Weld Studs Manufacturer in India | ISO 13918 PT Threaded Weld Studs

Overview

ISO 13918 PT Threaded Weld Studs (CD Weld Studs): Manufacturer & Stockist

A weld stud is fixed by welding its end to a sheet, so the sheet needs no hole and the back stays flat. The PT stud of ISO 13918 is the threaded stud for capacitor discharge (CD) welding: a short burst of current through its ignition tip welds the whole flange face in a few milliseconds.

Exotic Alloy manufactures and stocks PT weld studs in Mumbai, India, for makers of electrical cabinets, appliances, HVAC equipment, vehicles and stainless kitchen and process equipment. We supply across India and export to Vietnam, South-East Asia, the Gulf and Africa.

Thread, flange and tip

The flange (d₂) is the weld area; its face is a very flat cone of 174° with the ignition tip in the centre. The length l₁ leaves the tip out, and the stud loses about 0.3 mm in welding. Nuts for the studs are on our nuts page; for studs that pass through holes see full threaded studs.

ISO 13918 PT M3–M8 CD tip ignition A2 / A4 stainless Copper plated 4.8

Weld studs at a glance

Standard: ISO 13918:2017 (EN ISO 13918), type PT
Process: Capacitor discharge, tip ignition
Sizes: M3, M4, M5, M6, M8
Lengths: 6 to 30 mm (l₁, tip excluded)
After welding: l₂ ≈ l₁ − 0.3 mm
Materials: 4.8 Cu plated, A2, A4, brass, Al, AlMg3
Former standard: DIN 32501

PT M6 × 16 before and after welding, to scale. The tip melts away and the stud stands about 0.3 mm shorter than l₁; the flange height h₁ is drawn at 1.0 mm, inside its 0.7–1.4 mm range.

Specification

Weld Stud Specification

The range we manufacture and stock.

StandardISO 13918:2017 / EN ISO 13918, type PT (formerly DIN 32501)

SizesM3, M4, M5, M6, M8; other threads by agreement

Lengths6 to 30 mm l₁, tolerance +0.6 / 0 mm; others by agreement

ProcessCapacitor discharge stud welding with tip ignition

Weld endFlange d₂ ±0.2, face 174° ±2°, ignition tip

Materials4.8; A2, A4, A5-50 / -70; CuZn37; Al99.5; AlMg3

Finish4.8 copper plated (C1E) as standard; stainless and non-ferrous plain

TolerancesAs ISO 13918 Table 14; otherwise product grade A, ISO 4759-1

CertificationEN 10204 3.1 with the tests of ISO 13918 clause 9; 3.2 on request

SupplyBoxes labelled to ISO 13918 clause 10, from stock or made to order

Dimensions

PT Weld Stud Dimensions, ISO 13918

Thread, flange and ignition tip for every size, mm.

Size d₁	Pitch P	Flange d₂ ±0.2	Tip d₄ ±0.08	Tip length l₃ ±0.05	Run-out h₅ max.	Flange height h₁	Face angle α	Lengths l₁ +0.6 / 0
M3	0.5	4.5	0.60	0.55	0.6	0.7–1.4	174° ±2°	6, 8, 10, 12, 16, 20
M4	0.7	5.5	0.65	0.55	0.6	0.7–1.4	174° ±2°	8, 10, 12, 16, 20, 25
M5	0.8	6.5	0.75	0.80	1	0.7–1.4	174° ±2°	10, 12, 16, 20, 25, 30
M6	1	7.5	0.75	0.80	1	0.7–1.4	174° ±2°	10, 12, 16, 20, 25, 30
M8	1.25	9	0.75	0.85	1.5	0.8–1.4	174° ±2°	12, 16, 20, 25, 30

ISO 13918:2017 Table 14. d₂ is the diameter at the weld area (the flange), h₁ the flange height, h₅ the thread run-out next to the flange, l₃ the tip length. Dimensions without a tolerance here follow product grade A of ISO 4759-1; for coated studs the tolerances apply before coating.

The five sizes side by side. The flange is 1.5 mm larger than the thread up to M6 and 1 mm larger at M8; hover a dot for the length after welding.

Lengths

Standard Lengths & Length After Welding

l₁ before welding	M3	M4	M5	M6	M8
6 mm	5.7	–	–	–	–
8 mm	7.7	7.7	–	–	–
10 mm	9.7	9.7	9.7	9.7	–
12 mm	11.7	11.7	11.7	11.7	11.7
16 mm	15.7	15.7	15.7	15.7	15.7
20 mm	19.7	19.7	19.7	19.7	19.7
25 mm	–	24.7	24.7	24.7	24.7
30 mm	–	–	29.7	29.7	29.7

Cells give l₂ ≈ l₁ − 0.3 mm, the length standing on the sheet after welding; – = not a standard length for that size.

