A booklet on weld design recently appeared on my desk. It contains this statement:

“Intermittent fillet welds are used in some work where the loads are small. They reduce the cost of welding and also reduce distortion.”

In a general way, these two sentences are probably correct.

However, neither is universally true. In this column, we'll re-examine intermittent fillet welds to see what they do and don't do.

When I started welding, intermittent fillet welds were an obvious choice for connections that did not require the strength of a continuous fillet weld.

The process I was using was stick: I can't say shielded metal arc, because back then, we were using bare electrodes.

With stick, it was easy to make intermittent fillet welds: After making the required length of weld, one would fill the crater and break the arc. Then the welder would move to the next location, re-strike the electrode, and continue.

With stick welding, the arc had to be stopped, the stub removed, and a new electrode inserted in the stinger due to the finite length of the filler metal — even when the welds were continuous. So, whether making intermittent or continuous welds, the welder always made a series of segments.

For continuous welds, the segments were joined end to end. For intermittent welds, ideally each segment consumed one electrode, and the segments were gapped.

Perhaps the welder used a travel speed of 10 ipm when welding with stick. Certainly, the welder could “index” ahead to the start of the next segment of intermittent weld faster. Where the design permitted intermittent fillet welds, they cost less than continuous welds.

Automatic welding changed that.

Submerged arc was the first widely accepted automatic process and it was not well suited to intermittent welds. Submerged arc was faster than stick, and the torch was propelled mechanically down the joint. Once the arc was initiated, keeping it going was usually easier than trying to make intermittent welds, with the corresponding starts and stops.

Today, robotic welding is the latest innovation, and gas metal arc welding usually is the process of choice. This technology has once again affected the proper view of intermittent fillet welds. Robots are very accurate, and can move quite rapidly. However, the robot is typically programmed to slowly move toward the arc starting point, and travel initiates after the arc is established.

At the end of a weld, a delay can be programmed into the travel, allowing the crater to be filled. Next, the robot moves the torch away from the joint and indexes to the start of the next weld segment. Slowly and carefully, the welding torch is again moved to the starting point of the next weld.

By now, I'm sure you understand the point: With robotic welding, it is often faster to make continuous welds, rather than intermittent welds.

I want to return to the quotation that prompted this column. The first sentence claims that “intermittent fillet welds are used …where the loads are small.” I've seen fillet welds used in applications where the loads are very large. No doubt, the author intended to communicate that intermittent welds may be used when the loads don't justify continuous fillets.

Next, the author claims that “they reduce the cost of welding.” The preceding examples challenge the universality of this statement.

Finally, the author states that intermittent fillet welds “also reduce distortion.”

Again, the intent was to compare the distortion of a continuous fillet weld to an intermittent fillet weld, all things being equal. And, with such caveats, this statement is true.

I'm reminded of a situation I encountered many years ago.

Some well-intended designer had apparently been taught that “intermittent fillet welds reduce cost and reduce distortion,” and proposed to put this principle into practice. The weld symbol on his drawing spelled out the desired intermittent weld:

If the welding is done in the horizontal position, any welder will immediately realize that this is a multiple pass weld, and a relatively short one at that. But, the problems don't stop there.