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. 


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Who Spec’d This?

A History of Specifications 

When you see a space shuttle sitting on the launch pad, there are two big booster rockets attached to the sides of the main fuel tank.  These are the solid rocket boosters, or SRBs.

The SRBs are made by Morton Thiokol at a factory in Utah.

Originally, the engineers who designed the SRBs wanted to make them much fatter than they are. Unfortunately, the SRBs had to be shipped by train from the factory to the launch site in Florida and the railroad line runs through a tunnel in the mountains.  The SRBs had to be made to fit through that tunnel. Now, the width of that tunnel is just a little wider than the U.S. Standard Railroad Gauge (distance between the rails) of 4 feet, 8.5 inches.

That’s an exceedingly odd number.  Did you ever wonder why that gauge was used?  Because US railroads were designed and built by English expatriates, and that’s the way they built them in England.

Okay, then why did the English engineers build them like that?

Because the first rail lines of the 19th century were built by the same craftsmen who built the pre-railroad tramways, and that’s the gauge they used.

I’ll bite, why did those craftsmen choose that gauge?  Because they used the same jigs and tools that were previously used for building wagons, and you guessed it, the wagons used that wheelspacing.

Now I feel like a fish on a hook!  Why did the wagons use that odd wheel spacing?

Well, if the wagon makers and wheelwrights of the time tried to use any other spacing, the wheel ruts on some of the old, long distance roads would break the wagon axles.  As a result, the wheel spacing of the wagons had to match the spacing of the wheel ruts worn into those ancient European roads.

So who built those ancient roads?

The first long distance roads in Europe were built by Imperial Rome for the benefit of their legions.  The roads have been used ever since.

And the ruts?

The initial ruts, which everyone else had to match for fear of destroying their wagons, were first made by Roman war chariots. And since the chariots were made by Imperial Roman chariot makers, they were all alike in the matter of wheel spacing.

Well, here we are.  We now have the answer to the original question.  The United States standard railroad gauge of 4 feet, 8.5 inches derives from the original specification for an Imperial Roman army war chariot.

Specs and bureaucracies live forever.

That’s nice to know, but it still doesn’t answer why the Imperial Roman war chariot designers chose to spec the chariot’s wheel spacing at exactly 4 feet, 8.5 inches.

Are you ready?

Because that was the width needed to accommodate the rear ends of two Imperial Roman war horses!!!

Well, now you have it.  The railroad tunnel through which the late 20th century space shuttle SRBs must pass was excavated slightly wider than two 1st century horses’ butts. 

Consequently, a major design feature of what is arguably the world’s most advanced transportation system was spec’d by the width of a horse’s behind!

So, the next time you are handed a specification and wonder what horses’ rear end came up with it, you may be exactly right. Now you know what is “behind” it all.

~Author Unknown~

CompuWeld© Program for Ultrasonic Welding


CompuWeld© Software is used for data acquisition with Branson 900 and 2000 series ultrasonic welders for monitoring weld data and providing real time SPC of the critical weld data from the ultrasonic welding process. CompuWeld© SPC or Statistical Process Control involves collecting data from a welder for the purpose of monitoring the process through the use of statistical tools, such as XBar and RBar control charts. Analyzing the output data is done to maintain control of the process and to improve performance of the process. In ultrasonic plastic assembly, the information available about the welding process comes in the form of data about WELD TIME, WELD ENERGY, PEAK POWER, WELD COLLAPSE DISTANCE, TOTAL COLLAPSE DISTANCE AND ABSOLUTE DISTANCE OR FINAL POSITION.

WELD TIME is the duration that ultrasonic energy is on during the weld cycle. ENERGY is the total value of the watts used during the cycle multiplied by the actual time used during the cycle. PEAK POWER is the largest percentage of watts used at a single point in time during the cycle. WELD COLLAPSE is the amount of distance the actuator traveled after the trigger switch was activated and before the hold time. TOTAL COLLAPSE is the amount of distance the actuator traveled after the trigger switch was activated and after the hold time. ABSOLUTE DISTANCE or FINAL POSITION is the total amount of distance traveled by the actuator after leaving the upper limit switch. By monitoring these process variables, we hope to minimize unwanted causes of variation and improve control of the ultrasonic welding process.

There are two types of variation evident in all processes. Natural or random variation and variation caused by special or assignable causes. A process is said to statistically be in control when the only source of variation is coming from natural or random causes. But as Deming said, “a state of statistical control is not a natural state for a manufacturing process. It is instead an achievement, arrived at by elimination, one by one, by determined effort, of special causes of excessive variation.” Types of special causes that can be found in the use of ultrasonic equipment include variation evident in differences in equipment, tooling, setup, operators, material, molding conditions and the environment. In order to use the statistical tools available in “CompuWeld© 2000″ for monitoring a stable process, the welding process must first be brought into statistical control by eliminating causes of variation created by special or assignable causes.

On the CompuWeld© 2000 run view screen, one can see (6) XBar, RBar charts on the screen at one time. The XBar chart is drawn with the XBar above the RBar chart. The values of XBar and RBar are displayed on the vertical scale and the sequence of subgroups are displayed through time on the horizontal scale. The variable being monitored is shown on the top left corner of the XBar chart. XDouble Bar and RBar are shown with dotted lines running horizontally. Control limits are shown with solid lines running horizontally. The last subgroup average measurement and the last subgroup range or variation is shown on the bottom left corner below the RBar chart. The process capability measurements known as the CP ratio and CPK are shown on the bottom right hand corner below the RBar chart. The picture above is illustrative of the data available from the Compuweld© software.

Ultrasonically Bonded Swimsuit

The Speedo LZR Racer swimsuit was used by gold medalists at the olympic games and was bonded with ultrasonic welding to reduce drag. Ultrasonic bonding helped provide the LZR Racer swimsuit with the necessary competitive edge.

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.

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