Ultrasonic welding
™
Eastman polymers
Ultrasonic welding
Eastman™ polymers
Ultrasonic welding is a common method for joining plastic
parts without using adhesives, solvents, or mechanical fasteners.
Ultrasonic welding machines operate on the principle of
converting electrical energy to mechanical vibratory energy.
This vibratory energy is transmitted to plastic parts by a
specially designed horn that also applies pressure to force the
parts together. The high-frequency vibration generated by
the welding machine creates frictional heat that softens the
plastic to create a bond at contact points between plastic parts.
Equipment for ultrasonic welding may be somewhat more
expensive than other joining methods. However, compared to
other methods, ultrasonic welding offers several advantages,
including
• Environmentally safe; no chemicals used
• Good joint appearance
• Improved product uniformity
• Fast bonding; higher productivity
• Process adaptable to multiple tasks (inserting,
swaging, etc.)
Some plastics soften and bond more easily than others, but
by selecting the appropriate welding parameters, strong bonds
can be obtained with most amorphous plastics. Parameters
that significantly affect weld strength and appearance include
vibration frequency and amplitude, horn pressure, load time,
and joint design.
Joint designs
Energy-director and shear joints (as shown in Figure 1) are the
two general types of joint designs most commonly used in
the plastics industry. A simple energy-director joint provides
a small raised ridge of polymer between two flat surfaces to
be joined. As the parts are pressed together by the vibrating
welder horn, the ridge softens and flows over the width of the
joint to create a bond. One or both surfaces to be joined may
be textured or have additional detail to enhance weld quality.
A crisscrossed design, such as shown in Figure 2, gives more
material flow for stronger bonds and hermetic seals. The
tongue-and-groove design ensures joint alignment, prevents
flash, and promotes a hermetic seal.
• Low energy consumption
•C
omputer-controlled process; suitable for statistical
process control
Figure 1 Typical joint designs
90°
Simple energy director
Single-sided shear joint
Double-sided shear joint
Figure 2 Improved energy-director designs
Slip Fit
Energy director with
tongue-and-groove joint
Crisscrossed or sawtoothed energy director
Simple energy-director joints may work satisfactorily in some
small parts, but in some situations, the band may not have
the tensile or impact toughness required for the application. If
an energy-director joint must be used, it should be incorporated
with a step joint or a tongue-and-groove joint as shown in
Figure 2.
Energy director
with step joint
Shear joints preferred for copolyesters
In contrast, a shear joint provides an interference fit between
the parts to be joined. The interference is typically in the
range of 0.2–0.3 mm (0.008–0.012 in.) and can be singlesided or double-sided, similar to a tongue-and-groove joint.
As the vibrating welder horn presses the parts together, the
interfering plastic softens and creates a bond at the interface.
For Eastman™ copolyesters, shear joints should closely follow
the design suggested in Figure 3.
Figure 3 Single-sided shear joint
After weld
Before weld
0.6W
W
0.025-mm
(0.010-in.)
gap (min.)
1.5 mm (0.060 in.)
R (typical)
0.5 mm (0.020 in.) min.
Flash relief
Slip-fit
Support
nest
20°–30°
Radius
A
A = 0.2 to 0.3 mm 0.025 mm
(0.008 to 0.012 in. 0.001 in.)
Interference per side
10° (min.)
1° Draft angle (typical)
Support nest
B (depth of weld) = 1.25 W
= 30°–45°
Welding Eastman™ copolyesters
Ultrasonic welding of Eastman™ copolyesters was performed
using standard industry specimens to form a 50.8-mm (2-in.)
long, welded I beam (see ANSI AWS G1.2M/G1.2: 1999).
Additional custom-designed specimens of similar overall
geometry were used to evaluate tongue-and-groove and
crisscross joint designs. Table 1 summarizes the ultrasonic
welding setup and conditions. Weld strength was evaluated
in a tensile pull test performed at a speed of 50.8 mm/min.
The results of tests using three joint designs are summarized
in Figure 4. The strength of a molded I beam is shown as a
control sample.
Figure 4 Tensile pull strength of copolyester welds
8,000
Tensile pull force (N )
7,000
6,000
5,000
4,000
3,000
2,000
1,000
0
Eastar™
copolyester
DN004
Sheara
Sheara
DuraStar™
polymer
MN611
Buttb
Buttb
Eastar™
copolyester
MN211
Eastar™
copolyester
MN100
Tongue and groovec
Eastar™
copolyester
MN021
Control
Tongue and groovec
Control
Double-sided shear joint with an interference of 0.2 mm (0.008 in.) between mating parts. See Figure 1.
