Deburring of Cross Holes in Titanium Using Industrial Robots
Authors: Pischan Matthias 
Published: September 2013

In aircrafts, hydraulic systems control moveable parts. For example parts like the front strut or the landing flaps. These parts are usually made from aluminium or titanium. Due to an increasing number of functions these valves show an increasing number of cross holes. The production process causes burrs at the intersection of the holes. Until now these burrs cant be removed reliably by an automated process. Remaining burrs can influence dimensional tolerances and reduce the efficiency and technical lifetime of the component. In some applications cross holes are used for the lubricant and coolant supply. In this case burrs can lead to blockades of critical passages or cause turbulences in the fluid. This can lead to leakage or bursting of the valve. Hence an uncontrolled removal of the burr during operation must be avoided. The consequence of these basic conditions is a time consuming manual deburring process. An automated deburring process of cross holes with industrial robots is usually performed with flexible abrasive brushes. Alternatively processes like AFM (Abrasive Flow Machining), ECM (Electro Chemical Machining) or TEM (Thermal Energy Machining) are used. Those processes are very efficient but require specialized equipment and cleaning processes for the used chemicals and the remaining abrasive paste. So they are not suitable for the deburring of safety related parts. This paper presents an experimental based approach for the robot based deburring of cross holes using industrial robots. For the deburring of cross holes several special tools are available. This article gives a short overview over the specific advantages and disadvantages of these tools. As the investigations revealed the best results can be achieved using the so called Orbitool developed by JWDone. The Orbitool is a tungsten carbide cutter developed for the deburring of cross holes. A better control of the required dimension at the intersection compared to brushes and other deburring methods is possible. Furthermore the tool can be used on machine tools and industrial robots and is flexible to a huge variety of bore diameters. The tool mainly consists of a ball shaped carbide milling cutter with a protective disk which is made of polished steel and a shaft of tool steel. To remove the burr the tool is moved along the bore axis into the smallest of the intersecting holes until the tip of the tool is close to the intersection. Then the tool is moved in radial direction to the bore surface until the tool axis corresponds to the interpolation diameter. This causes a deflection of the tool. In this situation only the protective disk is in contact with the bore surface. While the tool rotates it is moved towards the intersection in a helical motion. When the tool tip has reached the intersection the cutting edges get in contact with intersection and the deburring process begins. After the tool has passed the whole intersection it stops its rotation and is moved to the bore hole centre and then moved out of the workpiece. This paper deals with the optimization of the deburring process. The result mainly depends on the parameters movement speed of the robot, slope of the helical movement and rotational speed of the tool. The experiments are planned using DOE (Design Of Experiment) methods. Initial values for the optimization of the movement speed were determined by grid encoder measurements. Robotic specific parameters like the number of interpolating points and the influence of the path smoothing caused by the controller were also investigated. For the analysis of the burr and the secondary burr an optical 3-D measurement system is used. The results show that with the presented approach the burrs can be reliably removed. Before the deburring process the average burr height is about 60 μm and can be reduced so that there is no secondary burr visible. The result is a chamfer between 150 μm and 85 μm that depends on the process parameters. It can be demonstrated that a chamfer that is smaller than 100 μm leads to a secondary burr. Anyway the cycle time can be reduced from about 3 minutes for manual deburring to 30 seconds using an industrial robot. Additional wear analysis show that about 200 bore holes can safely be deburred.