In 1972 a manufacturing engineer stated that approximately 90% of the cost of the farm equipment his firm made was involved in making and finishing holes. This seemed astounding but has since been confirmed for most moving machinery, including automobiles. Since the pleasing shapes, unique weight,cost, design flexibility, and ease of fabrication of FRP are now being used with success in automobiles, the chemist turned machinist must now develop the skills and experience to utilize modern tooling which has been designed for FRP. Slightly modified cast iron tooling is not acceptable if we want to achieve true potential of FRP. Efficient, high volume, high speed, cost effective drilling of FRP can best be accomplished with tooling engineered to perform productively with long life and to exact tolerances. Modern technology must be used to establish our unquestioned leadership in automobile manufacturing. Imagine, press fitting bearings into FRP material that has only been drilled, it is being done today.

Completely turning our backs on the machining expertise that the metal chip makers have refined and refined and refined into one of the highest art forms and most efficient energy resource skills in the world is not wise. Rather, we as engineering professionals must test the fundamental assumptions of the metal chip maker and the plastic chip maker to separate the elements into those that are transferable to plastic machining and those that are not.

This paper is limited to hole making. Other machining areas will be the subject of subsequent papers. Exotic techniques using lasers and the more familiar piercing and punching techniques have future potential along with high pressure water jets and ultrasonic machining. But, initial costs are great and there are limitations caused by physical application restrictions.Most of these unusual fabrication techniques have not demonstrated an ease of practical and NOW applicability on the current production floors. The tooling we are discussing is AVAILABLE NOW and APPLICABLE with EXISTING WORK FORCE PERSONNEL.

The basic tool for hole making is "The Drill Bit" which has been in use for over 5000 years. In that time the shape has changed little because it is efficient and cost effective. Industrialization has made the art of drilling of a supreme importance because of cost and the need for increased productivity. The major emphasis for improvement of the cutting tool has been on materials, coatings, or different heat treating processes. The cutting tool geometry has been improved little and is a result of the fabrication process.

The precise nature of drilling is complicated. Tooling used in the manufacturing of FRP products must be designed specifically for FRP not just modified from the older cast iron/metal chip making technology. The tooling must be effective in producing a quality hole must be cost effective with existing work forces and machine tools.

FRP is a heterogeneous material. This is the most important and basic difference between FRP machining and homogeneous metal chip making. Each element or component of FRP (and even subgroups) must be dealt with individually to get the desired results.

The three major FRP elements are ,fillers, resins, and fibers.

Most commonly used fillers are chemically inert, abrasive, and insensitive to temperature variations. They tend to be heavy, and once jarred loose from the binding action of the resin system are easily moved out of the cutting zone. The material must be moved out of the hole. The nature of the material makes it unresponsive to cutting tool geometries and accept for its abrasiveness is not a major consideration of tool design. Because of the bulk of the chips developed and the possibility that they could become air borne and therefore harmful to operators, vacuum collection at the source is suggested when ever possible.

All resins are sensitive to heat. They burn, sublimate, or become sticky or tacky. Each of these conditions is not desirable and is not necessary with modern tooling. The least heat producing geometry is a high rake shearcut (See Figure 1) with no tool drag. The efficient shearing of resin is effected by speed (RPM) and feed rate (inches per minute or millimeters per minute) plus tool geometry. Resins do not crumble under cutting pressures.They shear if properly cut. The blending of different types of resins effect the performance of a cutting tool. The addition of 'a little ABS' will achieve different end products and also create different demands on cutting tool performance.

Reinforcing fibers must be separated into two main subgroups, organic and inorganic. The fine edge of cutting tool technology has recently been extended to easily and efficiently machine the aramid fibers made by duPONT. This paper is limited to inorganic fibers made of glass and graphite. As the hybridization of fiber structures become common, each fiber will have to be considered separately.

Fiber orientation has little effect on the performance of a correctly functioning and sharp cutting tool. This is because of the complicated multi-dimensional helical plane path of the cutting edge. The impact between the cutting edge and the fiber is the only condition for which we have developed parameters. The cutting tool does not cut the glass/graphitefibers. The fibers are shattered by impact or crushed by pressure. You do not break a window by leaning on it. You strike it with a hard object. The faster you hit it the more dramatic the fracture. The same is true for modern cutting tools machining FRP. Another problem with drilling in FRP is the faster the cutting edge goes the greater the chance of developing heat which will effect the resin adversely. We recommend a speed between 300 and 600 surface feet per minute with a feed rate of 0.010" inches per revolution (ie. 100 to 200 meters per minute and .25mm feed per revolution).These cutting conditions have worked well in all fiber densities from 65%to 15% and resin densities of 75% to 6%. These conditions will produce clean holes at the rate of 60 inches per minute with a inch cutter. (1.5 meters and 12.7mm) (See Figure 2).

