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Technology at Work Feature
Making Prototypes
By Laser
Story and Photos by
Julian Edgar
Apart from the "flip top" cranium, this is an
absolutely perfect replica of the skull of a real, live
person – down to the tiniest detail and blemish.
No moulds, no artists and, as the magicians say,
10 S
C
it's
all done
with mirrors!
ilicon
hip
The skull opposite was crafted by lasers, using information derived from
a medical “CAT” scan. It is an example of the amazing work carried
on by the South Australian Centre for Manufacturing. What they can
produce borders on fantastic – in the truest sense of the word!
A key requirement of manufacturing
industry is the development of working prototypes, before expensive investment is made in the final machine
tools and metal moulds.
The South Australia Centre for
Manufacturing uses two laser-based
machines to develop prototypes in
either plastic or laminated paper.
Both use carbon dioxide (CO2)
lasers and sophisticated drive mechanisms to form the objects, layer by
layer.
Companies employed in activities
as diverse as manufacturing power
tools, cars and white goods use the
processes, while the Royal Adelaide
Hospital Cranio-Facial Unit has also
developed skull models using the
techniques.
The Sinterstation 2000
With a process called Selective Laser Sintering (SLS) the Sinterstation
produces prototypes using the heat
generated by a CO2 laser to fuse powdered material together, layer by layer.
Fig.1 shows a diagram of the SLS
process.
The object is formed in a chamber
heated to approximately 180-190 degrees Celsius - just below the melting
The Sinterstation 2000 uses the action of a laser on Nylon powder to produce
functional plastic prototypes.
point of the Nylon powder usually
employed. A thin layer of heat-fusible powder is distributed across the
Fig.1: The Selective Laser Sintering process develops 3-dimensional objects by
using a laser to fuse powder, one cross-sectional layer at a time.
workspace by the action of a roller,
with the layer of powder generally
0.1mm thick.
The system’s software uses CAD
drawings to produce a series of a
cross-sectional slices of the component to be built and the heat-generating
laser traces these slices, one by one, on
successive layers of the powder. The
Laminated Object Manufacturing
can also be used to produce small
parts. This adjustable spanner was
formed by the machine, including the
adjustment thread formed in situ!
September 1996 11
The Selective Laser Sintering process
can produce very complex shapes.
This is the base of the relay box from
the yet-to-be-released Holden VT
Commodore. Four of these parts were
produced simultaneously, actually
standing on their ends.
This whistle – incredibly, complete
with internal ball –was produced on
the SLS machine.
movement of the laser is controlled
by scanning mirrors, which in turn
are controlled by the system’s dedicated PC.
The powder on which of the laser
falls is heated to the point of sintering,
fusing the powder particles and forming a solid mass. The unfused powder
remains in place. The working surface
then drops by about 0.1mm and the
roller distributes another layer of
powder across it. The laser traces out
the next cross-section of the object,
with this sintered layer fusing to the
one beneath.
And so it goes on with layer after
layer being formed.
The object is produced at a vertical rate of about 10mm per hour,
with the exact rate dependent on the
cross-sectional area of the object being
formed. When the process is complete
the chamber is allowed to cool, the
workspace container is removed and
the unsintered powder is then brushed
away to reveal the part(s).
Because of the way in which the part
is formed, extremely complex shapes
with thin walls can be developed. For
example, a referee’s whistle –complete
with internal ball – can be made,
with the ball developed in situ! As
long as there is an opening through
which the unsintered powder can be
removed, parts can be formed inside
other objects.
In addition to various grades of Nylon, materials such as polycarbonate
and proprietary casting compounds
can be used. The quality of the object’s
surface finish is dependent on the
thickness of powder layers used and
the material used but it is generally
slightly rough to the touch.
Post-production sanding and waxing can be used to give an extremely
smooth finish if required.
In addition to the speed of production, the greatest advantage of the
process is that the prototypes can be
functional. Flexible Nylon hinges and
click joins can be incorporated and
components with sufficient strength
to be tested in actual operating conditions can be produced.
Fan blades produced by this technique, for example, can be assessed
for flow properties, noise and vibration.
