Roller burnishing application for turned parts made of Austempered Ductil iron.
Fernandez Valdivielso, Asier ; Rodriguez, Adrian ; Urbikain, Gorka 等
Abstract: In this paper, roller burnishing as a finishing process
of revolution parts made of Austempered Ductile Iron is studied. It is a
well-know material used for decades, but in the last five years its use
has exponentially increased due to their mechanical properties. In this
way, the reduction of time and cost of finishing operations is a
necessary issue to improve the manufacturing productivity.
This work presents experimental tests using burnishing techniques
after roughing operations. Different burnishing conditions have been
used. Results show that the application of this technique can be of
great interest, especially when eliminate the directionality pattern of
turning is necessary.
Key words: roller burnishing, ADI 1000, finishing, turning,
roughness directionality, mechanical treatments
1. INTRODUCTION
Austempered Ductil Iron (ADI) began to be used industrially in the
80's. One of its first applications was the automotive sector for
the design, manufacture and optimization of components for high-end
vehicles; since then, the increase of their use has been spectacular.
This is mainly because the parts made of this material show an excellent
strength-to-weight ratio, improving significantly the typical values
offered by aluminum alloys, steel and other castings. ADI castings offer
an interesting combination of mechanical properties derived from both, a
precise percentage of alloying and a controlled thermal treatment
('austempering'). ADI castings are characterized by a special
microstructure of Fe-C which must be uniformly distributed (Cakir et
al., 2008; Klocke et al., 2010). The first choice for ADI removal are
carbide inserts, as for the rest of ADI castings. However, ADI castings
have a lower machinability than other castings, resulting in an
increased tool wear due to abrasion and adhesion phenomena, which reduce
tool life. In order to reduce the machining time, burnishing techniques
could be feasible to eliminate semi-finishing and finishing turning
operations. The idea is to maintain roughing operations and later on
burnishing, achieving the final surface roughness reducing time and
cost. Moreover, combining turning and burnishing in the opposite
direction, it is possible to eliminate the directionality roughness
pattern on turning parts. Another fact to take into account is that
residual stresses are also important (Budic et al., 2007), and
burnishing process introduce compression residual stresses on workpiece
surface.
In this paper, roller burnishing as a suitable technique for
finishing this type of components is presented. Burnishing is a simple
operation, inexpensive and which generates high quality final surfaces
(El-Khabeery et al., 2001; Lopez de Lacalle et al., 2011; Radulescu et
al., 2009). Roller burnishing technology applied in lathes allows finish
surfaces within the quality of grinding (i.e., less than 1 [micro]m Ra).
Thus, roller burnishing can replace finishing processes such as
grinding, shot peening or hand polishing. In addition, burnishing is
applied on the same machines, using an additional burnishing tool.
2. BALL BURNISHING EFFECTS
[FIGURE 1 OMITTED]
Burnishing is a cold-working process performed on a previously
machined surface. The process is based on making small plastic
deformations on part surfaces, which causes material displacement from
the "peaks or ridges" to the "valleys or
depressions" of surface micro-irregularities. This mechanism is
performed by a rolling element (tool, a ball, or a roller) that moves
close to the tool paths on the surface, applying a regular compression
force at the same time. The 'crushing' causes four effects on
the surface:
* Reduction of surface roughness in more than an order of
magnitude. The final quality is similar to grinding, even reaching a
mirror-like aspect.
* Generation of high compression residual stresses on workpiece
surface, which is beneficial for the fatigue behaviour of the component.
Moreover, the absence of heat produced by this mechanical surface
treatment prevents metallurgical changes on surfaces.
* Surface hardness increment between 30%-60% (HBN) in common
steels.
* Dimensional tolerances are kept (<0.01 mm), for example in
burnished holes. Special tools for hole finishing is a typical
application of spring-type burnishing devices.
3. ADI 1000 BURNISHING APPLICATION
The cutting experiments were conducted in a CMZ TC25BTY turning
center with a FANUC@ 31iT HVi numeric control. The work-piece, a
cylinder of ADI 1000, was rigidly clamped and machined using the
established cutting conditions for roughing operations. After machining,
the burnishing tests were carried out. An Ecorrol EG5-1 burnishing tools
was used and the values used in tests are shown in Table 1.
Table 2 shows the roughness results obtained in burnishing tests;
burnishing in the same rotation direction than in the previous turning
(M03). However, in table 3 the rotation direction is the opposite (M04)
(helix-crosses). Using this direction, eliminate the directionality
pattern generated by the previous turning is possible.
