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Air gaging was first developed as a technique to measure automotive parts. The gage worked by sending a stream of air into a bore and comparing the resulting airflow to a fixed amount of airflow. Air gaging has changed over the years, but the principle remains the same. Modern air gages measure the backpressure while the old gages were known as flow gages. Modern approaches to air gaging take different forms. Here are some of the commonly used methods.

Back Pressure Bleed System

This is a versatile form of air gaging where the air gage has an air regulator to control incoming air pressure. The gage also has a second restriction where the operator can adjust for various air gage tooling and readouts. This is done by adjusting the air pressure to match the kind of tooling being applied at the moment. This system also has its magnification controlled by the restriction between the regulator and the air gage. The second restriction serves to calibrate the tool and helps to establish the tolerance range of the tool.

The advantage of the bleed system is that it allows this air gage to operate at higher pressures than most other systems. These air gages also last much longer than most other systems because the nozzles are situated further away from the measuring surface thus reduced wear and tear.

Back Pressure System

This is simply a variation of the bleed system without the second restriction. This lack of a second restriction severely limits the applications of this air gage. For accurate readings, this air gage requires tooling and amplifies with restricted ranges. For this reason, many manufacturing processes do not use this kind of air gage.

Differential System

This type of air gaging is also known as a balanced system where the air is split into two and moves through these two channels. One end has a zero valve which is used to balance the pressure on the second airflow which terminates at the air plug.  A differential pressure meter measures the difference between these two legs and the gage is usually set to zero. One of the drawbacks to this kind of tooling is that the single-master system has a fixed magnification. This means that any bad or worn-out tooling must be taken back to the manufacturer as this would have an adverse effect on the readings being taken by the tool. This kind of air gaging also has each amplifies accommodating only one full-scale value. For that reason, different tolerances require several amplifiers.

Flow System

As discussed, these were among the original air gage and worked by measuring the airflow variation in a tube which holds a float. Flow systems are fairly accurate as they work with a two-master system and the range of magnification can be adjusted by changing flow tubes. Flow gages require a larger amount of air and nozzle sizes generally vary from brand to brand.

Are you new to the term: air gaging? Firstly, you will need to know how gage is defined. It is basically a tool and service used to measure a physical quality. This means that the gage can be used in any scheme of quantity production interchangeably. In addition to measuring the contents of something, these gages also come with visual displays that output certain facts such as time. Secondly, we look at air gaging. This concept relies on a law of physics that states pressure and flow react inversely to each other and/or are directly proportional to the clearance. In other words, air pressure increases, and air flow decreases when the clearance decreases. Air flow increases and air pressure decreases when the clearance increases.

The
Birth of Air Gaging

Air
gages were first used in quality assurance programs in the late 1910s. After flow
meter instruments with operating pressures of 10 PSIG (pounds per square inch
gauge) were developed in the late 1930s, practical dimensional air gages
started to surface. During the 1940s, however, there was an increased
demand for tighter tolerances.

By
combining the power of computers and microprocessors, electronic pressure
sensors were instruments that drove the air gage display into the 21st century.
Compared to mechanical gages, air gages were significantly simpler and more
affordable to engineer. Oftentimes, these types of gages do not require linkages
to transfer mechanical motion. These unique features allow for the contacts to
be spaced at virtually any angle and very closely.

Which
Physical Qualities can be Measured via Air Gaging?

Below
is a quick look at the common physical qualities that can be measured via air
gaging:

• The definition of thicknesses
• A liquid’s flow pressure
• Diameters of materials
• Spaces between gaps

What
makes all these possible? You see, gages are instruments used to compare or
measure a component, as well as for dimensional control applications. In
addition to displaying measurement units on a digital monitor, the needles and
pointers work together by moving along a calibrated scale. By employing the
instrument in the sense that it has a fixed dimension, one can use it to determine
whether the size of one or more components exceed or is less than the gage’s
size.

Why
does Air Gaging Matter Today?

Due to
the accuracy of air gages, they are increasingly used in a wide range of
physical quality measurement applications. They offer adequate reliability and magnification
to measure small tolerances. The gages can also measure fluctuations in flow
rates and pressure (thanks to compressed air). In today’s time, tolerances on
the shop floor have gotten tighter. Many operators heavily rely on air gaging
to quickly and easily perform routine checks.

