Transcript No Slide Title

ISE 311
Machining I Lab
in conjunction with
Chapters 21, 22, and 23 in the text book
“Fundamentals of Modern Manufacturing”
Third Edition
Mikell P. Groover
April 17th, 2008
Outline
• Introduction
• Basic Principles of Machining
• Background Information on Drilling, Turning and
Other operations related to them
• Objectives of the Lab
• Overview of Lab– Materials and Equipment Used
• Demonstration of Machining – Drilling, Facing, and
Turning – Pictures
• Summary
2
Introduction
Basic Principles of Machining
Machining is a manufacturing process in which a cutting tool is
used to remove excess material from a workpiece. The material
that remains is the desired part geometry. The cutting tool
deforms the workpiece in shear and creates scrap called “chips.”
As chips fall off the workpiece a new surface is exposed.
A schematic showing a
simple machining process
3
Introduction
Basic Principles of Machining
Almost all solid metals, plastics, and composites can be machined
by conventional machining.
Machining can create any regular geometry, i.e., planes, round
holes, and cylinders.
Machining can produce dimensions to tolerances of less than
0.001” (0.025mm)
Surface finishes of better than 16μin (0.4 μm) can be produced by
machining processes.
4
Introduction
Basic Principles of Machining
A cutting tool has one cutting edge (facing tool or turning tool) or
more than one cutting edges (drill, end mill). The cutting edge
separates the chip from the workpiece.
The rake face of a tool guides the chip from the surface of the
workpiece and is oriented at an angle α. The rake angle α is
measured relative to a plane perpendicular to the work surface.
The flank of a tool provides clearance between the cutting tool
and the newly exposed surface to protect the surface from
abrasion. The flank is oriented at an angle called the relief angle.
The picture below illustrates the make-up of a cutting tool.
5
Machining I
Basic Principles of Machining
The three most common types of conventional
machining processes are:
– Drilling
– Turning
– Milling
Other conventional machining processes include:
–
–
–
–
–
Shaping
Planing
Broaching
Sawing
Grinding
6
Machining I
Drilling
Drilling is used to create round holes in workpieces using a
rotating tool with two cutting edges. This rotating tool is called a
drill or drill bit. This operation is normally performed on a drill
press.
Two types of holes can be made:
– through holes, in which the drill exits the opposite side of the work
– blind holes , in which the drill does not exit
(a)
(b)
Figure depicting
(a) through holes and
(b) blind holes
7
The figure below depicts a twist drill – the most
commonly used drill bit.
Twist drill bit
8
Machining I
Drilling
The body of a twist drill has two spiral flutes which
usually have a 30° helical angle. These flutes act as a
passageway for chip extraction from the hole and for
coolant to enter the hole (however, cooling is not
effective since chips and coolant move in opposite
directions).
The thickness of the drill between the flutes, also called
the web, provides support over the length of the drill
body.
The point of the twist drill is in the shape of a cone and
the point angle is typically 118°.
9
Machining I
Drilling
The twist drill is fed into the workpiece while rotating
and the relative motion between the cutting edges of the
drill and the workpiece results in material removal and,
hence, chip formation.
The flutes provide enough clearance to allow the chips
to be extracted. During drilling, however, friction
between the chip and cutting surface (rake face) as well
as between the outer diameter of the drill and workpiece
generates a large amount of heat and, thus, the
temperature of the workpiece and drill increases
dramatically.
10
Machining I
Drilling
Drills are limited to a depth of no greater than 4 times its
diameter because of the high temperature and the high
load on the drilling bit, which:
• Decreases the strength of the drill and makes it easier to
break.
• Negatively affects the surface finish of the hole.
• Increases the deflection in the drill, which affects the
straightness and dimensional accuracy of the hole
11
Machining I
Drilling
To solve the temperature rise problem, the following is
common:
• Peck drilling: the drill is periodically withdrawn from the
hole to clear chips
• Some drills have internal holes in the drill body through
which cutting fluid is delivered to the cutting interface.
Increasing flute size makes it easier to clear chips from
the hole but results in smaller web thickness and affects
the drill rigidity (the opposite is also true).
12
Machining I
Drilling
Prior to drilling, centering (or center drilling) is used to
create a starter hole (using a center drill). This is used
to:
• Define the location of the hole.
• Solve the “Walking” or “Wandering” problem which
happens because of drill deflection before the chisel
penetrates the workpiece.