The three basic type of tool geometry are best described as a function of the rake angle on the inside of the cutting edge. (See Figure 1) The negative and neutral rake shapes have a useful place in the metal chip making process. They do NOT have a useful place in high performance fiber glasshole making. The more exaggerated the positive rake angle the more fragile the cutting edge. The cantilever bending force on the cutting edge demands strength if the cutting edge material. The bending moments encountered in normal drilling are difficult to predict, suddenly applied, and large (like the break out shock upon exiting). The material best suited to resist bending, flexing, torquing, and general abuse is High Speed Steel. High Speed Steel is the material most often used in the manufacture of metal cutting drills. High Speed Steel does not have enough abrasion resistance to have a useful life as a cutting edge in FRP. The cutting geometry groundon the modern HSS twist drill has approximately 60% of its diameter ina neutral or negative rake shape which will produce unwanted heat. Tungsten carbide has the abrasion resistance and hardness to be very effective as a long lived cutting edge material. Tungsten carbide, though does not have the ability to bend and flex. It is hard but brittle.

The ideal cutting edge material would be as hard as diamond and as toughas High Speed Steel. The recently perfected sub-micron tungsten carbide can fit this description. This new material is harder than regular tungsten carbide and has greatly improved resistance to bending (almost double conventional tungsten carbide). The newly developed (grade C-2) DG-106 a proprietarysub-micron tungsten carbide is able to survive the bending moments and shocks of drilling without breaking as easily as older conventional grades.As a result of this improvement we have been able to achieve very strong tools with acute positive rake angles. The positive rake angles are soacute that normal tungsten carbide would fracture. Because DG-106 is so much harder the material has a resistance to wear which is increased by a factor of about four.

A positive cutting edge is the most effective rake angle, the chisel edge at the very center of the cutter is also very important. If it is to large it will produce heat and require large thrust loads to push the cutting edge into the work piece. The ability if tungsten carbide to resist compression is well known. With this new grade of carbide, DG-106, we have been able to grind a very thin chisel edge which reduces the required thrust load. This geometry has proven that it will stand up to production requirements and longer wear life.

The production improvements are most dramatically effected by increased feed rates. Feed rate increases have reduced machining time by several fold. Individual machine operation improvements have been reported to have decreased the floor to floor time by 75%. Or said another way, at the end of a shift four time more parts have been completed. The quality of the hole produced has eliminated the costly hand deburring operations which can result from the use of modified cast iron tooling. Conversion to the high performance cutting tool is direct and does not require modification of existing machines accept for increasing the spindle speed. The acute angle on the cutting tool edge allows the tool to penetrate faster and as a result the thrust required to penetrate drops to about 8 pounds or4 kilograms. Since the thrust pressure is often less than the force necessary to over come static friction in the drill feed mechanism, care must be exercised to see that hydro-checks or similar devises are properly maintained and the tool is not allowed to jump into the work piece. If this condition exists, the tool may cut the material for a while but the sudden forces on the cutting edge will eventually bend or break something. Let the cutting tool cut. If you do, the quality of the hole will equal that which is routinely achieved in metal working.

The tooling is available now to greatly improve your fiberglass and graphite drilling operations. The tools are proprietary and unique, but by no means "special," since they are available "off the shelf". These tools are designed to make maximum use of the physical strengths of DG-106 with extreme positive rake angles and minimal chisel edges. Three separate methods of cutting edge delivery are offered (See Figure 3). The solid shank style (WONDER DRILL) shown on the left, and the twist drill (WONDERTWIST DRILL) shown on the right are used in automatic drilling equipment.The drill guide system (Hole-O-Magic) is designed to be used with air or electric hand drilling motors. When fitted with a socket adapter, the standard drill motor can drive all sizes from 0.118" to 1.0 inch. An internal compression control spring regulator withdraws the tool after drilling. Its pressure control compensates for the "break through lurch," or sudden and uncontrolled increase in feed rate as the tool breaks through the last few fibers. It eliminates partially drilled holes, because the operator must depress the unit completely each time. He does not feel the changes in pressure as the hole nears completion. This new tooling can at least double production output. This new tooling requires a maximum of 15 pounds pressure for compression,and most applications require only 6 to 8 pounds thrust. The machines and fixtures used to hold the guide units now can be much lighter weight than those used in metal working. This results in fixtures and machines which are much less costly to build and maintain.

To achieve the promise of FRP we must use tooling which is designed to be efficient and cost effective. Metal cutting technology must be critically analyzed for specific applicability. You can achieve metal working tolerances with the proper tooling and cutting conditions.

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International Carbide Corporation
Last Update April 30, 2002