TRINSEO ACRYSPA Machine User Guide
- September 18, 2024
- TRINSEO
Table of Contents
ACRYSPA Machine
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Specifications:
- Brand: ACRYSPA
- Product Type: Acrylic Sheet
- Language: English
- Manufacturer: 2024 Global
- Websites: aristechsurfaces.com,
trinseo.com
Product Usage Instructions:
1. Fabrication and Finishing
1.1 Machining
ACRYSPA Acrylic Sheets can be machined using woodworking shapers
and routers for edge finishing and cutting thermoformed parts.
High-speed steel drills with modified cutting edges are recommended
for drilling.
1.2 Routing and Shaping
Woodworking shapers and routers are used for edge finishing
operations. Portable routers are suitable for large or awkward
parts.
1.3 Drilling
For drilling, use modified high-speed steel twist drills with
slow spirals and wide polished flutes. Back up the surface with
wood when drilling through a second surface for accuracy and
safety.
1.4 Cutting
Power saws are recommended for cutting ACRYSPA Acrylic Sheets.
Avoid cold punching or shearing as they may cause material
fracture. Circular saws are ideal for straight cuts, while jig saws
and saber saws are suitable for small radii curves.
FAQ:
Q: What is the recommended method for cutting thin ACRYSPA
Acrylic Sheets?
A: It is advantageous to cut thin material at an elevated
temperature using rule and blanking dies. Avoid cold punching or
shearing as they may cause material fracture.
Q: Can I use standard twist drills for drilling ACRYSPA Acrylic
Sheets?
A: Yes, standard twist drills with modified cutting edges are
recommended for drilling ACRYSPA Acrylic Sheets. Ensure you back up
the surface with wood when drilling through a second surface for
accuracy and safety.
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ACRYSPATM FORMING AND FABRICATION GUIDE | 1
ACRYSPATM
Forming and Fabrication Guide
2024 Global | English Connecting ideas with solutions
aristechsurfaces.com trinseo.com
Contents
Fabrication and Finishing 1.1 Machining
3 3
1.2 Routing and Shaping
3
1.3 Drilling
3
1.4 Cutting
4
1.5 Laser Cutting and Engraving
5
1.6 Finishing
6
1.7 Sanding
6
1.8 Buffing and Polishing
7
1.9 Flame Polishing
7
2. Cementing 2.1 Prevention of Internal Stresses
8 8
2.2 Joint Preparation
8
2.3 Safety Precautions
8
2.4 Types of Cement
8
2.5 Cementing Techniques
9
2.6 Venting
10
2.7 Filling Voids
10
2.8 Clamping
10
2.9 Polishing or Machining
10
2.10 Cementing ACRYSPATM Acrylic Sheet
to Other Materials
10
3. Annealing
11
4. Thermoforming 4.1 Thermoforming Temperatures and Cycles
12 13
4.2 Heating Equipment
14
4.3 Bending
15
4.4 Three-Dimensional Forming
15
4.5 Molds
17
4.6 Thermoforming with Polyethylene Film
19
ACRYSPATM FORMING AND FABRICATION GUIDE | 3
1. Fabrication and Finishing
1.1 Machining
The usual rules of good machining practice apply to the machining of ACRYSPATM
Acrylic Sheet. An experienced machinist will have no difficulty handling the
materials as its working properties are similar to those of brass, copper, and
fine woods. Tools should be held firmly to prevent chattering. Standard metal
or wood working equipment can be used: such as, milling machines, drill
presses, lathes, planers, and shapers. In general, machine tools should be
operated at high speeds with slow feed rates, ACRYSPATM Acrylic Sheet being a
thermoplastic material, softens when heated to its forming temperature of 320
to 380°F (160 to 195°C). The frictional heat generated by machining tends to
soften the acrylic in the immediate vicinity of the cut and can cause gumming
and sticking of the tool, unless proper speed, feed rate, and cutters are
used. Properly machined surfaces will have an even, semi-matte surface that
can be brought to high polish by sanding and buffing. If tools are sharp and
properly ground, coolants are seldom required for machining. They may be
desirable for an unusually smooth finish or for deep cuts. If coolants are
employed, only detergent in water or 10% soluble oil in water should be used.
These machines should have a minimum no-load spindle speed of 10,000 rpm.
Higher speeds are desirable and should be used if they are available. Two or
three flute cutters, smaller than 1.5″ (38 mm) in diameter, running at high
speeds, produce the smoothest cuts. At slower spindle speeds, the cutter
should have more flutes, or may be larger in diameter to produce the necessary
surface speeds. The cutter should be kept sharp and should have a back
clearance of 10° and a positive rake angle up to 15°.
Figure 1 – Trimming formed part with table mounted router
Figure 2 – Edging with a portable router
1.2 Routing and Shaping
1.3 Drilling
Woodworking shapers and overhead, or portable routers are used in edge
finishing operations and for cutting flat thermoformed parts. For edging small
parts, the table router is convenient. (see Figure 1)
A portable router is useful when the part is too large or awkward to bring to
the machine. (See Figure 2)
When drilling ACRYSPATM Acrylic Sheet, best results are obtained when using
standard twist drills which have been modified as follows:
1. High speed steel drills should be selected, having slow spirals and wide
polished flutes.
