thesis
Lubrication in metal cutting under built-up edge conditions
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Abstract
The effect of a mineral oil lubricant and sulphur (an EP additive) on machining of medium
carbon steel has been investigated. The lubricant was applied with several different concentrations
an additive containing sulphur. The concentrations were 0%, 1 %, 2%, 3%, 4% and 5% of the
additive. The results were compared with dry conditions. The effect of cutting speed and feed rate
was also investigated. During the tests cutting force, transient surface temperature and surface
finish were measured. Cutting force and surface finish were measured using traditional equipment.
measure the temperature of the workpiece a new method was developed. The temperature of the
transient surface was measured at three different positions below the cutting edge during the cut
using an infrared sensor. The results were then extrapolated to obtain the temperature of the
transient surface close to the cutting edge (the maximum temperature of the surface). The
temperature results can be used to calculate the cooling rate of the surface. Quick stop tests were
also used to obtain chip samples and information about BUB size and shape. The lubricant had no
effect on forces, temperature or BUB size, but improved surface finish. This works suggests that the
enhanced surface finish obtained when lubricant is applied is not due to lubrication on the rake face
(preventing a BUE), but action on the machined surface after it has been formed. The BUE is
squeezed parallel to the cutting edge and touches the workpiece altering the surface finish, by a
rubbing action and also because periodically part of the BUB bonds to the surface. The lubricant
works on this rubbing action and can avoid bonding of the squeezed BUE and also of debris
particles that are inevitably formed during the operation. It has been shown that a very low volume
of lubricant is enough to improve the surface finish because the area that requires lubrication is
small