Tuesday, May 25, 2010

The Benefit of Resilient Fixtures for Ultrasonic Plastic Welding

When is it a better choice to use a resilient fixture made from a Polyurethane casting in place of using aluminum or stainless steel? This question needs to be answered with a series of other questions. The most important of those are: what is the shape of the part, the material being welded, the process being used and the wall thickness?

Parts that have special shapes or that are not flat on the bottom would be considered contoured parts. The shape of these parts could be machined into aluminum or stainless steel but would require programming a CNC machine to cut the detail. Another added step would be that fixture would also need to have the machine tool marks polished out. Pouring a Polyurethane fixture would eliminate the need for programming time and polishing. Although the Polyurethane would need to cure (harden) overnight, this additional time spent is still less costly than programming, machining and polishing. When cured, the Polyurethane casting just needs minor machining before being mounted to a leveling plate.

Amorphous materials and most semi-crystalline materials are good candidates for Polyurethane fixtures. The exceptions are Polypropylene (PP) and Polyethylene (PE) parts; which are considered “softer” materials. Since PP and PE already absorb much of the ultrasonic vibrations, Polyurethane is normally not recommended. If the parts have a textured surface, the texture could be damaged if using aluminum or stainless steel. Using a Polyurethane fixture instead could significantly reduce the surface damage. The reason is that the Polyurethane is poured directly onto a production part (always preferred) so that the textured surface is somewhat incorporated into the casting.

The process being used is important in that normal ultrasonic welding of two plastic components is usually successful if thought out properly. However, when inserting brass or steel inserts, there are times when this process could be problematic due to excessive heat build-up directly under the inserting area that could cause the Polyurethane material to distort and become damaged. In some cases, Brass “plugs” can be added to the fixture directly under the inserting area to eliminate excessive heat and damage to the Polyurethane material.

Thin wall sections may need extra support that the Polyurethane may not be able to provide. In this case, a combination of Polyurethane and aluminum or stainless steel can be used to stabilize the thin wall areas of the assembly.

These are just some of the basic guidelines. Every application is examined on an individual basis to determine which fixture material will produce the best results.

Tuesday, May 11, 2010

Dynamic Balancing of Linear Vibration Weld Tooling

The balancing of Vibration Weld Tooling is critical to the longevity of any manufacturer’s vibration welding equipment. With proper design of the moving half of the vibration tools used in the Linear Vibration Welder, the manufacturer can expect a much longer life from his welding equipment. Also by running unbalanced tools you can significantly shorten the life of your machine and incur tens of thousands of dollars in repair costs.

First let’s discuss the dynamics of the moving half of the tool in a vibration welding tool set. Usually this is the upper half of the tool. The partial g loading chart below shows that at 1.8 mm amplitude and 240 Hertz we get 208 g’s of dynamic load. Therefore, a 100 pound tool moving at 240 Hertz and 1. 8 mm peak to peak displacement becomes 20,800 pounds of dynamic load on the machine.

The following table is g loading calculations (click table for larger view):

So let us assume that a tool is 20 pounds out of balance, 12 inches from the center line of the tooling. This would mean that we have:

(20 pounds) X (12 inches) X (208g) = 49,920 inch pounds of torque on the machine.

This will cause the Linear Vibration head to move in a non linear fashion. It will damage components in the head and make the frequency drives work harder to keep the tool running the application. This eventually will take critical components in the vibration head to a fatigue failure point, thus causing the expensive repair bills.

If you look at the weld tool representation, you will see lightening holes on the upper tooling plate to the back side of the tool. These are there to counter balance the thick portion of the poured urethane nest, thus bringing the tool into balance.

Extensive use of tool balancing was used on the tool illustrated below. Here, not only was the tool plate lightened but the tooling segments themselves needed to be weight reduced to balance the tooling.

The use of steel counter balances can also be used, just remember the upper tool must fall within the manufacturer’s recommended tool weight specifications. The use of good CAD tools can also aid in the balance analysis of a tool before you even cut the materials.

Finally, the tool being balanced in the direction of welding is not as critical. The tool balance from front to back in most machines or 90 degrees to the direction of vibration or along the direction of the weld axis is what must be considered for all good vibration tooling.

For further information contact:
Ray Laflamme
Worldwide Automotive Marketing Manager
Dukane Corporation

Tuesday, May 4, 2010

Composite Ultrasonic Horns

A composite horn is actually a half-wave “coupler” horn with two or more half-wave, tuned horns attached to it. This technology was patented by Dukane in 1973. Because composite ultrasonic horn designs can often eliminate the need to invest in additional assembly systems, they reduce equipment costs and minimize production time for customers.

