A GUIDE TO SCREWDRIVING SYSTEMS
Modern screwdriving systems increase efficiency while also optimising quality processes and reducing costs. But where are screwdriving systems used? Which modern screwdriving methods are available? We explain everything here.
Modern screwdriving systems are used in the electrical, timber and aviation industries as well as in the e-mobility sector, in mechanical engineering, telecommunications and in household appliances and medical devices. The automotive industry and car body construction are the largest area of application for WEBER.
https://www.weber-online.com/en/screwdriving-technology-for-automotive-and-body-construction/
Maximum reliability and permanent connections or detachable individual parts are key elements in the manufacturing of car bodies. This requires screwdriving systems from professionals, because the materials requirements are high. The required fasteners have to be lightweight, strong and cost saving.
This used to mean: welding. Modern production is different, though. Professionals today use automated screwdriving systems – highly flexible, very reliable and with an error rate that moves towards zero. In addition, the products are easier to dismantle and recycle at the end of their life cycle. How does it all work? Our guide offers insights.
Michael Steidl
Head of Product Management
Reliable assembly processes are the core competence of modern screwdriving systems. Industrial customers want high-quality processing of fasteners for their expensive goods. With the highest quality benchmarks and optimised cycle times, screwdriving systems ensure thorough, reliable and fast joining of individual parts. Advance test parameters help to avoid product recalls.
The top priority of a screw connection is to join two or more components – in the correct way: In the end, they have to act as a single component. The required clamping or pre-tension force has to be generated accurately and reproducibly. Different screw connections require different pre-tension forces. These are determined in advance so that all parameters for the screwdriving systems are correct. The objective here is to apply the calculated pre-tension force as accurately as possible, because precision work results in a reduction of materials and costs.
Rudolf, 1992
Here, we give you an overview of the 4 most common screwdriving processes:
For screwdriving to depth, on timber connections for example, the head of the screw is countersunk.
Diagram of a screwdriving curve for screwdriving to depth
Rudolf, 1992
The objective of torque-controlled screwdriving is to tighten the screw to a pre-tension force below the yield point. The screw is tightened until a preset torque has been reached. Then the screwdriving unit is switched off. For most of our customers’ applications, we use torque-controlled screwdriving.
Diagram of a screwdriving curve for screwdriving to torque
Rudolf, 1992
For angle-controlled screwdriving, the screw is tightened until it reaches the plastic range. The screwdriving process starts with tightening of the screw until the pre-defined threshold torque (M) has been reached. This is when the angle measurement starts. The screwdriving unit is switched off when the pre-defined rotation angle has been reached.
All calculations concerning angle-controlled screwdriving have to account for any – including extreme – weather conditions, temperature fluctuations and signs of wear in advance.
Diagram of a screwdriving curve for screwdriving to rotation angle
Rudolf, 1992
The objective of the gradient screwdriving method is to tighten the screw to just before the yield point is reached. The switch-off here occurs based on a falling gradient, not on a torque or angle. The controller continuously calculates the gradient from the torque increase per rotation angle. The screwdriving process stops when the gradient falls by a pre-defined percentage of the maximum.
This screwdriving process is still in its early days. This process could only be developed with powerful screwdriving process controllers with reaction times in the millisecond range.
The advantage of this method is the highly precise shut-off just before the yield point is reached. This eliminates friction in the thread as much as possible.
The drawback is that the shut-off torque can have a large spread depending on the application. This often poses a problem for traditional quality assurance.
Diagram of a screwdriving curve for screwdriving using the gradient screwdriving method
Rudolf, 1992
Selecting the best screwdriving method is essential for the result. We are always working on improving our process quality and are always available for questions on screwdriving systems.
https://www.weber-online.com/en/fixtured-screwdriving-systems/
A handheld screwdriver is manually operated by just one person. Handheld screwdrivers are used when the screw connection has to be flexible and the number of elements to be joined is between 20,000 and 50,000 per year.
More information on different handheld screwdrivers can be found here: https://www.weber-online.com/en/handheld-screwdrivers/
For non-manual stationary screwdrivers, the screwdriving unit/spindle is attached to a robot. Stationary screwdrivers are used for high quantities (> 50,000 fasteners/year) and short cycle times. In contrast to handheld screwdrivers, they offer a reliable process: The screw depth monitoring function can be used to accurately calculate how deep the screw has already been installed. This also avoids tilted positioning of the screws.
Find an overview of our stationary screwdrivers here: https://www.weber-online.com/en/fixtured-screwdriving-systems/
In many applications in automated screwdriving, there are locations that are hard to reach. This is where vacuum screwdriving systems come into play. The screw is aspirated through an intake hose. Negative pressure is generated in this hose. A screwdriving head with a hose adapted to the application ensures that the fastener is reliably positioned exactly in the right place, even if it is hard to reach.
The swivel arm is a key functional element of the screwdriving process. A screw is blown towards the screwdriving head in the swivel arm. The screwdriver moves the swivel arm sideways into the correct position. The next screw is already fed into the swivel arm while the first one is being installed. The swivel arm is released as soon as the screw has been positioned and screwed in. This allows it to return to its original position and the process can start again.
The swivel arm is consequently a very time-saving element of modern screwdriving systems.
Due to the currently predominant requirements in the industry, EC servo motors have become established in modern screwdriving systems. With regard to durability and precision, it is the best solution among current drive systems.
Rudolf, 1992: Rudolf, H.: Schraubtechnik. Grundlagen, Schraubsysteme, Anziehverfahren. Die Bibliothek der Technik. Landberg: Verlag moderne Industrie 1992.