A Branson 450 texture on one surface and an energy director with a height of 0.5 mm (0.020 in.) on the mating surface. See Figure 1.
c
An energy director with a height of 0.36 mm (0.014 in.) on the groove surface and a crisscross pattern with a height of 0.58 mm
(0.023 in.) on the tongue surface. See Figure 2.
a
b
Table 1
Typical ultrasonic welding setup conditions
Horn type
Aluminum or titanium
Booster type
Green 1:1
Welder power, watts
1,000 (typical)
Frequency, kHz
20
Fixture/nest
Rigid or semirigid
Options
Collapse control, constant
weld energy, computer control
Typical ultrasonic welding conditions
Welding time, s
0.3–1.0
Hold time, s
0.3–0.5
Welding pressure, MPa (psig)
0.1–0.35 (15–50)
Trigger pressure
Minimize
Downspeed
Minimize
In general, it was found that
• E astar copolyester MN211 gave the best overall performance
approaching 90% of the strength of the control samples.
™
• Tongue-and-groove joints formed the strongest bonds.
• In the absence of a groove, butt joints were prone to
misalignment resulting in abnormally weak welds.
•T
he strongest welds were formed at long weld times
(≥ 0.7 ms) and low weld pressures (≤ 0.2 MPa).
•H
old time had no effect on weld strength.
• E nergy directors must be used in both tongue-and-groove
and butt joints to obtain the strongest welds.
Since actual part design may have a significant effect on
performance, these results should only be used as guidelines
for resin selection. Note that these results are for tensile
strength only and may not indicate weld performance in
parts that experience flexing or impact.
Ultrasonic staking
Ultrasonic staking is an assembly method in which a plastic
stud is melted to capture or lock two components together
(see Figure 5). This method offers several advantages, including
fast cycle times, good repeatability and control, tight locking,
and the ability to form multiple stakes at one time.
Figure 5 Ultrasonic/heat staking methods
2D
Radius
at stud
base
required
Staking horn
D
Radius
2
2D
D
0.5D
1.6D
General welding practices
suggested for Eastman™ polymers
Your welding equipment supplier can provide valuable
assistance for equipment selection, setup, and part design.
The following suggestions include some of the more important
considerations for ultrasonic welding of Eastman™ polymers.
• Design parts with tongue-and-groove joints or shear joints
for added strength and toughness.
• Design joint with anticipated loads applied in shear mode
rather than leverage or tension mode.
Nonthermoplastic plate
• Provide 0.2–0.3-mm (0.008–0.012-in.) interference in shear
joints.
• Provide 0.2–0.25-mm (0.008–0.010-in.) flash flow gaps at
flash lines to minimize micronotch formation.
• Provide minimum radius of 0.75 mm (0.03 in.) to minimize
flex fatigue cracking during welding.
This method is suitable for joining parts made of Eastman™
plastic to other materials such as steel and dissimilar
plastics. However, it may not be suitable for joining parts
that are both made of Eastman materials. In such cases, there
is the opportunity for the softened head of the stake to weld
to the mating part and form sharp notches, which concentrate
stress and embrittle the joint. For best results, limit ultrasonic
staking to applications in which the plastics to be joined have
a melting/softening temperature difference of at least 22°C
(40°F).
• Locate joint within 6 mm (0.25 in.) of horn mating surface
to avoid far-field welding effects.
• Provide adequate draft angles to eliminate the need for
topical mold releases that may hinder welding.
• Provide adequate nest support under protruding parts to
prevent flex fatigue during welding.
• Design part with adequate horn contact area to reduce
horn marks.
• Use flat, parallel mating surfaces to optimize weld contact
area.
Alternative assembly methods
If ultrasonic welding is judged to be inappropriate for the
application, designers may consider alternative assembly
methods such as permanent snap fits, hot-plate welding,
screws, inserts, or adhesives.
Conclusion
Ultrasonic welding of copolyesters can be successfully
accomplished with proper joint design, material selection,
and the use of proper welding parameters. Part designers
must carefully select the joint design that provides the optimum
performance and utility to satisfy the end-use requirements
of the functional part. Because ultrasonic welding may not be
appropriate for the specific part to be assembled, designers
should consult their welding equipment supplier or Eastman
technical representative and conduct rigorous real-life enduse testing as the product is being developed. A list of equipment
suppliers follows.
Branson Ultrasonics Corporation
41 Eagle Road
Danbury, CT 06813 U.S.A.
