Direct answer: Fume control follows the part before the process. An enclosed part blocks the way out, so the extraction point has to follow the opening the machine works through, and a fixed wall hood stops working once the unit repositions. The same process in an open bay vents straight up, which makes overhead draw height the question. Arc shielding is not the machine footprint: portable screens go where people approach from.
Who this is for: Written for fabrication engineers and EHS coordinators specifying extraction, screening and layout for robotic welding stations.
Scope: This EVST guide covers what to verify about fume path, arc shielding and heat accumulation across three different station conditions: a part that encloses its own fume, an open bay, and multi-pass work. It does not quote fume concentrations, air volumes, exposure limits or interpass temperatures; those come from measurement and from your welding procedure.
Three station conditions, one process
The reference footage puts three separate welding stations side by side. They are not one line and not one workpiece; they are shown together because the same class of process behaves completely differently depending on where it happens.
In the first, two mobile welding units work opposite sides of a large three-sided steel enclosure. In the second, a robot welds a bent plate on an open station with portable screens behind it. In the third, a close-up shows multi-pass welding laying one bead over another.
Put together they make the point that a fume and shielding specification cannot be written from the welding parameters. The parameters are similar in all three; the conditions are not.
What welding fume arc light and heat control depends on first
An enclosed part blocks the way out. Fume produced inside a three-sided box has nowhere to go, so it builds up rather than dispersing, and natural convection does not clear it at the rate the process produces it.
That makes the position of the extraction point the deciding variable, not the extraction capacity alone. In the footage a unit parks at the opening of the enclosure and welds inward: the fume has one route out, and the capture point has to sit on that route.
A hood fixed to a wall solves this once. As soon as the unit repositions – and a mobile unit repositions constantly – the relationship between the working face and the capture point changes, and the capture that worked at the first position no longer applies.
According to ISO 21904-1:2020, equipment for the capture and separation of welding fume is specified with its intended capture position and working conditions stated, which is exactly the part of the specification a moving station makes non-trivial.
An open bay is a different problem, not an easier one
Move the same process to an open station and the fume rises straight up. What has to be managed is no longer how to get fume out of a cavity but the height and position of overhead draw.
That height is bounded from both sides. Too high and the capture velocity at the arc falls away; too low and the hood interferes with the robot’s working envelope or with loading the part.
The order matters in practice. Set the hood position from the largest workpiece the station has to take, then check the robot’s reach and posture against it. Doing it the other way round tends to produce a layout where the hood sits exactly where the arm needs to be.
The sequence EVST works in is the same each time: establish the fume path from the part, then the capture position, then the shielding, and only then the layout.
| Station condition | Where fume goes | What to settle first |
|---|---|---|
| Part encloses the arc (box, tank, hopper) | Trapped; leaves only through the opening | Capture point on the opening, and how it follows the machine |
| Open bay, fixed station | Rises above the arc | Overhead draw height against the largest part and the robot envelope |
| Open bay, mobile unit | Rises, but the source moves | Whether capture and screening travel with the unit |
| Multi-pass on thick section | Rises, and heat accumulates with it | Interpass temperature and dwell alongside extraction |
Arc shielding follows people, not the machine outline
In the open-bay footage the shielding is a few portable welding screens standing behind the station. Their position is a decision about people, not about the equipment: they belong on the side from which someone actually walks in.
The same station placed mid-floor and placed against a wall needs different screening. Mid-floor, a person can approach from three sides; against a wall, from one. This is settled at layout time rather than added afterwards.
A mobile unit changes the problem again. Fixed screening protects a fixed station; when the equipment drives to the work, the screening has to travel with it or be re-established at each position.
According to ISO 25980:2014, transparent welding curtains and screens are specified by their protective properties for the process and viewing conditions they are used in, so the selection is tied to the arc and the sightlines rather than being generic.
Multi-pass stacks heat as well as fume
The close-up segment shows multi-pass welding: bead laid over bead, with fume and spatter visible between passes. What the sequence adds is accumulated heat, because each pass starts on material the previous pass already warmed.
That makes extraction and thermal management the same design question rather than two. Extraction removes heat along with fume, so an aggressive setting can pull interpass temperature below the range the procedure calls for, while an insufficient one leaves both in the cell.
Interpass temperature and dwell between passes are specified in the welding procedure for the material and the joint, and they are checked by measurement on the part rather than inferred from the appearance of the weld.
What belongs to measurement, and safety around the station
Fume concentration, air volume, capture velocity and interpass temperature are measured values. None of them can be read from footage of welding, and none of them are quoted here.
According to ISO 10218-2:2025, the safeguarded space of an integrated station follows from the movement of the whole system. For a mobile welding unit that includes its travel path and its trailing services, not only the arm.
According to ISO 12100:2010, arc radiation, fume, hot surfaces and the cable route belong to the same risk assessment as the robot motion, and access for consumable changes belongs there too.
Every EVST application review opens from the same project inputs – part geometry, bay conditions and existing ventilation – so selection rests on evidence and acceptance is agreed against your own station rather than a datasheet.
Frequently asked questions
Why does an enclosed part change the extraction design so much?
Because the fume cannot disperse. Inside a box or tank the only route out is the opening, so capture has to sit on that route, and a hood fixed elsewhere in the bay captures very little of it. If the welding unit moves during the job, the capture point has to move with it.
Is a bigger extraction fan the answer to a difficult part?
Not on its own. Capture velocity at the arc depends on the distance and geometry between the source and the capture point far more than on total flow, which is why the position of the capture point is settled before the capacity.
How should welding screens be positioned?
By where people actually approach the station. A station in the middle of a bay can be approached from three sides and one against a wall from one, so they need different screening even with the same equipment. For a mobile unit the shielding has to travel or be re-established at each position.
What should we send to get a useful answer?
Part geometry including whether the part encloses the arc, the largest size the station has to take, bay height and existing ventilation, and whether the equipment is fixed or driven to the work.
Project inputs for an application review
To have this checked against your own station rather than a generic cell, send:
- part geometry, and whether the part encloses the arc
- largest workpiece the station has to take
- bay height and the ventilation already installed
- whether the welding equipment is fixed or driven to the part
Send the part geometry and the bay conditions and the extraction and shielding layout can be worked through against them. Related reading: automatic welding system solutions, large workpiece robotic welding.