Investigations on Reducing Burr Formation in Metal Cutting

Abstract: Metal cutting is a very common operation in the manufacturing industry. Drilling and other hole-making operations perhaps account for 50% of all metal cutting, according to some investigations. All metal cutting including drilling always produces burrs, as a by-product. Actually burrs are nothing but uncut metal at the beginning and at the end of the operations. Yet, despite burr's omnipresence in drilling, comparatively, very little energy has been spent on this aspect, by way of research. Drilling burrs is a very common problem in the Swedish metal cutting industry. The problematic burrs in the industry are removed by the various deburring processes available. Deburring is both time consuming and costly. Sometimes, the cost of deburring is unacceptably high. This research project was started at the behest of the Swedish heavy engineering industry, facing such deburring problems. The main idea behind the project is, if burrs cannot be avoided, it should be possible to minimize their size. With this in mind, an extensive survey of the existing literature was carried out. Literature on all aspects of the burr problem was reviewed and analyzed. Process of burr formation was studied. Various theoretical and empirical models for the prediction of burr properties were analyzed. A comparative study of the various burr formation mechanisms and the burr prediction models was carried out. Based on simple parameter analysis, a simpler version of one of the burr prediction models was arrived at. Experimental and other results on the influence of process parameters on the size of burrs were analysed and reviewed. A comparative study of these investigations was also conducted. There are a number of techniques for reducing burr sizes. These techniques were studied, analysed and reviewed. It may be concluded from this extensive litterature survey and the comparitive study of the various investigations, that most of the reported works are rather limited in the range of parameter variables. Results of the effect of process variables on burr height and thickness are sometimes of contradictory nature, rather than being complimentary in nature. Most of the authors have studied either burr height or thickness, thereby limiting the usefulness of the results. Agreement between theoretical models and the corresponding experimental results are often of a qualitative nature. The number of parameters affecting burr properties is rather too many. Nevertheless, the following conclusions were drawn from the study. The most important parameter affecting the burr size is feedrate. Reducing the feedrate at the starting and the terminating stages of the drilling process, reduces the burr size significantly. Among the drill geometry parameters, helix angle, point angle and the chisel edge (length and angle) are the most important ones. A significant reduction in burr height and thickness should be possible by a correct selection of the feedrate, helix angle and point angle. If feedrate can be varied both up and down by some sort of adaptive control system, it may be possible to decrease both the burr size, and simultaneously increase the productivity. These conclusions also point to a need of further comprehensive research in these areas.