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While inexpensive 3D printers are allowing designers to quickly see their work without enlisting expensive machine shop personnel and without experiencing long turn-around times, they have limitations such as small build volumes, warping of thin objects, relatively low-precision, etc. This work demonstrates a new device, a 3D pen, which can be used for (1) repairing 3D-printed parts by adding material, (2) for “welding” the ABS or PLA plastic parts together, (3) for personalizing and decorating 3D printed objects, or (4) for creating free-hand 3D plastic objects. For each one of these processes, an appropriate example with instructions is provided. During the demonstration, three 3D pens from three different manufacturers are used on appropriate 3Dprinted objects to show the above-mentioned processes. Creation of free-hand 3D plastic objects is also illustrated. Two laboratory exercises using 3D pens for welding plastic and for personalizing 3D-printed objects are described. Introduction Experimenting with physical models is a well-documented advantage of engineering education as justified by the Kolb’s Experiential Learning Cycle Theory 1 . The 3D-printing technology based on inexpensive 3D printers and inexpensive plastic materials is at a stage of enabling student designers in creating quick, inexpensive, and functional design iterations in support of experimentation in engineering education 2,3 . However, more complicated designs and/or assemblies sometimes fail to print correctly 4 . Also, an object may be just too large to fit in the 3D-printer’s build volume and thus it must be redesigned to include multiple parts that require assembly. There is scant literature on post-processing of 3D-printed objects 4,5 created by inexpensive 3D printers. Griffin 5 describes “friction welding” and riveting using a high-speed rotary tool like Dremel, sanding, surface reheating, and gluing/filling (for ABS parts only) with ABS slurry. A 3D pen manufactured by Nanjing Yahong Electrical Technology Company 6 used here for “afterprinting touch-ups and rework” is also addressed previously 4 . Even though 3D pens are designed for free-hand 3D-drawings using plastic, in this work, 3D pens are used for  Repairing 3D-printed parts by adding material,  Welding ABS or PLA plastic parts together,  Personalizing and decorating 3D printed objects, and/or  Creating free-hand 3D plastic objects. Curricular context in which 3D pens are used is addressed next. In the section that follows, three 3D pens from three different manufacturers are compared. Specific operating instructions for each of the 3D pens are provided and differences between them are noted. Then, 3D-printing post-processing 3D-pen applications stated above are described in detail. Finally, descriptions of two lab exercises are provided for possible adoption by others. Curricular Context Our institution offers two undergraduate engineering degrees: Bachelor of Science in Engineering with specialization in Mechatronics and Bachelor of Science in Industrial Engineering. The two programs use inexpensive 3D printers in a number of courses. A newlyestablished 3D-printing lab includes: nine inexpensive 3D printers (two MakerBot Replicator 2, three MakerBot Replicator 2X, two UP Plus, one Thing-O-Matic, and one Replicator Z18) based on Fused Deposition Modeling technology, one inexpensive 3D laser scanner (Next Engine 3D scanner HD), one 3D printer filament extruder (Extrusionbot EB), one plastic shredder (FilaMaker mini XXL shredder), and 3D pens from three different manufacturers. During the last two years students logged over 3,000 3D-printing hours and printed over 1,000 parts for their classes, senior projects, independent projects, and outreach activities. 3D-printing technology has become a part of our engineering education culture. Students are well-aware of 3D printing capabilities and limitations 4 . However, except for simple post-processing procedures (removing parts from 3D printers, removing rafts and other support material, using soldering irons for shaping and gluing, and supergluing broken parts) most of the students rarely used any other process. Since 3D pens started shipping at the beginning of 2014 there was little student exposure to this technology in the past. To introduce students to 3D-printing post-processing operations using 3D pens two new laboratory exercises are developed for the Engineering of Manufacturing Processes Lab course (a fifth semester, one credit, required, engineering lab course that accompanies our 3-credit, required, lecture course on engineering of manufacturing processes). The 3D pen lab exercises are scheduled after the topics on joining processes (including welding). Thus, before starting this lab, students are already familiar with welding processes and types of joints and welds 7 . They also had practical experiences with arc welding using continuous wire electrodes and creating continuous welds. A short lecture on post-processing of 3D-printed objects (tools, benefits, and applications) is delivered just before the lab. 3D pens Characteristics and Operating Instructions Originally, a 3D pen named 3Doodler was developed as a Kickstart project that started shipping in March 2014. However, a Chinese company, Nanjing Yahong Electrical Technology Co., Ltd. started selling a similar product even earlier (January of 2014). For this study, 3Doodler was not chosen because it uses 3mm diameter filament that is not compatible with the lab 3D printers’ 1.75mm diameter filament. While all 3D pens are like hand-held, manually-controlled 3D-printer extruders, they do differ in operating procedures and capabilities. As the first generation products, they are bulky and thus somewhat hard to use. The second generation of 3D pens is planned for release in mid-2015 by another Kickstart project (illustrating the project’s popularity is the fact that the project leaders requested $30,000 and received over $1.5M). The new 3D pen will be slimmer and will be able to use different diameter nozzles 8 . 3D pens, Ahiro-002A (Ahiro) by Nanjing Yahong Electrical Technology Co., Ltd. operating on 12 VDC, 3D AirPen 9 operating on 12 VDC, and 3D printing pen (rainsun pen 10 ) by Rainsun international, Ltd., operating on 24 VDC, are shown in their original boxes in Figure 1. Ahiro Ahiro 3D pen is depicted in Figure 2. While most of the 3D printers use 0.4mm diameter nozzles 3D pens usually use 1.0mm diameter nozzles. Some features of the Ahiro 3D pen are the temperature display, temperature control, and a Back button for powered unloading of filament. All 3D pens have a small fan that creates airflow around the nozzle for quick cooling and solidification of extruded plastic. Ahiro 3D pen also includes a motor with appropriate bidirectional motor drivers, a mechanism for filament feeding, a heater, and a nozzle – just like basic extruders in 3D printers. Temperature control is a feature that allows extruding ABS and PLA plastics at their optimal temperatures which depend on filament color, environment temperature, humidity, and elevation 3 . The manufacturer suggests an initial setting of 230°C for ABS and 190-200°C for PLA. Figure 1. 3D pens used in this study Ahiro 3D pen is easy to use. After it is plugged in for the first time it heats automatically to a factory set temperature of 50°C. Otherwise, the pen heats to the last previously used temperature. Then, if necessary, the heater is adjusted to the desired temperature by pressing an appropriate temperature adjust button. The desired temperature is reached when the temperature display stops flashing (about 5 seconds). Filament is loaded by hand through the filament inlet until it comes to a stop. Then, the Forward button is pressed (engaging the 3D pen’s motor) until material starts extruding from the nozzle. At this time, the pen is ready for use. The 3D pen will extrude material as long as the Forward button is pressed. Note that it takes a couple of seconds for filament to stop flowing out of the nozzle after the Forward button is released. This should be taken into consideration when using the 3D pen. When changing filaments, the filament that is already in the pen can be partially unloaded by pressing the Back button. When the motor stops moving the filament, the remaining filament needs to be pulled out by hand the rest of the way.

BYOE: Using 3D Pens for Enhancement and Rework of 3D-Printed Parts