Today, latitude and longitude are precise
markers used by many navigators. But back in the pirate days,
measuring instruments weren’t the most accurate, and, the individuals
interpreting the information weren’t always precise. Oftentimes,
a navigator met his untimely demise due to inaccurate directions.
To help with navigation – and save the dwindling
pirate population – maps were marked with geographic landmarks
to further aid in the retrieval of treasure. Latitude and longitude
would get a pirate in the vicinity of the treasure, but it was
the landmarks – from which a pirate then counted off so many paces
– that would pinpoint the booty’s exact location.
Of course, when it came to counting off paces,
the size of a pirate’s boot had great impact. If the pirate who
buried the treasure wore a size 10 boot and the pirate looting
the treasure wore a size 12 boot, six paces wouldn’t put him and
his shovel-baring crew in the right spot. No wonder it took them
so long to find buried treasure – if they ever found it at all.
In modern car manufacturing, there are literally
thousands of “Xs” marking the spots. Unlike in the pirate
days, tolerances aren’t measured in miles, yards or even feet;
they’re in fractions of an inch – millimeters to be exact. Tolerances
of plus or minus 1 mm to 2 mm were unheard of just a few years
ago; now they’re common.
One of the ways in which car makers perform
these amazing feats of accuracy is by using a process called form
and pierce to a “net” build position. This process improves
the accuracy of locating fenders, doors, hoods, etc.
What is Form and Pierce?
Form and pierce is a manufacturing process
that forms a flat surface with a pierced (punched) hole. This
process is used right after the main structural components are
welded together. The form-and-pierce process provides a 3-D reference
and fastening point for attaching other sheet-metal components
or suspension parts.
When main structural components (superstructure)
are fixtured, clamped and then welded, there’s always some misalignment
or variation. This misalignment is small compared to manufacturing
methods of only five years ago, but it’s an area in which all
car companies are working to improve.
To compensate for the slight shifting of the
main structural parts during assembly and welding, the formed-and-pierced
locations now take out most of the variation by locating mounting
points or holes to a “net” position. The “net”
position, in real terms, is an imaginary line that’s the goal
or standard car companies are shooting for. Fasten a front fender
to a formed-and-pierced upper rail using this process, and the
fit of the front fender in relationship to the hood and front
door becomes extremely accurate.
Formed-and-pierced components virtually eliminate
the need for shims and washers. If you’ve ever worked on one of
GM’s SMC minivans, the mill and drill pads that correctly locate
the SMC panels perform the same function as the formed-and-pierced
locations on steel production vehicles.
Repair Instructions
The challenge for repairing a vehicle made
in the form-and-pierce process isn’t difficult if you understand
a few basic procedures.
First, the majority of replacement panels
will come with the hole already “pierced.” Because the
forming operation is a function of the factory, you’ll have to
duplicate the formed portion with shims or washers. The washers
and/or shims should come with the service part.
Examples of vehicles using the form-and-pierce
process are the 1997 Buick Park Avenue and the 1993 and newer
“F”-body Camaro/Firebird. All of these vehicles have
a formed-and-pierced upper front rail. If the rail of the Camaro/Firebird
is replaced, the only way to restore exact locations for the fender
is to duplicate the formed portion of the rail with adhesive washers.
The washers must be applied to the inside
of the service part. To do this, the mounting surface must first
be cleaned with soap and water and then with a wax and grease
remover. GM cautions against using just any old washer because
of improper positioning of the rail – so the washers that have
been piling up in your tool- box won’t work.
Installing a new upper rail to either the
Park Avenue or the Camaro/Firebird will also require careful and
accurate 3-D measuring to ensure the exact location of the service
part. In the Park Avenue Service Manual, the upper-rail fender-mounting
bracket has three formed-and-pierced locations that are dimensioned.
What about repairing a formed-and-pierced
panel versus replacement? Repairing a damaged formed-and-pierced
location can be done with hammer-and-dolly techniques. If the
hole is deformed, accurate redrilling is a must. Use 3-D measuring
to ensure the exact location of the formed surface and drilled
hole.
What do you do if the service part comes with
no holes? Service parts without holes must have a template and
instructions included with the service part. To improve the accuracy
of drilling, you might want to try an automatic center punch and
a step drill versus the hammer, center punch and single-drill
routine. Automatic center punches can be purchased at industrial
jobbers who serve machine shops and tool-and-die shops.
Note: As vehicles become more accurate
or closer to perfect, measuring becomes a vital part of the repair
procedure. Even though a vehicle may be symmetrical, it’s in the
best interest of quality repairs to follow OEM measuring data
instead of measuring the undamaged side of the vehicle and then
using those dimensions to measure the damaged side of the vehicle.
If a measurement is off by 2 mm on the undamaged side and you
then use that measurement on the damaged side, you could potentially
have a dimension off by 3 or even 4 mm.
Navigating Uncharted Waters
Having the correct, up-to-date service manuals
and/or service bulletins is an important part of the repair process
now. In the future, when the form-and-pierce process becomes
more common during vehicle assembly and service parts need to
be drilled prior to installation, the instructions and template
that come with the service part must also become part of the repair
process. Think of them as your map.
With mediocre measurements and a rickety ship,
a pirate got only one chance to find the buried treasure. If he
succeeded, he was rich; if he failed, he walked the plank and
swam with the sharks. With far more accurate instructions, you
won’t find buried treasure, but you will be rewarded with quality
repairs.
Fred Kjeld is a contributing editor to BodyShop
Business.
