Manufacturing Engineering Technology in SI Units, 6th Edition Chapter 24: Machining Processes: Milling, Broaching, Sawing, Filing and Gear Manufacturing Presentation slide for courses, classes, lectures et al. Copyright © 2010 Pearson Education South Asia Pte Ltd

Chapter Outline Introduction Milling and Milling Machines Planing and Shaping Broaching and Broaching Machines Sawing Filing Gear Manufacturing by Machining Copyright © 2010 Pearson Education South Asia Pte Ltd

Introduction Machining operations can produce many other parts with more complex shapes Complex shapes need to be produced to very close tolerances and a fine surface finish Die casting and precision forging can achieve such goals to some degree Copyright © 2010 Pearson Education South Asia Pte Ltd

Milling and Milling Machines Milling is machining operation for a variety of configurations with the use of a milling cutter Copyright © 2010 Pearson Education South Asia Pte Ltd

Milling and Milling Machines: Peripheral Milling The axis of cutter rotation is parallel to the workpiece surface The cutter body has a number of teeth along its circumference When the cutter is longer than the width of the cut, the process is called slab milling Conventional Milling and Climb Milling The cutter rotation can be clockwise or counter-clockwise Copyright © 2010 Pearson Education South Asia Pte Ltd

Milling and Milling Machines: Peripheral Milling Conventional Milling and Climb Milling In conventional milling (also called up milling), the maximum chip thickness is at the end of the cut Advantages are: Tooth engagement is not a function of workpiece’s surface characteristics Contamination or scale (oxide layer) on the surface does not adversely affect tool life In climb milling (also called down milling), cutting starts at the surface of the workpiece where the chip is thickest Copyright © 2010 Pearson Education South Asia Pte Ltd

Milling and Milling Machines: Peripheral Milling Milling Parameters The cutting speed in peripheral milling is the surface speed of the cutter is Copyright © 2010 Pearson Education South Asia Pte Ltd

Milling and Milling Machines: Peripheral Milling Milling Parameters The approximate undeformed chip thickness (chip depth of cut) is Feed per tooth is determined from The cutting time, t, is given by The material-removal rate (MRR) is Copyright © 2010 Pearson Education South Asia Pte Ltd

Milling and Milling Machines: Peripheral Milling Milling Parameters Copyright © 2010 Pearson Education South Asia Pte Ltd

Milling and Milling Machines: Peripheral Milling EXAMPLE 24.1 Material-removal Rate, Power, Torque, and Cutting Time in Slab Milling A slab-milling operation is being carried out on a 300-mm- long, 100-mm-wide annealed mild-steel block at a feed f 0.25 mm/tooth and a depth of cut d 3.0 mm. The cutter is D=50 mm in diameter, has 20 straight teeth, rotates at 100rpm and, by definition, is wider than the block to be machined. Calculate the material-removal rate, estimate the power and torque required for this operation, and calculate the cutting time. Copyright © 2010 Pearson Education South Asia Pte Ltd

Milling and Milling Machines: Peripheral Milling Solution Material-removal Rate, Power, Torque, and Cutting Time in Slab Milling The linear speed of the workpiece is The material-removal rate is The power required is Copyright © 2010 Pearson Education South Asia Pte Ltd

Milling and Milling Machines: Peripheral Milling Solution Material-removal Rate, Power, Torque, and Cutting Time in Slab Milling The torque acting on the cutter spindle is The cutting time is Copyright © 2010 Pearson Education South Asia Pte Ltd

Milling and Milling Machines: Face Milling In face milling, the cutter is mounted on a spindle having an axis of rotation perpendicular to the workpiece surface As the relative motion between the cutter teeth and the workpiece, face milling leaves feed marks on the machined surface Copyright © 2010 Pearson Education South Asia Pte Ltd

Milling and Milling Machines: Face Milling Lead angle of the insert in face milling has a direct influence on the undeformed chip thickness As lead angle increases, the undeformed chip thickness decreases and the length of contact increases Cutter diameter and their position relative to the milled surface will determine the angle at which an insert enters and exits the workpiece Copyright © 2010 Pearson Education South Asia Pte Ltd

