1.0 Overview: Optimized drilling parameter
1.1 Background: Cost minimization in drilling operation
The formation of burrs is a significantly undesirable by product of drilling operations in manufacturing plants. A burr, which is the rough edge that remains on a work piece after drilling, is formed whenever a drill bit approaches the exit surface of a work piece, appearing as a short mound of material (see Fig. 1) . Because of their uneven shape, burrs cause a multitude of problems in manufacturing. For example, burrs not only cause jamming and misalignment during assembly by interfering with the component parts, but also reduce the life of these parts by promoting crack initiation. Furthermore, the sharp edges of these burrs present a safety hazard to the personnel handling these parts. For these reasons, it is necessary to include a process of removing burrs as part of drilling operations. This process is known as deburring.
Figure 1. Burr formation at exit in drilling with a conventional drill
However, it is only feasible to incorporate this deburring process only if its inclusion as protocol into drilling operations does not hamper the cost effectiveness of the entire drilling operation. The measure of cost effectiveness is represented by the total cost of a drilling operation that includes a deburring process, which is the sum of the cost of drilling and the cost of deburring.
According to a study, both the cost of drilling and the cost of deburring are affected by the feed rate and the rotational speed of the drill bit used in the drilling process, although with opposite effects . On one hand, the cost of drilling is reduced when the feed rate and rotational speed of the drill bit is increased, because this reduces the time to machine work pieces and, subsequently, overhead costs.