13
Machining I
Drilling
The following operations are all related to drilling and
can be performed once a hole has been created:
– Reaming: a reamer (usually with multiple straight flutes) is
used to ream a hole, i.e., slightly enlarge a hole and
improve its surface finish and provide tighter tolerances.
– Tapping: a tap is used to create internal screw threads on
an existing hole.
– Counterboring generates a stepped hole, i.e., a larger
diameter hole is created over a smaller diameter hole. This
process is used to seat bolt heads below the surface of a
workpiece or flush with the surface.
14
Machining I
Drilling
Operations related to drilling (continued)
– Countersinking is similar to counterboring, but the hole step
is conical and is used for flat head screws. Countersinking
is used also for deburring.
– Spotfacing is similar to milling. This process is used to
provide a flat surface on the workpiece.
15
Machining I
Drilling
The figure below illustrates the various operations
related to drilling.
(a)
(b)
(c)
(d)
(e)
(f)
Reaming
Tapping
Counterboring
Countersinking
Center drilling
Spot facing
16
Machining I
The Drill Press
The drill press is the most commonly used machine tool for
drilling and the related operations mentioned previously. The
most common drill press, and also the one used in the lab
procedure, is the upright drill press. The base sits on the
floor, has a table for holding the workpiece, a head with a
powered spindle for the cutting tool, and a bed and column
for support.
Figure showing
upright drill press
17
Machining I
Turning and Facing
Turning is a machining process performed on a lathe in
which a single point tool removes material from a
rotating cylindrical workpiece. The cutting tool is fed
linearly and in a direction parallel to the axis of rotation
of the workpiece as shown in the figure below.
*NOTE*
In drilling, the cutting tool rotates, while in turning the workpiece rotates.
18
Machining I
Turning and Facing
The lathe provides the power to rotate the workpiece,
feed the tool at the specified rate and cut the workpiece
at the necessary depth. Other operations related to
turning that can be accomplished by using a lathe
include:
– Facing: the tool is fed radially into the rotating workpiece to
create a new surface (face) on the end.
– Taper turning: the tool is fed at an angle to the axis of rotation to
create a conical geometry.
– Contour turning: The tool follows a contour that is other than
straight, thus creating a contoured form in the turned part.
19
Machining I
Turning and Facing
Other operations related to turning (continued):
– Form turning: a formed cutting tool is fed into the workpiece
radially
– Chamfering: the cutting tool cuts an angle on the corner of the
cylinder. A very small chamfer can be used to remove burrs
usually formed during machining processes and to eliminate
sharp corners (for safety reasons).
– Cutoff (or parting): the tool is fed radially (like facing) at some
length along the workpiece to cut off the end of the part
20
Machining I
Turning and Facing
Other operations related to turning (continued):
– Threading: a pointed tool is fed linearly across the outside
diameter of the workpiece (similar to turning) at a large feed
creating external threads on the cylinder
– Boring: a tool is fed linearly and parallel to the axis of rotation to
correct a previously drilled hole and/ or to enlarge the diameter
of an existing hole in the part
– Drilling: drilling can be performed on a lathe by feeding the drill
into the rotating part along its axis.
– Knurling: a knurling tool produces a cross-hatched pattern on the
outer diameter of the workpiece
21
Machining I
Turning and Facing
The figure below displays operations related to turning
(a)
(g)
(f)
(e)
(h)
(d)
(c)
(b)
(a)
(b)
(c)
(d)
(e)
(f)
(g)
(h)
(i)
(j)
Facing
Taper turning
Contour turning
Form turning
Chamfering
Cutoff
Threading
Boring
Drilling
Knurling
22
(i)
(j)
Machining I
The Lathe
The engine lathe is a manually operated machine tool
which is widely used in low to medium production.
Initially, these machine tools were powered by steam
engines, hence the term “engine” lathe.
The figure to the left shows the
principal components of an
engine lathe. The drive unit used
to rotate the spindle is enclosed in
the headstock. The spindle rotates
the workpiece. The tailstock is
occasionally used to support one
end of the workpiece.
23
Machining I
The Lathe
The cutting tool is held in the tool post. The tool post is
mounted on the cross-slide. The cross-slide is mounted
on the carriage. The carriage slides along the ways. The
ways are built into the bed of the lathe.