The data input required is a 3-dimensional CAD drawing of the object
in the form of an industry standard
binary STL or IGES 5.1 text file, or
Computervision CADDS 5 part database. Factors such as scaling, feed rates
of the powder, temperature and so on
are adjusted to suit the individual parts
being produced.
The Sinterstation 2000 cost $600,000
when purchased in 1993 and it has
been working almost continuously
since then. The manufacturer of the
The capability of the SLS process to
produce functional prototypes can be
seen here. This fan was assessed for
flow properties, noise and vibration
after it was produced.
Part of a rear view mirror adjustment
mechanism, produced for a
manufacturer of automotive rear
vision systems. From this, the moulds
for castings can be directly made.
12 Silicon Chip
Fig. 2: The Laminated Object Manufacturing uses adhesive-coated paper. The
laser cuts out the cross-sectional slices of the object, with a heated roller fusing
the paper layers together.
machine is DTM Corporation, based
in Austin, Texas. The company was
formed specifically to commercialise
Selective Laser Sintering, with the
patent for the SLS process held by the
University of Texas.
Laminated Object
Manufacturing
The other prototype manufacturing
machine used by the Centre produces
objects larger than those made in the
Sinterstation 2000. Laminated Object
Manufacturing (LOM) can also rapidly
produce complex shaped parts by the
action of a computer-controlled laser
but instead of using plastic powder,
adhesive-backed paper is used as the
raw material.
Fig.2 shows the LOM system. The
adhesive-backed paper is fed from a
continuous roll across the working
surface. A heated roller then passes
across the paper, melting the adhesive
and bonding the paper to the layer
below.
In much the same way as the SLS
system, the laser then traces that particular cross-section of the object onto
the paper - however in this system the
laser cuts the paper rather than fusing
it. Where there is excess paper the
laser crosshatches it, allowing later
removal.
The build platform then descends
and the process is repeated, with the
object again being formed layer by
layer. Once all the layers have been
laminated and cut, the cubes of crosshatched material are removed and the
finished object is revealed. The end
result has the appearance and characteristics of laminated wood.
One of the advantages of the LOM
process over other prototype development approaches is that the LOM object can be used in investment casting.
Investment casting - once called “lost
wax” casting - uses the LOM object as
the plug in a mould.
There are seven processes in turning
a LOM object into a metal casting.
Once the LOM object has been made,
wax channels to feed molten metal
to various parts of the casting are
attached to the object. The assembly
is then dipped in alternating layers of
ceramic slurry and fine sand, until a
thick coating has been added.
The coated object is fired in a furnace, hardening the ceramic and at
the same time burning away the LOM
plug, which after all, is made only of
paper!
The residual ash is removed and
then metal is poured into what has
now become a mould. The ceramic
coating is removed, excess metal
from the feed channels cut off and the
newly-created metal object is ready
for final finishing. The cast object can
then be pressed into prototype service,
Laminated Object Manufacturing uses
the action of a laser to cut out the
cross-sectional shape of the part in
a sheet of special paper, here cutting
out the shape of a transmission bellhousing. Note the smoke released
when the laser cuts the paper. Areas
of material which will later be
removed are crosshatched.
Removing the laminated object from
its ‘block’ is done by hand, with
crosshatched surplus material pulled
out.
The end result: automotive
transmission manufacturer BTR
Engineering is using the LOM process
to form one-off bellhousing adaptors,
allowing the attachment of their
transmissions to a variety of engines
for testing and evaluation purposes.
The bellhousing on the right of the
above photo is one cast from the LOM
processed prototype on the left.
Another example of investment moulding using the LOM process, where LOM
objects become the plug for investment casting moulds. The LOM form is burnt
away after it is has been coated with a hard ceramic layer. The casting of
metals into the resulting mould can then be easily carried out.
A close-up of the LOM bellhousing
shows the ‘laminated wood’
appearance of the finished prototype.
An object like this costs around $8000
and takes 40 hours to produce.
September 1996 13
VISIT OUR WEB SITE
OUR COMPLETE CATALOGUE IS ON OUR SITE.
