Sustainable Undergraduate Engineering 3-D Printing Lab

Recent proliferation of inexpensive 3D printers allowed most educational institutions to purchase and deploy them. Students at all levels now print plastic objects due to the low cost of plastic materials used. However, failed and/or unwanted prints, as well as support material, are discarded. In this work, a sustainable 3D printing laboratory is described. 3D printed objects and supporting structures are recycled by first shredding the plastic parts using a two-step process, then mixing the resulting material with virgin material, and finally re-extruding the material as filament appropriate for use in 3D printing. Students became aware that the recycling of plastic parts is a large step towards sustainable 3D printing processes. Introduction The importance of experiential learning in engineering education is well established through a number of learning theories. For example, in Kolb’s experiential learning cycle theory 1-3 , active experimentation is regarded as an essential part of learning 4-7 . Experiential education philosophy and practice further reinforce the importance of active learning experiences 8, 9 . The importance of physical models and working prototypes in engineering education is also well documented in engineering education literature 10-12 and supported in engineering texts 13, 14 . 3D printing is an additive rapid prototyping (or manufacturing) process based on material addition. A few years ago companies started selling inexpensive 3D printers which in turn enabled their wide acceptance in engineering education 15 . Authors of engineering textbooks added chapters on 3D printing and additive manufacturing 16, 17 . This 3D-printing revolution is enhancing all facets of engineering education due to the low cost of printers and materials. While this technology’s great potential for unlocking students’ creativity is well recognized, not much is known about what happens with 3D-printed parts after they are made. Students are printing thousands of objects which are slowly taking over university labs and offices. ABS plastic can be recycled. PLA plastic can also be recycled, and is even biodegradable (albeit only in special plants). However, the failed prints and unwanted printed objects often end up as trash in land fields. To minimize waste the number of failed prints could be minimized 18 and the rest of the failed or unwanted plastic objects could be recycled. In this work, a sustainable 3D printing lab consisting of nine inexpensive 3D printers, a desktop plastic shredder, and a desktop filament extruder is presented. Technical project objectives, laboratory development and implementation, engineering/economic analysis, and educational assessments are provided. An integration of plastic object recycling as a part of the life-cycle of 3D printed objects in an undergraduate engineering 3D printing lab is presented. The process and equipment required to accomplish this task are developed and described. Assessment of student perceptions and attitudes towards sustainability due to the implementation and operation of this novel sustainable 3D printing lab is provided. Apart from the reduced cost of operation, this sustainable 3D printing lab has inspired engineering students, university visitors, and K-12 students and teachers. Curricular Context The 3D-printing lab addressed in this work is described partially elsewhere 15, 18 . The lab is used by undergraduate engineering students in most of the engineering courses. Two part-time student technicians help students to minimize the number of failed prints through sharing 3D printing best practices including selection of materials and colors (not all colors print equally), object designs for 3D printing, object placement and orientation, 3D printing process parameters (temperature, speed, fill, rafts, etc.), rework, and post-processing 19, 20 . Currently, students use nine inexpensive 3D printers based on fused deposition modeling (FDM) technology to print mostly with acrylonitrile butadiene styrene (ABS) or polylactic acid (PLA) 1.75 mm diameter filaments. These filaments are widely used in FDM 3D printers and can be obtained from many suppliers. During the last three years, students logged over four thousand 3D-print-time hours and produced over two thousand objects ranging from simple give-away keychains to sophisticated multi-part assemblies of students’ own designs. Students and faculty, in special projects, are experimenting with additional materials (nylon, magnetic filaments, metal-like filaments, conductive filaments, etc.) and technologies (3D printing with metallic clay). This paper concentrates on the newest addition to the sustainable 3D printing lab – the system for recycling plastic parts. The project for recycling 3D printed parts was initiated in January 2015 when the engineering department purchased a desktop extruder that could produce 3D printing filament from plastic granules. Then, a graduate student was tasked to find an acceptable mixture of recycled and virgin material for successful 3D prints. After the proof-of-concept stage was completed successfully, a small manual shredder of plastic parts was purchased, motorized, and modified to accept most of the 3D printed objects. Some objects printed by a large volume Z-18 MakerBot printer still need to be pre-cut before shredding. In the Fall 2015 semester, student technicians were trained to use the recycling equipment, and engineering students were asked to recycle their unwanted objects. These requirements were aligned with the principles of our sustainability minor and with sustainability topics in three engineering courses, Introduction to Engineering, Introduction to Industrial Engineering, and Senior Seminar. Technical Project Objectives In this section, project objectives are defined, justified, and analyzed. Also, an implemented solution is presented. To increase efficiency of the engineering 3D printing lab, the amount of scrap has to be minimized and all scrapped objects have to be recycled. The scrap material originates from failed prints, design iterations, and structural material. To minimize the number of failed prints a few methods are implemented. First, the student technicians working in the lab are well-trained ensuring that they can help students and resolve 3D printing problems as they arise. The technicians are selected from among engineering students. The selection is based on their enthusiasm towards 3D printing and their previous experiences. Usually, technicians are employed until they graduate. Consequently, 3D printers are well maintained, frequently calibrated, and quickly repaired as needed. Before printing, each new design is critiqued and preprocessed with the help of a technician. Here, technicians instruct students about best practices in “printability” and position/orientation of parts to be printed. During printing, students are required to oversee the process for the first few layers to make sure the plastic adheres well to the printing platform. Then, the technicians are required to observe parts for the rest of the time as they are printed. This allows early detection of failed prints thus minimizing the amount of wasted material and time. In some cases (proven designs) long jobs are allowed to run overnight. Removal of finished objects from 3D printers is mostly left to a technician to protect the 3D printers. With PLA prints, students are allowed to remove the non-heated printing platform and release their own parts. While most post-processing operations such as part cleaning, polishing, assembly, etc. are left to students, some post-processing tasks (minor repairs and small modifications) may require technicians’ assistance. Material recycling in a laboratory setting is at the core of this work. Even though the scrap material due to failed prints is mostly eliminated due to the diligence and expertise of technicians, other scrap sources like support material and scrap due to design errors are still present. In general, the amount of support material used in 3D printing has been decreasing as the printing process has been improving. However, for some object geometries rafts and support structures are still necessary. In addition, due to the lower costs of prints, student designers are more likely to print incomplete or unproven designs and adopt a more-incremental design philosophy. Of course, now designers can try more complicated designs than before. Again, these two design practices create a larger number of discarded objects. Originally, the engineering 3D printing lab was envisioned to be a lab for all university students. Any student could walk into the lab with an STL file and walk out with a physical object in hand. Most of the equipment was purchased with internal grants. As the number of students using 3D printers grew (creation of objects for most of the engineering courses, senior designs, independent studies, research, etc.) so did the amount of material used, as well as scrap. Since the cost of materials (ABS or PLA) was deemed high ($40 to $60 per kg) a solution was sought. Also, since both ABS and PLA plastics are thermoplastic materials, it was reasoned that these materials could be recycled back into filament. Recycling 3D printed materials is well-aligned with sustainability principles, thus, a desktop recycling system was envisioned to meet the recycling needs of the 3D printing lab. Laboratory Development and Implementation When a desktop extrusion machine by ExtrusionBot was offered for sale the department purchased one of them. About 5 kg of ABS and 5 kg of PLA were also purchased for testing. Now, the lab technicians could make filament for about $10 per kg. However, the extrusion machine depicted in Figure 1 was relatively hard to use. While the extruder had a classic PID (Proportional Integral Derivative) temperature controller, the spool motor did not work as intended. It seems that its motor driver would quic