Hole Surface Quality Research Articles

Investigating Twist Drill Design Influence on Thrust Force and Surface Roughness in Drilling AFRP/ Al7075-T6 Stacks Materials

Drilling Aramid Fiber-Reinforced Plastic (AFRP) presents unique challenges when compared to drilling other composite panels. These difficulties arise from the high-toughness characteristics of aramid fibers, which exhibit a tendency for ductile deformation during the drilling process. This research explores the influence of drill bit design on the drilling process stack-up materials, which comprise Aramid Fiber Reinforced Plastic Composite Laminates (AFRP) and Aluminum Al7075-T6. Three distinct bit designs were employed in the experiment, conducted on a Computer Numerical Control (CNC) machine operating at a spindle speed of 2000 rev/min and a feed rate of 0.05 mm/rev. To measure thrust force during drilling, a dynamometer was integrated into the setup. Subsequently, a roughness tester was utilized to assess the hole surface roughness of the stack-up materials. For AFRP materials, the w-point drill design emerged as the optimal choice, reducing thrust force by approximately 5% to 13% compared to other drill bit designs. Conversely, for Al7075-T6 panels, the tapered web drill design demonstrated exceptional results, lowering thrust force by approximately 21% and 50% in comparison to burnishing and w-point drill bits, respectively. In terms of hole surface roughness, the burnishing drill type consistently produced the smoothest surfaces, boasting significant improvements of 44% and 82% when compared to the tapered web and w-point drill bits for AFRP panels. Similarly, for Al7075-T6 panels, the burnishing drill type consistently outperformed the tapered web and w-point drill bits by 74% and 88%, respectively, in achieving a superior hole surface finish. These findings underscore the critical importance of selecting the appropriate drill bit design to optimize thrust force reduction and hole surface quality when working with stack-up materials.

Improving the fatigue property of diffusive film cooling holes in nickel-based single crystal superalloy via ultrashort pulse laser drilling coupled with abrasive flow machining

A novel hole-making technique, which combines ultrashort pulse (UP) laser drilling with abrasive flow machining (AFM), has been developed to enhance the surface quality and fatigue resistance of diffusive holes in nickel-based single crystal (NBSC) superalloys. This study conducted a comprehensive analysis of the surface morphology and metallurgical characteristics of the hole wall, evaluated by fatigue testing at elevated temperatures and fractography analysis. The findings demonstrate that AFM can effectively eliminate the solidified debris generated during UP laser drilling, significantly reducing surface roughness and inducing a rounded effect at the outlet acute zone of the diffusive hole. Such improvements have been shown to increase the fatigue life of the holes by up to 50.6 % compared to those without polish. Furthermore, the crystal plasticity finite element method (CPFEM) was employed to investigate the localized stress concentration and the accumulation of plastic slip around the diffusive hole, elucidating the mechanisms behind fatigue failure in NBSC superalloys. The study also discusses the influence of the different hole-making technology on the fatigue properties of diffusive holes, integrating CPFEM results with analyses of surface quality and fatigue fractography. The study conducted in this study can provide valuable guidance for the fabrication of diffusive holes in turbine blades. Furthermore, it can also improve our understanding of the fatigue failure mechanism of diffusive holes in NBSC superalloy.

Ultrasonic assisted pecking drilling process for CFRP/Ti laminated materials

Carbon fiber reinforced polymer (CFRP)/titanium alloy (Ti) laminated materials are widely used in aerospace and marine industries because of their excellent physical and electrochemical properties. The extensive demand requires a higher level of hole making technology to reduce the material damage caused by hole making. In this paper, we adopt a novel machining method, which combines Ultrasonic Assisted Drilling (UAD) and pecking drilling to generate a new machining method, Ultrasonic Pecking Drilling (UPD). Based on this, this study compares Conventional Drilling (CD), UAD and UPD in terms of thrust using orthogonal test method. In this paper, CFRP exiting delamination damage is investigated for three processing methods, and indirect measurement of interface temperature as well as detection of CFRP entrance delamination damage are carried out for UPD process. In addition, the tool wear and the exit burr of titanium alloy are analyzed for the three processes under different parameters. The test results show that UPD performed better in terms of thrust, the lowest thrust force is reduced by 35.1 % and 14.8 % at low feeds, respectively. CFRP exit delamination and tool wear are also good compared to both CD and UAD. Compared to CD, the maximum delamination damage decreased by 6.37 %. Besides, UPD results in better hole surface quality, where the roughness can be reduced by up to about 40 %. The obtained results show that UPD is a worthwhile option for drilling CFRP/Ti laminated materials.

