For example, many technicians who repair plastics
with adhesives do so because they’re familiar with adhesives;
they feel comfortable using them. The problem with adhesives is
that, oftentimes for a strong repair, a backer is recommended
– and sometimes a plastic part won’t fit back on the vehicle when
it’s doubled in thickness.
What then?
You can throw it away and buy new. Or you
can repair it by plastic welding.
Another reason to learn plastic welding is
that a bumper cover normally replaced with an aftermarket cover
could be saved. While some aftermarket parts are OK, others aren’t.
And there’s nothing more frustrating to a technician than mounting
holes on an aftermarket cover that don’t line up. But what if
all that could be avoided? What if you learned to repair damaged
bumper covers instead of tossing them in the plastic graveyard?
If that doesn’t convince you, what if you’re
repairing a “new” car and you can’t get replacement
parts? What if you get a wrong part and the vehicle was promised
in three days?
Yet another reason to learn plastic welding
is that it might prove to be a good profit niche for older cars,
particularly when people are paying for repairs out of their own
pockets. Remember five years ago when the whole concept of paintless
dent repair seemed pretty humorous? Today, shop owners are laughing
– all the way to the bank. They invested in tools and a new technique,
and they practiced.
Why not learn to repair plastic with welding?
“The equipment is expensive.” “I don’t know how.”
“I don’t want to practice on my own time.” “It’s
cheaper to replace than to weld.” “When I do repair
plastic, adhesives are simpler to use.” “It takes too
much time to identify the plastic.”
All right already.
At the least, you owe it to yourself – and
to your business – to investigate the feasibility of plastic welding.
Plastic Identification
There are two common types of plastic-welding
equipment: hot air and airless. The hot-air method can be used
on thermoplastics only, while the airless method can be used on
both thermoplastics and thermoset plastics.
Significant differences exist between the
two classes of plastics.
Thermoplastics can be remelted, making welding
possible. Thermoset plastics cannot be remelted; they can, however,
be joined by a bonding process that’s similar to brazing or soldering
steel. The brazing or solder bonds to the outer surface of the
steel, with no mixing of parent metal and filler material.
Identifying the plastic you’re about to work
on is one of the key elements of making good repairs.
While the color and flexibility of the part
can help to identify plastic, the year, make and model of the
vehicle can really help. The plastic- welder manufacturers usually
have a quick reference chart to help in the identification process,
too. If that fails, call the manufacturer’s (800) technical/help
phone number.
Hot-Air Plastic Welding
Hot-air plastic welding uses an electric heating
element to heat air between 450 to 650 degrees F. The air is supplied
from the shop’s air compressor or a small compressor that comes
with the plastic welder. Most hot-air plastic welders come with
three types of tips: tacking tips, round tips and high-speed welding
tips. The high-speed tips are nice when doing long welds because
the rod is preheated, as well as the base material.
When hot-air plastic welding, the following
tips will come in handy:
- Clean the material with soap and water. Follow up with an
approved plastic cleaner. - Prepare the area, which usually means some type of joint preparation
or grinding. Removing paint and primer is critical. - Identify the type of plastic and proper filler material.
- Hold the parts in alignment while tack welding.
- Select the diameter of filler based on the material thickness.
The filler rod should be approximately the same diameter as the
material is thick. - Because hot-air plastic welding can cause too much distortion
on thin plastics (less than 1/8 inch), make sure you correctly
set the welding temperature and air flow for the type of plastic
being welded. Allow the unit time to warm up.
With the preliminary steps out of the way, it’s time to weld.
If you’re using the round tip on your welder, hold and feed the
filler into the joint with the other hand. Direct the hot air
at both the base material and filler at the same time.
When the filler rod and base material become tacky or sticky,
it’s time to progress across the joint. Hold the rod at almost
90 degrees to the joint, and push the rod into the joint as it
melts (maintaining the correct downward pressure and traveling
across the joint requires skill that comes with practice).
Remember that overheating thermoplastics is not good. Discolored
or charred plastic means too much heat or a travel speed that’s
too slow. If you haven’t welded for a while, practice.
Hot-air plastic welding is like any other skill. Those who practice
it get better; those who don’t grumble about not being able to
do it or that it’s impossible to master. Wasn’t it Yoda who told
Luke Skywalker, “Do or do not. There is no try.”
Airless Plastic Welding
Consider these general steps for successful airless plastic welding:
- Clean with soap and water. Clean with the appropriate plastic
cleaner. - Remove the basecoat/clear-
- coat and primer from around the repair area.
- Vee out the crack.
- When welding from one side, the depth of preparation should
be slightly deeper than two-thirds the thickness of plastic. When
making a two-sided repair, depth of preparation is about one-half
the thickness. - Hold the pieces in proper
- alignment.
- Properly match the filler rod to the base material.
- Set the welder at the recommended temperature.
- Make sure the welding tip and filler metal are both clean.
Airless plastic welding is no different than hot-air plastic welding,
with regard to practice: You need to know your equipment and practice
before actually making a welded repair.
Note: A recent addition to one of the airless plastic welders
is a universal method for repairing plastics. This system is based
on a meltable plastic adhesive and a special shoe for the equipment.
It’s also possible to add a mesh screen to the repair for increased
strength. This method works best when the repair is performed
on both sides of the damage.
Getting Started
Plastic welding can be a cost-effective method to repair plastic
– if you’re willing to purchase the equipment and learn how to
use that equipment properly.
For best results, follow the plastic-welder manufacturer’s recommendations
for using the equipment. Don’t make up your own rules, and don’t
forget to read and understand the plastic-welder manufacturer’s
safety instructions.
You also need to remember that not all plastic repairs are profitable.
The consensus seems to be that bumper covers are the most common
plastic repair because repairing plastic bumper covers is often
a viable economic option to replacement. The deciding factor is
often the cost of a new cover or an aftermarket one compared to
repairing the damaged cover.
This is where knowing the actual cost per inch of weld is helpful.
If you don’t know what your costs are, it’s difficult to know
when to weld or when to replace a plastic part. Don’t forget that
some plastic parts are very complex and that accessing the damage
may be difficult or impossible, regardless of the repair method.
Know when to say no!
Once you do, you can say yes to a long, profitable relationship
with plastic welding.
Writer Fred Kjeld is a contributing editor to BodyShop Business.
