Measure to optimise.

01 Opportunity → stable, capable spot weld
02 Simulation → predict nugget and energy
03 WeldParameter → new DRAFT version
04 Approval → UNDER_REVIEW → APPROVED
05 Measurement → confirm Cpl ≥ 1.33

Getting started

How to use this wiki

The wiki is organised in three layers: the technical fundamentals, quality and defects, and use of the platform. Each technical concept points to the place in Weldia where it applies.

Structure

Section	What for	Key pages
Fundamentals	Understand why a spot weld turns out well or badly	Principle, Cycle, Eight factors
Quality and defects	Diagnose and prevent problems	Process window, Common problems, Root cause
Weldia in practice	Use the platform day to day	Sessions, SPC Cockpit, Opportunities
Reference	Look up standards, terms and sources	ISO standards, Glossary, Frequently asked questions

Conventions

In Weldia

Blue boxes link the concept to the screen, field or rule of the platform.

Caution

Amber boxes flag common mistakes or quality risks.

Good practice

Green boxes summarise the recommendation to apply.

Platform field names, statuses and rules appear in monospace: NEEDS_REVIEW, CPL_BELOW_1_33.
Technical terms give common synonyms in brackets on first occurrence: expulsion (splash).
The figures are illustrative: they show qualitative trends, not data from a real line.

Wiki shortcuts

Key	Action
/	Go to search
↑ ↓ Enter	Navigate the search results
Esc	Close the search or the menu

Content source

The full technical content is in the file docs/wiki/conhecimento-soldadura-resistencia.en.md, and the figures in docs/wiki/images/en/. To update a figure, edit docs/wiki/tools/gerar_imagens.py and regenerate them.

Fundamentals

Principle of resistance welding

No arc and no filler material: a high current passes through the sheets clamped between two electrodes, and the electrical resistance locally melts the metal at the interface.

Cross-section of a spot weld: copper electrodes, two sheets, molten nugget at the interface, force and current — **Fig. 1**The electrodes apply the force F and carry the current I; the nugget forms at the interface between the sheets.

Joule's law

Q = I² · R · theat [J] = current² [A²] × resistance [Ω] × time [s]

Symbol	Meaning	Order of magnitude in car bodies
`I`	Welding current (RMS)	6 – 14 kA in steel; > 20 kA in aluminium
`R`	Total resistance along the path	tens to hundreds of µΩ
`t`	Current flow time	100 – 600 ms

Current counts squared. +10 % current gives about +21 % heat. It is the most sensitive parameter.
The heat has to originate at the interface. Design and parameters exist to concentrate the heat where the nugget is wanted.
Heat is also lost. The electrodes are water-cooled; below a minimum current, more time does not form a weld.

The role of force

Force is applied before the current, to ensure contact; during it, to contain the molten metal; and after it, to forge the nugget as it solidifies.

Resistances in series

Contact resistances (R2, R4, R6): dominate the first milliseconds and decrease with pressure and temperature.
Material resistance (R3, R5): increases with temperature.
Dynamic resistance: the R(t) curve that results from the two. It is the signal most used in real-time monitoring.

In Weldia

The result that is measured is the nugget diameter, recorded in each NuggetMeasurement and compared with the minimum diameter of the WeldSpot.

Fundamentals

Process families

Resistance welding processes differ in how they concentrate the heat: through the electrode, through the part or through an additional element.

Three families: heating through the electrode, through the part and with an additional element — **Fig. 3**Families A, B and C.

Family	How the heat is concentrated	Examples
A, through the electrode	Shape of the electrode tip	Spot (RSW), single-sided, series, indirect, seam, parallel gap
B, through the part	Projections, embossments or the natural shape of the parts	Projection, nuts and studs, cross wire, butt, battery terminals
C, with an element	Element between the parts	Element welding, brazing, weld bonding, soldering

Spot welding

It is the dominant process in car body assembly (body-in-white): a typical car has between 3,000 and 6,000 spot welds. The shape of the electrode tip defines the contact area and, with it, the size of the nugget.

Projection

The projection must concentrate the current without collapsing too quickly. As a rule, it goes on the part that has more difficulty heating up: the thicker one, if the materials are the same, or the one with lower resistivity, if they differ. Fast electrode follow-up is critical, because the projection collapses within milliseconds.

In Weldia

The platform focuses on family A, spot welding with robotic guns.

Fundamentals

Weld cycle and weld schedule

Each spot weld is made according to a weld schedule with well-defined phases. In Weldia, that schedule is stored and versioned in WeldParameter.

Fig. 4Two-pulse weld schedule: the force is held from squeeze to the end of hold.

