ScienceDirect Available online at www.sciencedirect.com Procedia Computer Science 232 (2024) 3131–3140 1877-0509 © 2024 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of the scientific committee of the 5th International Conference on Industry 4.0 and Smart Manufacturing 10.1016/j.procs.2024.02.129 10.1016/j.procs.2024.02.129 1877-0509 © 2024 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of the scientific committee of the 5th International Conference on Industry 4.0 and Smart Manufacturing Available online at www.sciencedirect.com Procedia Computer Science 00 (2023) 000–000 www.elsevier.com/locate/procedia 1877-0509 © 2023 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of the scientific committee of the 5th International Conference on Industry 4.0 and Smart Manufacturing 5th International Conference on Industry 4.0 and Smart Manufacturing Advancing Free-Form Fabrication: Industrial Robots' Role in Additive Manufacturing of Thermoplastics Rayko Tosheva*, Dennis Bengsb, Petri Heloa, Miguel Zamoraa a School of Technology and Innovations, University of Vaasa, Wolffintie 32, 65200 Vaasa, Finland bNOVIA University of Applied Sciences, Wolffintie 33, 65200 Vaasa, Finland Abstract This paper presents a comprehensive study on the advancements and potential of industrial robots in the field of additive manufacturing of thermoplastics. As the manufacturing industry continues to embrace Industry 4.0 and smart manufacturing principles, the integration of robotic systems has gained significant attention due to their flexibility, precision, and automation capabilities. This article explores the utilization of industrial robots in achieving free-form fabrication, particularly focusing on the additive manufacturing process for composite materials. It looks into the hardware setup, software systems configuration, and platform development that combines FDM with robotic arm technologies. It discusses the merits, limitations, and prospective uses of freeform additive manufacturing and the interoperability between traditional additive manufacturing and robotic additive manufacturing. The experimental results show that this integration is feasible and advantageous, with better process flexibility and production capacities when compared to typical FDM systems. © 2023 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of the scientific committee of the 5th International Conference on Industry 4.0 and Smart Manufacturing Keywords: Additive manufacturing; 3D printing; Free-form fabrication; Industrial robotics * Corresponding author. Tel.: +358-408485994. E-mail address: rayko.toshev@uwasa.fi Available online at www.sciencedirect.com Procedia Computer Science 00 (2023) 000–000 www.elsevier.com/locate/procedia 1877-0509 © 2023 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of the scientific committee of the 5th International Conference on Industry 4.0 and Smart Manufacturing 5th International Conference on Industry 4.0 and Smart Manufacturing Advancing Free-Form Fabrication: Industrial Robots' Role in Additive Manufacturing of Thermoplastics Rayko Tosheva*, Dennis Bengsb, Petri Heloa, Miguel Zamoraa a School of Technology and Innovations, University of Vaasa, Wolffintie 32, 65200 Vaasa, Finland bNOVIA University of Applied Sciences, Wolffintie 33, 65200 Vaasa, Finland Abstract This paper presents a comprehensive study on the advancements and potential of industrial robots in the field of additive manufacturing of thermoplastics. As the manufacturing industry continues to embrace Industry 4.0 and smart manufacturing principles, the integration of robotic systems has gained significant attention due to their flexibility, precision, and automation capabilities. This article explores the utilization of industrial robots in achieving free-form fabrication, particularly focusing on the additive manufacturing process for composite materials. It looks into the hardware setup, software systems configuration, and platform development that combines FDM with robotic arm technologies. It discusses the merits, limitations, and prospective uses of freeform additive manufacturing and the interoperability between traditional additive manufacturing and robotic additive manufacturing. The experimental results show that this integration is feasible and advantageous, with better process flexibility and production capacities when compared to typical FDM systems. © 2023 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of the scientific committee of the 5th International Conference on Industry 4.0 and Smart Manufacturing Keywords: Additive manufacturing; 3D printing; Free-form fabrication; Industrial robotics * Corresponding author. Tel.: +358-408485994. E-mail address: rayko.toshev@uwasa.fi http://crossmark.crossref.org/dialog/?doi=10.1016/j.procs.2024.02.129&domain=pdf 3132 Rayko Toshev et al. / Procedia Computer Science 232 (2024) 3131–31402 Author name / Procedia Computer Science 00 (2023) 000–000 1. Introduction The rapid progress in