STL Dropbox link

In preparation for our 3D printing lab, this is a link to our parts, as STL files.

https://www.dropbox.com/sh/brb5cdrb9a8pvod/AAB4-0LjuwFiUK_bDNTlQ7vra?dl=0

Blog Deliverable II

Blog Deliverable II

An in depth look at our Connector Piece Molds:

Description:

               Pictured above are the connector piece molds that are ready for injection molding.  The 

cavity has the important details for injection molding (sprue, runner, and gates) while the core has the important details of the actual part and the ejector pin holes. 

The key features of this mold design are the:

-    ejector pin holes

o   to allow the ejector pins to push the piece out

-    drafted sides

o   for the piece to pop off the mold easily

-    duplicate copy

o   to speed up the injection molding process

Dimension Justification:

The dimensions for this piece are based off of the two parts that it is connecting: the bearing and the hamster.  The inner diameter of the bearing is 6mm or .236 inches.  Meanwhile, the pin sticking out of the hamster is .15 inches in diameter.  To account for these two press fitting features, the hole for the bearing has a tolerance of +.005in while the pin for the hamster has a tolerance of -.005in.  To account for the shrinkage, the entire piece was scaled up by about 2%, like the rest of the pieces that we are injection molding, including the hamster. 

Manufacturing Process:

The manufacturing process for these molds is done all on the mill.  A detailed explanation can be found in our process plan.  The reason that we have two copies of the connector piece on the molds is to save time during the injection molding process.  Each copy of the connector piece takes about 25 minutes to machine.  By having two copies of the piece we cut our injection molding time from roughly 50 minutes to 25 minutes (assuming roughly 30 seconds per injection molding cycle).  This seems to be an equal trade-off but since there is only one injection molding machine in the shop, the time spend on the injection molding machine is worth more. 

Overall Time Estimates:

               We have created a machining time estimate sheet to help us predict the over time spent machining.  The spreadsheet can be viewed here.  Our schedule for the yo-yo production depends heavily on how quickly we can finish machining our molds.  As of now, we have completed the connector piece molds, the thermoform piece mold, and most of our hamster molds.  Any changes to our estimates will be reflected in our spreadsheet.

Other Molds:

               Our other completed mold at this time is for the thermoform piece.

Description:

               Pictured above is the thermoform piece mold that is almost ready for draft thermoforming.  The only thing that is missing are the small 1/32 holes that allow vacuum pressure to be distributed to the plastic.

The key features of this mold design are the:

-    locator pin holes

o   to easily center the piece for cutting

-    drafted sides

o   for the piece to pop off the mold easily

-    ridge

o   to fit the outer wheel bar

We expect that our thermoform piece will work well but some anticipated issues that we may have are the fit with the outer wheel bar and the clearance for the hamster in the yo-yo.  If we run into these issues we will have to re-size and re-machine the part.  

Blog Deliverable 1: Initial Yo-Yo Design + Semester Plan

Description of Initial Yoyo Design:

Our yo-yo consists of 4 distinct injection-molded parts and 1 thermoformed part. Below, we discuss how each part will be manufactured and assembled, and any considerations that we made for manufacturing. The Solidworks model of our initial yo-yo design is shown here: 

Injection Molded Parts:

1. Hamster: The hamster will be injection-molded in a multi-cavity mold. The back of the hamster has a press-fit attachment that fits with the connector piece. We tried to make the hamster small enough that it could be made in a multi-cavity mold, because this will speed up our manufacturing process.

2. Connector piece: The connector piece will also be injection-molded in a multi-cavity mold, out of the same color plastic as the body pieces. The connector piece has a hole that press-fits with the hamster, and a peg that will be press-fit into the ball-bearing in the center of the yo-yo.

3. Outer wheel: The outer wheel has a ring and pegs which form the outside part of the hamster wheel. This piece will be injection-molded. The pegs will press-fit into matching holes on the centerpiece.

4. Centerpiece: The centerpiece will be injection molded. This piece contains holes around the rim (into which the pegs will be press-fit) and a hole in the center for the bearing (also a press-fit around the OD of the bearing). The centerpiece also contains a hole in the center on the opposite side for the shoulder bolt/nut. The inside of the centerpiece has been hollowed out to allow for shrinkage (if it were solid, there would be too much material there and shrinkage would be very significant). The centerpiece also contains a ridge that holds the base of the thermoformed piece; when designing this ridge, we made sure to think about the minimum dimensions for tooling (i.e. cutting out the mold on the lathe) and sized our piece accordingly.

Thermoformed part: We will thermoform a clear plastic “shell” which will sit just inside the wheel pegs and rest in a ridge on the centerpiece. The purpose of this shell is to add a bit of support to the outer wheel piece, to shield the hamster & connector piece, and to help us gain experience in thermoforming. The thermoformed piece looks similar to a dome, with straight sides. 

Additional parts: The bearing in the middle of each side of the yo-yo (used to allow the hamster/connector piece assembly to rotate freely with respect to the yo-yo body) will be purchased from an outside vendor.

Table of Specifications:

Spec	Value	Tolerance	How to measure
Mass	.034 kg		Scale
Diameter	2.5 inches	All dimensions should be within +/- .005	Calipers
String Gap	.075 inches		Calipers
Moment of Inertia	2.72*10-5 kg*m2
Maximum Rotational Speed	8200 rpm
Snap fit tolerance		+.003 for OD, -.003 for ID'	Micrometer

We have also created a Gantt Chart, to track our progress and help us plan for the semester. The Gantt Chart can be viewed here.

First Meeting + Inspiration

Tonight we met to finalize the initial design of our yo-yo. As we begin this epic journey towards producing a beautiful, rodent-themed children's toy, I wanted to share our inspiration for this design. The following video perfectly encompasses our team's philosophy, motivation, and spirit. Stay tuned for more information about our design and manufacturing plans. Thanks for reading.