Milling and Milling Machines: Face Milling The same insert may engage the workpiece at different angles, depending on the relative positions of the cutter and the workpiece width The first contacts are at an angle and away from the tip of the insert Copyright © 2010 Pearson Education South Asia Pte Ltd

Milling and Milling Machines: Face Milling EXAMPLE 24.2 Material-removal Rate, Power Required, and Cutting Time in Face Milling Assume that D = 150 mm, w = 60 mm, l = 500 mm, d = 3 mm, v = 0.6 m /min and N = 100 rpm.The cutter has 10 inserts, and the workpiece material is a high-strength aluminum alloy. Calculate the material-removal rate, cutting time, and feed per tooth, and estimate the power required. Copyright © 2010 Pearson Education South Asia Pte Ltd

Milling and Milling Machines: Face Milling Solution Material-removal Rate, Power Required, and Cutting Time in Face Milling The material-removal rate is The cutting time is The feed per tooth is The power is Copyright © 2010 Pearson Education South Asia Pte Ltd

Milling and Milling Machines: End Milling End milling is versatile and capability to produce various profiles and curved surfaces An end mill has a straight shank or tapered shank which is mounted into the spindle of the milling machine End milling can produce a variety of surfaces at any depth, such as curved, stepped, and pocketed Copyright © 2010 Pearson Education South Asia Pte Ltd

Milling and Milling Machines: End Milling High-speed End Milling High-speed end milling has applications as the milling of large aluminum-alloy aerospace components and honeycomb structures with high spindle speeds Machines must have high stiffness and accuracy The production of cavities in metalworking dies (die sinking) can be done The machines have four-axis or five-axis movements Copyright © 2010 Pearson Education South Asia Pte Ltd

Milling and Milling Machines: Other Milling Operations and Milling Cutters In straddle milling, two or more cutters are mounted on an arbor and are used to machine two parallel surfaces on the workpiece Form milling produces curved profiles using cutters that have specially shaped teeth Slotting and slitting operations are performed with circular cutters Copyright © 2010 Pearson Education South Asia Pte Ltd

Milling and Milling Machines: Other Milling Operations and Milling Cutters Slitting saws are thin and T-slot cutters are used to mill T-slots A slot is first milled with an end mill and the cutter machines will then complete profile of the T-slot in one pass Shell mills are hollow inside and are mounted on a shank which allows the same shank to be used for different-sized cutters Copyright © 2010 Pearson Education South Asia Pte Ltd

Milling and Milling Machines: Toolholders Arbor cutters are mounted on an arbor for peripheral, face, straddle and form milling In shank-type cutters, the cutter and the shank are made in one piece Hydraulic toolholders and arbors are available Stiffness of cutters and toolholders is important for surface quality and in reducing vibration and chatter during milling operations Copyright © 2010 Pearson Education South Asia Pte Ltd

Milling and Milling Machines: Milling Process Capabilities Milling process capabilities include surface finish, dimensional tolerances, production rate, and cost considerations Copyright © 2010 Pearson Education South Asia Pte Ltd

Milling and Milling Machines: Milling Process Capabilities Copyright © 2010 Pearson Education South Asia Pte Ltd

Milling and Milling Machines: Design and Operating Guidelines for Milling Additional factors relevant to milling operations include: Standard milling cutters should be used as much as possible Chamfers should be specified Internal cavities and pockets with sharp corners should be avoided Proper clearance should be provided in the design for milling cutters Workpieces should be rigid to minimize deflections Copyright © 2010 Pearson Education South Asia Pte Ltd

Milling and Milling Machines: Design and Operating Guidelines for Milling Guidelines for avoiding vibration and chatter in milling: Cutters should be mounted as close to the spindle base Toolholders and fixturing devices should be rigid Tool shape and process conditions should be modified and cutters with fewer cutting teeth Copyright © 2010 Pearson Education South Asia Pte Ltd

Milling and Milling Machines: Milling Machines Milling machines are among the most versatile and useful machine tools Standard milling machines are now being replaced with computer controls and machining centers Column-and-knee-type Machines Column-and-knee-type machines are common milling machines Copyright © 2010 Pearson Education South Asia Pte Ltd