Phases

Phase	Field	Function	Too short	Too long
Squeeze	`squeeze`	Close and stabilise the force	Initial expulsion	Lost cycle time
Pulse 1	`weld1`	Preheating, coating, gaps	—	Surface overheating
Cool 1	`cool1`	Pause between pulses	—	—
Pulse 2	`weld2`	Nugget growth	Cold weld	Expulsion, wear, indentation
Cool 2	`cool2`	Optional pause	—	—
Hold	`hold`	Solidify under force	Porosity, cracks, LME	Brittle nugget in hardenable steels
Force	`force`	Contact and forging	Expulsion	Less heat, indentation
Stepper	`stepper`	Compensate for electrode wear	Nugget shrinks	Expulsion at end of life

Units

On AC machines times are often given in mains cycles (1 cycle = 20 ms at 50 Hz). On MFDC they are given in ms. Check the unit before comparing weld schedules.

Current types

AC, three-phase DC, MFDC and capacitor discharge waveforms — **Fig. 5**Typical waveforms.

Type	Characteristics	Use
Single-phase AC	50/60 Hz, conduction angle	Older installations
Three-phase DC	Reduced ripple	Large guns, aluminium
MFDC	~1 kHz, fast response, compact transformer	Standard in automotive robotics
Capacitor discharge	Short, intense peak	Micro-welding, conductors

Fundamentals

The eight influencing factors

More than a hundred variables have been identified in the literature. In practice, they group into eight factors, and diagnosis works through them.

#	Factor	Main effect	Typical sign
1	Current	Heat ∝ I²; the nugget grows quickly up to expulsion	Expulsion (high) · cold weld (low)
2	Time	Heat ∝ t; below the minimum current it is not enough	Electrode sticking with long times
3	Force	Defines the contact: too little → expulsion; too much → less heat	Indentation, initial expulsion
4	Contact resistance	Decides where the heat originates in the first cycles	Batch-to-batch variation, oil, oxides
5	Material	Resistivity generates heat; conductivity dissipates it	Change of supplier
6	Coatings	Zinc, AlSi: contact and electrode contamination	Accelerated wear
7	Geometry	Tip, thicknesses, no. of sheets, edge, pitch	Off-centre nugget, shunting
8	Machine	Current rise, inductive losses, stiffness, follow-up	Differences between "identical" guns

In Weldia

Factors 1–3 → WeldParameter. Factors 5–7 → WeldSpot (sheet stack, thicknesses, minimum diameter) and GunConfiguration (electrode, tip dressing, maximum force). Factor 8 → robot and gun in the hierarchy.

Contact resistance in detail

All surfaces are rough at the microscopic scale. With more force, the asperities flatten, the real contact area increases and the resistance drops. With temperature, contaminants (water, oil) burn off and the metal softens, and the resistance also drops. Although it only dominates in the first cycles, it defines the initial heat distribution and, with it, where the nugget starts.

Machine characteristics

Electrical: current rise time and inductive losses, which grow with the gun's throat opening and the steel inside the window.
Mechanical: arm stiffness and electrode follow-up speed. Slow follow-up causes expulsion, especially in projection welding.

Fundamentals

Materials and weldability

Weldability is the ease with which a combination of materials and thicknesses produces good spot welds within a window wide enough for stable production.

General rule: metals with high resistivity and low thermal conductivity weld better.

Material	Behaviour	Precautions
Low-carbon steel	Very good weldability	Reference
AHSS (DP, TRIP, MS, PHS)	Heats more; narrower window; expulsion at lower currents	Higher force, multi-pulse, suitable `hold`
Galvanised (GI, GA)	The zinc melts and alloys with the copper	More force and current; dress more often; LME risk
AlSi (hot stamping)	The coating becomes more resistive in the furnace	Adjust current; watch the projections
Aluminium	Low resistivity, high conductivity, oxide	Very high current, short time, cooling, cleaning
Copper	Generates little heat and dissipates it quickly	Projection, brazing, tungsten electrodes

Heat balance

Comparison between two identical sheets and a three-sheet combination — **Fig. 6**With different thicknesses and resistivities, the heat shifts towards the thick, resistive sheets.

The thicker sheet and the more resistive sheet heat up more.
Thickness ratio (total ÷ thinnest): as a rule of thumb, up to 3:1 to 4:1.
Three sheets with a thin, soft outer sheet is the most critical case in the car body.
Solutions: electrodes of different diameters, pre-pulse, multi-pulse, ramped current, or revising the design.

Minimum diameter

d_min ≈ 4·√t d_nominal ≈ 5·√tt = thickness of the thinnest sheet [mm]; rule of thumb used in manufacturer standards and in ISO 18278-2

t (mm)	0.7	1.0	1.2	1.5	2.0
4·√t (mm)	3.3	4.0	4.4	4.9	5.7
5·√t (mm)	4.2	5.0	5.5	6.1	7.1

In Weldia

The minimum diameter is an attribute of each WeldSpot and is the LSL used throughout SPC. When the material or the supplier changes, review weldability before assuming the old weld schedule.

Fundamentals

Electrodes and tip dressing

The electrode is the component that changes most during production. With wear, the face widens, the current density drops and the nugget shrinks.

