VIEW THE ONLINE EDITION
High-Tech Contract Decorating at Emerald Corporation
2012 SGIA Expo Show Preview
Ask the Expert
Plastics Surface Energy Wetting Test Methods
Scratch-resistant in One Step
Letter from the Chair
TopCon Rolls Through Indy
Digital Decorating Webinar Scheduled for August 28
Ultrasonic Welding: The Need for Speed Control
How to Close Sales that are Over the Budget
PLASTEC West, Anaheim Convention Center, Anaheim, CA, www.plastecwest.com
Plastics Crossroads Summit,
Sheraton Hotel, Anaheim, CA, www.rjginc.com/plasticscrossroads
PLASTEC South, Orange County Convention Center, Orlando, FL, www.plastecsouth.com
AWA DecTec USA, Orange County Convention Center, Orlando, FL, www.awa-bv.com
SPE ANTEC® 2013, Duke Energy Convention Center, Cincinnati, OH, www.antec.ws
HBA, June 18-20, Jacob K. Javits Convention Center, New York City, NY, www.hbaexpo.com
PLASTEC East, , Pennsylvania Convention Center, Philadelphia, PA, www.plasteceast.com
Copyright 2010 Peterson Publications, Inc.
Plastics Decorating Magazine
2150 SW Westport Dr., Suite 101
Topeka, KS 66614
(785) 271-5801Â Fax (785) 271-6404
The Process of Vibration Welding
by Jordan Rotheiser, Rotheiser Design Inc.
In my day, Boy Scout manuals described a method for creating a fire by
rubbing two pieces of dry wood together. However, this particular Boy Scout was
never successful at creating anything more than a sore arm with this technique.
I now realize that the problem was that I never achieved speeds of 120 cycles
per second in rubbing the two pieces of wood together. Crudely, that, in effect,
is the concept behind vibration welding: pressure plus friction combining to
create heat. In this case, however, the parts being rubbed together are made of
Orbital Vibration Welding
This is the principal rotational type of vibration welding. It was created to
fill a gap in the market for a mid-size machine that can handle parts up to 305
mm (12 in) in diameter and to accommodate some parts that cannot be made with
ordinary vibration welding. With this technique, the two platens rotate in a
circular pattern relative to each other as illustrated in Figure 1. Unlike
linear vibration welding, which has a non-uniform welding velocity because it
must start and stop at each end of its cycle, orbital welding is continuous.
This reduces the time necessary to create the weld, which lessens the amount of
energy required. It also requires less weld amplitude, thus reducing the
clearance required for the weld motion and providing better control of the
flash. It has less effect on flexible walls and can produce stronger bonds.
Unfortunately, orbital vibration is application sensitive and cannot be used for
Figure 1. Orbital Welding Motion
Linear Vibration Welding
Vibration also can be applied in either a linear or rotational fashion. Linear
welding is by far the oldest and most commonly used variety with thousands of
machines in use. It provides the best value and a wide range of sizes. Whereas
orbital vibration operates best at off-resonance frequency, linear vibration
welding is used at resonance frequency. The manner in which the parts are driven
is dependent on its shape and rigidity. The driving force is applied on the
external shoulders in Figure 2a. However it also can be applied from a recess in
the part as shown in Figure 2b. When internal ribs or midwalls are to be welded,
a fixture such as the one in Figure 2c. would be required where pressure is
applied over the internal joint.
Figure 2. Fixtures for Linear Vibration Welding: a.
external shoulder fixture, b. recessed fixture and c. multiple internal
The equipment for linear vibration consists of a vibrator located in the upper
section of the machine frame, consisting of a vibrating platen suspended from
springs and driven by electromagnets. In the lower section of the machine frame
there is a clamp plate, which is operated by a hydraulic cylinder that lifts it
to meet the vibrating platen and supplies the pressure for welding. Fixtures
that are custom-made to fit the contours of each application are attached to the
vibrating platen and clamp plate.
Figure 3. Basic Linear Vibration Welder.
The cycle begins with the loading of one of the parts to be welded in the nest
or fixture of the lower clamp plate of the machine as illustrated in Fig. 3. The
mating part is then placed in position on the lower part. The lower clamp plate
is then raised to the vibrating platen in which rests the upper fixture. It fits
the mating part closely and fixes its location. The two parts are clamped
together under a controlled load and the part in the vibrating platen is
vibrated through an amplitude ranging from 0.75 mm (0.030 in) to 5.0 mm (0.200
in) at a frequency from 120 Hz to 300 Hz to create frictional heat at the
interface between them. The pressure is important because, without the pressure,
no heat is generated. Low weld pressures result in increased cycle times.
