A method for boring well defined holes in a composite material such as graphite/epoxy is discussed. A slurry of silicon carbide powder and water is projected onto a work area of the composite material in which a hole is to be bored with a conventional drill bit. The silicon carbide powder and water slurry allow the drill bit, while experiencing only normal wear, to bore smooth, cylindrical holes in the composite material

Clemons, Johnny M.

Daniels, Julia G.

Ledbetter, Frank E., III

Penn, Benjamin G.

White, William T.

English

NASA Technical Reports Server

United States Patent 1191 p i ]  Patent Number: 4,680,897 
Daniels et al. [45] Date of Patent: Jul. 21, 1987 
METHOD FOR MACHINING HOLES IN 
COMPOSITE MATERIALS 
Inventors: 
Assignee: 
Appl. No.: 
Filed: 
Julia G. Daniels, Madison; Frank E. 
Ledbetter, 111, Huntsville; Johnny M. 
Clemons, Trinity; Benjamin G. Penn; 
William T. White, both of Huntsville, 
Ala. 
The United States of America as 
represented by the Administrator of 
the National Aeronautics and Space 
Administration, Washington, D.C. 
804,039 
Dec. 3, 1985 
Int. c1.4 .......................... B24C 1/08; B23B 35/00 
U.S. C1. .................................. 511’281 R, 408/1 R 
Field of Search ...................... 29/557; 408/1, 144, 
408/145, 59, 60; 51/281 R, 328, 292, 323 
References Cited 
U.S. PATENT DOCUMENTS 
2,478,846 8/1949 Smith .................................... 408/59 
3,074,392 1/1963 Fisher ..................................... 408/1 
3,699,719 10/1972 Rozdilsky ............................. 51/328 
4,519,732 5/1985 Sutcliffe .............................. 408/1 R 
FOREIGN PATENT DOCUMENTS 
41885 4/1978 Japan ................................... 408/144 
3180 1/1981 Japan ................................ 51/28] R 
Primary Examiner-William R. Briggs 
Attorney, Agent, or Firm-Joseph H. Beumer; John R. 
Manning; Leon D. Wofford, Jr. 
[571 ABSTRACT 
A method for boring well-defined holes in a composite 
material such as graphite/epoxy. A slurry of silicon 
carbide powder and water is projected onto a work area 
of the composite material in which a hole is to be bored 
with a conventional drill bit. The silicon carbide pow- 
der and water slurry allow the drill bit, while experienc- 
ing only normal wear, to bore smooth, cylindrical holes 
in the composite material. 
2,272,271 2/1942 Mallory ................................... 408/1 5 Claims, 2 Drawing Figures 
https://ntrs.nasa.gov/search.jsp?R=19870016058 2020-03-23T15:34:39+00:00Z
U.S. Patent JuL 21,1987 4,680,897 
1. 
1 
4,680,897 
METHOD FOR MACHINING HOLES IN 
COMPOSITE MATERIALS 
ORIGIN OF THE INVENTION 5 
The invention described herein was made by employ- 
ees of the United States Government and may be manu- 
factured and used by or for the Government for govern- 
mental purposes without the payment of any royalties 
thereon or therefor. 
BACKGROUND OF THE INVENTION 
The invention relates to the machining and drilling of 
holes in composite materials mainly of the class charac- 
terized by being filament or fiber reinforced plastics. l5  
These composite materials are finding wide application 
in aircraft industries and in space programs of the Na- 
tional Aeronautics and Space Administraction. How- 
ever, continued use of composite materials requires 
routine experimental investigation to determine speci- 20 
men properties such as mechanical, strength, elastic, 
etc. Most important of the properties is the in-plane 
shear strength which is a property of composite materi- 
als such as graphite/epoxy which needs to be routinely 
determined. 25 
Shear tests typically require drilling of holes in the 
composite materials. Due to the nature of composite 
materials, the problem occurs routinely that damage to 
the drill bits as well as to the materials occur during the 
boring of holes in the materials which are required for 30 
performing the above tests. Typically, a conventional 
drill press is utilized to drill these bores in the material. 
Even when silicon carbide or low-carbon steel drill bits 
are utilized, the damage to the drill bits still occurs. No 
conventional drill bits have been found on the market 35 
which can stand the rigors of routine drilling of the 
holes in the composite materials heretofore described 
without damaging the bit. In testing the composite ma- 
terials for the above noted properties, a test commonly 
referred to as the “three-rail shear test” is commonly 40 
employed. This test is discussed in Composite Material 
Design Guide, University of Delaware, Vol. 1, Newark, 
