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中英文资料外文翻译文献
TRANSFER AND UNIT MACHINE
While the specific intention and
application for transfer and unit machine vary
from
one
machine
type
to
another,
all
forms
of
transfer
and
unit
machine
have
common
benefits.
Here
are
but
a
few
of
the
more
important
benefits
offered
by
TRANSFER AND UNIT MACHINE equipment.
The first benefit offered by all forms
of transfer and unit machine is improved
automation. The operator intervention
related to producing workpieces can be reduced
or eliminated. Many transfer and unit
machine can run unattended during their entire
machining
cycle,
freeing
the
operator
to
do
other
tasks.
This
gives
the
transfer
and
unit
machine
user
several
side
benefits
including
reduced
operator
fatigue,
fewer
mistakes caused by human error, and
consistent and predictable machining time for
each workpiece. Since the machine will
be running under program control, the skill
level
required of the
transfer and unit machine operator
(related to
basic machining
practice)
is
also
reduced
as
compared
to
a
machinist
producing
workpieces
with
conventional machine tools.
The second major benefit of transfer
and unit machine technology is consistent
and
accurate
workpieces.
Today's
transfer
and
unit
machines
boast
almost
unbelievable
accuracy
and
repeatability
specifications.
This
means
that
once
a
program
is
verified,
two,
ten,
or
one
thousand
identical
workpieces
can
be
easily
produced with
precision and consistency.
rd
benefit
offered
by
most
forms
of
transfer
and
unit
machine
tools
is
flexibility. Since these machines are
run from programs, running a different workpiece
is almost as easy as loading a
different program. Once a program has been
verified
and
executed
for
one
production
run,
it
can
be
easily
recalled
the
next
time
the
workpiece is to be run.
This leads to yet another benefit, fast change
over. Since these
machines are very
easy to set up and run, and since programs can be
easily loaded,
they
allow
very
short
setup
time.
This
is
imperative
with
today's
just-in-time
(JIT)
product requirements.
Motion control - the heart of transfer
and unit machine
The most basic
function of any transfer and unit machine is
automatic, precise,
and consistent
motion control. Rather than applying completely
mechanical devices to
cause
motion
as
is
required
on
most
conventional
machine
tools,
transfer
and
unit
machines allow motion control in a
revolutionary manner2. All forms of transfer and
unit
machine
equipment
have
two
or
more
directions
of
motion,
called
axes.
These
axes
can be precisely and automatically positioned
along their lengths of travel. The
two
most
common
axis
types
are
linear
(driven
along
a
straight
path)
and
rotary
(driven along a circular path).
Instead of causing motion by turning
cranks and handwheels as is required on
conventional
machine
tools,
transfer
and
unit
machines
allow
motions
to
be
commanded
through
programmed
commands.
Generally
speaking,
the
motion
type
(rapid, linear, and circular), the axes
to move, the amount of motion and the motion
rate (feedrate) are programmable with
almost all transfer and unit machine tools.
A transfer and unit machine command
executed within the control tells the drive
motor
to
rotate
a
precise
number
of
times.
The
rotation
of
the
drive
motor
in
turn
rotates
the
ball
screw.
And
the
ball
screw
drives
the
linear
axis
(slide).
A
feedback
device (linear
scale) on the slide allows the control to confirm
that the commanded
number of rotations
has taken place3. Refer to fig.1.
Fig.1
Though a
rather crude analogy, the same basic linear motion
can be found on a
common table vise. As
you rotate the vise crank, you rotate a lead screw
that, in turn,
drives the movable jaw
on the vise. By comparison, a linear axis on a
transfer and unit
machine
machine
tool
is
extremely
precise.
The
number
of
revolutions
of
the
axis
drive
motor precisely controls the amount of linear
motion along the axis.
How axis motion
is commanded - understanding coordinate systems
It
would
be
infeasible
for
the
transfer
and
unit
machine
user
to
cause
axis
motion by trying to tell each axis
drive motor how many times to rotate in order to
command
a
given
linear
motion
amount4.
