Monday, October 14, 2013

Dukane Japan at the Medical Device Development & Manufacturing Expo in Osaka, Japan

The Dukane Japan team participated for the first time at Manufacturing World Osaka 2013.  Dukane had a booth at the 4th annual Medical Device Development & Manufacturing Expo. 

Dukane Japan team at the Medical Device Development &
Manufacturing Expo in Osaka, Japan.
The staff in Tokyo is ready to assist with your next project – from concept to build. Services include running tests in the lab with a variety of welders including Dukane iQ servo-controlled ultrasonic welders in 15, 20, 30, 40, and 50 kHz and servo-controlled spin welders, and commissioning welding equipment for launch at customer sites with Dukane’s expert resourcing available for each step of the process.

Pictured in the stand from left to right are
Kunihiko Shinjo, Kohei Tajima, and Sunao Nagashima. 
The Dukane Japan Tech Center team has expertise working on projects in various markets, including medical device, automotive, packaging, and electronics. Wherever parts assembly solutions are needed, Dukane can offer its wealth of knowledge combined with an advanced line of hardware and software to meet the most demanding requirements.

Kunihiko Shinjo demonstrating Dukane's iQ Servo Ultrasonic welder.

You are welcome to visit the Dukane Japan Tech Center at First Building 6F, 17, Kanda-Higashi-Matsushita-cho,  Chiyoda-ku, Tokyo 101-0042  TEL: +81-3-3525-8301   For more information you can also email Dukane Japan: Japan@dukane.com or the Dukane Japan website at http://www.dukane.jp.

Tuesday, July 16, 2013

Aesthetic Assembly - The Art to Attractive Bonding

Miranda Marcus
Dukane Corporation - Intelligent Assembly Solutions

After carefully molding a beautiful product, nothing is worse than seeing it destroyed during assembly. Every joining process is capable of causing marking, flash, particulate, damage to appendages, or other aesthetic defects. However, with proper part design and processing, a finished weld can be imperceptible or even a cosmetic asset. The art to attractive bonding is specific to each process or type of product. Whether processing parts through ultrasonic, spin, vibration, hot plate, laser welding or thermal staking, methods do exist to improve the appearance of the overall product after bonding.

Welding is a common necessity for a wide variety of industries, including automotive, medical, electronics, and consumer products. Whether there are components that must be securely enclosed or the part geometry is too complex to be processed in one piece, a secondary joining step is often required.

A wide variety of products must have aesthetic welds, or bonds. Packaging, especially clamshells, are probably the most prominent example. Some other demanding cosmetic applications are vehicle headlamps and taillights, spoilers, battery enclosures, medical devices, toys, dishware and utensils, electronics housings, facemasks, fencing, furniture, and filters. For these products, and many others, melt flow must be contained, flash or particulate eliminated, tool marks prevented, and any other part damage eradicated.

The methods for preserving cosmetics are as varied as the welding processes available. Each assembly process can produce its' own variety of decorative debacle. Fortunately, for each potential aesthetic issue, there is a solution.

Ultrasonic Welding

Ultrasonic welding uses piezo-electric ceramics that convert electrical current into mechanical motion. High frequency (15 kHz up to 90 kHz) vibrations are transmitted through the plastic part to the joint where intermolecular stress and strain cause melting of the surface of both parts, and welding. Ultrasonic welding is used for a wide variety of applications including clamshells, electronics housings, medical applications, and fabric welding.

Joint Design,

One of the most common cosmetic defects that result from ultrasonic welding is flash; melted material that is pushed out of the joint at the weld interface. In addition to being unsightly, this flash can also be a functional defect in certain applications. For example, air or water filter housings usually cannot have flash internally.

Fortunately, flash can be easily avoided through proper joint design. Generally, in production, there is balance between weld strength and amount of flash. In order to get greater strength, more collapse of the joint is required, and more flash is produced. Simply adding a flash trap to the part design, however, can allow sufficient strength with no flash. Figure 1 shows some common ultrasonic joints that can effectively hide flash and produce a strong weld.

Figure 1: Ultrasonic Joints that Hide Flash


De-Gating

A second common defect with ultrasonic welding is de-gating of small features in the assembly during the weld. Because ultrasonics depends on high frequency vibration of the parts, there is a chance for cracks to form in areas with sharp corners or small cross-sectional areas. Sometimes these cracks are so severe that small features can be complete sheared off, or de-gated.