New and worn tip; stepped current and tip dressing over the electrode life — **Fig. 7**The stepper raises the current in steps; tip dressing periodically restores the geometry.

Mechanisms

Geometric: the face widens (mushrooming), forms craters (pitting) or loses material. Typical with galvanised steel.
Metallurgical: the copper alloys with zinc or aluminium, recrystallises and softens. With aluminium this happens very quickly.

Electrode life ends when the minimum diameter can no longer be reached. In the lobe, wear shifts the window towards higher currents.

Compensation

Method	How it works	In Weldia
Stepped current	Raises the current in steps every N spot welds	`stepper` in the `WeldParameter`
Tip dressing	Restores the geometry and cleans the face every N spot welds	`GunMillingProgram` 241 / 242 / 250
Adaptive control	Adjusts the current from the dynamic resistance	Future device integration

Good practice

A sawtooth measurement series (drops and recovers) synchronised with tip dressing is normal. A continuous decline with no recovery indicates failed tip dressing, insufficient stepper or poor cooling.

Standards

Cap geometry is in ISO 5821 (for example, F shapes with 16 and 20 mm faces, such as the references FF16A00 and FF20A00 in GunConfiguration). Electrode materials are in ISO 5182 (CuCr1Zr, CuCo2Be, …).

Quality and defects

Process window

The nugget is hidden between the sheets and cannot be inspected visually. Quality is ensured by working within a known parameter window.

Growth curve

Only the current varies, with force and time fixed. It is useful when force and time are already defined.

Nugget diameter as a function of current, with the window between the minimum current and expulsion — **Fig. 8**The current window runs from the minimum diameter up to expulsion.

Weldability lobe

It maps two variables, current × time or current × force, and gives a more complete view of the process (ISO 14327).

How to choose the working point

Stay inside the lobe. Outside it there are cold welds or expulsions.
Prefer the expulsion side, with margin. Wear and other disturbances reduce the nugget over time. Starting near the upper limit gives more headroom to the lower one.
Keep a margin to expulsion (typically 0.5 – 1 kA in steel), and more if there are gaps or misalignments.
Higher force widens the lobe, but shortens electrode life and increases indentation.
Stronger steels have the expulsion limit at lower currents.

In Weldia

SPC shows when a weld spot leaves the window on the low side (mean falling, Cpl dropping). Opportunities show weld spots with margin to reduce time or energy without leaving it.

Quality and defects

Defects and failures

Defects fall into three classes, and the class already points to the likely cause.

Three classes of defects: material, nugget and external — **Fig. 10**Classification of defects and failures.

Class	Dominant cause	Where to act
Material defects	Materials and coatings at critical temperature and stress	Choice of materials; `hold` and multi-pulse
Nugget failures	Parameter setting	Weld schedule optimisation
External failures	Excess heat or force	Reduce energy, adjust force and fixturing

Acceptance criterion

In the peel test or the chisel test (ISO 10447), a good spot weld fails with full button pull-out (full plug). Interfacial fracture generally indicates an insufficient weld, although in ultra-high-strength steels it should be assessed case by case.

Recording a defect in Weldia

Measure the diameter of the pulled-out button and enter it in the session task.
If it is below the minimum, the platform asks for an explicit decision: keep MEASURED or change to NEEDS_REVIEW.
To flag for review in any case, use the R key.
Saving creates a new revision and queues the SPC recalculation for the weld spot.

Quality and defects

Common problems in production

Cold weld, expulsion, gaps and misalignment: the most common causes, how to recognise them and how to reduce them.

Cold weld / stuck weld

No nugget of sufficient size forms, or it forms at only one of the interfaces. It is one of the most serious problems in multi-sheet stacks.

Cause	Example	Action
Poor contact	Electrode poorly seated, gap	Ensure contact, close the gap during squeeze
Poor parameters	Low current, short time, large face	Optimise current/time/force; dress the tips
Heat balance	High ratio, different resistivities	Different electrodes, pre-pulse, multi-pulse

Expulsion / spatter

Molten metal is ejected from the nugget. It causes defects, cosmetic problems, risks to operators, dirt on the line and wasted energy.

Parameters: high current, long time, low force.
Small contact: unevenly worn face, misaligned electrodes.
Surface: dirt, oxides, anything that increases the surface resistance.
Gap between sheets.

Signal

Frequent expulsions indicate a process too close to the upper limit of the window. Lowering the current blindly, however, pushes the process towards the lower limit: check the electrode and the gap first.

Gap between sheets

Unclosed gap with expulsion versus gap closed before the current — **Fig. 11**The gap has to close before the current flows.

It comes from stamping or fixturing tolerances.
It shifts the expulsion limit to lower currents and narrows the lobe.
Robust strategy: parameters in the zone common to the lobes of the expected gaps (0, 0.2, 0.5 mm…).
Direct solutions: longer squeeze, more squeeze force, low-current pre-pulse.