Del. (1983), and in Experimental Mechanics of Fiber 
Reinforced Composite Materials, by 3. M. Whitney, et al., 
Prentiss-Hall, Brookfield, Conn., Pg, 160 (1982). In 45 
performing the three-rail shear test, nine holes of 178 
inch diameter are drilled through the thickness of a 
board of composite material. The thickness of the 
board depends on the nature of the particular compos- 
ite material. For the above referred to graphite/epoxy 50 
composite material, a board of 0.06 inches is utilized. 
During preparation of the sample board, considerable 
trouble may be encountered in attempting to bore the 
nine holes with conventional drill bits such as described 
above. Various combinations of tool speed and pres- 55 
sures may be used, however, even when using water 
cooling, the end result is usually an unusable hole. 
Accordingly, an object of the present invention is to 
provide a method for drilling test holes in a board of 
composite material during a three-rail shear test without 60 
damaging the drill tool or the material specimen. 
Another object of the present invention is to provide 
a method for machining a hole in a composite material 
of the fiber-reinforced plastic type without damaging 
the drill tool or the material. 
Still another object of the invention is to provide a 
method for drilling or machining a uniform regular bore 
in a test specimen of composite fiber-reinforced plastic 
10 
65 
material so that accurate testing of the material for shear 
strength may be had. 
SUMMARY OF T H E  INVENTION 
It has been found that the above objectives can be 
accomplished according to the present invention by 
adding a liquid slurry mixture of water and silicon car- 
bide powder to the composite material board at the 
location where the board is to be drilled or machined. It 
has been found that using a water slurry of silicon car- 
bide powder directed on the composite board being 
tested results in a test operation that proceeds smoothly 
and efficiently. Normal wear is encountered by the tool 
bits, whereas in the past the edges of the drill fluting and 
sides of the drill would become pitted and chipped. A 
bore having a smooth, well-defined interior surface is 
formed in the test material having an accurate and uni- 
form diameter, whereas in the past only a jagged, non- 
uniform opening was formed in the material. The holes 
are bored rapidly through the boards whose thicknesses 
range from 0.04 inches to 0.06 inches and whose ply 
orientations range from unidirectional, quasi-isotropic 
symmetrical, and cross-ply. 
DESCRIPTION O F  T H E  DRAWINGS 
The construction designed to carry out the invention 
will hereinafter be described, together with other fea- 
tures thereof. 
The invention will be more readily understood from 
a reading of the following specification and by refer- 
ence to the accompanying drawings forming a part 
thereof, wherein an example of the invention is shown 
and wherein: 
FIG. 1 is a schematic illustration illustrating the 
method of the present invention for drilling and ma- 
chining bores in a fiber-reinforced composite material 
specimen; and 
FIG. 2 is an illustration of the layout for conducting 
a three-rail shear test for testing the properties of a 
composite material specimen in a conventional manner. 
DESCRIPTION OF A PREFERRED 
EMBODIMENT 
Referring now in more detail to FIG. 1, a reservoir 10 
is illustrated for containing a water slurry of silicon 
carbide or other suitable material which may be used 
with the method of the invention. It is believed that 
other materials such as tungsten carbide or silicon ni- 
tride may also be used with the method of the invention. 
The reservoir 10 contains a water slurry of silicon car- 
bide wherein the slurry silicon carbide powder effec- 
tively consists of about 30 to 60 percent of the weight of 
the water slurry. It has been found that percentages of 
silicon carbide powder outside this range are not effec- 
tive. 
A pump 14 is connected to the reservoir 10 by means 
of a conduit 16. A conduit 18 connects the pump to an 
area disposed above the specimen board 20 of compos- 
ite material, such as graphite/expoxy being drilled or  
machined. The specimen board 20 being machined is 
supported on a support platform 22 of a conventional 
rotating boring tool such as a drill bit 24 carried by a 
drill press 26. Beneath the support board 22 is a collec- 
tion reservoir 28 for collecting the water slurry as it 
turns off of the specimen board 20. The conduit 18 may 
be a suitable length of copper piping or  other suitable 
