A
simple 1-2-3 process using force measurement techniques can differentiate
between an acceptable product and a reject.
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| Medical
tubing terminal pull-off ensures proper functioning in the field. Source:
Mark-10 Corp. |
|
There
are many ways with which to assess product quality, and these vary depending on
the item being manufactured. Typical parameters to check include physical
dimensions, chemical composition and hardness. One parameter of particular
interest to companies in virtually every industry is force.
When using products in everyday life, varying amounts of force are constantly
exerted on them. Similarly, these products contain numerous mechanical
components, each of which interact with and produce force on each other. In
order for one’s experiences using products to be pleasant, it is often critical
to perform force measurement testing to ensure the product performs to
expectations.
Three-step process
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| A
tension spring test yields force and deflection values. Source: Mark-10 Corp. |
|
Determining
if a product is good entails a simple three-step process:
- Understand what needs to be tested and
how.
- Obtain appropriate force measurement instrumentation. Subject samples
to standardized or internally developed test procedures.
- Analyze and interpret the results, using simple criteria or advanced
analysis software.
What needs to be tested?
 |
| A
typical wire terminal pull-off test performed in the wire harness industry.
Source: Mark-10 Corp. |
|
In
short, almost everything needs to be tested. Virtually every industry has
applications for force measurement. A selection of typical applications
includes:
- Automotive industry. Vehicles’ bills of materials typically
include many different types of springs. In a compression spring test, the
sample will typically be compressed to a specified height, and the force will
be measured at that point. The resulting relationship of force to displacement
is called the spring rate. A similar procedure is performed with tension and
torsion springs.
Vehicles also have many driver-operated
electronic controls, such as the turn signal stalk, buttons on the climate
control panel and knobs on the radio. A common force test is to press on the
control until it makes contact or snaps to its intended
position.
Other applications in the automotive industry
include door latch opening force, wire terminal pull-off testing and weld force
testing.
- Medical and pharmaceutical industries. In recent years, the medical
and pharmaceutical industries have adopted many stringent requirements for
quality testing, some of which are related to force measurement. One example is
medical tubing. When healthcare professionals use this tubing in the field, it
is essential that the tubing does not become disconnected from fittings and
devices. In order to prevent this from occurring, tubing is typically subjected
to terminal or connector pull-off testing. The force at which it disconnects
from the body of the tube is of crucial importance.
Sutures
need to be tested in the same fashion. When a surgeon has completed a procedure
and is using sutures to close a wound, he should be confident that the stitches
will hold long enough for the skin to heal. Manufacturers of sutures need to
test their products prior to shipping to ensure durability in the
field.
Other applications in the medical and pharmaceutical
industries include needle sharpness testing, catheter torque testing and pill
crush testing.
Force measurement instrumentation
|
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| Components
of a typical force measurement system. Source: Mark-10 Corp. |
|
Force
measurement instrumentation is generally quite affordable when compared to the
materials testing machines many quality professionals are familiar with from
their engineering classes or their company’s research and development
lab.
One of the most basic force measuring instruments is the electronic force gage,
a handheld instrument that integrates a load cell with electronics and display.
The gage will typically display force in units of pounds (lb), Newtons (N) or
kilograms (kg).
Force gages are typically used in conjunction with a manually operated or
motorized test stand. By regulating the speed of tests, test stands help ensure
consistency between tests.
Force gages and test stands are available in a wide range of force capacities,
reflecting the great number of different products that need to be tested.
Various grips and fixtures are available for use with these instruments, which
vary based on the sample being tested. Many force gages and some test stands
can output measurement data for further analysis.
Interpreting force data
|
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| Force
measurement software can help analyze the behavior of a particular product. Source:
Mark-10 Corp. |
|
Force
data can yield a wealth of information for quality assurance professionals. The
value of most interest in many testing applications is the maximum force, that
is, the force at which a sample broke, engaged or loosened. This ultimate
strength is often how companies gauge the performance of their product.
As important as the maximum force is, in many cases more data is desired. That
is where having the correct instrumentation and software is important. Force
measuring instruments are capable of providing a continuous stream of real-time
force data that can be output to a PC or data collector for further analysis.
Force measurement software can accomplish a number of goals for quality
professionals, including:
- Plot force vs. time or force vs. distance. Graphical force
data can be helpful in analyzing a sample and visualizing its behavior under
stress. The slope and behavior of a curve can be analyzed to yield such values
as the modulus of elasticity, modulus of toughness, resilience, yield point and
work.
Besides plotting real-time data for a single test,
software may be used to accumulate results from multiple tests in order to
provide statistical analyses of the production process for an entire batch or
lot.
- Statistical calculations. Values such as minimum, maximum, mean and
standard deviation can help quantify the quality of a
product.
- Data management. Data can be formatted into customizable reports that
include data in tabular and graphical format, or only selected data points.
Data export capabilities allows the operator to customize data presentation to
their needs through the use of programs such as Microsoft
Excel.
There are many reasons to consider assessing quality through force measurement.
Facility audits often require documentation for such testing. Government
regulations in some industries may also necessitate some testing. But even if
these factors were not present, it still makes sense to force test your
products.
This 1-2-3 process is a quantifiable approach to quality testing, enabling one
to make a well-informed assessment of a product’s quality. Use these techniques
so when the next time someone asks you how good your product is, you can say
with certainty that it is in fact “good.”