Electrode misalignment

It results from assembly errors or from the elastic deflection of the gun: the electrodes end up tilted or with offset centres. The nugget becomes irregular and there are expulsions. Checking the gun's squareness is part of preventive maintenance.

Hot-stamped parts

22MnB5 parts with AlSi arrive with a transformed coating of higher resistance and with very high hardness. Changes in the furnace later show up as variations in welding. On projection nuts, the difference in hardness can make the projection collapse before the weld forms.

Shunting effect

Part of the current is diverted through nearby spot welds that have already been made. The new spot weld receives less current and turns out smaller.

Top view with an existing spot weld, a new spot weld and the shunt current between them — **Fig. 12**The shunt current is greatest at the start of the pulse.

Factor	Effect on shunting
Smaller pitch	↑ strong, the most influential factor
More spot welds already made	↑ cumulative along a row
Thicker sheets	↑ less resistive lateral path
Mild steel	↑ compared with high-strength steels
Start of the pulse	↑ the new contact is still very resistive

In a row of spot welds, the diameter reduction can accumulate to 20–30 % at the last spot weld, and the nuggets lean towards their neighbours. In a three-sheet combination, the interface with mild steel is the most affected.

Mitigation

Respect the minimum pitch, order the welding sequence and compensate the current of the spot welds in sequence.

In Weldia

Weld spots in the same cell with systematically smaller diameters in a dense zone (Drilldown and Equipment tabs) are shunting candidates. Compare with the sequenceNo and the X/Y/Z coordinates.

Quality and defects

Liquid metal embrittlement (LME)

Cracking of zinc-coated high-strength steels, when liquid zinc penetrates the grain boundaries under stress.

Cross-section with the LME-sensitive zones at the shoulder of the indentation — **Fig. 13**The shoulder of the indentation cools poorly and is left in tension.

Three simultaneous conditions

Temperature in the steel's low-ductility range.
Local tensile stress, which increases with the heat input and with abrupt cooling.
Liquid zinc in contact with the steel.

How to reduce it

Avoid excess heat, especially near expulsion.
Multi-pulse to reduce stress peaks, or a pre-pulse to push the zinc away.
Electrodes without sharp edges in the contact zone.
Sufficient hold for the zinc to solidify before the electrodes open.

Caution

Automotive industry studies (WorldAutoSteel) indicate that relevant LME cracks appear mainly when there are deviations from the correct parameter and assembly conditions. A process well centred in the window is the first line of defence.

Quality and defects

Root cause analysis

All root causes fit into three categories. Investigate in this order: a design problem cannot be solved with parameters.

Design, parameter setting and dynamics — **Fig. 14**Three root cause categories.

Category	Key question	Typical SPC pattern
1 · Design	Does the heat concentrate at the right interface?	Low Cpl from the start, on every gun with that combination
2 · Parameter setting	Is the working point centred in the window?	Stable mean but close to the LSL; `CPL_BELOW_1_33`
3 · Dynamics	Did something change during production?	`DOWNWARD_TREND_6`, `SAME_SIDE_BELOW_MEAN_8`, `BELOW_LCL`

Checklist when a weld spot goes into alert

Confirm the measurement: method, operator, previous revision.
Isolated or grouped? See the Equipment tab: weld spot, gun, robot, cell or tag.
Grouped by gun: electrode, tip dressing, alignment, cooling.
Grouped by product/tag: material batch, stamping, gaps.
Isolated but persistent: parameter setting of that weld spot (window, shunting, edge).
Record and act: if you change parameters, create a DRAFT version for approval and measure to validate.

Quick diagnosis table

Symptom	Likely causes	First check
Diameter falling gradually	Electrode wear, insufficient stepper	Spot weld counter and last tip dressing
Sudden drop on one gun	Failed tip dressing, cap changed, cooling	Face condition and water flow
Drop across a whole product	Material batch, coating, stamping	Batch certificate, supplier
High scatter, good mean	Gaps, misalignment, unstable contact	Fixturing and gun squareness
Smaller spot welds in a dense zone	Shunting	Pitch and sequence
Expulsions and irregular diameter	High current, low force, gap	Approved vs. executed weld schedule

Quality and defects

Quality beyond diameter

A spot weld can meet the minimum diameter and still be bad: with expulsion, excessive indentation, insufficient fusion or degraded metallurgy.

Radar chart with six quality factors for two weld schedules — **Fig. 15**Two weld schedules with a similar nugget and different overall quality.

Factor	What it measures	Why it matters
Expulsion	Stability	Defects, safety, energy
Diameter	Size of the fused zone	Strength
Penetration	Fusion into each sheet	Critical in 3-sheet stacks
Indentation	Surface deformation	Appearance, fatigue
LME risk	Susceptibility to cracking	Durability in AHSS
HAZ softening	Drop in hardness	Load-bearing capacity

Hold and hardness

Short hold → slow cooling → lower hardness → lower strength.
Long hold → fast cooling → higher hardness → more brittle fracture.
Optimal hold → balance between strength and ductility.

