Ultrasonic welding has been in existence as an assembly process for over 40 years. As a method of bonding plastics, it has become one of the most accepted processes because it is clean, energy efficient and fast.

The birth of ultrasonic welding was discovered quite by accident, as many modern marvels are similarly invented. In the early years of the technology, the energy was applied to the plastic part by an operator who would manually pull the lever arm of an arbor press, which held an ultrasonic transducer and horn. In those days, the pressure would vary during the process and the amplitude would droop tremendously as the load was applied to the material. The process control was crude, but an industry had been launched.

During the late 1960’s and early 1970’s, ultrasonic machines were produced with pneumatic delivery systems and manufacturers called these components, presses or actuators. As a means for delivering the converter and the horn to the plastic, these systems were significantly advanced when compared to the previous hand controlled choice. In the 1980’s and 1990’s new products were produced that controlled the amount of energy delivered to the plastic. Ultrasonic welding machines were developed allowing welding by distance. Other significant electronic advances were made to the power supplies to control amplitude and stay current with the digital revolution. However, the delivery system for bringing the vibrating horn to the plastic has continued to be the standard actuator or press comprised of pneumatic components.

Back in the mid 90’s I predicted that I would be surprised if by the year 2000 manufacturers of ultrasonic plastic welding equipment had not incorporated the servo controlled technology into their standard product line. It just made sense. These innovative machine motion control systems provide the ability to control and profile force with the acceleration and deceleration features embellishing the welding process. I thought that servo controlled ultrasonic systems would become as common place as servo controlled injection molding machines.

Wow was I way too early with my prediction. However, one manufacturer has finally seen the light. Dukane has developed a new delivery system that looks like it could provide users a degree of control not previously realized in the industry. I am sure it is expensive and not meant for all applications, but for those companies looking for precise control of the process it is probably worth investigating.

Gary Clodfelter
Plastic Assembly Technologies, Inc.

Through our own product development group the InfraStake process was created and patented, and in the last 7-years thousands of modules and hundreds of systems have been serving in production in various industries.

The advantages of a low impact, non-intrusive staking process are many. The consistency offered by InfraStake with its clean and efficient light energy have many of our users specifying “across the board” this process on all staking applications.

The system pictured on the right is a standard 6-point InfraStake machine built to assemble an automotive interior trim component. The InfraView power supply/controller is mounted below the working surface – integrated into our standard, adjustable height ErgoStation table. The intuitive, color operator interface is ideally positioned for ease of use. The model shown has our typical guarding package with safety light-curtain and single opto-touch start switch package. ‘Back lighting’ is provided for operator convenience and positioned in such a manner as to prevent glare. A CNC machined fixture with part presence sensors is very typical on such a system.

When we break down the actual science of light energy and the manner it is applied in a standard InfraStake cycle, it is a relatively straight-forward process. Please review the schematic below:

The cross-section views depicted reveal the internal components of a typical InfraStake module. The embedded lamp, the integrated staking punch, the reflector, and the concentrator. Not shown is the low-force, pneumatic cylinder which is mounted directly on top of the module. The staking punch detail is tied to this cylinder through a clever mechanism that allows for for easy and quick disassembly for inspection.

1) Clamping & Heating

During this phase, the InfraStake head(s) are presented to the sub-assembly on a main press/slide mechanism, this action positions the concentrator directly on the staking surface which provides optimum integrated part clamping. The heating cycle is initiated through the illumination of the lamp. This 100watts (typical) ‘technical application’ grade lamp emits infrared (IR) light energy which is collimated and radially oriented in such a manner as to generate a focal point ideal for consistent, even heating of the subject boss or stud. The highly polished, gold-plated reflector and concentrator elements achieve this ‘management’ of the IR light energy as a function of the engineered geometries.

Heat time is a programmed function controlled by the user. In multiple head applications, each module is independently controlled – both heat and punch (hold) times. The InfraView power supply can drive up to (24) heads simultaneously and in addition to providing calibrated and conditioned power output for each module, the lamp current is a monitored function in order to assure process consistency and to provide potential lamp fault alert messages.

