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Drilling Operations and Machines
Published in Zainul Huda, Machining Processes and Machines, 2020
The drilling machining operation has been introduced in the preceding section. In drilling, a rotating cutting tool (drill bit) is pressed against the workpiece while ensuring the presence of lubricant; the latter is important to reduce surface roughness of the machined material and to improve its fatigue life (Sun et al., 2016). Besides the basic drilling operation, there are several drilling-related operations in practice in industry; these operations include (a) tapping, (b) reaming, (c) counter-boring, (d) counter-sinking, (e) center drilling, (f) spot facing, and the like. All drilling and the related operations involve the use of rotating cutting tools. Most of these operations follow the drilling operation i.e., a hole must be made first by a drilling method, and then the hole is modified by one of the other drilling-related operations; however, center drilling and spot facing operations are exceptions to this rule. Figure 6.2 illustrates drilling and some commonly used drilling-related operations, which are explained in the following paragraph.
Material removal
Published in Roger Timings, Fabrication and Welding Engineering, 2008
The purpose of spot-facing is to produce a flat surface as shown in Fig. 6.31(a). This provides a seat for a bolt head or a nut in an otherwise uneven surface. Bolt heads and nuts must always sit on a surface that is smooth and square to the axis of the bolt hole so that the shank of the bolt does not become bent. The spot-facing cutter is similar to a counterbore cutter except that the cutter diameter is much larger relative to the diameter of the pilot that fits in the previously drilled hole. This is because the spot-facing cutter has to provide a seating large enough to clear the corners of the hexagon bolt or nut for which it is providing a seating as shown in Fig. 6.31(b).
Drilling techniques and drilling machines
Published in Roger Timings, Engineering Fundamentals, 2007
As well as drilling holes the following operations can also be performed on a drilling machine: Trepanning.Countersinking.Counterboring.Spot facing.
Experimental investigation on boring of HSLA ASTM A36 steel under dry, wet, and cryogenic environments
Published in Materials and Manufacturing Processes, 2019
C. Chandrasekhara Sastry, P. Hariharan, M. Pradeep Kumar, M. A. Muthu Manickam
Pipes play a major role in transporting liquids and gases in our day-to-day lives. In order to achieve this, drilling operation is carried out to produce holes of required dimensions. Drilling being an intricate process, the hole quality produced is contrived by different conditions such as workpiece material, attribute of the operation, tool material, cutting zone temperature, and cutting force.[1] Secondary operations, viz., reaming, broaching, boring, etc., are carried out to overcome the defects caused in drilling and to obtain close geometric tolerance values of the hole produced. In the reaming process, a reamer is used, which is a multi-tooth cutter which rotates and moves linearly into a drilled hole or an existing hole. Reaming operation provides close tolerances compared to other secondary operations. The main drawback of the reaming process is that it follows the already existing hole produced during the drilling cycle. Thus, reaming will not provide any significant changes if hole misalignments are present. Additionally, any misalignment which is preexisting due to the drilling process will damage the reamer if mounted on a conventional spindle for machining operation due to the high flexibility of the tool.[2] Furthermore, in secondary hole-making operations, the major constraint and limitation are when the hole machined is to be enlarged to a non-standard dimension. This is where boring finds its footing and is applicable in hole making of standard and nonstandard dimensions by choosing an appropriate tool. Ihsan Korkut et al.[3] after repeated experimental analysis in studying the deviation of circularity of bored holes by using Taguchi method determined that in boring operation, the length/diameter value of tool should be less than 3 for optimum results. Sudhanshu Kumar et al.[4] performed a nonconventional boring operation, and it was observed that the radial strategy of electrical discharge machining (EDM) is better suited for a boring operation compared to helical boring operation as the wear ratio is minimum. Operations that are also hole making include counterboring, spot facing, and countersinking. For all these operations, boring is the primary operation to accommodate different types of tools required for further enlarging the hole or for improving its surface characteristics.