The carriage moves in a direction parallel to the axis of
rotation and controls the feed rate of the tool. The crossslide feeds perpendicular to the workpiece. Thus, by
moving the carriage, a turning operation can be
performed; by moving the cross-slide a facing operation
can be carried out.
24
Machining I
The Lathe
The size of a lathe is determined by its swing and
maximum distance between centers.
The swing of a lathe is the maximum diameter of the
workpiece that can be rotated in the spindle. This
diameter is determined as twice the distance from the
axis of rotation to the ways of the machine.
The maximum distance between centers is the maximum
length of a workpiece that can be mounted between the
centers of the headstock and tailstock.
25
Machining I
The Lathe
There are 4 common methods to hold the workpiece in a
lathe as shown in the figure below: (a) mounting
between centers, (b) chuck, (c) collet, and (d) face plate.
26
Machining I
The Lathe
When mounting the work
between the centers, one end of
the workpiece is held in place by
the headstock and the other end is
supported by the tailstock. This
method is used for long parts with
relatively small diameters.
The chuck (shown to the right)
utilizes either three or four jaws
to hold the workpiece by its
outside diameter. Some jaws are
manufactured in a way such that
they can hold a tubular workpiece
by the inside diameter.
27
Machining I
The Lathe
A collet (shown below) has a tubular bushing with slits over half
of its length. These slits allow the collet to be squeezed to reduce
its diameter and grasp the cylindrical workpiece. Collets must be
made in many various sizes to match the diameter of the
workpiece since there is a limit to the amount the diameter of the
collet can be reduced.
28
Machining I
The Lathe
A face plate is mounted onto the spindle and is used to hold
workpieces with non-cylindrical shapes. The face plate is
equipped with custom designed clamps which are manufactured
specifically to a particular application.
29
Machining I
Cutting Parameter in turning
The three cutting parameters in turning are (see the figure
below) :
• The cutting speed v (ft/min): the tangential speed
• The depth of cut d (in): the penetration of the cutting tool
below the original surface of the work.
• The feed f (in/rev): distance (parallel to the axis of rotation)
traveled by the tool per one revolution of the work
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Machining I
Required Calculations for this lab
[The following applies for both turning and drilling]
• Look for v and f in tables
• To calculate the spindle RPM (rev/min) from v
(ft/min), use the following equation:
12 v
N
D
• The Material Removal Rate RMR (in3/min) is the
volume of material removed (in3) divided by time
(min)
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Machining I
Required Calculations for this lab
• Machining power, P, is the energy per unit time
required to perform a machining operation (usually in
Horse Power, HP)
1 HP = 33, 000 lb*ft/min
• Unit Power Pu or Specific Energy U is the power
divided by the Material Removal Rate
• For each material, there is an approximate value of the
Unit Power. Look for Pu in tables.
• To calculate P:
P  PU  RMR
32
Machining I
Tool materials
The most important properties in tool materials are:
• Toughness
• Hot Hardness
• Wear resistance
There is always a trade-off between these properties. For
example, increasing the hot hardness and wear resistance
of the cutting tool generally results in a reduction in
toughness.
High Speed steel (HSS) tools are the most common and
will be used in this lab.
33
Lab Objectives
This lab has the following objectives:
• Become familiar with basic lathe and drill press operations
• Get firsthand experience at trying to maintain tolerances in
machining
• Learn to calculate cutting speed, material removal rate, and
spindle horsepower
34
Lab Safety
• Everyone MUST wear approved safety glasses
• Remove or secure anything which might become caught in
rotating machinery.
– Remove all jewelry from the hands and wrists. Remove necklaces that
will dangle when stooped over.
– Short sleeves are recommended – roll long sleeves up to the elbow.
– Loose clothing is not advised. Very baggy shirts, sweaters, sweatshirts,
etc. are not allowed. Unbuttoned shirts or jackets are not allowed.
– Secure long hair. When looking down at the ground, if your hair hangs
more than 4” beyond your nose, you need to secure it.
• Do not touch rotating tools or chips clinging to rotating tools.
• Exercise extreme care when touching chips – they are very
sharp and can be very hot.
35
Lab Procedure – Part A
• You will need to use the drill press and perform
drilling operations in order to make the bracket.
• The equipment you will use in this part includes:
–
–
–
–
–
–
–
Scribe
Drill press
Center drill
2 drill bits
Reamer
Counterbore tool
Countersink tool
36
Lab Procedure – Part A
Speed adjustment
Head
Forward/Reverse lever
Spindle
Column
Chuck
Table
37
Lab Procedure – Part A
23/64” Drill
Counterbore tool
0.375” Reamer
Countersink tool
Center Drill
7/32” Drill
38
Lab Procedure – Part A
Procedure: (refer to the drawing in appendix A)
1.
