Robotic versus manual welding cost: the crossover

A genset base frame with 4.2 m of 6 mm fillet weld takes about 35 paid minutes on a manual bench and about 19 in a robotic cell, load and unload included. The 16-minute difference is what a robotic versus manual welding cost comparison is actually measuring, and it is small enough that the fixture has to be counted properly before the cell looks attractive.

The frame pays back when 60–100 hours of fixture and programming divide into 16 minutes per part, which puts the crossover at roughly 230–320 parts. That number is rate-free. It holds at any labour rate, because both routes multiply the same rate by different minutes. Only the fixture hours and the minutes saved have to be known.

Robotic versus manual welding cost starts with arc-on time

Start with the arc, not the price. A 6 mm leg fillet runs at 300–400 mm/min with 1.2 mm wire. Take 300 mm/min: one metre of weld needs 3.33 minutes of arc time.

The rest of the paid hour is not welding. On a bench it goes on picking up the part, tacking, turning it, chipping spatter, changing wire, and waiting for a crane. That overhead leaves the arc on for 35–45% of the hour, so one metre costs 3.33 ÷ 0.40 = 8.3 paid minutes.

In a cell the same seam is welded at the same speed, but the arc is on for 75–85% of the time the cell is running, because the torch does not stop to think, wipe, or reposition itself. At 80%, one metre costs 4.2 minutes, before the load and unload.

The load and unload is the part of the comparison people forget in the other direction. A frame that takes 90 seconds to clamp and release adds 1.5 minutes to every part regardless of weld length. On the 4.2 m frame, the cell's 17.6 arc minutes plus 1.5 becomes 19.1, and the saving over the bench falls from 17.7 minutes to 16.

Why travel speed does not decide it

It is tempting to assume the robot welds faster. It does not. Wire feed, current and travel speed are set by the joint, the thickness and the leg size, and the same 240 A at 1.2 mm wire produces the same bead whether a hand or a wrist holds the torch.

A cell can run higher current on a given joint only because it holds the angle and stick-out constant and the fixture holds the gap closed. That is a consistency gain, not a speed setting, and it is worth 10–20% of travel speed at best on a well-fitted joint.

The break-even is a part count, not a price

Every cost figure in the table above is a time. Cost is time multiplied by a loaded rate, and if both routes carry the same rate, the rate disappears from the comparison.

That gives a clean rule. Divide the one-off hours by the hours saved per part. A 60-hour fixture at 16 minutes saved per part breaks even at 225 parts. Add 25 hours of programming and path proving, and the same frame breaks even at about 320 parts. With 90 fixture hours plus that programming, the answer moves to roughly 430.

The labour type changes the arithmetic in one direction. A cell replaces a qualified welder per station with a loader and a setter, so the loaded rate on the cell is lower even before the minutes are counted. That makes the cell pay back sooner than the rate-free model says, which is why the rate-free model is the conservative one to defend to a finance team.

What the model cannot absorb is a design change. A fixture is built around datums, and moving a clearance hole 2 mm or widening a door cut-out can mean a new location pin, a re-clamped stop and a re-taught path. Two changes in the first year is a normal rate for a new programme, and each one costs a fraction of the original fixture.

Where the saving actually comes from

Time on the arc is the visible saving. The larger one, on thin sheet, is the parts that do not come back.

A 2 mm canopy panel welded freehand distorts unevenly between operators. The same seam welded in a fixture with a repeating sequence distorts the same way, and a known distortion can be designed out — a pre-set gap, a clamped sequence, a stitched weld. Rework on a bench run of thin panels typically lands at 4–8% of parts. In a cell with a proved sequence it lands at 1–3%.

Straightening a distorted 2 mm panel is 10–15 minutes of a fitter's time plus a re-inspection. On a 1,000-part release, moving from 6% to 2% rework removes 40 panels of straightening, which is 400–600 minutes, or roughly the weld time of 25 more parts.

Spatter is the third saving and the smallest. A cell at the right parameters produces less spatter, so the 5–10 minutes of chipping and wire-brushing per frame drops. It is not a reason to buy a cell, and it is a real line in the quotation if the part is painted after welding.

Two things the cell does not save. Material cost is identical, because the weld consumes the same wire and the same plate. Finishing is identical too: the part still goes through pretreatment and the powder booth, and a welded assembly still needs its masked faces and its threaded inserts. A business case that credits the cell with a coating saving is crediting it with something it did not do.

