General dynamics-deburr

1. Society of
Manufacturing
Engineers
1991
CJALL RIGHTS RESERVED
MR91-125
Deburring and Finishing
Processes at General Dynamics
author
THOMAS T. BUMP
Manufacturing Technology Engineer
General Dynamics
Fort Worth, Texas
abstract
Mechanical deburring and finishing processes used in the highly specialized aerospace
industry are cost-effective methods for meeting demanding standards. The processes
discussed address both flat sheet metal and machined parts. These processes Include
sheet deburr with cylinder, disc, and belt and also machined parts with robot. machlne
tool and slurry. Also addressed are results which have been obtarned from development
activities during recent years.
conference
Deburring and Surface Conditioning ‘91
February 19-21, 1991
Orlando, Florida
index terms
Blasting
Deburring
Finishing
Slurries
Society of Manufacturing Engineers l One SME Drive l P.O. Box 930
Dearborn, Michigan 48121 l Phone (313) 271-1500

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3. MR91-125
INTRODUCTION
General Dynamics Fort Worth Division is a high-
technology aerospace manufacturing company. Our
principal products are weapons systems and electronic
products whic:h are built to very demanding standards.
Achieving these high standards cost-effectively requires
that part finishing, including deburr, becomes a maljor
cost-reduction objective. Lowering deburr and finish
costs is therefore an ongoing effort at General Dynamics
as it is throughout industry. Our approach is to
implement mechanical equipment to minimize the time-
consuming and expensive process of hand deburr and part
finishing.
General Dynamics is expert at building weapons systems,
but we are not builders of manufacturing equipment.
When there is a need for a new process or for an
improvement on an existing one, the experts in that
field are ca.Lled in for consultation. Of course, we
often do limited experimentation so that we can more
clearly define our requirements: however, suppliers are
the key to our success.
For example, mechanical methods for deburring and
finishing bo,th sheet metal and machined parts have
evolved greatly in the last ten years. Manual,

4. MR91-125-Z
vibratory, and wide-belt sanding were the three main
methods for finishing parts at that time. Today, there
are chemical processes, EDM, drums, discs, robotics,
blasting, machine tools and other methods for part
finishing. We use most of these processes at our Fort
Worth plant.
This paper addresses: (1) current capabilities for
mechanically deburring aluminum parts and 2) plans for
future automation of required deburr processes. The
discussion of our current capabilities will be divided
into two areas: sheet metal parts and machined parts.
Parts made from sheet stock up to 3/8-inch thick are
fabricated in the Sheet Metal Shop. The Machine Shop
fabricates all parts from plate stock and sheet stock
3/8-inch thick and above. The deburr equipment and
procedures for each shop will be discussed separately.
The results we have obtained from development activities
during the past few years will also be discussed.
Manual and tumble deburr are used extensively throughout
industry and will not be included in the discussion
except in the Future Automation section. Also, aluminum
will be the only metal addressed.
BACKGROUND
The Fort Worth Division's principal product is the
F-16 fighter aircraft. Parts for the F-16 are produced
to demanding specifications with the same tight
tolerances and finish requirements as in all of the
aerospace industry's advanced products. Machined parts
range from bulkhead, spars and formers down to small (2-
inch by Z-inch) parts. Some typical machined parts are
shown in Figure 1. Sheet metal parts also vary by about
the same dimensions.
Finishing requirements for all parts are established by
Engineering. After a burr has been removed, an edge
break requiring a . 015 inch radius or chamfer (with tol-
erances) is the primary quality concern. Our equipment
must produce the required finish or we have to complete
the parts by hand. By presenting the equipment, parts
and requirements, attention may be focused to help
resolve our types of problems.
Sheet METAL
Two types of mechanical deburr equipment are used in the
Sheet Metal Shop for flat parts. The most recent type
consists of a horizontally-mounted rotating flat media
disc which deburrs the.parts. The parts are fed into
the machine on an endless conveyor belt and are held on
the belt by '*vacuumV@. The second type of equipment is
a horizontally-mounted media cylinder which both rotates

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and oscillates. Parts are fed into this machine on
driven rollers. Both types of equipment have single
pass capability and utilize flood coolant. (The Fort
Worth Division does not use wide endless-belt sheet
deburr machines). Vibratory and manual methods are also
used for flat and formed parts, but only the sheet
deburr equipment will be discussed.
Figure 2 Sheet Finishing System With 50 Inch
Wide Capability
The newest system (Figure 2) is two machines operating
together to allow single-pass finishing of parts.
Deburring is accomplished by a 66 inch diameter
rotating, abrasive impregnated nylon disc pad. As the
part travels through the machine on the conveyor belt,
part of the disc comes in contact with the workpiece.
In addition, the disc is attacking the part from many
directions. This is significant because with sheet
metal parts the burr is not always in the same location
nor is the burr always consistent.