Using the scribe, mark the locations of the holes to be drilled
on the workpiece. Make sure to set the correct measurement
on the scribe using a scale. Refer to the drawing in appendix
A for the correct dimensions.
39
Lab Procedure – Part A
Procedure: (refer to drawing in appendix A)
2. Once the center lines for the 3
holes have been marked,
clamp the workpiece in the
holder on the drill press.
3. Locate the center drill in the
chuck and, without turning the
drill press on, manually align
the center drill to one of the
cross hairs that are inscribed
on the workpiece
*NOTE*
DO NOT attempt to drill the workpiece
with the drill press in the reverse position!
NEVER adjust the speed while the
machine is off!
40
Lab Procedure – Part A
Procedure: (refer to drawing in appendix A)
4.
5.
6.
7.
Once the center drill is aligned, return it to its home position.
Turn the drill press on by moving the lever to FORWARD
and then adjust the speed as stated in appendix A. Apply
lubricant as necessary.
Hold the workpiece in place with your left hand and with
your right hand bring the center drill down to the surface of
the workpiece.
Slowly create a starter hole. Once a hole has been created
return the drill press to its starting position and turn the
machine off.
Repeat step 3 for the remaining 2 holes. The speed will
remain the same. Apply lubricant, if necessary.
41
Lab Procedure – Part A
42
Lab Procedure – Part A
Procedure:
(refer to drawing in
appendix A)
8.
Remove the center drill
once all three starter holes
have been created and
replace it with the 23/64”
drill.
9. With the drill press off,
manually align the drill bit
with the middle hole.
10. Turn the machine to
FORWARD, adjust the
speed accordingly, and
apply the lubricant as
necessary. Drill a through
hole and return the drill
press to its home position.
43
Lab Procedure – Part A
Procedure: (refer to drawing in appendix A)
11. Remove the 23/64” drill bit from the chuck and insert the
3/8” reamer.
12. Turn the machine on, adjust the speed, apply the lubricant
and ream the 0.360” hole to 0.375”. Turn off the drill press.
Note: If the tool holder was not moved, you do not need to
manually align the cutting tool in this step.
44
Lab Procedure – Part A
Procedure: (refer to drawing in appendix A)
13. Remove the reamer and insert the 7/32” drill into the chuck. Manually
align the drill to the center of one of the outside holes.
14. Once aligned, turn on the drill press, adjust the speed, apply the lubricant,
and drill a through hole. Once the through hole has been drilled, turn off
the machine.
15. Repeat step #15 for the third and final hole.
45
Lab Procedure – Part A
Procedure:
(refer to drawing in appendix A)
16. Remove the 7/32” drill and place the counterbore tool into
the chuck.
17. Manually align the counterbore tool with one of the outside
holes. Turn on the drill press, adjust the speed, apply the
lubricant, and drill a blind hole approximately 3/8” deep.
46
Lab Procedure – Part A
Procedure:
(refer to drawing in appendix A)
18. Turn off the drill press. Remove the counterbore tool and
insert the countersink tool into the chuck.
19. Manually align the countersink tool with the third hole. Turn
on the drill press, apply the lubricant, and drill a countersink
hole.
47
Lab Procedure – Part A
Procedure:
(refer to drawing in appendix A)
20. If time permits, deburr the bottom face of the bracket using
the countersink tool. Align the countersink tool with each of
the three holes that have been drilled and remove only
enough material to remove the burrs created by drilling.
48
Lab Procedure – Part B
• You will need to use the engine lathe to perform
facing, turning, drilling, and tapping operations in
order to make the shaft.
• The equipment you will use in this part includes:
–
–
–
–
–
–
Engine lathe
Facing tool
Turning tool
Center drill
Drill
Tap
49
Lab Procedure – Part B
Headstock
Chuck
Tool post
Tailstock
Spindle speed
selector
Cross slide
Cross feed
handwheel
Feed selector
Feed handwheel
Ways
Lead screw
Bed
On/Off levers
50
Lab Procedure – Part B
Facing tool
Tap
Turning tool
Tap holder
Tap guide
51
Lab Procedure – Part B
Procedure: (refer to drawing in appendix B)
1.