4 | ACRYSPATM FORMING AND FABRICATION GUIDE
2. Drills should first be ground to a tip angle of 60° to 90°.
3. Modify the standard twist drill by dubbing-off the cutting edge to zero
rake angle.
4. Grind the back lip clearance angles to 12° – 15°.
are suggested for large radii curves and for straight cuts in thick acrylic. Routers and wood working shapers can be used for trimming the edges of formed parts. Tempered alloy steel saw blades are the least expensive to buy, give reasonable service, and are discarded when worn out. Carbide tipped blades are more expensive, give longer service, and can be resharpened. The following table can be used as a guide in selecting the proper circular saw blade:
Figure 3 – Alterations to drill bits for drilling ACRYSPATM Acrylic Sheet
ACRYSPATM Acrylic Sheet may be drilled using any of the conventional tools:
portable electric drills, flexible shafts, drill presses or lathes. In
general, drills should rotate at high speed and feed should be slow but
steady. Use the highest available speed with a drill press, usually 5,000 rpm.
An exception to this rule should be made when drilling large holes where the
drill speed should be reduced to 1,000 rpm. The drill should always run true,
since wobble will affect the finish of the hole.
When drilling holes which penetrate a second surface, it is desirable to back
up the surface with wood and slow the feed as the drill point breaks through.
For accuracy and safety, the acrylic should be clamped during drilling.
Figure 4 – Cutting ACRYSPATM Acrylic Sheet on table saw
Thickness of Acrylic Sheet Inches (mm)
.080 – .100 (2.0 – 2.5)
.100 – .187 (2.5 4.7)
.187 – .472 (4.7 12.0)
Blade thickness Inches (mm)
1/16 3/32 (1.6 2.4)
3/32 1/8 (2.4 3.2)
3/32 1/8 (2.4 3.2)
Teeth per Inch (cm)
8 14 (3 8)
6 8 (2 3)
5 6 (2 3)
1.4 Cutting
As a general rule, a power saw is the best method of cutting ACRYSPATM Acrylic Sheet. It is sometimes advantageous to cut thin material at an elevated temperature with rule and blanking dies. Cold punching and/or shearing should not be used since these methods will fracture the material.
Figure 5 – Cutting ACRYSPATM Acrylic Sheet with saber saw
The type of equipment selected should be based on the work to be done. Circular saws are preferred for straight cutting. Jig saws and saber saws are suggested for cutting small radii curves and thin materials. Band saws
Figure 6 – Cutting formed ACRYSPATM Acrylic Sheet part on band saw
ACRYSPATM FORMING AND FABRICATION GUIDE | 5
Circular saws should: 1. Be run at 8,000-12,000 RPM. 2. Be hollow ground to
aid cooling. 3. Be slotted to prevent heat warping the blade. 4. Have teeth
with a uniform rake angle of 0° – 10°. 5. Have a slight set to give clearance
of .010″ to .015″
(.254 mm to .381 mm) and 6. Have teeth of uniform height.
An 8″ (20.3 cm) diameter blade is used for light work and a 12″ (30.5 cm)
blade for heavy work. A two-horsepower motor is suggested for driving these
blades.
Masking tape applied over the area to be cut will reduce the tendency to chip
during cutting. Acetone, toluene, or methylene chloride can be used to clean
blades. Tallow or bar soap applied to the blade, helps to prevent gum build-up
on the blade when cutting sheet masked with adhesive backed paper.
Traveling saws cutting at 10 to 25 feet (3 to 7.6 meters) per minute are
recommended for making straight cuts longer than 3 feet (91 cm) and for
cutting sheets when it would be undesirable to slide them across the saw
table.
Sheet. The following table can serve as a guide for selection of a blade:
Min. radius to be cut Inches (mm) 1/2 (12.7)
3/4 (19)
1-1/2 (38)
2-1/4 (57)
3 (76)
4-1/2 (114)
8 (203)
12 (305)
20 (508)
Blade width Inches (mm) 3/16 (4.7)
1/4 (6.3)
3/8 (9.5)
1/2 (12.7)
5/8 (15.9)
3/4 (19)
1 (25.4)
1-1/4 (31.7)
1-1/2 (38.1)
Blade thickness Inches (mm) 0.028 (.71)
0.028 (.71)
0.028 (.71)
0.032 (.81)
0.032 (.81)
0.032 (.81)
0.035 (.89)
0.035 (.89)
0.035 (.89)
Teeth per Inch (cm) 7 (3) 7 (3) 6 (3) 5 (2) 5 (2) 4 (1.5) 4 (1.5) 3 (1.5) 3 (1.5)
The blade speed should be approximately 4,500 RPM for ACRYSPATM Acrylic Sheet thicknesses from .125″ to .375″ (3.2 to 9.5 mm) thick. Fine teeth with no set will produce a smooth cut if fed slowly. Sheets should be fed continuously and with even pressure to prevent the blade from binding and breaking. The blade should enter and leave the work slowly to prevent chipping. Should a burr form on the cut edge due to overheating, it can be removed with a scraper or other straight edged tool. This is particularly important if the sheet is to be silk screened.
