Conventional Milling Machine

Gegas

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Conventional Milling Machine

Mohd Zaid Akop17 February 2008

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CONTENTS Introduction Machine Component Milling Cutters Milling Operation Milling ParameterFAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA

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1. INTRODUCTIONIntroduction to Milling Process

Milling is the method of machining by cutting in which the tool carries out a rotary motion while the work piece is fixed on a movable table. Milling is a machining process used to produced various shape of products / parts except round.Milling machines are used to:Machine plain and rough surfaceMake a tapping and gearingDrillingBoringSlottingDivided into two (2) types Vertical milling machineHorizontal milling machineFAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA

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1. INTRODUCTION-(contd)Vertical Milling MachineFAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA

Vertical milling machines are the most commonly used machine in tool and die maintenance and job shop Some machines have milling head that can be tilted Can produce horizontal surface, Vertical surfaces, angular surface, Shoulders, grooves, fillet, keyways, T slot and dovetails5

1. INTRODUCTION-(contd)FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA

Horizontal Milling Machine6

2. MACHINE COMPONENT Vertical Milling Machine(R.R.Kibbe, 2006)FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA

Vertical Milling Machine

The major assemblies of a vertical milling machines are:Base and ColumnKneeSaddleTableRamToolhead7

2. MACHINE COMPONENT-(cd) FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA

Vertical Milling Machine: Components and FunctionsBase & column are one piece, and are the major structural components.Knee supports the saddle and table. It can moves up and down.Vertical traverse crank controls the knee up and down movement.Saddle supports the table. It can moves in and out.Cross traverse handle controls the saddle in and out movement.Workpiece or work-holding device is secured to the table. It can moves right and left. Table traverse handle controls the table right and left movement.Ram engages the swiveling slide on top of the column. It moves in and out by turning the ram positioning pinion gear.Toolhead is attached to the end of ram and contains motor, which powers the spindle.Quill is nonrotating and contains rotating spindle. It can be extended or retracted into the tool head by adjusting the quill feed hand lever or handwheel.8

2. MACHINE COMPONENT-(cd) Horizontal Milling Machine(R.R.Kibbe, 2006)FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA

Horizontal Milling Machine

The major assemblies of a horizontal milling machines are:Base and ColumnKneeSaddleTableSpindleOverarm and Arbor Support

Similar toVerticalMillingMachine9

2. MACHINE COMPONENT-(cd) FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA

Horizontal Milling Machine:Spindle is located at in the upper part of the column. It is used to hold, align, and drive the various cutters, chucks, and arbors.Overarm engages the slide on the top of the column and can be moved in and out by loosening the overarm clamps. Arbor support contains a bearing that is exactly in line with the spindle.10

3. MILLING CUTTERS Milling Cutters

Characteristic of milling cuttersMust be tougher than workpiece that is going to be machined.Able to withstand high pressure during cutting.Able to withstand high temperature.Must have high wear resistance.Most of the milling cutters are made of high speed steel or tungsten carbide.It is consist of ferrum, carbon, molebdenum, vanadium and cromium. carbon harder agenttungsten & molebdenum to maintain the hardness at high temperaturevanadium to increase the toughnesscromium to increase the hardness and resistant to worn outTungsten carbide used for harder workpiece. Long last but higher costFAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA

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3. MILLING CUTTERS-(contd)Cutters for Vertical Milling Machine

i) Face Milling CutterUsed to machine the surface of workpiece.Consist of several insert teeth attached to cutter wheel.Insert teeth are using high speed steel or tungsten carbide.FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA

Face Milling Cutter12

3. MILLING CUTTERS-(contd)ii) End Mills CutterUsed to machine slot and certain shape. Consist of cutting teeth from end to the top.FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA

End Milling Cutter

iii) Ball Nose CutterUsed to machine slot and concave shape.Same as end mill cutter except round shape at their end.

Ball Nose Cutter13

3. MILLING CUTTERS-(contd)iv) T-slot cutter Used to machine T-slot after using end mill cutter.FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA

v) Keyseat cutter Used to machine slot to match with standard woodrooff keys at shaft.

T-slot CutterKeyseat Cutter14

3. MILLING CUTTERS-(contd)FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA

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3. MILLING CUTTERS-(contd)Cutters for horizontal milling machine

i) Plain milling cuttersCylinder shape with cutting teeth at the outside.Cutting teeth < 19mm width, straight shape & suitable for machining slot and plain surface.Cutting teeth > 19mm width, spiral shape & suitable for machining rough surface.FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA

Plain Milling Cutter

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3. MILLING CUTTERS-(contd)ii) Angular cuttersTheir teeth is not parallel or not 90 degree with cutting axis.Used for grinding surface or machining with angle.FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA

Angular Cutter

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3. MILLING CUTTERS-(contd)iii) Form cuttersUsed to machine certain shape, same as the cutter shape.Eg: convex and concave surfaceFAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA

Form Cutter

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3. MILLING CUTTERS-(contd)iv) Metal slitting sawUsed to machine deep slot or cutting length of the workpiece.Size of the cutter is smaller at center than outside to make a clearance between cutter and workpiece. FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA

Metal Slitting Cutter

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4. MILLING OPERATIONCutting Direction

Based on the direction of movement of the milling cutter and the feeding direction of workpiece.There are two types (horizontal milling machine)Up millingDown milling

i) Up millingCutting tool rotates in the opposite direction to the table movement.The chip start at zero thickness and gradually increases to the maximum.Also known as conventional millingFAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA

Up Milling

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4. MILLING OPERATION-(contd)Advantages: No backlash-(normal wear between table screw and the nut in which it turn)Suitable for casting or hot rolled steel.Lower milling force

