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Signature Redacted Department of Mechanical Engineering June, 2017 Certified By: Signature Redacted Design and Manufacturing of A Benchtop Thermoforming Machine By Akwasi Owusu-Akyaw Submitted to the Department of Mechanical Engineering In Partial Fulfillment of the Requirements for the Degree of Bachelor of Science in Mechanical Engineering at the Massachusetts Institute of Technology June 2017 C 2017 Akwasi Owusu-Akyaw All Rights Reserved The author hereby grants to MIT permission to reproduce and distribute publicly paper and electronic copies of this thesis document in whole or in part in any medium now known or hereafter created. Signature of Author: Signature redacted Department of Mechanical Engineering June, 2017 Certified by: Signature redacted. David E. Hardt Professor of Mechanical Engineering Signature redacted Thesis Supervisor Accepted by: Rohit Karnik Professor of Mechanical Engineering OF TECHNOLOGY, JUL25?2017 LIBRARIES ARCHIVES 1 Design and Manufacturing of a Benchtop Thermoforming Machine By Akwasi Owusu-Akyaw Submitted to the Department of Mechanical Engineering on June 2017 In Partial Fulfillment of the Requirements for the Degree of Bachelor of Science in Mechanical Engineering ABSTRACT The following work details the design and fabrication of a tabletop thermoform machine with the goal of making this machine cheaper than the ones on the market, yet able to fulfill specific requirements. These functional requirements include creating parts that have dimensions within .05" of the original part; thermoforming plastics that range between a 3" x 3" and 12" x 12" size; and having the ability to heat the plastic to at least 150'C in order to thermoform plastics such as polycarbonate. In addition, this machine had to be simple to manufacture and use. In order to achieve these requirements, a top to bottom drape forming architecture with a four bar linear slider and carriage, was constructed. In order to constrain the plastics of different sizes, two similar, modular wooden plates were used such that the plastic was held in between them via t-nuts and screws. When the user clamps the plastic onto the carriage, he or she slides the carriage upwards to an oven that radiates heat via nichrome wire on a mica sheet. Once the desired temperature is reached, the user then slides the carriage down onto a vacuum box platform, where a mold is present, and forms the plastic over the mold. While that happens, a negative pressure is applied inside the box via a standard commercial vacuum, so that the plastic adheres more closely to the mold. For the testing process, this work focuses on two manufacturing strategies for thermoforming parts: heating the air to the glass transition temperature before thermoforming, and heating the plastic to the glass transition temperature before thermoforming. Once this test was performed, the dimension of each plastic part was examined in order to see if the tolerance levels were reached. In addition, this test determined whether or not there was a statistical significance between the qualities of parts made by either of these processes. In the end, the thermoform machine was only able to reach an average tolerance of .07" for the created parts. In addition, there was no statistical significance between the part qualities of either one of the tested manufacturing processes. Some of the main reasons behind this include having an ineffective vacuum box and clamp design issues, which will be focused on in the future iteration of this project. Thesis Supervisor: David E Hardt Title: Professor of Mechanical Engineering 2 ACKNOWLEDGEMENTS The author would like to thank his thesis supervisor Professor David Hardt for his continual support in completing this project, whether it was with design concepts or thesis documentation structure. In addition, he would like to acknowledge Mr. David Orozco and GenOne LLC in Cambridge, MA for proposing this thesis idea and providing pecuniary support for the completion of this project. As for the manufacturing of the machine, the author would like to thank the machine shops in MIT D-Lab, Hobby shop, and MITERS for providing the necessary tools for fabrication. 3 4 TABLE OF CONTENTS Intro du ction ................................................................................................... 8 1.1 B ackground .................................................................................... 8 1.2 Theory of Process............................................................................. 9 1.3 Thermoforming Scale........................................................................ 10 1.3.1 Mass Production Scale......................................................... 10 1.3.2 Prototyping Scale............................................................... 11 Requirements and Strategy................................................................................. 12 2.1 Functional Requirements..................................................................... 12 2.2 Additional Requirements..................................................................... 12 2.3 Strategies....................................................................................... 12 Mechanical Design.............................................. ............ 14 3 .1 Structure ................................................................... 15 3 .2 O ven ............................................................................................. 15 3.3 V acuum B ox ................................................................................... 2 1 3.4 Slider and Carriage.......................................................................... 22 3 .5 C lam p .......................................................................................... 2 3 Electrical D esign ................................................ .................. ............. ......... 25 4 .1 S trategy ......................................................................................... 25 4.2 C ircuit L ayout.................................................. ........................... 26 F abrication ............................................................................................. ..... 27 5.1 Structure...................................... ................. ............................ 27 5 .2 O v en ........................................................................................... 2 9 5.3 V acuum B ox ..................................................................................... 30 5 5.4 Slider and C arriage............................................................................. 30 5 .5 C lam p .......................................................................................... .. 3 1 Testin g ............................................................................................................ 3 2 6.1 Objective......................................................................................... 32 6.2 P rocedure......................................................................................... 32 6 .3 A n aly sis............................................................................................ 34 6.4 C onclusion ....................................................................................... 35 Future W ork................................................................................................... 37 7.1 Further M odifications............................................................................ 37 R eferences..................................................................................................... 38 LIST OF FIGURES Figure 1: Typical thermoforming process with heater and vacuum chamber.[1]..................... 10 Figure 2: Thermoforming Machine for Mass Production[2]............................................ 10 Figure 3: (a) Centroform EZFORM Machine[3] and (b) ProForm Vacuum Former[4]............... 11 Figure 4: (a) Preliminary ideas for thermoform design. (a) One design consists of translational motion between the oven and the mold. (b) The other design transports the plastic between the heater and the mold via rotation. The black arrows represent the motion of the plastic between the oven and vacuum b o x ............................................................................................................ .. .. 13 Figure 5: Overall 3D model of thermoform machine..................................................... 14 Figure 6: Overall frame of the thermoform machine with L-brackets..................................15 Figure 7: Icarus crossing layout with numbers showing nichrome path............................... 16 Figure 8: Side View of Oven With Component Directions.............................................. 17 Figure 9: 1 -D Thermal resistance map of oven for thermoforming machine..........................20 Figure 10: Vacuum Box Design With Small Hole Array.....................................................22 iure 1: Slider - at one corner of e f . m.hin..............................................23 Figure 12: (a) C-clamp idea for holding plastic; (b) Adjustable clamp for different plastic sizes......23 6 Figure 13: Two plate clamping system for holding plastic between plates via wing nuts.........24 Figure 14: (a) TRIAC circuit symbol with usual form of component in circuit. (b) TRIAC operation theory. Pulses are sent to the TRIAC at every zero crossing, so that power continually flows to the load. These pulses can be delayed so that the power delivered is modulated............................25 Figure 15: (a) Circuit layout for heater controller
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