Effects of compaction pressure on microstructure, mechanical properties, and machining characteristics of sintered AISI 316L steel

Abstract In this study, the effect of compaction pressure on the properties of AISI 316L and its machining performance was evaluated. AISI 316L powders were subjected to three different compaction pressures (550, 650, and 750 MPa). Subsequently, the samples were sintered in an argon atmosphere at a constant temperature of 1523.15 K. The microstructure, hardness, and mechanical properties of the materials were investigated. To examine the effect of compaction pressure on drilling characteristics (thrust force, torque, surface roughness, chip formation, and burr formation), the samples were subjected to dry drilling at different feed rates and cutting speeds. It was observed that increasing the compaction pressure resulted in smaller grain sizes in the microstructure, increased hardness, and higher tensile strength. Higher compaction pressure led to higher thrust force and torque, whereas lower compaction pressure resulted in improved hole surface quality and shorter chips. Additionally, at higher cutting speeds, the color of the chips changed due to the elevated temperatures associated with increased cutting speeds.

Reducing the taper and the heat-affected zone of CFRP plate by Micro fluid assisted laser induced plasma micro-drilling

Carbon Fiber Reinforced Plastics (CFRP) with superior mechanical properties are widely used in aerospace, automotive, and medical fields. The characteristics of CFRP with anisotropy and inhomogeneous result in poor machining performances by conventional drilling techniques. Laser drilling is a non-contact high precision machining technique without tool wear but leads to a large heat-affected zone (HAZ) and taper. Although underwater laser drilling could reduce thermal damage on CFRP surface, bubbles produced in the machining process severely affect the machining stability and surface quality. In this study, a micro fluid-assisted laser-induced plasma drilling (MFA-LIPMD) method was proposed to relieve the negative effect of bubbles as well as reduce the taper and HAZ. A comprehensive analysis of hole surface quality, HAZ, taper, and mechanical properties was conducted, and MFA-LIPMD performed more advantages over laser in the air (LIA) and laser-induced plasma drilling (LIPMD). It was found that the taper of micro-holes was reduced by 42.8%–51.78%, and the thermal damage rate of micro holes processed by the MFA-LIPMD process was reduced by 65.3%–68.1% compared with the LIPMD process, and the maximum tensile load of samples was increased by about 7.68%. Therefore, MFA-LIPMD has great potential for machining high-quality micro holes of CFRP plates.

Advancing electrochemical drilling process via coupling of flow field and electric field in pulsating state generated by a novel tube tool

This paper introduces an improvement to electrochemical drilling process by coupling flow field and electric field in pulsating state. A novel tube with half-wedged shape at the end (HW-tube) is prepared, with both sidewall and wedged part of the HW-tube insulated. Only the flat part is utilized to provide electric field for electrochemical drilling. By rotating the HW-tube, both flow field and electric field in pulsating state are generated, alternating in different positions within the inter-electrode gap (IEG). The pulsating flow field enhances the mass transfer process, while pulsating electric field disperses material dissolution process and distribution of electrolytic by-products. Both pulsating fields are coupled at the same frequency, further enhancing the electrochemical drilling process. Simulation results indicate that both flow field and electric field in pulsating state are generated. Compared to the traditional tube, the HW-tube significantly reduces the number of residual particles in IEG, and this number is further reduced by increasing the rotation speed. Experimental results reveal that the surface quality and dimensional uniformity of small hole are improved with HW-tube. With feed rate of 2.22 mm/min, a small hole with diameter of 1.52 ± 0.017 mm is drilled, resulting in a surface roughness of 0.331 μm.

