Define Milling.Recognize and explain the purpose of four milling machines.Know the purposes of the main parts of the horizontal and vertical milling machines.

Milling is the process of cutting away material by feeding a workpiece past a rotating multiple tooth cutter. The cutting action of the many teeth around the milling cutter provides a fast method of machining. The machined surface may be flat,angular, or curved. The surface may also be milled to any combination of shapes.

The machine for holding the workpiece, rotating the cutter, and feeding it is known as the Milling machine. Milling machines are among the most versatile and useful machine tools due to their capabilities to perform a variety of operations.

Milling Machines are made in a wide variety of types and sizes. They may be classified as:Manufacturing typeSpecial TypeKnee-and-column type

64-*Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

The four most common types of manually controlled milling machines are listed below in order of increasing power (and therefore metal removal capability):1. Ram-type milling machines2. Column-and-knee-type milling machinesa. Horizontal spindleb. Vertical spindle3. Fixed-bed-type milling machines4. Planer-type milling machines

Milling machines whose motions are electronically controlled are listed in order of increasing production capacity and decreasing flexibility:1. Manual data input milling machines2. Programmable CNC (Computer Numerical Controlled) milling machines3. Machining centers (tool changer and pallet exchange capability)4. Flexible Manufacturing Cell and Flexible Manufacturing System5. Transfer lines

Most mills consist of column-and-knee designsThe column is mounted on a base and the Table mounted on a knee extending from the column.The knee has vertical movementThe material in mounted on a table with longitudinal movement, and the table is mounted on a saddle with transverse movementMost common of this type mill is the Ram mill which has a motor and pulley system mounted on the top of the column.

59-*The ram-type knee-and-column milling machine is one of the most versatile and popular milling machine tools ever designed.

Major components of a plain column-and-knee-type milling machine, which can have horizontal spindle shown on the left, or a turret type machine with a vertical spindle, shown on the right. The workpiece and workholder on the table can be translated in X, Y, and Z directions with respect to the tool.

Used for general purpose milling operations, column and knee type milling machines are the most common milling machines. The spindle to which the milling cutter is mounted may be horizontal (slab milling) or vertical (face and end milling).

Work table, on which the workpiece is clamped using the T-slots. The table moves longitudinally with respect to the saddle.Saddle, which supports the table and can move transversely.Knee, which supports the saddle and gives the table vertical movements for adjusting the depth of cut.

Overarmin horizontal machines, which is adjustable to accomadate different arbor lengths.Head, which contains the spindle and cutter holders. In vertical machines the head may be fixed or vertically adjustable.

Made for deep cuts and heavy material removal, the bed only had horizontal movementOnce the bed is set up, the spindle height is not changed during operation.These machines are very common due to their ease of use.

Bed-typevertical-spindle heavy-dutyproduction machine tools formilling usually have three axesof motion.

Planer type mills can have several heads to remove large amounts of material while the material is fed slowly into the machine.Systems are setup typically for single pass operations.These are advantageous for large work pieces requiring heavy material removal.

FIGURE 24-17 Large planertype milling machine. Inset shows 90 head being used.(Courtesy of Cosa Corporation.)

When purchasing or using a milling machine, consider the following issues:1. Spindle orientation and rpm2. Machine capability (accuracy and precision)3. Machine capacity (size of workpieces)4. Horsepower available at spindle (usually 70% of machine horsepower)5. Automatic tool changing

When purchasing or using a milling machine, consider the following issues:The Table Length And Width.Maximum Longitudinal Cross And Vertical Travel Of The Table.Number Of Spindle Speeds And Feeds.Power Of Driving Motor.Floor Space And Net Weight.

Peripheral MillingEnd milling

Peripheral MillingIn peripheral (or slab) milling, the milled surface is generated by teeth located on the periphery of the cutter body. The axis of cutter rotation is generally in a plane parallel to the workpiece surface to be machined.

Face MillingIn face milling, the cutter is mounted on a spindle having an axis of rotation perpendicular to the workpiece surface. The milled surface results from the action of cutting edges located on the periphery and face of the cutter.

End MillingThe cutter in end milling generally rotates on an axis vertical to the workpiece. It can be tilted to machine tapered surfaces. Cutting teeth are located on both the end face of the cutter and the periphery of the cutter body.

There are two methods that may be used in milling operations. These are:

Up milling or Conventional millingDown milling or Climb milling

Up MillingUp milling is also referred to as conventional milling. The direction of the cutter rotation opposes the feed motion. For example, if the cutter rotates clockwise , the workpiece is fed to the right in up milling.

This is the most common method used. The work is fed against the rotational direction of the cutter.

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Can be used on milling machine without backlash eliminator.Good for milling hot rolled steel, surface hardened and steels with a surface scale.Good for milling castings or forgings where there is a hard abrasive surface due to scale and sand.Causes less stress on the machine.