1.5 Laser Cutting and Engraving
Figure 7 – Typical saw blade for cutting ACRYSPATM Acrylic Sheet
ACRYSPATM Acrylic Sheet, backed with fiberglass reinforced plastics, is best
cut by diamond abrasive wheels. Carbide tipped blades will do a good job but
require frequent resharpening. Small diameter disposable alloy steel blades on
high-speed air powered saws are also effective, especially in portable
situations.
Variable speed band saws, which can run at 5,000 feet (1524 m) per minute and
have a 28″ to 36″ (71 to 91 cm) throat, are best suited for production work.
Metal cutting blades are the best type for cutting ACRYSPATM Acrylic
Lasers, when in expert use provide the most precision, high quality cutting and engraving of acrylic sheet. The only real difference between cutting and engraving is that in cutting you go all the way through the sheet and in engraving you manipulate the speed and power of the laser to go a set depth into the sheet. While there are other types of industrial lasers, CO2 lasers are the workhorse type for this application. The power requirements of the laser depend upon the thickness of the sheet, its pigment content, and the required processing speed. Low power lasers tend to be used for engraving while the higher power lasers are needed to cut sheet with a crisp polished edge.
6 | ACRYSPATM FORMING AND FABRICATION GUIDE
When the laser cuts into acrylic, it thermally depolymerizes the acrylic to
methyl methacrylate vapor. This vapor is highly flammable, so it is necessary
to have a gentle stream of air or nitrogen to blow it away from the cutting
point and prevent ignition. This stream should be optimized to prevent
frosting at the newly cut edge. Excellent ventilation is a must in the cutting
area. While cutting, the equipment should never be left unattended.
Cast acrylic is most suited for laser fabrication due to its high molecular
weight. It can be laser cut to provide a high gloss edge with no further
fabrication required (other methods require a secondary step in the process to
give a polished edge). Laser etched cast acrylic sheet offers optimum
engraving definition. Both of these benefits make cast acrylic sheet
particularly suited to LED light coupling for edge illumination for lighting
and signage applications. Often fabricators won’t laser cut extruded sheet
because odor and melt lip. Melt lip occurs while the laser operates. While the
laser operates, the extruded acrylic melts and on the bottom side creating a
lip or burr that fabricators then must remove. Additionally, the engraving
definition on extruded sheet is very poor due to its low melting point.
You should look to the laser manufacturer for detailed guidance on
specification of the laser for your application. It is understandably
desirable to get the lowest power system that can still give you a quality
result. This must be carefully balanced as laser system costs increase
dramatically with the power density. For general specification, the rule of
thumb is for every 10 Watts of power you will be able to cut 1mm / 0.04 inch
of material. That ratio will give you a system capable of both good production
speed and a smooth flame polished edge. Start with high frequencies from 20 to
25 kHz for a smooth flame polished edge, backing off until you reach an
optimum suitable for the quality of your application. Some applications merely
require that the material be cut but do not require a flame polished edge. In
that case, you can start at frequencies as low as 9 to 12 kHz. Cutting speed
is optimized in similar fashion. Focal length should be from 2 to 2.5 inches.
Also note that power and speed need to be adjusted to the particular design to
reduce stress when there is an abrupt directional change or cutting sharp
angle.
1.6 Finishing
The original high-gloss surface of ACRYSPATM Acrylic Sheet can usually be
restored by a series of finishing operations. Finishing often involves an
initial sanding operation, followed by buffing, then finally a polishing
operation. During all these operations, heat should be avoided. The plastic
should be kept in constant motion with a minimum of pressure against the
finishing wheels. Air cooling devices can be used to reduce frictional heat.
1.7 Sanding
Minor and shallow scratches on a clean ACRYSPATM Acrylic Sheet surface can be
filled with a paste wax to improve the appearance. Hard automobile paste wax
should be used, applied in a light even film with a soft cloth. The surface
should then be polished to a high gloss with a clean, dry, cotton flannel
cloth. Hard or rough textured cloth such as cheesecloth and muslin should not
be used. Deeper, yet light, scratches may be removed or reduced by hand
polishing, using a soft cloth and a rubbing compound (see source list). Do not
“sand” acrylic unless surface blemishes are too deep to remove by light
buffing. When it is necessary, usually 320-A wetor-dry paper is as coarse as
will be required and may be followed by a 400-A or finer paper. Soak the
sandpaper in water for a few minutes before using and use plenty of water
while sanding. Sanding of large areas should not be attempted unless power
buffing equipment is available. Final sanding should be in one direction only
to prevent distortions and/or “bull’s-eyes.”
Machine sanding can be done with belt, disc, vibrator or drum sanders. Large
optical grade jobs require expensive, precision grinding equipment. In all
cases,
ACRYSPATM FORMING AND FABRICATION GUIDE | 7
when sanding acrylics, keep the tool, or the work, moving and use water freely.
feet (610 to 732 m) per minute. This is the recommended procedure for finishing edges.