Machinability analysis for drilling Ti6Al4V ELI under sustainable techniques: EMQL vs LCO2

As a result of the widespread use of Ti6Al4V ELI in the medical industry for implants that are subjected to high loads, these biomedical implants must be accurately machined to prevent unfavourable joint or muscular inflammatory conditions. This oftentimes involve drilling holes into the implants for joint assembly during surgery. It is well known that titanium is a very difficult to machine material and therefore, requires appropriate cooling and lubrication during machining. With the help of SEM and line-scan EDS analysis, the current study focuses on analysing various sustainable machining techniques, such as electrostatic minimum quantity lubrication (EMQL) and liquid carbon dioxide (LCO2 cryogenic coolant), while drilling Ti6Al4V ELI (Grade 23) holes in terms of hole surface quality, wear mechanisms, and chip morphology. Poor surface quality of the hole was produced under EMQL cutting, with around 42–71% larger surface roughness values (Rz) compared to cryogenic LCO2 conditions. The hole surface consisted of different defects such as adhesion, microfractures, smearing etc., as a residue of the drilling operation under both EMQL and cryogenic LCO2 conditions. Tool life was significantly improved under LCO2 cutting environment (approximately by 416%) in comparison with EMQL technique. Adhesion and abrasion were found to be the main tool wear modes. Likewise, the machined chips exhibited cracks and adhered particles further demonstrating that EMQL coolant did not provide sufficient lubrication and heat extraction capability. Cryogenic LCO2 coolant outperformed EMQL lubrication for all machinability indicators, according to the study, making it a superior cutting environment for machining Ti6Al4V. Moreover, cryogenic LCO2 coolant dissipates into air during the machining process rendering it a sustainable and environmentally friendly machining coolant fluid.

Cumulative effect of Shearing parameters and Ramp angle on Hole surface quality in Ti6Al4V by Helical milling strategy

Hole creation is a common contour in drilling and milling. However, drilling big holes in Ti6Al4V is difficult. It is due to the thermally increased metallurgical behavior of Ti6Al4V, which mortifies drill bits and degrades hole quality. To solve this issue, the current research investigates Helical milling through Computer Aided Tool Path as a viable option for Hole production by functionally managing shearing parameters. This approach drives the process parameters helically at a certain Ramp angle to achieve improved surface quality in the Hole. The analysis of variance reveals that the Cutting Speed and Feed/tooth affect the Circularity of the Hole. Furthermore, Axial DOC and Ramp angle significantly impactHole surface texture. The cumulative impact of Cutting Speed at 60 m/min, Feed/tooth at 0.06 mm, and Axial Depth of Cut at 0.6 mm applied at a Ramp angle of 1.50 through theHelical milling tool path under Hybrid nano Flood lubrication catch the outstanding Hole Quality.

Drilling of GFRP with Liquid Silicon Rubber Reinforced with fine Aluminium Powder on Hole Surface Quality and Tool Wear using DOE

Drilling of GFRP with Liquid Silicon Rubber Reinforced with fine Aluminium Powder on Hole Surface Quality and Tool Wear using DOE

Performances of cryo-treated and untreated cutting tools in machining of AA7075 aerospace aluminium alloy

The quality of drilled holes in aluminium alloys used in the aerospace industry is vital to ensure high-precision structural integrity. For this reason, optimum selection of cost-effective cutting tools and cutting parameters is of great importance. Nowadays, due to their high cost and supply difficulties, there is a great interest in improving the performance of traditional HSS cutting tools as an alternative to ceramic, carbide and coated cutting tools. HSS cutting tools are widely used in different industries due to their cost-effectiveness and suitability to improve tool performance. In this research, the performances of cryo-treated (DC&T) and untreated (UT) HSS cutting tools used in dry machining of AA7075 aluminium alloys were investigated. Thanks to DC&T processes applied to HSS cutting tool, improvements have occurred in its microstructure. The hardness value of HSS cutting tool increased by 6.89% with the effect of DC&T processes applied. When the highest and lowest Ra values obtained using DC&T and UT HSS cutting tools were compared, it was seen that DC&T HSS cutting tool performed better by 11.05% and 25.91%, respectively. It has been determined that the hole surface quality of the aluminium workpiece machined with DC&T and UT HSS drills is negatively affected by the increase in spindle speed and feed rate. The highest S/N ratios calculated according to Ra values of holes drilled on aluminium workpieces using DC&T and UT HSS cutting tools were found to be -7.12 dB (2.27 μm) and -9.62 dB (3.03 μm), respectively. In the ANOVA analysis, it was determined that the most effective parameters on Ra values were spindle speed (70.62%), tools (18.19%) and feed rate (9.98%), respectively. In the regression analysis, R2 value for Ra values was calculated as 98.30%. High R2 value result shows that the model developed is quite successful in estimating Ra values.

