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Drilling Operations and Machines
Published in Zainul Huda, Machining Processes and Machines, 2020
Function. Drill bits are the cutting tools that are used to remove material to produce a hole in a solid. Although drill bits can create different kinds of holes, the holes’ cross-section is generally circular. Drill bits come in many sizes and shapes and made of different materials. In order to produce a hole, the drill bit is usually attached to a drill machine, which powers them to cut through the workpiece by rotation (see Figure 6.1).
Overview and introduction
Published in Tom Denton, Automobile Mechanical and Electrical Systems, 2018
Drilling is a cutting process that uses a drill bit to cut or enlarge a hole in a solid material. The drill bit cuts by applying pressure and rotation to the workpiece, which forms chips at the cutting edge (Fig. 1.83). The flutes remove these chips.
Site investigation and geological data collection
Published in Duncan C. Wyllie, Christopher W. Mah, Rock Slope Engineering, 2017
Duncan C. Wyllie, Christopher W. Mah
It is essential that the drill bit be continuously flushed with a fluid, usually water, to cool the bit and remove the cuttings. The circulating water also lubricates the drill string to reduce the torque required to turn the rods, and reduces vibration of the rods. Water is usually supplied to the site by pumping from a nearby river, or by a tanker truck. Factors to consider in the supply of water include the pumping head between the supply and the site, freezing of the pipeline, and available road access. It is usual that the return drill water is collected in a settling tank at the site to remove the cuttings, and is then recirculated down the hole. This reduces the quantity of supplied water, and eliminates environmental contamination by silt-laden water.
Experimental characterization and finite element modeling of critical thrust force in cfrp drilling
Published in Machining Science and Technology, 2018
Kamlesh Phapale, Ashwin Ahire, Ramesh Singh
Delamination is most prominent interply damage mechanism induced in drilling and is highly undesirable. Interply failure reduces the material resistance to fatigue loads and it significantly affects the strength of the material, thereby compromising the long-term performance. Several methods are used to access delamination around the periphery of the hole. Area assessment methods based on image processing of exit hole damage can be used to calculate one- and two-dimensional delamination factors (Liu et al., 2012). Several nondestructive damage assessment techniques, such as optical microscope, stereomicroscope, ultrasonic C-scan, and digital photography technique are also used to observe delamination. It may be noted that the thrust force is a key entity to describe machinability of composite laminates as it directly affects the quality of drilled holes. The size of delamination zone is dependent on thrust force acting during drilling, there is a “critical thrust force” below which no delamination occurs (Hocheng and Tsao, 2005). Apart from thrust, torque is also developed during drilling and plays significant role in delamination (Singh and Bhatnagar, 2006). Torque is related to the feed rate and increases with an increase in the feed rate (Ramulu et al., 2001; Singh et al., 2008). The cutting forces (axial and tangential) in drilling have been found to be proportional to the axial feed rate which can be correlated with the interlaminar damage (Lazar and Xirouchakis, 2011). Since thrust force is a dominant factor affecting delamination, several researchers have tried to decrease the thrust force during drilling or somehow enhance the critical thrust force. The critical thrust force can be reduced using a support plate under the workpiece (Capello, 2004). Different techniques have been adopted to minimize drilling-induced delamination. Researchers have tried optimizing the operating parameters, tool geometry, tool material, theoretical modeling of drilling forces, and some unconventional methods to drill damage-free hole in laminates (Davim, 2009). Advanced drilling techniques, namely, vibration-assisted twist drilling and high-speed drilling have been developed to reduce drilling-induced delamination (Lin and Chen, 1996). Use of special drill bits over conventional twist drill bit is found to increase overall process efficiency and provides higher control on delamination. Several special drill bits have been developed, including straight flute drill bit, step drill bit, core drill bit, hollow grinding drill bit and step core drill bit to perform delamination-free drilling (Liu et al., 2012). The chisel edge of the twist drill bits is the major contributor to the thrust force developed in the drilling. Therefore predrilled pilot holes can reduce delamination significantly (Tsao and Hocheng, 2003).
Influence of ultrasonic vibration assistance in manufacturing processes: A Review
Published in Materials and Manufacturing Processes, 2021
Pankaj Sonia, Jinesh Kumar Jain, Kuldeep Kumar Saxena
Drilling is most commonly used machining process to make a hole in the material or component. The tool involved in drilling process is well known as a drill bit. During machining operation, drilling tool always associated with cutting force in different direction. However, the drilling operation suffers with a common problem of design constrained of tool that is, L/D (length/diameter) ratio. The L/D ratio in drilling restricts the drilling hole diameter with depth of hole. But the L/D ratio can be improved by reducing the axial thrust force in drilling operation. Additionally, longitudinal vibration assistance in drilling can enhance the capability of conventional drilling for hard to machine material like Ti and Ni alloys.[131,132] Thus, UV influence the chip formation mechanism and overcome the complex machining conditions, in results, better surface finish with significant reduction in force required for drilling. In the similar context, Azghandi et al.[133] reported the reduction in thrust force and torque by 20% & 32% respectively in the drilling of high alloyed steel X20Cr13. Additionally, chip morphology also improved significantly using UV assistance in micro-drilling of Ti64, in results much fragmented and small compared with conventional drilling. Some actual pictures of chip formation is shown in Fig. 11. The chip morphology in Fig. 11 indicates that the chip thickness reduction and chip breakage is influenced by feed and UV assistance. Moreover, the thrust force in LTUAD (longitudinal torsional ultrasonic-assisted drilling) decreased by 1.90% to 24.9%.[134] The assistance of UV in drilling (torsional ultrasonic-assisted drilling) of polymeric composites (CFRP) reduce the thrust force and delamination.[135] The similar study conducted by Wang et al.[136] and reported a reduction in exit delamination defects. The analysis also reported that the amplitude of vibration significantly affect the drilling performance up to a certain limit and beyond that it adversely affect the drilling performance. The safe amplitude of vibration is reported as 12 μm for drilling process.[36] In drilling, Lotfi et al.[39] reported a reduction in the formation of built-up edge at the tool due to reduction of contact time between tool and workpiece.[39] The Kadivar et al.[137] analyze the chip morphology and the effect of amplitude on the cutting force, found that the increase the amplitude, force required for cutting will reduce up to 10 μm amplitude, beyond that it increases. The higher scale of amplitude increases the impact or hammering effect, which significantly alter the value of cutting on the basis of workpiece softness and brittleness.[138] Whereas the higher amplitude discontinues the cutting action and increases the plastic deformation and in results, higher burrs formation. The chip morphology represents that by increasing the % of SiC, hardness of MMC increased. On improved hardness, high amplitude force dominantly affects the cutting conditions. Whereas cutting force in soft material does not affect significantly on higher impact developed due to high amplitude.[137]