— PROJECT NAME
Engineering & Design for Injection Molding
— DATE
January '23 to March '23
(10 Weeks)
In this injection molding project, we designed and manufactured a unique part consisting of a penguin head emerging from a UFO.
My Role:
- CAD/CAM
- CNC Machining
- Manual Milling
- Injection Molding
Part Design
involved CAD models with features suitable for injection molding, such as uniform wall thickness and appropriate draft angles.
Mold Design
- carried out with careful consideration of part orientation, parting lines and GD&T
CNC Machining
- creation of CNC programs for precise machining of the molds and using 3 axis Haas mills to manufacture them.
QA & Metrology
metrology was conducted on the produced parts to ensure they met the desired dimensions and tolerances.
Part Design
We were tasked with designing this injection moldable toy with 2 sets of molds, GD&T, press fits and parting lines.
CAD models of each individual component as well as the assembled Space Penguin
Here is an X-Ray view of the assembled Space Penguin!
Dimensioned part drawings for each component. Scroll through to see them all!
Mold Design
Gates, runners, vents and sprues all machined out of metal molds!
Mold Design Considerations
We chose a parting line that accommodated for the largest cross-sectional area, which eliminated any undercuts.
We designed all our minimum radii to the same value to allow for efficient machining!
Draft Angles and Fits
We only had 2 surfaces that required draft, so we added 3 degrees of taper to those vertical faces and planned to machine them with a 3-degree tapered end mill.
As for fits, we created an interference fit for the dowel pins we would have to press in by under sizing the holes by 0.025" each, which allowed for tight fits later in the process. The holes on the opposite molds were sized exactly, allowing the tool wobble to create a natural clearance fit and adjust with the dowel pins.
Above are the key features for Mold Set A
Above are key features for Mold Set B
Scrol
CAM & Machining
Holding the Block in Place
(The Jig)
The jig had three pins and was machined to precision!
So, we first slid the block against the two back pins and then rested it flush against the side pin, this made a repeatable process so we could use the same attachment method for all 4 blocks of Aluminum.
Injection Molding & Assembly
We conducted a product test run of 25 assembled parts to study the consistency of our process and design.
Calibrating the Machine
We were given access to Polypropylene, which melts at around 425C. So, we set the nozzle and barrel temperatures accordingly and tried a few trial runs with varying pressures and cooling times to optimize the injection for our test runs.
Key Learning I: Pin Placement
We placed some of the pins on the mold that was attached above, which made part removal tricky.
Key Learning 2: Assure pin alignment!
As you can see above, although our penguins were colorful and fit well, an eye pin broke off during the clamping process, making our space penguin a pirate penguin.
Metrology & Part Quality Study
We aimed to have all our parts on spec and used this as a test run to decide the overall tolerances for this part.
Details about our metrology study
From the data, using the 3𝜎 definition for the production tolerances, the production tolerances for Set 1 were 0.498 ± 0.011′′ for the UFO inner diameter and 0.375 ± 0.009′′ for the penguin head radius. For Set 2, the production tolerances were 2.5 ± 0.063′′ for the UFO outer diameter and 0.375 ± 0.007′′ for the penguin head radius.
Metrology
We measured dimensions across all parts and tried to find the range, std. deviation and other metrics regarding the deviation from the desired spec.
Key Learnings
A small amount of material waste short term saves large scale material long term. We had some experiences with flashing and short shots.
