Ensuring quality assembly of threaded fasteners begins with proper setup of the assembly tools and may include periodic testing of the tools on the assembly line, torque audits of assembled fasteners, and the capability of testing and analyzing fasteners if problems arise. These efforts should begin with an understanding of the behavior of individual fasteners, recognizing the interaction of the material properties of the fastener, clamped components, and internally threaded components, as well as the influence of coatings, lubricants, and adhesives on the performance of fasteners in bolted joints.
The following tests are typically conducted in the fastener assembly area:
Power Tool Setup -
In many assembly applications threaded fasteners are tightened using a pneumatic or electric power tool. Beyond normal maintenance considerations, setting up a power tool for an assembly operation involves adjusting the tool and its controller (if outfitted) to run at a particular speed and shut off when a specified torque is reached. In the case of a torque to turn tightening strategy, it may also be necessary to set up the tool to shut off when a specified angle of turn is reached. Some modern tools, especially newer DC electric tools, may be outfitted with an internal torque sensor and angle encoder. The setup of the tool can be confirmed by running a series of tests on the tool using an external rotary torque or rotary torque-angle transducer and torque analyzer. A useful option is a joint simulator that can be adjusted to simulate the type of joint on which the tool will be used.
Performance Verification -
Once a tool is installed on the line, it may be necessary to verify its performance on some periodic schedule, such as once an hour, once a shift, once a day, once a week, etc. This can be easily accomplished using a rotary torque or torque-angle transducer and a portable data collector. A series of runs can be recorded and compared to the initial setup. In this way, the tool’s performance can be confirmed and continued quality assembly ensured.
Post-Assembly Audits -
After the fastener is tightened it may be desirable to audit a sample of the tightened fasteners to ensure that the proper amount of torque was applied. This is done using an electronic hand torque wrench and a data collector whereby the operator applies just enough torque to get the fastener to turn. This peak torque is compared to the assembly specification to determine if the fastener was tightened acceptably or not. Some advanced post-assembly audits may include angle measurement or the patented M-Alpha analysis.
Hand Torque Wrench Calibration -
Many assembly operations are completed using a hand torque wrench with a mechanical “click” feature that releases the torque momentarily when a certain level is reached. To verify that this “click” point is accurately reached, it can be tested using a stationary torque transducer and data collector. The transducer measures the torque and the data collector determines the point at which the wrench “clicked.” Testing the wrench in this way lets the operator adjust the tool for best performance.
Products and accessories specifically for use in all of these fastener assembly tests, including:
- Rotary Torque Transducers, Series PC9000
- Hand Torque Wrenches, Series HT7000
- Hand Torque-Angle Wrenches, Series HTA7000
- Stationary Torque Transducers, Series ST7000
- Force Washer Transducers, Series FT4000
- Portable Peak Meter, Model 910
- Portable Digital Transducer Instrument, Model 920
- LabMaster Portable, Model 3210
- Joint Simulators, Series JS2000
- Portable Digital Recorder, Model 962