Stitch weld is often mistaken with seam weld, which is a continuous weld produced by overlapping members to be jointed.
It is an informal term used for intermittent weld, sometimes referred as skip welding. It is a welding instruction, methodology used for depositing weld beads along a joint at an interrupted interval. The number of “stitches” (welds), the space between them and the length of each weld are illustrated symbolically.
This welding symbol is the same as an intermittent welding symbol. It can be used in resistant welding, arc welding, beam welding, gas welding; you name it. It is not associate to a specific welding process but to a welding instruction.
Related: Lead Welding: The Ultimate Process [Explained]
Benefits of stitch welding
Stitch welding is beneficial where full weld bead is not required, it reduces the amount of weld to be deposited. The amount of weld can be reduced by half depending on the intermittent arrangement, weld size and the quantity.
It reduces the amount of heat to the work piece, there for, minimising the risk of distortion caused by heating and cooling associated with a longer weld bead.
On thinner metal sections, e.g. 4mm or less, stitch welding is often used specially when static loading capacity is not an issue. It reduces the risk of overheating the sheets. Economically, it saves electricity and welding consumables due to smaller weld bead compared to a continuous weld bead.
How to make? Where to do it, What you need?
Stitch welding can be done by various welding processes. it can be done on butt joint, lap joint or fillet joint. The welding variables like heating, current, voltage, travelling speed, and shielding gas must be adjusted to produce a sound weld. When stitch on thinner sections, faster welding speed is preferable to avoid burn thought.
Stich welding can be achieved on few basic steps:
Cleaning before welding
Rust, oil, and other impurities along the surfaces to be jointed may hinder the welding process and cause weld imperfections such as of porosity and lack of fusion.
Marking the stitches
Since stitch weld is an intermittent welding, the weld joints should be marked according to the welding symbol before the welding starts. The location of each weld, the length, and the gap between them should clearly be identified.
Welding
Welding according to an applicable procedure
Cleaning after welding
Removal of welding spatter and slags if applicable.
Types of stitch welding
There are 3 types of welding applicable for both but and fillet welds.
- Intermittent weld – welded on a single side of the joint
- Chain intermittent weld – welded on both sides of the joint. The welds are opposite to each other along the joint
- Staggered intermittent weld – welded on both sides of the joint. the weld on one side of the joint alternates with the weld on the other side.
Common welding symbols
1. EN ISO System
2. System by American National Standards Institute (ANSI)
How do you read?
The basic of titch welding are weld length and the gap between the welds. exist two methods of reporting the space between the welds, the EN ISO and the ANSI.
EN ISO system, the space is measured from the edge of the welds, while in ANSI system, the space is measured from the center of the welds and is termed “pitch”.
Notes:
- Weld symbol (plug weld).
- Number of welds.
- Length of each weld.
- Distance between the welds (Pitch for ANSI).
Examples of use
Stitch welding is widely used in car frames for welding many of the chassis’ components together. They are also used in railways industry for welding many parts together whenever is possible.
For base frames with a plate on top like a table, resting on horizontal beam profiles. Stich welding are often the preferable type of welding technique.
It can be used on joints where design against fatigue and the load bearing capacity are not major concerns.
Advantages/Disadvantages
Pros
- Less distortion due to less welding and less heating
- Economically cheaper, less consumable is used
- Reduction in welding time.
Cons
- Increased risk of imperfection due to too numerous stops and starts.
- For mechanised process, continuous weld is considered better rather than using several short “stitches” welds.
- Reduction of the joint load bearing capacity due to fewer welds.
- Not applicable for seal welds.
Conclusion
It is a desirable choice of welding due to the reduced amount of weld and less deformation of the welded joint, but it comes with a price, a reduction of the structure’s loading capacity, unclosed welds, and possible sites of weld imperfections.
There are two variation of illustrating symbols on technical drawing. The major difference between them is the way the space among the weld is indicated in the stich welding symbol and how it is marked on the weld joint.
