machining 2 lab presentation

8/12/2019 Machining 2 Lab Presentation

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ISE 311Machining II lab

in conjunction with

Section 22.3 and 22.4 in the text book

Fundamentals of Modern Manufacturing

Third EditionMikell P. Groover

5/8/2008


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2

Outline

Introduction to milling

Cutting conditions in milling

Milling machines, milling cutters, and tool holding

3-2-1 approach

Edge finding CNC machining

CAD/ CAM

Lab objectives

Lab Procedure Summary


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Millingis a machining operation in which a workpart is

fed past a rotating cylindrical tool usually with multiple

cutting edges.

The cutting tool in milling is called a milling cutterand

cutting edges are called teeth.

The geometric form created by milling is a plane surface.

Other geometries can be created either by means of the

cutter path or cutter shape.

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The machine tool that traditionally performs this

operation is a milling machine (Mill).

Milling is an interruptedcutting operation; the teeth

enter and exit the work during each revolution. This

subjects the teeth to a cycle of impact force and thermal

shock on every revolution. The tool material and cutter

geometry must be designed to withstand these

conditions.

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There are two basic types of milling operations:

- Peripheral milling: the axis of the cutter is parallel to

the surface being machined, and the machining is

performed by cutting edges on the outside periphery of

the cutter.

- Face milling: the axis of the cutter is perpendicular to

the surface being milled, and machining is performedby cutting edges on both the end and outside periphery

of the cutter.

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Peripheral milling Face milling


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In peripheral milling, the rotation direction of the cutter

distinguishes two forms of milling:

Up (conventional) milling: the direction of motion of

the cutter teeth is opposite the feed direction when theteeth cut into the work.

Down (climb) milling: the direction of motion of the

cutter teeth is the same as the feed direction when theteeth cut into the work.

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Conventional milling Climb milling


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The cutting speed (v) is determined at the outside

diameter of the milling cutter and is related to the

diameter of the cutter (D) and the spindle rotational

speed (N) in number of Revolution Per Minute (RPM) as

follows:

v = *D*N

To find the spindle RPM, first look for v in tables and

then calculate N using the above formula

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The feed f in milling is usually given as a feed per

cutter tooth; called chip load.

Look for the chip load in tables.

To calculate the feed rate fr (in/min):

fr = f * nt * N

Where:f: chip load (in/ tooth)

nt: number of teeth on the cutter

N: spindle speed (rev/ min)

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The material removal rate (RMR) in milling is

determined using the cross sectional area of the cut

and the feed rate.

RMR = w * d * fr

Where:

RMR

: Material Removal Rate (in3/min)

w: width of cut (in)

d: depth of cut (in)

fr: feed rate (in/min)

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Neglecting the approach and travel distances of the

cutter, the time required to mill a work piece of length L

can be calculated as follow:

Tm = L / fr

where:

Tm : time to mill (min)

L: workpiece length (in)

fr: feed rate (in/min)

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Milling Machines

Milling machines can be classified as horizontal and

vertical:

1. Horizontal milling machines:

Horizontal spindle

Suitable for peripheral milling

2. Vertical milling machines:Vertical spindle

Suitable for face milling

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Milling Machines

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Horizontal milling machine Vertical milling machine


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Milling Machines

Instead of the name verticalknee-and-column mill,

you will hear the name BridgePorta lot in the

Machine shop

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Milling machines

In milling machines:

The knee can move in the z-direction.

The saddle is placed over the knee and can move in the

y-direction .

The table is placed over the saddle and can move in

the x-direction.

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Milling machines

To move the knee, saddle, or table, you have to rotate

corresponding traverse cranks.

A micrometer is associated with each of the three

cranks. Using these micrometers, you can measure thedistance travelled. (some mills have digital readouts to

display the x, y, and z coordinates).

The simplest and most common way to clamp the

work during milling is to use a vise. (you will use a

vise to clamp the work in the lab).

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Milling machines

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The Vise you will be using in the lab


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Milling Cutters

The milling cutter you will use in the lab is a:

HSS, ,4-flute, non-center cutting end mill

Machine Tool Practices, by R. Kibbe, R. Meyer, J. Neely, and W. White

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Material: High Speed Steel

Diameter

A flute

There are no cutting

edges at the center


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Tool holding

There are many ways to mount the cutter in the machine

spindle. The most common ways are:

1- Collets

2- Chucks

In the lab, you will use a 3-jaw chuck

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3-2-1 approach

In order to define the location of the work in the three

dimensional space, the 3-2-1approach is usually used:

To define the location in the z-direction, place the work on a

plane with known z-coordinate. [a plane is defined by 3

points].

While the work is on the plane, slide it until it touches a line

with known y-coordinate (for example). [a line is defined by 2

points].

While the work is touching both the plane and the line, slide itin the x-direction until it touches a pin (1point) with known

x-coordinate.

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Edge Finding

In order to machine a feature in the work in the proper location,

the location of the cutter should be defined with respect tocertain references, usually the DatumPlanesof the work.

Assuming that a datum surface is perfectly flat, the cutter can be

located with respect to this datum using a tool called the OffsetEdge Finder.