There are two main ways to prevent this type of damage. Either increase the radii or cross-section of the troubled area, or decrease the amplitude of the process. However, reducing amplitude often has a negative impact on the weld, as it essentially reduces the energy available to weld the parts. Therefore, whenever possible, it is best to eliminate small or fragile features when ultrasonic welding will be used.

Surface Marking

When welding textured parts, there is a strong possibility that the ultrasonic horn will mar the contact surface. On textured surfaces, there may be shiny places where the texture has been removed during welding. To prevent this occurrence, simply put a layer of thin film between the part and the horn. Figure 2 shows an example of this type of cosmetic flaw.

Figure 2: Ultrasonic Welding can cause damage to the parts texture.


Marking can also occur when the horn leaves a residue on the part, see Figure 3. This is most often seen with aluminum horns or with titanium horns that are welding white parts. Using chrome plated aluminum horns is the best way to prevent this type of problem.

Figure 3: Ultrasonic welding with an aluminum horn can leave residue on the part.


Film &Fabric

As mentioned in the introduction, clamshell packaging is one of the biggest areas where cosmetic assembly is required. Ultrasonic welding is one of the processes most often used for such applications. A wide range of weld patterns have been developed to improve the appearance of such welds. Figure 4 shows some common welding patterns used for clamshells.

Figure 4: Examples of patterns used to weld clamshells


These same patterns can also be used for welding of fabrics, as is often done for shower curtains, plastic bed sheets, or even clothing. In fact, fabrics can be welded using ultrasonics, very similarly to how they can be sewn, using a rotating anvil under a stationary horn that is operated by a foot pedal. An even wider range of attractive patterns can be used for fabric welding; some are shown in Figure 5 below.

Figure 5: Patterns used to weld film or fabric



Spin Welding

Another common welding process is spin welding. In this process, one of the parts is held stationary, and the other is spun at high revolutions per minute to generate frictional heat at the circular joint. While spinning, the parts are pressed together to form a weld. Spin welding is often used to join pipes, insulated cups or bowls, and filter housings, among others.

Joint Design

The biggest drawback, cosmetically, to spin welding is that it generates a significant amount of flash. Unlike ultrasonic welding, the parts are moving during the weld process, meaning that the melt layer is also in motion. Subsequently, more melt must be generated to ensure good contact between the parts and a strong weld. Figure 6 shows an example of the type of flash generated during spin welding.


Figure 6: Spin weld flash

Therefore, for every application where aesthetics is a concern, the part should be designed to hide that melted material, some weld joints that can hide flash are shown in Figure 7. With out-of-round parts, however, it is often not possible to contain the flash simply by using a different joint design. In these instances, a secondary flash removal step is required.

Figure 7: Spin weld joint designs that can hide flash while providing a strong weld.


Particulate

In addition to solid pieces of displaced material, spin welding tends to generate particulate (tiny particles of plastic dust). Most times, this can be blown out after welding, but sometimes it cannot be present at all (as with medical or food industry applications). Reducing the rotational spin welding speed reduces the generation of particulate. Additionally, soft materials like polypropylene tend to produce much more particulate during welding, as shown in Figure 8.

Figure 8: Spin welding particulate


Tooling Marks

Like most other welding processes, there is the possibility of leaving tooling marks on the parts. Typically, this occurs on the upper part when it is not securely held in place using designed driving features. Tooling marks occur when the upper part slips in the tool. When the fixture is made of urethane, this can cause black marks on the parts. When it is made from stainless steel or aluminum, it can leave gouges in the parts, see Figure 9.

Figure 9: Spin welding tooling marks


To avoid this type of marking, it is essential to provide driving features on the part itself. A "driving feature" is simply some type of protrusion or depression on the upper part upon which the upper tool can apply rotational force. In addition, the parts should have relatively consistent external dimensions.

Vibration Welding

Vibration welding is one of the most often used welding processes for large parts, such as vehicle headlamps and taillights, glove boxes, intake manifolds, fencing, and even furniture. In this process, one part is held stationary while the other is vibrated horizontally on top of it at low frequency (120 Hz - 240 Hz) and high amplitude. During this vibration, the upper part is also pressed down on to the lower part to create the weld.

