S. Sheu et al., TOOL SURFACE TOPOGRAPHIES FOR CONTROLLING FRICTION AND WEAR IN METAL-FORMING PROCESSES, Journal of tribology, 120(3), 1998, pp. 517-527
A conceptual framework is introduced for the design of tool surface to
pographies in bulk metal forming processes. The objective of the desig
n is to control friction to desired levels while minimizing wear of th
e workpiece and tool surfaces and adhesive metal transfer between the
workpiece and tool. Central to the design framework are the tool/workp
iece interface properties of lubricant retention and interface permeab
ility. Lubricant retention refers to the capacity of an interface to r
etain lubricant rather than freely channel it to the exterior of the t
ool/workpiece conjunction. Permeability refers to the capacity to dist
ribute lubricant to all areas within the conjunction. These properties
lead to the concept of two-scale surface topography consisting of a f
ine scale background of interconnected channels on which is superimpos
ed an array of coarser-scale cavities. Control of friction and wear is
achieved by designing the tool surface topographies at these two scal
es to address the unique tribological conditions of specific bulk meta
l forming processes. The coarser scab is designed to ensure adequate s
upply of lubricant within the conjunction. The finer scale is designed
to ensure adequate delivery of lubricant to all parts of the conjunct
ion where nascent workpiece surface is being formed The design concept
s are illustrated with results from laboratory experiments using the r
olling process as an example, and comparing the performance of various
roll surface topographies under similar processing conditions. A two-
scale surface topography consisting of hemispherical cavities distribu
ted across a background surface of finer scale, interconnected channel
s was shown to reduce friction compared to a single-scale ground finis
h, but nor as much as a single-scale coarse topography consisting of d
ensely-packed cavities produced by an electrical discharge treatment O
n the other hand, the smoother cross-sections of the cavities, especia
lly when elongated in the direction of greatest relative motion, produ
ced significantly less wear than either of the single-scale tool surfa
ce treatments. It is concluded that two-scale engineering of tool surf
ace topographies based upon the concepts of lubricant retention and in
terface permeability can provide a broad basis for achieving desired l
evels of interface friction while minimizing workpiece surface wear an
d adhesive material transfer in many metal-forming processes.