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By Dave Salverson
Production Manager
Display Connection
West Chicago, Illinois
Switching from a pin router to a CNC
router has cut the time required to produce point of purchase
displays by up to 80% while substantially improving their
appearance. The major drawbacks of the pin router are the lengthy
period of time required to build the pattern and the difficulty of
following the pattern when cutting the display which leads to
inaccuracies. The CNC router makes it possible to define the
geometry of the display on the computer in a fraction of the time
required to build a pattern. Once the geometry is defined, it can be
produced with perfect accuracy without relying on the operator. The
use of CAD/CAM software and the CNC router originally appeared
daunting to a small shop with no automation experience, but the
simplicity and ease of use of this technology was a pleasant
surprise. It is now possible for Display Connection to easily beat
the prices, quality and delivery time of competitors who still
mainly produce displays by hand.
Display Connection produces wood, plastic and laminate point of
purchase displays, prototypes and models. In the past, the company
produced these products with a pin router. Layouts for these parts
were produced in actual size on a piece of paper on the pattern
material itself. Either a bandsaw or jigsaw was then used to cut the
pattern along the layout line. The pattern was then fastened to the
actual material so that it could serve as a guide for the router.
One problem with this approach was the amount of time required to
produce the pattern. Another was that any inaccuracy in the pattern
or in the way that the operator followed the pattern was immediately
transmitted to the finished part. The pencil line itself produced a
built-in error that limited the level of precision that could be
achieved. If the customer wanted to make a change in the part, it
usually meant that the pattern had to be rebuilt from scratch. The
pin router was also poorly suited to certain types of displays such
as a design with a large number of cut-out shapes. Each shape
required that a hole be drilled and the router bit dropped into the
hole to finish out the shape, a difficult job for all but the most
experienced workers.
Display Connection executives realized that CAD/CAM technology could
alleviate some of these problems, but when they looked at
computer-controlled woodworking machines, they saw prices in the
neighborhood of $60,000. That was impossible to justify at the
company's current workload. Then the company heard about the Series
III PC-driven CNC wood router (Techno, Inc., New Hyde Park, New
York) which costs less than $16,000 and is designed for production
routing and drilling on a wide variety of materials including wood,
plastic, MDF, solid surfacing materials and nonferrous metals.
Working area for the router is 56 inches by 96 inches and Z-axis
height options range from 4.0 inches to 19 inches. Table technical
specifications include a rapid travel rate of 200 inches per minute,
a Z-axis cutting force of 200 lbs. maximum, 0.0005 inch resolution
and repeatability and 0.003 inches/ft. absolute accuracy.
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The system includes the Mastercam CNC
programming system (CNC Software Inc., Tolland, Connecticut) which,
although originally designed for metalworking, is ideally suited for
point of purchase displays because of its ability to generate the
most complex contours with little programming effort. The program
features true 3-D geometry construction plus IGES, DXF and CADL
converters so that geometry can be uploaded from nearly any CAD
system.
Now, the company uses the CNC
programming software to define the geometry for the display. This
takes far less time than is required to produce an equivalent
pattern. Better yet, the computer program draws perfect lines and
circles and allows geometry to be copied, moved, rotated, and so on
with perfect accuracy. Once the geometry is defined, it can be
precisely cut with the operator only needed at the beginning to load
the machine. If the customer makes changes, they can be easily
incorporated into the program. The changes can usually be made in
minutes on the screen and a new display cut directly without having
to spend hours creating a new pattern.
A 25 inch wide by 18 inch high display has 4 rows of 10 triangular
holes that are later filled with golf clubs. Producing this type of
display with a pin router was difficult because it took a long time
to set up a drilling jig and the operator had to follow the pattern
very carefully to avoid jumping the pin. It took about 2 hours to
build the pattern and 15 minutes to drill and route each hole. With
the pin router, it takes only 10 minutes to produce the pattern
using CNC programming software. One of the reasons this goes so fast
is that the operator only has to draw one triangle, copy it nine
times to create one row, then copy the row three times. Each hole
can then be produced in 5 minutes by a relatively inexperienced
operator.
Another typical display produced by the company requires a large
script letter. The problem in producing this letter with a pin
router is that it has several thin spots where, if the operator
isn't very careful, the pattern will start to vibrate and produce a
rough cut or even knock the pin off track and destroy the material.
It took several hours to produce the pattern and 15 minutes to drill
and route each hole with the pin router. It takes only 10 minutes to
produce the pattern using the CNC router and CAD/CAM software.
Display Connection recently produced 18,000 plastic meal holder
displays for a fast food company with the CNC router. The company
never would have received the job without the new machine because
cost and delivery time would have been too great. The CNC router
made it possible to program the geometry in about one hour and then
cut each piece in about 2 minutes with a bull nose end mill. A bull
nose end mill is like a conventional square end mill except that it
has radiused corners. |
The Techno machine has a positioning
accuracy of +.1 mm (+0.004) in 300 mm and a repeatability of +0.01
mm. Since this is far greater than hand cutting, manual finishing
operations are minimal. This also cuts down on the time Display
Connection must allot for its projects. The accuracy of the router
is the result of several features inherent to the table, such as the
use of ball screws and servo motors. For example, anti-backlash ball
screws in Techno routers permit play-free motion that makes it
possible to produce circles accurate to the 0.0005 inch machine
resolution. These ball screws also make it possible to produce
wooden parts as accurate as the machine resolution. The ball screws
have excellent power transmission due to the rolling ball contact
between the nut and screw. This rolling contact also ensures longer
life and greater rigidity during the life of the system because of
the reduced wear as compared to ACME screws and nuts, which have a
sliding friction contact.
In two years of operation, the company has never had any problems
with the machine. This is partly due to the strength and rigidity of
the table. The Techno machine is constructed from extruded aluminum
profiles that can support all the materials that Display Connection
uses and provides easy clamping capability. The machine also 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.
When Display Connection recently purchased a second and third Techno
CNC router, it opted to have them equipped with a servo motor rather
than stepper motor because it provides smoother curved cuts. A servo
motor is better than a stepper motor in providing continuous motion
because it works on the principle of constant feedback. The program
tells the router to follow a specific path by giving it a series of
voltages. It drives to the locations by getting constant feedback
along the way. Stepper motors are less expensive than servo motors
and are fine for straight line motions and simple circular arcs.
But, in general, servos are up to three times faster and more
reliable when performing arbitrary curves like splines or 3D
carvings.
All in all, Display Connection has improved productivity by 200% to
1000% in producing a wide range of point of purchase displays and
prototypes. Quality of the company's products has increased by a
similar factor. Productivity gains of this magnitude have made it
possible for the company to increase profit margins even while
lowering its prices to its customers by as much as 50%. The
relatively small investment in the CNC router and CAD/CAM software
has provided a dramatic return on investment. The result is a
dramatic improvement in the company's competitive position -- it can
do the job better, faster and for less money.
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