Destructive tests

Test	Standard	Assesses
Peel / chisel	ISO 10447	Button diameter and fracture mode
Tensile shear	ISO 14273	Shear strength
Cross tension	ISO 14272	Normal strength
Mechanised peel	ISO 14270	Force-displacement curve
Torsion	ISO 17653	Torsional strength

In Weldia

Today the diameter is measured. The model already provides for indentationDepthMm, confidenceScore and the methods CAMERA, LASER_SCANNER, ULTRASOUND and AI_ASSISTED, for a multi-factor assessment.

Quality and defects

Energy and efficiency

Optimising is not only about getting acceptable spot welds: it is quality, stability and zero wasted energy, all at the same time.

E ≈ ∫ I(t)² · R(t) dtenergy of one spot weld [J]

Lobe with energy contour lines and two weld schedules with the same nugget — **Fig. 16**Weld schedule B produces the same nugget with less energy.

Two rules

Avoiding expulsion also saves energy. The energy used to melt the expelled metal is lost, and the spot weld turns out worse.
Within the lobe there are more economical weld schedules. Shorter times, with slightly higher current, lose less heat to the cooled electrodes.

Scale matters

Quantity	Illustrative value
Energy saved per spot weld	0.5 kJ
Spot welds per vehicle	4,000
Vehicles per year	300,000
Annual saving	6 × 10¹¹ J ≈ 167 MWh

A shorter weld time also reduces the cell's cycle time.

See: Cycle time and energy opportunities.

Weldia in practice

Overview and roles

Weldia brings together in a single workspace weld spot engineering, shop floor measurement, statistical control, optimisation and, soon, simulation and AI recommendation.

Modules

Module	What it does	Status
Weld spot engineering	Registration, versioning, CSV	available
Sequential measurement	Nugget diameter weld spot by weld spot	available
SPC	Charts, capability, alerts, risk	available
Opportunities	Margin to reduce cycle time and energy	heuristic
Parameters and approval	Versioned weld schedules	read-only
Simulation	Predict the nugget from the parameters	demo
AI recommendation	Suggest parameters	planned

Roles

Role	Main use
`TECHNICIAN`	Runs measurement sessions (fast, keyboard-driven flow)
`QUALITY_ENGINEER`	Follows SPC, alerts, weld spots below the minimum and capability
`PROCESS_ENGINEER`	Manages weld spots, parameters and guns; analyses opportunities
`ADMIN`	Manages the organisation and the users
`VIEWER`	Consultation (management, executives)

Access requires login. Actions you cannot perform are hidden in the interface, and the server always validates the permission. All data is isolated per organisation.

Hierarchy

Plant, line, cell, robot, gun and electrode; assembly and spot weld — **Fig. 17**Physical and logical hierarchy.

Physical hierarchy (Project Explorer): plant → line → cell → robot → gun.
Tags (Tag Explorer): cross-cutting groupings by product, zone, inspection route, operation or campaign.

Weldia in practice

The application

One route per flow, with a sidebar, a top bar with the scope, a command palette (Ctrl + K) and an inspector docked on the right.

Sections

Route	What for
Home (`/`)	Starting point, by profile
Measure (`/measure`)	Rounds; a round opens in focus mode at `/measure/<code>`
Quality (`/quality`)	Alert inbox, weld spots, overview; SPC detail of each weld spot
Optimise (`/optimize`)	Cycle time and energy reduction opportunities
Changes (`/changes`)	Parameter versions in review, validation and history
Spots (`/spots`)	Catalogue, CSV import, orphans
Settings (`/settings`)	Appearance, account and administration
Simulation (`/simulation`)	Result of the latest simulation

The scope (machines and tags) is chosen at the top and kept in the address, as are the filters and the inspector: a link reproduces the screen. The inspector shows the weld spot detail, the parameter set and the gun configuration. Old /workspace links redirect to the equivalent route.

Weldia in practice

Measurement sessions

A flow designed for the technician: fast, keyboard-driven and never overwriting history.

Fig. 18Flow of a session.

Step by step

Select the scope (machines and tags) in the top bar and see the preview with the number of weld spots.
New round (in /measure) creates the session and one task per weld spot, in order. It can include several assemblies.
Measure weld spot by weld spot. The field starts empty; the last previous measurement appears separately, so as not to influence the reading.
Choose the source: manual, test device or future Weldia device.
Below the minimum, decide explicitly: keep MEASURED or change to NEEDS_REVIEW.
Each save creates a new revision of the measurement and queues the SPC recalculation for the weld spot.
Close the session at the end. A closed session opens read-only; it can be reopened (resumes at the first pending task), archived and restored.