1.9 Flame Polishing
Figure 8 – Final sanding (use back and forth motion and liberal amounts of
water)
1.8 Buffing and Polishing
An abrasive wheel may be used first, which consists of wheel buffs made of
stitched cotton or flannel, and an abrasive compound of very fine alumina or
similar abrasive combined with tallow wax binders. The abrasive wheel should
run at about 1,800 surface feet (548 m) per minute.
After reducing most of the scratches on the abrasive wheel, a wheel buff to
which only tallow has been applied may be used to remove any remaining
imperfections. Speed of the buff should be between 1,800 and 2,200 surface
feet (548 and 671 m) per minute.
Next, the acrylic part is given a high polish on a finish wheel on which no
abrasive or tallow is used. As an alternate method, a coat of wax can be
applied by hand.
Edges and inaccessible areas can be polished with a hydrogen-oxygen flame.
However, flame polishing cannot be fully recommended because it can cause
“crazing” which may not show up for several weeks. The tendency toward crazing
can be substantially reduced if you have a good, clean saw-cut to start with,
if the saw-cut has been properly wet-sanded or jointed, and if the flame is
applied correctly.
The risk of crazing can also be reduced by annealing the pieces in an oven for
approximately 2 to 4 hours at a temperature of 170 to 180°F (77 to 82°C). Use
a welding torch with a No. 4 or No. 5 tip. Set the hydrogen pressure at 5 psi
(.35 kg/cm2). Ignite the hydrogen first, then turn on the oxygen and adjust
the flame.
The flame should be bluish, nearly invisible, approximately 4″ (10 cm) long,
and narrow. Hold the torch so that the tip of the flame touches the edge of
the ACRYSPATM Acrylic Sheet. (See Figure 10) Move the torch along the edge at
a speed of approximately 3 to 4″ (7 to 10 cm) per second.
Overheating and bubbling may occur if the flame is moved too slowly. If the
first pass does not produce a completely polished edge, allow the piece to
cool; a second pass will often improve the surface finish.
Figure 9 – Buffing ACRYSPATM Acrylic Sheet on power driven buffer
The finish wheel should be very loose and made of imitation chamois or flannel
10″ to 12″ (25.4 to 30.5 cm) in diameter, running at a speed of 2,000 to 2,400
surface
Figure 10 — Flame polishing edge of fabricated part
8 | ACRYSPATM FORMING AND FABRICATION GUIDE
2. Cementing
Strong transparent joints can be obtained in bonding actions of ACRYSPATM Acrylic Sheet together, by giving careful attention to preparation of the mating surfaces, proper choice of cement and following correct cementing techniques.
Edges to be cemented should never be polished, as this tends to round the corners and decrease the contact area in the joint. There are several types of joints that may be used (see Figure 11) the selection of which will usually depend upon the end use application.
2.1 Prevention of Internal Stresses
Heat generated by machining operations, and/or thermoforming at reduced
temperatures, will often induce internal stresses which make the material
susceptible to crazing after contact with solvents and certain cements. Such
stresses can be avoided by the proper choice of thermoforming or machining
conditions, or can be relieved by heat treating. Refer to the Annealing
Section in Technical Bulletin 135 for proper heat-treating conditions.
2.2 Joint Preparation
For the best strength in a cemented joint, the contact area should be as large
as possible. Where two curved surfaces are to be joined, each should have the
same radius to provide uniform contact over the entire joint area..
2.3 Safety Precautions
Most solvents are highly flammable, toxic, and may be irritating to the skin
and eyes. As a safety measure, cementing operations should be carried out in a
wellventilated area away from open flame. Eye protection and respiratory items
should be afforded. See section on Material Safety Data Sheets for more
information.
Surfaces to be jointed should be clean and fit together with uniform contact throughout the joint. In order to obtain close fitting edges, which is especially important, it may be desirable to accurately machine the mating surfaces.
2.4 Types of Cement
Sections of ACRYSANTM Acrylic Sheet can only be bonded together with one of
two general types of cement commercially available the monomer-polymer-
solvent type or the monomer-polymer-catalyst type.
Figure 11 – Joint selection
ACRYSPATM FORMING AND FABRICATION GUIDE | 9
ACRYSPATM Acrylic Sheet can only be joined with the monomer-polymer-solvent
type or the monomerpolymer-catalyst type, this product is highly solvent
resistant, partially crosslinked continuous cast acrylic sheet.
Monomer-polymer-solvent type cements
These types of cements usually consist of methyl methacrylate monomer, methyl
methacrylate polymer and assorted solvents. M-P-S type cements available are
Weld-On 16 and Weld-On 1802. M-P-S cements do not allow rapid assemblies.
Usually 15 to 30 minutes after cement is applied, part can be handled very
carefully. High to medium strength joints are obtained which have good to fair
weathering resistance.
The syringe method
In those cases where the mating surfaces are well matched, the joint may be
secured in a jig and the cement introduced to the edges of the joint by means
of a hypodermic syringe, eye dropper or squeeze bottle. In this manner, the
cement will spread throughout the joint area by capillary action. In the event
a thicker coating of cement is desired, fine wire may be inserted into the
joint as it is assembled in the jig. Thus spaced, the joint is ready for the
cement to be introduced into it. The syringe should always be cleaned after
use to prevent adhesion of the plunger to the walls of the syringe. See Figure
12 for typical syringe method techniques.
