E29 Spring 2023 - HW4 - Forming processes

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University of California, Berkeley *

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Mechanical Engineering

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Apr 3, 2024

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1 University of California, Berkeley Department of Mechanical Engineering E 29: Manufacturing and Design Communication Spring 2023 Homework 4 Forming processes Due: Friday March 10, 11.59pm on Gradescope In all questions, please show your working or reasoning clearly. Responses showing only a final answer with no working or explanation will not receive full credit. Important note: uploads to Gradescope must be in image (e.g. .png) or .pdf format, and not .docx format (which is very cumbersome to download and grade). Also, we require that you use the Gradescope interface to identify the location of each part of your solutions in the file(s) you upload, so the reader does not have to scroll through a large document to find each of your answers. The instructions on how to do this are here . Total points: 40 1. Lego bricks [10 points] In this question we consider the design and manufacture of Lego bricks. The photographs below show some bricks that have suffered from certain defects during the injection molding process. (A) (B) (C) (D) http://bricksetforum.com/discussion/16396/marbled-lego-bricks-and-other-parts
2 1.1. Briefly name and describe the possible cause of any manufacturing defect(s) that you can identify in each photograph (A) to (D) above (some defect types may occur in more than one photo) [4 points]. An example of a drawing showing a typical Lego assembly is below: https://www.toysperiod.com/lego-set-reference/universal-building-set/basic/lego-507-1-basic-building-set/ 1.2. From a fit and tolerancing perspective, explain how Lego bricks work. What type of fit do you think exists between assembled Lego bricks? You do not need to give a specific numbered tolerance grade like “RC4”; we are looking for the general category of fit, like clearance, interference, transition, snap, shrink, or expansion. [3 points] 1.3. By considering fit and manufacturing issues, explain why the features on the underside of the bricks shown in photo B above are tubes rather than solid cylinders. [3 points] 2. Design for manufacture (DfM) by injection molding [6 points] In this question you will explore some key elements of a Solidworks tutorial on mold design for injection molding. Completing the whole tutorial would take longer than you are expected to take on this homework, so we have selected a few key steps to focus on below. You are welcome to work through the tutorial in detail if you have the time and interest. Steps: Load Solidworks (you can use the CAD labs computers if needed; also, the whole class has had remote ME CAD computer enabled) Click on the help icon (question mark in top right), then Tutorials, All SOLIDWORKS Tutorials, scroll down and click on Mold Design. Advance to the page on “Opening the model”, and click on the link to open a 3D model of half of a telephone handset that could be injection-molded. Save a local copy of the .sldpart file. Skip over the “Inserting mounting bosses” section to the “Checking for Draft” section.
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