Reading the lengths

l₁ is the overall length before welding, without the ignition tip; tolerance +0.6 / 0 mm.
l₂ is the nominal length after welding; for PT studs it is about l₁ − 0.3 mm.
With proper control of the welding, l₂ stays within ±1 mm (ISO 13918, 6.1).
The box label states which length is meant, l₁ or l₂.
Pick a length that leaves the nut fully engaged over the part you clamp.

CD welding

How Capacitor Discharge Stud Welding Works

Four steps, one trigger pull. The tip lights the arc, the stud is driven home and the weld is done in milliseconds.

The process

The welding unit charges a capacitor bank; the gun holds the stud with its tip on the sheet (contact method) or just above it (gap method).
The discharge current flows through the tip, which vaporises; the arc spreads over the flange face and melts a thin layer of stud and sheet.
The gun drives the stud into the molten layer, which solidifies at once.
No ferrule, no shielding gas and no weld collar.

What it means for the sheet

The weld takes a few milliseconds: welding-unit makers quote 1 to 3 ms, other references up to 6 ms.
Made for thin sheet; equipment makers quote from about 0.5 mm. Your welding procedure (ISO 14555) sets the limit.
With the right settings, thin sheet need not show burn-through on the back.
Weld steel to steel, stainless to stainless, aluminium to aluminium.

Stud types

ISO 13918 Weld Stud Types & Processes

The tip is what makes a CD stud. PT, UT and IT studs carry an ignition tip; PS studs have a flange but no tip; PD studs are welded inside a ceramic ferrule.

Welding process	Threaded	Unthreaded	Internal thread	Other	Ferrule / gas
Drawn arc, ceramic ferrule or shielding gas	FD, MD, PD, RD	UD	ID	ND insulation pin, SD shear connector	Ferrule (UF, PF, RF, DF) or gas
Short-cycle drawn arc	PS (with flange)	US	IS	–	–
Capacitor discharge, tip ignition	PT	UT	IT	–	–

Stud symbols of ISO 13918:2017 Table 1. This page covers PT; we make UT and IT studs and drawn arc studs to order.

Finder

Weld Stud Finder: Dimensions & Designation

Pick size, length and material; get the weld end, the load and the order line.

Stud & order

Size

Length l1, mm

Material

Quantity, pcs

Dimensions from ISO 13918:2017 Table 14 as on this page; l₂ ≈ l₁ − 0.3 mm. Our calculation: minimum tensile load of the thread = stress area × minimum R_m of the material (ISO 898-1, ISO 3506-1, ISO 13918 Table 2), not the strength of the weld; mass ≈ pitch-diameter cylinder plus flange, approximate. Sample size from ISO 13918 Table 18, taking the order as one test lot.

Result

15.7

mm l2 after welding (±1)

10.06

kN min. tensile load, thread (R_m 500 MPa)

Flange d2 / h1:7.5 ± 0.2 / 0.7–1.4 mm

Ignition tip d4 × l3:0.75 × 0.80 mm

Pitch / run-out h5 max.:1 / 1.0 mm

Length l1 before welding:16 +0.6 / 0 mm

Mass (approx.):3.02 g each, 3.02 kg

Test sample for 3.1:2 studs

Designation:1000 pcs Stud ISO 13918 – PT M6×16 – A2-50 (length l1)

Materials

Weld Stud Materials & Strength

Material	Standard	R_m min. MPa	Yield MPa	Notes
Steel, property class 4.8, copper plated	ISO 898-1	≥ 420	R_eL 340	Copper plated (C1E) unless ordered otherwise
Stainless A2-50 (304 family)	ISO 3506-1	≥ 500	R_p0.2 210	Usual stainless PT stud
Stainless A2-70	ISO 3506-1	≥ 700	R_p0.2 450	Cold worked, higher strength
Stainless A4-50 (316 family)	ISO 3506-1	≥ 500	R_p0.2 210	Molybdenum stainless for chlorides
Stainless A4-70	ISO 3506-1	≥ 700	R_p0.2 450	Cold worked A4
Brass CuZn37 (copper-zinc, group 32)	ISO/TR 15608	≥ 370	–	For brass and copper parts
Aluminium Al99.5 (group 21)	ISO/TR 15608	≥ 100	–	For pure aluminium sheet
Aluminium AlMg3 / 5754 (group 22.3)	ISO/TR 15608	≥ 230	–	For Al-Mg sheet

Materials for PT studs, ISO 13918:2017 Table 2: property classes to ISO 898-1 and ISO 3506-1 (A5-50 and A5-70 also allowed), non-ferrous groups to ISO/TR 15608 (Cu-Zn group 32, aluminium group 21, Al-Mg group 22.3); CuZn37, Al99.5 and AlMg3 are the alloys we use in those groups. Only weldable materials: non-alloy steel generally up to 0.20 % carbon, no free-cutting grades.

