Two Quotations, One Machine: How to Compare Them Line by Line

A buyer sends the same enquiry to three suppliers. Two come back thirty per cent apart, both describing "a 160 kVA medium frequency spot welder". One of them is not expensive and the other is not cheap. They are describing machines that differ in the parts nobody photographs.

This article is about how to read two quotations against each other, in the order that actually decides the money: what the machine has to do, what is inside it, and what is missing from the page altogether.

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The head of a platform welder on our assembly floor: cylinder, upper head, copper arm, and the control cabinet with its touch screen. Two quotations for "a spot welder" can differ in every one of these parts.

Start With the Duty, Not the Price

Two prices are only comparable if the two machines are being asked to do the same work. Before looking at either number, write down the duty in your own words: material and coating, stack thickness, number of welds per part, parts per hour, shifts per day, and the longest the machine will run without a break.

That last item is the one buyers skip, and it is the one that changes the transformer. A machine welding twenty spots an hour in a job shop does not need the same duty rating as one welding four hundred an hour on a three-shift line, even at identical kVA. If one quotation is priced on a light duty cycle and the other on a heavy one, the gap in price is not a gap in margin. It is a gap in copper.

The Transformer and the Controller

The kVA figure is a nameplate number. What you want next to it is the duty cycle it is rated at, whether the machine is AC or medium frequency inverter, and what the controller does when the incoming voltage sags. A controller that holds current constant will keep the weld the same through a voltage dip; one that fires on a fixed percentage will not.

Ask who makes the controller, and ask what happens when it fails in year three. A branded controller bought in from a third party is usually easy to replace anywhere in the world. A controller designed in-house is fine until the day you need a board and the supplier has changed the model. Neither answer is wrong, but you should know which one you bought.

Ask also how many weld schedules the controller holds, and whether the schedule can be locked. On a line with several operators that single feature is the difference between one schedule and four versions of it.

Two more lines belong in this section and are almost always left to the word "standard". Arm length and shape decide whether the machine can reach the joint at all, and electrode material decides how often caps are changed on coated steel. Ask for the arm drawing with the quotation, laid over your part. A machine that cannot reach the joint is not cheaper; it is the wrong machine.

What Is Behind the Panel

This is where most of the real difference sits, and it is invisible in a photograph of a painted cabinet. Three items are worth naming explicitly in the enquiry, because a supplier who is cutting cost will cut exactly these.

The first is the air preparation unit: inlet valve, filter, regulator with a gauge, and a lubricator if the valves need one. A machine without it will run, and will run worse every month as the water trap fills. If one quotation includes it and the other assumes your plant already has dry regulated air at the machine, the difference is not decoration.

The second is the cooling circuit: whether a water manifold with individual valves for transformer, thyristor and electrodes is included, whether there is a flow switch that stops the machine when water stops, and whether a chiller is in the price or in your scope. We have seen an installation stand still for a week because both sides assumed the other was supplying the chiller.

The third is the secondary circuit: the cross-section of the busbar between transformer and arm, whether the joints are bolted or welded, and the length of the arms. Two machines with the same transformer and different secondary lengths are not the same machine at the electrodes.

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The air preparation unit on the same type of machine: inlet valve, filter, regulator with gauge and lubricator. In one quotation this is a line item; in another it is assumed to exist in the buyer's plant.

What Is Not On the Machine At All

A quotation is a price for a delivery, not a price for a machine. The lines that decide whether the project goes well are usually the ones at the bottom, and they are easy to leave vague on both sides.

Installation and commissioning: how many days are included, who pays for the engineer's travel and visa, and what happens if the site is not ready when he arrives. Training: how many people, how many days, in what language, and whether it is at the machine or in a classroom. Spares: what is in the box that arrives with the machine, and what the supplier keeps on the shelf for you afterwards.

Then the commercial frame: warranty on parts only or parts and labour, Incoterms and who clears customs, packing specification, and which language the manual and the electrical drawings are in. A manual in a language your maintenance team cannot read turns a cheap machine into an expensive one at the first fault.

Payment terms and lead time belong in the same table, because they are the part of the quotation that the production team is judged on. A deposit percentage, a balance trigger tied to a shipping document, and a lead time counted in weeks from deposit are three separate promises, and usually only one of them is written down. A supplier who will not put a date in the quotation has not committed to one.

Put Both Quotations In One Table

The practical method is to stop reading the two documents and build a third one: a table with your questions down the left and the two suppliers across the top. Anything a supplier cannot answer in writing goes in as a question, not as an assumption.

Question	The cheap answer	The answer that costs money later
Duty cycle at rated kVA?	Not stated, or "standard"	Below your shift pattern, discovered in summer
AC or inverter?	Whichever the price allows	AC bought at inverter expectations
Controller brand and spares?	In-house board, no model number	No replacement available in year three
Air preparation included?	Assumed to exist on site	Water in the valves within a season
Chiller in scope?	Not mentioned	Installation stops while it is sourced
Commissioning days?	"Assistance available"	Invoiced daily, at the worst moment
Manual and drawings language?	One language, not yours	Maintenance guessing at the first fault
Warranty covers?	Parts only	Labour and downtime on your account

When the table is finished, the price gap usually explains itself. Sometimes it does not, and that is the useful case: it means one supplier has priced something you did not ask for, or has left out something you will pay for twice.

Three Answers That Should Send You Back

Some replies are not answers. When a supplier cannot state the duty cycle at rated kVA, cannot name the controller and its spare part number, or cannot put the commissioning days in writing, the quotation is not comparable to one that can. Ask again rather than guessing, because the guess will be resolved later by the machine.

Requirements vary by destination market. Always confirm against the current edition of the applicable standard and with your certification body.

PDKJ continues to provide customized laser welding and resistance welding solutions based on different materials, workpiece structures, welding requirements, and production applications.

Two Quotations, One Machine: How To Compare Them Line By Line