Design and Manufacturing Guidelines for Additive Manufacturing of High Porosity Cellular structures A thesis submitted to the Graduate School of the University of Cincinnati In partial fulfillment of the requirements for the degree of Master of Science In the Department of Mechanical and Materials Engineering of the College of Engineering and Applied Science (CEAS) by Nikhil Kabbur Bachelor of Engineering (B.E.) – Mechanical Engineering S.D.M College of Engineering and Technology, Dharwad, India. – 2011 Committee Chair: Dr. Sam Anand i Abstract Additive Manufacturing (AM) is a layer by layer manufacturing approach for building parts. Additive manufacturing as a technology provides immense design freedom, especially in the field of medical implant design. Revolutionary technologies such as Direct Metal Laser Sintering (DMLS) and Electron Beam Melting (EBM) have the potential to customize metal implants to an individual patient. To take advantage of this technology it is important to develop rules that can transform concepts to real world designs. There are many applications that can potentially use additively manufactured cellular structures, but there is a need to provide design guidelines for manufacturability of such structures. This thesis explores the opportunities and challenges in manufacturing high porosity cellular structures, and provides a measure of manufacturability of different cellular structures and design guidelines to improve manufacturability. Cellular structures are defined as structures made from repeating a certain unit cell to form a block, and the characteristic length of each cell is in the range of 0.1 mm to 10 mm. The additive manufacturing technique considered in this work is laser powder bed fusion process (DMLS). This research studies and tests the effect of unit cell type, unit cell size, volume fraction, and orientation on the manufacturability of the cellular structures using experimental builds. Based on these parameters the manufacturability of each cellular structure is evaluated and design guidelines are provided to design and manufacture high porosity cellular structures. ii iii Acknowledgements I would like to take this opportunity to express my appreciation to the people who contributed, in different ways, to the completion of this work. First, I would like to thank my academic advisor Dr. Sam for his guidance and support for successful completion of this research. I also take this opportunity to thank Dr. Murali Sundaram and Dr. Ashley Paz y Puente for serving as members on my master’s thesis defense committee. I would also like to thank Mr. Dustin Lindley, Additive Manufacturing Center Manager, University of Cincinnati Research Institute for his insightful comments during the course of this research. I would like to dedicate this thesis to my parents and my family. Thank you for the love and support. I would like to thank my past and present lab mates who were always there to help me. I would like to thank Rohit Vaidya, Rohan Vaidya, Sushmit Chowdhury, Vinay Jakkali, and Kunal Mhapsekar for their support. I also would like to thank my friends and roommates Swarup Zachariah, Kalayarasan Seranthian, Hitesh Das, and Krishna Kenja for making this MS journey a ride to remember. iv Table of Contents Design and Manufacturing Guidelines for Additive Manufacturing of High Porosity Cellular structures ....................................................................................................................................... i Abstract ......................................................................................................................................... ii Acknowledgements ...................................................................................................................... iv Table of Contents .......................................................................................................................... v List of Figures ............................................................................................................................... x List of Tables .............................................................................................................................. xiv Introduction ................................................................................................................................... 1 1.1 Motivation for Research ........................................................................................................ 3 1.2 Objective and Impact of Research ......................................................................................... 4 1.3 Thesis Outline ........................................................................................................................ 4 2 Literature Review ....................................................................................................................... 6 2.1 Support Structure Minimization ............................................................................................ 6 2.2 Design for Additive Manufacturing Guidelines .................................................................... 6 2.3 Cellular Structures Manufacturing using AM........................................................................ 7 3 Methodology ............................................................................................................................ 10 3.1 Materials and methods ......................................................................................................... 10 3.1.1 Powder Material ........................................................................................................... 10 3.1.2 Manufacturing Machine Setup ..................................................................................... 11 v 3.1.2.1. Concept Laser Mlab cusing R Process Parameters ...................................................... 11 3.1.2.2. Scanning Pattern ........................................................................................................... 12 3.1.2.3. Part File Setup .............................................................................................................. 15 3.1.2.4. Post Processing ............................................................................................................. 17 3.1.3 Measurements ............................................................................................................... 17 3.1.3.1. Weighing Machine ....................................................................................................... 17 3.1.3.2. Optical Microscope ...................................................................................................... 18 3.1.3.3. Vernier Calipers ........................................................................................................... 18 3.2 Design of High Porosity Cellular Structures ....................................................................... 19 3.2.1 Unit Cell Types ............................................................................................................ 19 3.2.2 Unit Cell Type, Size and Volume Fraction Characterization ....................................... 20 3.3 Support Structure Minimization through Optimal Orientation ............................................ 20 3.4 Experimental Framework to Test Manufacturability Of High Porosity Cellular Structures 21 3.4.1 Development of CAD models to Test Manufacturability of High Porosity Cellular Structures ..................................................................................................................................... 22 3.4.1.1. CAD model for Build 1 ................................................................................................ 24 3.4.1.2. CAD model for Build 2 ................................................................................................ 25 3.4.1.3. CAD model for Build 3 ................................................................................................ 26 3.4.1.4. CAD model for Build 4 ................................................................................................ 27 3.4.1.5. CAD model for Build 5 ................................................................................................ 28 vi 4 Results and Observations on Manufacturability of High Porosity Cellular Structures ............ 30 4.1 Results of Build 1................................................................................................................. 30 4.1.1 Observations And Discussions ..................................................................................... 30 4.1.2 The Curling phenomenon ............................................................................................. 31 4.1.3 Design Rules for Part Orientation and Placement ........................................................ 34 4.1.4 Warping effect .............................................................................................................. 34 4.1.5 Design Rule for Interface of Support structures and Solid part ................................... 35 4.1.6 Results of modified Build 1 .......................................................................................... 35 4.2 Results of Build 2 and 3 ....................................................................................................... 36 4.2.1 Observations and discussions based on Build 2 and 3 ................................................. 38