Abstract

The purpose of this project was to create a device that could join two strands of 3D printing filament with the goal of being simple to use, efficient, and inexpensive. The benefits are for companies and hobbyists that are using 3D printers to be able to reduce waste and cut down the costs of wasting materials. The individual tasks of this device were split up into three teams; heating, feeder, and display. The heating team ensured the quality of temperature control, the feeder team cared for the precision of feeding the filament into the system, and the display team was responsible for developing a user interface. The subgroups were able to combine their mini-projects into one, incorporating what they learned to make the 3D filament splicer prototype. The project overall was successful in developing an affordable and accurate method to join filament. It was found that for PLA, the optimal binding temperature was between 125-165 C, 125 C for PETG, and 150-155 C for ABS. It was also found that PETG is not a good filament to be used with the splicer and binding temperatures may fluctuate between brands.

Introduction

When sending a print job to a 3D printer, one must determine if there is enough plastic filament to complete the job. If this is not the case, the old spool of filament is replaced with a full one and the plastic in that old spool is often wasted. In other cases, rolls of filament can have slight imperfections that can cause them to snap in the middle of the printing process. The next course of action would often be to discard the stray filament strand. Over time, this waste of material can build up as erroneous expenditures and a detriment to the environment if not properly recycled. Existing 3D splicers can cost to the tune of $800 (Mosaic Palette), and do-it-yourself models tend to be inaccurate and require a manual feed and heat source, such as a flame. This project explores the possibility of creating an inexpensive yet effective splicer using easy-to-obtain parts, including stepper motors, filament extruders, a heating core, an LCD display, a rotary encoder, and an Arduino. Through experimentation, this project investigated the temperature at which the filaments best melted and fused with each other, the compression to be used when extruding the filament, and the speed at which to run the motors. Success was defined by extruding the filament after it has been fused together as a continuous strand ready to be directly fed into a 3D printer.

Methods

To begin the project, we split up into three teams: a display team to construct a menu for the 3D filament splicer user interface and assemble the LCD unit; a heating team to manage a heating element and fan that essentially fuses together the 3D filament; and a feed team to control and navigate the motors that will be guiding the 3D filament through the device. Rather than collecting data, each group researched their own portion of the project, created their own code, and constructed their physical setups. After, the groups combined their codes with the display team's user interface, integrating common variables and functions to operate harmoniously. The physical three models were integrated for a single prototype that was tested, refined, and of course, 3D printed.

Findings

Despite several known improvements to be discussed in the following section, the 3D filament splicer was a success in joining two separate strands of filament into one. It was found that the optimal temperature for the operation was specific per type of plastic and between brands of the same plastic. The ideal action of binding is to see the filament get soft, but not liquid enough to stick to the Bowden tube and deform before it enters the heating core. It must also not be so hot as deforms in the stepper motor feed after exiting the heating core. The temperature should also not be so cool as to form cold joints, where the filaments come out as one but are easily separated.

PLA was the best plastic for the splicing operation, being the most consistent and durable enough to extrude the melted joint without stretching and compressing too much. In other words, the filament was fairly consistent in diameter after it came out of the core. Two brands of PLA were tested, one from 3D-fuel, which fused at 125 C (figure 3), and the another from Polymaker, fusing at 160 C (figure 4, Bottom). What was also interesting was from the first test of the heating chamber in its ability to join the filament. As figure 4, Top display, the manual feeding of filament can lead to a misaligned joint, where as compared to the image seen on figure 4, Bottom, the advantage of automated stepper motors are clear.

ABS filament also benefitted from the splicer as successful bonds were found at a temperature of 150 C (figure 5). The range towards 155 C was recommended as the joint resembles a cold splice, it is strong and consistent in diameter enough to be used with a 3D printer, but has the capability of snapping at the joint if enough strain was applied. At higher temperatures, the filament became too fluid and would compress at the entryway, resulting in a blockage.

For a similar problem as the ABS plastic, the PETG filament had fused but it became too fluid before it could reach a temperature suitable for splicing (figure 6). Even at temperatures as low as 125 C, the times it was able to bond and extrude were inconsistent and the filament diameter could not retain an acceptable thickness. The filament would also tend to melt towards the entrance and block the entryway, preventing sufficient compression to flow to the center of the heating core.

Discussion

Regardless of the filament used, a difference in filament thickness joined compared to the original strand resulted due to the Bowden tube chosen for the splicer (figure 7 & figure 8).

Originally, the Bowden tubes that came with the heating kit were of an inner diameter of 1.8mm, making it suitable for a 1.75mm thick filament to run through and retain its approximate thickness. However, the kit had to be slightly modified to fit the needs of the project, to be specific, the Bowden tube needed to be replaced by one twice its length to fit two metallic threaded rods (figure 9).

