Plastic Assembly News

CompuWeld© Program for Ultrasonic Welding


CompuWeld© Software is used for data acquisition with Branson 900 and 2000 series ultrasonic welders for monitoring weld data and providing real time SPC of the critical weld data from the ultrasonic welding process. CompuWeld© SPC or Statistical Process Control involves collecting data from a welder for the purpose of monitoring the process through the use of statistical tools, such as XBar and RBar control charts. Analyzing the output data is done to maintain control of the process and to improve performance of the process. In ultrasonic plastic assembly, the information available about the welding process comes in the form of data about WELD TIME, WELD ENERGY, PEAK POWER, WELD COLLAPSE DISTANCE, TOTAL COLLAPSE DISTANCE AND ABSOLUTE DISTANCE OR FINAL POSITION.

WELD TIME is the duration that ultrasonic energy is on during the weld cycle. ENERGY is the total value of the watts used during the cycle multiplied by the actual time used during the cycle. PEAK POWER is the largest percentage of watts used at a single point in time during the cycle. WELD COLLAPSE is the amount of distance the actuator traveled after the trigger switch was activated and before the hold time. TOTAL COLLAPSE is the amount of distance the actuator traveled after the trigger switch was activated and after the hold time. ABSOLUTE DISTANCE or FINAL POSITION is the total amount of distance traveled by the actuator after leaving the upper limit switch. By monitoring these process variables, we hope to minimize unwanted causes of variation and improve control of the ultrasonic welding process.

There are two types of variation evident in all processes. Natural or random variation and variation caused by special or assignable causes. A process is said to statistically be in control when the only source of variation is coming from natural or random causes. But as Deming said, “a state of statistical control is not a natural state for a manufacturing process. It is instead an achievement, arrived at by elimination, one by one, by determined effort, of special causes of excessive variation.” Types of special causes that can be found in the use of ultrasonic equipment include variation evident in differences in equipment, tooling, setup, operators, material, molding conditions and the environment. In order to use the statistical tools available in “CompuWeld© 2000″ for monitoring a stable process, the welding process must first be brought into statistical control by eliminating causes of variation created by special or assignable causes.

On the CompuWeld© 2000 run view screen, one can see (6) XBar, RBar charts on the screen at one time. The XBar chart is drawn with the XBar above the RBar chart. The values of XBar and RBar are displayed on the vertical scale and the sequence of subgroups are displayed through time on the horizontal scale. The variable being monitored is shown on the top left corner of the XBar chart. XDouble Bar and RBar are shown with dotted lines running horizontally. Control limits are shown with solid lines running horizontally. The last subgroup average measurement and the last subgroup range or variation is shown on the bottom left corner below the RBar chart. The process capability measurements known as the CP ratio and CPK are shown on the bottom right hand corner below the RBar chart. The picture above is illustrative of the data available from the Compuweld© software.

Speak Your Mind

Tell us what you're thinking...
and oh, if you want a pic to show with your comment, go get a gravatar!

Plastic Assembly News