Monomer-polymer-catalyst type cements
These type cements consist of methyl methacrylate monomer, Methyl Methacrylate Polymer (Part A) and a catalyst (Part B). M-P-C cements available are Weld- On 10, Weld-On 28, and Weld-On 40. These type cements yield excellent bond strengths, and weathering resistance. Assembly times are slow.
2.5 Cementing Techniques
Solvent cements can be applied to parts fabricated from ACRYSPATM Acrylic Sheet by a soak, dip, syringe or a brush method. The best method depends on type of joint to be mated, physical configurations of parts, personal preference, etc. Temperature and humidity can affect the quality of cemented joints: ACRYSPATM Acrylic Sheet should not be cemented at temperatures below 65 °F (18 °C), over 95 °F (35 °C), or when the relative humidity is over 60 percent. Excessive moisture can cause cloudy joints which are usually weaker than normal.
Figure 12 – Syringe method technique
The brush method
If the cement is sufficiently viscous, it can be brushed on the surfaces to be
joined. Viscosity of solvent or monomer type cements can be increased by
dissolving acrylic chips or shavings in them. The solvent is then brushed on
and allowed to soften the surface of the acrylic sufficiently for formation of
a cohesive bond. The joint is then placed in a jig until hardened, as is the
case in other methods.
10 | ACRYSPATM FORMING AND FABRICATION GUIDE
Cemented joints should reach full hardness in 24 hours, provided the proper
techniques have boon used and the cementing operations have been carried out
in a suitable temperature and humidity environment.
2.6 Venting
When hollow articles are cemented, enclosed areas should be vented to prevent
entrapment of solvent vapors which could promote crazing of the acrylic.
2.10 Cementing ACRYSPATM Acrylic Sheet to Other Materials
Often it is desirable to cement parts made from ACRYSPATM Acrylic Sheet to
other materials such as metal, wood, other plastics, etc. Industrial
PolyChemical Service, manufacturer of Weld-On Cements, has a complete line of
products for these types of jobs. Consult IPS for recommendations.
2.7 Filling Voids
Before a cement sets, small crevices or voids can be filled by inserting
cement with a hypodermic syringe.
2.8 Clamping
For maximum bond strength, jigs or clamps should be used to hold the joint
together with uniform pressure, no greater than 6 psi (.4 kg/cm2), while the
cement is setting. No part of the jig or clamp should be allowed to touch the
joint, for the reason that capillary action will draw the cement under the jig
resulting in its being attached to the joint.
2.9 Polishing or Machining
The cemented joint should be thoroughly hardened before polishing, sanding or machining. Thermoforming should be done prior to cementing operations whenever possible. If thermoforming must be done on precemented joints, a monomer- polymer catalyst type cement should be used and the joint annealed to provide maximum bond strength during the forming operation. A close fitting “V” joint generally gives the best cemented bond for thermoforming.
3. Annealing
ACRYSPATM FORMING AND FABRICATION GUIDE | 11
When plastics parts are molded, fabricated or formed in any fashion these
processes inherently induce stress into the part. Just like glass, ceramic and
metals, this stress can be relieved by a process called annealing. In
annealing we heat the part heating to near the glass transition temperature,
maintaining this temperature for a set period of time, and then slowly cooling
it to room temperature.
A part undergoing annealing should be completely supported. If it is simply a
sheet it can be laid flat in the oven. More complicated parts can require jigs
to ensure that the part is not distorted during the annealing process.
For acrylic, the typical temperature that it is heated to is 176°F (80°C) and
then cooled slowly. Generally, you heat the sheet one hour for each millimeter
of thickness. It is critical that the sheet be cooled at a controlled rate. If
you took the part out of the oven after it achieved 176°F (80°C) and cooled it
under running water you would build more stress into it rather than relieve
it. Specially configured annealing ovens can program the annealing schedule.
Most ovens will require that you reset the temperature at intervals. The part
does not have to be cooled all the way to room temperature before removing it
from the oven. It can be removed once the temperature goes below 140°F (60°C).
Thermoformable polyfilm can remain in place during annealing. Any other paper masking, tape, etc must be removed.
Annealing schedule
Thickness 2 2.5 3 3.2 4.5 6 9.5 12
Heating time (hours) 2 2.5 3 3.2 4.5 6 9.5 12
Cooling time (hours) 2 2 2 2 2 2 2.5 3.5
Heating rate (degrees °C per hour)
15
15
15
15
15
15
12
11
If the part has been cemented it must be allowed to cure at least five hours before annealing. Rapid solvent evaporation can cause bubble formation.
12 | ACRYSPATM FORMING AND FABRICATION GUIDE
4. Thermoforming
ACRYSPATM Acrylic Sheet is partially crosslinked with unparalleled performance for the demanding thermoforming applications that require stain and chemical resistance. This product is most commonly used in the sanitaryware and spa markets.
