Transcript Machining Lab- Part II

ISE 311
Machining II lab
in conjunction with
Section 22.3 and 22.4 in the text book
“Fundamentals of Modern Manufacturing”
Third Edition
Mikell P. Groover
5/8/2008
Outline
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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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Introduction to milling
Milling is 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 cutter and
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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Introduction to milling
The machine tool that traditionally performs this
operation is a milling machine (Mill).
Milling is an interrupted cutting 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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Introduction to milling
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 performed
by cutting edges on both the end and outside periphery
of the cutter.
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Introduction to milling
Peripheral milling
Face milling
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Introduction to milling
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 the
teeth cut into the work.
• Down (climb) milling: the direction of motion of the
cutter teeth is the same as the feed direction when the
teeth cut into the work.
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Introduction to milling
Conventional milling
Climb milling
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Cutting conditions in milling
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 = π*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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Cutting conditions in milling
• 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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Cutting conditions in milling
• 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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Cutting conditions in milling
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
Horizontal milling machine
Vertical milling machine
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Milling Machines
Instead of the name “vertical knee-and-column mill”,
you will hear the name “BridgePort” a 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 the
distance 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
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, ½”, 4-flute, non-center cutting end mill
Diameter
There are no cutting
edges at the center
A flute
Material: High Speed Steel
Machine Tool Practices, by R. Kibbe, R. Meyer, J. Neely, and W. White
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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 3-2-1 approach is usually used:
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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 it
in the x-direction until it touches a pin (1 point) 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 to
certain references, usually the “Datum Planes” of 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 “Offset
Edge Finder”.
• The “Offset Edge Finder” consists of a shank with a floating tip
that is retained by an internal spring. The edge finder tip is
accurately 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
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Edge Finding
The edge finder you will use in the lab
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.
Machine Tool Practices, by R. Kibbe, R. Meyer, J. Neely, and W. White
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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
suddenly moves sideways. Stop movement at this moment. The
machine 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, then
you have to move the work a distance equal to 1 in plus the
radius of the edge finder.
Machine Tool Practices, by R. Kibbe, R. Meyer, J. Neely, and W. White
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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.
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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 controlled
simultaneously.
• In 3-axis milling machines, the x, y, and z axes can be
controlled simultaneously.
• In 2 ½ 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/ ComputerAided 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 before
actual production and corrects the program mistakes
accordingly.
• Portion of the tool path generated can be automated such as
milling 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
Feed direction
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Pictures
A picture showing the face milling operation
Feed direction
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Pictures
Pictures showing center drilling on the vertical mill
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Pictures
The part you will machine using the CNC milling machine
Machined part
Initial stock
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Pictures
The CNC milling machine you will use in the lab
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Summary-Machining II Lab
This lab preparation material introduced:
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Basic principles of milling
CNC machining and CAD/ CAM systems
Lab objectives and procedures
Pictures
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Appendix A
The part you will machine in the lab
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