|
Although it is still early afternoon as the 1191 sedan eases
onto the freeway, the driver switches on his headlights. It is
the law in Canada. A sophisticated electronic module immediately
senses the presence of day-light, automatically reduces wattage
to the headlights by 20 percent and switches off the unnecessary
tail lights, prolonging the life of the lamps. The electronic
circuitry that controls the process is only one of a wide
variety of electronic and electro-mechanical systems and
components manufactured by Lectron Products, a major supplier to
the Big Three automakers. This particular module, however,
presented the Rochester Hills, Mich., manufacturer with a
special set of problems.
Due to the part’s underhood location, the automaker specified
that not only must the part itself meet strict quality
standards, but it also must be able to withstand the rigors of
an environment where it would be subjected to water, salt, oil,
gasoline and extreme temperature fluctuations. A two-part
reactive polyurethane, manufactured by Biway Corp., Des Plaines,
Ill., had already been tested and approved as the specified
potting material. Lectron turned to Thermal Innovations Corp.,
Manasquan, J.J., for an engineered design proposal on how best
to employ the new potting material.
Thermal Innovations responded by custom-designing an automated
turn-key potting system that combined in its own Seal-Cure
high-purity, special infrared pre-heat oven and infrared curing
oven; an automatic meter, mix and dispense system manufactured
by Sealant Equipment & Engineering, Plymouth, MI.; the Biwax
polyurethane potting material and a series of index conveyors to
join them together in a closed-loop system. The idea was to
combine the state-of-the-art technology in each area into a
relatively simple cost-effective potting process that could be
operated by a few people and produce high quality modules.
Production Steps
In the first step of the operation, modules are loaded manually
onto the conveyor for delivery to the pre-heat oven. Modules are
heated to approximately 70°C to remove any moisture retained by
the PC boards and to help ensure uniform flow of the potting
material around the board’s intricate electronic components.
This pre-heat oven is rated at 7.2 kw and is approximately 5.5
ft long.
After pre-heating, the modules are automatically indexed and
positioned underneath the automatic meter, mix and dispense
machine, a See Flo7. After a sensor indicates that a module is
in place, the machine automatically dispenses a 100-cc shot of
the mixed potting material. The module then moves along the
conveyor to the curing oven, an infrared Seal-Cure oven which is
the heart of the system. The oven heats and accelerates the
two-component (resin/catalyst) chemical reaction at much lower
ambient temperatures than conventional convection ovens. The
infrared oven transmits electromagnetic waves through the air
which are directed at the target module and absorbed. The
special quartz infrared emitters can be fine-tuned to
accommodate the potting material’s absorption characteristics as
well s the thickness of the material. This ability to control
energy output ensures that the material, rather than the heat
sensitive electronic components, warms and cures quickly. The
Sure-Cure oven fully cures the potted assembly in just 3 min
with total energy efficiency. This particular final cure oven is
rated at 14.4 kw and is approximately 10 ft long. The module
never reaches a temperature above 65°C.
After the curing process, modules are conveyed through a forced
ambient air cooling section so that an un-gloved operator can
immediately unload the system.
System Components
The Lectron system uses a central command electrical control panel
for temperature zone control, conveyor indexing speed and
automatic dispensing. The system is easily monitored and was
designed to plant specifications. However, Thermal Innovations
has the capability to design and install sophisticated
computer-controlled systems that can be integrated into the most
complicated computerized manufacturing, inventory and
information systems.
The potting material, Biwax 82.643, has been custom formulated
to meet and exceed automotive requirements and for use in
infrared curing operations. The material is a two-part reactive
polyurethane that exhibits many beneficial characteristics, such
as long pot life, low exotherm, low viscosity, non-abrasiveness,
1:1 mix ratio, high-low temperature stability and environmental
resistance. It will cure at room temperature in the event of
power failure. In this application, the material needs to be
fairly elastomeric when cured, so that it protects delicate
electronic components.
The See-Flo 7 meter, mix and dispense machine was selected for
its compatibility with the potting material and its ability to
be interfaced with automated turn-key system. The part A and B
material components are supplied to the inlets of the metering
cylinder assemblies by gravity feeding from double-stacked
55-gal drums. Precision volumetric metering is accomplished by
positive displacement, double-acting balanced metering
cylinders. When the signal to dispense is received from the
central command control panel, the air powered system
reciprocates, forcing a pre-determined volume (100cc shot) of
metered material through the non-moving (static) mixer muzzle
assembly. The disposable static motionless mixer produces a
high-quality and air-free blending of dual-component materials.
The volume of mixed material in the system is kept to a minimum
y blending immediately in the nozzle prior to dispensing. When
the dispense cycle is completed, the No-Flush spool valve
direction at the tip and ensuring a positive No-Drip cut-off of
the mixed material.
Benefits
Currently the system is producing approximately 200 potted
modules/hr. Rather than a normal cure time of 13-15 min, 3 min
in the Seal-Cure oven is sufficient. This greatly reduces oven
bottlenecks and work-in-process inventory. The oven is also much
more energy efficient than its convection counterpart, so
savings are realized in that area as well. Benefits in the labor
area are obvious; the system was designed specifically for a
single operator and a comparatively simple operation. Lower oven
temperatures and reduced need for solvent use in the dispensing
equipment make the system safer and more user-friendly.
Installation is quick and easy, as all components are pre-wired
and pre-tested. A single exhaust system ties directly into
existing plant systems, and wiring is simplified. The system
also is compact and offers good use or floor space.
“The entire potting operation is proving what cooperation and
communication among industry resources can accomplish in a
relatively short time,” Biwax’s Les Schober says.
“Thermal Innovations, Sealant, Lectron and Biwax all
contributed, and each of us learned the benefits of the team
effort approach.”
Thermal Innovations’ Nick Fusilli puts it another way. “We want
manufacturers everywhere to become aware that the resources are
available for turn-key systems just like the Lectron project.
We’re working together to keep one step ahead not only of our
own competitors, but also of our own customers’ needs. New
materials, new ways to dispense them, new curing processes – all
of these things can come together in one integrated system if
you are working with suppliers who have established
relationships among the various disciplines.” |
|