The replacement Bowden tube kept a continuous shell as the original would have introduced gaps that would have caused jamming. The commercial tubing used as a replacement is usually used for guiding the filament to the heating end, so it must be wider than the filament to allow ease of movement, therefore the large excursion. This also required the redrilling of the outer threaded rods to allow the thicker filament to extrude without being caught or jammed. Since this was a proof of concept, such a problem does not hinder the prototype from success as filament strands were still able to join in as a homogenous structure. If a finished product were made, some improvements may include adding Bowden lines between the filament feeders and the heating core to reduce manual alignment. Doing so may also prevent the melted filament from blocking the entrance to the heating chamber, allowing for better joints with ABS and PETG plastics. Improvements on the user interface may be viable as well, adding options and controls to the user such as variable compression values, excursion speed, fan speeds, and cooldown time before extrursion. A better power supply would be useful in replacing the two power supplies currently used for the convenience of setup and use.

In regards to the process of making the splicer prototype, a few minor problems arised as a result of splitting the project into group tasks. Primarily, it was difficult to combine the code in a coherent form with non-conflicting variables and functions. That is, it took several weeks of debugging to remove unnecessary and redundant lines, reorganizing the three team’s arduino code, and adjusting the parameters to get a reliable file with efficient runtimes. The physical assembly of the project was difficult as well as the students were spread across far distances. We were able to meet once at the New Brunswick Free Public Library, but even then only a select few were able to attend and put together the prototype. The prototype had not worked at first either, but within a time span of a week and research of some documentation, simple readjustments to the wiring diagram and added lines of code was able to allow the splicer ready for testing and data collection of the filament tusion process.

Conclusion

The concept of our device works, especially in our selection of PLA filament and in some range of brands, ABS plastic. If the project were to continue out of the prototyping phase, a final device would prove to be a cost-effective method, allowing for hobbyists and corporations alike to cut back on expenses while combating the future threat of dramatically increased waste from 3D printers before it has an impact on our environment. Although the main goal was to create a 3D printer accessory that would reduce filament waste for commercial and hobby use, the path to obtaining this goal seemed to be an excellent educational and engineering opportunity for the students as well. Notably, some students have never touched a soldering iron, coded, or played with a 3D printer. By the end of the research, the students, whether it was together or in their subgroups, were able to learn to code in the Arduino IDE, follow a circuit diagram, create 3D designs, learn about electronics like the transistor, create a website, and most importantly, work as a team. This project is open-sourced and can be viewed through the following link: (https://www.filamentsplicer.com/home) which provides more information about the project such as a materials list, a GitHub link for the code, and a link to a Thingiverse page for the 3D printable files. For anyone who would like a fully-encompassing project that challenges one in engineering and electronics, the team advises such individual or group to take on the task of replicating or improving our 3D filament splicer prototype.

References and Acknowledgements

Our gratitude belongs to professor Assimina Pelegri and professor Alberto Cuitino for advising the 3D filament splicer prototype project. Without their belief in our abilities, we would not have been able to start the project on time nor receive the necessary extra funds from the Rutgers LSAMP grant, which was used to provide more materials to form each group (heating, feeder, and display groups). We are also thankful to the New Brunswick Free Public Library for allowing us to use their space to assemble the prototype (figure 10).

Finally, the following links below in the references section assisted in the prototype’s circuit design and were viable instructional videos for learning about specific components and operations.

References

Circuit Basics. (2015, November 18). Make an Arduino Temperature Sensor (Thermistor Tutorial) [Video]. YouTube. https://www.youtube.com/watch?v=-_XkGju35MI&t=106s

Educ8s.tv. (2017, August 8). Arduino Menu Tutorial with a Rotary Encoder and a Nokia 5110 LCD display [Video]. YouTube. https://www.youtube.com/watch?v=ak5TsUFhyf8

Electronic Clinic. (2020, February 26). Oled i2c Arduino, Arduino Oled 128x64 i2c library, Oled 128x64 i2c display issues solved [Video]. YouTube. https://www.youtube.com/watch?v=QIR3VQ-qO94&t=278s

Electronoobs. (2018, April 8). PID temperature controller DIY Arduino [Video]. YouTube. https://www.youtube.com/watch?v=LXhTFBGgskI&t=67s

How To Mechatronics. (2015, August 26). How To Control a Stepper Motor with A4988 Driver and Arduino [Video]. YouTube. https://www.youtube.com/watch?v=5CmjB4WF5XA&t=189s