Composite ultrasonic horn designs are common on applications that cover a large surface area and on applications where there are multiple insertion, staking, or welding points. Some of automotive customers use composite ultrasonic horns to attach insulator pads to door panels.

Another common application that benefits from composite ultrasonic tooling is clamshell packaging (a vacuum-formed blister package). The composite horn saves manufacturers production time and costs, as it welds the package simultaneously at several different points, instead of using a multiple-head system or having an operator weld each point separately.

Composite ultrasonic horns are also instrumental in applications where it’s difficult to create enough amplitude to weld. The amplitude at the face of a composite horn is higher than what could ever be achieved by a single large horn. The amplitude is designed into each of the individual half-wave horn attachments, not the coupler, a higher amplitude is generated at the weld area; this avoids causing excessive stress to the coupler horn.

Although composite horns can eliminate the need for additional assembly systems, cut production times, and lower labor costs, they are more expensive than standard horns. The added cost is due to the extra metal and machining the composite horns require.

Typical composite horns have aluminum couplers and titanium half-wave attachments. In addition to the expense of titanium, all of the half-wave attachments must be tuned within 50 cycles of each other. And they must be properly mounted onto the coupler horn.

The most common mounting method utilizes a 1/2- or 3/8-inch threaded stud at the top of the half-wave attachment; it’s screwed into a threaded hole at the output face of the coupler. It’s also possible to use a “tuned bolt” to fasten the half-wave attachments. The bolt is mounted through the coupler; then the horn attachments are bolted to the coupler. The “tuned bolt” method is primarily used on composite horns that have two or more blade horn attachments.

In addition to the extra metal and machining that’s required, composite horns have more design considerations than a standard horn. We always have to make sure the horn we’re designing is balanced. But when we deal with composite horns, all of the horn attachments have to be positioned evenly around the coupler, so the weight is evenly distributed. Sometimes the attachments are different lengths and different shapes, but you still have to keep the horn balanced.

But despite the added challenges in the design and manufacture of composite horns, they have provided consistent performance and productivity for Dukane customers. If an application can use a composite horn, the increase in productivity and the cost savings are so great that the initial added cost in tooling is more than justified.

For more information on ultrasonic assembly and other horn designs, you can view our Guide To Ultrasonic Plastic Assembly.

Dukane Participated in 2010 UIA Symposium

The 39th Annual UIA (Ultrasonic Industry Association) Symposium held in Cambridge, MA, included 80 participants from 48 organizations representing 11 countries. The program included one day of industrial presentations on Monday April 12th, two workshops, a poster session on Tuesday April 13th and a day of medical presentations on April 14th.

Dukane was a proud Sponsor, as well as an exhibitor and presenter in a poster session. Our poster presentation was “What is New in iQ Series Ultrasonic Systems?”

Dukane made equipment was used in several presentations, including the keynote presentation of the industrial session by Prof. Avi Benatar of OSU (see below). Other presentation, where Dukane ultrasonic generators and transducers were used included the following: “Determining Bond Quality from VHPUAM Process Parameters” by Matt Short, EWI, The Ohio State University; “UAM Fabrication of Metal-Matrix Smart Material Composites” by R. Hahlen and M. Dapino (presented by Mark Norwood), EWI, The Ohio State University; “Advanced Analysis and Characterization of the UAM, VHP UAM Bonding Process” by D. Schick, R. DeHoff, M. Sriram, M. Dapino and S.S. Babu (presented by Mark Norwood), EWI, The Ohio State University.

Both the Newcomers to Ultrasonics Workshop and the Finite Element Modeling Workshop were highly rated by symposium participants. Keynote presentations by Prof. Avi Benatar, The Ohio State University on “Servo-Driven Ultrasonic Welding of Semi-Crystalline Thermoplastics” and Robin Cleveland, Boston University on “Medical Applications of Shock Waves” provided fascinating information on diverse ultrasonic applications.

“Protease Inactivation in Milk by Thermosonication and Impact on Milk Characteristics” by Sakthi Vijayakumar, David Grewell, Stephanie Jung, and Stephanie Clark, Iowa State University represented an evolving ultrasonic application. “Propagating Ultrasound Energy through a Catheter Around Bends” by David Constantine, James Sheehan and Jeffrey Vaitekunas presented a unique medical ultrasound application.

An electronic copy of the proceedings on a flash-drive pen is available for $95 from UIA by emailing uia@ultrasonics.org

The 40th UIA Symposium will be held in Glasgow, Scotland, UK on 23 – 25 May 2011. Professor Margaret Lucas, University of Glasgow, will serve as the Symposium Chair. For a copy of the Call for Presentations, go to www.ultrasonics.org or contact UIA at +1.937.586.3725.