SLAPS: Self-tuning and user-independent laser material processing units

• Research unit: EU RFP
• Project number: 98.0232-1

Key words (English)

Back-reflected laser; molten pool; DSP; pre-pulse; welding phase; reliability; feedback closed loop

Alternative project number (English)

EU project number: BRPR-CT98-9008

Research programs (English)

EU-programme: 4. Frame Research Programme - 2.1 Industrial and materials technologies

Short description (English)

See abstract

Partners and International Organizations (English)

Coordinator: Philips CFT (NL)

Abstract (English)

The project has been closed with very good results obtained in general by all the partners and by EPFL/IOA specifically. The preliminary study on sensing by photo-diodes has brought to fruitful ideas for the actual application of this research project, i.e. the laser welding.

In particular, the activity of the last period of the project has been focused on the implementation of a strategy for the welding process, after having found several useful relations between the physical process and the features of the four sensors signals (back-reflected laser (Ge sensor), laser monitoring (Ge sensor), heat emission (IGA sensor), plasma plume emission (Si sensor)). In particular the relation between the BR (back-reflected laser) signal fall and the molten pool dimension had to be verified realizing an active control of the laser power. To build this active control a DSP unit has been installed in the system and programmed in Assembler code which has been then connected to an MS Visual Basic® code for an easier interaction with the user. One of the relations found at the beginning has brought to the actual possibility to control the molten pool dimension. After achieving this result, we intended to add to the molten pool dimension control phase (pre-pulse) a temperature control phase (welding phase) by a feedback closed loop, which has been implemented by writing a further part of program for the DSP. Further work has been then focused on process data storing with the goal to create a data bank collecting the main features of the creation of every single weld spot.
The reliability that has been achieved is very good for clean and slightly oxidized copper surfaces. Looking at the bottom diameters of the weld spots, passing from the pulse shaping technique to the complete composite control technique (i.e. dimension control followed by temperature control) corresponded to a decrease of the standard deviation from 20% down to about 2%, fact that demonstrates that a rather strong stability of the process has been achieved.

A PhD thesis about the mechanisms of laser welding of copper has been started in order to scientifically investigate this process. The final goal will be to make laser welding of copper reliable by means of a robust feedback control of the laser power.

References in databases (English)

Swiss Database: Euro-DB of the
State Secretariat for Education and Research
Hallwylstrasse 4
CH-3003 Berne, Switzerland
Tel. [phone]
Swiss Project-Number: 98.0232-1