Instrucciones para la preparación de los trabajos a presentar en el XV congreso Nacional de Ingeniería Mecánica

 
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2. EXPERIMENTAL SETUP 
The tests were carried out with a ROFIN
™
DC 025 CO
2
laser with a maximum power of 
2,500W. The head optic has a focal distance of 127 mm (5"), obtaining a minimum spot 
size of 0.21 mm. Focal point is determined previous to each test by emitting short pulses 
with different focal positions. The result is a pattern of different diameter points, 
engraved in the sheet metal part. The optimum focus position corresponds with the 
smallest point.
The main parameters were varied with the aim of studying its influence on the quality 
and geometry of cutting in the different types of AHSS sheet steels used in the car 
industry [14] (see table 1). The aim was to obtain the best cutting conditions.
ZStE260 is a type of high strength steel, designation DIN EN 10292 (SEW093 and 
SEW094) draft standard. Grain refining and precipitation hardening is used to increase 
the strength of these types of steels. The material presents a fine-grained microstructure 
with Ti- and/or Nb-carbonitride precipitations. Tests have been carried out with 
different coatings and treatments: Zinc coating (Z100), Zinc electro galvanized (ZE) and 
Re-phosphoresced (P) treatment. 
The GXE 450B AHSS contains components of residual austenite in a ferritic-bainitic 
matrix that transforms into hard martensite during forming. 
DP 750 is a Dual Phase steel that is characterized by a ferrite-martensite microstructure, 
which exhibits low yield strength but a very high work hardening. The properties are 
controlled by the relative proportions of the two phases and their size and morphology. 
Typical composition for Dual Phase steels is 0.08-0.18%C, 1.6-2.2%Mn, 0.4%Cr+Mo. 
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Table. 1 Test steel sheets 
Thickness (mm) 
Cutting length (mm) 
ZStE260P
0.8 250 
ZStE260+Z100 
0.7 250 
ZStE260+ZE 
1.75 350 
DP750 
1.5 350 
GXE 450B 
1.5 350 
Table 2 shows the ranges of variation of the cutting parameters that have been tested. 
Table. 2. Cutting parameters used 
Power [W]
200 ─ 600 
Gas pressure [bars]
3 ─ 8 
Cutting speed [mm/min]
2,000 ─ 8,000 
Focus position [mm from the surface of the steel sheet]
-1.5 ─ +1 
The controlled parameters have been the top kerf, i.e. the width of the resultant cut 
(Figure 
2
), the heat affected zone (HAZ) and the rectangularity tolerance, as well as 
checking that no pittings and burrs are present in the cut [15]. The kerf width has been 
measured using a digital photo method, measuring the pixels of the images of the cut