Understanding
the Overall Service Lifespan of Air Gages

It
goes without saying that the true value of a gage is measured by its service
lifespan and accuracy. Oftentimes, air gages are also subject to regular and
rough use. If you want to get an air gage that lasts, you will have to pay
attention to the product’s workmanship and materials used to manufacture it.

Repeatability
and accuracy form an inseparable pair in the world of precision measurement.
Although both terms share the same level of importance, repeatability has a
huge influence over the precision of a measurement. Read on to learn more about
the concept of repeatability and its place in the field of metrology.

An
Introduction to Repeatability

Repeatability refers to the degree to which consecutive measurements are taken successively under the same conditions. In other words, the concept informs technicians how close a series of measurements of a workpiece were when they were taken in a row with the same operator, tool, and machine.

It is useful to note that test-retest reliability is another term for repeatability. It involves re-measuring or re-testing an area or item and expecting to get essentially the same output. If the same measurement is not achieved, it indicates that the device or tool is not reliable. In this case, the operator has encountered variability issues. Variability can be caused by various reasons:

• Stability of the part that’s being measured
• Room temperature
• Operator’s skills and experience
• The measurement tool has not been properly
  calibrated

To
summarize what repeatable measurements are again; it is when operators get the same
values every single time the measurement is taken.

How
Important is Repeatability in Precision Measurements?

If you
gave measurements some thought, it will become obvious that it is often part of
a bigger project. Whether you are checking the standards, irregularities, size,
or alignment of a part, that part typically ends up a piece of a bigger end-product
that is going to be manufactured. Whether you are adjusting, cutting,
assembling, or machining a part, it will also be incorporated into that BIGGER
end-product.

While
measurements may seem like a small step in the creation of a final product,
machine, or device, the eventual manufactured piece will not be reliable
(contains irregularities) if previous measurements are not consistently the
same. That’s why operators and manufacturers need to achieve repeatability in
their measurements to guarantee quality in their products.

Repeatability
is a Stamp of Consistency

Oftentimes,
metrologists rely heavily on consistency for precision. That’s why they conduct
tests to guarantee, maintain, and check the repeatability of their
measurements. Below is how a typical test looks like:

• One part, environment, device, or person
  becomes the subject.
• The measurement device or tool is calibrated before commencing the test.
• The operator defines a set of constant
  factors, e.g. the amount of data to be collected, environmental conditions,
  method of measurement, the operator, the test date, and test equipment.
• Operator collects as much data as possible.
• Operator assesses the repeatability of the
  measurement process by analyzing an array of descriptive statistics.

With
that in mind, it is highly recommended that measurement facilities conduct repeatability
tests on a regular basis.

Combine
Repeatability with Accuracy for Truly Precise Measurements

Although
repeatability is highly important for precise measurements (in its own right),
one must remember to pair it with accuracy to achieve an ultimately precise
measurement.

Conducting
repeatability tests need not be difficult at all as one can consider consulting
with metrology experts, such as Willrich Precision. Whether you specialize in the
medical or aerospace industry, we have got your back.

Medical
implants need to be made from high quality orthopedic components so that they
can be used and kept by patients for as long as possible. This reduces or even
eliminates the need for additional surgical and non-surgical procedures down
the road. A good way to ensure the level of quality required is for orthopedic
device manufacturers to measure with high-precision air gages during the
product’s development and production phases.

Orthopedic
Device Manufacturing Challenges

Machining
and cutting are some of the individual manufacturing steps that must be consistently
stable in order to achieve precise orthopedic components that meet the necessary
high-quality standards. Oftentimes, as parts move through the manufacturing
process from raw materials to final products; geometric characteristics, surface
finish, and dimensional tolerance become increasingly critical.

Tight
tolerance is a dimensional characteristic that is often measured at the end of
the orthopedic device manufacturing process. It focuses on the tolerance on the
tapers that are used to match the components together. For example, most knee
and hip implants utilize tapers to enable optimal alignment and to secure (or
lock) the parts into position. During these processes, the control of both size
and taper will determine the performance of the orthopedic implants over their
service lifespan.

Air
Gaging: The Preferred Method

From
having the proper resolution to measure tolerances to having the right design
characteristics to fix parts together, today’s gages have to be robust when it
comes to manufacturing orthopedic implants. For many manufacturers, air gages
have become the inspection tool of choice for controlling such critical
parameters. Air gaging has proven itself to be an extremely precise measurement
method that provides very high resolution. It is now often used in applications
(e.g., precision medical tapers) where the tolerance tightness is less than
±0.001 in.