Keyboard shortcuts

Key	Action
Enter	Save and advance
Ctrl + S	Save
← →	Previous / next task
Esc	Leave the field / navigate
R	Flag for review
Skip button	Skip the task (no shortcut, on purpose)

Good practice

Always measure in the proposed order and do not skip tasks without a reason. The order helps detect sequence effects, such as shunting, and skipped tasks leave gaps in the control charts.

Caution

Correcting a measurement does not delete the previous one: it creates a new revision. SPC uses the most recent revision of each task.

Weldia in practice

Weld spot management

In /spots you create, edit, import (/spots/import) and export weld spots, always with revision history.

Create and edit

Each weld spot has a hierarchy, gun, sheet stack, X/Y/Z coordinates, minimum diameter and tags. Each change generates a WeldSpotRevision with the reason, which is mandatory.

Import CSV

Download the CSV template to make sure the columns are right.
Import the file. Operations are applied row by row, with staging.
Rows without a match are left as orphans.
In the orphan queue, link each row to an existing weld spot or ignore it.

Export

CSV export returns the filtered weld spots. The revision history of each weld spot can be consulted in the weld spot detail.

Good practice

Change the minimum diameter only with technical justification (thickness, standard, customer). It is the SPC LSL: changing it changes the capability of the weld spot's entire history.

Weldia in practice

Parameters and guns

The weld schedule of each weld spot and the configuration of each gun are versioned, so that it is always known with which settings each measurement was made.

WeldParameter

Complete weld schedule per weld spot: squeeze, weld1/cool1, weld2/cool2, hold, force and stepper. See Weld cycle.

Approval statuses

Status	Meaning
DRAFT	Proposal being edited
UNDER_REVIEW	Under review
APPROVED	Approved for production
REJECTED	Rejected
ARCHIVED	Replaced by a more recent version

GunConfiguration

Fluids: water (electrode cooling) and air.
Electrode: cap type (e.g. FF16A00, FF20A00). See Electrodes and tip dressing.
Tip dressing: programs 241, 242 and 250, with cutter and frequency.
Maximum force of the gun.

Current status

Parameters are currently read-only. Editing and the approval flow are the next step of the improvement cycle.

Weldia in practice

SPC Cockpit

The nugget diameter only has a lower limit. That is why Weldia uses individual value charts and lower one-sided capability.

Tabs

Tab	Use
Summary	KPIs and automatic insights for management
SPC	List of weld spots with status, Cpl, risk and alerts; chart for each weld spot
Opportunities	Weld spots with margin to reduce cycle time and energy
Equipment	KPIs by line, cell, robot, gun and tag
Drilldown	Detail of a weld spot or group

You can filter by line, cell, robot, gun, tag, severity and statuses, and sort by priority, Cpl, risk, rejection or date. Bulk recalculation redoes the SPC for an entire scope.

Official series

The latest revision of each MEASURED task is included, ordered by measurement date.
The calculations use the last 50 samples of each weld spot.
A measurement can be excluded with a reason (for example, a proven reading error). It stays visible in Drilldown but is left out of the calculations, and the exclusion is audited.
Any change (new measurement, revision, exclusion) queues the recalculation for the weld spot.

Caution

Exclude only measurements that are proven to be wrong. Excluding "inconvenient" low values hides the problem and inflates the Cpl.

I-MR chart

Individual values chart with CL, UCL, LCL and LSL, and moving range chart — **Fig. 19**A downward trend ends below the LCL, before reaching the LSL.

Element	Formula
Centre line	`CL = mean`
Moving range	`MRᵢ = \|xᵢ − xᵢ₋₁\|`, `MR̄ = mean(MR)`
Short-term σ	`σ_within = MR̄ / 1.128`
Control limits	`CL ± 2.66·MR̄` (≈ ±3σ_within)
Overall σ	sample standard deviation (n − 1)

Control limits ≠ specification

The UCL/LCL say what the process does; the LSL says what the customer requires. A weld spot can be within the control limits and below the LSL.

Capability

Two distributions: one capable and one not capable relative to the LSL — **Fig. 20**The area below the LSL is the predicted rejection.

Cpl = (mean − LSL) / (3 · σ_within)
Ppl = (mean − LSL) / (3 · σ_overall)
predicted rejection = Φ((LSL − mean) / σ_overall)

Cpl	Status	Reading
≥ 1.33 and stable	GOOD	Capable, with margin
1.0 – 1.33	MARGINAL	Capable, without margin
< 1.0	POOR	Not capable
< 10 samples	UNKNOWN	Insufficient data

The process status is INSUFFICIENT_DATA (fewer than 10 samples), STABLE or UNSTABLE. See Alert rules and risk score.

Weldia in practice

Alert rules and risk score

The rules follow the classic Western Electric and Nelson logic, adapted to the lower side, which is the only one that represents a quality risk.

