Fabrication of Dry Connection through Stamping and Milling of Green-State Concrete

This study explores efficient fabrication strategies for producing geometrically diverse dry connections in concrete, addressing challenges related to cost, production time, and geometric precision. The research focuses on developing rebar-free dry joints using two complementary processes: stamping and green-state CNC milling. Each method is systematically evaluated in terms of dimensional accuracy, tool wear, and energy consumption. In the stamping investigation, a design-of-experiments (DOE) framework was applied to assess the effects of water content, concrete age, stamping load, and operational variables (vibration and formwork type) across four geometries: cone, truncated cone, truncated pyramid, and pyramid. Results indicate an optimal working window between 90 and 120 minutes after mixing, with the most favorable performance typically around 90–105 minutes. Specific deviations—such as ~68 minutes for the truncated cone and ~130 minutes for the pyramid—were attributed to geometry–age interactions rather than outliers. Among the parameters tested, water content most strongly affected lateral dimensional deviation (diameter/width), while age primarily governed vertical accuracy. For green-state milling, both extrusion-printed and shotcrete-printed specimens were machined at 90 minutes, 1 day, and 1 week. Results show that tool abrasion and energy consumption increase with curing time, and that extrusion-printed stock required slightly higher energy than shotcrete at equivalent ages. Two engagement modes—side (flank) milling and end-face (head) milling—were analyzed independently. The end-face mode caused markedly higher tool wear, accounting for tolerance drift in the final joint geometries. In addition, a soil-based forming approach was demonstrated, in which a stamp was pressed into oil-treated fine sand to create a reversible mold. This method achieved high-fidelity replicas with smooth release surfaces, offering a practical alternative when friction or demolding limitations restrict direct stamping. This study explores efficient fabrication strategies for producing geometrically diverse dry connections in concrete, addressing challenges related to cost, production time, and geometric precision. The research focuses on developing rebar-free dry joints using two complementary processes: stamping and green-state CNC milling. Each method is systematically evaluated in terms of dimensional accuracy, tool wear, and energy consumption. In the stamping investigation, a design-of-experiments (DOE) framework was applied to assess the effects of water content, concrete age, stamping load, and operational variables (vibration and formwork type) across four geometries: cone, truncated cone, truncated pyramid, and pyramid. Results indicate an optimal working window between 90 and 120 minutes after mixing, with the most favorable performance typically around 90–105 minutes. Specific deviations—such as ~68 minutes for the truncated cone and ~130 minutes for the pyramid—were attributed to geometry–age interactions rather than outliers. Among the parameters tested, water content most strongly affected lateral dimensional deviation (diameter/width), while age primarily governed vertical accuracy. For green-state milling, both extrusion-printed and shotcrete-printed specimens were machined at 90 minutes, 1 day, and 1 week. Results show that tool abrasion and energy consumption increase with curing time, and that extrusion-printed stock required slightly higher energy than shotcrete at equivalent ages. Two engagement modes—side (flank) milling and end-face (head) milling—were analyzed independently. The end-face mode caused markedly higher tool wear, accounting for tolerance drift in the final joint geometries. In addition, a soil-based forming approach was demonstrated, in which a stamp was pressed into oil-treated fine sand to create a reversible mold. This method achieved high-fidelity replicas with smooth release surfaces, offering a practical alternative when friction or demolding limitations restrict direct stamping.

本研究探索了制备几何多样化混凝土干式连接的高效制造策略，以应对成本、生产时长与几何精度相关的挑战。本研究聚焦于采用两种互补工艺开发无钢筋干式接头：冲压工艺与生坯CNC铣削（green-state CNC milling）工艺。针对两种方法，本研究均从尺寸精度、刀具磨损与能耗三个维度开展系统评估。
在冲压研究中，本研究采用实验设计（design-of-experiments, DOE）框架，针对四种几何形状——圆锥、截头圆锥、截头棱锥与棱锥，评估了含水量、混凝土龄期、冲压载荷以及操作变量（振动与模板类型）的影响。结果表明，拌合后90至120分钟为最优作业窗口，最佳性能通常出现在90~105分钟区间。特定的偏差值——例如截头圆锥约68分钟、棱锥约130分钟——可归因于几何形状与龄期的交互作用，而非异常值。在测试的参数中，含水量对横向尺寸偏差（直径/宽度）影响最为显著，而龄期则主要决定垂直精度。
针对生坯CNC铣削工艺，本研究分别在拌合后90分钟、1天及1周对挤出打印与喷射混凝土打印的试样进行铣削加工。结果显示，刀具磨损与能耗均随养护时长增加而上升，且在相同养护龄期下，挤出打印坯料所需能耗略高于喷射混凝土打印坯料。本研究还独立分析了两种切削模式——侧（刃面）铣削（side (flank) milling）与端面（刀头）铣削（end-face (head) milling）。结果表明，端面铣削会造成显著更高的刀具磨损，这也是最终接头几何形状出现公差漂移的原因。
此外，本研究还演示了一种基于土壤的成型方法：将冲压头压入经油处理的细砂中以制备可逆模具。该方法可获得保真性极高的复制品，且脱模表面光滑，当摩擦或脱模限制阻碍直接冲压时，可作为一种实用替代方案。
本研究探索了制备几何多样化混凝土干式连接的高效制造策略，以应对成本、生产时长与几何精度相关的挑战。本研究聚焦于采用两种互补工艺开发无钢筋干式接头：冲压工艺与生坯CNC铣削（green-state CNC milling）工艺。针对两种方法，本研究均从尺寸精度、刀具磨损与能耗三个维度开展系统评估。
在冲压研究中，本研究采用实验设计（design-of-experiments, DOE）框架，针对四种几何形状——圆锥、截头圆锥、截头棱锥与棱锥，评估了含水量、混凝土龄期、冲压载荷以及操作变量（振动与模板类型）的影响。结果表明，拌合后90至120分钟为最优作业窗口，最佳性能通常出现在90~105分钟区间。特定的偏差值——例如截头圆锥约68分钟、棱锥约130分钟——可归因于几何形状与龄期的交互作用，而非异常值。在测试的参数中，含水量对横向尺寸偏差（直径/宽度）影响最为显著，而龄期则主要决定垂直精度。
针对生坯CNC铣削工艺，本研究分别在拌合后90分钟、1天及1周对挤出打印与喷射混凝土打印的试样进行铣削加工。结果显示，刀具磨损与能耗均随养护时长增加而上升，且在相同养护龄期下，挤出打印坯料所需能耗略高于喷射混凝土打印坯料。本研究还独立分析了两种切削模式——侧（刃面）铣削（side (flank) milling）与端面（刀头）铣削（end-face (head) milling）。结果表明，端面铣削会造成显著更高的刀具磨损，这也是最终接头几何形状出现公差漂移的原因。
此外，本研究还演示了一种基于土壤的成型方法：将冲压头压入经油处理的细砂中以制备可逆模具。该方法可获得保真性极高的复制品，且脱模表面光滑，当摩擦或脱模限制阻碍直接冲压时，可作为一种实用替代方案。