Disadvantages: Length of chips is longer than down milling, more engagement of tool and w/p, reduce tool life.Force tends to lift the workpiece from the table, needs good fixturing.Lower cutter life.Rough Surface / machine mark creating rubbing and burnishing effect with excessive friction, high temperature.FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA

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4. MILLING OPERATION-(contd)ii) Down milling Cutting tool rotates in the same direction to the table movement. The chip start at maximum thickness and gradually decreases to the zero thickness Most preferred technique. Also known as climb milling or in cut milling

FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA

Down Milling

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4. MILLING OPERATION-(contd)Advantages:Eliminating the feed marks and obtain better surface finish.Suitable to machine thin and hard to hold parts since the workpiece is forced against the table.Consistent parrallelism and size can be maintained particularly on thin parts.It can be used where breakouts at the edge of workpiece cannot be tolerated.Length of chip is less than up milling-less engagement of tool and w/p (less force to unit volume of material removed). Up to 20% less power.Longer cutter life.

Disadvantages:Possibility that backlash present in the table.Cannot be used unless the machine has backlash eliminator and the table jigs have been tightened.Cannot be used for machining casting or hot rolled steel, since the harder outer scale will damage the cutterFAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA

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4. MILLING OPERATION-(contd)Typical Milling OperationsThere are several types of milling operation depends on types of milling machine and cutting tools provided.

Plain MillingPlain milling is the milling of a flat surface with the axis of the cutter parallel to the machining surface. It can be carried out either on a horizontal machine or a vertical machine as shown below.FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA

Plain Milling26

4. MILLING OPERATION-(contd)End MillingEnd Milling is the milling of a flat surface with the axis of the cutter perpendicular to the machining surface as shown below.End milling is used to produce features like steps, squaring, milling a cavity or pocketing, and slot cutting.Clip mill_slotFAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA

End Milling

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4. MILLING OPERATION-(contd)Gang MillingGang milling is a horizontal milling operation that utilises three or more milling cutters grouped together for the milling of a complex surface in one pass. As illustrated in below figure, different type and size of cutters should be selected for achieving the desire profile on the workpiece.FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA

Gang Milling

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4. MILLING OPERATION-(contd)Straddle MillingIn straddle milling, a group of spacers is mounted in between two side and face milling cutters on the spindle arbor as shown below. Used for the milling of two surfaces parallel to each other at a given distance.

Work HoldingA variety of work holding devices can be used for holding the workpiece depending upon the types of workpice and types of milling to be done.For example: vice, universal chuck, fixture and clamp.FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA

Straddle Milling29

4. MILLING OPERATION-(contd)i) Vice The most common device. Used for holding small and regular workpieces. The vice is mounted on the table using T-slots.FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA

Vice Jaw

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4. MILLING OPERATION-(contd)ii) Universal chuck Used for holding round workpieces for machining of end slots, splines, etc.

iii) Fixture The most common form of work holding device used in production milling operation. Used to reduce the set-up time and increase the locational accuracy and repeatability.Clip mill_holddnFAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA

Fixture 1

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4. MILLING OPERATION-(contd)FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA

Fixture 2

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5. MILLING PARAMETERMilling Parameter

i) Cutting speedIt is important to control the cutting speed because high-speed may results in excessive cutters worn out but if too slow, it will increase the cutting time.Cutting speed measured in meter per minutes (m/min).It is varies for different metals due to the hardness, microstructure and machinability.Table below shows example of cutting speed for various types of the material.


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5. MILLING PARAMETER-(contd)FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA

Data for Milling

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5. MILLING PARAMETER-(contd)Cutter Speed

Cutter speed is measured in rotation per minute (rpm). It is depends on :Types of work piecesCutter materialsCutter diameterRequired surface finishToughness of the machine

In mathematically, cutter speed, N : N = 1000 x V N = cutter speed (rpm) x DV = cutting speed (m/min)D = cutter diameter (mm)FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA

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5. MILLING PARAMETER-(contd)Feeding rate

Rate of feeding work pieces to the machine cutter.Feeding rate is measured in millimeter per minute (mm/min).It is depends on:Cutting depth and widthWork piece materialsTypes of cuttersSharpness of cuttersRequired accuracy In mathematically, feeding rate, v: v = fNn v = feeding rate (mm/min) f = feed / tooth (mm/rotation) N = cutting speed (rpm)n = number of teeth FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA

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5. MILLING PARAMETER-(contd)Cutting Depth

Depth of metal cutting will affects the surface roughness and cutter life.For guidelines (table for metal trade -Serope Kalpakjian) a 5.0 mm for roughness a 0.5 mm for finishingIt is normal practice to reduce the cutting speed when increase the cutting depth to avoid machine cutter from broken.FAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA

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5. MILLING PARAMETER-(contd)Example:A surface 115 mm wide and 250 mm long is to be rough milled with a depth of cut 2 mm by a 5-tooth tungsten carbide face mill 70 mm in diameter. If the work material is stainless steel with cutting speed 85 m/min and feed rate of cutter is 0.13 mm /tooth, calculate:a) Cutter speedb) Feeding rate of the work piece


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5. MILLING PARAMETER-(contd)Answer

a) Cutter speed, N = 1000 x V x D= 1000 x 85 3.14 x 70= 387 rpm

b) Feeding rate, v = fNn = 0.13 x 387 x 5= 251 mm/minFAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA

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THE ENDFAKULTI KEJURUTERAAN MEKANIKALUNIVERSITI TEKNIKAL MALAYSIA MELAKA

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Conventional Milling Machine