Good formability is one of the most important and useful properties of
ACRYSPATM Acrylic Sheet. When ACRYSPATM Acrylic Sheet has been properly
heated, it feels like a sheet of soft rubber. In this state the material can
be formed to almost any desired shape. On cooling, the acrylic becomes rigid
and retains the shape to which it has been formed. Forming thermoplastic sheet
is probably the simplest type of plastic fabrication. The cost of molds and
equipment is relatively low. Both two and three dimensional forming of
ACRYSPATM Acrylic Sheet can be accomplished by a number of different methods.
The selection will depend on the shape, thickness, tolerance, and optical
quality required for the formed part as well as the equipment available and
number of parts to be made.
It is imperative that ACRYSPATM Acrylic Sheet be heated properly for
thermoforming. Using temperatures that are too low will leave stresses in the
formed part (cold forming) that could be relieved by solvents in the
reinforcing resin, paint, and adhesives causing cracks and crazing. A cold
formed part is also susceptible to crazing due to heat sources in the
surrounding environment. Too high forming temperatures can cause blistering.
While continuous cast acrylic sheet is used in a wide range of thermoforming
applications, the most common use is baths and spas. Following is the
narrative of a tub or spa being produced: 1. An acrylic “shell” is
thermoformed. Acrylic is
expensive so the producer starts with a sheet that is as thin as possible
while insuring good finished parts. The acrylic only forms the interior and
deck “skin” of the vessel. It provides no structural support. 2. The back side
is “sprayed up” with FRP (polyester and fiberglass composite) or polyurethane
to create a rigid support body. This is often supplemented with wood or
plastic secondary supports that are buried in the spray up. 3. Once cured, the
part is trimmed and drain and fitting holes are drilled. 4. Fittings are
installed.
Note that polyurethane spray up is usually only used on ABS backed acrylic, but can be sprayed directly to acrylic using specific chemistry.
4.1 Thermoforming Temperatures and Cycles
ACRYSPATM FORMING AND FABRICATION GUIDE | 13
The following curves (Figures 13 & 14) were derived from tests performed with the experts at Trinseo. Due to the large variety of heating equipment available, heating times may vary. The following heating cycles should be used as a starting point only in obtaining optimum forming temperature times and cycles. The temperature and cycle times depend upon the thickness of sheet as well as the type of heating and forming equipment used.
Using equipment with a double-oven (top and bottom heat) allows for the best
results regarding heating cycle times. This also provides for a bit more
forgiveness in the thermoforming cycles. Target temperatures of 370 to 390 °F
(188 to 199 °C) for the top surface are good, with a target of 340 to 360 °F
(171 to 182 °C for the bottom surface. Heating cycle times of approximately 2
minutes are possible with this set-up. Again, should your equipment require
more time you would target the lower range and the higher range if your
equipment allows for faster heat up. If the equipment allows for processing at
shorter heating cycles, then there is more leeway for higher processing
temperatures.
Figure 14 outlines the heating cycles when using electric infra-red radiant
heaters on one or two sides. Again, heating times can vary depending on the
type of heating equipment used, percentage times, distance between sheet and
heaters, and heat loss factors.
Figure 14 – Electric infra-red radiant heating
Several other methods can be used to determine if a sheet has been
sufficiently heated. The most common is the ripple method by which the
operator shakes the heated sheet with a non-combustible object (See note).
When the sheet ripples uniformly across the surface, it is ready for forming.
Another commonly used technique is the “sag method”. By trial and error the
amount of sag in a hot sheet can be correlated with the optimum time to be
thermoformed. The best procedure for determining when the sheet is ready for
forming is to accurately control the temperature by the use of heat sensors
and/or temperature indicating stickers. The actual cycle, temperature settings
and techniques most suitable for a particular forming job are best determined
on one’s own equipment.
Note: Care must be taken to make sure the operator does not endanger him/herself due to exposure to electricity, hot oven components, or hot sheet.
Figure 13 – Forced air circulating oven at 350°F (177 °C)
14 | ACRYSPATM FORMING AND FABRICATION GUIDE
4.2 Heating Equipment
1. Forced air circulating ovens
Forced air circulating ovens generally provide uniform heating at a constant
temperature with the least danger of overheating the acrylic sheet. Electric
fans should be used to circulate the hot air across the sheeting at velocities
of approximately 150 ft./minute (46 m/minute). Suitable baffles should be used
to distribute the heat evenly throughout the oven. Heating may be done with
gas or electricity. Gas ovens require heat exchangers to prevent the
accumulation of soot from the flue gas. Electric ovens can be heated with a
series of 1000-watt strip heating elements. An oven with a capacity of 360 ft3
(10 m3), for example, will require approximately 25,000 watts of input. About
one-half of this input is required to overcome heating losses through the
insulation, leaks and door usage. An oven insulation at least two inches thick
is suggested. Oven doors should be narrow to minimize heat loss, but at least
one door should be large enough to permit reheating of formed parts which may
require reforming. The oven should have automatic controls so that any desired
temperature in the range of 250 to 450 °F (121 to 232 °C) can be closely
maintained. In addition, temperature recording devices are desirable, but not
essential. Uniform heating is best provided when the sheet is hung vertically.
