Drilling Burr Formation With Tool Wear

Abstract

Automated assembly processes are being widely used in aircraft manufacturing as a hole must be drilled before fastener installation. Burr formation is of importance for machining processes including drilling. A burr, an unwanted by‐product of machining, is a raised edge that remains attached to a workpiece because of the loss of shear action. In drilling, burrs form as the drill enters and exits the part, particularly when the tool becomes worn. Burrs require an additional process to deburr, incurring extra cost and time. To understand drilling burr formation, this dissertation presents a new model that combines a burr model with a tool‐wear model. The first adopted model describes a burr with respect to its height and thickness and relates burr formation to the drilling thrust force generated from drilling with a sharp tool. This model comprises a number of key factors: part material property, tool geometry, and drilling parameters. In reality, these factors will vary. Preliminary work was done to use this model to develop a sensitivity matrix for the purpose of studying the effect of variation in the key factors on burr formation. Unfortunately, tool wear, which is a major issue, cannot be simply considered as a variation in tool geometry. When a tool becomes worn, the cutting edge radius becomes large, and the cutting action changes from shearing to ploughing. A second model adopted is a tool wear model, leading to the core work of this dissertation. The aim of this study is to develop a drilling burr‐formation model for realistic conditions, incorporating variance within the tool and process parameters. The proposed method applies a weighting model that can consider the wear/no‐wear condition for each segment, thereby leading to a hybrid model for drilling burr formation. The research method is validated through simulation and an experiment entailing the generation of drilling burrs in conditions mimicking those in aerospace manufacturing. The results show that the model successfully estimates burr height and thickness trends with increasing levels of tool wear, for penetrated holes. The methods and results presented in this dissertation show good promise for understanding the effects of tool wear on drilling burr growth.