Tungsten Carbide Twist Drills Research Articles

Modeling of drilling process of GFRP composite using a hybrid random vector functional link network/parasitism-predation algorithm

Non-laminated glass fiber-reinforced epoxy composites (GFREC) have shown promising applications in various engineering fields. In this study, an experimental investigation followed by artificial intelligent modeling is carried out on the drilling of GFREC under two cooling conditions, namely internal and external. The damage factor of the drilled holes and the temperature of the drill tip were considered as main process responses. The experiments were conducted under different combinations of feed, spindle speed and coolant pressure. All holes were drilled using fresh tungsten carbide twist drills coated by TiN/TiAlN layer. A fine-tuned random vector functional link network (RVFL) model incorporated with a new optimizer called parasitism-predation algorithm (PPA) was developed to model the drilling process. PPA acts as an advanced metaheuristic optimizer to obtain the best model variables of RVFL. The developed model was compared with the stand-alone RVFL as well as the fined-tuned RVFL using particle swarm optimizer (PSO). RVFL-PPA outperformed other models in terms of coefficient of determination, root mean square error and other measures. The coefficient of determination of RVFL-PPA for different responses and cooling conditions ranges between 0.995 and 1.

Subsurface integrity studies on the drilling of Al/B4C/mica hybrid metal matrix composites

ABSTRACTWhen components are drilled for use in critical applications, some components might undergo surface defects and subsurface deformations. These defects arise due to microstructural and microhardness variations. This leads to sudden failure of these components. The present investigation focuses on Al/B4C/Mica hybrid composites and Al/B4C composites specimen with drilled surface and sub-surfaces. The goal is to identify measures to reduce surface integrity issues like microhardness, drilled surface morphology, and chip morphology on these specific components. Moreover, as a novel research, elemental and microstructural characterization of mica particles is carried out. The evaluation techniques used are Optical, EDX, SEM, and Vickers microhardness test. The stir cast specimens are drilled with process parameters of weight % B4C and mica at specified cutting speed and feed rate. Tungsten carbide twist drill of 8 mm diameter is used. The investigation reveals that addition of mica particles causes reduction in the microhardness of drilled surfaces. The % of reduction observed is up to 13.7, 5.2 and 3 (in Hv) on 4%, 8%, and 12% B4C reinforced Al/B4C/3%mica hybrid composites, respectively, in comparison with that of Al/B4C composites.

Influence of Materials and Machining Parameters on Drilling Performance of Syntactic Foams

Abstract The effects of drilling parameters and material properties are investigated on epoxy matrix syntactic foams reinforced with 20, 40, and 60 volume percent glass microballoon. The influences of cutting speed, feed, drill diameter, and filler content on drilling performance are studied based on the full factorial design of experiments using tungsten carbide twist drills. Based on experimental results, machinability aspects within the range of the chosen input parameters are predicted using response surface methodology-based models, which can guide industrial practitioners for choosing the appropriate process parameters. Microscopy is conducted on the drilled specimens to understand crack initiation and propagation mechanisms. The thrust force and specific cutting coefficient of syntactic foam are 40 % lower as compared to those of neat epoxy. The surface roughness of syntactic foams is higher than that of neat epoxy. The micrographs of drill bits show negligible tool wear. These results show the possibility of using syntactic foams in industrial applications in which the drilling of material is required for reasons such as joining using bolts.

Hole Quality Assessment in Drilling of Glass Microballoon/Epoxy Syntactic Foams

Syntactic foams reinforced with glass microballoons are used as alternatives for conventional materials in structural application of aircrafts and automobiles due to their unique properties such as light weight, high compressive strength, and low moisture absorption. Drilling is the most commonly used process of making holes for assembling structural components. In the present investigation, grey relation analysis (GRA) is used to optimize cutting speed, feed, drill diameter, and filler content to minimize cylindricity, circularity error, and damage factor. Experiments based on full factorial design are conducted using a vertical computer numerical control machine and tungsten carbide twist drills. GRA reveals that a combination of lower cutting speed, filler content, and drill diameter produces a good quality hole at optimum intermediate feed in drilling syntactic foams composites. GRA also shows that the drill diameter has a significant effect on the hole quality. Furthermore, damage on the hole exit side is analyzed using a scanning electron microscope.

An experimental investigation on ultra-precision instrumented smart aerostatic bearing spindle applied to high speed micro-drilling

High speed drilling of small diameter holes ranging from 0.1 to 1mm in printed circuit board (PCB) drilling industry has been largely carried out by using tungsten carbide twist drills and high speed spindles. In high speed drilling, however, the tool wear leads to increased cutting forces and results in poor hole quality as well as the hole location inaccuracy. Both hole quality and location accuracy are further considered as significant issues in drilling multilayer and heavy copper layered PCB workpieces. This paper presents the experimental development of an instrumented smart spindle, which can examine the tool wear by measuring the axial shaft displacement (known as the axial displacement) on the fly and thus applicable to real-time drilling processes. Cutting trials using the instrumented smart spindle and a Kistler dynamometer (9345A) on the customized multilayers PCB workpiece have shown a good correlation between the axial displacement and axial drilling force measurements. The axial displacement is capable of being used to detect the drilling engagement with each copper layer. Furthermore, the instrumented smart spindle can additionally be used to prevent a thrust bearing from being over-loaded and most importantly to detect tool wear in process.

