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ABSTRACT
In the routine of a Vehicles Assembler Company, bolts and nipples threading are the most
frequent operations. An assembly, fixations and tube sealings uses threading as a
irreplaceable project resource. The phenomena involved in those operations, however, it is
not completely understood by the involved professionals. This can be notice when
participate in the tasks related with the quality of products and processes. The interruptions
in the sequence of the assembly lines, due to the break of screws or rejections of operations
for automated machines, not always are understood by the operators, because they involve
subjective phenomena occult inside the operational parameters and inside the properties of
the fixation elements. When a screw or a tube connection is pressed, used energy is divided
in losses by attrition and tightening of the bolted joint. The squeeze can be insufficient or
excessive, depending on the tribologic state of the surfaces. The consequences can be
drastic if the deviation is passed to the product and discovered for the final user. The field
quality flaws are always more serious and important than those discovered inside of the
company. It is more important still to avoid them, specifying and controlling the parameters
of the attrition at surfaces responsible for the obtaining of the assembly force. The
demonstration that the torque applied in the threading doesn't have any direct relationship
with the assembly force obtaining, and the control of the lubricating elements is the best
way to provide an efficient result in a dismountable junction, projected for a certain
function in the vehicle, is the objective of the present study. The explanations for the
professionals, directly involved with the problems in the assembly lines, will come when
the information about the guiding conditions of the attrition coefficients in the fixation
elements were correctly specified and quickly obtained in the processes of production of
the suppliers. The study is limited to the more often used form of control for the attrition
coefficient that is the use of phosphate with a bath in lubricating oil. It was not made any
analysis regarding the variation of the properties of the several types of existent lubricating
oils in the market. Even the oil used in the tests was not described. The target of the study
was concentrated in the demonstration that the attrition coefficient can only be measured
through a statistical interpretation with the use of a test machine, advised by a computer
program that calculates the statistical parameters, indicators of the situation of the applied
phosphate or similar lubricant. Complementing the study, an analysis of the pieces checked