Sophisticated systems can optimize the process control by varying the pressure
during the cycle.
Basically, there are four phases to vibration welding. In the first phase, the
vibration of the rigid members creates Coulomb friction, which generates heat at
the joint interface. No penetration (movement of the parts toward each other)
takes place in this phase. When the glass transition temperature is reached and
viscous flow occurs, the second phase begins wherein heat is generated by
viscous dissipation in the molten polymer. Lateral flow of the polymer permits
the penetration to take place. In the third phase, the melt and flow have
reached a steady state at which heat losses through the wall due to flash equal
that being generated. At this point, melt is flowing laterally and weld
penetration increases linearly with time. This part of the cycle is
application-dependent and will require 0.5 to 10 seconds; about two-thirds of
the welding cycle. The penetration required to reach steady-state condition
increases with the wall thickness of the part, but decreases with increasing
When sufficient heat has been generated to melt the material at the interface,
the vibrations are halted and the fourth phase commences. Weld penetration
continues because the clamping pressure causes the molten polymer to flow until
it solidifies. The parts are held clamped in the desired final position while
they cool sufficiently to withstand handling, a period ranging from 0.5 to 5.0
seconds. This is critical because there is no means of controlling lateral
location of the two parts to each other beyond the final position of the
vibrating platen. Once this is accomplished, the lower clamp plate is lowered to
its original position and the completed assembly is removed. The equipment is
now ready to commence a new cycle.
Advantages of Vibration Welding
1. NO ADDITIONAL MATERIALS - Vibration welding uses no additional materials such
as fasteners, inserts, electromagnetic preforms, adhesives or solvents.
Therefore, it is inherently lower in cost than methods, which do use additional
materials, and is less expensive to disassemble for recycling.
2. LOW SURFACE PREPARATION - Vibration welding is relatively insensitive to poor
3. EASE OF ASSEMBLY - Vibration welding requires only the placement of the two
parts in the fixture of the vibration welder.
4. ENTRAPMENT OF OTHER PARTS - Additional parts can be captured between the two
parts to be vibration welded provided they are located such that they do not
interfere with the welding.
5. PERMANENCE - Vibration welding creates permanent assemblies that cannot be
reopened without damaging the parts. Owing to material limitations, differences
in thermal expansion and moisture absorption are rarely of concern once the
parts are welded. .
6. INTERNAL JOINTS - In some cases, internal walls can be vibration welded
provided they meet at the welding plane.
7. SHAPE FREEDOM - Vibration welds can be made with parts of practically any
shape so long as the horizontal joining surfaces can be created within the
required limits. Vibration welding is not dependent on the vibration
transmission qualities of the plastic, therefore it can weld parts that are not
well suited to ultrasonic welding because they are too flimsy, contoured, have
holes in the walls or do not have a surface well suited to ultrasonic horns.
8. HERMETIC SEALS - Vibration welding is capable of creating hermetic seals.
9. ENERGY EFFICIENCY - Relative to other welding processes, vibration welding is
highly energy efficient. This also means that there is no excess heat that must
be removed from the workplace.
10. CLEAN ATMOSPHERE - Unlike adhesive and solvent joining systems, no
ventilation equipment is necessary for the removal of toxic fumes.
11. IMMEDIATE HANDLING - Assembled parts can proceed on to other operations at
once without waiting for parts to cool and for adhesives or solvents to set.
12. HIGH PRODUCTION RATES - Depending on the application, vibration welding is
capable of production rates of 4 to 30 parts per minute based on a single
weldment per cycle and not taking into account the part handling time which
varies with each application. Higher rates are possible if multiple parts are
welded with each cycle.
13. PROCESS FREEDOM - Parts made from virtually all the thermoplastic processes
can be vibration welded.
14. LARGE PART CAPABILITY - Equipment is available that can weld parts up to
1016 mm (40 in) by 2032 (80 in). A 1524 mm (60 in) automobile bumper has been
successfully vibration welded.
15. PRECISION CONTROL - Vibration welding permits precision control of process
16. QUICK CHANGEOVER - Vibration welding equipment can be quickly changed from
one job to the next.
17. CONTROLLABILITY - This process is readily controlled and is not likely to
result in surface degradation due to overheating.
