Once the control is removed as a source of variation, spot welding operations can still face problems from variations such as:
- Monitoring can detect problems from surface contamination and material coating variations, and alert the operator, to keep these poor-quality and inconsistent welds from leaving the factory.
- Adaptive features can prevent these problem welds from being made in the first place by automatically making adjustments to burn through the coating or contamination in a controlled fashion, and completing the weld to specifications.
- Monitoring can detect welding problems from parts that were fit together poorly, and alert the operator, to keep these poor-quality and inconsistent welds from leaving the factory.
- Adaptive features can prevent these problem welds by automatically making adjustments to squeeze the parts together, and completing the weld to specifications. This reduces the variations on the welded result to levels approaching what it would be if no part fit-up problem existed.
- Flattening electrodes. As the electrodes gradually become flattened during production, the programmed current becomes less concentrated at the site of the weld. This causes the welds to become smaller.
- Shunting. A weld made in close proximity to a previously produced weld is often undersized because a portion of the programmed current gets diverted through the electrical path that was created by the existing weld.
- Monitoring will recognize that an undersized weld was produced and alert the operator, preventing the undersized weld from leaving the factory. In the case of flattening electrodes, the operator can also respond by changing the electrodes.
- Adaptive features can be added to detect these types of problems as the weld is taking place, automatically adjust the heat by the right amount to compensate for the condition, and produce a consistent weld. In addition to improving weld consistency and preventing problem welds from occurring, the adaptive control extends the number of welds that can be produced before the electrodes have to be changed.
- This occurs when the electrodes lose their ability to contain the molten nugget during weld formation. Expulsion can result in excessive surface indentation as well as cracks and porosity inside the weld. When expulsions occur, welds that are X-ray tested often don’t pass.
- Monitoring can detect these expulsions and allow the operator to reject the part, without having to X-ray the part to detect that the expulsions took place.
- Adaptive features allow you to detect expulsion the instant it occurs during the weld, instantly cut off the heat to minimize damage, then perform a repair operation in place. These actions, which take place automatically, have been demonstrated to effectively mediate the effects of expulsion, and produce welds that consistently pass X-ray testing.
Adding monitoring to the control can keep poor-quality and inconsistent welds from leaving the factory by automatically alerting the operator when these problems are detected. And adding adaptive features on top of that can provide the best solution of all, by effectively compensating for all of these sources of variation to produce consistent welds, and prevent problem welds from occurring. When the variations are too severe to correct, it can instantly notify the operation about the problem.
Seam welding operations are traditionally faced with such problems as:
- inconsistent heat from weld to weld
- inconsistent spot spacing
- inconsistent wheel velocity
- inconsistent force over the length of the seam
- edge variation
- inconsistent wheel acceleration at the start and end of the seam
- inconsistent face contact area of the seam wheel rolling on the part
- wheel-to-brush contact resistance variations
- Variable loading of the part presented to the machine, motor torque limitation, gear backlash, belt oscillation, motor speed control instabilities and machine mechanical resonances are factors that cause instantaneous wheel velocity fluctuations on seam welding machines. These velocity variations translate into variations causing hot and cold spots that affect the size of the welds produced.
- Adding Adaptive features is the easiest way to minimize these variations by automatically adjusting the heat up and down in response to these instantaneous velocity fluctuations.
- Conventional seam welding controls set a motor speed and then depend on a fixed programmed time between welds to control the spot spacing. This practice is based on the often-false assumption that the wheels operate at a perfectly uniform speed. In actuality, the same factors that cause wheel velocity fluctuations on the seam are also responsible for causing inconsistent spot spacing.
Adaptive features eliminate this problem completely by precisely placing each spot at the desired location, based on actual measured position of the wheel on the part, instead of depending on timing and the hope that the wheels are rolling at a perfectly uniform speed.
- Weld cylinder and ram friction, air pressure fluctuations or servo anomalies, wheel cyclic variations and machine vibration are factors that cause force variations as the wheels roll along the seam. These force variations translate into irregularities in the size of the welds produced.
- Adaptive features offer the easiest way to minimize these variations, by automatically adjusting the heat up and down in response to the instantaneous force fluctuations.
