Digital controls are basically similar for different types of welding equipment.
Whether it’s hot-plate welding, spin welding or ultrasonic welding, digital controls allow more precise plastic assembly, with more consistent performance. All output signals can be digitally adjusted and are not affected by the manufacturing tolerances of built-in components.
Digital controls use microchips and sensors to transmit signals via a keypad or a touch-screen. Data and functions are managed precisely at very fast speeds. Data-carrying signals are electronic or optical pulses. The amplitude of each signal represents a logical 1 (pulse present and/or high) or a logical 0 (pulse absent and/or low).
The biggest advantage of using digital controls for plastic welding applications is speed and accuracy. Timing accuracy provides more repeatable weld cycles and, therefore, more accurate parts assembly.
With one digital controller, end users can set many different parameters, such as weld time, hold time, delay time, after-burst time, distance energy, trigger force, pressure, distance, pre trigger, converter amplitude and quality windows. They can also save and recall multiple jobs, set alarms and display all of these functions after the weld is completed.
Digital controls are basically similar for different type of welding equipment. “The objective is to control the parameters needed for that particular type of welder, whatever the process may be, but the parameters to be controlled may be different,” says Janet Devine, president of Sonobond Ultrasonics (West Chester, PA).
“Most of the welding processes are similar in nature,” adds Sylvio Mainolfi, worldwide director of product marketing at Branson Ultrasonics Corp. (Danbury, CT). “It is possible to use the same digital controls platform for different welding equipment.” However, hardware and software modification may be required to support specific functionality for a given piece of welding equipment.
“Digital controls are similar for vibration welders and spin welders as they require [similar process parameters such as] weld time and hold time,” explains Robert Soloff, president of Sonics & Materials Inc. (Newtown, CT). “For the vibration welder, changing the amplitude, pressure and speed of the lower platen before and during welding is important in vibration welding.
“Most vibration welders use either a touch-screen PLC or a touch-screen industrial PC as the primary controller,” Soloff points out. “Using PLCs and PCs as controllers allows for data collection without using an additional computer. For the spin welder, one must control the motor speed. For an orienting stepper motor spin welder, controlling the stopping point is essential.”
“The basic items controlling a weld cycle are very similar across all of our welding equipment,” adds Bill Simon, director of research and development at Sonics & Materials. “Weld cycles are programmed for time, distance and energy with multi-function control capability commanding higher pricing.
“For example, our new GX-Series power supplies can be purchased with different welding mode capabilities,” adds Simon. “Specifically, purchase options range from the continuous duty and time-based welding modes to the more expensive models that offer both digital time or constant energy. At the top end, maximum control and flexibility [is available] with the trifecta of digital time, constant energy and distance-based welding modes. Various window qualifications for these parameters can be used as quality examinations after a weld cycle is completed.”
Forward Technology (Cokato, MN) offers a line of digital vibration welders that Andrew Tapper, engineering manager, claims is “unique and revolutionary in the marketplace. We use a Delta Tau PMAC2 servo controller to precisely control the signals going to each voice coil based on the current position of the welding head and the required amplitude. This results in a machine with better welding output power using approximately half the incoming power.”
According to Tapper, using this system also eliminates the need for auto tuning. Frequency becomes a byproduct instead of a control parameter,” he points out. “With the increase in precision of control of the welding head, the time it takes for the head to reach the desired vibration amplitude is dramatically reduced, as well as ringing or hunting around the set amplitude.
While this new technology increases component cost, it eliminates that need for specialized proprietary amplitude control boards. “Everything we use in our digital vibration welders are standard off-the-shelf parts,” claims Tapper.
With its other welding products, Tapper says his company’s digital servo controls are more traditional. “In hot-plate welding, servo actuation replaces air or hydraulic systems,” he explains. “This allows the machine to run without hard tooling stops for control of melt and seal depths, meaning that a major set of welding parameters that took a technician significant time and experience to change can now be done quickly from the HMI.
“The challenge becomes making the machine rigid enough to run without the structural advantages of tooling stops and hold tolerances of +/- 0.001-inch or better,” adds Tapper. “Also, sizing a servo motion that move quickly enough to keep the open time small and yet yield high forces can result in very large, expensive actuators. Servo hot-plate welders can cost between 3 and 4 times what a standard welder would be.”
For spin welding, servo control is typically used to achieve a specific orientation between parts or to assure that each weld is precisely the same every time. “In servo spin welding, a servo motor replaces the traditional air motor-flywheel combination as the motive force for the spin welding head,” notes Tapper. “This allows for a servo spin welder to orient the two parts within +/- 1 degree or better.
“We also know that if we set the machine to spin for 10 revolutions and stop, it will do precisely that or give us a fault telling us that it could not accomplish the weld,” adds Tapper. “The biggest challenge here again tends to be sizing the servo system.”