Joint Design

Vibration welding depends on the movement of large amounts of melted material to generate a weld. Therefore, for this process as well, the joint design is critical for flash containment. With the proper design, a strong flash free weld can be achieved consistently. Figure 10 diagrams some joint designs that can produce a strong weld with no flash.

Figure 10: Vibration joint design diagrams


De-Gating

As with ultrasonic welding, the movement of the parts during vibration weld can cause de-gating of small features. The high amplitude used in vibration welding causes excess stress on large projecting features. De-gating is especially likely to occur when the base of the feature has a small cross-sectional area or sharp corners.

Tooling Marks

Vibration welding is similar to spin welding in that driving features on the part are required to prevent tooling marks. In the absence of such features, a knurl pattern may be used to grip the part. The use of a knurl, however, will cause abrasions on the part, as shown in Figure 11.

Figure 11: Vibration welding tools often use knurling to grip the parts.

If such marking is not acceptable a urethane upper tool combined can sometimes be used to prevent scratches on the part. Often, a vacuum must be used with urethane tooling to provide sufficient holding force. Whatever tooling material is used, the parts must still be kept as dimensionally consistent as possible.

Hot Plate Welding

In hot plate welding, the two parts to be joined are pressed against or brought into close proximity of a heated surface to generate a melt layer, then pressed against each other to complete the weld. In this style of welding, the joint may be contoured quite extensively and strong hermetic welds are generally achievable. Nothing can be captured inside the parts, however, as any internal components would be damaged by the hot plate. Hot plate welding is often used for large pipes or tanks.

Joint Design

Although hot plate welding generates a lot of flash, it is the most controlled, good-looking flash of any weld process. The melted material pushed of the joint when the two parts are pressed together forms a very nice rounded line that can almost look as if it was designed to be there, this can be seen in Figure 12. However, if the double line of melt does not suit the application at hand, it can be hidden with a change of joint design.

Figure 12: Hot plate flash can look very controlled and nice


Out-Gassing

One of the unique potential cosmetic issues with hot plate welding is out-gassing. When plastic is heated, it emits gasses that can discolor the parts when they are welded, especially on metalized surfaces. The effects of out-gassing are identified in Figure 13. This can be eliminated by applying a vacuum to one of the parts to extract the fumes before they can cause any discoloration or degradation.

Figure 13: Hot plate out-gassing


Warping

Due to the high heat input used in hot plate welding, the parts can be warped during welding. The best way to prevent this is to use thicker part walls. Excess warping can also be avoided by using vacuums and clamping in the tooling to keep the parts in the correct shape during the weld.

Laser Welding

One of the newest polymer joining processes is laser welding and is growing in popularity, particularly for medical applications. This assembly method uses a focused laser beam to heat the weld joint. The two parts are simultaneously pressed together to create the weld. Laser welds are known for being very clean; flash and particulate free. Laser welding never causes de-gating of features and generally never causes warping. Still, for some components, there is potential for cosmetic defects.

Surface Degradation

If improperly set up, there is a chance that surface degradation will occur during welding. This happens if the top part absorbs too much of the laser energy or if the bottom part absorbs too little. This can be somewhat adjusted for by changing the focal point of the laser, but it is best avoided by choosing the materials with good laser welding properties at the outset.

Burning

The greatest potential for aesthetic flaws in an established process is marring from dirt or dust that is burned by the laser during the weld. Any dust in the path of the laser will absorb the weld energy and cause a disparity in the weld. To prevent this, it is important to maintain the cleanliness of the lens and the weld joint.

Burning can also appear in the process set-up phase as over-welding. An example of over-welding by laser is shown in Figure 14. To resolve this issue, decrease wattage to lessen the laser energy or increase the travel speed of the laser. In some systems, over-welding can be eliminated by adjusting the focus point of the laser so that it is further from the part.

Figure 14: Laser over-welding causes burns at the joint


Thermal Staking

Thermal staking is a method of mechanically bonding two parts by melting and reforming one of the parts to contain the other. Most often, a post on the part with the lower melting temperature is melted and formed into a dome shape to hold in the second part, similar to a rivet. Thermal staking is frequently used to contain circuit boards or to replace screws on consumer products.

Stake Design

The most common cause of unattractive stakes is improper post or tool detail design. It is vital that the staking detail has the same volume as the unformed post. If it is too small, excess material can be pushed out around the base of the stake. If it is too larger, the detail will be only half-formed and uneven in appearance. Figure 15 shows two of the most common staking detail design.


