Final Design

Each of our components reduces the time required to use the machine for injection molding by approximately 43% and improve the user experience of the machine. Each of the previously mentioned components can be found below in detail, followed by the final table of timing improvements.

Currently, the plastic in the barrel is only heated using heating bands that are attached to the exterior of the barrel. This works fine but requires a long waiting time for the user (~15 mins) for the plastic to be ready to be injected. We found that the coolest part of the plastic was in the center of the cylindrical barrel and that changing the ratio of inner and outer diameters of the plastic mass in the barrel can greatly affect its heating. In order to further increase the heating rate of the plastic and consequently reduce the required plastic melting time, we decided to insert some sort of a core mechanism inside of the barrel. This was modeled in MATLAB with three different setups: the current heating rate of the plastic, the rate if a core was added into the center of the barrel, and the rate if we reduced the barrel size down to this core size.

Upon modelling on MATLAB the plastic temperature over time for different core setups as shown in Fig 1, we noticed introducing even a heatless core inside of the barrel decreases more of the required melting time compared to reducing the barrel size. Following that discovery, we came up with 2 potential core implementation designs:

• A Temporary Core Design: Involves a temporary core that will be stuck up from the bottom of the barrel during the plastic melting process. The core will then be removed before injection. We succeeded testing and verifying that the idea works.

• A Permanent Core Design: Involves remanufacturing of the barrel and piston system in order to introduce the permanent core idea. Additionally, a heating element could be inserted inside of the barrel core to further reduce required melting time. We have finished the early prototype CAD for the design; However due to time and machine shop constraints, we are unable to manufacture it and will instead hand off the idea to the following team.

With our force sensor, we intend to measure and observe the lever force required for each of our injections. Through working in parallel, we have narrowed down the possible force sensors into these 2 possible options:

Load Cell

A button loadcell, to continuously monitor the force applied by the piston on the plastic. Could assist in various future applications, including injection force reduction, injection automation etc.

Design includes a force sensor adapter that minimizes lateral forces on the sensor, increasing the sensor reading's accuracy.

S-Beam Force Sensor

An S-beam force sensor, to continuously monitor the force applied by the piston on the plastic. Could assist in various future applications, including injection force reduction, injection automation etc.

A custom piston is manufactured to fit the S-beam into our injection machine.

In determining which force sensor to be permanent applied to the machine, we consider the differences of both components:

Considering these differences, we ended up deciding on the S-beam due to it's flexibility in force measurements.

We used a meat grill probe as a temperature probe to measure the centerline temperature of the plastic and stuck inside from the bottom of a barrel. We observe the temperature of our different plastic types using our temperature probe, and we observed a dip in temperature for each of the plastic type in which we hypothesize plastic melting to occur. We then validated our hypothesis through inject plastic at regular time intervals to observe the actual meltiness of the plastic during these different intervals.

Through this discovery, we hope to concurrently observe the plastic temperature during melting - and signal the user, through a green light indicator, when the plastic is ready for injection.

For the set up of this temperature probe, we used a bung cap that fit the bottom of the barrel, drilled a hole in it with a tight fit for the temperature probe, and used this cap to hold the probe inside the barrel.

With an inclinometer attached to the lever of the barrel, we can track lever angle data and use this, with the force profile readings, to create a more comprehensive sensor package. With this package, we can calculate the following data about the injection machine's performance:

Using our sensor package, further combined with our temperature probe, we hope to be able to continuously monitor the injection machine/plastic parameters throughout the injection cycle.

With this information, we would open up various potential features for future teams to develop including an calculating plunger depth, injection automation etc.

We also experienced some difficulties when removing the molded product from the mold cage. A mushroom like sprue formed by the hardened molten plastic prevents the user from removing the mold from the mold cage easily.

We came up with several solutions to the problem:

• Mold cage adapter: Designed an adapter that has a tapered hole to prevent mushrooming on the top of the mold cage and for easy removal of the plastic sprue.

• Escape vents: Suggested adding escape vents into the current mold and cage design. This will prevent pressure buildup in the mold cage that exacerbates the mushroom plastic sprue in the mold cage.

A handheld hopper, used to improve shredded plastic efficiency for different types of plastic consistencies. A handheld hopper was chosen due to the fact that a permanent hopper often developed plastic buildup at the barrel entrance due to the hopper heating up with the barrel. With this handheld design, users will have to remove it when they are done using it, preventing the hopper from ever reaching high temperatures to melt the plastic and cause this buildup.

This hopper is simple to manufacture through bending sheet metal. Our team was unable to manufacture this prototype of the handheld hopper but was able to fabricate and test an older prototype that reduced plastic loading time by 50% and increased loading efficiency by approximately 25%. With this data, we can guarantee that this iteration will at least have this same, if not more, improvement.

A cleaning brush to ensure minimal plastic buildup inside the barrel after each injection cycle. Without proper cleaning and minimal residual plastic in the barrel, the required force from the user to put on the lever will increase significantly and cause the machine to be difficult to operate. This brush can possibly attached to a drill to increase speed and cleaning rate. With a drill, cleaning time reduced from 2 minutes to 10 seconds.

In the table below, we have listed each of the steps in the user experience of the injection machine, and the baseline time from when we first got the machine, compared to the improved time when adding our final components in. The percentage improvements are given on the very right.