Transcript Document

Advanced
Manufacturing
Choices
ENG 165-265
Spring 2015, Dr. Marc Madou
Class 2 Manufacturing Types and
Mechanical Machining
7/18/2015
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Table of Content
• Manufacturing types: Primary, secondary and
tertiary manufacturing
• Mechanical machining definition
• Recognized categories of mechanical machining:
turning, milling, drilling and grinding.
• CNC machining
• Precision machining
• Ultra-precision machining and nanotechnology
• Desk top factories (DTFs)
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Manufacturing Types
• Manufacturing dominates world trade. It is the main wealth
creating activity of all industrialized nations and many
developing nations. A manufacturing industry based on
advanced technologies with the capability of competing in
world markets can ensure a higher standard of living for an
industrial nation (McKeown, 1996).
• Where primary manufacturing processes involve casting* and
molding**, secondary manufacturing processes constitute the
main mechanical removing techniques involving turning,
drilling and milling. Abrasive processes to super-finish a workpiece are called tertiary manufacturing processes.
Casting*/molding**: The act or process of making casts or impressions, or of shaping
metal or plaster in a mold; the act or the process of pouring molten metal into a
mold.
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Manufacturing Types
• The difference between casting and
molding is that in "traditional"
casting processes, the mold is
destroyed/ consumed when
removing the work-piece from it
while in molding, the mold is reused multiple times (this difference
is not often respected in naming
different processes).
• Lost wax casting process: see video
• Sand casting: see utube
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Mechanical Machining
• In mechanical removal processes, stresses induced by
a tool overcome the strength of the material.
• The process produces complex 3D shapes, with very
good dimensional control, and good surface finishes.
• The method is wasteful of material, and expensive in
terms of labor and capital.
• How well a part made from a given material holds its
shape with time and stress is referred to as the
dimensional stability of the part and the material.
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Mechanical Machining
• To maximize dimensional stability, the machine design engineer
tries to minimize the ratios of applied and residual stress
(residual stresses are stresses that remain in a solid material
after the original cause of the stresses has been removed) to
yield strength of the material.
• A good rule of thumb is to keep the static stress* below 10 to
20% of yield strength.
• Increased heat at the work-piece causes uneven dimensional
changes in the part being machined, making it difficult to
control its dimensional accuracy and tolerances. Thermal errors
are often the dominant type of error in a precision machine, and
thermal characteristics such as thermal expansion coefficient
and thermal conductivity deserve special attention.
* A stress in which the force is constant or slowly increasing with time. A test of failure without shock is an example of
static stress.
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Mechanical Machining
• In mechanical subtractive machining, physical removal of
unwanted material is achieved by mechanical energy applied at
the work piece.
• Mechanical material removing technologies are also categorized
as single point machining or abrasive machining i.e., multipoint machining.
• Mechanical removal processes can be broken down into four
commonly recognized categories: turning, milling, drilling and
grinding.
First lathe as depicted in an Egyptian
bas relief; about 300 B.C. Shown here
in a line drawing is turning. The man at left is
holding the cutting tool. The man at the
right is making the workpiece rotate back
and forth by pulling on a cord or thong.
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Mechanical Energy Based Removing
• What is milling? The use of a rotating multi-point cutting tool to
machine flat surfaces, slots, or internal recesses into a work-piece.
• Milling is one of the more versatile machining processes. There are
three degrees of freedom associated with milling. The tool can move
up and down, left to right, and front to back. In this process the tool
spins while the part remains stationary. Although milling is a more
versatile process than turning or grinding, it is not as accurate and
tends to leave a rougher surface finish than the other two processes.
• What is turning ? Turning is the machining operation that produces
cylindrical parts. In its basic form, it can be defined as the machining
of an external surface with the work-piece rotating and with a singlepoint cutting tool.
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Mechanical Energy Based Removing
• The main difference between turning and milling is that in
turning the work-piece spins while the tool remains stationary.
Because of this, turning can be used to create a great surface
finish on cylindrical parts (also single point vs multiple point).
• Turning is done on a machine called a lathe. The lathe spins
the workpiece, while the lathe operator can position the tool to
remove the material. The work-piece is held in the chucks of
the lathe.
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Mechanical Energy Based Removing
• Drilling can be defined as a rotary
end cutting tool having one or
more cutting lips, and having one
or more helical or straight flutes for
the passage of chips and the
admission of a cutting fluid. Could
also be boring (it often is).
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Mechanical Energy Based Removing
• Grinding is a finishing process that is used to remove
surplus material from the work-piece surface. It is
usually used on almost any surface that has been
previously rough machined and is among the most
expensive process for it is generally quite slow in
removing material.
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Mechanical Energy Based Removing
• Numerical control is a method of automatically
operating a manufacturing machine based on a code
of letters, numbers, and special characters.
• By 1977, highly precise instruments such as
servomotors, feedback devices, and computers were
implemented, paving the way for computer numerical
control machining, commonly called CNC machining,
which is now standard in many types of machine
shops. At the start, the smallest movement these
machines could reproducibly make was 0.5 µm.
• The resolution of the steps a machine can make, of
course, is a determining factor for the manufacturing
accuracy of the work-piece.
