Welding Works in Manual Mode but Not in Automatic Mode: Cycle Diagnosis

Before examining the welding cycle settings, the A.T.S. technician needed to establish whether the fault could be reproduced consistently.

Tests were carried out on several industrial accumulators to determine whether the unsuccessful weld was an isolated occurrence or a recurring problem under the operating conditions being investigated.

The comparison between manual and automatic operation confirmed a clear difference:

• Manual mode: the cap could be welded.
• Automatic mode: the welding process failed to produce a satisfactory joint.

Since the same behaviour was observed during the checks, the investigation moved towards the timing of the automatic sequence.

The next step was to examine how the individual stages of the welding cycle were coordinated, rather than treating the problem as an occasional welding defect.

The investigation revealed a timing mismatch between the electrode movement and the application of welding current.

In automatic mode, current was being applied before the electrode had properly reached and settled against the accumulator cap.

The time allowed by the programmed sequence was too short for the electrode to complete its downward movement and establish the required contact with the component.

As a result, part of the welding current application period was effectively taking place while the electrode was still moving, rather than with the electrode correctly positioned against the cap.

This affected the conditions under which the weld was formed and explained why the automatic cycle failed to produce the same result as manual operation.

The issue was therefore linked to the coordination between electrode positioning and welding current timing, rather than simply to the ability to weld the component.

In automated resistance welding, the machine sequence and the welding parameters need to be considered separately. The PLC coordinates the machine's movements and operating sequence, while the welding controller manages the welding cycle and its associated settings.

In this case, the investigation identified a timing issue within the PLC-controlled sequence.

Welding trials were carried out using a TECNA TE550 microprocessor-based welding controller, designed to manage resistance welding parameters and cycle functions.

The investigation went beyond checking whether welding current was being supplied. The technician examined how the different stages of the operation were timed in relation to one another:

• Command to lower the electrode;
• Electrode movement towards the component;
• Contact and correct seating against the cap;
• Application of welding current;
• Execution of the weld.

By comparing these stages, A.T.S. was able to narrow down the part of the automatic sequence requiring further investigation.

The issue was not simply whether current was available, but whether it was being applied at the correct point in the welding cycle.

The welding trials took place at TECNA, using the industrial accumulators intended for the customer's actual production application.

Rather than testing unrelated components, the assessment focused on the behaviour of the equipment when welding the parts involved in the reported problem.

The tests covered:

• Inspection of the component to be welded;
• Welding in manual mode;
• Operation of the automatic welding cycle;
• Comparison of the results from both modes;
• Adjustments to the available welding parameters;
• Observation of the process under different test conditions.

The purpose was not to establish a standard set of welding parameters. It was to understand how this particular application responded when the operating conditions were changed.

The trials at TECNA helped identify the differences between manual and automatic operation and pinpoint the timing-related issues affecting the automatic welding sequence.

The most revealing finding was not the failed weld itself, but the fact that the same accumulator cap could be welded in manual mode and not during automatic operation.

This difference gave the A.T.S. technician a much clearer starting point. If welding was possible under manual control, the investigation needed to look beyond the component and examine how the automatic cycle was being executed.

The checks therefore focused on the relationship between:

• The programmed welding sequence;
• Cycle timing;
• Electrode movement towards the cap;
• The moment welding current was applied;
• The welding parameters used during automatic operation.

Comparing these stages helped narrow down the problem considerably.

What had initially been reported as “the cap is not being welded” could now be described more accurately:

“The automatic welding sequence does not correctly synchronize the welding current timing with the electrode contact phase.”

This distinction provided a specific technical direction for the investigation, rather than treating the unsuccessful weld as a general equipment fault.

After approximately 2 hours of inspections and welding trials, the fault had been diagnosed and narrowed down to the timing of the automatic sequence.

The tests showed that the programmed cycle did not allow sufficient time for the electrode to complete its downward movement and establish proper contact with the accumulator cap before welding current was applied.

The outcome was a technical diagnosis, not a completed modification of the production equipment. The case does not document a permanent change to the machine or the immediate purchase of a replacement system.

Instead, the customer now has a clearer understanding of the process limitations and the technical information needed to consider the available options.

Any future investment will need to take account of:

• Expected production orders;
• Required production volumes;
• The level of automation needed;
• The characteristics of the welding application;
• The equipment configuration best suited to the process.

The investigation therefore provided a technical basis for the customer's next decision, without assuming that replacing the existing equipment was necessarily the right solution.

A successful manual weld does not guarantee a successful automatic cycle

When resistance welding is automated, the timing of the individual operations becomes part of the process.

A component may be perfectly weldable, yet the automatic cycle can still produce an unsatisfactory joint if electrode movement, contact with the workpiece and welding current are not correctly synchronized.

Look at the welding sequence, not just the finished joint

Inspecting a defective weld may reveal that something went wrong, but it does not always explain when or why the problem occurred.

In this case, comparing the electrode descent time with the moment welding current was applied helped identify the timing mismatch responsible for the different results in manual and automatic operation.

Test the application before committing to new equipment

Trials using the actual production component can provide valuable information when deciding whether the existing system needs adjustment or a different welding machine should be considered.

A technical trial does not have to lead directly to an equipment purchase. Its purpose is to establish what the process requires and give the customer a sounder basis for evaluating the available options.

A.T.S. helps manufacturers investigate resistance welding applications, examining how the process behaves under actual operating conditions and how the welding machine, controller and automation system work together.

When production problems arise, testing the actual component can help identify the parameters or operating conditions that need further investigation. These trials also provide technical information for assessing whether the existing equipment can meet production requirements before considering an investment in a new welding system.