Development of a quick-stop device for drilling processes

Abstract

In the drilling of small diameter cilindrical holes, tipically smaller than 12 mm, the most employed tool is the twist drill. In this kind of tool, the geometrical complexity and the impossibility on observing the process makes difficult to study the phenomena that appears during the cutting process. To make it possible is important the preservation of the chip roots generated during the machining, as they can be useful to understand this machining process. By observing the chip root’s microstructural modifications is possible to establish relationships between the workhardening levels in differents regions inside the drilled hole with the strain levels, drilling temperatures and the shear angles as well, using metallography techniques and microhardness measurements. By simply turning-off the machine-too, the cutting process doesn´t stop suddenly. Then the cutting continues under other conditions that are different than the original cutting parameters, interfering by this way the real chip root´s characteristics cutting condition. For this reason it becomes essential the development of a device that sudden stops the drilling. This equipment, often referred as Quick-Stop Device (QSD). It is widely used for turning process, however for drilling tests its use is not common. On the going behind the objective to increase the knowledge about the drilling process, one QSD for drilling was design, built and tested. This device worked and with good repeatability, allowing the freezing of the cutting process and enabling the subsequent study the chip roots in their formation stage, by the analysis of the shear-plane angles, the degree of work hardening and other aspects as well as. Here the main project design factors and the methodology employed for the drilling experiments were discussed and analyzed. Cutting speeds below 120 m/min and feed rates below 0,3 mm and carbide twist drills were used in the drilling experiments.