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Getting the Most from Your AMADA WELD TECH Closed Loop Resistance Welding Power Supply

One of the keys to manufacturing success is simply to know your equipment so you can maximize its usage. Today’s post focuses on eight key features found on AMADA WELD TECH’s closed-loop resistance welding power supplies: what they are, where to find them, how they work, and when to use them.

  1. Closed loop control – At a high level, resistance welders are either “open-loop” or “closed-loop.”
    • Open-loop welders provide no feedback during the weld; they just supply the programmed energy regardless of any process variation. This can lead to variation in weld quality. Example power supplies include most AC welders and some capacitive discharge welders.
    • Closed-loop welders, on the other hand, use current, voltage, or power feedback to precisely control the energy delivered to the parts. This ability to accurately control weld energy is a key factor in overcoming problems associated with process variation and the rapid changes in resistance that happen during the weld. Examples include high frequency inverters and linear DC power supplies.When to use the different power supplies depends on the process, its sensitivity to variation, and the budget. For safety critical parts, we always recommend closed loop power supplies to get consistent results.
  2. Feedback modes – Most of our closed-loop resistance welding power supplies feature three feedback modes: constant current, constant voltage and constant power.
    • Constant current (kA):
      • Delivers the same current for each weld
      • Voltage and power will vary based on resistance
    • Constant voltage (V):
      • Voltage is held constant for each weld
      • Current and power will vary based on resistance
    • Constant power (kW):
      • Holds power constant
      • Varies both the current and voltage during the weldHow do you know which feedback mode to use? This depends on the part and weld design, and any process variations that might occur. The table below illustrates some common scenarios:Closed Loop Resistance Welding Feedback Modes
  3. Combo mode – a special variation of feedback modes, “Combo Mode” combines constant voltage and constant current during one weld event. Constant voltage addresses high contact resistance at the start of the weld, and constant current addresses resistance drop at the end of the weld. Combo mode is a good choice for wire welds, which tend to experience high contact resistance at the beginning of the weld, reduced resistance when the wires deform, and a severe resistance drop as the parts melt.
  4. Dual pulse – Dual pulse is (as it sounds) two pulses. The first pulse’s current level is typically lower – e.g. one-third that of the second pulse – and is used to seat the electrodes on the parts and reduce contact resistance that might result from contaminants on the surface. The second pulse, with higher current, produces the actual weld.
  5. Pulse shaping – Pulse shaping is the ability to adjust both the upslope and downslope of the weld pulse to address different manufacturing challenges. Upslope refers to the gradual ramping of a controlled weld parameter like current, voltage, or power. The upslope of current, for example, helps to reduce the initial contact resistance, focusing weld heat into the parts and reducing weld splash. The length of the upslope period can be programmed to suit the application. A long upslope is recommended for very hard or resistive parts. Much like upslope, downslope refers to the gradual ramping down of a weld parameter. Downslope of the weld current allows the metal to cool more slowly than it would without downslope control. This can help remove some impurities in the weld and reduce stress induced cracking that might occur without the downslope.
  6. Built‐in monitoring – Built-in monitors in the power supplies provide information that can help improve the process and provide data about the weld. While not as effective as an “external” monitor, e.g. MM-400B, WM-200A, it can be a first line of defense in your process. You’ll find buttons to access these screens right on the front panel of your AMADA WELD TECH welding power supply. Typically, you’ll have a run screen and monitors for power, resistance, current and voltage.Buttons on front of AMADA WELD TECH Closed Loop Power Supply
  7. Monitor limits – the fact that we are monitoring the weld parameters, means we can also set limits around the desired signal to ensure that you fall within a process boundary. You can set upper and lower limits, individually, for each pulse.You want to set the limits around the parameter that is not controlled. That is, if you are running in constant current mode, you want to set the boundaries on voltage.Monitor Limits on AMADA WELD TECH Closed Loop Power SupplyWhat’s the purpose of these limits? The purpose is to identify outliers/defects in the process or to monitor process shift.
    • Outliers or defects might indicate something wrong for one particular part/weld – for example, a misplaced or incorrect part, change in material or coating, or damage on the parts.
    • A process shift or trends will show the process over time and show when maintenance might be needed to exchange or clean the electrodes.

    In addition to those benefits, weld data can be stored for future reference and traceability. This is a cornerstone for quality control.

  8. Process Control Tools
    Finally, AMADA WELD TECH power supplies often have a few advanced features to control the process and improve manufacturing results. In this final bullet, we outline several advanced features that can be implemented.
  • Active Part Conditioner (APC) – APC utilizes the dual pulse feature to help generate good welds. In simple terms, APC actively adjusts the first pulse time to bring the parts to the same resistance for the welding pulse. This is most often used with oxidized parts.
  • Resistance Set – Resistance Set is similar to APC. It utilizes the same concept: use the first pulse to condition the parts and bring them to same resistance. Instead of a square pulse, however, it’s all upslope. Current starts low. Why? Sometimes you don’t want to put high voltage into the part all at once. Purpose: generate good welds and avoid splash.
  • Pre‐Weld Check – Use pre-weld check to find problems in the welder that would normally cause the weld to expulse material or the part to overheat. Put a very small pulse in – if voltage goes out of limits, the weld will stop before the second pulse fires. This saves parts and electrodes! Purpose: identify suspect welds, and flag the unit to stop prior to further damage to electrodes.
  • Weld Stop – Similar to pre-weld check but done in one pulse vs two. If the process moves out of limits it will stop the weld altogether. Purpose: Identify suspect welds, and flag the unit to stop prior to further damage to electrodes.
  • Weld to a Limit – Run the weld to a current limit. When weld stops, it’s good. Purpose: prevent over-welding a part. Good when parts vary in thickness.
    Understanding your equipment improves understanding of your process, while maximizing equipment usage enhances process success. Advanced features can increase consistency and improve the resistance welding process. These advanced process control tools can help to reduce scrap and increase throughput. However, these advanced features, as cool as they sound, are not beneficial for every part – and because they often may add time to the welding process may actually lower throughput!

We encourage everyone to start simple and add complexity, as needed. Although some of these features may not be needed for your current process, it is good to know that the equipment has them should the process or material change.

As always, we have a team of engineers to help advise when to use these features. If you are unsure, give us a call to discuss further.

Category: Resistance Welding