Investigation on cutting performance in ultrasonic assisted helical milling of Ti6Al4V alloy by various parameters and cooling strategies

Ti6Al4V alloy is one of the typical difficult-to-machine materials and often results in rapid tool wear, leading to poor machining quality in aircraft assembling. Compared to conventional helical milling, the ultrasonic assistant helical milling (UAHM) process has indicated its superior performance; however, it is still a great challenge to improve the hole surface quality and accuracy. In addition, few studies have been conducted on the effect of different variables and cooling strategies on the hole-making performance in longitudinal-torsional ultrasonic assisted helical milling (LT-UAHM). This paper, for the first time, reports effects of machining variables on geometric precision and surface roughness in LT-UAHM of Ti6Al4V. In addition, the lubrication/cooling mechanism on the simultaneous application of LT-UAHM and MQL is theoretically analyzed. The design approach of Taguchi experiment was employed to study how major variables such as the cutting speed, tangential feed, axial feed, and the workpiece hardness influence the dimensional and geometrical tolerances and surface roughness. This paper also discussed the effect of three cooling strategies, i.e., dry condition, air coolant, and minimum quantity lubrication (MQL) in LT-UAHM. Theoretical analysis demonstrated that the MQL coolant can be nebulized into hyper-fine droplets owing to the resonant cavitation phenomenon. Combined with the penetrating action caused by the separate-cutting principles of LT-UAHM, the cooling and lubrication performance of MQL was further enhanced. As a result, LT-UAHM with MQL had the most positive effect on circularity, cylindricity, nominal diameter, and surface roughness, contributing to 34%, 32%, 39%, and 40%, respectively. The second important machining factor was the cutting speed, contributing to 31%, 29%, 36%, and 22%, respectively. The tangential feed and workpiece hardness have the negative effect on geometrical accuracy, respectively.

STUDY THE EFFECTS OF THE MULTINITE COAT OF THE HIGH SPEED STEEL DRILL BIT IN DRILLING

Drilling is an important metal manufacturing processes. Drill bits are used in drilling to create holes. Wear of drill bits can have an adverse effect on the quality of the drilling hole. To increase the wear resistance of drill bits, surface modifications have been introduced and studied their effectiveness. Multinite coating is a candidate for surface modification techniques to increase wear resistance of the drill bits. In this study, the effect of multinite coating on the wear resistance of drill bits has been investigated. Two types of 6 mm diameters drill bits, the uncoated high speed steel, and the multinite coated high speed steel drill bits, were used to create the hole with 30 mm in depth on ASTM A36 steel. The drilling parameters were 1,100 rpm of rotation speed and 135 mm/min of the feed rate. The thrust force and the cutting torque during drilling were measured by a force sensor. Flank wear on the drill bits were measured by overlap image technique. Also, the roughness of hole surfaces were investigated. Results showed that the higher surface hardness of multinite coated high speed steel drill bit led to a lower flank wear rate at the beginning of drilling. Consequently, built-up of chip on the multinite coated high speed steel drill bit was less compared to the uncoated one. We conclude that the higher surface hardness of multinite coated high speed steel drill bit improves the wear resistance of drill bit by a decrease of wear rate at the beginning of drilling and a lesser amount of chip built-up on the cutting edge and the surface quality of hole after drilling.

Reducing plasma shielding effect for improved nanosecond laser drilling of copper with applied direct current

Laser drilling of copper faces challenges due to its high reflectivity and high thermal conductivity of the laser beam. To enhance laser drilling efficiency and hole surface quality, the copper substrate was applied with a direct current (DC) during a 355 nm nanosecond laser drilling process. It was found that introduction of the DC current played a noticeable role in reducing the entrance hole diameter, increasing the depth of the blind hole, decreasing the taper angle, improving the inner surface finish, and enhancing the hole integrity with less amount of debris at the hole exit. Explanation of the processing mechanism is provided by investigation effects of key processing parameters and modeling of DC current-induced magnetic field on the laser-induced plasma. The applied DC current through the copper substrate during laser drilling generated an induced magnetic field and the Lorentz force of the induced magnetic field limited the expansion of the laser-induced plasma in the direction parallel to the laser beam, which weakened the shielding effect of the plasma and thus improved the processing efficiency and hole quality of the nanosecond laser drilling. The study results may open a new path for efficient and high quality laser machining of reflective, high thermal and electrical conductive materials.