Figure 15: Thermal staking design diagrams

Sticking

Even if the post and staking detail are properly designed, however, there is a chance that the formed dome can be marred if the melted material sticks to the thermal tool. This is especially common with soft materials, like polyethylene. Happily, it can easily be avoided through temperature modulation and the use of post cool. Figure 16 shows the type of stringy wisps of material that can be left behind when the parts sticks to the thermal tool.

Figure 16: Thermal sticking


Conclusion

If an application must be beautiful, then it is best to begin considering the assembly method early in the design process. Most of the common cosmetic defects can be avoided with proper part design. Planning for aesthetic assembly in these early stages will help allow a widened processing window in production and reduce reject rate.

However, if a part is already in production without having planned for the welding process, do not panic. There is plenty that can be done to prevent unsightly flash, marking, or other defects. Figures 17-20 show some examples of attractive welds.


Figure 17: A well-designed ultrasonic joint results in a strong, flash free, weld


Figure 18: An attractive spin weld, free of tool marking, particulate, and flash


Figure 19: A properly designed vibration joint shows no flash zig-zag_with_penny



Figure 20: Laser welding is one of the cleanest joining methods available. Photo courtesy of Leister Corporation.


Figure 21: A nicely formed thermal stake



Wednesday, June 5, 2013

Assembly Demands Grow for Medical Plastics


Published:  May 6, 2013
By:  Plastics Today

A study done at Value Plastics, a molder of precision molded couplers for medical applications, shows that a servo welder produces hermetic welds with a standard deviation of 0.4% compared to 2.9% when using a pneumatic welder.

Those results were reported last month at ANTEC in Cincinnati, OH by three officials at Dukane Corp., which has been testing potential benefits of its recently developed servo-driven ultrasonic welder.


iQ Series Servo-Driven Ultrasonic Welder
with Melt0Match technology
"These benefits include increased precision and repeatability, increased weld strength, the ability to precisely define velocity control, reduced residual stress in parts, and almost complete control of the process," the three authors reported. "Our most recent experiments have shown that the optimal weld velocity can be calculated and that residual stresses can be further minimized through careful hold phase control."

The authors of the Dukane ANTEC paper are Miranda Marcus, applications engineer; Satish Anantharaman of the Technology Demonstration Center in Tamil Nadu, India; and Bob Aldaz, a senior project engineer.

Dukane developed the iQ series Servo-Driven Ultrasonic Welder with Melt-Match technology in response to a growing call, particularly in the medical market, for more controlled and consistent ultrasonic welding processes as part designs become more complex and requirements escalate.  There is also a need for strong, dimensionally consistent parts with good cosmetics.

Weld data can be exported to Excel or Minitab for process optimization analysis.

Experiments at Ohio State University have shown a standard deviation of weld strength of 5.1% when using Dukane's servo-driven ultrasonic welder, compared to 9.4% when using a pneumatic welder.

Original Article from Plastics Today:
http://www.plasticstoday.com/articles/assembly-demands-grow-medical-plastics0506201301

Tuesday, April 30, 2013

Experiments in Reducing Residual Stress with Dukane’s Servo-Driven Ultrasonic Welder


Miranda Marcus & Satish Anantharaman

Even on parts with good weld strength, failure can occur in the field due to residual stresses [A].  With ultrasonic welding, residual stresses are typically in the range of 35 MPa due to the rapid cooling of the small amount of melt [A, B].  Recent experimentation at Turku University of Applied Sciences in Finland have demonstrated that parts welded with a servo welder have significantly less residual stress than parts welded with a pneumatic welder.  This research also demonstrated that parts with shear joints retained less residual stress than parts with energy directors [C].

Experimentation
While residual stress due to cooling is a characteristic of the ultrasonic welding process, orientation induced residual stresses are affected by the hold force applied after the weld phase. Control over the hold force could therefore result in reducing orientation induced residual stresses and thereby minimize the overall stress in the part due to welding. In order to test the validity of this theory, molded polycarbonate parts were welded at a variety of hold speeds and distances. 
For all the samples the weld speed was 2 mm/s.  One part was welded with no hold time.  Three parts were welded at a hold speed matching the weld speed (2 mm/s) with varying hold collapse distances.  The last three parts were welded to 0.5 mm collapse at half, double, and quadruple the weld speed.