Development of single step drilling technology for multilayer metallic-composite stacks using uncoated and PVD coated carbide tools

The paper details experimental trials to evaluate the performance of uncoated and PVD coated tungsten carbide twist drills, for single shot drilling of 3-layer metallic-composite stack workpieces. A full factorial experiment was undertaken involving variations in feed rate (0.05 and 0.08mm/rev) and drilling strategy (with and without pecking cycle), in addition to the tool coating (TiAlN/TiN). All of the uncoated drills machined 180 holes without exceeding the flank wear criterion of 0.3mm, regardless of feed rate level or drilling strategy. In contrast, tool life for the coated drills was ∼20-50% lower (90–148 holes). Thrust force decreased by ∼12% when operating at the higher feed rate while use of coated drills led to an increase of up to 18% due to the larger cutting edge radius. Conversely, the hard/ceramic coating provided greater wear resistance at the peripheral corner of the drill resulting in lower torque (up to ∼10%) compared to the uncoated tool. Furthermore, holes produced utilising the TiAlN/TiN coated drills typically exhibited superior geometrical accuracy in terms of diameter, out of roundness and cylindricity. Drilling at the lower feed rate of 0.05mm/rev however generated larger exit burrs by up to ∼90%.

Effect of drilling parameters and tool geometry on drilling performance in drilling carbon fiber–reinforced plastic/titanium alloy stacks

An experimental study on drilling of carbon fiber–reinforced plastic/titanium alloy was conducted using three kinds of drills to investigate the cutting process. This research was mainly focused on the drilling forces, drilling temperatures, chips, and delamination area with respect to the cutting parameters and tool geometries. One type of tungsten carbide twist drill and two types of chemical vapor deposition diamond-coated drills which were multi-facet drill and brad spur drill, respectively, were used in this research. The influence of drilling parameters and tool geometries was analyzed and the conclusions were drawn that the proper selection of drilling parameters and drill geometries could lead to better hole quality. Experimental results indicated that the drilling forces and hole quality have a strong connection with feed rate while the impact of cutting speed is small. Research results also showed that the use of multi-facet drill could reduce the delamination greatly and thus produced a better surface integrity. Besides, drilling temperature and titanium alloy chips were studied in this research.

Experimental investigation of the effect of different cooling methods on drill-induced damage in pultruded composites

Pultruded (nonlaminated) composites find application in construction of bridges, prefabricated walkways and platforms, ballistic applications, and so forth. However, literature on the drilling of nonlaminated composites is scarce. In addition, many researchers have also proposed that standard twist drill is not suitable for making quality holes in composites under dry conditions. Hence, this study is to analyze the influence of external and internal cooling methods on drill-induced damage factor while drilling glass fiber-reinforced epoxy pultruded composites and thereby to find the suitability of widely available twist drill. The drilling experiments using TiN/TiAlN-coated tungsten carbide twist drills of diameter of 10 mm were conducted using response surface methodology. From this investigation, it is evident that the internal cooling method is significant for obtaining high hole quality followed by external cooling method, and thereby suitability of twist drill has been proved. POLYM. COMPOS., 37:2855–2859, 2016. © 2015 Society of Plastics Engineers

Influence of cooling on the performance of the drilling process of glass fibre reinforced epoxy composites

Non-laminated composites find application in construction of bridges, ballistic applications, etc. However, literature on the drilling of non-laminated composite materials and literature on the drilling of thick composite materials under different cooling methods (dry, external and internal) is scarce. Hence the present study is aimed to investigate the influence of different cooling methods on quality characteristics (drill temperature and damage factor) while drilling glass fibre reinforced epoxy (GFRE) non-laminated 20mm thick pultruded composite rods having 80% fibre weight fraction and 0° fibre orientations with respect to the drill. The drilling experiments using TiN/TiAlN coated tungsten carbide twist drills of diameter 10mm were conducted using response surface methodology (RSM). The experimental values obtained for quality characteristics are empirically related to process parameters by developing a response surface model using Design-Expert software. The effects of process parameters on quality characteristics were analysed by using response surface graphs. The process parameters (feed, spindle speed and coolant pressure) are also optimized within the selected range. The optimal parameter levels are confirmed by validation test. From this investigation, it is evident that the internal cooling method is significant for obtaining high hole quality.

