The welding process takes place through the passage of a current, generated by a capacity of 1 F charged to a voltage proportional to the energy required according to the following law:
- E : energy;
- V : voltage to which the capacitor is charged;
- C : capacitor capacity.
The current flowing through the two points to be welded heats the materials that melt together. To avoid titanium oxidation, welding occurs in an Argon-saturated atmosphere.
Welding is influenced by numerous factors mainly related to the two parts to be welded. For this reason the need arises to define experimentally which are the best welding parameters or the necessary energy and the relative time.
A table set by the user allows you to define energy and times for each of the stored welding processes.
To have the energy required for welding available as quickly as possible, the capacitor C is charged when the equipment is switched on, recharged after each welding and maintained during the waiting phase.
A specific circuit checks for continuity in the welding circuit; if there is no continuity, no welding consent is given and a special buzzer warns the user of the anomaly.
The activation of closing of the SCR (welding) is generated by a double electronic circuit which by means of two distinct commands ensures the correct efficiency of the microcontroller.
The welding cycle takes place through the following phases using the parameters defined in the table for the specific Job.
- Gas activation;
- Disconnection of the capacitor charging circuit via RL relay;
- Electrical circuit continuity check;
- Generation of the SCR closing command.
When the welding machine is turned on, the MOSFET controls the relay which in turn activates the charge circuit of the capacitor bank.
When the pedal is activated, the relay commands the disconnection of the charging circuit; the safety circuit supplied between VCAP_POS and RS- checks that there is electrical continuity between the electrodes and the parts to be welded, if this condition is verified then the SCR diode closing command is generated, thus creating a discharge circuit for the capacitors that generate the necessary current in phase 1 to the sintering and therefore lower than the melting point. In phase 2 the impulse reaches the melting temperature which leads to deep syncrystallization. If there is no electrical continuity between the electrodes and the parts to be welded, the SCR opening signal is not generated and a buzzer warns the operator of the anomaly.
Electrode holder pliers
The gripper is the essential tool for successful welding. In fact, it is responsible for the pressure of the two joints in order to limit the resistance and make the parts in contact interpenetrate in the fused area from the passage of the current. Thanks to the pliers, the pressure exerted on the joints turns out to be constant and not subject to variations, as it would be if it was exercised directly by the operator.
The two handles are insulated and end with interchangeable copper tips; this is because the heat generated during welding leads to a gradual deterioration of the characteristics of the tips themselves.
A tensioning spring exerts the necessary pressure during welding, giving a constant pressure. Thanks to this spring, the surgeon does not have to pressurize.
A tube conveys the gas to the welding site.
The magnitude of the pressure is fundamental to cause the breaking of superficial crystalline prisms causing the compaction that leads to circumferential sintering.