Frequently Asked Questions

Applications and Setup

Thermoplastic Assembly

Ultrasonic Staking

I want the stud to melt at the face of the horn to form a rivet head. Instead, the stud is melting at its base. What’s going on?

Energy is transmitting through the stud to the base. Try pretriggering so that the ultrasonic horn starts vibrating before it contacts the stud. This will help maintain an out-of-phase relationship between the stud and the horn, which will prevent the coupling that’s occurring. Also try altering the horn velocity, or descent, using the hydraulic speed control to match the velocity with the flow of molten plastic.

Finally, check the radius of the stud. If it’s at a 90 degree angle, that’s not good. That means the stud is acting as a stress riser, and energy tends to migrate there. Radius the base of the stud.

What causes the head of the formed stud to sometimes stick to the horn as it retracts?

The head is not solidifying before the horn retracts. Try increasing the hold time. If the stud head still sticks, it likely means the horn tip is getting too hot. Apply cooling air to the ultrasonic horn’s tip during production. You can also program a short afterburst of ultrasound that turns on as the horn is retracting.

Ultrasonic Noise

When I’m ultrasonic welding two components, the application emits a noise when the ultrasound is applied. What causes this noise and how can I eliminate it?

Sometimes when large, rigid parts are welded, the parts will resonate. To prevent this, dampen any areas that are not critical to the welding of the part (e.g., protrusions, flanges, etc.). Also, check your fixture to ensure it’s mounted properly (a loose fixture can generate noise during assembly). Check the stack components (transducer, booster, and horn), too. If any component is loose, dirty, or broken, that will cause noise, too.

If the noise persists, enclose the tooling or the entire system in a soundproof area. Require hearing protection be used by those people in proximity to the assembly system.

In addition to noise generated from welding applications, noise can occur with inserting applications as well. When the ultrasonic horn contacts a metal insert, noise will be emitted. To stop that noise, turn the part over so that the horn contacts the plastic. (Note: this is not feasible on all inserting applications.) Pretriggering the ultrasound may also reduce or eliminate noise.

Mold Release Agents

What effects might a mold release agent have on an ultrasonic assembly?

Mold release agents reduce surface friction between parts and contaminate the thermoplastic resin. Both are bad for ultrasonic assembly. A good ultrasonic bond depends on the plastic parts’ surface friction to create the frictional heat needed for assembly. Therefore, use of a mold release agent can cause uneven welds, inconsistent welds, or prevent welds completely.

If you’re using mold release and experiencing problems, clean the parts’ joint surfaces with solvent. Use a mold release agent that is a paintable/printable grade; those agents interfere the least with the ultrasonic process and they often require no pre-assembly cleaning. It’s a good idea to stay away from mold releases such as zinc stearate, aluminum stearate, fluorocarbons, and silicones because they are particularly difficult to work with when using ultrasonics.


Do colorants affect the weldability of thermoplastics?

Liquid or dry colorants don’t affect thermoplastic welding unless the percentage of colorant to resin is especially high. This is most common with white or black parts, which often need more pigments than other colors.

One thing to be aware of is possible color variation between different batches of the same part. Color variation will sometimes necessitate a change in the setup parameters of your ultrasonic equipment. Do some experimenting prior to starting full production runs.


Will adding a lubricant to my adversely affect its ultrasonic weldability?

Yes, more than likely because lubricants such as wax, zinc stearate, aluminum stearate, and fatty esters reduce the amount of friction between parts. Since friction is critical to ultrasonic assembly, a lubricant can actually work against the ultrasonic process.

Before using a lubricant, call our Applications Department at (630) 797-4930. Our engineers can discuss the properties of the lubricant to be used to help you determine what effect(s) it would have on your assembly process.

Recycled Parts

Can ultrasonically processed parts be recycled?

Yes, as long as the plastic you’re using is recyclable. Likewise, you can also ultrasonically process parts made of recycled plastic (i.e., regrind) as long as 1) the plastic did not become degraded or contaminated in its previous use, and 2) the parts don’t contain more than 20% regrind.


Fabric & Film

Ultrasonic Cutting and Sewing Fabrics

What kinds of fabrics can ultrasonic systems cut and sew?

Ultrasonics can be used to cut, sew, and seal synthetic materials, such as nylon, polyester, polyethylene, polypropylene, urethanes, and PVC, as long as they have at least a 60% thermoplastic composition. Material structure can vary -- woven and nonwoven material, knits, coated materials, laminates, and films can all be ultrasonically processed.

Seam Strength

When ultrasonic cutting and sealing fabric, is the seam as strong as that sewn with a needle and thread?

Yes. In fact, the seam ultrasonics creates is stronger than regular needle and thread bonds, because needles create holes in the fabric that can weaken the material. Also, if you lose one needle and thread sewn stitch, the whole seam is compromised, since all the stitches are connected. If you lose one "stitch," or weld, in an ultrasonic seam it will maintain its integrity, because each ultrasonic weld is independent.

