# Region-Based Approach for Machining Time Improvement in Robot Surface Finishing
###### Abstract  
Traditionally, in robotic surface finishing, the entire workpiece is processed at a uniform speed, predetermined by the operator, which does not account for variations in the machinability across different regions of the workpiece. This conventional approach often leads to inefficiencies, especially given the diverse geometrical characteristics of workpieces that could potentially allow for different machining speeds. Our study introduces a region-based approach, which improves surface finishing machining time by allowing variable speeds and directions tailored to each region's specific characteristics. This method leverages a task-oriented strategy integrating robot kinematics and workpiece surface geometry, subdivided by the clustering algorithm. Subsequently, methods for optimization algorithms were developed to calculate each region's optimal machining speeds and directions. The efficacy of this approach was validated through numerical results on two distinct workpieces, demonstrating significant improvements in machining times. The region-based approach yielded up to a 37% reduction in machining time compared to traditional single-direction machining. Further enhancements were achieved by optimizing the workpiece positioning, which, in our case, added up to an additional 16% improvement from the initial position. Validation processes were conducted to ensure the collaborative robot's joint velocities remained within safe operational limits while executing the region-based surface finishing strategy. robot surface finishing; collaborative robot; region-based machining; clustering; workpiece optimization; task-oriented machining; machining time optimization 202  
a pneumatic or electromagnetic hammering tool that impacts the surface of a workpiece frequently [5]. The primary goal of MHP is to enhance the surface's mechanical properties related to the surface quality, fatigue strength of metal parts, and improved overall durability [6; 7]. Existing MHP research primarily explores its impact on workpieces' mechanical and structural properties [8]. These studies extensively report enhancements such as improved surface hardness and smoothness, increased compressive residual stresses, and beneficial microstructural changes, as shown in recent research by [9], which analyzed the effects on stainless steel and mild steel. The authors in [10] explored the surface integrity of bearing steel, and another study by [11] expanded on integrating laser cladding with MHP for repairing and strengthening surfaces, further highlighting the process's capability to enhance wear and fatigue resistance. Additionally, research in [12] demonstrates that MHP introduces plastic deformation in the surface, effectively reducing residual tensile stress and enhancing grain refinements. However, these studies typically do not address the optimization of machining time, which is a critical factor given the inherently time-consuming nature of the MHP process due to the very dense machining toolpaths. Standard practice in robotic MHP often involves using classic zig-zag machining patterns [13], which are not specifically optimized for the unique geometrical characteristics of each workpiece and the robot kinematics involved. Further complications arise when less capable robots are paired with complex workpieces. In such scenarios, the robot may not have the reach or dexterity to access all points on the workpiece to follow the machining path successfully. This is a common challenge in manufacturing, prompting numerous research efforts to optimize the workpiece positioning or the robotic system to enhance the machining process. A placement optimization of the robot--workpiece or vice versa--is performed for several reasons, such as for energy consumption [14], wear reduction [15], cycle time optimization [16], or stiffness reduction [17]. In [18], the optimal workpiece placement is searched by maximizing the achievable linear velocity along the predefined machining toolpath based on the Decomposed Twist Feasibility (DTF) method [19].