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By Glen Whetherby
President
Artistic Plastics / Mansfield, Texas
Two CNC routers that cost a total of
$40,000 annually generate $750,000 worth of plastic display products
at Artistic Plastics. The PC-controlled routers produce as many
parts as five people working with hand routers. The use of these
machines has lowered the labor cost of router operations, enabling
Artistic Plastics to charge less for this work and win more of this
type of business. The use of the CNC machines also ensures customer
satisfaction by producing parts with a better surface finish than is
possible to achieve with hand routers.
The company's products include items
such as acrylic sign frames, jewelry holders, and chinaware stands
that are used by retailers such as J.C. Penny's to display their
wares. Orders range in size from 1,000 to 50,000 pieces, and
Artistic Plastics normally ships about $100,000 worth of product
each week. This market is very price-sensitive and typically the
lowest bidder gets the job. The challenge for Artistic Plastics is
to operate as efficiently as possible so that its prices are
competitive while still making a profit on the job.
Ninety percent of Artistic Plastics'
products consist of square pieces of plastic that are cut with saws.
Because it is fast and efficient to cut straight pieces with
conventional power tools, there isn't much that automation can do to
improve efficiency in this area. But the remaining 15 percent of its
parts, the pieces with curves, are not efficiently produced by hand.
In the manual production process, operators guide a hand router
along a template representing the desired shape. Typically the
templates are cut from a piece of fiberboard, either by hand or with
a router. The templates must accurately depict the radius of the
curve, and making good templates requires patience and a skilled
employee. Frequently, templates are ruined and new ones must be made
before the job can continue. The other drawback to using templates
and hand routers is the fact that the plastic parts must be trimmed
flush to the template. This requires the operator to closely follow
the template and introduces the potential for human error.
Heavy-duty requirements
In the early 1990s, company management
learned about CNC (computer numeric controlled) technology and
decided to try this as a way of boosting the productivity of router
operations. When they began evaluating CNC routers, one requirement
was uppermost in their minds. The system had to be reliable. They
knew, from the volume of router work they had, that the machine
would need to operate seven to eight hours a day, Monday through
Friday, and sometimes continuously over three shifts when the
company had a large order to fulfill. A breakdown was unacceptable
because it would cause a loss of sales volume and potentially
jeopardize customer relations if Artistic Plastics was late with an
order.
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A second requirement for the CNC router
was that its price was affordable. This combination of requirements
ruled out a number of products on the market at the time. CNC
routers that cost several hundred thousand dollars were well made
but out of Artistic Plastics' price range. Those that were more
affordable appeared to be made with low-end components that didn't
seem like they would hold up to a large volume of work.
Then the company found the Techno Series III PC-driven CNC router
from Techno, New Hyde Park, New York. This machine sold for the
right price, about $18,000 at the time, and featured the heavy-duty
construction Artistic Plastics required. Each Techno router is
constructed from rigid and optimized extruded aluminum profiles. It
has four ground and hardened steel shafts and eight re-circulating
bearings in each axis. This shaft-and-bearing system produces very
smooth, play-free motion and an extremely rigid system that produces
high-quality cuts. It easily supports the plastic sheets that
Artistic Plastics uses as well as the vacuum table the company added
to quickly change setups. Another feature of the machine that
contributes to its durability is the use of anti-backlash ball
screws. These screws have excellent power transmission due to the
rolling ball contact between the nut and screws. This type of
contact ensures low friction, low wear, and long life. The ball
screws also make it possible to produce parts to the machine
resolution of 0.0005 inch.
The technical specifications of the
Techno machine that Artistic Plastics purchased include a working
area of 49 inches by 41 inches and z-axis height of 6". This router
was designed for production routing and drilling on a wide variety
of materials including wood, plastic, MDF, solid surfacing
materials, and nonferrous metals. The price included the Mastercam
CNC programming software. Although that program was originally
designed for metalworking, it is ideally suited for cutting plastic
because of its ability to generate the most complex contours with
little programming effort.
High-volume efficiency
Once the CNC router was installed and
some pieces were programmed in Mastercam, Artistic Plastics began
shifting router jobs to the new machine. It performed so well that
it was soon handling 95% of the router work. In fact, within the
first few weeks, it had produced enough parts to pay for itself. A
key feature of the Techno machine is its ability to cut 3D
continuous contours at up to 200 inches per minute, far faster than
most machining centers. Compared to a hand router, the Techno
machine takes about the same amount of time to cut a single part.
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The speed advantage of the CNC approach
comes when there are multiple parts to produce and several can be
put on the table and cut in one operation. This really pays off on
high volume jobs, when one operator can turn out as much work as
five people working by hand. For example, to produce an order of
50,000 parts by hand, Artistic Plastics would have had five people
working for two weeks with each producing about 1,000 parts per day.
That same amount of work can be accomplished by one person running
the Techno router for the same amount of time.
Because Artistic Plastics' products are
visible to the public, customers insist on an excellent appearance,
which includes perfectly smooth edges. This is an area where having
the CNC router has also been beneficial because it can produce
smoother cuts compared to a hand router. The human variability
caused by having an operator closely follow a template has been
replaced by a machine that never deviates from a computer-controlled
path. The machine has a positioning accuracy of ±0.1 mm in 300 mm
and a repeatability of 0.01 mm. The CNC router features a rapid
travel rate of 200 inches per minute, a z-axis cutting force of 200
pounds maximum, 0.0005 inch resolution and repeatability, and 0.003
inches/foot absolute accuracy.
After using the original Techno router
for several years, Artistic Plastics was producing many more
routered pieces than it had previously. This was the result of the
company's ability to produce higher quality parts for a lower price,
and deliver them faster, using the CNC machine. The company then
purchased a second Techno machine to keep up with the demand. That
CNC router, which cost $22,000, differed from the first in that it
was equipped with servo motors rather than stepper motors. The servo
motor allows the new router to make even smoother cuts.
Both Techno machines are in use every
day, usually for the entire day. Both have proved to be as durable
and reliable as Artistic Plastics had hoped. Techno was the first
low cost router manufacturer in North American and has an excellent
reputation for service and support.
The two Techno routers generate about
$15,000 of parts each week or $750,000 annually. Because the CNC
machines provide a five-fold increase in productivity over hand
routers, this income is available to Artistic Plastics at a much
lower labor cost, creating an overall increase in the bottom line.
With the efficiency provided by the CNC approach, Artistic Plastics
is able to keep its prices as low as the competition's while
ensuring that the work is done profitably.
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