For automated assembly line processes, consistency and quality control are key. Depending on how products are assembled, it may not always be straightforward to rectify issues with earlier stages of the manufacturing process. This can then result in expensive and time-consuming delays.1
To avoid these issues in automated industrial processes, one approach is to use built-in sensors as part of the manufacturing process. For many applications, including automotive assembly, one obvious use of sensors for quality control is the inclusion of torque sensors for fastening tools.2
The Right Torque
Tightening bolts and nuts to the correct torque settings ensures optimum performance and lifetime of components. Too little torque and bolts can vibrate, and in the worst case, come loose, damaging components and with obvious safety risks. Too much torque and then risks include both shearing of the bolt, which wastes both material for the bolts and potentially destroys the threading in the component, or, even if the bolt withstands the additional force, this can lead to greater component fatigue and earlier failure. The risk with incorrect torque settings is not just to the bolts themselves – where bolts are used to hold together flanges for fluid systems, excessive or insufficient torque on the bolts joining components can result in damaged gaskets or leaks.3
For automated processing, torque settings can be checked either through a post-assembly audit, where bolts are individually checked or through sensors that are built-in for use with torque wrenches. As audits can be a lengthy and time-consuming process, online sensors that can be connected to data logging and monitoring are an appealing alternative and the same sensors can also be used to check tool calibrations and fluctuations with time.4
Inclusion of torque sensors is also important for meeting certain calibration standards. For example, some industries require products to have been manufactured in such a way that meets calibration standards (such as the ANS/ISO/IEC 17025:2005 and ANSI/NCSL Z540.3-2006) which require torque verification and monitoring systems to be in place alongside tool calibrations.5
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Depending on the desired application, torque sensors may need to be designed very differently. For example, for crankshaft pulleys in engines that require large amounts of torque, then strain-gauged based torque sensor designs may be most appropriate. These are very often highly cost-effective sensors and can deal with very large loads. For other applications where extreme precision is required, piezoelectric based sensors have excellent sensitivity and their high stiffness makes them preferable for dynamic applications.
HITEC Sensor Developments
As choosing the ideal sensor for the application is crucial, it can be highly beneficial to work with a company that has many years of experience in both conventional and custom sensor design. HITEC Sensor Developments have 85 years of combined experience in providing just this and are world leaders in the areas of force measurement and sensor design.6 HITEC Sensor Developments have a substantial portfolio of products, spanning many types of vehicle test sensors, load cells, and torque sensors. Within their torque sensor range, they offer numerous designs including an ultra-light torque sensor 7 and pulley torque sensors based on a cogwheel design, ideal for where traditional detachable pulley gears cannot fit due to space requirements.8 For these sensors, the size of the cogwheel and sensor specifications are all fully customizable.
At present, HITEC Sensor Developments torque sensors are widely used in the automotive and paper mill industries. Their strain gauge sensor range is used for torque measurements for diesel engine bolts, where the ability of the sensor to have compensated temperature readouts at engine operating conditions of 350◦C helps to ensure always accurate torque measurements.9 Here, the torque sensors, based on a robust strain gauge design, can be applied directly to a bolt, so that when the fastener is used the resulting force can be easily recorded, also making it straightforward to calibrate fastening tools.
Another sensor line that is ideally suited for use with fastening tools in manufacturing are the socket sensors line.10 These are very straightforward to integrate into fastening tools and suitable for use with torque loads ranging from 25 to 7000 ft-lbs. They have excellent hysteresis of 0.1 % of the full specification operating conditions. Carefully crafted from alloy steel, the socket sensors have an elastomer coating to protect against mechanical damage and have temperature-compensated outputs spanning from 70 to 170◦F. These are based on full, four-arm Wheatstone bridge circuits and can come with SDI connectors for interfacing the sensors with either a single data-logging computer or networked infrastructure for monitoring and refining manufacturing processes.
As part of their service, HITEC Sensor Developments offers an extensive support process, including a review of the initial application and suitability of product, along with installation and calibration if required. For certain applications, protective coatings may be used to improve sensor durability and lifetimes. All of this and their in-house knowledge for custom design applications mean that HITEC Sensor Developments offers the best service in the market for bespoke and standard torque sensors for industrial automation.
1. Son, Y. K. (1991). A cost estimation model for advanced manufacturing systems. International Journal of Production Research, 29(3), 441–452. https://doi.org/10.1080/00207549108930081
2. Tlusty, J., & Andrews, G. C. (1983). A Critical Review of Sensors for Unmanned Machining. CIRP Annals – Manufacturing Technology, 32(2), 563–572. https://doi.org/10.1016/S0007-8506(07)60184-X
3. Sears, G., & King, D. (2004). Joint integrity management of critical flanges. International Journal of Pressure Vessels and Piping, 81(6), 513–519. https://doi.org/10.1016/j.ijpvp.2003.12.021
4. Mendoza, M., Mendoza, M., Mendoza, E., & González, E. (2015). Augmented Reality as a Tool of Training for Data Collection on Torque Auditing. Procedia Computer Science, 75(Vare), 5–11. https://doi.org/10.1016/j.procs.2015.12.186
5. Calibration Standards (2019), http://www.ncsli.org/i/i/sp/z540/z540s/iMIS/Store/z540s.aspx?hkey=ebe5ca19-e0f7-4c5c-a6dc-70121c857d05
6. HITEC Sensors (2019) https://www.hitecsensors.com/about-us/history/
7. Ultralight Torque Sensor (2019) https://www.hitecsensors.com/sensor_products/reaction-torque-sensors-ultra-light-torque-sensor-01040/
8. Cogwheel Torque Sensors (2019) https://www.hitecsensors.com/sensor_products/torque-sensors-cog-wheel-01034/
9. Applications (2019) https://www.hitecsensors.com/applications/automotive/
10. Socket Sensors (2019) https://www.hitecsensors.com/sensor_products/reaction-torque-sensors-socket-sensors-01190/
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