Production Machining Article January 2009

Measurement Technologies Step Up to Production Machining Needs
The increasing capabilities of high-production turning equipment such as Swiss machines have also
raised expectations for inspection technology. Determining the best solution requires a close look at
the application and the needs of the end user.
Article from: Production Machining, Contributed by: Javier O. Vera, Application Engineer, Hexagon
Metrology, Inc.
Posted on: 11/25/2008
Editor's Commentary
For more information from Davromatic Precision, visit www.davromatic.co.uk.
Advancements in manufacturing equipment such as Swiss screw machines
and high-speed CNC milling systems have revolutionized precision part
production. Some Swiss screw machine lathes have guideways that hold
barstock of lengths as long as 12 feet in steel, polymer and composite
materials. Part features are generated by moving the barstock and the cutting
tool simultaneously to create the component. This capability has introduced
speed advantages and optimized cutting of shapes for higher throughput than
ever before. Part accuracy is superb (± 0.00002 in) and part-to-part
consistency is drastically improved.
With the evolution of this machinery and its related processes, manufacturers
of medium- to high-volume turned parts are facing increased inspection
requirements in terms of frequency, feature measurement and production
statistics, as well as rising accuracy specifications. Manufacturers are seeking
advancements in measurement technology, such as the speed of measurement
cycles, the ability to check parts with greater accuracy and the ability to
precisely measure geometric features and free-flowing forms.
Metrology technology has come a long way in the last 5 years, and tools are
available to meet such exacting inspection requirements. The right solution, of
course, depends on the particular needs of the end user. The following
information explains three different, but effective, approaches to accurate
measurement of turned parts in the medium- to high-volume production
environment.
Non-Contact Turned Part Measuring
Centers
The dental implant industry is a compelling example of an industry making
use of opto-electronic, non-contact measuring systems. Manufacturers are
producing many size and shape variations of the core components of a dental
Click Image to
Enlarge
A touch probe is
used on a
multisensor vision
inspection system to
inspect an
automotive valve.
On a rotary profile
measurement
system such as the
Tesascan, the object
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implant via turning/thread cutting as performed using CNC turning
technology in a high-volume production environment. The implants, also
known as prosthetics, are human spare parts, and therefore, quality is of
utmost importance; all functional dimensions must be inspected on a 100
percent basis.
The components are very small (typically less than 4 mm in diameter), with
many dimensions that are difficult and time-consuming to measure using
traditional gaging methods (optical projectors, toolmaker’s microscopes or
hand-held tools such as micrometers). With increased levels of production and
quality demands, and the variety and volume of components produced with
increasing measurement criteria, non-contact measuring systems helped fulfill
this industry’s metrology needs.
Today, a single non-contact automatic rotary profile measurement device such
as a Tesascan 25 from Hexagon Metrology can be dedicated to a cell of two
or three CNC lathes producing one product type. The object to be measured is
fixed in a rotary mandrel and turns (if required) while a light projects the
profile onto a collection sensor array, which digitizes the image. The software
then measures the pre-programmed features using the digitized image as a
guide. Typical cycle time for 12 dimensions on a part is 28 seconds. Often,
production engineers are responsible for part programming, which is
performed online and offline, while the operators use the measurement system
to automatically inspect the components. CNC operators can check all critical
external dimensions with a single piece of equipment. Profile devices such as
the Tesascan offer advantages over laser systems in terms of overall accuracy,
speed and the types of features that can be measured.
Once each component is measured, the results can be displayed numerically
and graphically together, with the ability to analyze measurement data
statistically in the form of histograms, control charts and capability reports.
This capability, previously impossible with manual methods of inspection, has
provided a statistical base for determining process trends and adjustment of
individual machine tools. An added bonus is that measurement data is
traceable to individual machines using either a batch number or machine tool
identification number entered by the operator.
Automatic thread measurement can be accomplished if the machine
incorporates a slewing device, which tilts the part for better measurement of
machined threads
(helix angle compensation).
Another advantage of this type of tool is scalability. If a shop producing
turned parts has the capability for various sized end products, turned part
centers can be purchased that will accommodate much larger turned parts (as
long as 500 mm and 80 mm in diameter). However, this type of tool has
limitations. Generally the tool can only accommodate a single part at a time
and must be loaded and unloaded manually, even though the measurement
cycle is automatic. If the feature for measurement cannot be seen in profile,
such as a machined channel, then it cannot be measured.
Vision Systems
to be measured is
fixed in a rotary
mandrel and turns
while a light
projects the profile
onto a collection
sensor array, which
digitizes the image.
A turned part is
mounted in a rotary
stage on a vision
measuring system,
which can provide
significant
throughput
advantages.
Martin Ollis helped
Davromatic
Precision Ltd.
implement an
infrared touch probe
system that allows
lathes with movable
heads to inspect
turned and milled
contours while the
part is still on the
machine in its
counterspindle.