additive manufacturing technologies has revolutionized the production of complex geometries and customized components. Fused Deposition Modeling (FDM) is one of the most popular additive manufacturing processes [1] due to its simplicity and versatility [2]. FDM utilizes a heated extrusion nozzle to deposit melted thermoplastic material in a series of 2D layers stack on top of each other. However, when it comes to free-form fabrication along curved surfaces, traditional 3D printing approaches face significant limitations [3]. This necessitates exploring alternative solutions, and industrial robots have emerged as promising tools for achieving free-form fabrication in additive manufacturing processes [4]. Integrating a 6 DOF robotic arm with FDM technology can enhance the overall manufacturing process by introducing increased flexibility and allowing the production of parts with less support structures and more design freedom [5]. This paper presents the research results of using a 6 Degree of Freedom (DOF) robotic arm for FDM-based additive manufacturing. The study explores the setup, configuration and installation platform combining FDM with robotic arm technology. It describe the interoperability between traditional Additive Manufacturing and Robotic Additive Manufacturing with focus on of freeform additive manufacturing discussing benefits, challenges, and potential applications. Experimental results demonstrate the feasibility and advantages of this integration, highlighting improved process flexibility and production capabilities compared to traditional FDM systems. 2. FDM Process Overview Fused Deposition Modeling (FDM) is a widely used additive manufacturing technology that finds applications in modeling, prototyping, and production. In FDM, 3D printed parts are created by extruding small flattened strings of molten material, which then solidify to form layers. This technique offers versatility and is commonly chosen for 3D printing projects. The process of FDM involves the use of a plastic filament or metal wire (option available for UltiMaker from BASF), which is unwound from a coil and fed into an extrusion nozzle. A worm-drive mechanism controls the rate at which the filament is pushed into the nozzle. The nozzle, heated to the melting temperature of the material, enables the thermoplastic to become molten. The molten material is then deposited by the extrusion head to create the desired shape [6]. A wide range of materials can be used in FDM, including Acrylonitrile Butadiene Styrene (ABS), Polylactic Acid (PLA), Polycarbonate (PC), Polyamide (PA), Polystyrene (PS), lignin, rubber, and many others. Each material offers different trade-offs between strength and temperature properties, allowing for customization based on specific application requirements [6]. Furthermore, FDM offers flexibility in terms of extruders, materials, filament thickness, and bed materials. Different extruder designs and configurations can be employed based on the specific requirements of the printing project. The choice of materials extends beyond thermoplastics and encompasses a wide range of options. Filament thickness can vary, allowing for adjustments in the level of detail and speed of printing. Additionally, bed materials can be selected based on factors such as adhesion properties and ease of part removal [7]. Ultimately, Fused Deposition Modeling (FDM) is an adaptable additive manufacturing technique that uses molten material extrusion to create 3D printed parts. FDM offers flexibility and adaptability for a variety of applications due to its wide range of materials and customization options. By improving layer adhesion, inert gas atmospheres can improve the mechanical properties of printed objects. Furthermore, FDM allows for the incorporation of various extruders, materials, filament thicknesses, and bed materials, increasing printing versatility [2]. 3. Industrial Robots in Additive Manufacturing Robotic arms, which resemble the human arm in structure, are mechanical devices capable of performing various tasks. These arms can be programmed to undertake activities that are highly repetitive in nature. Examples of such tasks include material handling, welding, painting, and assembling. The programming of robotic arms often involves Rayko Toshev et al. / Procedia Computer Science 232 (2024) 3131–3140� 3133 Author name / Procedia Computer Science 00 (2023) 000–000 3 a teach-and-repeat technique, where the operator or programmer utilizes a portable device to instruct the robot in performing its designated task [8]. Robotic arms come in a wide range of shapes, sizes, and configurations. The most notable distinctions between robotic arms lie in the number of joints, which determines the degrees of freedom (DOFs), as well as the reach and maximum load capacity of the arm. The configuration of the arm also plays a significant role in its capabilities. The majority of robotic arms are driven by electrical motors, which can be either AC or DC motors. In many cases, these motors are servo motors equipped with sensors to precisely determine the position of the arm's joints. For larger articulated arm robots, it is common to find an electrical motor accompanied by a gas spring on the second axis [8]. This configuration helps reduce the load on the motor, allowing for smoother and more efficient arm movement. 