This thesis aims to implement and calibrate the digital twin based-robotic system for drilling of curved CFRP. The suggested system in this study is constructed in accordance with the essential objectives of modern industry, improvement in hole quality and energy consumption. Firstly, formation of delamination mechanism and methodology of delamination quantification was analyzed preliminarily.
Then, calibration method using a single laser profiler was presented. To calculate the normal at drilling point, 2D Lagrangian interpolation model was adopted to generate the surface of curved workpiece. For the angle feedback, communication platform that connects physical robot system and the normal computation software system was established, integrating data from various devices. Subsequently, digital twin model was added to the communication platform by transmitting, integrating and storing large amount of data from different devices. The robotic system in physical space was synchronized with the virtual model by using the motion data of robot arm. During virtual machining, tool- engagement region is computed based on tri-dexel model to calculate the material removal rate. Based on the calculated material removal rate, energy consumption during drilling process is estimated in real- time.
To verify the implement and calibrated digital twin based-robotic drilling system, actual drilling experiment was conducted. The constructed system was evaluated based on two criteria: hole quality and cutting power estimation. When applying calibration, delamination was diminished in terms of qualitative and quantitative aspects. Besides, the cutting power of digital twin-based model showed similar aspects to measured cutting power after applying calibration. This is because both virtual drilling and calibrated robotic drilling ensured perpendicular drilling. Whereas, the cutting power was measured much higher without applying the robotic calibration. The experimental comparison implies that perpendicularity of drilled hole ensures desirable energy consumption which is one of the key performance indicators in machining process.
There are several research areas for future works to improve the efficiency and accuracy of the robotic drilling system. In calibration method, accuracy of normal vector calculation depends on the number of control points. Especially, workpiece having complex shape requires more control points to be precisely interpolated. In this case, generating point cloud which is a set of data points can be utilized for scanning of complex object. As for virtual machining in digital twin, only bulk of removed volume of material is considered in this study. If the engaged area is detected in the form of vector which involves the directional information, elemental cutting forces exerted on the material can be predicted in different directions.
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ACKNOWLEGEMENTS
First and foremost, I would like to express my sincere gratitude to my advisor Prof. Hyungwook Park for all the support and advice for this research. I deeply appreciate his guidance and kindness through all the process. His extensive knowledge and experience have encouraged me in all the time of my academic research. It was a great honor for me to study under Prof. Hyungwook Park.
I also appreciate all the committee members, Prof. Youngbin Park and Prof. Sanghoon Kang. Their advice and suggestion helped complete this thesis.
I would like to thank all of the members in Multi-scale Hybrid Manufacturing Laboratory at UNIST;
Dr. Deka, Dr. Ankita, Dr. Jaewoo Seo, Hyunmin Park, Dongchan Kim, Yunjae Hwang, Haegu Lee, Changhyeon Mun, Sangmin Yang, Anand Prakash Jaiswal, Taesoo Jang, Sinwon Kim and Yunseok Kang. I feel grateful for the understanding workplace.
My special thanks are extended to the ModuleWorks company. This research has been supported by ModuleWorks software to implement the system presented in this research. Especially, I express my thanks to Denys Plakhotnik, research program manager at research team. He provided technical support and advice whenever I ran into troubles.
Finally, I wish to thank my family for their support, love and encouragement. They are by my side all the time. Without them, no accomplishment would have been achieved. I feel grateful for my supportive family.