Milling and Milling Machines: Milling Machines Bed-type Milling Machines The worktable replaces the knee and can move only longitudinally Other Types of Milling Machines Planer-type milling machines are equipped with several heads and cutters to mill different surfaces Computer numerical-control (CNC) machines are for low production quantities Copyright © 2010 Pearson Education South Asia Pte Ltd

Planing and Shaping Planing A simple machining operation where flat surfaces are produced along the length of the workpiece Usually done on large workpieces Due to reciprocating motion of the workpiece, the non-cutting time elapsed is significant Chips produced can be long which interfere the planing operation and becoming a safety hazard Copyright © 2010 Pearson Education South Asia Pte Ltd

Planing and Shaping Shaping Same as planing except that it is the tool, and not the workpiece workpieces are smaller In a horizontal shaper, the cutting tool travels back and forth along a straight path Vertical shapers (slotters) are used to machine notches, keyways, and dies Copyright © 2010 Pearson Education South Asia Pte Ltd

Broaching and Broaching Machines Similar to shaping with a long multiple-tooth cutter and is used to machine internal and external surfaces In a broach the total depth of material removed in one stroke is the sum of the depths of cut of each tooth of the broach Copyright © 2010 Pearson Education South Asia Pte Ltd

Broaching and Broaching Machines Broaches The rake (hook) angle depends on the material cut Too small a clearance angle causes rubbing of the teeth against the broached surface The pitch of the teeth depends on factors such as the length of the workpiece (length of cut), tooth strength, and size and shape of chips Copyright © 2010 Pearson Education South Asia Pte Ltd

Broaching and Broaching Machines Broaches The pitch for a broach to cut a surface of length is Broaches are available with various tooth profiles, including some with chip breakers Copyright © 2010 Pearson Education South Asia Pte Ltd

Broaching and Broaching Machines Turn Broaching Used for broaching the bearing surfaces of crankshafts and similar parts Turn broaching is a combination of shaving and skiving Broaching Machines Simple in construction, have only linear motions, and actuated hydraulically, crank, screw or rack The force required to pull or push the broach depends on strength of the workpiece material, total depth and width of cut, cutting speed, tooth profile, and cutting fluids Copyright © 2010 Pearson Education South Asia Pte Ltd

Broaching and Broaching Machines Process Parameters Majority of broaches are coated with titanium nitride for improved tool life and surface finish Ceramic inserts are used for finishing operations in some applications Smaller, high-speed steel blanks for broaches can be made with powder-metallurgy techniques for better control of quality Copyright © 2010 Pearson Education South Asia Pte Ltd

Broaching and Broaching Machines Design Considerations Broaching requires certain guidelines: Parts should be designed so that they can be clamped securely Use of standardized parts is important for broaches Balanced cross sections are preferable Chamfers are preferred Inverted or dovetail splines should be avoided Broaching blind holes should be avoided Copyright © 2010 Pearson Education South Asia Pte Ltd

Broaching and Broaching Machines EXAMPLE 24.3 Broaching Internal Splines Example of a part with internal splines that were produced by broaching Copyright © 2010 Pearson Education South Asia Pte Ltd

Sawing Cutting tool is a blade (saw) having a series of small teeth, each tooth removing a small amount of material with each stroke or movement of the saw Can be used for all metallic and nonmetallic materials and is capable of producing various shapes Copyright © 2010 Pearson Education South Asia Pte Ltd

Sawing A wide variety of sizes, tooth forms, tooth spacing, and blade thicknesses and widths are available Saw blades are made from high-carbon and high- speed steels Carbide or high-speed steel-tipped steel blades are used to saw harder materials Copyright © 2010 Pearson Education South Asia Pte Ltd

Sawing Types of Saws Hacksaws have straight blades and reciprocating motions Hand hacksaw blades are thinner and shorter than power hacksaw blades Circular saws are used for high-production-rate sawing, a process called cutting off Band saws have continuous, long, flexible blades and have a continuous cutting action Vertical band saws are used for straight and contour cutting of flat sheets Copyright © 2010 Pearson Education South Asia Pte Ltd

