Mastering Welding Tolerances: The Power of Seam Tracking

Welding can be a challenge, especially when it comes to meeting position tolerances. Poorly prefabricated components, clamping issues, and heat distortion can all throw a wrench in the works. Sound familiar? 

Manual welding allows for some flexibility, as skilled welders can adjust on the fly. However,  automated and robotic welding are different stories. Some try to solve the problem by adding more welding wire, while others rely on automated optical seam tracking to avoid costly rework or rejects. 

In this blog, we'll explore different approaches to meeting welding tolerances in automated and robotic welding. You might be surprised at what works and what doesn't and how some solutions that may seem cheap upfront can end up costing you more in the long run. 

Joint Variations: A Welding Reality Check 

Before a robot or welding machine can make a seam, it needs to know where the joint is. Easy enough right? But heres the thing: joints are rarely in the exact same spot every time. So, the challenge is to get a good weld despite these tiny variations. 

If things don't line up quite right, you'll end up with a defective weld that needs to be reworked or even scrapped. 

So, how do you deal with these variations? Here are three common approaches: 

1. Conventional Process Management 
2. Seam Finding 
3. Seam Tracking 

Most commonly used: Conventional process management

Conventional process management is all about finding ways to get good weld quality while keeping things simple. Here are some common strategies: 

1. Using extra welding wire to make sure the joint is covered 
2. Trying to get components ready for welding by fine-tuning previous process steps 
3. Using more complex clamping fixtures 
4. Changing the welding sequence to minimize heat distortion 
5. Programming the robot more precisely (though this can be an ongoing battle) 
   
   

Advantage:

• Little to no upfront investment, except for optimized clamping fixtures (which are usually more expensive) or further training for robot programmers.

Disadvantages:

• These methods can be time-consuming, especially when: 
  • Too much filler material is used, requiring later rework 
  • Reprogramming the robot is needed, which demands frequent adjustments and skilled staff 
  • Defective components are produced, requiring rework 
• Hidden costs can add up, including: 
  • Reworking poorly produced components 
  • Increased shielding gas consumption and slower welding speeds 
• Quality assurance becomes more challenging due to the high volume of rework and re-inspection required 

Seam Searching 

There are two ways to find seams and account for welding tolerances: tactile and optical. 

Tactile seam finding is like a robot using its sense of touch. It detects where the weld should start by making contact with the component using a welding wire or gas nozzle. 

Advantages: 

• You likely already have everything you need in your system 
• No additional costs 

Disadvantages: 

• The weld joint needs to be relatively big (at least 2-3 mm) 
• Only works for short welding paths and not for online seam tracking 
• Doesn't measure seam geometry like gaps or offsets 
• Requires reprogramming the welding robot 

Optical Seam Search Offers Three Different Methods: 

This method uses a laser spot to scan the component's surface without touching it. The robot receives the information needed to start the welding process. 

Advantages: 

• Faster than tactile seam tracking 
• Generally cost-effective 
• Suitable for short and long seams 

Disadvantages: 

• Requires a clear weld feature 

• Investment costs for the sensor system and installation 

  
  

2. Laser Line Sensor 

This technology uses a laser triangulation method for no-contact distance measurement. A semiconductor laser diode projects a laser line onto the workpiece, and a camera records the shape reflected by the workpiece to measure the joint's position. 

Advantages:

• High speed system, side and height measurements are possible in less than 1 second
• Flexible and suitable for many seam types 
• Touchless detection 

Disadvantage:

• Higher capital costs for the sensor system and installation 

A camera uses an algorithm to identify the joint's position based on brightness differences. This method works before arc ignition but can be disrupted by changes in illumination, surface finish, or materials. 

Advantages:

• Quickly measures joint sides 
• Suitable for short and long seams 

Disadvantages:

• Requires contrast to recognize joints and features 
• Sensitive to surface finish and optical interference 
• High investment costs for the sensor system and installation 
  
  

Seam Tracking: Efficient Way to Maintain Welding Tolerances 

Seam tracking is the most reliable way to maintain welding tolerances. It saves rework costs and ensures efficient production. There are two main approaches: Tactile and Optical seam tracking. 

Tactile Seam Tracking

Advantages:

• No additional investment needed 
• Suitable for long weld seams and tracking 

Disadvantages:

• Slow seam search 
• Longer cycle time 
• Requires thicker sheets 
• Lower welding speeds 

Advantages:

• Relatively cheap 
• Easy handling 

Disadvantages:

• Inaccurate measurement
• No adaptive welding possible
• Only suitable for machine welding 

Optical seam tracking 

1. Laser triangulation – This technology uses a laser to measure the seam geometry and track it in real time. 

Advantages:

• Fast seam search 
• Measurement of seam geometry for adaptive control 
• Suitable for various seam types and long weld seams 

Disadvantage:

• High capital costs 
• Requires experience with connection to robot controller or PLC

Advantages:

• Fast procedure
• Suitable for long welding seams and tracking

Disadvantages:

• Expensive technology 
• Limited flexibility 
• Can be challenging to interpret weld images 

Conclusion

Optical seam tracking using laser triangulation is the most flexible and reliable technology for maintaining welding tolerances. It's the only method that can recognize dynamic deformations and compensate for welding tolerances in real time. 

If you are looking for an optical seam tracking solution, consider the iST ARC sensors from ABICOR BINZEL. These sensors correct the weld path in real time, recognizing and tracking workpiece joints from a gap width as small as 0.1mm. 

While there's no one-size-fits-all solution for seam tracking, optical seam tracking with laser triangulation often stands out for its exceptional speed, robustness, and flexibility. 

Have you explored this option or other seam tracking methods? Share your experiences with us below! 

Source Image 4: https://www.carpano.it/tactile-seam-tracker-ig-3/