2) Staking & Cooling

At the end of the heating cycle the lamp is switched off, the low-impact air cylinder with integrated staking punch is activated which forms over the semi-molten stud. When we mention “low-impact”, it is important to note that the stud is heated so evenly that the force required is typically as low as 15 – 25lbs of true force. That means low stresses in the plastic and less potential damage to sensitive components in the proximity of the operation – such as PCB applications. The staking punch is not heated; it is positioned in the module outside of the IR focal point. Cooling or hold time therefore is very efficient as the formed stud re-solidifies under pressure. Stringy/sticky plastic adhering to the punch is also a non-issue with InfraStake due to the ‘cool’ punch surface.

 
3) Punch Retracts

At the end of the programmed hold or punch time, the internal staking punch mechanism retracts.

4) Head Retracts

At cycle completion the main press/slide mechanism retracts.

Two 1.25 InfraStake modules are pictured below, the unit on the left is partially dis-assembled to show the body, the reflector/punch/lamp assembly and the concentrator. The unit on the right is a fully assembled module. Both are shown with the air cylinder and mounting spacer installed. The main power cable is shown as well as the full-stroke sensor and related cable.

General 1.25 module dimensions for reference (less mounting spacer): 1.25″ O.D x 6.75″ O.L.

InfraStake modules are available in three standard sizes: the 1.25, 1.70 and 2.30…as you can guess, model numbers depict the maximum O.D at the concentrator – in inches. Module sizes are determined for each application based on stud O.D., wall thickness, and stud height.

For reference, a Linear Zone InfraWeld unit is shown below. Through the application of clever engineering and design, the focal point of the IR energy can be delivered outside of the concentrator for zone area heating. The application opportunities are numerous…

Infrastake heads can be mounted in various configurations as shown in this picture where a flexible steering column closeout – or ‘gap hider’ is being secured into location with (4) stake locations. A horizontal mounting of the modules makes sense as the additional functions of clip driving, part presence sensors and bar code reading are executed in the same fixture.

The picture below shows multiple heads active during the clamping/heating cycle. The main machine platen is in the clamped (down) position which presents all (21) InfraStake heads to the work surface – clamping both components securely together…at each stake point, which is optimum.

Solid part design is critical to achieving ideal results. Note the surfaces that the InfraStake concentrators are contacting, the molded surfaces extend in a plane perpendicular to the protruding studs (hidden) and the direction of pressure of the modules. This allows for one common press mounting surface on this seat back application eliminating complex slide action and/or angled mounting surfaces of the InfraStake modules. Another benefit of such a design is strong, uniform final stud displacement, smart…

The consistency and quality of the formed studs with the InfraStake process is demonstrated on this instrument cluster sub-assembly, nice…

The InfraStake/InfraView components can be purchased as a ‘tooled’ set ready for installation. This 4-point package is ready to be integrated into a special system. Customers with an ‘internal machine’ group and custom machine builders benefit from this type of package.

Various Infrastake applications pictured show the versatility of this process. Amorphous and Semi-Crystalline resins alike respond well to the IR light energy. Highly sensitive ‘A’ surface finishes are protected through this low impact, focused energy, Elastomer seals and highly sensitive PC board components are not subjected to super-heated punches or vibratory energy.

•                                                                                                                             Features of the PAT Palm Button Sets:       
• PAT palm buttons initiate ultrasonic welder cycle
• All pre-wired for direct plug in to welder
• Includes emergency stop button to terminate cycle  
• Includes 9’ cable and D shell connector
• Includes mounting hardware                                          
• Built from aluminum tubing and aluminum plate 
• PALM-1 includes light touch mechanical switches      
• PALM-2 includes capacitive touch switches
• Easily adapt to Pat’s slim line welder table

  Palm Button Set Models
PALM-1 Palm button set with (2) light touch start buttons and emergency stop button
 PALM-2 PALM button set with (2) capacitive start buttons and emergency stop button

Plastic Assembly Technologies, Inc., located in Indianapolis, Indiana, has a complete line of accessories for ultrasonic welding.

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

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© 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.