Updated: Nov 11, 2020
"Injection molding is more and art than a science". This is something you will hear a lot from us. The process of heating a plastic to a specific temperature and injecting it into a mold cavity sounds very straight forward....but its not and we hope to help provide some clarity to how this art is performed with an example tool for what is a relatively simple part output goal.
Most often in design/engineering we focus on the parts of the assembly, the bits and pieces that go together to make our idea, prototype or product come to life and function as intend. Good engineering practices require that we design each part with how its going to be produced in mind. But what is often overlooked is how much design and engineering goes into the tooling that makes the piece or widget we need for our project or product.
Below we have captured the process we used to make a very simple part. At first glance the part we need is just a simple shaft bushing, however even for simple parts the tooling can quickly become complex and require some creative engineering solutions to achieve a successful part output.
We started out this project in CAD and created a simple shaft bushing. The part has a 1 inch inner diameter through hole with a shoulder that is slightly larger in outer diameter. Because we need 100's of this part we want to utilize the automatic production mode feature of the MicroMolder and have to design our tooling to work in that mode.
Though this part is quite simple it does have a challenge associated, it has an undercut feature. To produce this part we were forced to think a little creatively about how to create a tool that has an undercut feature. (more on undercut in plastic part scan be found here). In addition we had to create a way for an ejector system to remove the part at the end of the injection cycle.
Our solution was a multi part tool that could be machined quickly and then bolted together allowing for the undercut geometry and other critical tolerance areas to be adjusted if needed.
Our final tool design uses multiple pieces of machined aluminum and 3d printed parts.
Incorporating printed inserts saved us some time on CNC machine for this project. Additionally, they give us the flexibility to make adjustments in output tolerances if needed.
The final tool assembly is shown below. Here you can see all how all the parts come together to form a tool that can produce 2 shaft bushings per shot and utilize the AutoRun Mode of MicroMolder.
Injection cycle with clamp closed and the machine injecting plastic into the tool
Here you can see the results from the first shots into the tool. The small void in the part is caused from the printed insert being too cold. Over a few shots the insert will increase in temperature and this defect will be eliminated.
Here you can see our first run of test shots. These first parts are typically reground and recycled as they have slight defects created from various machine settings not being optimized. The MicroMolders tool settings menu options must be adjusted to achieve the ideal output results fore every different tool design. Expect to run through a few dozen shots dialing in all the variables.
After about 20 test shots we started to zero in on the sweet spot settings for this tool design. Once those settings have been identified MicroMolder can save them for future use.
We hope you found this example helpful. If you have any questions or comments feel free to contribute!