Sawing Friction Sawing Friction sawing is a process in which a mild-steel blade or disk rubs against the workpiece Frictional energy is converted into heat, which rapidly softens a narrow zone in the workpiece Heat generated in the workpiece produces a heat- affected zone on the cut surfaces Friction sawing process is suitable for hard, ferrous metals and reinforced plastics but not for nonferrous metals Copyright © 2010 Pearson Education South Asia Pte Ltd

Filing Filing involves the small-scale removal of material from a surface, corner, edge, hole or burrs Files can have many tooth forms and grades of coarseness Filing machines with automatic features are available for high production rates Band files consist of file segments that are riveted to a flexible steel band Rotary files and burs are used for deburring and removing scale from surfaces Copyright © 2010 Pearson Education South Asia Pte Ltd

Gear Manufacturing by Machining Casting, forging, extrusion, drawing, thread rolling, and powder metallurgy can be used to manufacture gears The dimensional accuracy and surface finish required for gear teeth depend on the intended use Poor gear-tooth quality contributes to inefficient energy transmission, vibration and noise Copyright © 2010 Pearson Education South Asia Pte Ltd

Gear Manufacturing by Machining: Form Cutting Cutting tool is similar to a form-milling cutter made in the shape of the space between the gear teeth Each cutter is designed to cut a range of numbers of teeth Precision of the form-cut tooth profile depends on the accuracy of the cutter and on the machine and its stiffness It is a slow operation Broaching can be used to machine gear teeth and is particularly suitable for producing internal teeth Copyright © 2010 Pearson Education South Asia Pte Ltd

Gear Manufacturing by Machining: Gear Generating Cutting tool used may be a: Pinion-shaped cutter Rack shaper Hob Copyright © 2010 Pearson Education South Asia Pte Ltd

Gear Manufacturing by Machining: Cutting Bevel Gears Straight bevel gears are roughed out in one cut with a form cutter on machines that index automatically The cutters will reciprocate across the face of the bevel gear as does the tool on a shaper Spiral cutter is a face-milling cutter with a number of straight-sided cutting blades protruding from its periphery Copyright © 2010 Pearson Education South Asia Pte Ltd

Gear Manufacturing by Machining: Cutting Bevel Gears Burnishing Surface finish of gear teeth is improved by burnishing The resulting cold working of the tooth surfaces improves the surface finish, induces compressive residual stresses and fatigue life Grinding, Honing, and Lapping For the highest dimensional accuracy, tooth spacing and form, and surface finish, gear teeth subsequently may be ground, honed, and lapped Copyright © 2010 Pearson Education South Asia Pte Ltd

Gear Manufacturing by Machining: Cutting Bevel Gears Grinding, Honing, and Lapping In form grinding, the shape of the grinding wheel is identical to that of the tooth spacing In generating, the grinding wheel acts in a manner similar to the gear generating cutter The honing tool is a plastic gear impregnated with fine abrasive particles Copyright © 2010 Pearson Education South Asia Pte Ltd

Gear Manufacturing by Machining: Cutting Bevel Gears Grinding, Honing, and Lapping Copyright © 2010 Pearson Education South Asia Pte Ltd

Design considerations for gear-cutting: Gear Manufacturing by Machining: Design Considerations and Economics of Gear Machining Design considerations for gear-cutting: Wide gears are more difficult to machine than narrow ones Gears should be machined prior to their assembly on shafts Sufficient clearance should be provided between gear teeth and flanges Blank design is important for proper fixturing and to ease cutting operations Spur gears are easier to machine than helical gears Dimensional tolerances and standardized gear shapes are specified by industry standards Copyright © 2010 Pearson Education South Asia Pte Ltd

The cost of gears increases with improved surface finish and quality Gear Manufacturing by Machining: Design Considerations and Economics of Gear Machining Economics The cost of gears increases with improved surface finish and quality The higher the number, the higher is the dimensional accuracy of the gear teeth Copyright © 2010 Pearson Education South Asia Pte Ltd

CASE STUDY 24.1 Ping Golf Putters Gear Manufacturing by Machining: Design Considerations and Economics of Gear Machining CASE STUDY 24.1 Ping Golf Putters Advanced machining practices is used in the design and production processes for a new style of putter, the Anser® series Copyright © 2010 Pearson Education South Asia Pte Ltd