Table 2: Hold phase settings used

After welding, the polycarbonate parts were exposed to various mixtures of Methanol and Ethyl Acetate for three minutes. The parts were examined under the microscope for crazing and cracking due to the solvent exposure [13]. The residual stresses were quantified using the chart developed by GE plastics shown in figure 4.  They were then examined for crack formations to determine the level of residual stress at the weld.


Figure 4: Graph showing critical stress levels in Polycarbonate as a function of solution concentration [13]
For these tests, AWS I-Beams with energy directors were used.  This was for two reasons.  First, previous studies indicated that higher stresses occur in energy director parts thereby allowing a greater range of stress to observe.  Second, it is far easier to observe cracks in the energy director parts than in the shear parts due to the part geometry.

Figure 5: Drawing of AWS I-Beam with Energy Director [12]

Results
Some differences in residual stress levels were noted after testing.  Crack formation was seen in varying locations and amounts in the parts.  For the purpose of this paper, number and location of cracks were not considered, only presence or absence.

Figure 6: Cracks shown in a weld joint after exposure to Methanol and Ethyl Acetate mixture.

The results show that increased hold distance may reduce residual stresses at the weld.  Additionally, lower stresses were observed when the hold speed was about double the weld speed.  Further investigation into the effect of hold settings on residual stress in the weld joint is merited based on these results.
Table 3: Stress level as determined by crack formation.


References
A.  S. Anantharaman and A. Benatar. “Measurement of Residual Stress in Laser Welded Polycarbonate using Photoelasticity” ANTEC 2003.
B. A. Benatar. “Servo-Driven Ultrasonic welding of Semi-crystalline Thermoplastics” 39th Annual Symposium of the Ultrasonic Industry Association. Cambridge, MA. 2010.
C. H. Turunen. “Ultrasonic Welding for Plastics” Bachelor’s Thesis, Turku University of Applied Sciences, Finland. 2011.

Thursday, April 11, 2013

Experiments in Velocity Control with Dukane’s Servo-Driven Ultrasonic Welder

Miranda Marcus, Satish Anantharaman, & Bob Aldaz

Even before the introduction of Dukane’s servo-driven welder, the need for velocity control was recognized.  As Mikell Knights wrote in 2005, “Research has proven that consistency of melting rate has a direct influence on bond strength,”  A linear velocity means a steady melt rate which, in turn, creates a homogenous molecular structure and a stronger weld [A]. 

In past years there has been much effort put into attempting to get consistent velocity control with pneumatic systems [2, 3].  These efforts have been in vain, as it is simply not possible to get precise velocity control with a pneumatic welder [C].   As one writer put it trying to achieve precise speed control with a pneumatic press was “the equivalent of sending a ship on an ocean voyage with a map and a compass from a box of cereal” [B].  Dukane’s servo-driven ultrasonic welder offers clear improvement in process control.

Studies using servo ultrasonic welders have shown that the programmed weld velocity can be directly correlated with weld strength [C, D, E, F].  In a study at The Ohio State University it was shown that by using a defined velocity profile with a slower speed during melt initiation and a faster speed in the middle and end of the weld, strength could be increased with less weld time and reduced surface marking [F].  Dukane has provided a unique new weld control to achieve this initiation of melt before collapsing the weld through the use of the patented “melt detect” feature.  This features allows the press to contact the parts and turn on ultrasonic vibration with no vertical movement until a drop in force is detected which indicates that welding has initiated [C]. 

Experimentation
One of the greatest benefits of servo-driven ultrasonic welding is the ability to program a specific weld velocity.  It has often been said of plastic welding that it is more art than science.  With the new controls available, this no longer needs to be the case.  In this experiment, we made both a finite element model and a finite difference model of a shear joint in a standard AWS I-Beam sample to determine the rate of melt formation and then welded parts at varying weld velocities to determine if the modeled weld velocity could be correlated to the optimum weld velocity through experimental data.


Figure 1: Drawing of AWS I-Beam with Shear Joint [12]

For the Finite Element Analysis, a ProE 3D CAD model was made of the AWS I-Beam part consisting of three individual pieces, the top part, the bottom part, and the shear joint.  The shear joint was assigned a heat generation rate based on the following equation:  Q = πƒ•ε²•Eloss, Where ε² is the strain amplitude at the shear joint calculated by amplitude divided by length and Eloss is the loss modulus of the material (Nylon 6,6 in this case).


