System solutions for conductivity and mechanical performance in grounding joints
PART 2
Now that we understand the important relationship between conductivity in the joint and mechanical performance, it is also important to understand how correct installation and ongoing joint performance can be achieved. Traditional methods have been unable to reach the high expectations of reliability emerging in the railway industry, with failed installations and poorly optimised joints commonplace.
Based on requests from a number of OEMs in the rail industry, Howmet Fastening Systems (HFS) based in Kelkheim, Germany have undertaken significant research and developed a system that addresses the weakness of traditional systems available in the marketplace.
The aim of the new system is to mitigate risk for OEMs in the rail and other industries where electrical short-circuit events are a concern.
As discussed in Part 1 (link) the system should achieve:
- The required level of conductivity appropriate to the short circuit event risk.
- The mechanical performance required to guarantee the long-term performance of 1).
The system must ensure the correct installation for all these combinations but also the quality feedback and quality documentation capabilities.
The resulting system consists of intelligent automated installation tooling, a barcode scanning and documentation function, and specially designed grounding studs and nuts, as well as a repair system for failed installations.
The article will explore the benefits of the Cam-Safe system in the context of reliably and consistently achieving the aims above.
Earthing or grounding is very much a safety concern for people and equipment. Today the trend is towards full control of components, processes, traceability, and documentation to comply with increasing quality regulations and auditing processes. It is no longer enough to provide a good process: the supplier must be able to demonstrate correct installations through continuous testing and documentation.
Cam-Safe mitigates the risk of earthing failures by:
- Improving installation quality
- Supporting quality management
- Documentation of installation success (traceability)
- Increasing installation speed and improving ergonomics
Improving installation quality
There are a number of different types of failure that can result from a poor installation process.
From a quality perspective poor installation resulting from misalignment is one of the major risks but can usually be detected easily by visual control. For misalignment issues the required installation force has usually been correctly applied, but incorrectly controlled (by tool or user).
This creates uncertainties in terms of torque resistance, correct contact pressure in the borehole, tightness, moisture access during operation and increased corrosion risk. The consequence is a lengthy rework which requires extra time and cost.
Another common problem is when the required installation force has not been applied. This is common with manual installation systems. Unfortunately this failure type is not visibly discernible and is traditional difficult to identify. The recommended solution is to calculate the performance using a second parameter: torque resistance. When the required torque resistance is achieved, the press fit into the borehole (as a function of the installation force) must be ok, too.
The Cam-Safe system provides a quick, single-step operation without the need for hand force and manual user control. The process is more operator independent; the operator has much less influence on the outcome. Therefore, the risk of misalignment is reduced.
The Cam-Safe installation tool has a high-resolution force sensor which measures for each installation both force and stroke. The software compares the measurements with predefined target values and gives the operator immediate feedback whether the values are met or not.
The combination of both stroke and force gives a distinctive set of parameters based on hundreds of real-life installations to account for varying installation configurations and environments.
All values can be customised to adapt the process to specific needs and requirements.
Examples of display configurations, available in different languages.
Force control and stroke control (windows). Customized measurements.
Immediate worker feedback for each single installation.
In the rare case of a failed installation the Cam-Safe system offers a repair solution where the fastener can be replaced to create a fully performing joint.
Supporting quality management
To back up the reliable installation process that the Cam-Safe system offers it also provides a fully functioning bar code system which can be assigned to a variety of sheet metal material and grounding stud configurations. When scanning the barcode on the fastener packaging the relevant installation parameters (stroke, force and time) are loaded to the tool, ready for installation.
Each installation can also be personalized to the user (when accepted by the union) or to a relevant workorder or product batch.
When a bad installation occurs, it offers an optional function to lock the tool until a supervisor scans a second barcode once the root cause of the problem has been identified. This means that every fault indication must be understood and corrected before production can continue.
Documentation of installation success (traceability)
Once the data has been captured throughout the course of production the installation history data can be exported from the tool to a PC via a USB connection.
For each installation the achieved force and stroke values are recorded as well as the OK or NOK status. Additionally, the date, time and associated barcode information for each installation is saved automatically by the tool.
In cases where further investigation of individual installations is required each can be selected and evaluated as shown in the following graphs.
Force control graph is shown (left) alongside stroke control (right).
In the unlikely event the quality of an installation or batch is uncertain then the data can be recalled as documented proof of successful installation.
Increasing installation speed and improving ergonomics
In addition to ensuring a performing joint, the installation process is also quick and easy, enabling efficient and fast assembly of grounding joints.
In contrast to the traditional manual hand installation tools the Cam-Safe intelligent tool has been designed to handle well and enable the operator to quickly and consistently execute the installation process.
The traditional hand method is an operator reliant, multi-step process, relying on repeated hand force actions which is both slow and requires a certain amount of skill and training. Slow cycle time can lead to errors and misalignment which creates the need for additional quality checks and in worst-case time-consuming rework.
The Cam-Safe tool by contrast offers a much shorter cycle time, which is beneficial for production in terms of both speed and quality. With the Cam-Safe battery driven installation tool the installation time can be reduced by approximately 70% for the complete process, including component handling. The setting itself is up to 10 times quicker (2-3 seconds) than a hand installation.
Based on a volume of 1000 installations per day the assembly time saving could be up to 8 hours.
Conclusion
The Cam-Safe system has been designed from the ground up to provide reliable and performing grounding joints time after time.
It addresses the industry driven need for reliable, provable (documented) joints than can be relied upon to deliver the correct level of conductivity at all times, and with mechanical performance to withstand the demands of the application.
To find out more about the Cam-safe system or to speak to an expert click here.