The OffsetEdge Finderconsists of a shank with a floating tip

that is retained by an internal spring. The edge finder tip isaccurately machined to a known diameter, usually 0.2 or 0.5 in.

Machine Tool Practices, by R. Kibbe, R. Meyer, J. Neely, and W. White 22


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Edge Finding

The edge finder you will use in the lab

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Edge

finder tip


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Edge Finding

The procedure for using an Edge Finder:

Secure the edge finder in a collet or chuck in the machine

spindle.

Set the spindle speed to about 600 to 800 rpm and slide the edge

finder tip over so that it is off-center.

Start the spindle and lower the quill or raise the knee so that the

edge finder tip can contact the edge of the part to be located.


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Edge Finding

The procedure for using an Edge Finder (continued)

Turn the table or spindle cranks and move the workpiece until it

contacts the rotating edge finder tip. Continue to slowly

advance the workpiece against the edge finder tip until the tip

suddenlymoves sideways. Stop movement at this moment. Themachine spindle is now positioned a distance equal to the edge

finder tip radius from the edge of the work.

Lower the work or raise the quill

If you want to drill a hole 1 in away from the datum plane, thenyou have to move the work a distance equal to 1 in plus the

radius of the edge finder.


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CNC machining

Numerical Control (NC) is a form of programmable automation

in which the mechanical actions of a piece of equipment are

controlled by a program containing coded alphanumeric data.

The data represent relative position between a workhead (the

spindle or cutting tool in case of NC machining) and the

workpiece.

Both the motion of the tool with respect to the workpiece and

sequence of motions can be controlled in NC machining.

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CNC machining

NC system consists of three basic components:

1. Part program: a code (set of commands) which describes the

sequence of operations to be done.

2. Processing equipment: the unit which performs the

manufacturing operations according to the part program.

3. Machine control unit (MCU): stores the program and executes

it by converting each command into actions by the processing

unit.

If the MCU is a computer, then the NC is called CNC

(Computer Numerical Control)

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CNC machining

In CNC machining, more than one axis can be controlled

simultaneously. These axis are:

- x, y, z axes (linear axes)

- a, b, c axes (rotational axes around x, y, z axes respectively)

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CNC machining

In 2-axis milling machines, the x and y axes can be controlledsimultaneously.

In 3-axis milling machines, the x, y, and z axes can be

controlled simultaneously.

In 2 milling machines, the z-axis is fixed at a certain value

and then the x and y axes are controlled simultaneously.

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CNC machining

G-code, M-code and others are used in CNC programming.

The two main advantage of CNC machining are:

1. Complex geometries can be machined.

2. The process is automated.

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CAD/ CAM

CAD/ CAM stands for Computer-Aided Design/ Computer-Aided Manufacturing.

The CAD software is used to construct the initial workpiece

geometry.

The CAM software is used to generate the cutting tool path. The

CAD geometry can be saved and retrieved at any time.

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CAD/ CAM

The programmer can see a simulation of the tool path beforeactual production and corrects the program mistakes

accordingly.

Portion of the tool path generated can be automated such asmilling around the outside periphery of the part, milling a

pocket into the surface of the part, surface contouring, and

certain point-to-point operations. These routines are usually

called Macros

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Lab Objectives

The objectives of this lab are:

To learn the fundamentals of milling operations.

To learn how to select/ calculate cutting conditions for milling

operations.

To observe the capabilities of a 3-axis CNC milling machine.

To understand the basics of how CNC machine tools are

programmed.

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Lab Procedure

The following procedure will be followed in the lab:

Part1: Manual Milling

1- Peripheral mill one end of the workpiece to form a flat and

perpendicular surface.

2- Reposition the work in the vice so that the unfinished end is

protruding .

3- Use the edge finder to establish at the front-left corner of the

part. (see part print in Appendix A)

4- Peripheral mill the protruding end to achieve the 1.75

dimension.

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Lab Procedure

Part1: Manual milling (Continued)

5- Face mill the top of the workpiece to achieve the 0.313

dimension.

6- On the mill, center drill the hole locations.

7- If time permits, move the workpiece to the drill press and drill

the holes.

Note: For all milling operations in this lab, do not exceed 0.025

depth of cut

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Lab Procedure

Part2: CNC demo

1- Observe the Haas machining center demonstration.

2- Observe the sample parts made on the CNC mill.

3- Observe the CAM demo.

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Pictures

A picture showing the peripheral milling operation

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Feed direction


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Pictures

A picture showing the face milling operation

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Feed direction

i


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Pictures

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Pictures showing center drilling on the vertical mill

Pi


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Pictures

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The part you will machine using the CNC milling machine

Machined part

Initial stock

Pi


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Pictures

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The CNC milling machine you will use in the lab

S M hi i II L b


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Summary-Machining II Lab

This lab preparation material introduced:

Basic principles of milling

CNC machining and CAD/ CAM systems

Lab objectives and procedures Pictures

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A di A


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Appendix A

The part you will machine in the lab

machining 2 lab presentation

Documents