2.
3.
Insert and secure the workpiece into the collet (or chuck).
Turn on the lathe by lifting on the lever.
Rotate the wheel that controls the feed counterclockwise and
place the tool in line with the workpiece.
4. While holding the feed to prevent it from moving, rotate the
cross feed in a clockwise direction to face the workpiece.
Bring the cross feed back to its starting position after
completing the facing operation.
5. Repeat this facing process 1 or 2 more times by slightly
feeding the tool to make sure that a flat surface has been
generated.
*NOTE*
NEVER power on the lathe if the tool is in contact with the workpiece
52
Lab Procedure – Part B
53
Lab Procedure – Part B
Procedure: (refer to drawing in appendix B)
6.
Remove the facing tool and insert the turning tool. Adjust the
feed stop to 3/8” from the initial position.
54
Lab Procedure – Part B
Procedure:
(refer to drawing in
appendix B)
7. Turn on the lathe and cross
feed the tool. Once the tool
slightly
touches
the
workpiece (chips will be
formed and a new surface
will be exposed), set and
lock the micrometer collar
to 0. Next, set the cross
feed to 25 (which will
remove 0.025” from the
diameter) and then feed the
tool to the stop.
55
Lab Procedure – Part B
Procedure:
(refer to drawing in
appendix B)
8. Bring the feed back to just past
the end of the shaft, adjust the
cross feed to 50 and repeat the
process until approximately
0.110” - 0.115” have been
turned.
9. Stop the lathe and measure the
diameter using micrometers.
10.Adjust the cross feed to make
the final cut and proceed to
turn the shaft to its final
0.386” dimension.
56
Lab Procedure – Part B
Procedure: (refer to drawing in appendix B)
11. Move the cutting tool away from the workpiece. Use the steel
file to deburr the edges.
57
Lab Procedure – Part B
Procedure: (refer to drawing in appendix B)
12. Turn off the lathe. Insert opposite end of workpiece into the
chuck.
13. Insert the center drill in the tailstock. Place tailstock near
workpiece and lock into position. Turn on lathe and center
drill a hole in the shaft.
58
Lab Procedure – Part B
Procedure: (refer to drawing in appendix B)
14. Return the tail stock to its starting position. Remove the
center drill and insert the #25 drill. Power on the lathe and
proceed to drill a blind hole approximately 5/8” deep.
59
Lab Procedure – Part B
Procedure: (refer to drawing in appendix B)
15. Stop the lathe, remove the drill and insert the tap guide into the chuck.
Align the #10-32 tap with the hole and the insert the tip of the guide into
the rear of the tap. Create a threaded hole by rotating the tap clockwise.
For every full turn clockwise, rotate the tap about ½ to ¾ of a turn
counterclockwise to remove any chip build-up.
60
Lab Procedure – Part B
Procedure: (refer to drawing in appendix B)
16. Once a hole has been created, remove the shaft from the
collet. Using the arbor press to assemble the shaft into the
bracket.
61
Summary – Machining 1 Lab
This lab preparation material introduced:
• The basic principles of machining operations with focus on
turning, drilling and related operations
• The objectives of and the expected outcomes from the
evaluation of experimental trials
• Calculations required for this lab
• The experimental procedure and equipment used
• A number of pictures to familiarize the students with
equipment, tools, and procedures related to this lab
62
Appendix A – Bracket
Operation
Description
Tool
1
2
3
4
5
6
7
8
Mark hole locations
Center drill (3) hole
Drill thru center hole
Ream center hole
Drill thru (2) outside holes
Counterbore (1) outside hole
Countersink (1) outside hole
Deburr reverse side
Scribe and 6” scale
Center Drill
23/64” Drill
0.375” Reamer
7/32” Drill
#10 Counterbore
#10 Countersink
#10 Countersink
RPM Oil
N/A
900
325
220
650
220
220
220
No
No
Yes
Yes
Yes
Yes
Yes
No
63
Appendix B – Shaft
Operation
Description
Tool
1
2
3
4
5
6
Face until perpendicular
Turn 0.376” x 3/8”
Face until perpendicular
Center drill
Drill 5/8” deep
Tap #10-32 x 1.2 deep
Facing Tool
Turning Tool
Facing Tool
Center Drill
#25 Drill
#10-32 Tap
RPM Oil
900
900
900
900
900
N/A
No
No
No
No
No
Yes
64