MPL I (MET 1321) Prof. Simin Nasseri Manufacturing Processes lab I Milling Machine- 1

MPL I (MET 1321)Prof. Simin Nasseri

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.


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 Machine

An endmillMilling products


Types of Milling MachinesThere are two main types of mill: the vertical mill and the horizontal mill.

Vertical machine

Horizontal 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.


Horizontal 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.


Various Parts of the Horizontal Mill


Types of Movements

X Y

Z


Column and KneeColumn guides the knee

in vertical (Z axis) Direction.

Knee provides the X and Y

movements for the table.

Types of Milling Machines

Fixed BedTable’s motion:

back/forth direction or X.

Cutter head providesup/down (Z) or in/out (Y)

motions.

Milling Machine

s

1. Horizontal,2. Vertical,3. Planar.

1. Plain (Horizontal),2. Vertical, 3. Universal.

XY

Z


Subcategories of Vertical Milling

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 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.

Stationary spindle 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.

surface

axis

surface

axis



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.

surface

axis



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.



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 MillingSlab 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).

Plain milling

surface

axis


Methods of Milling

1. Up milling:

2. Down milling:

cutting

feed

cutting

feed

DOWN

UP


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 ToolsCutting tools for horizontal milling:

a. Slab MillsFor heavy cutting of large and flat surfaces.

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.

c. Slitting Saws For cutting deep slots or for parting off.

From: Hong Kong Polytechnic University


Cutting ToolsCutting tools for vertical milling:

a. End MillsCommonly used for facing, slotting and profile milling.

b. Rough Cut End MillsFor rapid metal removal.

c. Slot Drills For producing pockets without drilling a hole before hand.

d. Face Milling CuttersFor heavy cutting.


Spindle Speed Spindle 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 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 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.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 cutterCutting speed and feed rate for some common material :

Tool Material

High Speed Steel Carbide

Material Cutting Speed

Feed (f) Cutting Speed

Feed (f)

Mild Steel 25 0.08 100 0.15

Aluminum 100 0.15 500 0.3

Hardened Steel --- --- 50 0.1

Table 1

Cutting speed and feed rate depend on the material to be cut and tool material and also type of operation!


Test yourself

Is this up milling or down milling?

Up milling


Test yourself!

Is this up milling or down milling?

Up milling


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

Horizontal millingVertical milling


Test yourself!

Specify the X, Y and Z directions:

XY

Z


Test yourself!Label each of the milling operations below. Choose

from Face milling, End milling and Slab milling.

Slab milling Face milling End milling


Test 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 Cutters

Slitting Saws

Horizontal milling


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


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.

RPM

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. rpmF = 0.008 x 16 x 127.39F= 16.25 inch/min

12


Have a look at this site!

http://www.metalworking.com/tutorials/ARMY-TC-9-524/ch8.pdf

Documents

MPL I (MET 1321) Prof. Simin Nasseri Manufacturing Processes lab I Milling Machine- 1