Rules

Code	Rule	Severity	Likely cause
`BELOW_LSL`	Measurement below the minimum	CRITICAL	Real defect
`PREDICTED_LOWER_REJECT_CRITICAL`	Predicted rejection ≥ 3 %	CRITICAL	Poorly centred or scattered
`PREDICTED_LOWER_REJECT_WARNING`	Predicted rejection ≥ 1 %	WARNING	Same, at an early stage
`CPL_BELOW_1_0`	Cpl < 1.0	CRITICAL	Parameter setting or design
`CPL_BELOW_1_33`	Cpl < 1.33	WARNING	No margin
`DOWNWARD_TREND_6`	6 consecutive decreases	WARNING	Wear, drift
`SAME_SIDE_BELOW_MEAN_8`	8 in a row below the mean	WARNING	Level shift
`LOWER_2_OF_3_2SIGMA`	2 of 3 below −2σ	WARNING	Imminent shift
`BELOW_LCL`	Below the LCL	WARNING	Special cause
`ABOVE_UCL`	Above the UCL	INFO	Change (opportunity or expulsion)

Alerts have an OPEN → RESOLVED life cycle and are synchronised on every recalculation: an alert whose condition no longer holds is resolved automatically.

Risk score

Each weld spot receives a score from 0 to 100 to rank priorities.

Component	Weight
Maximum severity of open alerts	40 %
Cpl shortfall against 1.33	25 %
Predicted rejection (saturated at 5 %)	20 %
Trend (series rules and LCL)	15 %

Good practice

Deal with CRITICAL alerts first, then sort by risk score. For each alert, follow the root cause checklist.

Weldia in practice

Cycle time and energy opportunities

Stable, capable weld spots, with a nugget well above what is needed, can be welded with less time and less energy.

Diameter distribution with the reducible margin above the threshold — **Fig. 21**The reducible margin lies between the safety threshold and the current mean.

How it is calculated

Only stable, capable weld spots are included (Cpl ≥ 1.33).
Safety threshold = LSL + 3σ·1.33 + margin.
Reducible margin = mean − threshold.
Conversion into an estimated reduction in weld time (maximum 15 %) and in energy.
Classification with an opportunity score and a confidence score.

Class	Meaning
READY_FOR_REVIEW	Ready to propose a new weld schedule
WATCH	Promising, but with insufficient data or margin
BLOCKED	Do not touch: unstable, not capable or with alerts

Caution

The estimate uses empirical constants and is not yet validated. An opportunity is a hypothesis: confirm it with a validation measurement before approving the new weld schedule.

Closing the loop

Opportunity, simulation, new parameter, approval, measurement — **Fig. 22**The continuous improvement cycle.

Weldia in practice

Simulation and digital twin

Simulation predicts the nugget before welding. The digital twin links that prediction to real production data.

Numerical simulation

It solves the electrical, thermal, mechanical and metallurgical problems together, usually with the finite element method, which handles large deformations and changing contacts well.

Inputs	Outputs
Geometry and materials of the sheets, coatings and electrodes	Temperature, formation and diameter of the nugget
Force, current and times	Expulsion limit, indentation
Mesh and time step	Stresses, hardness, defect risk

Good practice

Run a mesh convergence study, use a time step below one millisecond in the current phases and always validate with a few physical tests.

Digital twin

Design, optimise, plan, produce, evaluate — **Fig. 23**The digital twin across the life cycle of the spot weld.

Each phase inherits the model from the previous one and adds data: from the generic machine at design time to the real measurements in production. The leap from "reacting to the defect" to "preventing the defect" is made by linking simulation to production data, and that is where SPC and AI come in.

In Weldia, today

A simulation job queues a calculation and shows the predicted nugget, the energy, the cycle time and the risk.
The current calculation is a linear demonstration formula. An adapter for an external simulation engine is planned.
The platform already covers produce and evaluate (measurements, SPC, opportunities).

Reference

ISO standards

The standards most used in resistance welding, grouped by topic. Check the current edition in the ISO catalogue.

Processes

Standard	Topic
ISO 17677-1	Vocabulary: spot, projection and seam welding
ISO 15609-5	Welding procedure specification (WPS)
ISO 14373	Spot welding of low-carbon steels
ISO 18595	Spot welding of aluminium
ISO 14327	Weldability lobe
ISO 18278-1/-2/-3	Weldability
ISO 15613 · ISO 15614-12	Procedure qualification
ISO 14554-1/-2	Quality requirements

Equipment and electrodes

Standard	Topic
ISO 669	Mechanical and electrical requirements for the equipment
ISO 5182	Electrode materials
ISO 5821	Electrode caps
ISO 17657-5	Verification of current measurement

Tests

Standard	Test
ISO 10447	Peel and chisel
ISO 14273	Tensile shear
ISO 14272	Cross tension
ISO 14270	Mechanised peel
ISO 17653	Torsion

Statistics

Standard	Topic
ISO 7870-2	Shewhart control charts
ISO 22514-2	Capability of time-dependent processes

Reference

Glossary

Terms in English, as they appear on the machines, in the standards and in the interface, with the Portuguese equivalent.

