Plastic Assembly News

What Plastic Welding Process Should You Use?

It’s impossible to say that one method or the other is absolutely the correct process due to the feasibility of welding your part with multiple processes.  Each process does have its advantanges and disadvantages and when considered in combination with material selection, part size, part geometry, part requirements and a host of other considerations, you will likely be on the path to selecting a process more suitable for your application.   We hope the chart below will be useful in your selection process.

 

          ULTRASONIC WELDING VIBRATION WELDING SPIN WELDING HOT PLATE WELDING LASER WELDING
Amorphous Plastics                     ?
Semi-Crystalline Plastics     ?             ?     ?
Parts with Complex Geometry     ?         ?         ?
Parts Requiring Welds on Internal Features         ?     ?        
Small Parts         ?            
Large Parts     ?         ?         ?
Round Parts                    
Non-Round Parts             X        
Long Unsupported Walls         X     X        
Viable Process    
Maybe     ?
Don’t     X  
           
                   
                   
                   
                   
                   
                   
                   
                   
                   
   
     
       

Machine Troubleshooting

MACHINE OVERLOADS – POWER SUPPLY, CONVERTER, BOOSTER, HORN OR OTHER FAILURE?

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 www.patsonics.com.  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.

PLASTIC MATERIAL REFERENCE GUIDE FOR ULTRASONIC WELDING

The chart below includes recommended amplitudes for ultrasonic welding. These values are reference points for the required gain needed to weld the plastic material. The amplitude may need to be adjusted to achieve the best results for a particular application. (The amplitude level presented in the chart is displayed in microns-to convert to inches, 25.4 microns is equal to .001 of an inch)

Material Welding Insertion Staking Near Field Welding Far Field Welding Ease of Staking Trade name(s
AMORPHOUS RESINS
ABS-Acrylonitrile Butadiene 30-70 20-50 30-80   1 1 1 Cycolac, Lustran
Styrene                
                 
ABS/PC-ABS/Polycarbonate 70-100 50-70 80-120   2 2 2 Cycoloy,  Pulse
                 
ASA-Acrylonitrile Styrene 30-70 20-40 70-90   1 1 3 Centrex, Geloy, Luran
Acetate                
                 
PC-Polycarbonate 50-90 40-70 50-90   1 2 3 Lexan, Calibre, Novarex
                 
PEI-Polyetherimide 70-100 40-70     2 4 5 Ultem
                 
PES-Polyethersulfone 70-100 40-70     2 4 5  Ultrason
                 
PMMA-Acrylic 40-70 30-60 70-90   1 3 3 Acrylite, Plexiglass, Zylar
                 
PPO-Polyphenylene Oxide 50-90 40-60 60-90   2 3 2 Noryl
                 
PS-Polystyrene 20-40 20-40 70-90   1 1 4 Dylark,   Styron
                 
PSU-Polysulfone 70-100 40-70 90-120   2 3 3  Udel
                 
PVC-Polyvinyl Chloride (Rigid) 40-80 20-50 70-100   2 4 2 Novablend, Ultrachem
                 
SAN-Styrene Acrylonitrile 30-70 20-40 70-90   1 1 3 Lustran, Styvex
                 
SBC-Styrene Block Polymers 50-90 30-50 80-100   2 3 2  K-Resin
                 
SEMI-CRYSTALLINE RESINS
PA- Polyamide  (Nylon) 70-120 40-80 60-120   2 5 3 Celstran, Ultramid,  Zytel
                 
PBT-Polybutylene terephthalate  70-125 40-80 90-120   3 5 4 Celanex, Ultradur,  Valox
(Polyester)                
                 
PE-Polyethylene 70-120 40-80 40-120   2 5 2 Aspun, Clysar, Dowlex
                 
PEEK-polyetheretherketone 60-125 40-80     3 5 5 Arlon
                 
PET-Polyethylene terephthalate  80-120 40-80 90-120   3 5 4 Mylar, Rynite, Cleartuf
(Polyester)                
                 
PMP-Polymethylpentene 70-120 40-80 90-120   4 5 2 TPX
                 
POM- Polyacetal 75-125 40-80 50-100   2 3 4 Acetal, Celcon,   Delrin
                 
PP-Polypropylene 70-120 40-80 40-120   2 5 2 Astryn, Fortilene, Marlex
                 
PPS-Polyphenylene sulfide 80-125 40-80     3 4 5 Fortron, Ryton, Supec

 

Notes: 

   Far and near field welder refers to the distance from the ultrasonic horn contact

            surface to the weld joint.  Generally, any distance in excess of 6.35 mm or .250″ is

            considered far field. 

