Gantt Chart

Here's that Gantt Chart!

UFO Yo-Yo Table of Specifications (Imperial Units)

Critical Dimensions [Custom]
Location	Value [in]	Measurement Method
Max Diameter of UFO	2.461	Calipers
OD of Snap Fit	1.990	Calipers
ID of Snap Fit	2.000	Calipers
Alien Height	0.652	Calipers
Alien ID Snap Fit	0.260	Calipers
Base UFO OD Snap Fit	0.250	Calipers
Height of Dome	0.688	Calipers
Width of Dome	1.580	Calipers
String Gap	0.100	Calipers
Total Width of Yoyo Half	1.138	Calipers
Total Mass	64.68 [g]	Scale
Estimated Maximum Rotation Speed 1271.4 rpm*
Tolerances (Unless listed here, tolerances are +/-.005”)
Location	(+) Value [in]	(-) Value [in]
OD of Snap Fit	.005	0.0
ID of Snap Fit	0.0	.005
Alien ID Snap Fit	0.0	.005
Base UFO OD Snap Fit	.005	0.0

Initial Yo-Yo Design

Hey-yo! This is UFO-Yo checking in again. We’re here to bring you some details on our initial yo-yo design and our plans for manufacturing.

Our initial design consists of two identical flying saucer-shaped parts held together by a set screw, an axle spacer, and two hex nuts. Each spaceship is made of four parts: the bottom of the UFO, the top of the UFO, a protective dome, and, of course, an alien navigator! Below are a few images of our SolidWorks assembly for our design.

                     

In addition to the features seen in the SolidWorks assembly, our yo-yo design includes a few other aspects. For aesthetic reasons, a vinyl sticker will be placed in each UFO to give the appearance of a screen for a technologically advanced, extraterrestrial electronic console. Additionally, pupils will be drawn onto the aliens’ eyes with a permanent marker to provide a contrast to the aliens’ green hue.

When designing our yo-yo, we took into account several principles we learned thus far in 2.008. For example, to ensure that our parts would fit together properly, we allowed a tolerance of +/-0.005 in, so that the snap fits that connect our parts have an interference fit of 0.01 in at all of our snap fit locations. If both the outer diameter and inner diameter dimensions of the snap fit are 0.005 in off from the nominal value, the two parts would still be in contact and we would have a secure bond. For the other critical dimensions of the yo-yo, we assigned a tolerance of +/-0.0005 in. A cross sectional image of our SolidWorks assembly below shows how our parts snap fit, and a brief overview of our plan to manufacture 100 of each of the four components follows.

The UFO top, the UFO bottom, and the alien will be injection molded; the dome will be made by thermoforming. The first step of our plan was to split up the group and have subgroups focus on one of the components. Since each injection molded part requires two molds and the thermoformed part requires a single mold, we will have two people working on the UFO top, two people working on the UFO bottom, two people working on the alien, and one person working on the dome.

Nick and Liz on the injection molded UFO top, plan to machine their aluminum molds primarily on a lathe. Focusing on the UFO bottom, Pavlina and Grant also plan to use a lathe in the machining of their molds, however, with some minute detail, like the “buttons” on the spaceship’s electronic console, they plan to use a mill as well. Since Pavlina and Grant are working on the body of the yo-yo, they must also machine shafts to support the hex nuts being embedded in the piece during the injection molding process.

Laura and Eleni will work on creating the molds for the alien. Because of the alien’s irregular shape, they will rely mostly on milling for their molds. In addition, Laura and Eleni will be maching their molds such that the parting line runs along the alien’s arms and antennae so the finished alien can be easily removed from the mold, and so that there’s no need for any side action during the injection molding. The design decision of removing side action during injection molding is practical because it minimizes injection molding time and allows us to create a two piece mold rather than a three piece mold.

After the molds are completed and tested, each group will schedule an appointment to manufacture a batch of 100 injection molded parts. The UFO top and bottom will be injection molded with metallic-looking polypropylene (PP) pellets, while the alien will be injection molded with green PP pellets.

Sara will be focusing on the dome. She will be using a lathe to machine the dome shape and a mill to create the holes necessary for the vacuum to draw the air in during the thermoforming process. Once the dome mold is tested, Sara will use clear polyethylene terephthalate glycol-modified (PETG) sheets to manufacture 100 dome pieces.

Once all the pieces are made, the team will work together to assemble the 50 yo-yos. A more detailed schedule in the form of a Gantt chart will be posted to show when we plan to undertake the different tasks of our yo-yo production. Also, as promised, we will be posting some specifications for our yo-yo design. And be on the lookout next month for some images of an injection molded part that is sure to be out of this world!

Intro

From left to right:

Back: Nick Fernandez, Elizabeth Porter, Grant Sellers, Eleni Pitses

Front: Sara Gonzalez, Pavlina Karafillis, Laura Malhotra

Front and Center: Spencer

Yo! We're UFO-Yo, a group planning to make a batch of 50 UFO yo-yos this semester as a part of 2.008: Design and Manufacturing II. The class teaches us all sorts of information on different manufacturing processes and what sort of design constraints or possibilities are associated with each. Outside of lecture we get the chance to apply our knowledge by machining molds to thermoform and injection mold parts for a yo-yo, which we've sat down to brainstorm and came up with the idea of a UFO. We're excited to get started! Next week we'll return with a SolidWorks model and some specifications of our final product.