Figure 2: Screenshots of finite element analysis (modeling half of the part)

The finite difference analysis was performed with the same initial steps.  However, instead of using a CAD model, Mathcad was used for the 1D analysis.

Figure 3: Screenshot of 1D finite difference analysis

Both methods were used to produce a graph of temperature vs. distance at discrete 0.05 second intervals.  The width of the melt layer was determined based on attainment of the melting temperature (354 °C).  From this, the rate of melt formation was calculated.

Table 1: Calculated melt formation rates for Finite Element
Analysis (FEA) and Finite Difference Analysis (FDA).

After determining the theoretical ideal welding velocity to match the melt formation, five parts were welded at each of five velocities: 0.5 mm/s, 2 mm/s, 4 mm/s, 6 mm/s, and 10 mm/s.  After the parts were welded, they were cut in half and each half was pull tested to determine the relative weld strength.

Results
After tensile testing, a clear relationship was observed between weld speed and strength, as expected.  Most interesting was that the maximum weld strength was observed at 4 mm/s and 6 mm/s which were modeled to be the initial melt formation rates in the part.

Another interesting result was that the toughness of the weld, as measured by elongation, followed the same general pattern as the weld strength, although the difference between weld speeds was not as distinct.

Figure 5: Weld strength and elongation as a function of weld speed


References
A. M. Knights. “Graphical Analysis Helps Find and Fix Ultrasonic Welding Problems” Plastics Technology. Sept 2005.
B. T. Kirkland. “Ultrasonic Welding: The Need for Speed Control” Plastics Decorating. July/August, 2012.
C. S. T. Flowers. “Servo-Driven Ultrasonic Welding of Biocomposites” ANTEC 2012.
D. A. Benatar. “Servo-Driven Ultrasonic welding of Semi-crystalline Thermoplastics” 39th Annual Symposium of the Ultrasonic Industry Association. Cambridge, MA. 2010.
E. M. Marcus, P. Golko, S. Lester, L. Klinstein. “Comparison of Servo-Driven Ultrasonic Welder to Standard Pneumatic Ultrasonic Welder” ANTEC 2009.
F. A. Mokhtarzadeh and A. Benatar. “Comparison of Servo and Pneumatic Ultrasonic Welding of HDPE Shear Joints” ANTEC 2011.

Friday, March 15, 2013

Tech Center Shines!

We invite you to come see us at Dukane’s Automotive Technical Center in Wixom, Michigan. The place has taken on a new, refreshing look, and really shines!

A recent upgrade to the facility coincides with some milestones for the company: 5 years for the Wixom Center, and 90 years for Dukane Corporation, St. Charles, Illinois. What a great way to salute the firm that has been providing innovative assembly solutions through its outstanding equipment and worldwide network of highly qualified experts.

At Wixom there’s a welding lab showcasing the latest Dukane technology in its full line of welders. We have the most recent additions, the iQ Series ultrasonic press systems, and hand probe units with their best-in-class ergonomics. You will also find systems that demonstrate Servo Spin welding, Thermo Press for heat staking or inserting, and Vibration Welding. Especially impressive is our Model VWB 4700 vibration welder, which is capable of handling a large range of part sizes.

From left to right - Thermal Press, iQ ultrasonic Hand Probe system,
Dual Servo Spin Welder, iQ ES pnuematic 20 kHz Ultrasonic Press System



Model VWB 4700 vibration welder capable
of handling a large range of part sizes.


The lab itself features an acoustical tile ceiling to keep things quieter, and the environment is temperature controlled, so the lab can be easily used year round.

The staff in Michigan is ready to assist with your next project – from concept to build. Services include commissioning welding equipment for launch at customer sites with Dukane’s expert resourcing available for each step of the process.

The Tech Center offers its expertise not only for automotive applications, but for other markets as well. Wherever parts assembly solutions are needed, Dukane can offer its wealth of knowledge combined with an advanced line of hardware and software to meet the most demanding requirements.
Stop by the Tech Center, 47757 West Road, Suite C101, Wixom, Michigan.

