BIZOMAT MAKEOS · Fabrication
Fillet Weld Joint Design and Cost
What fillet weld size does this joint need, and what will the weld metal, time and cost be?
Design of a fillet-welded joint loaded in shear on the throat: the throat and leg size required for the load, weld length and allowable throat stress, the leg used after a minimum size for the plate, utilisation, then weld metal mass, arc time, welder time and cost from deposition rate, operating factor, filler efficiency and rates.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Strength | ||
| Load on the weld group | kN | Total load the welds carry, treated as shear on the throat. |
| Total effective weld length | mm | Total effective length of fillet welds sharing the load. |
| Allowable throat shear stress | MPa | Allowable shear stress on the throat for the electrode and code. |
| Minimum leg for the plate thickness | mm | Smallest leg your code permits for the thicker plate joined. |
| Thinner plate thickness | mm | Thickness of the thinner part (a leg larger than this is wasted). |
| Cost | ||
| Convexity and overfill allowance | % | Extra metal for convexity and overfill. |
| Weld metal density | kg/m³ | Density of the weld metal. |
| Deposition rate | kg/h | Deposition rate of the process and wire. |
| Operating factor (arc-on share) | % | Share of the welder’s time with the arc on. |
| Filler deposition efficiency | % | Share of filler bought that ends up in the weld. |
| Welder labour and overhead rate | $/h | Cost of welder time including overhead. |
| Filler price | $/kg | Price of the filler metal. |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
Strength
What this means: Load on the weld group
- What it is
- Total load carried by all the fillet welds in the joint together, treated as shear on the weld throat.
- Units and format
- Enter a number in kN: kilonewtons (1 kN = 1000 N). The form accepts 0.000001 kN to 100000 kN. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 60 kN as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Required throat and leg rise in proportion to the load.
- Get it right
- Enter the whole load shared by the welds, not the load per weld run; eccentric loads need a separate weld-group analysis.
What this means: Total effective weld length
- What it is
- Combined effective length of every fillet weld run sharing the load, excluding start and stop craters your code does not count.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 1000000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 200 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Longer welds reduce the throat and leg needed but add weld metal to the cost.
- Get it right
- Add up all runs that carry the load; a weld on both sides of a plate counts twice.
What this means: Allowable throat shear stress
- What it is
- Allowable shear stress on the weld throat for the electrode and the welding code or standard you design to.
- Units and format
- Enter a number in MPa: megapascals (1 MPa = 1 N/mm²). The form accepts 0.000001 MPa to 1000 MPa. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 120 MPa as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Required throat falls in proportion as the allowable rises.
- Get it right
- Take it from the applicable welding code for your electrode classification and load type.
What this means: Minimum leg for the plate thickness
- What it is
- Smallest fillet leg the welding code permits for the plate thicknesses joined. The tool uses it when strength needs less.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 50 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 5 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Look up the minimum size in your code; it is based on plate thickness, not on load.
What this means: Thinner plate thickness
- What it is
- Thickness of the thinner of the two parts being joined. The tool checks that the chosen leg does not exceed it.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 200 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 10 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Use the thinner part, because a leg larger than the thinner plate cannot be fully formed.
Cost
What this means: Convexity and overfill allowance
- What it is
- Extra weld metal deposited above the ideal flat triangular fillet, from convexity and overfill, as a percentage of the ideal amount.
- Units and format
- Enter a number in %: percent: the number is read as a percentage, so type 8 for 8 %. The form accepts 0% to 100%. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 10% as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Raises the weld metal mass and with it time and filler cost.
- Get it right
- Type a percentage of the ideal fillet volume; measure from sectioned test welds if possible.
What this means: Weld metal density
- What it is
- Density of the deposited weld metal, used to turn weld volume into mass for the time and filler cost.
- Units and format
- Enter a number in kg/m³: kilograms per cubic metre. The form accepts 0.000001 kg/m³ to 20000 kg/m³. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 7850 kg/m³ as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Weld mass and cost rise in proportion.
- Get it right
- Use the density of the filler metal family from the consumable or material data sheet.
What this means: Deposition rate
- What it is
- Mass of weld metal the process and wire deposit per hour of arc-on time, from the consumable maker’s data at your settings.
- Units and format
- Enter a number in kg/h: kg/h. The form accepts 0.000001 kg/h to 50 kg/h. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 3 kg/h as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A higher rate shortens arc time and welder time in proportion.
- Get it right
- Use the rate at your actual wire size and current, per hour of arc time, not per shift.
What this means: Operating factor (arc-on share)
- What it is
- Share of the welder’s paid time with the arc actually on; the rest goes to setting up, cleaning, repositioning and handling.
- Units and format
- Enter a number in %: percent: the number is read as a percentage, so type 8 for 8 %. The form accepts 5% to 100%. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 40% as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A lower operating factor raises welder time and labour cost.
- Get it right
- Measure it from time studies on similar work; type the percentage of time, not a fraction.
What this means: Filler deposition efficiency
- What it is
- Share of the filler metal bought that ends up in the weld; the rest is lost to spatter, stub ends, slag or fume.
- Units and format
- Enter a number in %: percent: the number is read as a percentage, so type 8 for 8 %. The form accepts 20% to 100%. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 90% as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Lower efficiency raises the filler mass bought and its cost.
- Get it right
- Take it from the consumable maker for the process; stick electrodes lose far more than solid wire.
What this means: Welder labour and overhead rate
- What it is
- Cost of one hour of welder time including wages, on-costs and the workshop overhead allocated to welding.
- Units and format
- Enter a number in $/h: money per hour. The form accepts $0/h to $10000/h. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with $80/h as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Labour cost rises in proportion.
- Get it right
- Use the fully loaded hourly rate from your costing, not the base wage.
What this means: Filler price
- What it is
- Price paid per kilogram of filler wire or electrodes. Gas and power are not included separately.
- Units and format
- Enter a number in $/kg: money per kilogram. The form accepts $0/kg to $10000/kg. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with $4/kg as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Filler cost rises in proportion.
- Get it right
- Use your current purchase price including freight; add shielding gas to the hourly rate if you want it counted.
Method and formulas
- Required throat = F ÷ (L τ); leg = throat ÷ 0.7071; chosen leg = max(required, minimum), rounded up to the next millimetre.
- Weld metal = leg² ÷ 2 × (1 + excess) × L × density.
- Arc time = mass ÷ deposition rate; welder time = arc time ÷ operating factor; cost = welder time × rate + mass ÷ efficiency × filler price.
- Example: 60 kN on 200 mm of weld needs a 3.5355 mm leg; a 5 mm weld costs about 1.5351.
Limitations
- Uniform shear on the throat; eccentric weld groups need a polar moment analysis.
- Structural welds must be designed to the applicable welding code.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Size and cost the welds on a bracket or frame
- Avoid over-welding that adds cost and distortion
- Quote welding labour and consumables
Who it is for
- Fabrication supervisors
- Welding engineers
- Estimators
What you get
- Required and chosen leg size
- Utilisation
- Weld mass, time and cost
Interpreting the result
- Weld cost rises with the square of leg size: a longer smaller weld is usually cheaper than a short large one.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 1433–1486. Topic reference; no source tables or recommended settings are reproduced.
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