Whiteboard Wednesday: Upset Control and Pressure Modulation with Dynamic Profile Modification

In friction welding, we always strive toward repeatability—even when there are differences in the length of incoming parts.  This is especially true in the automotive and aerospace industry where finished parts are held to rigid standards.  Using Torque Modulation with Dynamic Profile Modification, we’re able to ensure our first welded part is the same length as our last welded part. 

A 5 Second Recap of Upset Control

In recent episodes of Whiteboard Wednesday, we’ve talked about upset control. Upset is the amount of shortening between two parts as a result of friction welding. 

To have closed loop upset control and achieve equal upset from one weld to the next, we can use either pressure modulation or torque modulation.  Pressure modulation indirectly controls upset by modulating the amount of weld pressure we have, while torque modulation directly controls upset by modulating the amount of energy—through motor torque—that a rotary friction welder’s electric motor will apply.  

We’ve also learned that torque modulation is at least 10x’s faster than pressure modulation—meaning it’s a much more accurate and repeatable form of upset control.

It’s All About Length Control

Now that we understand upset control, we’ll want to apply it to length control. Since our incoming part lengths can vary, we’ll need to do things a bit differently.  This time, we need a way to get more or less upset from the friction weld in order to achieve a consistent target length for the finished part.

Using torque modulation with dynamic profile modification, we can use upset control to create length control by following these three steps:

Step 1 – Create an Upset Profile
We start by creating an upset profile.  To do so, we perform a standard inertia weld without the use of any upset control.  This means no torque modulation and no pressure modulation—just a standard inertia weld.  Then, we record a profile of upset versus time to generate an error signal in the future. 

Step 2 – Mathematically Adjust the Profile Weld & Starting Energy
Next, we mathematically adjust our profile weld and starting energy to vary the amount of desired upset, depending on the incoming part length.

More Upset: If our incoming part length is too long, then we need to create more upset.  So, we mathematically adjust our upset profile to achieve more upset. We can also increase our target weld energy, or starting weld speed, to start with more energy.

Less Upset: If our incoming parts are too short, then we need less upset.  So, we mathematically adjust our upset profile to get less upset.  And, we can even start the weld speed lower to have less energy to start the weld. 

Step 3 – Close the Loop with Torque Modulation
Finally, we use torque modulation to close the loop on upset control and achieve a new target upset.  Remember, to close the loop we compare the new weld to the upset profile in order to generate an error signal.  The error signal provides feedback to the welding control system, which then adjusts spindle drive motor torque until we have zero error signal between the new and profile welds. 

More Upset:  If we need more upset between our new weld and our profile weld, we increase our weld torque so that the electric motor adds energy to the flywheels system.

Less Upset: If we need less upset in this new profile weld, we apply braking torque so that the electric spindle drive pulls energy out of the flywheels system.  

A Very Powerful Length Control Technique

Torque Modulation with Dynamic Profile Modification is a very powerful length control technique.  We’re mathematically adjusting the profile and the starting energy in order to target a desired upset. Then, we’re using torque modulation to close the loop and to achieve the new target upset.  This is a very responsive system that happens very quickly,  with the entire process taking place in just mere seconds. 

Torque Modulation with Dynamic Profile Modification can be used in Inertia Friction Welding, Direct Drive Friction Welding, or Rotary Hybrid Friction Welding.

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