Reduces tool life.The cutter tends to push the work along and lift it upwards from the table. This action tends to loosen the workpiece from the fixture.In up milling, chips can be carried into the newly machined surface, causing the surface finish to be poorer than in down milling.

Down MillingDown milling is also referred to as climb milling. The direction of cutter rotation is same as the feed motion. For example, if the cutter rotates counterclockwise , the workpiece is fed to the right in down milling.

When cutter and workpiece going in same directionThe machine must be equipped with backlash eliminatorCan increase cutter life up to 50% 60-*

Increased tool life (up to 50%)Chips pile up behind or to left of cutterLess costly fixtures requiredForces workpiece down so simpler holding devices requiredImproved surface finishesChips less likely to be carried into workpiece60-*

Less edge breakoutThickness of chip tends to get smaller as nears edge of workpiece, less chance of breakingEasier chip removalChips fall behind cutterLower power requirementsCutter with higher rake angle can be used so approximately 20% less power required60-*

Method cannot be used unless machine has backlash eliminator and table gibs tightenedCannot be used for machining castings or hot-rolled steelHard outer scale will damage cutterThe maximum chip thickness is at the point of tooth contact with the work piece. Dulling the teeth more quickly, especially for workpiece with a hard surface.

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(1) Plain milling cutters,(2) Side milling cutters,(3) Face milling cutter,(4) Angle milling cutters,(5) End milling cutter,(7) T-slot milling cutter,(8) Formed cutters,(9) Metal slitting saw,

Milling cutters are made from the following metalsTool steel, carbon tool steel, and high-speed steel

Milling Cutters must be:Harder than metal being machinedStrong enough to withstand cutting pressuresTough to resist shock resulting from contactResist heat and abrasion of cuttingAvailable in various sizes and shapes*

Iron with additivesCarbon: hardening agentTungsten and Molybdenum: enable steel to retain hardness up to red heatChromium: increases toughness and wear resistanceVanadium: increases tensile strengthUsed for most solid milling cutters*

Higher rates of production (3-10 times faster)Must select proper type of carbideStraight tungsten carbide: cast iron, plasticsTantalum carbide: low/medium-carbon steelTungsten-titanium carbide: high-carbon steel*

Open and closed pocketsFacing operations for small areasCounterboring and spotfacingPeripheral end millingMilling of slots and keywaysChannel groves, face grooves and recessesChamferingPerformed with HSS, cobalt, solid carbide, or indexable insert type end mill

Most widely used Cylinder of high-speed steel with teeth cut on peripheryUsed to produce flat surfaceSeveral typesLight-dutyLight-duty helicalHeavy-dutyHigh-helix

Less than in. wide, straight teethUsed for light milling operationsThose over in have helix angle of 25Too many teeth to permit chip clearance

Have fewer teeth than light-duty typeProvide for better chip clearanceHelix angle varies up to 45Produces smoother surface because of shearing action and reduced chatterLess power required

Have helix angles from 45 to over 60Suited to milling of wide and intermittent surfaces on contour and profile millingUsually mounted on milling machine arborSometimes shank-mounted with pilot on end and used for milling elongated slots

Called arbor-type cuttersUsed for Milling forms from solid metalRemoving inner sections from solidsInserted through previously drilled hole and supported at outer end with type A arbor support

Comparatively narrow cylindrical milling cutters with teeth on each side and on peripheryUsed for cutting slots and for face and straddle milling operationsFree cutting action at high speeds and feedsSuited for milling deep, narrow slotsStraightStaggered

Used when only one side of cutter requiredAlso make with interlocking faces so two cutter may be placed side by side for slot millingHave considerable rakeAble to take heavy cuts

Generally over 6 in. in diameterHave inserted teeth made of high-speed steel held in place by wedging deviceMost cutting action occurs at beveled corners and periphery of cutterMakes roughing and finishing cuts in one pass

Face milling cutters under 6 in.Solid, multiple-tooth cutters with teeth on face and peripheryHeld on stub arborMay be threaded or use key in shank to drive cutter

Single-angleTeeth on angular surfaceMay or may not have teeth on flat45 or 60Double-angleTwo intersecting angular surfaces with cutting teeth on bothEqual angles on both side of line at right angle to axis

Concave Convex Gear Tooth

Used to cut wide horizontal groove at bottom of T-slot After narrow vertical groove machined with end mill or side milling cutterConsists of small side milling cutter with teeth on both sides and integral shank for mounting65-*Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Similar to single-angle milling cutter with integral shankUsed to form sides of dovetail after tongue or groove machinedObtained with 45, 50, 55, or 60 angles65-*Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Similar in design to plain and side milling cuttersSmall (up to 2 in) solid shank, straight teethLarge mounted on arbor with staggered teethUsed for milling semicylindrical keyseats in shaftsDesignated by number system65-*Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

T-slot cutting with a milling cutter.

Cutters for (a) straddle milling, (b) form milling, (c) slotting, and (d) slitting with a milling cutter.

******State which milling machine contain a) Overarm b) Head*************

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