Plastic Assembly News

Full Wave Ultrasonic Horn Resolves Problem

Full wave ultrasonic horns are known to have resolved horn failure issues when half wave designs have proven unsuccessful.  Most ultrasonic horns are manufactured based upon a half wave design.  The half wave design is used to reduce material and machining costs.  However, there are applications and specific design situations that warrant the use of a full wave ultrasonic horn.

One example that justifies consideration of a full wave ultrasonic horn is an application that requires a deep pocket in the working face of the tool.  When a deep center pocket is placed in a half wave ultrasonic horn, the result is usually more stress on the tool than when the pocket is placed in a full wave ultrasonic tool. This is because deep pockets in half wave horns can result in secondary frequencies, indicating that there are undesirable flexural or bending motions in the tool. These flexural or bending directions of vibration are not in the desired axial direction of motion and can result in increased stress, which can cause a horn to fail prematurely.

Horns are designed to resonate in an axial mode of direction. Deep pockets in a half wave horn are so close to the nodal area of the horn that the axial mode is contaminated by the proximity of the pocket to the back mass of the tool.  When an ultrasonic horn is driven at ultrasonic frequencies, it is driven from the center element of the tool.  When a half wave tool has a deep pocket in the center element, the horn has to do more work to drive the center element at the desired frequency and this results in undesirable bending or flexural motions. By making a full wave tool, solid mass is added to the center element and this additional mass pushes the center element with more force. This additional mass driver results in a purer direction of motion on the tool and drives the tool more uniformly in the desired axial motion, reducing the flexural motion and stress. 


Plastic Assembly Technologies has solutions to your ultrasonic horn problems. Contact Us

Routine Ultrasonic Plastic Welder Maintenance

The routine maintenance items for an ultrasonic welder are simple unless there is a machine failure.  The following are recommended maintenance procedures.


1.      Make sure that you have a Mylar washer between the converter and booster and between the booster and horn.  We recommend replacing these washers every 6 months.  A bag of (10) Mylar washers can be purchased for $12.00 from Plastic Assembly Technologies, Inc. at


The Plastic Assembly Technologies part numbers are as follows:


·         MW-12 for a bag of (10) Mylar washers for use on ultrasonic horns and boosters with ½-20 studs

·         MW-38 for a bag of (10) washers for use on ultrasonic horns and boosters with 3/8-24 studs.


2.      When disassembling the stack (ultrasonic converter, booster & horn) for replacing the Mylar washers, check the studs to make sure they are properly torqued.  The stud torque is 290 inch/lb for 3/8-24 studs and 450 inch/lb for ½-20 studs.  When reassembling the stack, the torque specification of the converter to the booster and the horn to the booster is 220 inch/lb.


3.      Drain the air filter as required if it has collected moisture.  Dry air is recommended as air with moisture will eventually impact the functionality of the pneumatic system.


4.      Once a year or more in dirty environments, use light air pressure or vacuum to clean the inside of the power supply. Make sure the power is disconnected before following this procedure.

Machine Troubleshooting


1. Begin by pushing the test button to see if the power supply overloads when running the converter, booster and horn in air.  If the power supply overloads in air, remove the converter, booster and horn from the welder and inspect the assembly carefully. Look to see if there are visible cracks, check to see if the horn is properly torqued to the booster and if the booster is properly torqued to the converter and then check to see the interconnecting studs are properly torqued. Loose horns, boosters and studs will cause overload conditions. If the stud is loose, torque the stud to 290 in-lb for 3/8-24, 450 in-lb for 1/2-20 and 70 in-lb for 8mm stud.  If the horn or the booster appears loose, tighten to these torque specifications: 220 in-lb for 20 KHz and 95 in-lb for 40 KHz.  If either of these components appears cracked, contact us at 317-841-1202 or  A word of caution is in order.  It is possible that you cannot visibly see a crack, but a crack does exist.

2. If everything appears to be okay in step 1, disassemble the converter, booster and horn. Make sure the mating surfaces of the converter, booster, and horn are clean. Check to see if there is a .003 thick Mylar washer between the interfaces.  If so, remove the washers. (Note: if the washers were in place it is likely that the interfaces will be clean.)  If the surfaces are not clean, wipe the interfaces with a soft cloth or paper towel. If the interfaces show pitting or residue buildup, they will need to be resurfaced. To resurface, remove the studs that connect the booster to the converter and the horn to the booster.  Place a sheet of 400 grit emery cloth to a flat surface and pull the component with the worn surface against the emery cloth.  The component should be pulled in a straight line, not in a figure 8 or other pattern, and held perpendicular to the emery cloth.  You should recondition the components by pulling in one direction only and then rotating the component 120 degrees and re-stroking.  It is not necessary to apply pressure as the weight of the converter, booster or horn should be sufficient to provide the needed force.  This process should be repeated until most of the pitting or residue is removed and this is usually accomplished within a few rotations. Note: It may not be possible to remove all of the pitting.  You don’t want to remove all of the craters if the pitting is deep because these are tuned components and too much removal of material will alter the frequency. Once you have the interfaces clean, the converter, booster and horn should be reassembled.