- Seam operations that need to maintain edge-to-edge control of a seam are plagued with edge variations, because synchronizing the heat with the dynamics that take place at the beginning and end of the seam is nearly impossible to achieve with a conventional control. Starting the heat too soon makes the front edge too hot and expulses material; starting the heat too late makes the front edge too cold, and an undersized front edge weld. Similar problems occur at the end of the seam; turning off the heat too late makes the back edge too hot and expulses material; turning off the heat too soon makes the back edge too cold, and an undersized back edge weld. These are some of the reasons why manufacturers employing traditional approaches to perform edge to edge welding are plagued with high scrap rates.
- Adaptive features solve this problem by accurately synchronizing the process and optimally sculpting the heat in coordination with the contour of the front and back edge of the part. As the wheel rolls up onto the front of the part, the control initiates the heat. The adaptive weld schedule traces the path of the seam welding wheel, while monitoring instantaneous wheel velocity, force, and other parameters as the part is being welded. It automatically adjusts the heat every millisecond to compensate for the velocity fluctuations, wheel bounces, and other sources of variation. Then it reduces and shuts off the heat as the wheel rolls off the back of the part.
All of these factors together result in:
- inconsistently sized welds that can have variable spacing on the seam
- the first few welds being hotter than the rest of the welds in the seam
- similar problems with the welds at the end of the seam
In edge-to-edge seam welding operations, where the seam wheels have to roll up on the front of the part, roll across the part, and off the back edge of the part, these problems are further compounded by:
- wheel bouncing
- vibration and dynamic geometry changes that occur on the front and back edges
Monitoring can detect all of these sources of weld variation, and keep poor-quality and inconsistent welds from leaving the factory. However, manufacturers can still end up with a very high, very expensive reject rate.
Operating with an adaptive seam schedule is the easiest way to prevent bad welds from occurring due to these types of problems. The WeldComputer® adaptive features can automatically detect and correct each of these problems to produce consistent welds, and prevent a bad weld from occurring in the first place. And when the variations are too severe to be corrected, the system can notify the operator instantly about the problem.
A number of factors contribute to inconsistent set-down of projection-welded parts, including:
- inconsistent heat control
- electrode force variations
- part projection geometry variations
- oil on the part
- other surface condition variations
Conventional controls that apply the same heat regardless of what combination of prevailing conditions exists, result in inconsistent welds. When variations are severe enough, a conventional control can degrade and even damage the tooling.
Monitoring can detect all of these sources of weld variation, and keep poor-quality and inconsistent welds from leaving the factory. But manufacturers can still end up with a very high, very expensive reject rate.
An adaptive projection weld schedule effectively compensates for these sources of variation by automatically adjusting the heat during each weld to obtain consistent set-down of each projection. If after making these adjustments the set-down target is still not reached by the end of the heat application, the adaptive schedule can extend the heat as needed to achieve the set-down target.
The Adaptive schedule is also able to recognize when serious tooling and part stack-up problems exist that would prevent a satisfactory weld from being produced. The adaptive schedule instantly cuts off the heat the millisecond such a problem is detected, and alerts the operator about the problem. In an automatic welding operation the adaptive control automatically rejects the problem part without causing any halt to production. This avoids unnecessary tooling wear or damage, maximizes production throughput and minimizes down time.
Adaptive projection schedule applied to projection nut welding: the adaptive schedule automatically detects missing nuts, upside-down nuts or incorrect nuts, and immediately notifies the operator or robot about the problem.
Flash welders can cause flicker and unacceptably severe demand on the factory power line.
- Control: in many applications, replacing the existing flash welder control with a WeldComputer® control has been demonstrated to reduce flicker on the power grid to acceptable levels.
- Adding adaptive features to the flash welding process further reduces current demand on the power line, while improving the flashing capability and flashing consistency of the machine, which increases upset consistency and the consistency of the welded product.
Butt welding operations using conventional controls are faced with:
- variations from lack of coordination of the heat control with the action of pressing the part together
- inability to compensate for the variable surface conditions of the contacting parts being welded
- inability to compensate for upset variations
- Adaptive features accurately synchronize the application of heat with the contacting parts, and automatically adjusts the heat to compensate for part variations. All of this is done while upsetting is in progress, to improve the upset consistency. The result is increased reliability of the welded result and reduced rejected parts.