(This
would
be
like
having
to
figure
out
how
many
turns
of
the
handle
on
a
table
vise
will
cause
the
movable
jaw
to
move
exactly one inch!) Instead, all
transfer and unit machine controls allow axis
motion to
be commanded in
a
much simpler and more logical
way
by utilizing some form
of
coordinate system. The two most popular
coordinate systems used with
transfer
and
unit machines are the rectangular
coordinate system and the polar coordinate system.
By far, the more popular of these two
is the rectangular coordinate system.
The program zero point establishes the
point of reference for motion commands
in
a
transfer
and
unit
machine
program.
This
allows
the
programmer
to
specify
movements
from
a
common
location.
If
program
zero
is
chosen
wisely,
usually
coordinates needed
for the program can be taken directly from the
print.
With this technique, if the
programmer wishes the tool to be sent to a
position
one
inch
to
the
right
of
the
program
zero
point,
X1.0
is
commanded.
If
the
programmer wishes the
tool to move to a position one inch above the
program zero
point, Y1.0 is commanded.
The control will automatically determine how many
times
to rotate each axis drive motor
and ball screw to make the axis reach the
commanded
destination point . This lets
the programmer command axis motion in a very
logical
manner. Refer to fig.2, 3.
Fig.2
Fig.3
All
discussions to this point assume that the absolute
mode of programming is
used6.
The
most
common
transfer
and
unit
machine
word
used
to
designate
the
absolute mode is
G90.
In the absolute mode, the end points
for all motions
will be
specified
from
the
program
zero
point.
For
beginners,
this
is
usually
the
best
and
easiest
method
of
specifying
end
points
for
motion
commands.
However,
there
is
another
way of specifying end points for axis motion.
In the incremental mode (commonly
specified by G91), end points for motions
are
specified
from
the
tool's
current
position,
not
from
program
zero.
With
this
method
of
commanding
motion,
the
programmer
must
always
be
asking
far
should
I
move
the
tool?
While
there
are
times
when
the
incremental
mode
can
be
very
helpful, generally speaking, this is the more
cumbersome and difficult method of
specifying motion and beginners should
concentrate on using the absolute mode.
Be
careful
when
making
motion
commands.
Beginners
have
the
tendency
to
think
incrementally.
If
working
in
the
absolute
mode
(as
beginners
should),
the
programmer should always
be asking
This position is relative to
program zero, NOT from the tools current position.
Aside
from
making
it
very
easy
to
determine
the
current
position
for
any
command,
another benefit of working in the absolute mode
has to do with mistakes
made during
motion commands. In the absolute mode, if a motion
mistake is made in
one
command
of
the
program,
only
one
movement
will
be
incorrect.
On
the
other
hand, if a mistake is
made during incremental movements, all motions
from the point
of the mistake will also
be incorrect.
Assigning program zero
Keep in mind that the transfer and unit
machine control must be told the location
of
the
program
zero
point
by
one
means
or
another.
How
this
is
done
varies
dramatically from one transfer and unit
machine and control to another8. One (older)
method is to assign program zero in the
program. With this method, the programmer
tells the control how far it is from
the program zero point to the starting position of
the machine. This
is
commonly done with
a G92 (or
G50) command at least
at
the
beginning of the program and possibly
at the beginning of each tool.
Another,
newer and better way to assign program zero is
through some form of
offset. Refer to
fig.4. Commonly machining center control
manufacturers call offsets
used to
assign program zero fixture offsets. Turning
center manufacturers commonly
call
offsets used to assign program zero for each tool
geometry offsets.
Fig. 4
Flexible manufacturing cells
A
flexible
manufacturing
cell
(FMC)
can
be
considered
as
a
flexible
manufacturing
subsystem. The following differences exist between
the FMC and the
FMS:
1.
An FMC is not
under the direct control of the
central
computer. Instead, instructions from the central
computer are passed to the cell
controller.
2.
The cell is limited in the number of
part families it
can manufacture.
The following elements are normally
found in an FMC:
?
Cell controller
?
Programmable logic controller (PLC)
?
More than one
machine tool
?
A
materials handling device (robot or pallet)
The
FMC
executes
fixed
machining
operations
with
parts
flowing
sequentially
between
operations.
High speed
machining
The term High Speed Machining
(HSM) commonly refers to end milling at high
rotational
speeds
and
high
surface
feeds.