A “STOP PRESS” SECTION LISTS NEW AND LIMITED
PRODUCTS AND SPECIALS. VISIT:
https://www.oatleyelectronics.com/
SWITCHED MODE POWER SUPPLY:Compact
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case, 240V AC in, 12V DC/2A and 5VDC/5A out: $17
...HP POWER SUPPLIES: Compact (120X70X30mm)
HP switched mode, power in plastic case, 100-240V
AC input, 10.6V/1.32A DC output, slightly soiled: $14
...LASER MODULE: Very bright (650nM/5mW) focusable module, suit many industrial applications,
bright enough for a disco laser light show, good
results with the Automatic Laser Light Show: $75
...AUTOMATIC LASER LIGHT SHOW KIT: 3 motors,
mirrors plus PCB and comp. kit, has laser diode reg.
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mode power supply, produces many different patterns, can be used with the laser module: $70
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diode: $65 ... LEDS SUPER PRICES, INCLUDING A
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flashing LEDS: $1.50 Ea. or 10 for $10 ... PHOTOTRANSISTORS: Enclosed in clear 5mm housing
similar to the 5mm LEDS, 30V/3uS/<100nA dark
current: $1.30 or 10 for $9 ...CONSTANT VOLTAGE
DIODES: 1.52-1.66V <at> 10uA: 10 for $7 ...MASTHEAD AMPLIFIER PLUS PLUGPACK SPECIAL: Our
famous MAR-6 based masthead amplifier plus a
suitable plupack to power it: $20, Waterproof box:
$2.50, bottom box:$2.50 ...17mm MAGNIFIERS:
Made in JAPAN by Micro Design these eyepiece style
metal enclosed magnifiers will see the grain of most
papers, used, limited qty.: $4 Ea. ...HF BALLASTS:
Single tube 36W Dimmable high frequency ballasts:
$18 Ea. ...12V SLA BATTERY CHARGERS: INTELLIGENT “PLUGPACK” 240V-12V GEL BATTERY
CHARGERS, 13.8V / 650mA, proper “switching”
design with LED status indicator: $8.80 ...LASER
POINTER KIT: A special purchase of some
660nM/5mW laser diode means that we can reduce
the price of our Laser Pointer kit, includes everything
except the batteries: $29 ...SPECIAL BATTERY AND
CHARGER OFFER: When our 7AHr/12V SLA battery
($30) is bought with the SLA battery charger the
total price for both is: $33 ...USED BRUSHLESS DC
FANS: 4"/12V/0.25A: $8, 24V/6"/17W: $12
...100,000uF ELECTROLYTIC CAPACITORS:
30V/40Vsurge, used but in exc. cond.:$10 ...12Hr.
MECHANICAL TIMERS: 55X48X40mm, 5mm shaft
(Knob not supplied), two hours timing per 45deg.
rotation, two 25V/16A SPST switches which close at
the end of the timing period: $5 ...USED IEC LEADS:
Used Australian IEC leads: $2.50 ...STANDARD
PIEZO TWEETERS: Square, 85X85mm, 4-40KHz, 35V
RMS: $8, Wide dispersion, 67X143mm, 3-30KHz,
35V RMS: $9 ...COMPUTER POWER SUPPLY:
Standard large supply as used in large computer
towers, +5V/22A, +12V/8.5A, -5V/0.5A, -12V/0.5A,
used but in excellent condition, guaranteed: $30
...MAGNIFIERS: Small eyepiece: $3, 30mm Loupe:
$8, 75mm Loupe: $12, 110mm Loupe: $15, a set of
one of each of these magnifiers (4): $30 ... NEW
NICAD BATTERY BARGAIN: 6 PACK (7.2V) OF 1.2V
/ 800 mAHr. AA NICAD BATT’s plus 1 X thermal switch,
easy to seperate: $4 per pack or 5 packs for $16,
FLAT RECTANGULAR 1.2V, 400mAh NI-CAD BATTERIES with thermal switch, easy to seperate, (Each
batt: 48x17x6 mm): $4 per pack or 5 packs for $16
...UV MONEY DETECTOR: Small complete unit with
cold cathode UV tube, works from 2 X AA batteries
( Not supplied), Inverter used can dimly light a 4W
white fluoro tube: $5Ea. or 5 for $19 ...MISCELLANEOUS USED LENS ASSEMBLIES: Unusual lens
assemblies out of industrial equipment: 3 for $22
...USED PIR MOVEMENT DETECTORS: Commercial
quality 10-15M range, used but tested and guaranteed, have O/C transistor (BD139) output and a
tamper switch, 12V operation, circuit provided: $10