That’s not all as air gages are particularly well suited for checking dimensional relationships. They are easy to use, produce results quickly, and can last for years, even under the toughest shop conditions. One of the reasons why air gages are so useful for measuring orthopedic tapers is that they feature air jets, which are small orifices that emit air, and can be used to measure parts at the point of manufacture.

Common
Air Taper Gage Variations

Below
is a quick look at the different types of air taper gages that are used in
modern applications:

• Jam-fit style air tool: Considered the most common type of air gage taper tooling. It
  features two pairs of jets and is designed to create a jam fit between the tool
  and the part (on opposing air circuits). This tooling does not measure part
  diameters but showcases the two points’ diametrical differences on a particular
  workpiece.
• Clearance style air tool: Also known as a shoulder style air
  tool, this gage is used when an air taper ring
  cavity needs to be sized to accept the entire taper part. In addition, the air
  gage can be used to inspect for barrel and bell-mouth shapes, as well as
  measure diameters at known heights.
• Simultaneous fit air tool: The third gage is a cross between the previous gages; it is essentially
  a jam-fit air gage that takes references from the face of the datum surface
  with the aid of an indicator. It is often used to indicate how far an air tool
  goes into the part that’s being measured.

One of the biggest manufacturing industry trends today is the automation of inspection processes with the use of robotics. This trend is also expected to last for some time due to the decreasing costs of industrial robots, continuous innovation, and soon-to-have ability to inspect 100 percent of the critical dimensions of any workpiece.

Air gaging is also expected to continue evolving and remaining a relevant form of metrology in the modern, automated world. Some individuals might ask, “How would air gaging fit into automated and high production manufacturing environments?” “Isn’t it just used as a GO/ NO-GO gage to check for good and bad parts?” Well, not anymore.

Widely
Utilized in Automated Measuring Stations

Due to the changing demands of customer requirements in recent years, air gaging has evolved to the stage where it is now used in fully automated measuring stations. Today’s air gages can provide feedback to the machine tool for offsetting applications. Air gaging probes and rings, however, are some of the elements that have not changed much. They are mostly used to measure smaller diameters.

Control
units are now more advanced, and they are referred to as measuring computers,
columns, and comparators. These devices also contain features, such as RS232,
USB ports, Profibus, Ethernet, analog and digital inputs/outputs, among others.
These communication protocols allow for air gages to function in fully
automatic and semi-automatic measuring modes.

A
Typical Measurement Procedure

So,
how are these air gages set up and utilized in high production and automated
manufacturing environments? The gaging system is first calibrated, either
automatically or manually. For example, if the operator chooses the automated
way, a robot will load the MIN and MAX masters onto the gage. Once the masters
are loaded, the calibration process can be initiated with a programmable logic controller (PLC). Oftentimes,
calibration cycles are controlled either by using a manual trigger, a parts
counter, or a timer. In addition, calibrations are typically performed one time
per shift. Some technicians, however, may require it much more frequently.

Understanding
Measurement Cycles of Workpieces

Now that you get the gist of calibrations, the current focus will be on measurement cycles. For starters, the process is pretty similar where the robot loads the workpiece onto the gage before signaling the start of the measurement. The robots will then “listen” to the control unit to determine if the part is good or bad and sort the parts according to the information. The great thing about this is that the control unit will report offset values back to the machine so that adjustments can be made automatically, without human intervention!

One Setup for One Diameter Measurement

It is
important to note that this setup can only be utilized to check one diameter.
If one needs to measure several features, he or she must set up multiple
stations for the robot to “pick and place.” It is also a good idea to
integrate tracking serial numbers via a data matrix engraved on the part. This
allows for the measurement data of each individual part to be recalled or
stored at any time.

Plenty
of Room for Integration

Air
gages no longer just measure outside and inside diameters. They are now used to
measure flatness, runout, parallelism, taper, perpendicularity, and many more. It
goes without saying that the capability of air gages will continue to grow rapidly,
and quality professionals will want and need more room for integration in the
near future.

Air gaging is one of the common ways of
measuring all manner of shapes and items in a machining environment. Being air-based,
it provides a quick, clean, and easy way of measuring dimensions. It is very
effective in gaging irregular shapes and the fact that it is non-contact makes
air gages durable.