For
instance,
the
routing
of
pockets
in
aluminum airframe sections with a very
high material removal rate1. Over the past 60
years, HSM has been applied to a wide
range of metallic and non-metallic workpiece
materials,
including the
production of
components
with
specific surface
topography
requirements and machining
of materials with hardness of 50 HRC and above.
With
most
steel
components
hardened
to
approximately
32-42
HRC,
machining
options
currently
include:
Rough
machining
and
semi-finishing
of
the
material
in
its
soft
(annealed) condition heat treatment to
achieve the final required hardness = 63 HRC
machining of electrodes and Electrical
Discharge Machining (EDM) of specific parts
of
dies
and
moulds
(specifically
small
radii
and
deep
cavities
with
limited
accessibility
for
metal
cutting
tools)
finishing
and
super-finishing
of
cylindrical/flat/cavity
surfaces
with
appropriate
cemented
carbide,
cermet,
solid
carbide, mixed ceramic
or polycrystalline cubic boron nitride (PCBN)
For many components, the production
process involves a combination of these
options
and
in
the
case
of
dies
and
moulds
it
also
includes
time
consuming
hand
finishing.
Consequently, production costs can be high and
lead times excessive.
It is typical in
the die and mould industry to produce one or just
a few tools of
the same design. The
process involves constant changes to the design,
and because of
these
changes
there
is
also
a
corresponding
need
for
measuring
and
reverse
engineering .
The main criteria is the quality level
of the die or mould regarding dimensional,
geometric and surface accuracy. If the
quality level after machining is poor and if it
cannot meet the requirements, there
will be a varying need of manual finishing work.
This work produces satisfactory surface
accuracy, but it always has a negative impact
on the dimensional and geometric
accuracy.
One of the main aims for the
die and mould industry has been, and still is, to
reduce or eliminate the need for manual
polishing and thus improve the quality and
shorten the production costs and lead
times.
Main economical and technical
factors for the development of HSM
Survival
The
ever
increasing
competition
in
the
marketplace
is
continually
setting
new
standards. The demands
on time and cost efficiency is getting higher and
higher. This
has forced the development
of new processes and production techniques to take
place.
HSM provides hope and
solutions...
Materials
The
development of new, more difficult to machine
materials has underlined the
necessity
to
find
new
machining
solutions.
The
aerospace
industry
has
its
heat
resistant
and
stainless
steel
alloys.
The
automotive
industry
has
different
bimetal
compositions,
Compact Graphite Iron and an ever increasing
volume of aluminum3.
The
die
and
mould
industry
mainly
has
to
face
the
problem
of
machining
high
hardened tool steels, from roughing to
finishing.
Quality
The
demand
for
higher
component
or
product
quality
is
the
result
of
ever
increasing competition. HSM, if applied
correctly, offers a number of solutions in this
area. Substitution of manual finishing
is one example, which is especially important
on dies and moulds or components with a
complex 3D geometry.
Processes
The demands on shorter throughput times
via fewer setups and simplified flows
(logistics) can in most cases, be
solved by HSM. A typical target within the die and
mould industry is to completely machine
fully hardened small sized tools in one setup.
Costly and time consuming EDM processes
can
also
be
reduced or eliminated with
HSM.
Design & development
One of
the main tools in today's competition is to sell
products on the value of novelty.
The
average product life cycle on cars today is 4
years, computers and accessories 1.5
years, hand phones 3 months... One of
the prerequisites of this development of fast
design changes and rapid product
development time is the HSM technique.
Complex products
There is
an increase of
multi-
functional
surfaces on components, such
as new
design
of
turbine
blades
giving
new
and
optimized
functions
and
features.
Earlier
designs allowed
polishing by hand or with robots (manipulators).
Turbine blades with
new, more
sophisticated designs have to be finished via
machining and preferably by
HSM . There
are also more and more examples of thin walled
workpieces that have to
be machined
(medical equipment, electronics, products for
defence, computer parts)
Production
equipment
The
strong
development
of
cutting
materials,
holding
tools,
machine
tools,
controls and especially CAD/CAM
features and equipment, has opened possibilities
that must be met with new production
methods and techniques5.
