Manufacturing Technology IME 307Chapter-22

MACHINING OPERATIONS AND MACHINE TOOLSTurning and Related OperationsDrilling and Related OperationsMillingMachining Centers and Turning CentersOther Machining OperationsHigh Speed Machining

References:Fundamentals of Modern Manufacturing: materials, processes, and systems, 4th Ed., by Mikell P. Groover, JOHN WILEY & SONS, INC., 2010. (Chapter 22, pages 519-523)

After Manufacturing Technology. Metal Cutting & Machine Tools. By P N RAO. 2002 by McGRAW-HILL.

Creates a round hole in a workpart Compare to boring which can only enlarge an existing holeCutting tool called a drill or drill bit ( cylindrical tool that has two cutting edges)Machine tool: drill pressFigure 21.3 (b) drillingDrilling

CUTTING CONDITIONS IN DRILLINGCutting SpeedThe cutting speed in a drilling operation is the surface speed at the outside diameter of the drill. (specified in this way for convenience)

FeedRecommended feeds are roughly proportional to drill diameter; higher feeds for larger diameter drills.Since 2 cutting edges -- the uncut chip thickness (chip load) taken by each cutting edge is half the feed.Feed f in drilling is specified in mm/rev (in/rev). It can be converted to feed rate using the same equation as for turning:fr = Nf(mm/min)

Throughholes - drill exits opposite side of workBlindholes does not exit work opposite sideFigure 22.13 Two hole types: (a) throughhole, and (b) blind hole.Through Holes vs. Blind Holes

Machining Time

CUTTING CONDITIONS IN DRILLINGApproach Allowance (A mm)represent the distance the drill must feed into the work before reaching full diameter,accounts for the drill point angle,

Rate of Metal Removal The product of the drill cross-sectional area and the feed rate:

Chisel-Point Drill and Crankshaft DrillFigure 23.19 Two common types of drills: (a) Chisel-point drill. The function of the pair of margins is to provide a bearing surface for the drill against walls of the hole as it penetrates into the workpiece. Drills with four margins (double-margin) are available for improved drill guidance and accuracy. Drills with chip-breaker features also are available. (b) Crankshaft drills. These drills have good centering ability, and because chips tend to break up easily, these drills are suitable for producing deep holes.

After Materials and Processes in Manufacturing. 8th ed. By E. Paul DeGarmo, J.T. Black, Ronald A. Kohser. 1997 by Prentice-Hall.

Point angles for various work materials

Work materialPoint angle, degreesMild steel and other general materialsDeep hole drillingHard materialsSoft non-ferrous materialsHardened steelWood and non-metals118

1281369012560

Cutting Process Parameters for Drilling

Work materialHardness BHNHSSSpeed, m/minFeed, mm/revCast IronCast SteelAISI 1020AISI 1040Manganese SteelNickel SteelStainless SteelSpring SteelTool SteelTool SteelTool SteelTool SteelTool SteelMalleable IronAluminumAluminum alloysCopperBrassBronzeZinc alloysGlass200280-300110-160170-200185-215200-240150400150200215300400110-13095170-19080-85190-200180-200110-12525-3512-1535255181562318151252627518217054704.50.13-0.300.06-0.190.20-0.500.13-0.300.06-0.190.06-0.190.13-0.300.06-0.190.20-0.500.13-0.300.13-0.300.06-0.190.06-0.190.20-0.500.13-0.900.13-0.300.06-0.190.20-0.500.20-0.500.20-0.500.06-0.19

Machining operations related to drillingFIGURE 22.14(a) reaming, (b) tapping,(c) counterboring,(d) countersinking,(e) center drilling,(f) spot facing.

MACHINING OPERATIONS RELATED TO DRILLINGReamingused to slightly enlarge a hole, to provide a better tolerance on its diameter, and to improve its surface finish.the tool is called a reamerUsually has straight flutes

Helical Reamer and Inserted-Blade Adjustable ReamerFigure 23.26 (a) Terminology for a helical reamer. (b) Inserted-blade adjustable reamer.

MACHINING OPERATIONS RELATED TO DRILLINGTappingoperation performed by a tap used to provide internal screw threads on an existing hole.

TappingFigure 23.27 (a) Terminology for a tap. (b) Tapping of steel nuts in production.

MACHINING OPERATIONS RELATED TO DRILLINGCounterboringprovides a stepped hole, a larger diameter follows a smaller diameter partially into the hole. used to seat bolt heads into a hole so the heads do not protrude above the surface.

MACHINING OPERATIONS RELATED TO DRILLINGCountersinkingsimilar to counterboring, except that the step in the hole is cone-shaped for flat head screws and bolts.

MACHINING OPERATIONS RELATED TO DRILLINGCenteringAlso called center drilling, drills a starting hole to accurately establish its location for subsequent drilling. The tool is called a center drill.

MACHINING OPERATIONS RELATED TO DRILLINGSpot Facingsimilar to millingused to provide a flat machined surface on the workpart in a localized area.

Fig 8.49 Various types of drills and drilling operationsAfter Manufacturing Processes for Engineering Materials, Fourth ed., by Serope Kalpakjian, Steven R. Schmid. 2003 by Prentice Hall.

Comparative characteristics of hole making operations

Hole ParameterDrillingReamingBoringCounter boringSmallest size, mm1.61.69.56Largest size, mm5010025075Negative tol., mm0.896 D-0.50.0100.0080.512 D-0.5 + 0.064Positive tol., mm0.896 D-0.5 + 0.0750.0100.0080.640 D-0.5 + 0.075Straightness, mm0.013 (l/D)3 + 0.0502.50.0130.250Roundness, mm0.1000.0130.075Parallelism, mm0.025 (l/D)3 + 0.0750.250.0250.250Depth limit, mm300400225500True position, mm0.2000.250.0030.003Surface finish, mm2.540.410.201.25

After Materials and Processes in Manufacturing. 8th ed. By E. Paul DeGarmo, J.T. Black, Ronald A. Kohser. 1997 by Prentice-Hall.

Types of DrillsFigure 23.21 Various types of drills.

Gun DrillFigure 23.22 (a) A gun drill showing various features. (b) Schematic illustration of the gun-drilling operation.

TrepanningFigure 23.23 (a) Trepanning tool. (b) Trepanning with a drill-mounted single cutter.

Upright drill press stands on the floor

Bench drill similar but smaller and mounted on a table or benchFigure 22.15 Upright drill pressDrill Press

Large drill press designed for large partsFigure 22.16 Radial drill press (photo courtesy of Willis Machinery and Tools).Radial Drill

Vertical Drill Press and Radial Drilling MachineFigure 23.24 (a) Schematic illustration of the components of a vertical drill press. (b) A radial drilling machine. Source: (b) Courtesy of Willis Machinery and Tools.

After Materials and Processes in Manufacturing. 8th ed. By E. Paul DeGarmo, J.T. Black, Ronald A. Kohser. 1997 by Prentice-Hall.

Three-Axis Computer Numerical-Control Drilling MachineFigure 23.25 A three-axis computer numerical-control drilling machine. The turret holds as many as eight different tools, such as drills, taps, and reamers.

Work Holding for Drill Presses Workpart in drilling can be clamped in any of the following:Vise - general purpose workholder with two jawsFixture - workholding device that is usually customdesigned for the particular workpart Drill jig similar to fixture but also provides a means of guiding the tool during drilling