Par. 10: Operating principle
The welding process is carried out through the current flow, generated by a capacity of F charged at a voltage proportional to the energy required by the following law:
- E: energy;
- V: voltage with which the capacitor has been charged;
- C: capacitor capacity.
The current flowing through the two points to be welded, warms the materials up and they melt together. To avoid the titanium oxidation, the welding is carried out in Argon’s saturated atmosphere.
Welding is being influenced by different factors related above all to the two parts to be welded. For this reason it is necessary to define experimentally which are the best welding parameters or rather the necessary energy and the relative time.
A table the user can set, enables to define energy and times for each one of the welding processes you can memorize.
To enable you to have at your disposal in the shortest possible time the energy necessary for welding, the capacitor C is being charged when you switch the equipment on, charging it again whenever you weld and keeping it charged during the stand-by time.
A specific circuit controls the presence of continuity in the welding circuit; if this is not present, you do not receive the ok for the welding and a proper signal advises the operator of the anomaly.
The closing activation of the SCR ( welding ) is being generated by a double electronic circuit which, through two different controls, verifies if the micro-controller is in perfect working order.
The welding cycle carries out through the following phases by using parameters defined in the table for the specific job.
- pedale pressure
- gas activation
- Disconnection of the capacitor charging circuit through the relay RL
- Check of electric circuit continuity
- SCR closing control
10a: Electric diagram
When you switch on the welding machine, the MOSFET controls the relay, which activates itself the charging circuit of the capacitors battery. Once the pedal is on, the relay acts on the charging circuit disconnection; the safety circuit, powered by VCAP_POS and Rs-, makes sure there is electric continuity between the electrodes and the parts to be welded; if this happens, the closing control of the diode SCR is being generated and so you meet with a discharge circuit for the capacitors that generate the necessary welding current for the sintering in phase 1 and so lower than the meltin point.
In phase 2 the pulse gets to the melting temperature which takes to deep syncristallization. If there’s not electric continuity between the electrodes and the parts to be welded, opening signal SCR is not generated a buzzer informs you of the anomaly.
10b: Electrodes-holder pincer
The pincer is an essential tool for a successful welding operation. Infact, the pressure of the two joints comes before to limit the resistance and let the parts in connection penetrate into the area that has been melted by the current flowing. Thanks to the pincer, the pressure exerted on the joints turns out to be constant and not subjected to changes, as it would be as exerted directly on the operator.
The two handles are insulated and they have two interchangeable copper ends; this because the warm ,generated during the welding phase, brings to a gradual worsening of the characteristics of the ends themselves.
A tensioning spring exerts the pressure you require during the welding phase, giving a constant presssure.
Thanks to this spring the surgeon has not to exert pressure himself.
A copper tube brings gas up to the welding place.
The entity of pressure is important to cause the breaking of the surface crystal prismes producing so the compaction and by consequence the circonferential sintering.