Experimental study on the hole quality during abrasive waterjet drilling of CFRP

Abrasive Waterjet (AWJ) machining is considered an excellent alternative to conventional machining processes due to its superb machining characteristics. More specifically, Abrasive Waterjet drilling is nowadays a promising non-conventional process for obtaining high quality holes. In the present study, drilling experiments based on Taguchi L9 orthogonal design method were conducted via AWJ on carbon fiber reinforced polymer (CFRP) plate at various waterjet parameters, namely, different pressure, abrasive mass flow rate and standoff distance values. The purpose of the experiments was to investigate the impact of these process parameters on the quality of holes. The hole quality was determined by measuring the hole diameter error as well as the hole taper. The optical evaluation was implemented with the use of optical microscope and special measuring software. The ANOVA analysis of the results showed a significant influence of standoff distance regarding the hole diameter error and a combined influence of waterjet pressure and standoff distance regarding the hole taper. Furthermore, the optimal process parameter values for the optimization of the hole diameter error and hole taper were determined. The hole quality in terms of defects appearance was also quantitatively inspected, through optical imaging.

CFRP composite drilling through electrical discharge machining using aluminum as fixture plate

Recent developments in manufacturing require holes on composite materials, especially on the carbon fiber reinforced polymer (CFRP) with smooth hole periphery, low delamination, burr formation, taper, better circularity, and a high processing speed. Its non-conductive surface (epoxy layering) limits its machining through electrical discharge machining (EDM). To overcome this limitation, an aluminum fixture has been designed to guide the copper electrode of EDM for producing holes on a CFRP sheet of 1 mm thickness at low machining complexity, cost, time, delamination, burr in hole periphery and without affecting the material’s surface quality and performance. Even components with high geometrical complexity can also be drilled through this approach. Here, a multi-quality analysis called grey relational analysis is developed for examining the hole quality attributes, considering peak current, pulse on and off time, and flushing pressure as input parameters. This approach points out the optimum factor level setting and critical parameters (pulse-on time and peak current) that regulate the hole attributes (entrance and exit diameter, circularity, taper, material removal, and tool wear rate). An artificial neural network model has been designed and trained through experimental data sets. This model can also be adopted during the determination of hole quality attributes when the parameter settings are beyond a defined boundary, as the regression analysis value is very close to 1, and model performance is 4.99e-10. Peak current = 4 A, pulse-on time = 25 µs, pulse-off time=25 µs, and flushing pressure = 0.6 MPa were the optimum drilling parameters. In the initial hole, average burr length is 391.75 μm, and delamination of 539.3 μm is noticed. But burr formation is very negligible with delamination of 350.7 μm being observed with uniform circularity (0.979), low taper angle (−0.81354°), and TWR (0.000069 g/min) under optimum drilling conditions through this drilling approach.

Effect of cutting edge geometry change due to tool wear on hole quality in drilling of carbon fiber reinforced plastics using advanced ceramic coated tools

This paper aims to study the evolution of cutting edge geometry due to tool wear and discuss its impact on the hole quality of a carbon fiber reinforced plastic (CFRP) laminate. A drilling experiment was conducted using three types of twist drills: uncoated, BAM (AlMgB14) coated, and (AlCrSi/Ti)N nanocomposite coated tungsten carbide tools. After generating 120 holes, the uncoated drill had the largest cutting edge radius (∼36 µm), while the BAM coated drill had the most extensive flank wear (∼287 µm) among the three drills. This relatively rapid tool wear results in a reduction of average hole size and a considerable variation on the hole profiles. The worn drills with the cutting edge radius greater than 19.3 µm form the fiber pull-outs in not only the 135° plies but also the adjacent 45° and 90° plies from the cutting direction, creating deep void networks. This type of networked fiber pull-out damage was observed with the holes machined by the uncoated and BAM coated drills. The (AlCrSi/Ti)N coated drill, which experienced the least amount of flank wear and the least increase of cutting edge radius, generated consistently sized holes up to 120 holes. However, the relatively sharp (AlCrSi/Ti)N coated tool results in the higher arithmetic roughness average (Ra) and the maximum roughness height (Rz) values than the other tools due to the localized fiber pull-outs and the absence of severe matrix smearing.

Simulation of laser drilling of Inconel X-750 and Ti-5Al-2.5Sn sheets using COMSOL

The ability of COMSOL Multiphysics 5.2 software to carry out the simulation of laser drilling processes in Inconel X-750 and Ti-5Al-2.5Sn sheets was investigated in this study. A JK 701 pulsed Nd:YAG laser was used for drilling through the entire depth of Inconel X-750 and Ti-5Al-2.5Sn plates of 2 mm and 3 mm thicknesses using laser pulses of a millisecond in time. The laser parameters are varied in different combinations for well-controlled drilling through the entire thickness of the plates. Effects of laser peak power and pulse duration have been determined via the studying of the temperature distribution on the cross-section of the images taken in the simulation tests. Characterizing the optimum conditions obtained from the combination of parameters that improve hole quality is an essential aim in this paper. This work's outcomes might be helpful for researchers in terms of the optimum parameters proposed when studying the laser drilling of the mentioned alloys experimentally.

Influence of the Kinematic System on the Geometrical and Dimensional Accuracy of Holes in Drilling

This article attempts to show how the kinematic system affects the geometrical and dimensional accuracy of through-holes in drilling. The hole cutting tests were performed using a universal turning center. The tool was a TiAlN-coated Ø 6 mm drill bit, while the workpiece was a C45 steel cylinder with a diameter of 30 mm and a length of 30 mm. Three kinematic systems were studied. The first consisted of a fixed workpiece and a rotating and linearly moving tool. In the second, the workpiece rotated, while the tool moved linearly. The third system comprised a rotating workpiece and a rotating and linearly moving tool, but they rotated in opposite directions. The geometrical and dimensional accuracy of the hole was assessed by analyzing the cylindricity, straightness, roundness, and diameter errors. The experiment was designed using the Taguchi orthogonal array method to determine the significance of the effects of the input parameters (cutting speed, feed per revolution, and type of kinematic system) on the accuracy errors. A multifactorial statistical analysis (ANOVA) was employed for this purpose. The study revealed that all the input parameters considered had a substantial influence on the hole quality in drilling.