Experimental Analysis of Tool Wear when Drilling Carbon Fibre Composite (CFC) without Cutting Fluid, with Cutting Fluid and with a Pre-Cryogenically Cooled Tool

Machining of Carbon Fibre Composites (CFCs) particularly drilling, is frequently employed in industry especially when dealing with joining, assembly and structural repair of the parts. However, the nature and heterogeneous structure of CFCs often results in rapid wear of the cutting tool. This research studied the relationship and compared the effect of drilling a CFC plaque without cutting fluid, with conventional cutting fluid and with cryogenic cooling at constant cutting speed of 94 m/min and feed rate of 0.065 mm/revolution using tungsten carbide twist drill. The conventional cutting fluid was supplied continuously to the drill and the CFC plaque during the drilling cycle; while for the cryogenic cooling tests, the drill tip was immersed in liquid nitrogen for 10 and 30 seconds prior to drilling the CFC. It was found that the tool wear increased with the increasing number of drilled holes at all machining conditions. After drilling of 325 holes, the largest tool wear observed was 181 μm which was produced when drilling the CFC plaque with conventional cutting fluid. The corresponding tool wear for drilling with cryogenic cooling was 164 μm and the smallest tool wear of 155 μm was observed during dry drilling. Dry drilling produced the smallest tool wear because the heat generated reduced the strength of the CFC, particularly polymer matrix. Therefore, this situation led to easier machining of CFC materials; consequently reduced the wear of the tool.

SURFACE ROUGHNESS ANALYSIS IN DRILLING OF GFRP COMPOSITES BY TUNGSTEN CARBIDE TOOL

Nonlaminated composites having superior mechanical properties than laminated composites is widely used in ballistic applications. Since literature on the machinability of nonlaminated composites is scarce, an investigation was carried out to study the hole quality in drilling thick nonlaminated Glass Fiber Reinforced Plastic (GFRP) composite rods using coated tungsten carbide twist drill. The GFRP composite rods were made by pultrusion method with high fiber weight fraction. The surface roughness of the drilled holes was measured using surface roughness tester. Taguchi’s orthogonal array and analysis of variance (ANOVA) were employed to study the influence of process parameters such as feed and spindle speed on surface roughness. The optimum level of process parameters towards minimum surface roughness of the drilled hole walls was obtained to achieve defect controlled drilling of pultruded GFRP composite rods. Correlation for surface roughness with process parameters was established using a statistical software MINITAB 16. The influence of feed and speed on surface roughness was insignificant. The optimal process parameter levels within the range examined was identified as 0.15 mm/rev feed and 750 rpm speed for drilling pultruded GFRP composite rods using 10 mm diameter twist drill. The influence of process parameters on hole quality in nonlaminated composite rods differs with drill geometry and also differs from the influence of process parameters on hole quality in laminated composites.

Drilling Force of SiC Particle Reinforced Aluminum-Matrix Composites with Ultrasonic Vibration

In recent years, particle reinforced metal matrix composites (PRMMCs）has been widely applied because of its excellent mechanical performances. But the machining is very difficult due to the rigidity of reinforced phase in it, thus the popularization of PRMMCs is restricted much. Here, a method of ultrasonic vibration drilling is presented to the hole-making of Aluminum-matrix composites based on cutting force analysis between common and vibration machining. In virtue of the self-developed ultrasonic drilling equipment, experiments of common and ultrasonic vibration drilling are performed on SiC particle reinforced Aluminum-matrix composites with different content of SiC by using two types of tungsten carbide twist drill. Since the tool life can be represented directly by drilling force, especially the torque, the study of drilling force is very important for the surface roughness, the design and life of drill. Drilling force and its variation in the machining process are analyzed by comparison of common and vibration drilling. It shows that the eviction of drilling chips can be meliorated to some extent, and the drilling torque can be reduced about 30% during the ultrasonic vibration drilling process.

Surface Texture and the Stress Concentration Factor for FRP Components with Holes

The influence of hole quality on the mechanical behavior of fiber reinforced laminates was studied. Holes were introduced in tensile specimens of a graphite/epoxy (Gr/Ep) laminate using an abrasive waterjet and commercial drills (diamond coated tungsten carbide twist drills or tungsten carbide drill-reamers). The machined surfaces were characterized using contact profilometry and the surface texture was used in estimating the effective stress concentration factor (øKt). Utilizing the macroscopic stress concentration posed by the hole and øKt, the total stress concentration was estimated using the principle of superposition. The Gr/Ep specimens were then loaded in tension and acoustic emission was used to monitor the failure process. The apparent stress concentration factor (øKt(app)) of the tensile specimens was determined from the ratio of tensile strengths of coupons without holes to that of specimens with holes. Based on results from tension tests the øKt(app) at first fiber failure ranged from 2.50 to 3.40. The stress concentration factors determined from experiments were within 6% of that predicted using superposition and øKt. Although the hole quality was dependent on the method of machining and drilling, results from this study confirm previous reports that there is no correlation between the surface texture and first fiber failure or ultimate tensile strength of Fiber Reinforced Plastics (FRPs) with open holes. Holes introduced using worn diamond coated twist drills exhibited the lowest surface roughness but resulted in a significant reduction in first fiber failure strength. Results from this study indicate that surface texture and øKt cannot be used for a reliable estimate of hole quality in FRPs, especially for holes produced with worn cutting tools.