material having an outlet 18a which is disposed above 
. 
~ 
4 
4,680,897 
providing a rotating boring tool for rotationally ma- 
chining the hole in a work surface of the composite 
material; 
fixedly supporting the composite material for receipt 
of said rotating boring tool in said work surface; 
applying a liquid slurry mixture of water and between 
thirty and sixty present silicon carbide powder to 
said work surface of the composite material; 
machinine the hole in said work surface on said com- 
3 
and in close proximity to the specimen board 20. By 
directing the water slurry directly onto the face of the 
specimen board 20, it has been found in accordance 
with the present invention that the drilling or machin- 
ing of regular three-rail shear test holes 32 illustrated in 
FIG. 2 may be done in a uniform and eficient manner. 
The water slurry provides a cutting medium for drill bit 
24 which allows drill bit 24 to produce well-defined 
cylindrical holes in specimen board 20. No tearing of io 
the material within the hole or pitting and chipping of 
the fluting of the drill bit occurs. The water slurry is 
recirculated after being collected in collection reservoir 
28 via a conduit 30 leading back to reservor 10. 
FIG. 2 shows a pattern for drilling the test holes in a 
composite specimen board according to the dimensions 
illustrated for the three-rail shear test specimen referred 
to above. No damange was done to the drilling tools 
during the curring operation except for possible loss of 20 material, having fiber reinforcement comprising: 
the cutting edge. However, it has been found that dull 
tools bore as fast, or even faster, than sharp ones. From 
observation of this phenomena, it was concluded that 
silicon carbide powder was actually boring the holes by 
the surfaces of the cutting tool and the surface of the 
composite material. It is Eo be understood, of course, 
that the process of the invention may be used for other 
reasons when it becomes necessary to drill holes in 30 
composite materials. 
Oils and other lubricants may not be used with the 
composite material to which the instant invention is 
directed because the oils tend to plasticize the polymer 
matrix of the composite material. 
While a preferred embodiment of the invention has 
for illustrative purposes only, and it is to be understood 
parting from the spirit or scope of the following claims. 
What is claimed is: 
1. A method for machining a Role in a composite 
material of the type having fiber reinforcement, com- 
posite Gaterial with said rotating boring tool while 
applying said liquid slurry mixture to said work 
surface; said liquid slurry mixture being allowed to 
become interposed between said rotating boring 
tool and the composite material as the hole is being 
machined, so that said liquid slurry mixture acts as 
a cutting medium for enabling said rotary boring 
tool to provide the hole with a well-defined, sub- 
stantially cylindrical interior surface. 
2. A method for machining a hole in a composite 
machining the hole in the composite material with a 
rotating boring tool while simultaneously applying 
a liquid slurry mixture of water and between thirty 
and sixty percent silicon carbide powder to the 
becoming interposed between said rotating boring 
tool and the hole for acting as a cutting medium. 
3. A method for machining a hole in a composite 
as set forth in claim or 2, further comprising: 
continuously recirculating said liquid slurry mixture 
during machining for continuous application of 
said liquid slurry mixture to the hole being ma- 
chine. 
4. The method of claim 2 wherein said composite 
3 5  material is a fiber reinforced plastic composite material. 
5. In a method for shear testing a fiber reinforced 
drilled into said material according to a prescribed pat- 
tern in a work area of said material, wherein the im- 
about 30 to 60 percent silicon carbide powder to the 
work area while said holes are being drilled by a rotat- 
ing tool to prevent tearing of said material providing 
uniform holes for effective reliable shear testing. 
15 
resulting action of the particles being trapped between 25 hole being machined; said liquid slurry mixture 
been described using specific terms, such description is composite plastic materia1 Of the type wherein are 
changes and variations may be made without de- 40 provement comprises introducing a water slurry of 
* * * * *  prising: 4 5  
5 
50 
5 5  
60 
65 


Method for machining holes in composite materials

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