Optimization of Milling Tool Geometry for CFRP/Nomex Honeycomb Sandwich Structures Based on Side-Milling Experiments

In the world of modern manufacturing, there is a constant tension between the need for lightweight strength and the difficulty of shaping those materials. Engineers often turn to sandwich structures, which combine a thin, tough outer shell with a lightweight, honeycomb-like core. These materials are essential for industries like aerospace and new energy, where saving weight is critical for efficiency and performance. However, the very features that make these structures so valuable—their mix of rigid carbon fiber layers and delicate, paper-like honeycomb cells—make them notoriously difficult to cut. When a machine tool tries to slice through this uneven mix, it often tears the delicate core or leaves behind jagged, unfinished edges. The challenge lies in finding a tool that can navigate this complex landscape without damaging the workpiece or wearing out too quickly.

Researchers at Shandong University set out to solve this specific puzzle by testing two different cutting tools on a panel made of carbon fiber reinforced polymer and a Nomex honeycomb core. They did not rely on computer simulations or theoretical guesses; instead, they performed a series of real-world milling experiments, slicing through the material at various speeds and feed rates. By measuring the forces exerted on the tools, the heat generated during the cut, the quality of the finished surface, and the amount of wear on the tools themselves, they aimed to determine which tool geometry offered the best balance of performance. The study focused on two specific types of milling cutters, both six millimeters in diameter but with distinct shapes and numbers of cutting edges. One tool, designated T1, featured a trapezoidal groove for breaking up chips, while the other, T2, had a crescent-shaped groove and more cutting edges.

The experiments revealed that the behavior of the cutting force was intimately tied to the structure of the honeycomb itself. As the tool moved through the material, the force it encountered rose and fell in a rhythmic pattern that matched the hexagonal cells of the honeycomb core. The highest forces occurred when the tool hit the points where three cell walls met, creating a momentary spike in resistance. When the tool reached these junctions, it often had to cut through two layers of material at once, requiring more power. However, the researchers observed that when the tool approached these junctions, the delicate walls sometimes bent away or retreated rather than being cleanly sheared off. This structural retreat meant the tool did not have to push as hard, causing the force to drop, but it also left behind small, uncut fragments of the honeycomb wall that marred the surface.

When comparing the two tools, the results showed a clear advantage for the tool with the crescent-shaped groove and more cutting edges, known as T2, particularly at lower cutting speeds. This tool produced smoother cuts with less fluctuation in force, likely because its additional edges allowed it to engage the material more continuously. At slower speeds, T2 generated lower average forces in all directions and maintained a more stable cutting process. However, as the cutting speed increased, the performance gap between the two tools narrowed, and their average forces became nearly identical. Interestingly, while T2 was better at managing force, the other tool, T1, proved superior at managing heat. T1 kept the cutting zone cooler and more stable, suggesting it dissipated heat more efficiently, which is crucial for preventing the resin in the composite from softening and causing damage.

Despite T1's advantage in temperature control, the overall picture favored the T2 tool. Microscopic examination of the tools after the experiments showed that T1 suffered from significant damage, including chipped edges and heavy buildup of carbon fiber debris that stuck to the cutting surface. In contrast, T2 showed only minor wear and very little material adhesion. The surface quality produced by T2 was also generally better, with fewer exposed fibers and more regular honeycomb walls, although there were specific conditions where T1 performed slightly better. The study concluded that the T2 tool, with its specific geometry, offered the best overall performance for milling these complex sandwich structures. It provided a more stable cutting process and left a cleaner surface, making it the preferred choice for manufacturing these high-tech materials. The findings provide a practical guide for engineers selecting tools, confirming that the shape and number of cutting edges play a decisive role in how well these difficult materials can be machined.