Welding is an integral part of metal fabrication. At Wiley, we do a lot of it, and if we do say so ourselves, we do it well. Most of our welding is carried out by highly trained and very experienced human welders, but we also have a number of robotic welding cells “on the team”. When current or future customers learn about our “foot in both camps” approach it often prompts the question, “Which is better – robotic welding or manual welding?” The simple answer is, it depends on what you want to achieve. Here’s a dive into the topic for anyone seeking a more thorough explanation.
Types of Welding
To weigh up the pros and cons of robotic welding versus manual welding it’s necessary to have an understanding of this process.
Welding is a means of joining separate pieces of metal. It works by putting them together and heating them locally until a small pool of molten metal forms. As the weld cools and solidifies, this fuses the two pieces into one.
There are several ways of creating and applying welding heat. The main ones we use are laser, gas-metal arc welding (GMAW), and resistance or spot welding. Resistance welding is used for joining overlapping pieces of thin gauge sheets while laser and GMAW are for heavier plates and angles, as well as some thin gauge work.
Robotic vs. Manual Welding: An Overview
In manual GMAW the pieces being joined are positioned and held in place with clamps or some kind of fixture. This “fit up” is one of the most important parts of the process because it largely determines the dimensions of the weldment and has a big influence on its strength. The welder holds the torch and brings it into the joint, using the heat of the arc to create a small pool of molten metal. This pool is then moved along the joint to form the weld.
Gravity plays a part when dealing with liquids, so welders try to keep the joint horizontal and angle the torch downwards. This isn’t so easy with large fabrications, so the workpiece is often mounted on some kind of rotary table or manipulator to improve access.
Robots are used extensively for resistance welding in the automotive industry. In these applications, the weld is performed by a pair of electrodes that the robot positions on either side of the joint. In smaller resistance welding setups the robot may bring the workpiece in between the electrodes.
For GMAW and laser welding the robot holds the welding head and moves the arc or beam along the joint, to create a weld pool, just as the human welder does. Again, the workpiece is often mounted on some kind of manipulator to improve access and keep the weld pool horizontal.
In most robotic welding an operator loads the metal pieces into a fixture, starts the welding cycle, and unloads when the job is done. This prompts the question of which is better: robotic or manual welding?
Precision and Repeatability
Industrial robots have advanced tremendously since their first appearance in the 1950s, but humans still have some advantages. One of these is precision, but not repeatability.
Each joint in a robot arm has a small degree of backlash or free play in the gearing. The cumulative effect over five or six joints is to create an appreciable amount of “lost motion”. This results in, what is to some people, a surprising level of inaccuracy. Command a robot to move its gripper to a specific point and it could end up as much as 0.75mm (0.030”) away from the target. (The exact level of inaccuracy depends on factors like the payload the arm is carrying, the direction it approaches the position from, and the ambient temperature.)
A skilled human welder can achieve a similar level of precision, providing they have good eyesight and aren’t too tired. The difference though is that the robot can maintain this accuracy over an entire shift and longer if needed, which is clearly impossible for a human. In fact, robot repeatability is better than its absolute accuracy, by a factor of around 10.
Complicating this comparison though is variation in fit-up. A batch of pieces being welded will have some dimensional variation, and they won’t necessarily go on the table in exactly the same position every time. A human welder can see this variation cycle-to-cyle and adjust for it accordingly. The robot however is dumb and just follows the same path every cycle, (unless it has a vision guidance system, which adds to the cost of the machine.)
To summarize, a welding robot is possibly more precise but is definitely more repeatable, than manual welding. Does that make it better? Only if the pieces it’s being supplied with to weld are very consistent.
Speed and Efficiency
A robot can weld at around 35” per minute. An experienced human welder can usually maintain 18” – 20” per minute, sometimes faster but also slower if they’re near the end of a long shift. The upshot is, a robot is going to complete the welds on fabrication in less time than the human welder. The robot will also maintain a consistent time from shift start to shift end. However, that’s not the whole story. Other factors to consider are:
- Loading and unloading
- Programming and prove-out
- Unexpected events
Loading and Unloading
The robot can’t start welding until the pieces are all positioned and clamped in place and the human loader hits the “cycle start” button. Likewise, the job isn’t finished until the completed weldment is lifted off the table and taken out of the cell. In short, the total floor-to-floor time for a robotic welding cell is still influenced by the human factor.
Programming and prove-out
The path the robot moves the torch through must be programmed. This is sometimes done on the robot, which stops it from doing productive work, so many companies are moving to offline programming. In either approach though, the program must be proven before an actual welding arc is struck. That all takes time the human welder doesn’t need and can consume material.
If something happens during the welding process a human welder can stop and adjust: the robot will just keep on going, unless fitted with sophisticated sensors. However, with highly consistent pieces to weld, the robot is probably going to create more consistent welds. On balance then, we would expect higher quality work from robotic welding.
Human welders are blessed with five senses, robots aren’t. This means getting good work from robotic welding requires that everything be predictable and consistent. Meet those requirements and the robot is hard to beat.
Which to Choose: Robotic Welding or Manual Welding?
The main consideration is the amount of welding to be done, followed closely by the consistency required. As robotic welding is faster per inch, it becomes increasingly beneficial as there’s more welding to be done. The number of pieces that need welding is also a factor as it’s desirable to amortize the programming and prove-out time over as long of a run as possible.
However, for short lengths of welding, and when only a few pieces need welding, the manual process is usually faster. It also has the advantage that the pieces being welded don’t need to be cut and prepared with such precision, which can be another time and cost-saving.
Talk to Wiley For All Your Welding Needs
Fabrication is a lot more than welding, but welding is a big part of what we do. Whether you need a large quantity of identical pieces welding, or just a few, talk to us. We have the equipment, experience, and capabilities to give you the fabrications you need.