Metal working – Method of mechanical manufacture – With testing or indicating
Patent
1998-05-26
2000-04-11
Echols, P. W.
Metal working
Method of mechanical manufacture
With testing or indicating
173180, B23Q 1700
Patent
active
060474556
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method for simultaneous tightening of two or more screw joints by means of a nut running tool having two or more output spindles.
BACKGROUND OF THE INVENTION
A problem concerned with previous tightening methods for pretensioning two or more screw joints at the same time is to obtain a balanced and even clamping force build-up between the parts being joined by the screw joints. One such method is described in Japanese Patent Application No.: JP 900335746 (Publication No.: JP 4201022). According to this know method, all joints are run down in a first step to a seated condition. Thereafter, the pretensioning phase is started for all joints, and during an initial stage, the individual torque growth characteristics for the joints are determined followed by an adjustment of the rotation speed of each spindle so as to aim at a simultaneous arrival of the screw joints to the desired torque level.
This known method for tightening process control is disadvantageous an that it is too slow, not only due to the tightening process being carried out in two steps, but also due to the torque growth adaptation by speed adjustment being too slow. The control of the process is also insufficient due to the speed adjustment being carried out only once. This may be sufficient to obtain some compensation at ideal joints having linear torque growth characteristics, but will result in unacceptable differences in tightening time for reaching a common predetermined torque or clamping force level at joints having different nonlinear torque rates, i.e. different torque/angle characteristics. This in turn would result in an undesired uneven claping force application on critical machine parts like shaft bearing caps and cylinder heads of internal combustion engines.
Another drawback concerned with this and other known methods for simuitaneous tightening of two screw joints is the risk for damage to the equipment and injury to the operator in case one of the two output spindles loosens its grip on the screw head or nut being tightened, because if the reaction support for one of the spindles is lost the entire nutrunner is exposed to the reaction torque from the other spindle. This is a safety risk for the operator who has to counteract the reaction torque by muscle force.
SUMMARY OF THE INVENTION
An object of the invention is to create a method for simultaneous tightening of two or more screw joints by means of a nut runing tool having two or more output spindles, whereby a balanced and even clamping of the joint parts is obtained. According to one aspect of the invention this is accomplished by a tightening process wherein all spindles are operated according to a predetermined tightening strategy with respect to at least one primary tightening parameter from among rotation speed, output torque, angle, time, clampload and screw joint elongation. The instantaneous value of such parameter on each one of the spindles is continuously detected and compared with the instantaneous parameter value on the other spindles, whereupon the rotation speed is continuously adjusted on that one of the spindles on which the highest (or alternatively the lowest) instantaneous value is detected sio as to maintain the continued torque load on that spindle within a predetermined boundary in relation to that one of the other spindles momentarily having the highest (or alternatively the lowest) torque load.
According to an alternative aspect of the invention, the tightening process is carried out under detection of the instantaneous value of a primary tightening parameter on each spindle, and adjusting continuously the rotation speed of each spindle but one spindle to accomplish a tightening parameter value on the individual spindle that is equal to that of that one spindle, thereby accomplishing a fast and universally useful tightening method.
A further object of the invention is to form a tightening method for a two-spindle nutruuner by which the safety risk related to a lost screw joint grip is eliminated.
The invention is belo
REFERENCES:
patent: 4081037 (1978-03-01), Jonsson
Patent Abstracts of Japan, vol. 16, No. 534 (M--1334) AB Date Apr. 11, 1992 Pat: A 4201022 of JP 4-201022.
Atlas Copco Tools AB
Echols P. W.
Hong John C.
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