Computers and software play a major role in force measurement and quality control. Whether in the engineering lab, quality control inspection area, receiving inspection, or on the production floor, the use of computers and measurement software is beneficial to product quality and production efficiency.
But with computers and application software comes a variety of ongoing support requirements, often involving IT personnel, and ranging from ensuring the current software drivers have been installed, to operating system updates, to security requirements that prevent unauthorized modifications, to test setups and measurement results.
Modern force measurement systems need to meet the exact requirements of research scientists, design engineers, quality managers, and the technicians responsible for material characterization, verification, and validation of products.
Product functionality in force gages has expanded greatly in the past 20 years. Gages can now detect break forces, or can be used for averaging forces and determining measurements such as coefficient of friction. Force gages have an inherent benefit in that their software is embedded. While provisions are still necessary when software updates are made, the demands on resources and the effects of external issues are generally much less of a concern. In many organizations, the use of force gages in lieu of computers and measurement software is preferred both from a usability standpoint and because these well-known and proven instruments are cost-effective and application-specific. And while force gages may have specific capabilities compared to the versatility that computers and application software have, they continue to be extremely reliable and their functionality is continually evolving. Compared to computer software-based systems, force gage systems are significantly easier and less costly to maintain with a high degree of security against unauthorized changes, viruses, malware, etc.
Automated testing, such as using a force gage with a digital force testing frame, has been commonplace in a wide range of modern manufacturing applications and industries. When working with a high volume of samples, automated testing reduces operator-to-operator error, saving time and repetitive work. In this scenario, the force gage is set up to measure the maximum force (peak force), or to measure and display the force result after the test frame's crosshead has moved for a specified distance. The user configures the force gage and the test frame independent from one another. At the completion of the test method, the test frame may display the active crosshead travel and current speed, and the resulting distance.
Handheld Force Gages
A handheld digital force gage can be a budget-friendly solution for basic testing applications, providing quick data such as real-time load, peak load, load averages, and even coefficient of friction.
Q. “If I pull or push at different angles, will it impact the data being collected?”
A. Some applications will have a more significant impact than others.
Some necessitate a portable device to test the ergonomics of push/pulling on a door or cart.
Simple snap closure or foil puncture testing is forgiving and can be performed reliably by hand.
For applications such as insertion and extraction, a handheld gage coupled with a mechanical stand adds a degree of reliability. The mechanical advantage is that a lever or hand-wheel-style stand allows for higher force. For more complex measurements, add a linear scale or an entry-level spring tester to these testers.
Communication between the force gage and test frame is typically via RS-232. The gage and test frame may require a communication protocol setup such as baud rate, word length, stop bits, etc. Mechanical travel limits are used on the test frame to help prevent accidental overloading of the force gage's internal load cell sensor. At the conclusion of the test, the user reads the force results on the gage and the distance result on the test frame.
Often, the independent results for force and distance need to be manually combined and used later in a separate application for reporting, such as merging data from two sources into an Excel® spreadsheet. So, while the force gage-force tester represents a fairly simple system configuration, there are a variety of pre-test setup requirements and post-test activities involved, leaving a risk of incorrect setup or problems with data integrity.
Ensure Data Integrity
Solutions are now available that extend the traditional force measurement functionality of a force gage. Ensuring data integrity is critical for industries such as medical, aerospace, and automotive where there are strict requirements for capturing data and maintaining testing records. Some force gages function as both a force gage and as a controller for digital force testers. With this technology, the user only needs to set up the gage since the gage has built-in testing templates for common force measurement test methods. Users can perform load limit, distance limit, and break limit testing. Within each test method, the user specifies the digital force tester functionality by using the gage. The user specifies the direction of crosshead motion, the crosshead velocity, and functions such as automatic zero of both force and distance prior to the actual testing, as well as automatic return to zero position once the test has concluded.
These gages also display both the force measured by the internal load cell sensor as well as the crosshead distance traveled during and at the completion of the test. When setting up the gage to perform a distance limit test, the gage is used to enter the distance limit and test velocity. The test is started by pressing a key on the gage. During the test, the gage displays the active force and the active distance in SI units of measure or imperial. The target set point limit is displayed so the operator knows the status of the test. At the end of the test, the gage displays both the load at the target distance and the distance. If a tolerance limit is used for pass/fail indication, the gage result is shown in red text, indicating a failed result. If performing a break limit test, the gage will display the maximum force and the distance at maximum force for the break event.
Motorized Force Testing Stands
For applications requiring more control, precision, and comprehensive computation, motorized force measurement stands are optimal. Versatile solutions can enable the user to mount on the stand a handheld force gage that functions as a controller.
Q. How will speed impact my testing and my data?
A. There are different considerations. For example, plastics such as low- and high-density polyethylene, thermoplastic elastomers (TPE), and thermoplastic urethanes (TPU) all react very differently under varying speeds. This is especially true for elongation, a measure of a sample's stretch before breaking. In these cases, a motorized stand has consistency from operator-to-operator by ensuring the same speed each time.
Look for options to create your test methods quickly using test templates (see screen of template above) that guide you through the test setup process, such as the following example. Consider a test setup with a clean fill-in-the-blank test stage where the testing requirements are specified — what load you are using, what distance your crosshead will move, and how fast your test speed is. Plus, you can easily add “exceptions” — events that can be used to automatically stop your test, if they occur.
The force gage also allows results to be saved to memory for export to a network device, such as a computer running ProLink® QC Calc statistical process control software. Bluetooth® technology in the gage also enables wireless data transfer to a device.
There is certainly a place for computer software-based systems for force measurement and analysis. These systems offer test method flexibility, analysis, and reporting. But they also require a higher-level support than force gage-based systems. Now, with new force measurement solutions, a range of applications can be addressed from load limit and distance testing, to break limit, time average, cyclic count and duration testing, constant hold, and more. Optimized for production and quality control testing, the versatile, innovative architecture of these systems is designed for reliable, fast, repeatable, and easy operation. Users get the performance of a computer software-based system without the concerns and support requirements often associated with traditional systems.
This article was written by James M. Clinton, Product Manager for Force and Material Test Products at L.S. Starrett Company, Athol, MA. For more information, Click Here.