Ea. or 4 for $32 ...CCD CAMERA WITH BONUS: Tiny
(32X32X27mm) CCD camera, 0.1lux, IR responsive
(Works in total dark with IR illumination), connects
to any standard video input (Eg VCR) or via a modulator to aerial input: $125, BONUS: With each
camera you can buy the following at reduced prices:
COMMERCIAL UHF TRANSMITTER for $15 (Normally $25), IR ILLUMINATOR KIT with 42 X 880nM LED’s
for $25 (Normally $35), REGULATED 10.4V PLUGPACK for $10 (Normally $25) ...PIR CASE FOR CCD
CAMERA: Used PIR cases of normal appearance, use
to hide the CCD camera, plenty of room inside: $2.50
Ea. or 4 for $8 ...CAMERA-TIME LAPSE VCR RECORDING SYSTEM: Includes PIR movement detector and interface control kit, plus a learning remote
control, combination can trigger any VCR to start
recording with movement and stop recording a few
minutes after the last movement has stops: $90
...GEIGER COUNTER KIT: Based on a Russian tube,
has traditional “click” to indicate each count. Kit includes PCB, all on-board components, a speaker and
Yes, the geiger counter tube is included: $30 ...RARE
EARTH MAGNETS: Very strong! 7X3mm $2, 10X3mm
$4, Torroidal 50mm outer, 35mm inner, 5mm thick:
$10 ...IR TESTER: Kit includes a blemished IR
converter tube as used in night vision and an EHT
power supply kit, excellent for seeing IR sources,
price depends on blemishes: $30 / $40 ...ARGON-ION
HEADS: Used Argon-Ion heads with 30-100mW
output in the blue-green spectrum, power supply
circuit provided, size: 350X160X160mm, weight 6Kg,
needs 1KW transformer available elsewhere for about
$170, head only for: $350 ...DIGITAL RECORDING
MODULES: Small digital voice recording modules as
used in greeting cards, microphone and a speaker
included, 6 sec. recording time: $9 ...WIRED IR
REPEATER KIT: Extend the range of existing IR remote
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other rooms: $18 ...12V-2.5W SOLAR PANEL KIT:
US amorphous glass solar panels, 305X228mm, Vo-c
18-20V, Is/c 200mA: $22 Ea. or 4 for $70 ...MIDI
KEYBOARDS: Quality midi keyboard with 49 keys, 2
digit LED display, MIDI out jack, Size: 655115X35mm,
computer software included, see review in Feb. 97
EA: $80, 9V DC plugpack: $10, also available is a
larger model which has mor features and has touch
sensitive response keys: $200 ...STEREO FM TRANSMITTER KIT: 88-108MHz, 6-12V DC supply, 8mA <at>
9V, 25X65mm PCB size, PCB plus all on-board
comp’s, plus battery connector and 2 electret mic’s:
$25, plastic case to suit: $4 ...WOOFER STOPPER
KIT: Stop that dog bark, also works on most animals,
refer SC Feb. 96, Kit includes PCB and all on board
comp’s, wound transformer, electret mic., and a horn
piezo tweeter: $39, extra horn piezo tweeters (drives
up to 4) $6 Ea. ...ALCOHOL BREATH TESTER KIT:
Based on a thick film alcohol sensor. The kit includes
a PCB, all on board comp’s and a meter : $30 ...CENTRAL LOCKING KIT (NEW): A complete central
locking kit for a vehicle. The kit is of good quality and
actuators are well made, the kit includes 4 actuators,
electronic control box, wiring harness, screws, nuts,
and other mechanical parts: $60, The actuators only:
$9 Ea. ...CODE HOPPING UHF CENTRAL LOCKING
KIT PLUS A ONE CHANNEL UHF REMOTE CONTROL:
Similar to above but this one is wireless, includes
code hoping Tx’s with two buttons (Lock-unlock), an
extra relay in the receiver can be used to immobilise
the engine, etc., kit includes 4 actuators, control box,
two Tx’s, wiring harness, screws, nuts, and other
mechanical parts: $109 ...ELECTROCARDIOGRAM
PCB + DISK: The software disk and a silk screened
and solder masked PCB (PCB size: 105 x 53mm) for
the ECG kit published in EA July 95. No further
components supplied: $10 ...SECURE IR SWITCH:
