Six Common Fastening Faults

This fault usually occurs as a result from the fastener, when it is driven in at an angle, causing incorrect thread engagement. A smart screwdriver with slow start function, can be programmed to rotate slowly at the beginning of the rundown, assisting with correct thread engagement. Simultaneously, it will also detect a crossed thread via the inbuilt angle encoder, usually signified by an error signal. This can be something like: “exceeds max angle” and rejected with a “Not OK” signal.

When the screw holes of mating parts are misaligned, and only a section of the bottom screw hole is exposed, the screw will bind-up because the bottom screw hole is undersized. This causes the fastener to reach torque before the screw has correctly seated and clamped the product together. A smart screwdriver (with the prevailing torque function), will apply the full power of the screwdriver during the rundown phase, then return to the programmed torque for the final seating of the fastener. Applying full power will pull the misaligned parts together, and the final seating torque will ensure the parts have been correctly assembled. Alternatively, an angle-monitoring process could be implemented and programmed to detect the misaligned parts. Usually the error signal “exceeds maximum angle” and rejected with a “Not OK” signal.

Damaged threads increase friction and if the prevailing torque is higher than the final seating torque, the screw will reach torque before it has seated correctly. A smart screwdriver with the prevailing torque function, will apply the full power of the screwdriver during the rundown phase, then return to the programmed torque for the final seating of the fastener. Full power will overcome the friction between the threads, and the final seating torque will ensure the part has been correctly assembled. Alternatively, an angle-monitoring  process could be implemented and programmed to detect the damaged threads. Usually, the error signal “exceeds maximum angle” and rejected with a “Not OK” signal.

An oversized screw fault, is usually associated with the quality of the fasteners. Oversized screws maybe caused by inconsistencies in the plating process, burrs on the thread, or wear on the tooling during manufacture etc. The process to overcome this problem, is the same as fasteners with damaged threads. An oversized screw increases friction and if the prevailing torque is higher than the final seating torque, the screw will reach torque before it has correctly seated. A smart screwdriver (with the prevailing torque function), will apply the full power of the screwdriver during the rundown phase, then return to the programmed torque for the final seating of the fastener. Full power will overcome the friction between the threads, and the final seating torque will ensure the part has been correctly assembled. Alternatively, an angle monitoring process could be programmed to detect the oversized screw. Usually, the error signal “exceeds maximum angle” and rejected with a “Not OK” signal.

Parts can become out of tolerance for a variety of reasons. For example, worn press tools or moulds, worn drills, change in material composition, or process changes etc. The process to overcome this problem is the same as fasteners with damaged threads. Undersized screw holes increase friction and if the prevailing torque is higher than the final seating torque, the screw will reach torque before it has correctly seated. A smart screwdriver (with the prevailing torque function), will apply the full power of the screwdriver during the rundown phase, then return to the programmed torque for the final seating of the fastener. Full power will overcome the friction caused by the undersized screw hole and the final seating torque will ensure the part has been correctly assembled. Alternatively, an angle monitoring process could be programmed to detect the undersized hole. Usually, the error signal “exceeds maximum angle” and rejected with a “Not OK” signal.

Sometimes, there is a fine line between achieving the correct tightening torque and damaging the product. Cracked or split parts due to overtightening is an insidious problem that can easily go unnoticed until the screw is removed. Under closer inspection, there may be a crack or split around the screw hole. A smart screwdriver with accurate torque control will assist in achieving repeatable, fine torque tolerances. If the part does crack or split, the error signal “exceeds maximum angle” and rejected with a “Not OK” signal will be displayed on your smart screwdriver.