  –The ease of welding and staking guide is rated from 1 to 5 with 1  

    equaling the easiest and 5 equaling the most difficult. 

 – The ability to weld plastic is based upon a lot of factors including joint design,    

    material fillers, process variables prior to welding, part geometry, good part design 

    practice, part size, amplitude, fixturing, properly designed ultrasonic horns and the 

    material flow during energy transfer. This chart displaying the ease of welding is meant to  

    serve as a guide only.

Criss-Cross Energy Director Design For Ultrasonic Welding

CRISS- CROSS ENERGY DIRECTOR DESIGN

 

 

The use of the criss-cross energy director design has proven to be beneficial for many ultrasonic plastic welding applications. This weld joint has been used in the medical, electronic and cc-energy-directorautomotive industries and has been a good joint design for achieving strong bonds with hermetic seals.  Essentially, the criss-cross energy director design utilizes the standard energy director shape where a triangular shaped bead of material is molded into the plastic wall. This molded-in triangular ridge of plastic is very effective at reducing the cycle time to achieve a weld and in compensating for non-uniform wall surfaces.  Depending upon the wall thickness and the application, the energy director typically varies in height in a range from .010 to .035 of an inch.  The peak of the energy director should be sharp with a triangular shape formed from a 60º or 90º included angle.  The energy director design has been used for years as a means of focusing the energy to improve weld strength and reduce cycle time.  The energy director has typically been placed only on one half of the part and runs along the surface to be welded. Without this energy director the weld quality would be suspect for many applications. The criss-cross design adds additional energy directors to the mating part, which increases the amount of material interaction.  On the mating surface opposite the perimeter energy director, a series of perpendicular energy directors are molded-in to mate with the perimeter energy director.  When a hermetic seal is desired these additional energy directors should take on a saw tooth pattern with each energy director repeating from the base of the proceeding energy director.  Because there are energy directors on both mating surfaces, the energy director height on each half should be reduced to prevent excessive material flash during welding.  Typically, it is recommended that the criss-cross energy director height be approximately 60% of the standard design. 

The joint is particularly effective when used in combination with a tongue and groove joint design.  The tongue and groove design provides the alignment necessary for a good ultrasonic weld joint and the groove serves as an excellent reservoir for the melted material. This pooling of plastic material helps contain the material and reduces the likelihood of a leak path.

tongue-and-grooveBecause of the increased material flow with the criss-cross energy director design, it is recommended that a tongue and groove joint be used to capture the additional plastic and contain the flash.

This criss-cross design certainly increases the mold cost, but we’ve seen applications where the weld strength has far exceeded expectations and hermetic bonds have been achieved that might not have been achieved using the standard energy director on one mating surface.   As always, each application is unique and should be evaluated thoroughly before implementing a joint design.       

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 www.patsonics.com.

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.

Ultrasonic Boosters

Monday, March 24, 2008

Ultrasonic Boosters

Plastic Assembly Technologies, Inc., www.patsonics.com, has recently introduced a new line of aluminum rigid mount ultrasonic boosters without spanner wrench holes. Boosters without spanner wrench holes result in a reduction of stress location points on the booster and provide for aluminum boosters that are less prone to fail. Additionally, these boosters are all of the same length, allowing the user to change the amplitude of the converter, booster and horn assembly without effecting the length of the assembly. Therefore, the amplitude can be mechanically changed without requiring significant adjustment in the welder setup. The rigid mount design reduces deflection during the ultrasonic welding process providing for less potential variation during welding. The boosters are priced to reflect the cost of conventional aluminum boosters, but provide a host of additional benefits. The ratio of gain changes available are 1:1, 1.5:1, 2.0:1 and 2.5:1. The boosters are designed to fit in Branson or Dukane ultrasonic welders using 3.250″ diameter ring mounts.

Vibration Welding Equipment

There are several manufacturers of vibration welding equipment.

This category will discuss ultrasonic welding of plastics.

Welcome!

Welcome to our site with information about welding plastic.  We will review many different types of processes for welding plastics and go in depth into our review of the many different methods for assembling plastics.  We’re just getting started, but we hope you enjoy!

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