Tel: (1) 203-796-0400
Dukane Corporation
2900 Dukane Drive
St. Charles, IL 60174 U.S.A.
Tel: (1) 630-584-2300
Sonics and Materials, Inc.
53 Church Hill Road
Newtown, CT 06470 U.S.A.
Tel: (1) 203-270-4600
Herrmann Ultrasonics, Inc.
620 Estes Avenue
Schaumberg, IL 60193 U.S.A.
Tel: (1) 847-985-7344
Ultra Sonic Seal
368 Turner Way
Aston, PA 19014 U.S.A.
Tel: (1) 610-497-5150
For ultrasonic welding with Eastman Tritan™ copolyester in
thin-walled applications, please refer to publication TRS-278.
Eastman Chemical Company
Corporate Headquarters
P.O. Box 431
Kingsport, TN 37662-5280 U.S.A.
Telephone:
U.S.A. and Canada, 800-EASTMAN (800-327-8626)
Other Locations, (1) 423-229-2000
Fax: (1) 423-229-1193
Eastman Chemical Latin America
9155 South Dadeland Blvd.
Suite 1116
Miami, FL 33156 U.S.A.
Telephone: (1) 305-671-2800
Fax: (1) 305-671-2805
Eastman Chemical B.V.
Fascinatio Boulevard 602-614
2909 VA Capelle aan den IJssel
The Netherlands
Telephone: (31) 10 2402 111
Fax: (31) 10 2402 100
Eastman (Shanghai) Chemical
Commercial Company, Ltd. Jingan Branch
1206, CITIC Square
No. 1168 Nanjing Road (W)
Shanghai 200041, P.R. China
Telephone: (86) 21 6120-8700
Fax: (86) 21 5213-5255
Eastman Chemical Japan Ltd.
MetLife Aoyama Building 5F
2-11-16 Minami Aoyama
Minato-ku, Tokyo 107-0062 Japan
Telephone: (81) 3-3475-9510
Fax: (81) 3-3475-9515
Eastman Chemical Asia Pacific Pte. Ltd.
#05-04 Winsland House
3 Killiney Road
Singapore 239519
Telephone: (65) 6831-3100
Fax: (65) 6732-4930
Material Safety Data Sheets providing safety precautions
that should be observed when handling and storing Eastman
products are available online or by request. You should obtain
and review the available material safety information before
handling any of these products. If any materials mentioned
are not Eastman products, appropriate industrial hygiene and
other safety precautions recommended by their manufacturers
should be observed.
It is the responsibility of the medical device manufacturer
(“Manufacturer”) to determine the suitability of all component
parts and raw materials, including any Eastman product, used
in its final product to ensure safety and compliance with
requirements of the United States Food and Drug Administration
(FDA) or other international regulatory agencies.
Eastman products have not been designed for nor are they
promoted for end uses that would be categorized either by
the United States FDA or by the International Standards
Organization (ISO) as implant devices. Eastman products are
not intended for use in the following applications: (1) in any
bodily implant applications for greater than 30 days, based on
FDA-Modified ISO-10993, Part 1, “Biological Evaluation of
Medical Devices” tests (including any cosmetic, reconstructive,
or reproductive implant applications); (2) in any cardiac
prosthetic device application, regardless of the length of time
involved, including, without limitation, pacemaker leads and
devices, artificial hearts, heart valves, intra-aortic balloons and
control systems, and ventricular bypass assisted devices; or
(3) as any critical component in any medical device that
supports or sustains human life.
For manufacturers of medical devices, biological evaluation of
medical devices is performed to determine the potential toxicity
resulting from contact of the component materials of the
device with the body. The ranges of tests under FDA-Modified
ISO-10993, Part 1, “Biological Evaluation of Medical Devices”
include cytotoxicity, sensitization, irritation or intracutaneous
reactivity, systemic toxicity (acute), subchronic toxicity
(subacute), implantation, and hemocompatibility. For Eastman
products offered for the medical market, limited testing
information is available on request. The Manufacturer of the
medical device is responsible for the biological evaluation of
the finished medical device.
The suitability of an Eastman product in a given end-use
environment is dependent on various conditions including,
without limitation, chemical compatibility, temperature, part
design, sterilization method, residual stresses, and external
loads. It is the responsibility of the Manufacturer to evaluate
its final product under actual end-use requirements and to
adequately advise and warn purchasers and users thereof.
DuraStar, Eastar, Eastman, and Tritan are trademarks of
Eastman Chemical Company.
www.eastman.com
© Eastman Chemical Company, 2011.
TRS-216B 9/11
Printed in U.S.A.