Estimate Machining & Optimization Times

Last week we machined out first mold. Looking ahead, below are our expected machining times for all our molds. After machining our molds, we will begin injection molding and process optimizations and have included estimates for that below too. 

Machine Time Estimate for Lathe and Mill

Once our molds are made in Solidworks, we import them to Mastercam where we plan out what machines and tools we will use to make them. Mastercam is sync with the 2.008 Mill and CNC Lathe and thus gives us estimates for machining times on both machines. 

Part	Lathe Time	Mill Time
Yoyo Body Cavity	7 min 9 sec	0
Yoyo Body Core	6 min 29 sec	1 min 30 sec
YYB w/Spin Stick Core	6 min 29 sec	6 min 24 sec
Retaining Ring Core	2 min 39 sec	3 min 13 sec
Retaining Ring Cavity	35 sec	0
Thermoform	3 min 12 sec	54 seconds
Letter Mold Core	0	25 min
Letter Mold Cavity	0	1 hr 30 min
Gold Board Mold Core	0	30 min
Gold Board Mold Cavity	0	9 min 21 sec
Entire Wheel of fortune board Mold Core	1 min 1 sec	1 hr 5 min 27 sec**
Entire Wheel of fortune board Mold Cavity	3 min 37 sec	1 hr 16 min 40 sec**

**Has to be machined after letters and board have been injection molded to account for shrinkage before overmolding parts (more on overmolding later this week!)

Projected Timeline

Process Optimization	October 20th - November 10th
Make Final Parts	November 10th -November 24th
Assembly	November 24th - Dec 5th

Previously we planned on having all our molds made last week. However, due to longer machine times than expected and how quick machines get booked up, we have shifted our first injection molding iteration back by a week and will have to shorten our optimization and final production run time. (this is reflected also in our Gantt Chart).

Projected Process Optimization Time

To optimize our process we will run iterations of injection molding parts, measuring parts for accuracy, and re-designing as needed. To get an estimate of how long this process will take we have estimated the time of these iterations. 

Injection Molding time is dominated by cooling time. From class lecture, we learned that cooling time can take upwards of half of the entire injection molding process. Cooling time for our parts can be derived from the equation Cooling Time=(thickness of part)^2/alpha, where alpha is the thermal diffusivity of the material. Our yoyos will be made from polypropylene with a thermal diffusivity of 0.096mm^2/s. Our parts have an average thickness of ~2.54mm, thus the average cooling time is about 67 seconds. To make 10 parts will thus take us about 20 minutes. For all our parts it will take us ~110 minutes (we have already booked 3 hours of IM time so we'll have our first iteration of all parts done this week!). Thermoforming each part also takes us about a minute, adding 20 minutes to our total estimate.

At worse we expect to have to re-machine all our molds and injections mold again. Our total machine time is about 5.5 hours. So our total process optimization time is roughly 16 hours of lab time plus the time to re-CAD any changes. We believe 3 weeks should be sufficient time to get this done between the five of us.