Manufacturing Rounded Shapes II Manufacturing Processes

Outline Specialized Turning Operations Cutting Screw Threads Knurling High-Speed Machining Ultraprecision Machining Hard Turning Cutting Screw Threads Knurling Boring and Boring Machines Drilling and Drills Reaming and Reamers Tapping and Taps Chip Collection

High-Speed Machining Decreases cutting time by increasing cutting speed Approximate Range of Cutting Speeds: High Speed: 2000-6000 ft/min Very High Speed: 6000-60000 ft/min Ultrahigh Speed: >60000 ft/min Decreases total energy required: - Power for high-speed machining ≈ .004 W/rpm Power for normal machining ≈ .2-.4 W/rpm Most important when cutting time is a significant part of the manufacturing time

High-Speed Machining Factors: Stiffness of the machine tools Stiffness of tool holders and workpiece holders Proper spindle for high speeds and power Sufficiently fast feed drives Automation A proper cutting tool for high cutting speeds Ability to hold the piece in fixtures at high speed

Ultraprecision Machining Used for very small surface finish tolerances in the range of .01 µm The depth of cut is in the range of nanometers Machine tools must be made with high stiffness

Ultraprecision Machining Factors: Stiffness, damping, and geometric accuracy of machine tools Accurate linear and rotational motion control Proper spindle technology Thermal expansion of machine tools, compensation thereof, and control of the machine tool environment Correct selection and application of cutting tools Machining parameters Performance and tool-condition monitoring in real time, and control thereof

Hard Turning Used for relatively hard, brittle materials Produces parts with good dimensional accuracy, smooth surface finish, and surface integrity May be used as an alternative to grinding

Hard Turning Procedure

Hard Turning Statistics Heat dissipated by chips Tool forces: radial force is greatest

Hard Turning Chip Formation Brittle materials form segmented chips, which cause a large force against the cutting edge

Hard Turning Advantages (as an alternative to grinding) Lower cost of machine tools Ability to machine complex parts in a single setup Ability to create various part styles or small part numbers efficiently Less industrial waste Ability to cut without fluids (eliminates grinding sludge) Easily automated

Hard Turning Surface Finish NO YES A hard journal bearing surface should have a surface with deep valleys and low peaks

Cutting Screw Threads Cutting threads on a lathe is slower than newer methods Die-Head Chasers used to increase production rate of threading on a lathe Solid Threading Dies used for cutting straight or tapered threads on the ends of pipes or tubing

Cutting Screw Threads

Cutting Screw Threads

Die-Head Chasers and Solid Threading Dies Straight chaser cutting die (top) Circular chaser cutting die (bottom left) Solid threading die (bottom right)

Screw Machine

Screw Machine

Cutting Screw Threads Design Considerations: Threads should not be required to reach a shoulder Avoid shallow blind tapped holes Chamfer the ends of threaded sections to reduce burrs Do not interrupt threaded sections with slots, holes etc. Use standard thread tools and inserts as much as possible The walls of the part should be thick enough to withstand clamping and cutting forces Design the part so that cutting operations can be completed in a single setup

Knurling Used to create a uniform roughness pattern on cylindrical surfaces Performed on parts where friction is desired (knobs, grip bars etc.) Types: Angular Knurls create a pattern of diamond-shaped ridges Straight Knurls create a pattern of straight longitudinal ridges

Knurling Results

Knurling Operation

Boring and Boring Machines Boring produces circular internal profiles Small pieces can be bored on a lathe; boring mills are used for larger workpieces

Boring Operation

Boring Operation

Boring and Boring Machines Design Considerations: Avoid blind holes when possible A higher ratio of the length to the bore diameter will cause more variations in dimensions because the boring bar will deflect more Avoid interrupted internal surfaces

Drilling and Drills Types of drill Twist drill (most common) Gun drill Trepanner Pilot Holes Sometimes, when drilling large-diameter holes, it is necessary to drill a smaller hole first to guide the large drill

Types of Drills and Drilling Operations

Drill Terminology

stainless steel, titanium Drill Point Angle Point Angle 118° Standard 135° Harder Materials stainless steel, titanium Minimizes burring 90° Softer Materials plastic

Trepanners

Drills and Drilling Deep Holes Complications may occur when drilling a hole longer than 3 times the drill diameter Problems Chip removal Coolant dispensing to the cutting edge Tool deflection

Drills and Drilling Small Holes Small drills .0059-.04 in Microdrilling .0001-.02 in

Microdrills

Pilot Holes

Drills and Drilling Forces and Torque Thrust force: acts perpendicular to the axis of the hole; large forces can cause the drill to bend or break Torque: the torque acting to turn the drill These values are difficult to calculate

Drill Feed and Speed V = πDN/12 V = cutting speed in ft/min; Velocity at which the drill edge moves along the workpiece surface D = diameter of the drill N = RPM of the drill Feeds for drills are listed as in/rev or m/rev. Multiply these by the RPM to obtain the feed in in/min or m/min. The feed cannot be controlled accurately on a drill press fed by hand.

Drill Feed and Speed

Drill Feed and Speed Example: Work Material: Aluminum Tool Material: High Speed Steel Drill Diameter: .5 in Recommended Cutting Speed: 200-300 ft/min (from table) N = 12V/πD N=12*(200-300)/(π*.5) =1528-2293 RPM Recommended Feed for aluminum, .5in = .006-.01 in/rev (from table) f = (.006-.01)*1528 RPM = 9.2-15.2 in/min

Drilling Material Removal Rate MRR = (πD2/4)f N D = drill diameter f = feed, in/rev or mm/rev N = RPM

Drilling Material Removal Rate Example: Drill Diameter: .5 in Feed: .006 in/rev RPM: 1528 RPM MRR = (πD2/4)f N = (π(.5)2/4).006*1528 = 1.8 in3/min

Drilling Operation

Reaming and Reamers Used to improve the dimensional accuracy or surface finish of an existing hole Types of reamers Hand reamers Rose reamers Fluted reamers Shell reamers Expansion reamers Adjustable reamers

Types of Reamers

Reamer Terminology

Tapping and Taps Used to make internal threads in workpiece holes Types of taps Tapered taps Bottoming taps Collapsible taps

Tap Terminology

Drilling, Reaming and Tapping Design Considerations: Holes should be drilled on flat surfaces perpendicular to the hole axis to prevent drill deflection Avoid interrupted hole surfaces The bottoms of blind holes should match standard drill point angles Avoid blind holes when possible; if large diameter holes are to be included, make a pre-existing hole in fabrication Design the workpiece so as to minimize fixturing and repositioning during drilling Provide extra hole depth for reaming or tapping blind or intersecting holes

Summary Specialized cutting procedures exist for unusual materials and requirements Proper procedure, securing of the workpiece, and feeds and speeds must be considered to prevent damage and injuries

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