Three numbers to ask a supplier for

The comparison is only as good as the inputs, and a supplier who cannot produce these three numbers is guessing at the route:

• Arc-on percentage for the cell, measured over a shift including load, unload and fixture service.
• Fixture and programming hours, quoted as a separate line against the part number.
• Rework percentage on the same part family, with the definition of what counts as rework.

Ask for the same three from the bench route. If the bench rework figure comes back as "negligible", treat it as unmeasured rather than zero.

Changeover, mix and the cost nobody quotes

A cell costs 20–40 minutes every time the part number changes: program recall, fixture swap, first-part check. A bench costs 5–10 minutes, because the drawing is on the table and there is no program.

That is fine on a single part running for weeks. It is ruinous on a family of eight canopy sizes at 90 pieces each, where changeover consumes a third of the cell's hours. The arithmetic to apply is changeover time × variant changes per month against available cell hours; above about 10% of the hours, the family belongs on a bench, or the variants need to share one fixture with a common datum.

Consumables rarely decide anything. A 6 mm fillet uses about 160 g of wire per metre either way, because the weld section is the same. Gas runs at 12–15 l/min during the arc, which is 40–50 l per metre at 300 mm/min. What differs is the loss: a bench run stops and starts more often, so stub and spatter loss runs a little higher.

What a quotation should show

A welded assembly quote that cannot be compared line by line will be compared on the total, and the total hides the route. These lines make the two routes visible:

• Material, with grade and thickness, at the bought-in size.
• Cutting and forming, to the flat developed from the bend allowance.
• Fixture or tooling, quoted separately with its amortisation basis.
• Weld time in minutes, at a stated arc-on assumption and a stated travel speed.
• Consumables per metre.
• Rework allowance, stated as a percentage.
• Finishing, per the coating system and the surfaces masked.
• Inspection: first article, PPAP, and the sampling level.
• Packing and the delivery basis.

The welded assembly quotation guide sets out the same structure from the supplier side. Comparing two suppliers on the total alone usually compares two different assumptions, and the one that looks cheaper has often assumed a lower rework rate and a lighter fixture.

How Ganesh prices and runs both routes

Ganesh runs three CLOOS robotic MIG cells and more than 30 manual MIG/MAG, spot and SPM stations, with fixtures designed and built in-house, as listed under welded assemblies. Because both routes sit on the same floor, the quotation can carry the route it was priced on and the fixture hours that belong to it, rather than a single blended piece price.

Upstream, the 12 kW fibre laser with its 40 ft × 16 ft bed produces the cut edge the cell locates against, and the 200 T, 5-axis brake forms flanges to 10 mm over 4,450 mm, so the fit-up that decides whether the cell can run is made in-house. Downstream, welded assemblies go through seven-tank pretreatment and the 18 ft × 14 ft powder booth.

Ganesh has manufactured sheet metal since 1992 across five units in Mumbai (Vasai) and Nagpur, holds ISO 9001:2015 and ISO 14001:2015, and offers PPAP and first article inspection. Customer work includes genset base frames for Mahindra Powerol, elevator frames for TKE and Eros Elevators, and railway assemblies for Indian Railways.

What to put in the RFQ for a cost comparison

• Weld lengths per assembly, by leg size, not a total weld index.
• Quantity per release and per year, with the variants and their split.
• Joint gaps the design assumes, and whether the parts are laser-cut or sheared.
• Fixture ownership: supplied, bought, or amortised in the piece price.
• Rework acceptance, since a 3% allowance and a 7% allowance are different prices.
• Coating specification and masked faces.
• Inspection level, and whether PPAP is required.

The robotic versus manual route comparison covers joint access and fit-up, the bending and welding assemblies hub collects the rest of the cluster, and the RFQ checklist is the list to attach to the drawing.

When the comparison flatters the robot

The cell looks cheapest when the part is stable, the volume is large and the weld is long. Reverse any one of those and the arithmetic moves against it.

A prototype with three design changes in a month never amortises its fixture. A part with 0.4 m of weld saves about 1.6 minutes per part, so the same 60-hour fixture needs roughly 2,250 parts to break even. Heavy multi-pass work in 10 mm plate takes so long per part that fixture investment is dwarfed by the weld itself, and a positioner with a manual welder gives more control over inter-pass temperature than a fixed program.

Ganesh does not weld on site, does not offer laser welding, and does not price a cell part at a bench price to win the order. Where the volume does not support a fixture, the manual route is quoted with the checking fixture it needs, and the part stays competitive.

Send the assembly with the weld lengths, the leg sizes and the quantity per release. The quotation will show the fixture hours, the weld minutes and the rework allowance as separate lines, so the route can be challenged before the order is placed.