A three-dimensional coupled thermal-mechanical model of ball burnishing process is
developed using commercial explicit finite element code MSC. Marc. The workpiece is modeled as being elastic-plastic, while its flowstress is taken as a function of strain, strain-rate, and temperature. Temperature-dependent material properties are also considered in this analysis. The burnishing ball is considered as rigid and only heat transfer analysis is carried out for it. In the zone of the workpiece and tool contact, the Coulomb friction is taken into account. Effects of ball burnishing parameters (burnishing force, feed rate, speed, ball diameter and number of tool passes) on residual stresses are analyzed. The results show that burnishing force, ball diameter, number of passes and burnishing feed have the most significant effect on the residual stresses. However, burnishing speed seems to just produce little effect on those. Larger burnishing force, larger number of passes, smaller ball diameter and small feed rate seem to be more effective in increasing in the maximum compressive residual stress and the depth of the layer at the compressive stress state.
Increasing density is the best way to increase the performance of powder metallurgy
materials. Conventional powder metallurgy processing can produce copper green compacts with
density less than 8.3g/cm3 (a relative density of 93%). Performances of these conventionally
compacted materials are substantially lower than their full density counterparts. Warm compaction,
which is a simple and economical forming process to prepare high density powder metallurgy parts
or materials, was employed to develop a Ti3SiC2 particulate reinforced copper matrix composite
with high strength, high electrical conductivity and good tribological behaviors. Ti3SiC2 particulate
reinforced copper matrix composites, with 1.25, 2.5 and 5 mass% Ti3SiC2 were prepared by
compacting powder with a pressure of 700 MPa at 145°C, then sintered at 1000°C under cracked
ammonia atmosphere for 60 minutes. Their density, electrical conductivity and ultimate tensile
strength decrease with the increase in particulate concentration, while hardness increases with the
increase in particulate concentration. A small addition of Ti3SiC2 particulate can increase the
hardness of the composite without losing much of electrical conductivity. The composite containing
1.25 mass% Ti3SiC2 has an ultimate tensile strength of 158 MPa, a hardness of HB 58, and an
electrical resistivity of 3.91 x 10-8 Ω.m.
Vibration Assisted Burnishing (VAB) is an advanced burnishing form incorporating dynamic force resulting from vibration into burnishing not only to change the loading type and contact method to greatly reduce friction and wear, but also to produce an excellent nanocrystalline surface by severe plastic deformation induced by high speed impact. The expression describing the relation between decrease of surface roughness and ball burnishing force is given. The dynamic model of ball VAB is established. The relations between VAB depth, VAB force and VAB time and their maximum values are derived, and the required maximum power of the vibration generator is then obtained. The theoretical equivalent burnishing force of ball VAB is only about 47.55% that of conventional burnishing, which prove validity of ball VAB.
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