Fabric Weight

How does a fabric’s weight affect an ultrasonic bond?

If your fabric weighs more than 2 ounces per square yard, it’s easy to create a bond with 20 kHz ultrasonic equipment. For fabrics weighing less than 2 ounces per square yard, the high amplitude of 20 kHz ultrasonics equipment can burn a hole in them. It’s better to use a 40 kHz ultrasonic system, which is designed for more delicate assembly operations.

Ultrasonic Bonding

What is ultrasonic bonding?

Ultrasonic bonding assembles two or more layers of material (usually nonwoven) between a vibrating horn and a rotary drum. Machined into the drum is a pattern of raised areas, which is where the bonding takes place. The high frequency mechanical motion of the vibrating horn combined with the compressive force between the horn and the drum create frictional heat at the point where the horn contacts the materials. Ultrasonic bonding results in a high degree of softness and breathability, which are important characteristics of nonwoven products.


Additional Joining Processes

Vibration Welding

What’s the difference between vibration welding and ultrasonic welding?

Vibration welding brings two halves of a part together under pressure, holding one part half stationary, while the other half is moved back and forth in a linear motion at 120 to 240 cycles per second. During vibrations welding, frictional heat is created as pressure and movement are applied to the parts.

Ultrasonic welding is the joining of two thermoplastics through the use of frictional heat generated from force and mechanical motion. It is accomplished by converting electrical energy into high frequency mechanical motion (vibrations) and applying that motion to parts under pressure. The vertical motion and force create frictional heat at the mating parts’ joint area, causing the plastic in the joint area to melt. As the molten plastic solidifies, a molecular bond forms between the plastic part halves.

Hot Plate Welding

What’s the difference between hot plate welding and ultrasonic assembly?

Ultrasonics and hot plate welding are heat-related processes that focus and direct heat/energy to the part interface. The main difference is in how the heat is created and transferred.

Hot plate welding uses a metal platen heated by electrodes to transfer heat to the two plastic part halves. Both part halves touch the platen and the plastic becomes molten. The platen retracts, the parts are pushed together, and a bond is created between the two parts.

Ultrasonic assembly uses a piezoelectric transducer to convert high frequency electrical energy into high frequency sound vibrations that are transmitted through two plastic parts under pressure. The vibrations, along with the pressure/force on the parts create frictional heat at the parts’ joint interface, causing the parts to melt at the joint. Within seconds the plastic cools, forming a molecular bond between the two parts.


Acoustic Tooling

Ultrasonic horns from other systems

Will horns from other ultrasonic assembly systems fit on a Dukane system?

Yes. It’s best though if we inspect the tooling and ensure that it’s running at minimum frequency before you begin production.

Horn Slots

Why do large ultrasonic horns have slots machined into their sides?

When a horn’s diameter or length is greater than 3.5 inches to 3.75 inches, side motion and transient frequencies can alter the amplitude at the horn’s face and create internal stress. Machining slots into the sides of the horns overcomes those problems. The slots divide the horn into smaller, individual horns, ensuring uniform amplitude and relieving the internal stress.

Maximum Horn Width

What is the maximum horn width (or length) that can be used in continuous cutting and sealing applications?

Because uniform amplitude is necessary in achieving consistent results, horns should be no more than 9 inches in width/length. This size limit can be overcome by mounting multiple ultrasonic thrusters across a rotary anvil, which is unrestricted in length.

Cooling - Continuous Duty

When running a continuous duty application, must stack components always be cooled?

Yes. To maintain ambient temperature, cooling air must be applied to the output end of the horn, to the transducer/booster interface, and to the transducer itself. The application and power draw may even necessitate refrigerated cooling.

Horn Frequency

How do I know if my horn is out of frequency?

A: Some problems you can encounter may also indicate an incorrectly tuned horn. Is heat developing away from the horn/booster interface? This could mean the horn is worn, causing it to be out of frequency. Are welds inconsistent? Inconsistent welds are a sign of an out-of-frequency horn, particularly when the horn has been re-machined.

If you’re having problems or questions about your tooling, contact your Dukane representative or our Tooling Department at (630) 797-4930.


Power Supply:  Generators/DPCs

Power Supply Cooling

Does the power supply need cooling when running a continuous duty application?

If you’re using a Dukane Dynamic Process Controller (DPC), you don’t need to worry about cooling. The DPC’s flow-through cooling design and thermostatically controlled fan rapidly dissipate heat. If you’re not using a DPC, your power supply needs to be cooled.


Process Controller:  DPCs/Ultra-Coms

Dual Pressure Assembly

What is dual pressure assembly? How does it differ from regular ultrasonic assembly?

