built our own machine as you can see below:
To read more about out final design: Final Design
Summary of Improvements
With the new part additions to the machine, the performance of the machine has improved dramatically in the metrics we identified at the start of the project:
In addition, we have verified that the thermal simulation we did matches closely with the physical data we captured, thus providing a 'digital twin' to help future groups who have to work on this project remotely as we did.
Final Presentation