Definition of
HSM
Salomon's
theory,
with
high
cutting
speeds...
on
which,
in
1931,
took out a German patent, assumes that
than
in
conventional
machining),
the
chip
removal
temperature
at
the
cutting
edge
will start to
decrease...
Given
the
conclusion:
seems
to
give
a
chance
to
improve
productivity
in
machining with conventional tools at
high cutting speeds...
Modern research,
unfortunately, has not been able to verify this
theory totally.
There is a relative
decrease of the temperature at the cutting edge
that starts at certain
cutting speeds
for different materials.
The decrease
is small for steel and cast iron. But larger for
aluminum and other
non-ferrous metals.
The definition of HSM must be based on other
factors.
Given
today's
technology,
speed
is
generally
accepted
to
mean
surface
speeds between 1 and 10 kilometers per
minute or roughly 3 300 to 33 000 feet per
minute. Speeds above 10 km/min are in
the ultra-high speed category, and are largely
the realm of experimental metal
cutting. Obviously, the spindle rotations required
to
achieve these surface cutting speeds
are directly related to the diameter of the tools
being
used.
One
trend
which
is
very
evident
today
is
the
use
of
very
large
cutter
diameters for these applications - and
this has important implications for tool design.
There are many opinions, many myths and
many different ways to define HSM.
Maintenance and troubleshooting
Maintenance for a horizontal MC
The
following
is
a
list
of
required
regular
maintenance
for
a
Horizontal
Machining Center
as shown in fig.5. Listed are the frequency of
service, capacities,
and type of fluids
required. These required specifications must be
followed in order to
keep your machine
in good working order and protect your warranty.
fig. 5
Daily
Top
off
coolant
level
every
eight
hour
shift
(especially
during
heavy
TSC
usage).
Check way lube
lubrication tank level.
Clean chips
from way covers and bottom pan.
Clean chips from tool changer.
Wipe spindle taper with a clean cloth
rag and apply light oil.
Weekly
?
Check for
proper operation of auto drain on filter
regulator.
On machines with
the TSC option, clean the chip basket on the
coolant tank.
Remove the tank cover and
remove any sediment inside the tank. Be careful to
disconnect the coolant pump from the
controller and POWER OFF the control before
working on the coolant tank . Do this
monthly for machines without the TSC option.
Check air gauge/regulator for 85 psi.
For
machines
with
the
TSC
option,
place
a
dab
of
grease
on
the
V-flange
of
tools. Do this monthly for machines
without the TSC option.
Clean exterior
surfaces with mild cleaner. DO NOT use solvents.
Check
the
hydraulic
counterbalance
pressure
according
to
the
machine's
specifications.
Place a dab
of grease on the outside edge of the fingers of
the tool changer and
run through all
tools
Monthly
Check oil level
in gearbox. Add oil until oil begins dripping from
over flow tube
at bottom of sump tank.
Clean pads on bottom of pallets.
Clean
the
locating
pads
on
the
A-axis
and
the
load
station.
This
requires
removing the pallet.
?
Inspect
way
covers
for
proper
operation
and
lubricate
with
light
oil,
if
necessary.
Six
months
Replace coolant and thoroughly
clean the coolant tank.
Check all hoses
and lubrication lines for cracking.
Annually
?
Replace the gearbox oil. Drain the oil
from the gearbox, and slowly refill it
with 2 quarts of Mobil DTE 25 oil.
?
Check oil
filter and clean out residue at bottom for the
lubrication chart.
Replace air filter
on control box every 2 years.
Mineral
cutting
oils
will
damage
rubber
based
components
throughout
the
machine.
Troubleshooting
This section is intended for use in
determining the solution to a known problem.
Solutions given are intended to
give the individual servicing the
TRANSFER AND
UNIT MACHINE a pattern to
follow in, first, determining the problem's source
and,
second, solving the problem.
Use common sense
Many
problems
are
easily
overcome
by
correctly
evaluating
the
situation.
All
machine operations are composed of a
program, tools, and tooling. You must look at
all three before blaming one as the
fault area. If a bored hole is chattering because
of
an overextended boring bar, don't
expect the machine to correct the fault.
Don't
suspect
machine
accuracy
if
the
vise
bends
the
part.
Don't
claim
hole
mis-positioning if you don't first
center-drill the hole.
Find the problem
first