3.1. Robotic Arm 3D printing – hardware integration The articulated robotic arm that was used for this project is the IRB-1200 90/5 from ABB. This is a compact 6-axis industrial robot. The 90/5 model has a reach of 90 cm and a maximum combined weight of the end effector and payload of 5kg. The 6 rotational axes are shown in Figure 1. A standard tool flange is used to mount a custom extruder and nozzle that functions as a 3D printer. There are several methods for transmitting data to the tool. The robotic arm has three connection points, two at the base of the robot and ten user power connections, each of which can handle a maximum of 49V / 500mA. There is also an ethernet connection with 8 data lines and four pneumatic lines with a pressure capacity of 5 bar [9]. During the project, several custom hardware components were designed and created to aid in the goal of robotic additive manufacturing. These include components like robot extruder end-effectors, air cooling systems, mainboard housing and filament holders. Most of these components were designed using Siemens NX 12. The prototype components and final designs were in PLA using Ultimaker 3D printer. The following chapter will detail these components. Fig. 1ABB IRB-1200 Robot and rotational axes 3134 Rayko Toshev et al. / Procedia Computer Science 232 (2024) 3131–3140 4 Author name / Procedia Computer Science 00 (2023) 000–000 For doing robotic additive manufacturing, a thermoplastic extruder tool end-effector was developed based on designs from previous projects involving RAM (see figure 2). This extruder tool acts as an end-effector for the IRB- 1200 robot The extruder tool is controlled by a separate MKS Gen 1.4 mainboard attached to the robot controller using a RS-232 connection (see figure 3). The IRB-1200 uses a separate controller cabinet called IRC5, which connects to and controls the robot from a few meters away. Fig. 2 Custom fabricated extruder Fig. 3 PCB control board and housing Rayko Toshev et al. / Procedia Computer Science 232 (2024) 3131–3140� 3135 4 Author name / Procedia Computer Science 00 (2023) 000–000 For doing robotic additive manufacturing, a thermoplastic extruder tool end-effector was developed based on designs from previous projects involving RAM (see figure 2). This extruder tool acts as an end-effector for the IRB- 1200 robot The extruder tool is controlled by a separate MKS Gen 1.4 mainboard attached to the robot controller using a RS-232 connection (see figure 3). The IRB-1200 uses a separate controller cabinet called IRC5, which connects to and controls the robot from a few meters away. Fig. 2 Custom fabricated extruder Fig. 3 PCB control board and housing Author name / Procedia Computer Science 00 (2023) 000–000 5 The IRC5 cabinet uses a FlexPendant. The FlexPendant is handheld device which allows full control over the robot. Among other things, the FlexPendant can be used to manually jog the robot and to start and stop robot tasks. The FlexPendant has a joystick built-in for fine control of the robot’s motion. Within the project, the FlexPendant is used to start and stop prints, to perform bed leveling and other utility tasks and to keep track of the print progress [9]. 3.2. Control software - ABB RobotStudio Rapid code Several pieces of software have been developed within the project to facilitate both regular and freeform additive manufacturing using the robotic arm. This includes slicing software, microcontroller firmware and robot program (see figure 4). G-Code (Geometric Code) is a programming language which is commonly used with CNC machines. G-Code has come to be the de-facto standard for 3D printers. While G-Code is mostly standardized, G-Code will not be the same for all machines. Each machine can have special commands and interpret G-Code commands in a different way compared to other machines. In the case of 3D printers, the difference in G-Code between machines is minor, but care must still be taken to avoid running incompatible G-Code files on the wrong machine which may damage the machine. In additive manufacturing, the slicing software is a program which take a 3D model, and outputs the instructions for turning it into a physical object through a process called additive manufacturing. Most slicing software works on the principle of layer-by-layer printing and will generate instructions on a per-layer basis. Slicers typically have many tunable parameters and features. These aid in finetuning and debugging the final quality of the printed object, as well in aiding in finding the optimal alignment and orientation to print the object or objects in [10]. The slicing software typically stores settings for different machines and filaments in slicing profiles. These profiles define the relevant settings required for that machine and filament, such as print bed dimensions, heater temperature, cooling fan speed, layer height and printing speed. RobotStudio is both a simulation and a programming software developed by ABB. The program features an Integrated Development Environment for developing robot program. In addition, RobotStudio can simulate compatible robots inside a three-dimensional environment, allowing the user to safely simulate the developed software Figure 1 Fig. 4 RAM software architecture overview 3136 Rayko Toshev et al. / Procedia Computer Science 232 (2024) 3131–3140 6 Author name / Procedia Computer Science 00 (2023) 000–000 from inside a virtual environment. RobotStudio can also connect to a real robot controller to allow the developer to upload and test the developed AM robot program on a real robot. In addition, the real robot can be visualized inside RobotStudio [9]. RAPID is a high-level programming language which runs on top of the robot controller software RobotWare. RobotWare is a family of robot controller software. RAPID has many features found in typical high-level programming languages. RAPID features procedures, functions, traps (error handling), standard arithmetic and multitasking. RAPID has many built-in data types and functions specifically used to control robots [9]. Common examples of these are: tooldata Definition of a tool (tool center point, weight etc.). robtarget A position and orientation in space. MoveL Command the robot to move linearly. MoveJ Command the robot to move by joint movement. The robot program used was written in RAPID. For controlling the robotic arm during the additive manufacturing process, a robot program nicknamed RoboP3D is used. The program was developed in-house for use within the TB- RAM CoE project and it is proprietory to University of Vaasa, NOVIA and VAMK organizations. The basic principle of RoboP3D is to translate G-Code commands into robot and extruder movements, as well as keeping track of the current state of the system. 4. Free-Form Fabrication By utilizing the flexible nature of robotic arms, it is possible to enable full freeform printing when doing robotic additive manufacturing. With freeform printing, the hotend can be positioned to and extrude material at most of the exposed surfaces of a 3D model. With regular FDM, only the topmost layer is considered a viable target for plastic deposition. Through the freeform printing process, complex objects can be created which would otherwise be impossible for standard 3D printers, such as negative overhang structures. Freeform printing was enabled by adding two additional G-Code parameters to the original robot program G-Code interpreter: G0 & G1 A and B. The A and B parameters define the hotend rotation about axis X and Y respectively. Regular slicing software do not use these parameters, as they do not allow for freeform printing. A separate slicing software was thusly written to enable testing and debugging of the freeform printing capability of the robot program. The freeform slicer program is a small program written in JavaScript, using the Three.js WebGL framework for model visualization. The slicing program is used produce freeform G-Code from a parametric/mathematical model. The program cannot be considered a general slicing software, as it does not take a 3D model as input. Instead, it relies on the user understanding 3D mathematics and programming their own parametric 3D model using JavaScript. When developing a model, a series of lines are given in spatial coordinates. Each line has a width, height and an orientation. To facilitate the non-planar nature of freeform additive manufacturing, the tool is capable of gradually adjusting the width and height of a line between endpoints. The slicer component handles the filament flow calculations, model visualization and other low-level details. The created model is then visualized within a 3D environment (see figure 5). The model is made from the line segments that the robot is expected to move along while extruding. Rayko Toshev et al. / Procedia Computer Science 232 (2024) 3131–3140� 3137 Author name / Procedia Computer Science 00 (2023) 000–000 7 Using this software, multiple freeform models have been created, and several of these models have been successfully printed using the robot (see figure 6). Fig. 5 Freeform nested pipes Fig. 6 Free-form prints of supportless pipes with negative inclines 3138 Rayko Toshev et al. / Procedia Computer Science 232 (2024) 3131–31408 Author name / Procedia Computer Science 00 (2023) 000–000 4.1. Freeform printing concerns and warnings There are several potential dangers when doing freeform printing with a robotic arm. Before doing a freeform print, special care must be taken so that the print may proceed safely. Unlike layer-by-layer additive manufacturing, freeform