Disadvantages of Vibration Welding
1. SHAPE LIMITATIONS - There must be a flat, horizontal welding surface.
2. DAMAGE TO ELECTRONIC COMPONENTS - Vibrations can damage some electronic
components or their assemblies.
3. ALIGNMENT - Locating pins or other devices cannot be molded into the part.
Alignment between the two parts is set by the final resting place of the two
4. MATERIAL LIMITATIONS - Materials for vibration welding are limited to
5. SOUND CONCERNS - The foghorn noise associated with vibration welding (90 to
95 db) makes the use of sound enclosures commonplace. These reduce the sound
level to approximately 80 db.
6. EQUIPMENT COST - Vibration welders are more expensive than hot plate welders
and cost considerably more than ultrasonic welders or spin welders, a
consideration that tends to limit their use to applications, which are too large
or poorly configured for these techniques.
Materials for Vibration Welding
Virtually all the thermoplastics can be vibration welded. In that respect, this
process is similar to hot plate and spin welding. This process is particularly
useful for the crystalline thermoplastics, which are difficult to join with
ultrasonic welding. As with ultrasonic welding, the amorphous resins are more
readily welded than the crystalline resins. However, the crystalline
thermoplastics are more readily vibration welded than ultrasonic welded.
Materials with low coefficients of friction may require higher vibration
frequencies for optimum weld quality. The process is claimed to have been
successfully employed with thermoplastic rubber and elastomers. High temperature
engineering thermoplastics have been successfully vibration welded.
Filled and reinforced resins are readily welded with vibration welding. However,
only the polymer welds, so the strength of the bond is that of the resin itself
and the strength of the joint is further reduced by the percentage given to the
filler. In particular, glass fibers may protrude through the surface of the weld
at its center. Conversely, this process is less affected by mold release and
other surface contaminants than either hot plate or ultrasonic welding and it is
somewhat less affected by moisture content, although highly hygroscopic polymers
like nylon must still be welded with care. Moisture can cause bubbles in the
joint due to the formation of water vapor. Pre-drying the parts can reduce
bubble formations and welding time. A high joining pressure can prevent the
formation of bubbles in the weld. At 50 percent RH, Nylon 6 weld strengths can
drop to around half those of dry welds. Nylon 66 fares somewhat better, dropping
less than a third.
Comparison with Ultrasonic and Hot Plate Welding
Vibration welding can be described as the process that picks up where ultrasonic
welding leaves off, particularly in terms of part size. That it is somewhat
similar in principle is true. Consequently, it shares many of the same
attributes. In addition, the equipment is made by manufacturers who also produce
ultrasonic welding equipment, so the two processes compliment each other nicely.
However, due to the considerable cost of the equipment, one normally uses
vibration welding only for those applications that are unsuited to ultrasonic
welding. There are some significant differences between the two techniques.
While both processes use high-frequency vibrations to create, they apply them in
a different manner and at much different frequencies. Ultrasonic welding
vibrations are vertical, range from 15,000 Hz to 72,000 Hz and create heat
through molecular friction. Vibration welding is horizontal with frequencies
between 120 Hz and 300 Hz and creates heat through surface friction as it
physically moves the whole part. The net result is that vibration welding can
handle much larger parts than ultrasonic welding and does not require the energy
directors that largely limit ultrasonic welding to parts made by the injection
molding process. While thermoset parts cannot be vibration welded, parts made
from virtually all of the thermoplastic processes can be joined by this process.
Hot plate or fusion welding also can be considered a competitor to vibration
welding because its joint strengths and material compatibilities are
approximately equivalent. However, while it has much lower equipment cost and a
greater range in size and shape, it has a much longer cycle time and higher
equipment, fixture, energy and maintenance cost than vibration welding.
Linear vibration welding has numerous applications in the automotive field
including manifolds, dashboards, bumpers and taillights. Appliance applications
include blower and pump assemblies, refrigerator bins and chain saw housings.
Examples of orbital vibration welding applications are taillights and electrical
This article is composed of partial excerpts from the chapter on vibration
welding in Jordan Rotheiser’s book, “Joining of Plastics, Handbook for Designers
and Engineers.” The book may be purchased from Hanser Gardner Publications at
Jordan Rotheiser is president of Rotheiser Design Inc. and the author of the
critically acclaimed, best selling “Joining of Plastics - Handbook for Designers
and Engineers”, the product design chapter of the “Modern Plastics Handbook” and
the plastics chapter of McGraw Hill’s “Handbook of Materials for Product