This can be accomplished by hanging the sheets of acrylic on overhead racks
designed to roll along a monorail mounted in the oven roof or in a portable
unit. Precautions should be taken so that the sheet cannot fold or come in
contact with another. A series of spring clips or a spring channel can be used
for securely grasping the sheet along its entire length.
2. Infra-red heating
Infra-red radiation can heat ACRYSPATM Acrylic Sheet three to ten times faster
than forced-air heating. This type of heating is often used with automatic
forming machines where a minimum cycle time is important.
Temperature control, however, is much more critical and uniform heating is
more difficult to obtain by this method. Acrylic plastic absorbs most of the
infra-red energy on the exposed surface, which can rapidly attain temperatures
of over 360 °F (182 °C). The center of the sheet is heated by a slower
conduction of heat from the hot surface. This usually causes temperature
gradients across the thickness. The gradient is more severe with infra-red
heating from one side only. Infra-red radiant heat is usually supplied with
reflector backed tubular metal elements, resistance wire coils or a bank of
infrared lamps.
More uniform heat distribution can sometimes be accomplished by mounting a
fine wire-mesh screen between the sheet and the heat source. A Temperature
Controlled technology, such as a solid state PLC or percentage timer on older
apparatus should always be used for consistent results. Top infra-red heaters
should be approximately 12″ (30 cm) from the sheet. Bottom heaters can be 18
to 20″ (45 to 50 cm) away.
Types of Infra-Red Heating A. Gas: Can be open flame (less common) or gas
catalytic. Economical to run but poor control of the heat, impossible to
control the heat profile. B. Calrod: Electrical resistance elements such as
the type used in domestic ovens. It is a nichrome wire surrounded by an
silicon or mica insulator. C. Nichrome Wire: An exposed nichrome wire without
insulation usually set into channels in a ceramic or other insulative panel.
D. Ceramic Heating Elements: A nichrome wire embedded in an insulator and then
sheathed in a ceramic tube. E. Infrared Panel Heaters: Tungsten wire elements
mounted in channels within an insulator panel. F. Quartz Heating Element: The
most common type of heating. You can better control the heat profile either by
screening off sections or if the system has it, automated control of each
heating zone. They use a tungsten wire element encased in a quartz tube.
ACRYSPATM FORMING AND FABRICATION GUIDE | 15
G. Halogen: Like the quartz heating element, this heat source is a tungsten
wire encased in a quartz tube but the tube is sealed and filled with an inert
halogen gas preventing oxidation of the element. This allows the element to go
to much higher temperatures without burning out. The very best control of heat
profile and heat flow. They are not as common because these systems are
comparatively more expensive.
4.3 Bending
Strip heating is sometimes used for specialized forming jobs. For example, a
strip heater can be used to make simple bends in ACRYSPATM Acrylic Sheet.
Strip heaters can be purchased from plastics suppliers or can be constructed
from “Nichrome” heating elements encased in ceramic or “Pyrex” tubing. To
prevent distortion or damage to the sheet surface, the ACRYSPATM Acrylic Sheet
should be kept at least 1/2″ (13 mm) away from the hot tube. See Figure 15 for
typical strip heater arrangement.
4.4 Three-Dimensional Forming
Techniques for three-dimensional forming of plastic generally require vacuum,
air pressure, mechanical assists or combinations of all three to manipulate
the heated sheet into the desired shape. The basic forming techniques used for
ACRYSPATM Acrylic Sheet are illustrated in the following drawings and
described below. 1. Vacuum forming
A. Heated sheet in clamp frame. B. Mold is mechanically positioned to heated
sheet,
forming a seal. Vacuum is then applied to form part.
2. Drape vacuum forming
Figure 15 Bending
A. Heated sheet in clamp frame. B. The mold is forced into the sheet to a
depth that
forms a seal around the periphery. Vacuum is then applied to form the part.
16 | ACRYSPATM FORMING AND FABRICATION GUIDE
3. Vacuum/snap-back forming
A. Heated sheet in clamp frame. B. Position vacuum chamber to heated sheet to
form seal. Apply vacuum to form bubble to predetermined height. C. Insert mold
into heated/pre-stretched sheet to form seal. Air control relieves vacuum in
preform vacuum chamber.
Apply vacuum to mold to form part. 4. Pressure bubble/snap-back forming
A. Heated sheet in clamping frame. B. Position pressure chamber into heated
sheet to form seal. Apply pressure to pre-stretched sheet to controlled
height. C. Insert mold into pre-stretched bubble at a controlled rate. Insert
to depth required to form a seal. 5. Heated plug assist forming
A. Heated sheet in clamping frame. B. Position mold into heated sheet to form
seal. Insert heated plug at controlled rate to the depth required for
preforming. C. Apply vacuum to form part.
6. Pressure bubble/plug assist/vacuum forming
ACRYSPATM FORMING AND FABRICATION GUIDE | 17
A. Heated sheet in clamping frame. B. Position mold into heated sheet to form
pressure seal. Apply pressure to pre-stretch sheet to controlled height. C.
Insert heated plug into bubble at a controlled rate to the depth required for
preforming. D. Apply vacuum to form part
4.5 Molds
Wood–Wooden molds are easily fabricated, inexpensive and can be altered
readily. Wood molds are ideal for short production runs where mold markoff is
not important and for prototyping.