Friday, February 22, 2013

Advantages of Servo Driven Ultrasonic Welder

Miranda Marcus

Ultrasonic welding is one of the most widely used processes for bonding polymers, valued for its speed, flexibility, and low cost. Recently, there has been a call for more controlled and consistent ultrasonic welding processes, as part designs become more complex and requirements more stringent.  There is also a need for strong, dimensionally consistent parts that show good cosmetics.  The process used to meet these increasing demands must be consistent and repeatable over time. Dukane has worked to meet this demand through the development of a new iQ series Servo-Driven Ultrasonic Welder with Melt-Match® technology.

In the ultrasonic welding process, there are three fundamental process variables that have a direct effect on weld quality: amplitude, force, and duration.  The first of these parameters, amplitude, has long been controlled through frequency selection, horn-booster design and modulation of the electrical input to the transducer.  The second of these parameters, duration, could only be controlled only by setting a specific weld time for 50 years.  In 1988 this was revolutionized by Dukane’s development of welding by distance, thus allowing greatly improved troubleshooting and process control.  

Recently, a new precise method of force control has been introduced with Dukane’s servo-driven ultrasonic welder in 2009.  This new development allows complete control of the third parameter that defines ultrasonic welding, force.  In recent years, there has been a plethora of research conducted with the new servo-driven ultrasonic welder.  Each of these experimental studies has demonstrated unique benefits of using servo-driven ultrasonic welders.

We are entering an exciting new age of ultrasonic welding.  Dukane’s servo-driven ultrasonic welder offers greater process control than was every possible before which will allow welding of ever more complex and demanding applications.

Process Control


It has long been known that better process control leads to improved part quality and consistency.  As Robert Leaversuch noted in 2002, “in automotive, medical, and other demanding sectors, use of advanced controls is critical to meeting strict quality requirements” [G].  In this, as so much else, servo welders are at the “top of the process-capability food chain” [F].  Because all of the process settings are controlled electronically, it is easy to switch between welders [I].  Also, this greatly simplifies the calibration and validation processes.  Dukane’s servo-driven ultrasonic welder further eases process optimization by allowing all the weld data to be exported in formats that can easily be imported to excel or Minitab for analysis [E].  The data produced by the generator in the form of graphs or weld data is very useful for process optimization and troubleshooting [H].  Simply said, servo welders “take control of the process away from the plastic” [F].  

Precision and Repeatability


The servo welder has been shown to consistently produce more repeatable results through multiple methods of evaluation.  A study done at Value Plastics, a manufacturer of precision molded couplers and components for various industries including medical, showed that the servo welder produced much more consistently hermetic welds (as measured using pressure decay) with a standard deviation of 0.4% compared to 2.9% when using a pneumatic welder [A].
15 kHz Ultrasonic Servo Press System

The servo-driven ultrasonic welder also offers “excellent repeatability of collapse distance from part to part” [B].  In a pneumatic system there is a limit to the speed at which air can escape the cylinder, preventing abrupt changes in velocity and reducing distance control.    Dukane’s servo ultrasonic welder can accelerate up to a rate of 1270 mm/s², allowing almost instantaneous velocity shifts during the weld and hold phases [I].  An initial study of the servo ultrasonic welder in 2009 showed that the servo welder was able to achieve a standard deviation of 1.1% in measured collapse distance compared to 3.9% achieved with the pneumatic welder [C].  Value Plastics was able to achieve a standard deviation of collapse of 0.9% in production using Dukane’s servo-driven ultrasonic welder [I].

Other studies have shown that using servo ultrasonic technology produces parts with more repeatable weld strength.  Experimentation at The Ohio State University has shown a standard deviation of weld strength of 5.1% when using Dukane’s servo-driven ultrasonic welder, compared to 9.4% when using a pneumatic welder [D].  At Turku University of Applied Sciences in Finland, experiments demonstrated that standard deviation in weld strength can be halved when switching from a pneumatic welder to a servo-driven welder on parts with shear joints [E]. 

Clearly, servo-driven ultrasonic technology offers improved repeatability, measurement accuracy and more precision.  This improved consistency will be needed as products become increasingly complex.

Weld Strength


In addition to increased repeatability, multiple studies have shown that servo-driven ultrasonic welders produce parts with increased weld strength over parts produced with pneumatic welders [1, 2, 6, 8].  Even under non-ideal circumstances (such as when grease is present in the joint or the energy director is damaged), servo welders were able to create stronger bonds than pneumatic welders [F].  Servo technology has proved to provide greater tolerance of part variations, allowing greater weld strength – as demonstrated by fracture occurring in the bulk material rather than in the joint as was seen when using pneumatics [A].