Dual pressure is an exclusive feature of Dukane Millenium DPC or Ultra-Com-equipped ultrasonic assembly systems that allows you to assemble parts at one pressure and hold the assembly at another (typically higher) pressure. Or the pressure can be changed during the weld portion of an assembly cycle, with the parts held at the second pressure during the hold portion of the cycle. Standard ultrasonic assembly processes weld and hold part assemblies at the same pressure.

Click here to find out more about the types of dual pressure welding.


Ultrasonic Thermal Presses/Thrusters

Air Pressure Gauges

How accurate are the air pressure gauge readings on a Dukane press or thruster?

The gauges we have in all our presses/thrusters have the following tolerances:

  • From 40 - 60 psig +/- 2 psig
  • All other settings +/- 3 psig
Compressed Air Volume Requirements

How much compressed air will I need to operate a press or thruster?

The amount of air needed depends on the number of cycles run per minute, stroke length, cylinder size, and air pressure used. For 20 kHz presses with standard 2.5-inch bore air cylinders, use the following formula for a rough estimate of air requirements:

cycles/minute X stroke length X .04 = air consumption

Example: 6 cycles/minute X 3 inch stroke X .04 = .72 scfm @ 70 psi

For 40 kHz presses with standard 1.5-inch bore air cylinders, use the following formula for a rough estimate of air requirements:

cycles/minute X stroke length X .02 = air consumption

Example: 6 cycles/minute X 2 inch stroke X .02 = .24 scfm @ 70 psi.

For optional size air cylinders and high pressures, consult your local Dukane representative.

Force exerted by a press

How much force does my welder exert?

For standard Millennium Model 210 and 220 presses and ULTRA Heavy Duty presses, the formula is:

air pressure setting X multiplier = lbs of force


For standard 2.5-inch bore air cylinders, the multiplier is 4.9

For optional 2.0-inch bore air cylinders, the multiplier is 3.1

For optional 3.0-inch bore air cylinders, the multiplier is 7.1

Example: 70 psi X 4.9 = 343 lbs of force

For standard 40 kHz presses, use a multiplier of 1.75

Example: 70 psi X 1.75 = 123 lbs of force

Weld Cycle Speed

How fast can a welder cycle?

Assuming a 7-inch stroke length, a Millennium Model 210 press or an ULTRA Heavy Duty press takes approximately 0.7 seconds to travel up or down that length. A narrow profile Millennium Model 220 press takes about 0.4 seconds.

To calculate total cycle time, add the downstroke time plus the weld time plus the hold time plus the upstroke time, and the time it takes to load and unload each part assembly. To reduce cycle time, use shorter stroke lengths, open the flow control valve, and consider using a smaller bore air cylinder (provided your application can weld using a lower force).

Trigger Setting

What does the trigger setting do?

Trigger is the point at which the trigger switch inside the press closes and the ultrasound turns on. The ultrasound may be turned on ("triggered") by reaching 1) a distance, 2) a lack of velocity (when the horn stops against a part), 3) or most commonly, a force on the part.

The trigger knob on our presses adjusts the preload, or the amount of compression force, applied on the part before turning on the ultrasound. The higher the number setting on the knob, the more compression force is exerted before the ultrasound is turned on. On presses equipped with load cells (i.e., force transducers), the trigger knob is not used. The compression force is set electronically.

Absolute Distance

Can absolute distance really be measured to a ten-thousandth of an inch (0.0001")?

Yes. The linear encoder used on Dukane presses is able to read in ten-thousandths of an inch increments. The Ultra-Com process controller interprets the measurement and displays it in this scale.

Downstroke distance & absolute distance

What is the relationship between downstroke distance and absolute distance?

Downstroke distance is the distance the horn travels until the ultrasound trigger point is reached. When this trigger point is reached, the trigger switch closes and ultrasound is "triggered", or turned on. Typically, this trigger point is where the horn contacts the part being welded. If pre-triggering (i.e., turning on the ultrasound prior to contacting the part) is being used to activate the ultrasound, downstroke distance is then the distance the horn travels until the pretrigger point is reached and not the contact point of the part being welded.

Absolute distance is the combination of the downstroke distance, weld distance, and hold distance. The weld distance is the distance the horn moves during the application of ultrasound to create the weld. Hold distance is the distance the horn moves during the hold or "cooling" portion of the weld cycle,

Downstroke distance & absolute distance - design considerations

If I were designing to meet a specific joined part width, should I be more concerned with downstroke distance or absolute distance?

Absolute distance gives the most accurate measurement of the final dimension of the welded part. Downstroke distance, in this case, is not a critical measurement for this requirement.

Bolt Pattern

What is the layout of the bolt pattern on your flange?

We use five (5) 1/2" or 12mm bolts. For the bolt pattern, see drawing #299-13.

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