While 3D printing is now easily accessible and inexpensive, there are still some use cases where you need the benefits of injection molding for small batches as well. Professional injection molding in small quantities can be quite expensive, and buying a manual machine can cost quite a bit. Of course, there are a number of DIY injection molding projects to choose from, but they usually require a fair amount of tools and manpower. [Bolzbrain] wanted to avoid all the heavy cutting, welding and frame assembly work, so he built a DIY injection molding press for little money with a standard 6-ton hydraulic press. At the last count, he spent about € 150 on the machine and another € 120 on tools to build the machine. He also managed to find a cheap local CNC service that got him a good deal on machining the dies. But of course you can’t put a price on the knowledge gained and the satisfaction of having built it by hand.
Choosing the hydraulic press is a great idea as it will provide the high pressure needed to do the job without the operator having to put in much effort, which is a major disadvantage with some other home improvement machines. As a bonus, the structural frame is pretty sturdy and well suited for this purpose. The other major part of such a machine is the heated injection block, and there are several ways to do it. After examining some possible solutions, he decided to build a heated aluminum block through which the plastic granules could be rammed with the hydraulic piston. Heating is provided by a pair of 500W heaters and a ‘k’ type thermocouple takes temperature sensing. An industrial PID controller regulates the block temperature via a semiconductor relay. Overall, the electrical and mechanical layout cannot be simpler.
[Bolzbrain] did a great job documenting its build through a series of videos and more cocky hackers watching it will squirm in their seats discovering the numerous bugs. He bought the cheapest pedestal drill he could buy and it is quite unsettling to watch the drill battle while he was drilling a 26mm hole in the aluminum block.
The electrical wiring has plenty of room for improvement – with 220V AC heaters, exposed cables, and judging rigging held in place with a pair of clamps. Installing and removing the die is a chore and requires a lot of fiddling with multiple C-clamps – something that needs to be repeated with each shot. Perhaps toggle clamps could help make it easier to attach and remove the die. As soon as he has found out about the mold release agent and the wall tension angle, he no longer has to try to remove the molded article from the die. Then there is the problem of the right impeller design so that the thermoplastic can completely fill the mold cavity quickly and without pockets.
But in the end all that matters is that it gets reasonably good moldings for its purposes. We are sure that with more tweaks and incremental improvements, he will get better results. The video after the break gives a brief overview of its build, but the project page has a number of detailed videos that cover all aspects of the project. For an introduction to desktop injection molding, see Benchtop Injection Molding for the Home Gamer.