IR remote controlled switch, both Rx and Tx have
Dip switches for coding, kit includes commercial 1
Tx, Rx PCB and parts to operate a relay (not supplied):
$22 8A/4KV relay $3 ...FLUORESCENT TAPE: High
quality Mitsubishi brand all weather 50mm wide Red
reflective tape with self adhesive backing: 3 meters
for $5 ...LOW COST IR ILLUMINATOR: Illuminates
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varied using a trimpot., operates from 10 to 15V,
current is 5-600mA ...IR LASER DIODE KIT: Barely
visible 780nM/5mW (Sharp LT026) laser diode plus
constant current driver kit plus collimator lens plus
housing plus a suitable detector Pin diode, for medical use, perimeter protection, data transmission,
experimentation: $32 ...WIRELESS IR EXTENDER:
Converts the output from any IR remote control into
a UHF transmission, Tx is self contained and attaches with Velcro strap under the IR transmitter, receiver has 2 IR Led’s and is place near the appliance
being controlled, kit includes two PCB’s all components, two plastic boxes, Velcro strap, 9V transmitter
battery is not supplied: $35, suitable plugpack for
the receiver: $10 ...NEW - LOW COST 2 CHANNEL
UHF REMOTE CONTROL: Two channel encoded UHF
remote control has a small keyring style assembled
transmitter, kit receiver has 5A relay contact output,
can be arranged for toggle or momentary operation:
$35 for one Tx and one Rx, additional Tx’s $12 Ea.
OATLEY ELECTRONICS
PO Box 89
Oatley NSW 2223
Phone (02) 9584 3563
Fax (02) 9584 3561
orders by e-mail:
branko<at>oatleyelectronics.com
major cards with phone and fax orders,
P&P typically $6.
with any required changes easily made
before final tooling is prepared.
An example of this approach has
been taken by automotive parts manufacturer BTR Engineering, who has
used the LOM investment casting
process to make unique bell housings
so that their transmissions can be
test-fitted to various cars.
LOM objects can also be used in
other casting techniques, involving
not just metals but also plastics and
silicone rubber.
The Laminated Object Manufacturing machine is produced by Helisys,
Inc, a Torrance, California-based
company.
Three-Dimensional Scanning
Both the SLS and LOM systems
require the input of precise CAD
data before development of an object
can occur. However, in the case of a
prototype developed from modelling
clay, for example, no such drawings
will exist.
A device called a Digibot II scanner
is used to develop this data.
The Centre’s Digibot II acquires the
x, y, z coordinates of complex shaped
objects by shining a point of laser
light at the object and detecting the
reflection of the light with traversing
sensors. Trigonometrical calculations
are then carried out within the Digibot
software to determine the distance
from the light source to the point on
the object’s surface.
Objects containing undercuts,
concavities and split contours do not
cause the system any problems and
because of the non-contact sensing
system, even soft objects can be reliably scanned.
In addition to the industrial applications of the machine, other uses
include the scanning of internal
ear models for the custom fitting
of hearing aids and the scanning of
fragile artefacts or fossils to enable the
production of durable replacements
for display.
The system can produce quite large
objects, limited only by the available
workspace; up to 460mm in diameter
sc
and 460mm high.
Contact: Jeff Groves, Manager,
Advance Manufacturing
Facility,
South Australian
Centre for Manufacturing.
Phone: 08 300 1500
Fax:
08 347 1033
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September 1996 15
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