Optimization of an autonomous robotic drilling system for the machining of aluminum aerospace alloys

This paper aims to identify the capability of a highly flexible industrial robot modified with a high-speed machine spindle for drilling of aluminum 6061-T6. With a focus on drilling feed rate, spindle speed, and pecking cycle, the hole surface roughness and exit burr heights were investigated using the Taguchi design methodology. A state of the art condition monitoring system was used to identify the vibrations experienced during drilling operation and to establish which robot pose had increased stiffness, and thus the optimum workspace for drilling. When benchmarked against a CNC machine the results show that the CNC was capable of producing the best surface finish and the lowest burr heights. However, the robot system matched and outperformed the CNC in several experiments and there is much scope for further optimization of the process. By identifying the optimum pose for drilling together with the idealized settings, the proposed drilling system is shown to be far more flexible than a CNC milling machine and when considering the optimized drilling of aerospace aluminum this robotic solution has the potential to drastically improve productivity.

Investigation on the Exit Burr Formation in Micro Milling

The burr on micro part has harmful effect on the dimensional accuracy and service performance. The original control of exit burr formation during micro milling is desirable and advisable. In this paper, the formation mechanism of exit burr was studied based on the varying cutting direction during micro milling. Three exit burr control strategies were concluded, the material properties embrittlement, the support stiffness increasing and machining parameter optimizing operations. Then, micro milling experiments were carried out to investigate the exit burr morphology and size. It was found that the exit burr formation was attributed to the change of material flowing path at the exit surface, which was caused by the negative shear deformation zone that was induced by the discontinuous shape features. Different exit burr morphologies were classified; the triangle exit burr type was caused by the varying exit burr growing direction along the exit surface. The optimal machining parameters in micro milling to obtain a small exit burr were suggested.

Drilling Characteristics of Bulk Metallic Glass in Various Cooling Conditions

Drilling is an indispensable machining operation for manufacturing bulk metallic glass (BMG) medical appliances, which generally have complicated shapes and require high dimensional accuracy. Unfortunately, the available research on the drilling of BMG is limited, and thus reliable guidelines for practical production are lacking. For this reason, this paper focuses on the BMG machinability in the industrial range. The high-speed drillings of BMG specimens were carried out in dry, wet (cutting fluid), and frozen (icing clamp) conditions. The relationship between the thrust force, torque, drilling energy, tool life, tool wear, as well as the hole quality (burrs, diameter deviation, taper angle, and circularity) were studied. The cooling methods and matching spindle speeds were optimized, and the investigation has shown that wet drilling with high spindle speed is the most suitable method for machining BMG as it resulted in the longest tool life and the highest hole quality. Tool failure modes for all cooling methods included plastic deformation and rake face abrasions, in addition to the abrasive and adhesive wear on flank face. The chip adhesion to the entry hole was identified as the primary cause for the large entry burr. Finally, the crown-shaped exit burr rupture triggered the warpage and tearing of the material around the hole.

Optimization of an Autonomous robotic drilling system for the Machining of Aluminum Aerospace Alloys

This paper aims to identify the capability of a highly flexible industrial robot modified with a high-speed machine spindle for drilling of Aluminum 6061-T6. With a focus on drilling feedrate, spindle speed and pecking cycle, the hole surface roughness and exit burr heights were investigated using the Taguchi design methodology. A state of the art condition monitoring system was used to identify the vibrations experienced during drilling operation and to establish which robot pose had increased stiffness, and thus the optimum workspace for drilling. When benchmarked against a CNC machine the results show that the CNC was capable of producing the best surface finish and the lowest burr heights. However, the robot system matched and outperformed the CNC in several experiments and there is much scope for further optimization of the process. Overall the proposed drilling system is far more flexible than a CNC milling machine and when considering the optimized drilling of aerospace aluminum this robotic solution has the potential to drastically improve productivity.

Numerical Modeling the Effects of Chamfer and Hone Cutting Edge Geometries on Burr Formation

A finite element based numerical model to simulate orthogonal machining process and associated burr formation process has been developed in the presented work. To incorporate simultaneous effects of mechanical and thermal loadings in high speed machining processes, Johnson and Cook`s thermo-visco-plastic flow stress model has been adopted in the conceived numerical model. A coupled damage-fracture energy approach has been used to observe damage evolution in workpiece and to serve as chip separation criterion. Simulation results concerning chip morphology, nodal temperatures, cutting forces and end (exit) burr have been recorded. Model has been validated by comparing chip morphology and cutting force results with experimental findings in the published literature. Effects of cutting edge geometries [Hone and Chamfer (T-land)] on burr formation have been investigated thoroughly and discussed in length. To propose optimum tool edge geometries for reduced burr formation in machining of an aerospace grade aluminum alloy AA2024, numerical analyses considering multiple combinations of cutting speed (two variations), feed (two variations) and tool edge geometries [Hone edge (two variations), Chamfer edge (four variations)] have been performed. For chamfer cutting edge, the “chamfer length” has been identified as the most influential macro geometrical parameter in enhancing the burr formation. Conversely, “chamfer angle” variation has been found least effecting the burr generation phenomenon.

Precision Cutting of the Molds of an Optical Functional Texture Film with a Triangular Pyramid Texture

Based on an analysis of the precision and preparation technology of an optical texture film with a triangular pyramid texture, the technical requirements of the original mold were determined, and precision shaping planning technology was adopted to process the original mold. The shape error of the optical texture mold of the triangular pyramid was assessed by defining the area ratio of the retro-reflection. The influence of the tool nose radius and exit burr on the area ratio of the retro-reflection were analyzed. By optimizing the cutting tools, cutting materials and cutting boundaries, a five-axis ultra-precision machining system was used to plan the triangular pyramid structure with a base length of 115 µm and an included angle between two sides of 70.5°. The experimental results indicate that the dimension error of the triangular pyramid element is less than 1 µm, the angle error of the included angle between two sides is less than 0.05°, and the average roughness of the side of the triangular pyramid can reach 9.2 nm, which satisfies the processing quality requirements of the triangular pyramid texture mold.

Experimental and Simulation Study on Tool Life Models in Drilling of Forging Brass Using Uncoated-WC and AlCrN Coated-WC Tools

Burr is an undesirable phenomenon occurring in drilling operation which is one of the essential operations in the machining industry since it is directly influencing the operating costs. Exit burr height (EBH) values as the function of drilling time during drilling the specific holes of the forging brass workpieces used for producing the water-valve components with the uncoated- tungsten carbide (WC) and the AlCrN coated-WC drills were discussed. The data sets of drilling time, corresponding to EBH values at the appropriate criterion were used to develop the tool life models in terms of cutting speed and feed rate using Taylor’s equation. Monte Carlo simulation was adopted to study the uncertainty of cutting speed and feed rate on tool life predictions for sensitivity analysis. The results showed that drilling with a low feed rate decreased the averages of EBH. The predicted tool life values of the AlCrN coated-WC drills were higher than those of the uncoated-WC ones based on the results of tool life predictions. The appropriate operating condition of the cutting speed of 60 m/min and the feed rate of 0.2 mm/rev was recommended for manufacturers in the drilling of the forging brass workpieces using the AlCrN coated-WC drills. Moreover, the predicted tool life values for the uncoated-WC and the AlCrN coated-WC drills were about 600 and 800 min, respectively. This indicated that the AlCrN coated-WC drill increased tool life by 30%.