Determination of strain via 3D scanning in a bimetal fabricated by explosion welding.

Benak, Michal ; Buransky, Ivan ; Turna, Milan 等

1. INTRODUCTION

Formation of welded joints at collision of two different materials was observed at the end of forties in the study of cumulative phenomenon. Since that time the explosion welding (EW) technology underwent a dynamic progress both in theoretical and application fields. In technological processing of metals by explosion the substrate and accelerated materials are bonded by acting of compression formed by detonation of a suitable explosive located over entire area of accelerated material (Referativnyj zurnal "SVARKA". (2005)). Compressive effect of explosive acts normally on accelerated metal, which is colliding on the stable metal at v0 velocity. Due to dynamic effect of collision not only bonding but also deformation of both metals occurs (Turna, 1989). An optical scanner was used for its measurement which measures with accuracy of 0.02 mm (Peterka et al., 2007).

2. PRINCIPLE OF EW TECHNOLOGY

Explosion welding is considered for a specific kind of cold pressure welding. Welded joints fabricated by explosion have a typical undulated boundary, characterizing both, welding process and bond quality. This methods allows to weld relatively broad assortment of metals and their alloys. Principal and kinematic schemes of explosion welding are show in Figs. 1. and 2 (Yuheng et al., 2005).

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

3. CHARACTERISTIC OF WELDED MATERIALS

In explosion welding process a stable material Al 99.5%, delivered in soft condition according to STN 42 4005 standard. Semi product was an aluminium plate of rectangular shape 15 mm in thickness.

CrNi austenitic steel type18/8 (304, 1.4310) was used as accelerated material, defined by STN EN 10 088 standard. This material was heat treated by solution annealing and by stress relief heat treatment. The delivered material was a sheet of rectangular shape 1 mm in thickness.

4. WELDING PARAMETERS

The input data for calculation of parameters and conditions of welding process are given in Table 1.

5. FABRICATION OF Al-CrNi BIMETAL

The mechanically machined weld edges were cleaned from surface impurities and degreased closely prior to welding. Aluminium plate was backed with chipboard, which created also relational plane for the ance spacing of stainless steel plate. A wooden frame was placed on accelerated material with dimensions (279 x 185 x 10.3 mm), to which a Semtex S 35 explosive was poured. The point of ignition and ignition explosive Semtex was selected in such a manner that the detonation wave would be directed approximately in parallel with material length. The charge was ignited with an electronic detonator inserted into ignition explosive. The fabricated bimetal Al-CrNi austenitic steel (see Fig. 3) was trimmed to final size 146 x 112 x 16 mm.

[FIGURE 3 OMITTED]

6. MEASUREMENT OF BIMETAL DEFORMATION

An optical 3D scanner type ATOS I 350 from GOM company was used for determination of formed deformation of Al-CrNi steel bimetal. The optical 3D scanner consists of two CCD cameras, projection lamp (projector), stand and a powerful computer with pre-installed GOM ATOS software. Uncoded reference points were stuck on Al-CrNi steel bimetal. A chalk spray was sprayed on material surface, since the glossy surface of bimetal is not suitable for optical scanning. The uncoded reference points were then cleaned form chalk spray, in order that optical scanner could sense them. The uncoded points are used for determination of 3D coordinates and are automatically detected with GOM ATOS software (ATOS v.6 User Manual.( 2006)). The result of bimetal scanning is a cloud of points. For creation of a digitalised model it was necessary to perform 12 scans form different sides. After scanning the bimetal, the ,,align" function was used, which serves for reducing the deviation from individual scans. The function ,,polygonized" was used, which created triangles from the cloud of points.

The digitalised model created (modelled) in DELCAM PowerSHAPE software was then compared with a CAD model in dimensions (146 x 112 x 16 mm). CAD model was subsequently imported to GOM ATOS software. The reference CAD model and the digitalised model of bimetal were placed into one coordinate system by use of "best-fit registration" function. For comparison of above-mentioned points the ,,deviation to mesh" function was used, which resulted in the colour map of deviations, (Fig. 4).

The colour map of deviation makes visible the greatest deformation along the sides of fabricated bimetal. The measured deviation is (0.8 az 1)mm (Fig. 5). The deviation varies on the surface and it attains values from -1.6 to 0.9 mm. Fig. 5 also shows Al-CrNi bimetal deflection. Deflection occurs mainly at smaller dimensions of bimetal, while it is rare at greater dimensions.

[FIGURE 4 OMITTED]

[FIGURE 5 OMITTED]

7. CONCLUSIONS

Development of combined materials Al-CrNi steel (aimed at utilisation of priority mechanical and physical properties of these metals) is at present relatively discussed topic also from the viewpoint of searching for optimum welding technology. Experimental results have shown that the quality of joints is acceptable and deformation of bimetal is not extreme. The greatest change in shape is observed on the fringe parts of bimetal, which may be removed by machining. Material deflection should be then solved, which was the subject of measurements in the mentioned work.

ACKNOWLEDGEMENT

This work is a part of VEGA no. 1/3191/06 project.

8. REFERENCES

ATOS v. 6 User Manual, GOM mbH, Germany 2006.

Peterka, J.; Janac, A.; Morovic L. (2007) Optical methods of capturing the metrological quantities of mechanicalparts, ICPM 2007, IV International Congress of Precision Machining, ISBN 978-83-88906-91-6

Referativnyj zurnal ,,SVARKA". (2005). Solid state welding. Explosion welding. Moscow.

Turna, M. (1989).; Special welding processes, Alfa, ISBN 8005-00097-9, Bratislava.

Yuheng Li.; Deming Shu.; Tuncer M. K.(2005). Explosion Bonding of Dissimilar Materials for Fabricating APS Front End Components, Available from: http://www.aps.anl.gov/Facility 2005 , Accessed: 2005-0612.

BENAK, M[ichal]; BURANSKY, I[van] & TURNA, M[ilan]*

Young Reseearcher and Scienntist Paper / * Supervisor, Mentor

Tab. 1. Parameters and conditions of welding process.

Name Designation Value

Accelerated
 metal thickness
 (austenitic steel
 type 18/8) [H.sub.D] [mm] 1
Material density
 (austenitic steel [rho] [kg. m-3] 7850
 type 18/8)
Thickness of
 stable metal
 (Al 99.5) [H.sub.D] [mm] 13
Material density
 (Al 99.5) [rho] [kg. m-3] 2700
Explosive thickness
 (Semtex S35) [H.sub.E] [mm] 10.30
Distance spacing h [mm] 2
Initial angle [alpha] [[degrees]] 0
 of setup
Collision speed [V.sub.0] [m.s-1] 606.34
 of sheet
Detonation pressure [P.sub.cj] [GPa] 1.87
Time constant [tau] [Us] 3.15
Dynamic [beta] [[degrees]] 19.9
 collision angle
Resultant [v.sub.d] 2164.89
 detonation speed [[m.s.sup.-1]]