STUDY ON BURR FORMATION IN TURNING Álisson Rocha Machado Almir Kazuo Kaminise Marcio Bacci da Silva Rafael Gonçalves Ariza Universidade Federal de Uberlândia, Faculdade de Engenharia Mecânica, Bloco 1M Campus Santa Mônica, 38400089, Uberlândia, MG, Brazil, mbacci@mecanica.ufu.br Abstract: Several deburring processes have been used for burr removal, rising the cost of the part machined and affecting productivity. Deburring processes depend on the type of burr formed and includes grinding, chamfering among others. Although important in machining operations there are few works concentrated on burr prevention, elimination or minimisation. The complexity of the parameters involved and the difficulty to control them have directed the works to the effect instead of to the cause of burr formation. According to the literature it is impossible to avoid burr formation, however, it can be possible change some characteristics and properties of the burrs to facilitate its reduction after the cut or to decrease its dimensions to acceptable magnitudes. This work presents a study of burr formation for semi-orthogonal cutting operation of carbon steel. The burrs are analysed and measured using scanning electronic microscope and tool microscope. The results showed that the cutting conditions and tool geometry control the characteristics of the burrs. Feed rate and entering angle are the main cutting parameters affecting burr dimensions. Microhardness results also show that the material is highly hardened during the process of burr formation. Keywords: Burr, Turning, Machining 1. Introduction Burr formation is one of the main problems on cutting operations of metals. It is detrimental to the cut and can cause premature failure of the tool, geometrical error in the workpiece and may result in a serious problem on assembly. One of the six tool wear mechanisms mentioned by Trent (1984), called notch wear, can be caused by burr formed during the cutting operation (Nakayama and Arai, 1987). Burr is also a risk for the operator and a problem for automatic operations. It is therefore necessary subsequent operations to get rid of the burrs to achieve the final dimensional and geometric workpiece tolerance. Deburring can be an automatic process, however, many of them are manmade operations. For both cases the result is an increase on production cost and reduction on productivity. Despite the importance of burr formation on metal cutting, there are very few works about the mechanism of its formation. The works are concentrated on deburring processes instead on burr formation mechanism or ways to eliminate or minimise it during the machining operation. Gillespie and Blotter (1976) may be exception of this. They have done very important work on this subject, proposing simple analytic models to predict some burr properties and geometry such as height, thickness and hardness. According to their models the burr geometry depends on the properties of the workpiece material particularly the moduli of elasticity and the geometry of the tool, including cutting edge radius. They indicated four basic mechanism for burr formation: deformation of the material on the direction of the cutting edge; chip curling on the cutting speed direction (during the exit of the tool at the edge of the workpiece); the separation of the chip from the workpiece during chip formation; the interruption of the cut at the edge of the tool due to lack of fixation. According to these mechanisms they divided the burr into four types: Poisson burr, roll-over burr, tear burr and cut-off burr. They have concluded that it is impossible to eliminate the burr during the operation by changing parameters like cutting speed, feed rate or tool geometry, but it can be possible to minimise burr geometry. According to Hashimura et al. (1995), for example, the thickness of the roll-over burr decreases and the height of the Poisson burr increases when the tool back rake angle increases. Nakayama and Arai (1987), studied orthogonal cut of an annealed brass and proposed two different systems of burrs classification. They are based on the cutting edge involved on the burr formation and in the mechanism and direction of its formation. In relation to the cutting edge directly concerned in the burr formation they are classified into main cutting edge burr and side cutting edge burr. For both cutting edges involved in the process, the burrs formed are also classified according to the direction and mechanism of their formation into backward burr or entrance burr, sideward burr, forward burr and leaned burr. Studying the effect of the cutting conditions on the characteristics of the sideward burr, they concluded that it is possible to decrease burr height and thickness decreasing underformed chip thickness and chip shear deformation (by increasing rake angle or cutting speed or applying cutting fluid) as it depends on the depth of cut and the stress during shearing of the material in the primary shear plane angle. Ko and Dornfeld (1991), in a theoretical and experimental work on burr formation at the end of the cut (roll-over burr) during orthogonal cutting of ductile materials, proposed a model to predict height and thickness of the burr as a function of cutting conditions, tool geometry and workpiece material. A mechanism similar to the foot formation