Review on design of hybrid longitudinal-torsional ultrasonic vibration horn for rotary ultrasonic machining (RUM) processes

Longitudinal-torsional (L-T) vibration machining process in rotary ultrasonic machining (RUM) technologies has been considered one of the most promising method in order to cope the machining problems of various difficult-to-machine materials (composites, metallic alloys, abrasives, ceramics and glass). However, design complexity of the L-T machining systems keeps it limited for commercial applications. Hybrid L-T horn is the key component to achieve the efficient performance of RUM systems. Design of hybrid L-T horn is highly intricate due to slots geometry, position, and number of slots. At present, there is no study available in the literature specifically focused on the design and implementation of hybrid L-T horn. Therefore, this study systematically describes literature review on the design, simulations and implementation of hybrid L-T vibration horn in RUM applications of difficult-to-machine materials. Furthermore, the present research reveals the critical design parameters of hybrid L-T horn such as incident angle 47.6° gives better surface quality of the machined hole compared to 67.2° at designed resonant frequency 35 kHz.

Comparative Analysis in Drilling Performance of AA7075 in Different Temper Conditions

The widespread use of heat treatable7075 aluminum alloy in the aerospace industry requires a high machinability performance. The main objective of this study is to examine the machinability and the surface quality conditions of the AA7075 material with different temper conditions. For this purpose, various temper treatments are implemented to evaluate the impact of microstructural properties on tool wear and the surface quality of the drilled holes. The drilling operations have been done on O, F, T4, T6, and T7 temper conditions. Process parameters were three different spindle speeds (715, 1520, and 3030 rev/min) and three feed rates (0.1, 0.2, and 0.3 mm/rev) with HSS-G high-performance ground standard twist drill bit. The present work deals with the effects of temper conditions on thrust force, drilling temperature, tool wear, surface integrity, and chip morphology. Response surface methodology was used in the evaluation of experiment results. The optimization results showed that while thrust force and torque are not significantly affected by a change in spindle speed, they are sensitive to an increase in feed rate. Heat-generation on the drill bit is the lowest at low levels of both the feed rate and spindle speed parameters. The AA7075-T6 condition specimen was machined with continuous chip formation, resulting in the best hole surface quality. 3D Finite element modeling of the drilling process was carried out. Numerical analysis revealed the drilling performance of AA7075-T6 in terms of thrust, heat generation and chip formation.

Effects of processing parameters on the surface quality of wrought Ni-based superalloy by ultrasonic-assisted electrochemical grinding

Ni-based GH625 superalloy has been widely employed in the aerospace industry due to its high strength, outstanding corrosion resistance, and high-temperature resistance. A novel hybrid processing method of ultrasonic-assisted electrochemical grinding (UAECG) can achieve a high effective removal rate for difficult-to-process materials and thereby avoid stray corrosion during the process. This study systematically investigated the electrochemical dissolution behaviors of GH625 alloy at low current density and the effects of processing parameters on its surface roughness. A qualitative model was proposed to further reveal its removal mechanism for GH625 alloy during the UAECG process. Polarization curves depicted that an efficient and stable electrochemical dissolution was achieved at an appropriate temperature (20 °C) and concentration (10 wt.%) of NaNO3 electrolyte. The findings also revealed that selective corrosion preferentially occurred on the grain boundary or near the NbC carbides under different current density corrosion circumstances. Compared with the ECG process, the excellent surface quality (Ra = 0.37 μm) and taper of the small holes (taper = 0.04 ± 0.005°) are obtained at the optimized condition of a pulse voltage of 5.8 V, feed rate of 0.6 mm/min, cathode speed of 12 kr/min and drive amplitude of 60% by UAECG technology.

Multiobjective Optimization of Cutting Parameters for TA10 Alloy Deep-Hole Drilling.

