Manufacturing Processes lab I Milling Machine- 1

Manufacturing Processes lab IMilling Machine- 1

Learning 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.

An endmill Milling Machine A 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). Milling products

Types of Milling Machines There are two main types of mill: the vertical mill and the horizontal mill. Horizontal machine Vertical machine

Vertical Mill In 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.

Simplex mills have one spindle, and duplex mills have two. It is also easier to cut gears on a horizontal mill. Horizontal Mill A 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.

Various Parts of the Horizontal Mill

Types of Movements Z Y X

Types of Milling Machines Milling Machines Column and Knee Column guides the knee in vertical (Z axis) Direction. Knee provides theXandY movements for the table. Fixed Bed Table’s motion: back/forth direction orX. Cutter head provides up/down (Z) or in/out (Y) motions. Z Y X • Horizontal, • Vertical, • Planar. • Plain (Horizontal), • Vertical, • Universal.

Subcategories of Vertical Milling Stationary spindle There 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 parallelto 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 motions Table’s motion

Types 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.

Typical Milling Operations Plain Milling Plain 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. axis axis surface surface

Typical Milling Operations End Milling End Milling is the milling of a flat surface with the axis of the cutter perpendicular to the machining surface as shown here. axis surface

Typical Milling Operations Gang Milling Gang 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.

Typical Milling Operations Straddle Milling In 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.

Classification 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). axis surface Plain milling

Methods of Milling • Up milling: • Down milling: UP cutting feed DOWN cutting feed

Methods 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.

Cutting Tools Cutting tools for horizontal milling: a. Slab MillsFor heavy cutting of large and flat surfaces. c. Slitting SawsFor cutting deep slots or for parting off. b. Side and Face CuttersThis type of cutter has cutting edges on the periphery and sides of the teeth for cutting shoulders and slots. From: Hong Kong Polytechnic University

Cutting Tools Cutting tools for vertical milling:

Spindle Speed Spindle speed in revolutionper minute (R.P.M.) for the cutter can be calculated from the equation (metric based): Where RPM = R.P.M. of the cutterCS = Linear Cutting Speed of the material in m/min. ( see table 1 ) d = Diameter of cutter in mm For inch based calculation, replace 1000 with 12. Cutting speed is in foot per minute and diameter in inch. RPM

Feed Rate Feed 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.N F = table feed in mm/min f = also known as ftr= movement per tooth of cutter in mm T = number of teeth of cutter N = R.P.M. of the cutter Cutting 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! Table 1

Test yourself Is this up milling or down milling? Up milling

Test yourself! • Is this up milling or down milling? Up milling

Vertical milling Horizontal milling Test yourself! Which one is the vertical milling and which one the horizontal one?

Test yourself! Z • Specify the X, Y and Z directions: Y X

Test yourself! • Label each of the milling operations below. Choose from Face milling, End milling and Slab milling. Slab milling Face milling End milling

Slab Mills Side and Face Cutters Slitting Saws Horizontal milling Test yourself! Are these tools for vertical or horizontal milling? Label them using: Side and face cutter, slitting saws and slab mills.

Test 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 cutter Rough cut end mill Slot Drill

RPM = (200x12)/(3.14x6) RPM = 127.39 rpm Mid-point in range for the feed rate: f= (0.005 +0.011)/2= 0.008” F = f. T. rpm F = 0.008 x 16 x 127.39 F= 16.25 inch/min 12 RPM Test 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 0.005 to 0.011 inches. Consider the midpoint in range.

Have a look at this site! http://www.metalworking.com/tutorials/ARMY-TC-9-524/ch8.pdf

Manufacturing Processes lab I Milling Machine- 1