Medical Design Briefs - April 2021 - 27

quality is improved because there is less
movement of a part and fewer variables
that can impact quality.
Process improvements such as these
can help achieve the goals of lean manufacturing by increasing use of automation,
improving manufacturing efficiency, and
reducing costs by eliminating waste.
Automated processes ensure a high
degree of accuracy, precision, and uniformity, and production is more economical
without sacrificing on part quality.
CNC Machining
For thicker-walled tubing, a computer
numerical controlled (CNC) machine is
typically required. A CNC machine takes
a raw material - in this case, metal -
and cuts, grinds, drills, turns, mills, and
shapes it into parts that meet exact specifications, using a computer program to
control the operation of machine tools
such as lathes and mills. When cutting
metal, CNC machines generate massive
amounts of heat. Consider that these
machines are made almost entirely of
metal. The latest CNC machines are
equipped to collect data in real time as
they run, and to control for factors such
as thermal growth.
To visualize this, think back to when
you were young and couldn't remove the
metal cap from the ketchup bottle
because it was too tight. We may remember our parents running it under hot
water in the sink. Miraculously, the cap
came off after that. The science behind
this home remedy is that metal expands

at a different rate than the glass when
heated. The heated cap ultimately became larger than it was in its cold state,
naturally releasing its grip on the bottle.
Therefore, imagine the expansion occurring with hundreds of metal parts bolted
and welded together, six feet high and
eight feet wide. In this situation, a part
produced in a CNC machine when cold
will be substantially different from a part
made when the CNC reaches operating
temperature, unless the machine selfadjusts to account for this.
Laser Cutting
Newer CNC lathes with integrated
laser cutting equipment can also be used
for fabricated tube production. In the
past, two machines were needed for
turning and laser cutting. Transfers from
one machine to another increases the
risk of misaligned features versus a single setup. This combination of capabilities allow laser cutting and machining in
one setup, with registration capability
within 0.0005 in. A Citizen L200 CNC
machining center combined with a Swiss
style 7 axis CNC lathe and an integrated
400 W laser cutter is particularly well
suited for fabricated tube production
and various metal tubing projects.
With this integration, laser-cut slots
and holes can be achieved while simultaneously machining different outside
diameters, reducing setup time, secondary processes, and handling costs. The
equipment uses long-length drawn metal
tubing with automatic feeding, cutoff,

Rolled Tubes

Seamless &
Drawn Tubes

Drawn tubing is usually better suited when additional processes are needed such as piercing and slotting,
whereas rolled tubing is best reserved for higher volume parts. (Credit: MICRO)

Medical Design Briefs, April 2021

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ToC

and part ejection. Automated work cells
can cut features and holes into tubing
while in-line inspection using a two-camera vision system ensures quality. These
machines also use algorithms to adjust
themselves in a timely fashion to maintain accuracy. The process can easily
accommodate when there is a design
change needed. All that is required is a
programming change versus a more
expensive tool change. These work cells
can help to reduce set-up time, the need
for secondary processes, and some associated assembly costs, thereby lowering
overall manufacturing costs.
Wire EDM
Wire electro discharge machining
(EDM) is another process that can be
used for cutting tube features. These
machines use a taught wire carrying
high voltage to remove metal. Wire
EDMs work differently than milling and
can be used to create unique features
such as window shapes, which are not
always suitable with a laser cutter. The
process also works well when the angle
of the cut in the tube wall needs to mate
with other components. EDM requires a
slower production process, but for creative fixtures on multiple stacked parts,
it can streamline production very effectively and cost-efficiently.
MICRO's tube fabrication center combined with its laser cutting technology,
automated work cells, and dedicated
tube mill, enables the company to meet
customers' requirements for manual,
semi-automated, or fully automated
products. The company is able to reduce
tubing costs on high-volume, disposable
instruments while adhering to strict
quality standards, resulting in products
that meet all functional, visual, and
dimensional requirements.
This article was written by Steve Santoro,
Executive VP of MICRO, Somerset, NJ.
MICRO is a full-service contract manufacturer
of precision medical devices, injection and
insert molding, metal injection molding, fabricated tube assemblies, subassemblies, and complete devices. With over 75 years of manufacturing excellence, the company offers product
development and design assistance capabilities
and excels in prototyping and validation to
full-scale production, with a mission " to help
customers save lives. " For more information,
visit http://info.hotims.com/79412-344.

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Medical Design Briefs - April 2021

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