In order to obtain better quality TA10 pipes, the Boring and Trepanning Association (BTA) deep-hole drilling process is used. However, this type of machining leads to difficult chip removal, tool wear, and poor hole-surface quality. In this study, a deep-hole drilling experiment was conducted on TA10 workpieces using the designed tool with different process parameters, and the process parameters were optimized by machining results with multiple objectives such as chip morphologies, tool wear, hole-axis deflection, and hole surface roughness. The results show that different process parameters have a great impact on the cutting process, with a higher feed resulting in smoother chip removal and a lower spindle speed resulting in lighter tool wear and less hole axis deflection. When the spindle speed is 145 r/min and the feed is 0.12 mm/r, the machined TA10 pipe meets both the accuracy requirement of roughness and the machining efficiency.

Longitudinal-torsional coupled rotary ultrasonic machining of ZrO2 ceramics: An experimental study

Zirconia (ZrO2) ceramics, as advanced structural ceramics, are gradually used in manufacturing, aerospace and other fields due to their excellent properties. However, it is problematic to process the ZrO2 ceramics by conventional machining. This study adopted the longitudinal-torsional coupled rotary ultrasonic machining to process the ZrO2 ceramics. Firstly, the material removal mechanism was clarified in the view of a single abrasive particle. Then, the longitudinal-torsional coupled rotary ultrasonic machining experiment was conducted to explore the effect of processing parameters on the cutting force, hole surface roughness, surface morphology, and single abrasive particle wear with those in the conventional machining. It was found that the cutting force reduced with the spindle speed and ultrasonic power, growing with the feed rate. The hole surface roughness declined with spindle speed, enhanced with feed rate, and decreased first and then increased with ultrasonic power. Compared with the conventional machining, both the cutting force and surface roughness were significantly reduced in the longitudinal-torsional coupled rotary ultrasonic machining. The test results proved that the hole surface quality was improved, and the single abrasive particle wear was reduced in the longitudinal-torsional coupled rotary ultrasonic machining. This study's results are considered instrumental in the longitudinal-torsional coupled rotary ultrasonic machining processing of hard and brittle materials.

Forming the geometric accuracy and roughness of holes when drilling aircraft structures made from polymeric composite materials

The subject of this study is indicators of the quality, geometric accuracy, and roughness of holes in aviation structures (AS) made from polymeric composite materials (PCM) produced by drilling. The indicators of quality, geometric accuracy, and roughness of PCM holes were investigated by using kinematic hole drilling schemes and the creation of PCM chips. A kinematic scheme has been built of the cutting forces operating in PCM when drilling with the distribution of zones from 0° to 360°. Experimental studies on the establishment of characteristic shrinkage zones in the drilling of PCM, as well as their values, have been implemented. The methods used are the analysis of the quality indicators of PCM holes, and the method of expert assessments. The following results were obtained. Based on the analysis and synthesis, it was found that with incorrectly selected geometric parameters for drills involving the work accompanied by the wear of drills on the back surface, stratification, cracks, or chips of PCM may appear. It is shown that the decisive factor is a comprehensive assessment, which is determined not only by the quality, accuracy, and roughness but also by the condition of the holes at the input and output of the drill. Features and characteristic contact zones for PCM drilling were identified. It has been established that within the drill operating areas from 0° to 90° and from 180° to 270° the cutting forces are reduced while the indicators of surface quality, roughness, and geometric accuracy of a PCM hole are improved. In zones from 90° to 180° and from 270° to 360° – on the contrary, low quality of the machined surface is assumed. The calculation of the required cutting forces and calculation of the height of roughness of drilling holes in PCM have been proposed, taking into consideration the bearing of chips under the action of the wedge. The results of experimental studies on the establishment of characteristic shrinkage zones when drilling PCM confirmed the adequacy of the results of theoretical studies on the kinematic schemes of drill operation in PCM

Ultrasonic Vibration and Cryogenic assisted drilling of Aluminum-CFRP Composite Stack – An innovative approach

The request for more resistant but still light components has focused the manufacturing industry’s interest in composite materials. The manufacturing of parts made of composite may require drilling operations; nevertheless, assuring a good hole quality still represents a challenge for these materials. The present work provides, for the first time, a comparison between different drilling technologies, namely ultrasonic drilling and cryogenic drilling, proposing them as alternatives to dry drilling. After drilling, the hole surface quality is characterized in terms of geometrical accuracy and delamination. Results show that innovative cutting methods can significantly improve the drilling performances within a well-defined process parameters window.