What is CD stud welding? (Capacitor Discharge StudWelding)

What is CD stud welding?
(Capacitor Discharge StudWelding)

Within the fastener world, there is many types of ways to weld metal together. Stud welding is one way to weld materials together. You may find CD is often shortened version of Capacitor Discharge. This is a term used in stud welding to refer to the type of conversion which takes place when using a one hundred and ten volt outlet. Studfast Stud welding has been supporting customers to make efficient and cost effective production solutions for over 30 years. We are based in Northamptonshire and provide our customers with a next day service for all their CD studwelding needs. Stud welding is a fast, reliable and accurate method of attaching a metal fastener to a metal part using an electric arc. Stud welding uses direct current electricity to create an arc between a fastener or stud and the parent material. The parent material or work piece can vary from thin sheet to thick plate. The arc melts the end of the stud and creates a molten pool in the parent material. The weld is completed when the stud is forged into the molten pool under pressure. Usually studs are externally threaded, plain pins (unthreaded) or internally threaded tapped bosses (pads). The equipment required depends on the diameter of the stud to be attached, the condition and thickness of the parent material and the type of material. Typical materials are mild steel, stainless steel, aluminium alloy, pure aluminium and lead free brass. The stud is held in a handtool or welding head which is used to initiate the weld and apply the forging pressure. The handtool and the parent material are connected to a power source (the controller). Stud welding can be used to weld studs from M2.5 to M24.

There are three types of stud welding;

  • Drawn Arc (DA),
  • Short Cycle (SC)
  • Capacitor Discharge (CD).

DA is used for larger diameters whereas SC and CD are used for smaller diameters. The weld duration varies from a few milliseconds for Capacitor Discharge to more than a second for large diameter DA. For DA and SC three phase mains power is transformed and rectified, for CD single phase power is used to store energy in capacitors. DA equipment is larger and less portable than SC equipment. The lightest and most portable equipment is CD. The DA process requires the use of a ceramic ferrule (arc shield), to contain and shape the weld fillet, this is not reusable. Weld spatter is evident with the SC process and this can be minimised using a shrouding gas. Capacitor Discharge is by far the cleanest process with only a small witness of molten metal visible around the flange. The DA weld zone extends into the parent material to a depth of one third of the stud diameter, so plate thickness will determine where it can be used in order to avoid burn through. The SC weld zone enable sheets as thin as 1.5mm to be used whereas Capacitor Discharge can be used on sheets as thin as 0.7mm.

The three types of studwelding are used in different circumstances.

The DA process is the most tolerant of surface imperfections. As long as a pilot arc can be established then rust, mill scale, oil and dirt will not prevent a weld.

Drawn Arc studs have a fluxed weld end and a length allowance for burn off. A good weld is represented by an even fillet and the correct length reduction of the stud. The SC process is also tolerant of surface imperfections and does not require a fluxed stud nor a ferrule.

The CD stud welding process is ideal for thin gauge sheet where reverse marking can be minimised or completely eliminated. For CD the sheet surface should be clean and flat and the weld stud must have a precise pip and cone angle on the weld end. CD studs and CD equipment are lowest in cost and the process is the fastest. Handheld Capacitor Discharge Machines can weld up to 6 studs per minute and automation can increase this to over 20 studs per minute. CD is easy to jig as it does not require ferrules nor shrouding gas and consequently is the most accurate process. The short duration pulse of energy in CD welding imparts local heating only to the weld area thus avoiding heat distortion. Studfast Studwelding supply the full range of all equipment, studs and accessories required to get your started and ensure you do not let your customer down or production coming to a stop.

The benefits of CD stud welding (Capacitor Discharge StudWelding) are:

  • The welds are clean and require no finishing.
  • The molten metal of a stud weld creates complete fusion across the whole diameter area of the stud which makes the joint stronger than either the stud or the parent material.

A destruction test demonstrates that either a slug of the parent material is pulled out (on thinner gauge sheet) or the stud breaks in the heat affected zone above the weld.
Reliable, repeatable stud welds are achieved under consistent conditions of applied power and weld time.

Why choose Studfast Stud welding?

Our extensive catalogue of CD weld studs has a fully stocked ranges of aluminium alloy, pure aluminium , stainless steel 316 (A4) and stainless steel 304 (A2), mild steel and lead free brass in many different sizes and diameters. We can offer CD weld studs from Metric threaded and unthreaded 2.5 diameter and 4 milli meter in length up to metric threaded and unthreaded 10 in diameter and 60 milli meter in length, along with all the variations in between.

We are also able to offer larger sizes if your process requires drawn arc, should you require this process instead of capacitor discharge.

As well as the CD Studs you will require we offer equipment which will get you started, you will require a CD Machine which is dependent on the size of stud you are welding. Our recommendation usually is CDM8 which will weld CD studs from 2mm up to diameter 10mm if you are welding mild steel, stainless steel, aluminium and brass. Watch this video to see what is included in a CDM8 and how to get started immediately, https://www.studfast-studwelding.com/weld-stud-clinic/what-is-included-in-a-cdm8-machine/

CD welding is ideal for thin parent material which are flat and clean. Once you CD weld on on the parent material the weld will be clean, neat and strong. You can watch this video to see how to test your weld strength, https://www.studfast-studwelding.com/weld-stud-clinic/how-to-use-a-bending-bar/

Introducing The Studfast CD Range


The CD Range stud welding Controllers: CDi Range, CDM Range, Multi-Gun, Automated photo, Automated, Automatic photo, Automatic, CNC Automated photo, CNC Automated, Micro-pistol photo, Micro-Pistol. Studfast has the most comprehensive range of Studwelding Equipment – we have the right controller/handtool combination to best suit your application and budget. From hand portable units for occasional use to high speed, fully automatic, production systems.

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Stud Welding Equipment

All electrical components are soak tested for reliability. Unintentional firing is prevented by safety circuits and in the event of a component failure, system shutdown will occur.

View CD Process
Capacitor Discharge Process

High speed production systems, custom built to exact specifications, achieve the best accuracy and productivity.

View SC Process
Short Cycle Process

From a simple bottom loaded pneumatic production head to automatic stud feed with CNC positioning and remote delivery/removal of components, Studfast Studwelding have the Right Studwelding Equipment solution for your business.

View DA Process
Drawn Arc Process

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