English	Português	Definition
Resistance spot welding	Soldadura por pontos	Joining of sheets by localised fusion between two electrodes
Weld nugget	Nugget	Fused and solidified zone at the interface
HAZ	ZTA	Base metal altered by heat, without melting
Electrode / cap	Elétrodo / capa	Copper part that carries the current and applies the force
Welding gun	Pinça	Tool with arms, electrodes and transformer
Tip dressing	Fresagem	Restoring the geometry of the electrode face
Stepper	Corrente escalonada	Programmed increase of the current with wear
Squeeze	Aperto	Closing before the current
Weld pulse	Impulso	Period with current
Cool	Arrefecimento	Pause without current between pulses
Hold	Manutenção	Force held during solidification
Expulsion / splash	Expulsão	Ejected molten metal
Cold / false / stick weld	Ponto frio / falso	Spot weld without sufficient fusion
Indentation	Indentação	Depression left by the electrode
Shunting	Shunt	Current diverted through neighbouring spot welds
Gap / poor fit-up	Folga	Separation between sheets
Liquid metal embrittlement	LME	Cracking caused by liquid zinc
Weldability lobe	Lóbulo	Parameter region with acceptable spot welds
Weld growth curve	Curva de crescimento	Diameter as a function of current
Dynamic resistance	Resistência dinâmica	Evolution of R during the spot weld
Full plug	Arrancamento total	Fracture with the whole button pulled out
Interfacial fracture	Rotura interfacial	Fracture through the nugget interface
Advanced high-strength steel	AHSS	Advanced high-strength steels
Galvanised / galvannealed	GI / GA	Zinc / zinc-iron coatings
Lower specification limit	LSL	Specified minimum diameter
Control limits	LCL / UCL	Statistical control limits
Lower capability index	Cpl / Ppl	Lower one-sided capability
Digital twin	Gémeo digital	Virtual model linked to real data

Reference

Frequently asked questions

Common questions from people starting to use Weldia.

Why does the measurement field start empty?

To avoid anchoring bias: if the previous value were in the field, it would be easier to confirm it than to measure. The last measurement appears separately, only as a reference.

Why is there only a lower limit (LSL)?

A larger nugget is not a defect in itself. The practical upper limit is expulsion, which is a process phenomenon and not a diameter specification. That is why capability is one-sided (Cpl).

How many measurements are needed to see the capability?

At least 10 per weld spot. Below that, the status is INSUFFICIENT_DATA and the capability UNKNOWN. With 20–30 measurements the estimate becomes considerably more stable.

A weld spot is within the control limits but below the minimum. How is that possible?

The control limits describe the natural variation of the process; the LSL is the requirement. A stable but poorly centred process stays within the control limits and still produces spot welds below the minimum. It is a parameter-setting case (see root cause).

I made a mistake in a measurement. Have I lost the history?

No. Each save creates a new revision; the previous one is kept. SPC uses the most recent revision. If the error can no longer be corrected in the session, an engineer can exclude the measurement from SPC, with a reason, in Drilldown.

What should I do with a READY_FOR_REVIEW opportunity?

Treat it as a hypothesis: propose a new weld schedule in DRAFT, submit it for approval and validate it with a measurement session before rolling it out.

The diameter falls and rises in a sawtooth pattern. Is that a problem?

If it coincides with tip dressing, it is the expected behaviour of electrode wear. Be concerned if the recovery stops happening or if the minimum of each tooth falls over time.

Reference

External references

Recommended public bibliography for going deeper into the topics of this wiki.

Resistance welding

Zhang, H.; Senkara, J. Resistance Welding: Fundamentals and Applications, 2nd ed., CRC Press, 2011.
American Welding Society. Welding Handbook, Vol. 3, chapter Resistance Spot Welding.
AWS C1.1. Recommended Practices for Resistance Welding.
AWS D8.9M. Test Methods for Evaluating the Resistance Spot Welding Behavior of Automotive Sheet Steel Materials.
WorldAutoSteel. AHSS Application Guidelines: ahssinsights.org.
ISO/TC 44/SC 6. Resistance welding and allied mechanical joining: iso.org.

Statistics and quality

Montgomery, D. C. Introduction to Statistical Quality Control, 8th ed., Wiley, 2019.
AIAG. Statistical Process Control (SPC) Reference Manual, 2nd ed., 2005.
NIST/SEMATECH. e-Handbook of Statistical Methods: itl.nist.gov/div898/handbook.
Western Electric. Statistical Quality Control Handbook, 1956.
Nelson, L. S. "The Shewhart Control Chart: Tests for Special Causes", Journal of Quality Technology, 16(4), 1984.

Simulation and digital twin

Grieves, M.; Vickers, J. "Digital Twin: Mitigating Unpredictable, Undesirable Emergent Behavior in Complex Systems", Springer, 2017.