printing allows the robotic arm to bend freely around the model. This greatly increases the chance of expensive and hazardous collisions between the robotic arm and the build platform, the printed object, or the environment. The goal of a robotic arm is to put its end-effector at the target position and orientation. This is usually done through a mathematical process called inverse kinematics. If the robotic arm has enough degrees of freedom, it is likely that there exists more than one way to reach the same point. This is an issue as it makes the robot program less predictable. For example, one solution may be safe, while the other solution crashes the arm into a table. This unpredictability can be alleviated by providing so-called axis configurations. These configurations force the robot joints into predetermined quadrants relative to each other. Even so, in the AM robot program we have chosen to disable axis configurations and allow the arm to instead use the closest configuration automatically. This allows the robot to change configuration during the additive manufacturing process. Care must be taken that the configuration changes do not twist, pull or otherwise damage the robot or the wires connected to the end effector. This is an issue which is likely to happen when passing through a singularity. 5. Experimental Validation- materials, slicers and test prints Several printing materials have been evaluated and tested with the robotic additive manufacturing platform in the project. Included in these materials are: - PLA (polylactic acid): One of the most common 3D printing materials. PLA melts at a relatively low temperature. The material is accessible and easy to work with. - ABS (Acrylonitrile butadiene styrene): Another common 3D printing material. ABS melts at a higher temperature than PLA. Due to warping, ABS prints generally require a heated bed for a successful print. ABS is stronger than PLA. - PETG (Polyethylene terephthalate glycol): A material which has grown in popularity in the last years. It has a higher melting temperature than PLA and is such more stable at a higher temperature. PETG is also relatively stable with a low shrink ratio. - PETT (Polyethylene coTrimethylene Terephthalate): Is a special type of PET which is semi-transparent. - PP (Polypropylene): PP is a relatively soft in comparison to the other materials. PP is resistant to some chemicals. Packing tape was used as a print surface to successfully make the PP adhere to the build platform. Multiple calibration prints were created using the different materials. The slicer profiles had to be updated based on various parameters for each material [10]. Other than the custom slicing software used for freeform printing, several widely available open-source slicing programs were used to create G-Code for RAM. These were Ultimaker Cura and PrusaSlicer (based on Slic3r). Cura was used at the start of the project as it is one of the most popular and fully featured slicing programs available. The prints created using Cura were successful based on the slicing settings. Over the course of the project, we switched to using PrusaSlicer more than Cura. While Cura has more features and quality of life improvements over PrusaSlicer, the simplicity of PrusaSlicer seemingly generated less complex G- Code which contained a smaller number of short quick movements [10]. This helped significantly result was less critical errors and failed prints. 6. Applications, limitations and future directions The potential for future development in this project is vast, as it can be further expanded and improved in various stages. At the design level [11], [12], techniques utilizing metals as 3D printing materials could be explored to create a more durable and consistent housing for the tool. This would make it less vulnerable to accidents that may occur with the robot, such as tool crashes into the printing bed. Rayko Toshev et al. / Procedia Computer Science 232 (2024) 3131–3140� 3139 Author name / Procedia Computer Science 00 (2023) 000–000 9 However, the most significant improvements can be made at the software level. One crucial area for enhancement is the communication between the tool and the robot. In the current project, a basic single-bit communication has been implemented. By incorporating serial communication without delays, it would be possible to transfer all the necessary data for full functionality, enabling greater automation and different printing speeds. Additionally, the G-code to RAPID converter was tested through simulations in RobotStudio and in real life. The results of these tests have been promising, demonstrating the feasibility of 3D printing with a robotic arm [13], [14], [15]. Nevertheless, this chapter will examine the different aspects of the project that could be further improved for future iterations. 