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Figure 3 Parts Are Dried After Single Pass
Finishing
The task of mechanically finishing a part consists of
removing the burr and radius the edge without doing too
much or too little. Using this system the conveyor
speed, each disc rotation speed and the media pressure
of each disc can be varied independently. This allows
the operator the required flexibility to control the
process. One pass, however, is not always adequate.
Hard material and parts with heavy burrs require manual
touch-up before or after the mechanical operation.
The machine that finishes the bottom side of the part /is
shown in Figure 3. As the part is going through this
machine it is held upside down on the conveyor belt.
The second type equipment we use for deburring does
little for finishing a part, but it does remove burrs
even on hard material. This equipment type (Figure 4)
also has single-pass capability. Horizontally-mounted
media cylinders are above and below the pass-line of the
part. Driven rollers carry the part through the machine
while the media cylinders both rotate and oscillate.
Uneven media wear is a big problem with this type of
machine as is maintenance because of all the moving

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Figure 4 Sheet Deburr With 24 Inch Width
Capability
parts. This type of machine has been used in the
aerospace industry for over ten years. Both these
systems are ideally suited for volume work.
MACHINED PARTS
For machined parts, many of the larger parts are
deburred by a pre-programmed robot with an abrasive
bristle brush. Another method for deburring machined
parts is to use the machine that produced the parts - a
method we employ in our Flexible Machining System (FMS).
Still another area in the FMS uses a robot to move a
part across a rotating brush to remove cutting tool
marks. This same robot is then used to feed the Slurry
Finishing System (SFS) which produces a matte finish on
the part.
With robotic deburring, the parts are presented to the
robot via a four-sided positioning cube (Figure 5). The
robot manipulates the rotating brush over one entire
face of the cube with four consecutive patterns of
motion. The cube then rotates a new surface to the
robot and the process is repeated while the just-
finished part is unloaded and another part is loaded.
Parts with deep pockets and internal corners require
manual finishing after mechanical finishing (Figure 6).
The most ambitious and challenging automated finishing

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Figure 5 Robotic Deburring With Positioning Cube
Figure 6 Deep Pocket Deburring On Bulkheads

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occurs in the Flexible Machining System (FMS) (see
Figure 7). A stainless steel wire brush is programmed to
deburr the surfaces that have just been machined. Many
configurations of brushes and tools were evaluated for
the FMS. Nonabrasive material and hard tooling either
did not do the job or were too difficult to control.
Abrasive materials produced the best results; however,
residue from the abrasives has been judged to be a
potential problem for the machine tool. The use of any
abrasive material is on hold at this time.
Figure 7 Overview Of The Flexible Machining
System
The brush judged best for the FMS is a one-inch diameter
stainless steel brush made with ,008 inch wire. A
plastic bridle is used to keep the brush from spreading
too much during finishing. Figure 8 shows one of the
test set-ups used to evaluate different brushes.
After an order of parts has been machined, inspected
by the coordinate measuring machines (cm) and
accumulated, the tooling tabs must be removed and the
attaching surface must be finished. These tasks are
combined with the Slurry Finishing System (SFS).

11. Figure 8 Testing Of Brushes And Resulting Finish
Figures 9 and 10 show the robotic station for tab
trimming and burr removal. The operational sequence is
to remove all but one tab and deburr the mismatch(s).
The part is then fed to the SFS (Figure 11) where it is
held by the remaining tab. The part is blasted with a
slurry mixture of aluminum oxide and water. After the
part is rinsed and dried, the robot unloads the part aind
removes the last tab and presents the finished part to
a Parts Marking System. Here a label is applied that
contains information required for final inspection. The
finished part is then returned to the tray.
FUTURE AUTOMAT:m
One of the near-term projects is a Two Table Burr (TT13)
system for machined parts. This will be a gantry
mounted brush with two tables for the parts to be
finished on (Figure 12). After the parts are manual:Ly
attached to a table, the system operates with the tab:Le
rotating as the rotating brush travels on the gantry.
While parts are being finished on one table, the second
table is available for load/unload activities.
The system is programmable to provide variable feed and
rotation speed for both the brush unit and the tables.
The brush roller unit is planned to be 12 feet long and
22-inches in diameter. It will be made up of separate

12. Figure 9 Robotic Removal Of Tool Tab
Figure 10 Robotic Finishing Of Attaching Surface
brush units about one-inch wide with 1-1/2inch spacers
between each unit. The brush bristles will be a unique
rectangular design. The tables will be approximately 8-
feet in diameter.

13. / 1
Figure 11 Robot Feeding Part To The Slurry
The TTB system is expected to be a significant
advancement for machined part finishing. Current
calculations show a high rate of return with a short
payback period.
A long-range finishing project under consideration
involves the combination of a robot, vision and a flow-
thru system for the FMS (Figure 13).
The system will. have a deposit and pickup station to
receive parts from the Automated Storage/Retrieval
System (AS/RS). Parts would be picked out of the AS/RS
trays by a robot and placed into a "Flow-Thru" vibratory
machine. The parts would also pass through a wash/dry
station before unloading on a conveyer. The conveyer
would bring the parts back in the order they were put
into the system.
Once within the robot's reach, a vision recognition
system would identify the correct orientation so the
robot can return the part to the tray. When all parts
complete the cycle, the tray is delivered back to the
AS/RS. At this; point the parts are in queue for the

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Figure 12 Two Table Burr System For Machined
Parts
Tool Tab and Removal Station.
Another process under consideration is the use of carbon
dioxide pellets (CO-2) blasting to clean composite and
metalic tools. Current methods require hand scrapping,
chiseling and sanding tools to remove built-up tape and
residue on tools. More testing and evaluation of this
process is needed before it is approved for production.
Although we employ many large automated systems for the
reduction of labor, the majority of work is still
performed by hand. New deburring techniques and
processes are still needed and there is a long way to go
to minimize hand finishing labor.

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