INTRAORAL ELECTRIC WELDING
Extract from original study by Prof. Pier Maria Mondani Figures Dr. De Bellis - Salerno

There are various types of welding, but here we will focus on autogenous welding executed using the invented machine. In autogenous welding the base metal is combined by fusion or syncrystallisation to create the welded joint.
It can be executed with or without additional metal. Syncrystallisation is the term used to describe the union of two metallic surfaces through the sharing of atoms constituting the crystal lattice in the joint zone.
IN WELDING SYNCRYSTALISATION IS ACHIEVED BY MECHANICAL PRESSURE.
Electric resistance welding is an autogenous welding procedure using pressure in which the heat required to bring the immediate surfaces to melting or forging temperature is provided by electrical resistance created by the transition of an electric current through the joint zone.
Spot welding is performed without additional metal.
The current passing from the primary to the secondary circuit generates an intense heat in the various sections that varies in relation to the resistance encountered, according to Joule's law:


I
Q = ----------- RI2t
J

where:

Q = quantity of heat expressed as calories (Cal)
J = mechanical equivalent of the great calorie, expressed as Joule/Ca (1 Cal = 4,18 X 10' Joule);
I = intensity of current in ampere;
R = electrical resistance in Ohm;
t = time in seconds

To recap, spot welding is based on three stages of execution:
- The intensity of the current in the welding circuit I
- The pressure on the welding surfaces depends on the compressive force exerted on electrodes P
- The welding stages are repeated for the execution of each spot.

The modern evolution of resistance welding leading to shorter welding times has resulted in the use of very strong currents with very low voltages.
The amount of heat needed to obtain spot welding is given by Joule's law, as shown above: a reduction in time (t) corresponds to an appropriate increase in I.
The degree of intensity varies in the first instance with the rapidity of welding; but it also depends on many other elements, in particular:
- pressure, which influences the contact resistances
- the thickness of the overlapping parts
- the shape of the piece to be welded
- the nature, shape and thickness of electrodes
- the length and distance of the electrode arms (to exert more strength)

In the most schematic form, an electric microwelder includes:
A. a transformer of intensity in which the secondary circuit joins the electrodes
B. a mechanical device placed under pressure by the electrodes
C. a switch used to turn the electric current on and off.

Pulsating current cycle. In this cycle, heat is caused by successive emissions of current interpolated by periods in which pressure alone continues to be exerted: this creates a succession of "hot" times when current is transmitted and "cold" times when current is blocked.

Functions of pressure

Pressure is applied for a longer period than current is transmitted: the pressure cycle starts before the current cycle and ends after it.
We can identify three stages in the overall welding cycle:

- squeeze time, when pressure alone is applied without the transmission of current
- welding, involving the contemporary application of pressure and the application of current until the core has melted
- cooling, when current is turned off but pressure continues to be applied.

SQUEEZE TIMES: the squeeze pressure generated by compression brings together the surfaces to be welded until they touch at the point between the electrodes.

WELDING PHASE: while the parts remain in contact under the pressure exerted during the squeeze phase, the welding current is applied to join the two surfaces.

COOLING PHASE: this is also an important phase because the metal crystallises during this stage and needs to be kept under pressure.

Force is only used to separate the "jaws" of the gun which plays the important role of keeping the stationary part under constant pressure when required by the cooling phase, but above all leaving the operator free to carry out other tasks without having to keep the gun under pressure to ensure a perfect joint between the parts to be welded.

It is also worth remembering that, owing to the different thermal conductivity of Ti=19 and copper=386 used to construct the welding electrodes, no heat is transmitted to the perimplant bone structure. In fact, Cu electrodes represent the preferred method of dissipating the heat generated by the electrical impulse = 250/300 msec.

Section of welding point using a different enlargement