Epoxy–Epoxy molds yield the least amount of mold markoff of any of the mold
materials used. Epoxy molds can be used for medium production runs and have
good durability provided they are properly fabricated.
Aluminum–Aluminum molds are used in high production operations. Aluminum moIds
will last indefinitely with little maintenance required.
18 | ACRYSPATM FORMING AND FABRICATION GUIDE
Thermoforming troubleshooting guide
Problem Blistering
Probable Cause · Sheet to hot
Poor definition of detail. Incomplete forming
· Sheet too cold · Low vacuum · Sheet too thick · Low air pressure
Excessive thinning at bottom of draw or corners
· Poor technique · Sheet too thin · Drawdown too fast
Extreme wall thickness variations
· Uneven sheet heating · Mold too cold · Sheet slipping · Stray air currents
Excessive sag Pits or pimples Part sticking to mold Mark-off
Distortion in finished part
· Sheet too hot · Vacuum holes too large · Vacuum rate too high · Dirt on mold
or sheet · Rough mold surface · Undercuts too deep · Not enough draft
· Dirt on sheet · Dirt on mold · Dirt in atmosphere · Sheet too hot
· Part removed too hot · Uneven heating
Corrective Action
· Reduce time heaters or reduce voltage
· Move heater farther away · Use screening if localized
· Increase heat input to sheet · Check for leaks in vacuum
system · Increase number and/or size
of vacuum holes · Add vacuum capacity · Use thinner caliper sheet · Increase
volume and/or pressure
· Change forming cycle to include billowing or plug assist
· Use screening to control temperature profile
· Use thicker sheet · Decrease rate of drawdown
· Check temperature profile · Change heaters to provide
higher uniform mold surface temp · Check cooling system for scale or plugs ·
Adjust clamping frame to provide uniform pressures · Provide protection to
eliminate drafts
· Reduce time or temperature
· se smaller holes · Decrease vacuum rate or level · Clean mold and/or sheet
· Polish mold · Reduce undercuts · Change to split mold · Increase draft of
mold
· Clean sheet · Clean mold · Clean vacuum forming area · Isolate area if
necessary and
supply filtered air · Reduce heat and heat more
slowly
· Increase cooling time before removing part
· Check cooling system · Check temperature profile · Correct mold design —
stiffen
to eliminate.
4.6 Thermoforming with Polyethylene Film
Temporary polyethylene film barrier
Polyethylene film (polyfilm) is used as a temporary protective film on the top
surface of the ACRYSPATM cast acrylic sheet. Some processors may choose to
leave the polyfilm on the acrylic surface during thermoforming. Trinseo does
not recommend or oppose the use of this procedure; however some manufacturers
use this procedure very successfully. Leaving the film on during thermoforming
can cause problems if not done properly. For example, if the acrylic surface
is overheated, the film may bond so tight that it is virtually impossible to
remove it. Also, film left on a finished part will gradually bond tighter and
tighter as time goes by. Film left on for more than one (1) year probably
cannot be removed.
It is recommended that if the sheets have been sitting unwrapped or exposed
for an extended period of time, to remove the polyfilm masking prior to
forming. Since the protective film can absorb moisture, it could possibly
transmit the moisture to the sheet when heating and cause blisters in the
finished part.
Damage to the film may make it desirable to remove the film prior to
thermoforming. Rough handling may scratch, tear or partially remove the film.
Forming with the film damaged may leave unwanted marks on the acrylic surface.
Once the film is removed from the sheet, it cannot be laid back on the
surface. Air or other contaminates can become trapped under the film and cause
markoff on the finished product.
ACRYSPATM FORMING AND FABRICATION GUIDE | 19
20 | ACRYSPATM FORMING AND FABRICATION GUIDE
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NOTE: for cautions and information on exposure to product by Trinseo PLC and its affiliated companies, including Aristech Surfaces (collectively “Trinseo”), please see the applicable material safety data sheet.
Questions pertaining to any procedure detailed herein should be addressed to the Technical Services Department. +1 800-428-6648 +1 505-864-3800 Fax +1 505-864-7790
Information contained herein is: a) based on Trinseo’s available technical data and experience; b) intended only for individuals having applicable technical skill, with such individuals assuming full responsibility for all design, fabrication, installation, and hazards; c)to be used with discretion and at one’s own risk, after consultation with local codes and with one’s independent determination that the product is suitable for the intended use; and d)not to be used to create designs, specifications, or installation guidelines. Trinseo makes no representation, or warranty, express or implied, and assumes no liability or responsibility as to: i) the accuracy, completeness or applicability of any supplied information; ii) results obtained from use of the information, whether or not resulting from Trinseo’s negligence; iii) title, and/or noninfringement of third party intellectual property rights; iv) the merchantability, fitness or suitability of the product for any purpose; or v) health or safety hazards resulting from exposure to or use of the product. Trinseo shall not be liable for x) any damages, including claims relating to the specification, design, fabrication, installation, or combination of this product with any other product(s), and y) special, direct, indirect or consequential damages.
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