Results show that roughness parameters obtained are better using
helix-crosses burnishing. In both cases the final roughness is better
with small values of feed per revolution. Regarding the cutting speed
variation, results do not make clear the influence of this parameter on
the surface quality obtained.
Figure 2 shows three 3D surface topographies. In up figure, the
topography of the turned surface after roughing conditions is shown.
Typical turning peaks and valleys are seen in this picture. In down
right figure, the topography after burnishing M03 is shown. A decrement
in surface roughness is observed, but the roughness peaks characteristic
of turning are still appreciated. It is in down left figure where the
directionality pattern elimination is shown. In this case, helix-crosses
burnishing has been used.
[FIGURE 2 OMITTED]
4. CONCLUSIONS
The influence of roller burnishing on ADI 1000 turned parts was
investigated. Based on the experimental results achieved, the following
conclusions can be stated:
* Roller burnishing process improves significantly the surface
roughness of ADI 1000 turned parts.
* Combining helix-crosses burnishing and low values of feed per
revolution, a high surface roughness improvement could be achieved.
* Directionality roughness pattern generated in turning operations
could be eliminated.
Future work on ADI 1000 roller burnishing research should consider
the following:
* Conducting additional tests using different burnishing pressure
values.
* Conducting tests using ball burnishing in order to compare the
finishing results.
* The use of a statistical approach to model the surface roughness
parameters.
5. ACKNOWLEDGEMENTS
Thanks are addressed to the company Gamesa and the MuProD project.
The authors would like to acknowledge the help of E. Sasia in conducting
experiments.
6. REFERENCES
Budic, I.; Vitez, I. & Marusic, V. (2007). Residual stresses in
iron castings, Chapter 49 in DAAAM International Scientific Book 2007,
B. Katalinic (Ed.), Published by DAAAM International, ISBN
3-901509-60-7, ISSN 1726-9687, Vienna, Austria
Cakir, M., Isik, Y. (2008). Investigating the machinability of
anstempered ductile irons having different austempering temperatures and
times. Materials & Design, Vol. 29 (5), pp. 937-942
El-Khabeery, M.M. and El-Axir, M.H. (2001). Experimental techniques
for studying the effects of milling roller-burnishing parameters on
surface integrity. Int. Journal of Machine Tools and Manufacture. Vol.
41, No. 12, pp.1705-1719
Klocke, F., Arft, M., Lung, D. (2010). Material-related aspects of
the machinability of Austempered Ductile Iron. Production Engineering,
Vol. 4(5), pp. 433-441
Lopez de Lacalle, L.N., Rodriguez, A., Lamikiz, A., Celaya, A.,
Alberdi, R. (2011). Five-axis Machining and Burnishing of Complex Parts
for the improvement of surface roughness, International Journal of
Materials and Manufacturing Processes, in press.
Radulescu, M.-C.; Radulescu, B. & Cozminca, I. (2009).
Employing Experimental Plans in Plane Metal Burnishing, Annals of DAAAM
for 2009 & Proceedings of the 20th International DAAAM Symposium,
25-28th November 2009, Vienna, Austria, ISSN 1726-9679, ISBN
978-3-901509-70-4, Katalinic, B. (Ed.), pp. 0539-0540, Published by
DAAAM International Vienna, Vienna
Tab. 1. Burnishing levels used in conducting experiments
Burnishing levels
1 2 3
av[mm/rev] 0.4 0.2 0.1
Vc[m/min] 80 100 120
Force [N] 1000
Tab. 2. Roughness results obtained before and after burnishing
M03 operation
Force [a.sub.v] [V.sub.c] Ra Rz
N [mm/rev] [m/min] [[micro]m] [[micro]m]
Tumin -- 0.4 80 2.12 11.5
Burnishing 1000 0.4 80 1.16 7.19
M03 0.4 100 1.21 9.97
0.4 120 1.02 6.09
0.2 80 0.94 6.74
0.2 100 1.21 9.67
0.2 120 1.07 10.5
0.1 80 0.90 7.01
0.1 100 0.82 4.99
0.1 120 1.03 10.0
Tab. 3. Roughness results obtained before and after burnishing
M04 operation
Force [a.sub.v] [V.sub.c] Ra Rz
[N] [mm/rev] [m/min] [[mciro]m] [[mciro]m]
Turnin -- 0.4 80 2.12 11.5
Burnishing 1000 0.4 80 0.92 7.34
M04 0.4 100 1.02 7.44
0.4 120 1.17 9.47
0.2 80 0.94 7.7
0.2 100 1.02 7.84
0.2 120 0.79 6.15
0.1 80 0.74 5.87
0.1 100 0.79 6.58
0.1 120 1.17 9.12