Size	A_s mm²	4.8 R_m 420	Class 50 R_m 500	Class 70 R_m 700	Brass R_m 370	Al R_m 100	AlMg3 R_m 230
M3	5.0	2.11	2.52	3.52	1.86	0.50	1.16
M4	8.8	3.69	4.39	6.15	3.25	0.88	2.02
M5	14.2	5.96	7.09	9.93	5.25	1.42	3.26
M6	20.1	8.45	10.06	14.09	7.45	2.01	4.63
M8	36.6	15.38	18.30	25.63	13.55	3.66	8.42

Minimum tensile load of the threaded section, kN = A_s × R_m min.; our calculation (it matches the ISO 898-1 values for class 4.8). The load the welded joint carries also depends on the sheet and the weld.

Stainless

A2 · A4 · A5

As in the photo.

304 316 316Ti

Aluminium

Al99.5 · AlMg3

For aluminium panels.

1050 Aluminium

Steel & brass

4.8 Cu plated · CuZn37

Mild steel and brass parts.

Brass

Manufacturing

How Our Weld Studs Are Made

1

Wire

Weldable, killed wire, certified by heat.

2

Head

Flange, face cone and tip cold formed.

3

Thread

Rolled up to the run-out at the flange.

4

Finish

Copper plated (4.8) or cleaned (stainless).

5

Inspect

Tip, flange and thread gauged per lot.

6

Pack

Boxed and labelled to ISO 13918.

Applications

Where Our Weld Studs Are Used

Electrical cabinets

Earthing studs and mounting points in enclosures.

Appliances

Panels of ovens, washers and cookers.

HVAC

Ducts, air handling units and housings.

Stainless equipment

Kitchen, food and pharma equipment.

Vehicles

Bus, rail and truck body panels.

Signs & nameplates

Fixings hidden behind the face.

Quality & testing

Weld Stud Inspection & Certification

Check	Method	Applied to
Ignition tip d₄, l₃	Optical measurement	Every lot
Flange d₂, h₁; length l₁	Calipers, height gauge	Every lot
Thread	GO / NOT GO ring gauges	Every lot
Chemical analysis	Delivery unit or raw material, all heats	3.1 orders (ISO 13918, 9.2)
Mechanical properties	To ISO 898-1, ISO 3506-1 or Table 2	Every test lot (9.3)
Trial welds	Welded and bent on your sheet	On request

Sample size for the mechanical tests

Studs per test lot	Sample size
up to 8 000	2
over 8 000 to 35 000	3
over 35 000	5

ISO 13918 Table 18; every sample must meet Table 2. The tests of clause 9 apply when an EN 10204 3.1 certificate is ordered.

Every box is labelled with

ISO 13918 and the symbol PT
Thread × length, saying l₁ or l₂
Material and finish
Lot number for traceability

Weld studs carry no head marking; ISO 13918 puts traceability on the packaging unit.

On request

EN 10204 3.1 / 3.2 certificates
Dimensional reports per size
Declarations on restricted substances

FAQ

Weld Stud Questions, Answered

PT is the ISO 13918 symbol for a threaded stud for capacitor discharge stud welding with tip ignition. It has an M3 to M8 thread, a thin flange that forms the weld area and a small ignition tip in the centre of the flange face.

When the capacitor discharges, the current flows through the tip, which vaporises and lights the arc across the whole flange face. The tip is 0.60 to 0.75 mm in diameter and 0.55 to 0.85 mm long, held to plus or minus 0.08 mm and 0.05 mm, because it governs ignition.

The length l1 is measured without the ignition tip. After welding the stud is about 0.3 mm shorter, so an M6 x 16 stud stands about 15.7 mm. ISO 13918 states that with proper control of the welding the length after welding stays within plus or minus 1 mm.

ISO 13918 lists M3 in lengths 6 to 20 mm, M4 8 to 25 mm, M5 and M6 10 to 30 mm and M8 12 to 30 mm. Other lengths and threads can be agreed.

Steel of property class 4.8, supplied copper plated unless ordered otherwise; stainless steel A2, A4 and A5 in property classes 50 and 70; copper-zinc alloys with a tensile strength of at least 370 MPa; aluminium of at least 100 MPa and aluminium-magnesium alloys of at least 230 MPa. Only weldable materials are used, chosen to suit the sheet.

Capacitor discharge welding with tip ignition is made for thin sheet; equipment makers quote sheet from about 0.5 mm. The real limit for your stud, sheet and machine comes from the welding procedure, qualified to ISO 14555.

By its designation, for example Stud ISO 13918 - PT M6x16 - A2-50 for a stainless M6 stud 16 mm long, or Stud ISO 13918 - PT M4x20 - 4.8 - C1E for a copper plated steel stud. Give the quantity and say whether the length is l1 before welding or l2 after welding.

Both are threaded studs with a flange. PT studs have an ignition tip and are welded by capacitor discharge; PS studs have no tip and are welded by short-cycle drawn arc welding.

Yes. DIN 32501 covered studs for capacitor discharge welding; it was replaced by ISO 13918, where the threaded tip-ignition stud is type PT.