Experimentation at a Finnish University showed that parts welded with Dukane’s servo-driven ultrasonic welder were 19.1% stronger when using a shear joint and 21.4% stronger when using an energy director than parts welded using a pneumatic welder [E].  In the first study performed by Dukane on the new servo welder, weld strength was 16.7% greater than pneumatically welded samples [C].  Even with just 59% of the energy input, parts welded with Dukane’s servo-driven ultrasonic welder were consistently more leak tight than parts welded with a pneumatic welder [A].

References


A. M. Marcus, K. Holt, A. Mendes. “Benefit of Servo-Ultrasonic Welder to Medical Industry – A Case History” ANTEC 2012.
B.     A. Benatar. “Servo-Driven Ultrasonic welding of Semi-crystalline Thermoplastics” 39th Annual Symposium of the Ultrasonic Industry Association. Cambridge, MA. 2010.
C.     M. Marcus, P. Golko, S. Lester, L. Klinstein. “Comparison of Servo-Driven Ultrasonic Welder to Standard Pneumatic Ultrasonic Welder” ANTEC 2009.
D.     A. Mokhtarzadeh and A. Benatar. “Comparison of Servo and Pneumatic Ultrasonic Welding of HDPE Shear Joints” ANTEC 2011.
E.    H. Turunen. “Ultrasonic Welding for Plastics” Bachelor’s Thesis, Turku University of Applied Sciences, Finland. 2011.
F. T. Kirkland. “Ultrasonic Welding: The Need for Speed Control” Plastics Decorating. July/August, 2012.
G.  R. Leaversuch. “How to Use those Fancy Ultrasonic Welding Controls” Plastics Technology. Oct 2002.
H.     M. Knights. “Graphical Analysis Helps Find and Fix Ultrasonic Welding Problems” Plastics Technology. Sept 2005
I. P. Golko. “Boost Performance, Speed, Economy with Servo-Controlled Welding” Plastics Technology. Aug 2011

Tuesday, February 12, 2013

Dukane Announces ISTeP - An Advanced Test Part

Dukane Corporation has taken a significant step to improve the ultrasonic industry’s standard test part. They’re calling it the ISTeP, a two-piece cylindrical part used to test a variety of welded parts’ characteristics. With ISTeP, ultrasonic weld quality and reliability can be determined with enhanced confidence.

ISTeP standard test part

Outside the I-beam – By rethinking the design of the standard part currently used for testing, it became clear there was room for improvement. Consider ISTeP’s cylindrical shape which allows for spin weld testing as well as ultrasonic weld testing.

Dukane’s investment to develop a better industry standard test part included a fresh part design, but also production of a quality injection mold. The ISTeP team took care to create the mold so that gates and knits insured a uniform mold fill, especially in the joint area. There are three joint design options – 60° or 90° energy directors, and a standard shear joint. In addition, the mold has inserts for the joint area. These allow for additional options manufacturers and designers may bring that are unique to their weld joint specifications. 

Standard shear joint


Pull Testing – This is simplified by the use of ISTep’s unique tabs, three on the top piece, and three on the lower portion. The tabs help reduce time spent assembling the test part into it’s pull test fixture.
     Bond strength of different plastic resins can be compared - polycarbonate vs. ABS as an example.
     When parts come apart under testing, they will do so evenly, avoiding the so-called “zipper effect” that was previously common.
Energy director joint
Pressure/Burst/Leak Testing - An integral port in ISTeP’s lower portion makes it easy to insert an air tube for a variety of checks that can be made.
 
Testing Weld Processes and Features – Welding methods each have their distinct advantages. To find which combination of process and features work best, ISTeP could be used with pneumatic and servo welders, using features such as amplitude profiling or Melt-Match® technology, for instance. Dukane’s enhanced iQ Series generators and software are available to provide even more versatility and possibility to make the testing process complete and comprehensive.

Mold Availability – ISTeP’s injection mold is available from Dukane for firms wanting test parts molded in their resin of choice. Dukane Corporation through its Intelligent Assembly Solutions experts offers experience and know-how for your application.
 
ISTeP exploded view
Side by side ISTeP standard part