Whitepapers
- Dissimilar Metal Welding:
Solving Weak Weld Issues in Axial Welded Parts - Volume Manufacture of Low Ohm .002 to .050, 1 to 5 Watt Metal Resistor Elements
- Resistance and Percussive Arc Welding in Diodes, Capacitors, and Power Rectifiers
Outline: Resistance and Percussive Arc Welding
- Page 1
- 1.0 Resistance Welding
- 1.1 Time Effect
- 1.2 Weld Pressure
- Page 2
- 1.3 Weld Power Supplies
- 1.31 Synchronous AC Supply
- 1.32 Capacitive Discharge Power Supply
- Page 3
- 1.4 Dumet To CCFE (Copper Clad Iron)
- 1.5 Pressed and Sintered Tantalum to Tantalum Wire
- Page 4
- 2.0 Percussive Welding
- 2.1 Applicability of Percussive Welding
- 2.2 Design of Work Pieces
- 2.3 Percussive Weld Power Supplies
- Page 5
- 2.4 Arc Time and Heat Affected Zone
- 2.5 Welding Energy
- 2.6 Welding Force
- 2.7 Arc Starting
- 2.8 Progress of the Percussive Weld
- Page 6
- 2.9 Control of Parameters
- 2.9.1 Welding Current
- 2.10 Molybdenum to Zirconium Copper
- 2.11 Tantalum Welding for Capacitors
- 2.12 Nickel Wire to Tantalum Anode Riser Wire
- Page 7
- 3.0 Glossary of Terms
- Page 8
- 4.0 Advantages and Disadvantages of Resistance Welding and Percussive Welding
Contact CIT
Component InterTechnologies
2426 Perry Highway
Hadley, PA USA 16130
Tel: 724-253-3161
Fax: 724-253-3853
Email:
Products & Services
- Welded Leads for Lighting
- Welded Leads for Electronics
- Metal Resistor Elements
- Small Diameter Wire
Roll Forming & Heading - Specialty Welds
- Cut Glass Tube & Rod
- Lamp Lead Wire & Small Diameter Welding Equipment
- Adolf Edelhoff Wire Distributor
CIT Innovations
- Compaction of Low Density Tantalum Anodes for Increased Weld Strength
- Preventing the Release of Contaminated Water into the Environment
Company Profile
Resistance and Percussive
Arc Welding
in Diodes, Capacitors, and Power Rectifiers
Resistance and percussive arc welding are the most commonly used methods for joining of metals used in the U.S. electronic component industry. The following applications for these welding techniques will be discussed:
- Dumet to CCFE for use in the manufacture of diodes;
- Pressed and Sintered Tantalum to Tantalum Wire for use in the fabrication of capacitors;
- Molybdenum to zirconium copper for use in power rectifiers;
- Nickel Wire to Tantalum Anode Riser Wire for use in capacitors.
See also: Advantages and Disadvantages of Resistance Welding, and Percussive Welding
1.0 Resistance Welding
A RESISTANCE WELD is produced by the heat obtained from resistance at the junction of metal objects to the flow of electric current through the junction. Generally, the junction is maintained by an external force, which presses the objects together.
OHM's law is fundamental to resistance welding. This law states that, "If the voltage remains constant, the current flowing through any circuit is inversely proportional to the resistance in that circuit." E=IR. E=volts, I=current in amps, R=resistance in ohms.
The principal requirement for resistance welding is the generation of heat. The formula for power dissipated in an electrical circuit is: P=I²R. P=power in watts, I=current, R=resistance. The current flow in amperes is the same in all parts of a single path circuit regardless of the resistance from point to point. However, the heat generated at a point will be directly proportional to the resistance at that point.
In resistance welding, the work pieces are designed to have the most resistance and therefore the most heat, at the point where the weld is desired. The connecting wires are designed to have very low resistance while carrying the same amperage.
Consequently, the connecting wires remain relatively cool.
At points A and C of Figure 1, the electrode to wire and electrode to slug resistance is kept to a minimum through the use of a copper tungsten material, which provides both low electrical resistance and good physical wear resistance.
At point B of Figure 1, a chisel point cut into the wire provides the initial point of high resistance that results in the point of highest heat.
The heat energy generated in the junction being welded and the connecting electrodes is expressed by Joules Law as: W=I²RT. W=heat energy in watt-seconds or joules, I=current in amperes, R=resistance in ohms, T=time of applied current in seconds.
Typically, a substantial amount of heat is dissipated in the D.C. resistance in the transformer, in all connecting joints, buss lines to electrodes, electrodes and interfaces, as well as A.C. inductive losses in the transformer. That is, heat is generated and lost at many points other than the junction itself.
With the loss effect added, the heat energy formula becomes: H=I²RTK. K=factor representing heat losses.
The losses are caused primarily by radiation from the fixtures and objects to the surrounding air. Because these losses are not easily controlled, the time of application of the current is an important factor.
1.1 Time Effect
If the heat generated by the applied current raises the temperature of junction above the melting point of the metal, gas pockets may form at various points, resulting in the explosion of minute particles, which is called "sparking." If the temperature is further increased, the heat-affected zone will move farther back into the lead wire and cause discoloration.
Since the heat generated at a point is proportional to the square of the current, neglecting losses, a doubling of the current will quadruple the heat produced over a given period of time. A change of heat generated may be obtained either by a change of current level or by a change in time duration. However, heat transfer through the metal surrounding the junction takes a finite amount of time. As a result, for the development of a proper-sized weld nugget the time duration cannot be shorted below a minimum, regardless of the increase in current. The usual effect of high current with insufficient time duration is heat generation so rapid that burning takes place at the contact surfaces.
1.2 Weld Pressure
The weld pressure is the force per unit area exerted on the WELD-INTERFACE and the BACKUP ELECTRODE by the WELD JAW ELECTRODE. An external force brings the work pieces together and maintains continued pressure at the junction during the weld process.
The weld pressure does not enter directly into the formula just discussed, but it does have a direct effect on welding current since it affects the resistance at the junction of the two work pieces.