For production machining, one of the most significant benefits attained with
vision measurement technology is faster throughput. Using a piston valve
automotive application as an example, conventional measuring can take an
hour or more to collect only the measurements of the piston valve. That
inspection time does not include the data compilation and statistical analysis
necessary for many of the components. With the introduction of rapid vision
measurement systems, the complete inspection process can be cut down to
less than 5 to 10 minutes per part.
A component such as a piston valve also has very exotic shapes and radius
blends that require inspection. Once again, vision measurement technology
provides an efficient solution. By using profiling calculation tools, the task of
measuring complex curves is cut down to a simple profile trace. Supportive
CAD referencing capabilities from software such as PC-DMIS Vision add
further simplicity. With some quick steps, the CAD model is adjoined to the
physical part to enable point-and-click support in measuring the complex
profiles. This process is possible for many types of parts such as small
medical components with profile tolerances of microns or electronic
components with gap and height measurements in the submicron levels.
Many other types of parts are especially useful for vision metrology. Part data
is generally collected in seconds and supported by pick-and-place trays that minimize operator handling.
Feature location and feature form can be measured from the data acquired. The price range of these
systems is normally based on capacity, speed and accuracy, resulting in systems that fit a large spectrum
of budgets. A vision system like the Brown & Sharpe Optiv 1 Classic fits an entry level budget. At the
other end of the spectrum, a Brown & Sharpe Optiv 3 Performance provides extreme precision with
submicron accuracy. Vision metrology can be called the micro metrology tool of the future.
The vision metrology world continues to evolve. The introduction of interactive multiple sensors has
revolutionized how 3D measurements can be performed in vision based systems. The various sensors
provide the building blocks to expand or enhance a vision system. Tactile systems such as touch probes
can hold tolerances down to a couple of microns and provide articulation when necessary. Articulation
permits the measurement of features that may not be inline with the vision sensor. Additionally, non-
contact sensors such as laser and white light scanning probes can drive precision down to submicron
levels and, in some very special cases, angstrom levels of precision. Lasers provide selective support for
measurements of form using a real-time rotary or tilt axis. White-light sensor technology is especially
useful for certain tiny features such as small steps and 3D forms. The correlation of these sensors in
combination with the optical sensor provides an unparalleled benefit for speed and agility of vision
systems.
Touch Probe Systems
The final solution for production machining offers the highest throughput option and involves
incorporating a measurement touch probe on the turning center itself. The following company has
reaped the benefits of such a system. Davromatic Precision Ltd. (Rugby, United Kingdom), is a second
tier supplier for aerospace, defense and heavy machinery industries. On any given day, the company
faces a balancing act as a manufacturer of precision turned parts. On one hand, it needs to produce
precisely turned and milled parts with tolerances of only ± 8 microns. On the other hand, it needs to
keep costs down to a minimum. The investment in a turn-mill center with an integrated touch probe
became an economical choice for the company.
With high volume production, each pause in production and each manual adjustment of the turning
center affects the productivity and the profitability of the job. In order to ensure the quality of parts with
The counterspindle
presents a
component to the
touch probe to
measure the turned
diameter. An air
pipe (the copper
tube on the left)
cleans the stylus
and component
before inspection
starts.

tight tolerances, and prevent process drift, an integrated metrology solution was needed for permanent
monitoring and adjustment of the machining
parameters.
Davromatic implemented a hard-wired infrared touch probe system by M&H Inprocess Messtechnik
GmbH that allows the turning lathes with movable heads to inspect turned and milled contours while the
part still is on the machine in its counterspindle. The touch probe is mounted on a mounting bracket
fixed near the main spindle head in order to move the cutoff workpieces for dimensional measurement to
the touch probe by the counterspindle.
Measuring critical dimensions such as the outside diameter, length, width of hexagon cross-sections and
milled surfaces is accomplished in seconds. Because the measuring process takes place on the
counterspindle, it can be done independently of the main spindle, reducing the impact to production
even further.
Davromatic has also realized secondary benefits of the system in terms of monitoring tool wear and
premature failure. Some alloys used in production were contributing to inconsistent and uneven tool
wear, which caused production to drift out of tolerance quickly. Sampling every part allowed real-time
monitoring of this situation so that inserts could be changed before a lot of expensive material was
scrapped and production time lost.
Overall, the ability to achieve a 100-percent sampling rate automatically and to do in-process
adjustments to the machine tools has enabled Davromatic to increase productivity by approximately 20
percent, while reducing scrap to virtually zero.
This scenario represents an extraordinarily successful result of in-process measuring. However, this
technique does have some important limitations. First, since this method employs a touch probe,
everything that has to be measured must be able to be touched. Depending on the part, some features
may be too small to be touched, or a single size touch probe may not adequately inspect everything that
needs to be inspected. Complicated geometry may be beyond the capability of such a system. Second,
this method does not represent an independent verification of the part quality. If the machine itself is
inaccurate, the results might be suspect. Some quality programs or customers require independent
verification of results. One option might be to use a touch probe system to monitor and control
production in combination with an offline solution for final verification.
Forward Looking
The good news is that there are now more choices to inspect turned parts, from offline to in-process as
well as hybrid solutions incorporating a combination of techniques and equipment. As the
manufacturing of cylindrical components continues to evolve and expand, a variety of metrology
systems are meeting the quality requirements and the specific budget needs of this industry. Everything
from bone screws to valves to plastic components can be measured with confidence and reliability.
Today’s manufacturing standards demand speed and accuracy, and the measurement industry is ready to
provide a solution. The result can be significant reductions in inspection time and improved process
control—both of which contribute heavily to a manufacturer’s bottom line.
Serving the Screw Machining Industries
© 2009 Gardner Publications, Inc

Production Machining Article January 2009

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