How
Air Gaging Works

Air gaging works by measuring the air backfill when a jet of air hits the surface of the object being measured. Air gages generally work on the principle of streaming a jet of air from nozzles into the surface that is being measured. When air hits the surface and bounces back, the gage is able to give the operator various readings of the surface being measured. Air gages come in all manner of sizes and types but all work on the same principle. Popular as this type of gaging is, it has some drawbacks which an operator has to be aware of when using it to measure surface dimensions.

Surface
Dimensions

The accuracy of air gaging can be affected by the surface of the object being measured. This is based on the principle that the measurement points of an air gage are really the sum total of the surface peaks and valleys. The magnitude of these can give different readings if you took the same measurement with a contact type gage.

Air
Backfill

This problem arises from the fact that
measurements are taken based on the back stream of air from the jets after they
hit the surface being measured. This means that if the process is hurried,
there is always a risk that inaccurate measurements will be taken. This sort of
inaccuracy is far more likely to happen in situations where rapid measurements
are being taken such as in an industrial process.

There are several ways to counter this and
one of the common ones is to ensure that not all air is expended from the
airways when moving from one measurement to another. This way, the backfill
takes a shorter time and measurements taken are more accurate. The other cause
of inaccuracy caused by air backfill could be that the air gage is using very
long air hoses which take time to fill up. In such a case, this can easily be
fixed by reducing the distance between the air gage and the part being
measured.

Damage
to Gage

Air gages generally suffer little surface
wear because they are a non-contact type of gage. Even if this is true, there
is still some level of contact between the gage and the part, especially if the
gage is continually used over the years. This contact can damage the nozzles of
the jet and this can affect the accuracy of the tool. One of the best ways of
fixing this is to re-orient the tooling periodically in order to move the worn-out
parts around.

While air gages are remarkably versatile
and easy to use, they also have various limitations which can affect their
accuracy. Being aware of these limitations is a great first step toward getting
more out of your air gage.

A vernier caliper is a measuring instrument
that can measure the internal and external dimensions of an object. These
useful instruments can also measure object depth. Vernier calipers have a jaw
that is fixed and one that moves along a well-calibrated scale. This moving jaw
is capable of measuring accurately to within a hundredth of a millimeter. Vernier
calipers are popular due to their highly accurate measuring capabilities. Here
are some of the applications that these highly popular instruments are used in.

Machine
Shops

One of the places that you are likely to find a vernier caliper is a machining shop. Most industries that make precise components, such as the auto industry and the aviation industry, use vernier calipers to ensure consistency in the parts that they produce. To use the car industry as an example, the springs that are produced by the auto assembly factory must all be very precise otherwise the car will be unstable. Vernier calipers help ensure consistency of parts in such industries.

Medical
Instruments

Industrial processes that produce medical
equipment must also adhere to very precise measurements. It means that quality
control experts in such manufacturing processes must measure precise dimensions
of parts produced and ensure that all of them adhere to these standards.
Mistakes in length or depth of some of these precise instruments would
inadvertently lead to injury and even loss of life.

Research
Applications

Research laboratories make use of vernier
calipers to understand the effect of heat and other reactions on the elements
that they are testing. Many research processes seek to understand the effect of
certain reactions and one of these reactions is expansion or contraction of the
test pieces. When researchers need to understand these effects at very precise
dimensions, they use vernier calipers to measure the test objects before and
after the reactions.

Locksmithing

Locksmithing involves working on very
precise locking mechanisms. For example, designing safes requires parts to
interlock in very precise patterns and this requires that these parts are
measured to very precise dimensions. For this reason, locksmiths and safe
makers use vernier calipers to ensure that the parts they are making adhere to these
standards. Keys that are used to open locks and safes must also be very
precisely tooled and vernier calipers are immensely useful in ensuring that
they adhere to the required standards.

Educational
Institutions

Another place where one is likely to find
vernier calipers in use include colleges, universities, and schools. Here,
vernier calipers are used to help students perform science experiments and work
as a teaching aid for various subjects.

When all is said, getting high-quality vernier calipers and using them properly is a first important step to getting the most out of these important instruments. At Willrich Precision Instrument, you are guaranteed a wide range of high-quality vernier calipers that can be used in all these applications and more.