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Mechanical Energy Based Removing
• Point-to-point control systems cause the tool to
move to a point on the part and execute an
operation at that point only. The tool is not in
continuous contact with the part while it is moving.
• Continuous-path controllers cause the tool to
maintain continuous contact with the part as the
tool cuts a contour shape.
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Mechanical Energy Based Removing
• These
continuous
operations
include
milling along any lines
at any angle, milling
arcs and lathe turning.
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Mechanical Energy Based Removing
• CNC milling machines
can
perform
simultaneous
linear
motion along the three
axis and are called
three-axes machines.
• More complex CNC
machines
have
the
capability of executing
additional
rotary
motions (4th and 5th
axes).
Vertical
milling
machine
Right hand
rule
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Mechanical Energy Based Removing
• Machining Centers, equipped with automatic tool
changers, are capable of changing 90 or more tools.
Can perform milling, drilling,boring* , turning, … on
many faces. * Boring is the process of using a single-point
tool to enlarge a preexisting hole.
• Process flow (see practicum):
▫ Develop or obtain the 3D geometric model of the part,
using CAD.
▫ Decide which machining operations and cutter-path
directions are required (computer assisted).
▫ Choose the tooling required (computer assisted).
▫ Run CAM software to generate the CNC part program.
▫ Verify and edit program.
▫ Download the part program to the appropriate machine.
▫ Verify the program on the actual machine and edit if
necessary. Run the program and produce the part.
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Mechanical Energy Based Removing
• In an integrated CAD/CAM
system, the geometry and
tool motions are derived
automatically from the CAD
database by the NC program
(Pro/E, Unigraphics, ….)
CNC milling is a cutting process in which material is removed
from a block of material by a rotating tool using a computer
numerically controlled program or code to achieve a desired
tool path to machine very accurate parts precisely and efficiently.
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Precision Machining
• Mechanical engineers define precision machining as machining in
which the relative accuracy (tolerance/object size) is 10–4 or less of a
feature/part size
• For comparison, a relative accuracy of 10–3 in the construction of a
house is considered excellent. It is important to realize that, while IC
techniques and silicon micro- and nano-machining can achieve
excellent absolute tolerances, relative tolerances here are rather poor
compared to those achieved by most mechanical machining
techniques.
• The decrease in manufacturing accuracy with decreasing size is rarely
mentioned in discussions of Si micro-machines; this probably is
because Si micromachining originated from electrical engineering
practice rather than mechanical engineering.
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Precision Machining
• In the 1980s advanced machine tools became equipped with
precision metrology and control tools. These machines used
laser interferometer and capacitance probe feedback controls,
temperature control and hydrostatic bearings, and featured
accuracies better than 0.1 micrometers. Precision
manufacturing methods were extended for industrial use for
cutting aluminum, which was used for making components for
scanners, photocopying machines and computer memory disks.
Also in the 1980s, cutting with very small diamond tools (e.g.,
22 µm diameter) was developed in Japan.
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Ultra Precision Machining-Nanotechnology
• Taniguchi coined the term
nanotechnology and in 1974, used
the term to define ultra-precision
machining.
• Taniguchi defines ultra-precision
machining as “the process by which
the highest possible dimensional
accuracy is achieved at a given
point in time.”
• Norio Taniguchi predicted
accuracies along with the processes
or tools used to achieve it (next
page)
Norio Taniguchi (谷口紀男) (27 May 1912 - 15 November 1999)
was a professor of Tokyo Science University.
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Precision and ultra-precision machining
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Ultra Precision MachiningNanotechnology
• By 1993, 0.05 µm became possible,
and today there is equipment available
featuring 0.01 µm and even nanometer
step resolution
(http://www.fanuc.co.jp/eindex.htm).
• This evolution closely follows the
predictions sketched in the Taniguchi
curves showing a machining accuracy
for ultra-precision machining of subnanometer resolution for the year
2008 (see previous slide) .
• Fanuc’s the ROBOnano Ui an ultraprecision micromachining station (cost
1 $ million) and a Noh mask made
with this machine
(http://www.fanuc.co.jp/en/product/r
obonano/index.htm).
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Desk top factory
• The fact that it often takes a
two-ton machine tool to
fabricate micro parts, where
cutting forces are in the
milli- to micro-Newton
range is a clear indication
that a complete machine tool
redesign is required for the
fabrication of micromachines.
• One approach is the desktop factory.
Commercial desktop factories (DTFs) at Sankyo Seiki.
Desk top factory
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• Desktop factories (DTF) constitute a rather interesting new manufacturing
philosophy involving flexible and modular table-top-sized automated
factories that feature minimal human participation in the manufacturing
process.
• An example of such a factory is shown below. Since the early nineties
progress has been made towards making such desktop factories (DTF) a
reality. A desktop factory as shown here has the potential of becoming the
factory of the future: a totally self-contained, robotic, desktop-size machine
tool that only requires materials, power and water as outside inputs, and out
come the finished machined products. The first R&D desktop factories
incorporated lathes, cleaning, gluing, punching and drilling stations. The
workpiece is transported between these different machining functions by a
“cart” moving from station to station.
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Desk top factory
• An example of a
desktop factory at
AIST, Japan.