6.2 Limitations of the System Despite the achievements of the system implementation, there are still limitations that need to be addressed. These limitations can be categorized into the following aspects: Cost of System- One significant limitation is the higher hardware cost associated with using a robot arm for fabricating models compared to a conventional 3D printer. However, the RoboFDM system offers increased flexibility in fabrication. Finding cost-effective solutions or exploring alternative robotic technologies could help mitigate this limitation. Deceleration Errors - During testing, the robot arm encountered difficulties in performing circular movements due to the nature of the G-code, which only consists of linear movements. The robot struggles to execute movements with very close distances without encountering issues. Developing techniques or algorithms to address deceleration errors and enable smoother circular motions would be beneficial. Better Collision-Free Strategies - The constraint implemented in this paper to prevent facing down base planes, while effective in preventing collisions, is overly restrictive. Consequently, the support-free printing of certain models, such as a tree with pointing down branches, may fail. Future efforts will focus on developing improved constraints for collision avoidance, allowing for more versatile printing capabilities. Regarding netshape accuracy and resolution and surface quality the parts produced with RAM system did not differ from standard FDM printers using same slicer settings. 6.3 Future Directions To overcome the limitations mentioned above and further advance the project, several future directions can be pursued: Exploring alternative materials and design techniques, such as metal-based 3D printing, to enhance the durability and reliability of the housing for the tool. Implementing advanced communication protocols, such as serial communication without delays, to enable seamless data transfer and facilitate more automation and diverse printing speeds. Conducting physical experiments and validations to complement the simulations conducted in RobotStudio, ensuring the reliability and accuracy of the system in real-world scenarios. Investigating cost-effective solutions or alternative robotic technologies to reduce the overall hardware cost and increase the accessibility of the RoboFDM system. Developing algorithms or strategies to address deceleration errors and improve the robot arm's ability to perform circular movements with precision and efficiency. Researching and refining collision avoidance constraints to enable support-free printing of complex models, expanding the system's capabilities and versatility. By pursuing these future directions, the project can overcome its limitations, enhance its functionality, and unlock its full potential in the field of 3D printing with robotic arms. 7. Conclusion This chapter presents the conclusions drawn from the experimental results obtained throughout the project, highlighting the feasibility and advantages of integrating the robotic additive manufacturing platform. The system has demonstrated enhanced process flexibility and production capacities compared to conventional FDM systems. Various objects, ranging from small and precise to large-scale, have been successfully printed using this platform. 3140 Rayko Toshev et al. / Procedia Computer Science 232 (2024) 3131–3140 10 Author name / Procedia Computer Science 00 (2023) 000–000 The designed extruder has proven to be effective, reliably extruding filament with regularity. The inclusion of fans has effectively cooled down the filament and the tube between the heating element and gears. The extruder controller has demonstrated proper functionality, responding to input from the robot and effectively controlling the stepper motor and heating element. In conclusion, the integration of the robotic additive manufacturing platform has proven to be feasible and advantageous. The system offers improved process flexibility and production capacities compared to traditional FDM systems. The designed extruder has demonstrated effective extrusion capabilities, and the overall functionality of the system has been successful in achieving the desired outcomes. With further improvements in the PID controller and enhanced communication capabilities, this platform holds great potential for advancing the field of additive manufacturing and opening new possibilities for large-scale, precise, and flexible object fabrication. References [1] ISO/ASTM52900-15. (2015) “Standard terminology for additive manufacturing—general principles—terminology.” American Society for Testing and Materials, West Conshohocken. [2] Wong, Kaufui V., and Aldo Hernandez. (2012) "A review of additive manufacturing." International scholarly research notices 2012. [3] Ngo, Tuan D., Alireza Kashani, Gabriele Imbalzano, Kate TQ Nguyen, and David Hui. (2018) "Additive manufacturing (3D printing): A review of materials, methods, applications and challenges." Composites Part B: Engineering 143: 172-196. 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