Tuesday, September 28, 2010

Ultrasonic Boosters

The boosters serve two purposes; second mounting point for the stack assembly and either amplify or reduce the amplitude.  Like the transducer, the boosters have a nodal point.  At the nodal point there is a mounting ring designed to fit into the press system or machine mount applications.   There are two types of mounting ring configurations.  Standard boosters have a split mounting ring that houses two “O” rings in a similar configuration as the transducer.    Resonant style boosters have no “O” rings.  These are designed for applications where solid fixed mounting of the stack assembly is critical for the application.  An example would be an application requiring two stack assemblies to weld a single part, because near horn proximity, motion in the stack may allow them to touch.  Resonant boosters eliminate this problem.

Standard and Resonant Boosters

The boosters are either titanium or aluminum.  Titanium boosters, while costly, are more robust and stud thread holes hold up to many assembly and disassembly cycles.  In continuous applications where heat dissipation is a benefit, aluminum boosters are recommended.

Boosters come in different “Gain” ratios.  The mass of the booster below and above the nodal point determine the amount of gain to the amplitude from the transducer.  This is the mechanical means for adjusting the stack amplitude to match the requirement to melt the particular plastic in each application.  It is best to use the optimum booster size for the application.  Leave the generator amplitude setting close to 100% and only make small generator amplitude adjustments when required.  On most horns, the recommended max gain booster size will be stamped on the horn.

Friday, September 24, 2010

Effect of Black Colorant on Ultrasonic Staking.

Sometimes it is difficult to disperse black pigments on polymers, resulting in agglomerates or clumps of pigment particles. These can make for places where cracking can occur when the plastic is stressed. This could be worse in the area of the ultrasonic staking, since the polymer is likely somewhat weakened by the welding process.

It is probably more likely that the black pigments could be increasing the thermal properties of the plastic, so that the material is heating faster causing more degradation than the other colored parts. It may be necessary to adjust the ultrasonic staking conditions for black parts with slightly lower amplitude, less energy input or shorter duration.

Finally, there can be problems with the way the color is added. Assuming that they are adding a color concentrate at the molding machine, if they are adding too much or maybe adding a concentrate that has an incompatible carrier polymer, like polyethylene or nylon, they may not fully blend in the plastic, creating contaminated layers of material.

Monday, September 13, 2010

The 6 quick steps to a successful ultrasonic assembly

Do you have an application that you think could be ultrasonically assembled? Wondering how to get from a couple of pieces of plastic to an assembled part?

This is how our sales engineers tackle an application. While we don’t expect our customers to perform each of these steps, it’s important they be involved in this process. That way they’ll have a better understanding of their systems and know how to maximize the ultrasonic equipment’s potential.

Step 1 - Determine the feasibility of ultrasonics

First examine the components to be ultrasonically assembled. They must be thermoplastics, and if dissimilar plastics are to be welded, they must be compatible (refer to Thermoplastic Compatibility Guide. The parts must also be designed so ultrasonic energy can be efficiently transmitted to the joint.

Using the Amplitude Reference Chart, determine the amplitude requirements of the thermoplastic you’re using. If possible, process a few parts to verify you have sufficient amplitude. Consider using special ultrasonic horn coatings or horn materials if fillers or additives are used in the plastic components.

The last step is to consider your ultrasonic tooling options. Is it even possible to build an ultrasonic horn that will provide the necessary amplitude to the part? Will you need multiple horns or a composite horn? Can the parts be properly supported in a fixture?

Step 2 – Choose the right ultrasonic welding equipment

Once you determine ultrasonics is a viable assembly method for your application, it’s time to choose your welding equipment. Your application and future project needs will dictate whether you need 15, 20, 30 or 40 kHz equipment. The 20 kHz ultrasonic welding system is more versatile, as it can process a variety of part sizes. It’s also ideal when higher amplitudes are needed to melt the plastic. A 40 kHz ultrasonic welding system is usually used for smaller, more delicate applications. Your application will also determine the wattage of your generator (200 to 5,000 watts). Traditionally, the bigger your part and horn, the more wattage you’ll need to run the horn at full amplitude.

How you’ll apply the ultrasonic energy to your parts is another consideration. Hand-held probes are ideal for applications where it’s more convenient to bring the ultrasonics to the part. When control and repeatability are critical, a press system would be recommended. If production rates require speeds that exceed what could be achieved by a standard press, a rotary index parts handling system should be used. Custom mounting and automation of ultrasonic thrusters are other possibilities.

Your ultrasonic sales engineer can help you design your system to meet other specific application needs such as process control and SPC, cooling requirements, and sound enclosures.

Step 3 – Assemble and Install the ultrasonic tooling

Because transducers alone cannot generate enough amplitude to melt the plastic material, your ultrasonic tooling and applications engineer will determine the gain factor that’s needed from the horn to match the amplitude requirement of the thermoplastic. Based on that gain factor, he or she will select the appropriate booster and horn combination.

You’ll need to assemble the transducer, booster, and horn but first examine all mating surfaces for flatness and cleanliness. Remove any foreign matter from the threaded studs and mating holes. Coat one contact surface of each stack component with a thin layer of high pressure grease – but do not grease the studs. Thread the components together and tighten by applying a torque of no less than 13 foot-lbs (17.63 Newton-meters), but no more than 18 foot-lbs. (24.40 Newton-meters).

Once you’ve assembled the stack, install it into your system by following the easy directions in the operations manual. Make sure it aligns with the fixture; use feeler gauges or carbon paper if this becomes difficult.

Step 4 – Set up the welding equipment

After following the simple setup procedures in the operations manual, you should be ready to set the initial press force, trigger force, weld time, and velocity. If your application requires precise melt velocity during the weld cycle, use hydraulic speed control, like the Kinechek® option, which is available on Dukane ultrasonic welding systems. Set the mechanical stop (so the horn and fixture don’t accidentally contact), then determine whether the ultrasonics need to be activated before contacting the parts. If so, use the pre-trigger feature.

If you’re using a process controller, determine and set the most effective primary process control. Welding by distance, peak power, and absolute distance are the most common controls, although welding can also be controlled by time and energy.

Step 5 – Adjust the setup

After you’ve set up your ultrasonic tooling and welding equipment, don’t go into full production – run a batch or two of sample parts. Examine and test (as needed) the assembled parts. If process adjustment is needed, refer to the application troubleshooting section in the “Guide to Ultrasonic Plastics Assembly” to help diagnose probable causes and solutions.

Step 6 – Maintain proper operating conditions

Ultrasonics is a low maintenance process, and Dukane’s ultrasonic welding equipment comes with a 3-year warranty. However, to maximize your welding equipment’s life and performance, it’s important to do some minor cleaning and inspecting after every 500 hours of operation. This includes: removing dust/dirt from the guide rods; applying light oil to the exterior of the air cylinder rod; inspecting wiring to the thruster head; inspecting the air filter; tightening the thruster and fixture mounting bolts (if needed); checking the setup parameters; and inspecting, cleaning, lapping and re-torquing the stack. Regional training programs are also available from Dukane, as is an extensive series of training workshops at the St. Charles facility.