2Learning Objectives Describe how milling machines operate, Identify the various types of milling machines,Select the proper cutter for the job to be done,Calculate cutting speeds and feeds.
3Milling MachineA milling machine is a power-driven machine used for the complex shaping of metal parts.Its basic form is that of a rotating cutter or endmill which rotates about the spindle axis (similar to a drill), and a movable table to which the workpiece is affixed.Milling machines may be operated manually or under computer numerical control (CNC).An endmillMilling products
4Types of Milling Machines There are two main types of mill: the vertical mill and the horizontal mill.Horizontal machineVertical machine
5Vertical MillIn the vertical mill the spindle axis is vertically oriented (Milling cutters are held in the spindle and rotate on its axis).The spindle can generally be extended (or the table can be raised/lowered, allowing plunge cuts and drilling.
6Horizontal MillA horizontal mill has the same sort of x–y table, but the cutters are mounted on a horizontal arbor across the table. A majority of horizontal mills also feature a +15/-15 degree rotary table that allows milling at shallow angles.Plain mills are used to shape flat surfaces. Special cutters can also cut grooves, bevels, radii, or indeed any section desired. These specialty cutters tend to be expensive.Simplex mills have one spindle, and duplex mills have two.It is also easier to cut gears on a horizontal mill.
9Types of Milling Machines Column and KneeColumn guides the kneein vertical (Z axis)Direction.Knee provides the X and Ymovements for the table.Fixed BedTable’s motion:back/forthdirection or X.Cutter head providesup/down (Z)or in/out (Y)motions.ZYXHorizontal,Vertical,Planar.Plain (Horizontal),Vertical,Universal.
10Subcategories of Vertical Milling Stationary spindleThere are several subcategories of vertical mills: the bedmill and the Turret mill.Turret mills, are generally smaller than bedmills, but are more versatile. In a turret mill the spindle remains stationary during cutting operations and the table is moved both perpendicular to and parallel to the spindle axis to accomplish cutting.In the bedmill, however, the table moves only perpendicular to the spindle's axis, while the spindle itself moves parallel to its own axis.Table’s motionsTable’s motion
11Types of Milling Machines A more complex form of the milling machine is the Universal milling machine, in which the rotating cutter can be oriented vertically or horizontally, increasing the flexibility of the machine tool.The table of the universal machine can be swiveled through a small angle (up to about 15 degrees), enabling tapered cuts to be made over the length of the table.
12Typical Milling Operations 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 here.axisaxissurfacesurface
13Typical Milling Operations End MillingEnd Milling is the milling of a flat surface with the axis of the cutter perpendicular to the machining surface as shown here.axissurface
14Typical Milling Operations Gang MillingGang milling is a horizontal milling operation that utilizes three or more milling cutters grouped together for the milling of a complex surface in one pass.Different type and size of cutters should be selected for achieving the desire profile on the workpiece.
15Typical Milling Operations Straddle MillingIn straddle milling, a group of spacers is mounted in between two side and face milling cutters on the spindle arbor as shown, for the milling of two surfaces parallel to each other at a given distance.
16Classification of Milling 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 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 Milling (The 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).axissurfacePlain milling
17Methods of Milling UP cutting feed cutting feed Up milling: Down milling:UPcuttingfeedDOWNcuttingfeed
18Methods of milling machine control Manual: Movements are made by hand lever control)Semi-automatic: Movements are controlled by hand and/or power feeds).Fully automatic: A complex hydraulic feed arrangement that follows 2 or 3 dimensional templates.CNC: Machining coordinates are entered into a master computer or computer on the machine, using a special programming language.
19From: Hong Kong Polytechnic University Cutting ToolsCutting tools for horizontal milling:a. Slab Mills For heavy cutting of large and flat surfaces.c. Slitting Saws For cutting deep slots or for parting off.b. Side and Face Cutters This type of cutter has cutting edges on the periphery and sides of the teeth for cutting shoulders and slots.From: Hong Kong Polytechnic University
20Cutting ToolsCutting tools for vertical milling:a. End Mills Commonly used for facing, slotting and profile milling.b. Rough Cut End Mills For rapid metal removal.c. Slot Drills For producing pockets without drilling a hole before hand.d. Face Milling Cutters For heavy cutting.
21Spindle SpeedSpindle speed in revolution per minute (R.P.M.) for the cutter can be calculated from the equation (metric based):WhereRPM = R.P.M. of the cutter CS = Linear Cutting Speed of the material in m/min. ( see table 1 ) d = Diameter of cutter in mmFor inch based calculation, replace 1000 with 12. Cutting speed is in foot per minute and diameter in inch.RPM
22Feed RateFeed rate (F) is defined as the rate of travel of the workpiece in mm/min. But most tool suppliers recommend it as the movement per tooth of the cutter (f). Thus,F = f.T.NF = table feed in mm/min f = also known as ftr= movement per tooth of cutter in mmT = number of teeth of cutter N = R.P.M. of the cutterCutting speed and feed rate for some common material :Cutting speed and feed rate depend on the material to be cut and tool material and also type of operation!ToolMaterialHigh Speed SteelCarbideCuttingSpeedFeed (f)Mild Steel250.081000.15Aluminum5000.3HardenedSteel---500.1Table 1
23Test yourselfIs this up milling or down milling?Up milling
24Test yourself!Is this up milling or down milling?Up milling
25Test yourself! Horizontal milling Vertical milling Which one is the vertical milling and which one the horizontal one?Horizontal millingVertical milling
26Test yourself!ZSpecify the X, Y and Z directions:YX
27Test yourself!Label each of the milling operations below. Choose from Face milling, End milling and Slab milling.Slab milling Face milling End milling
28Test yourself!Are these tools for vertical or horizontal milling? Label them using: Side and face cutter, slitting saws and slab mills.Slab MillsSide and Face CuttersSlitting SawsHorizontal milling
29Test yourself!Specify the following vertical mill cutting tools (choose from slot drill, end mill, face milling cutter and rough cut end mill).End mill Face milling cutterRough cut end mill Slot Drill
30Test yourself!Determine the approximate cutting speed and feed for a 6” (152 mm) diameter side cutter (High Speed Steel or HSS) with 16 teeth, when milling free cutting steel.Consider the cutting speed for free cutting steel 200 fpm. The feed rate for free cutting steel for side cutter is between to inches. Consider the midpoint in range.RPMRPM = (200x12)/(3.14x6)RPM = rpmMid-point in range for the feed rate:f= ( )/2= 0.008”F = f. T. rpmF = x 16 xF= inch/min12