3.  Before reassembling the converter, booster and horn, inspect the interface studs that were removed in step two above. It is possible that these studs have failed and will need to be replaced. If the studs are in good condition they can often be reused, but this is a great opportunity to replace the studs if they are available.  Reinstall the studs using the specifications provided in step 1. The interfaces between the converter and the booster and the booster and the horn should be treated before reassembling.  If you have Mylar washers available, this would be the preferred way of protecting the interfaces.  Place one Mylar washer over the stud of the booster and one Mylar washer over the stud of the ultrasonic horn.  A bag of Mylar washers can be purchased from Plastic Assembly Technologies, Inc. for $10.00.  If Mylar washers are not available, you should use a small amount of silicone grease between the interfaces.  Be careful not to apply the silicone grease to the mating studs.  Reassemble the converter, booster and horn assembly and retest the stack for the overload condition.

This post will be updated frequently in an effort to provide you with additional information on machine troubleshooting. Please check back for more updates. Thanks for visiting.

Setup of Ultrasonic Plastic Welding Applications – Part 1

Obtaining the optimum setup conditions for a given application using ultrasonic weld equipment usually requires a series of tests to determine the welding parameters that provide the best results. Although there is no solution for circumventing this testing procedure, a proper understanding of the principles and components of an ultrasonic assembly system will help to expedite the process of reaching the optimum setup conditions for a given application. To begin our understanding of the optimizing process, it is necessary to understand the basic components that make up an ultrasonic welding system. The system usually consists of six basic components.

1) The POWER SUPPLY changes 50/60 hz electrical energy into high frequency electrical energy and the power supply is rated in watts of available output power. Frequencies are typically available in 15, 20, 30 and 40KHz. Power output ranges from 150 watts to 4000 watts of power. It is important to remember that just because a unit is rated at a certain output power capacity does not mean that an application will require full power from the supply or that the power supply will have adequate power for a given application. The power supply provides power on a demand basis depending upon the amount of power required for the application and under a given set of conditions. The size and shape of the part, the material being welded, the joint design and welder setup variables that control the ultrasonic process can alter the amount of power drawn from a power supply.
2) The CONVERTER is the motor of the ultrasonic system. This component produces a motion via a piezoelectric effect, which is to say that the converter expands and contracts when electrically excited by the power supply. At 20Khz, this expansion and contraction is approximately .001 of an inch at the face of the converter and the movement is in an axial motion. The converter is matched to the output frequency of the power supply.

3) The BOOSTER is a machined piece of aluminum or titanium metal, which is tuned to resonate at the desired frequency and designed to increase or decrease the motion that is produced at the face of the converter. The following decreases/increases can be obtained depending upon the booster used. The booster is sometimes color coded to ease identification of the booster amplification. The booster is attached to the face of the converter via a mechanical stud.

Converter Amplitude (.001) * Booster Gain = Output at Booster

Purple Booster .001 * 0.6: 1 = .0006 output at Booster

Green Booster .001 * 1:1 = .001 output at Booster

Gold Booster .001 * 1.5:1 = .0015 output at Booster

Silver Booster .001 * 2.0:1 = .002 output at Booster

Black Booster .001 * 2.5:1 = .0025 output at Booster

The booster is an important element in determining the output amplitude of the converter/booster/horn assembly. The correct booster and horn combination is very important because amplitude is a critical variable in achieving a successful results with a given application.

4) The ultrasonic HORN is a machined tool that resonates at the desired frequency. The horn is usually manufactured of titanium, aluminum or steel. The primary purpose of the horn is to uniformly transfer the ultrasonic energy to the work piece. The horn is usually made to match the shape of the part to most efficiently transfer this energy. Depending upon the size of the horn, there are various shapes of horn designs to increase the amplitude of the converter/booster/horn assembly. The horn is attached to the booster through the use of a mechanical stud. You can find more information about ultrasonic horns at

5) The ACTUATOR is the pneumatic delivery system of the ultrasonic power. Its components consist of:

  • Solenoid valve
  • Cylinder
  • Flow control valve
  • Pressure regulator
  • Air gauge
  • Carriage to hold the converter/booster/horn assembly
  • Slide mechanism to deliver the carriage with the horn to the part
  • Triggering mechanism to determine the amount of pressure delivered to the part before the ultrasonic energy is activated or turned on.
  • Communication ports to interface to the power supply

Ultrasonic welding systems can be as simple as on/off or more intelligent units providing greater control and monitoring. Both deliver ultrasonic power to the work, but the intelligent systems provide the ability to weld to distance, monitor distances during welding, digitally monitor the pressure gauge, electronically set the trigger force, monitor the trigger switch distance range and control and monitor the forces seen by the system during welding. Pressure is a key variable in the delivery of ultrasonic power to the work. The dynamics and control of this variable are not well understood by many manufacturers that use the ultrasonic welding process.

6) The POWER SUPPLY PROGRAMMER is the control component that determines the sequencing, the duration, the delivery and monitoring of ultrasonic power applied to the work. On less sophisticated ultrasonic units, the duration of ultrasonic vibration is controlled primarily by time. Specifically, once ultrasonics is turned on or activated by a trigger switch, ultrasonic power continues to stay on until the duration of time is complete as established by the preset programmed time. With this type of programmer, there is limited control and monitoring of other system variables.With the advent of technology, the capability to expand the modes of welding and the monitoring of the welding process has grown dramatically. The more sophisticated units allow the ultrasonic welding machines to weld by distance, weld by energy, weld by peak power, weld by compensation modes and to monitor time, energy, force, power, down speed, amplitude, trigger distances, etc. It is the power supply programmer coupled with other system devices that provides all the modern day control and information about the process.

These six basic components provide the basis upon which we will continue our exploration of the dynamics of ultrasonic welding. It is important to understand the function of the basic components before continuing with our discussion of optimizing the ultrasonic setup.

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