Method of machining composites

Abstract: According to invention there is now provided a method of machining and shaping a through opening in a fibre reinforced composite material starting from a preformed hole. At least one rotation symmetrical milling body (3) with substantially smaller diameter than that of the preformed hole (2) is placed in it and the opening is machined and shaped by the milling body partly rotating around its own axis, partly performing a translational movement relatively the edge of the opening. According to the method the fibre reinforced material is hereby oriented in such a way that the axis of rotation of the milling body (3) is essentially perpendicular to the longitudinal direction of the fibres at the edge of the opening. The size and/or form of the finished opening differ significantly from that of the preformed hole. The radial spread of the damages and/or the defects define a lower limit for amount of material removed.

Description: The present invention relates to a method of machining and shaping a through opening in a fibre reinforced composite material. International patent application WO-A-93/23200 (& EP-A-0 641 272, prior art according to Art.54(3) EPC) discloses a method of machining and shaping a through opening with damagefree edges in a fibre reinforced composite material with high precision by placing a rotation symmetrical grinding body in a preformed hole with the composite material being oriented in such a way that the axis of rotation of the grinding body is essentially perpendicular to the longitudinal direction of the fibres at the edge of the opening. The opening is machined and shaped by the grinding body partly rotating around its own axis, partly performing a revolving motion relatively to the edge of the opening. The grinding tool may be used also for preforming of the opening. It has now turned out that by using a milling body significantly higher rate of cutting, less heat generation as well as better machining economy can be obtained. This has been attained by the features of claim 1. By using a so called drilling mill the whole operation can be performed with only one tool. The invention is described closer in the following under reference to the accompanying drawings which are not embodiments of the invention but show examples useful for understanding the invention. Figures 1 and 2 illustrate how a through opening is shaped in a fibre reinforced composite plate using a rotation symmetrical milling body according to the invention. In figure 1, 1 is fibre reinforced laminate, 2 - preformed hole, 3 - milling body, 5 - axis of rotation of the milling body and 6 - damages and/or defects. Figure 3 shows a side view of a milling cutter provided with inserts according to the invention and figure 4 shows a top view of the mill in figure 3. In figures 3 and 4, 10 is - milling body, 11 - insert, 12 - central hole in the insert, 13 - side surface, 14 - clearance face and 15 - edge surface. The method is described for the case that the material is present in form of a plane plate 1, a laminate composed of a number of lamellas containing continuous fibre reinforcements whereby the lamellas are piled on top of each other. The fibres lie oriented in planes parallel to the plane of the laminate, whereby the fibre directions are 0°, 90°, 45° and -45°. An opening 2 in the laminate is shaped first by, for example, drilling. Hereby damages and/or other defects 6 frequently arise at the edge of the opening. In the preformed hole 2 a rotation symmetrical milling body 3 is placed. Hereby the laminate is oriented in such a way that the axis of rotation of the milling body 5 is perpendicular to the longitudinal direction of the fibres, i.e., perpendicular to the plane of the laminate. The opening 2 is machined by the milling body 3 partly rotating around its own axis 5, partly performing a translational movement relatively to the edge of the opening 2 so that damages and other defects 6 are removed. The size and/or form of the finished opening differ substantially from that of the preformed hole 3. The milling body is suitably a so called milling cutter in high speed steel, solid cemented carbide or with brazed or indexable inserts of cemented carbide, titaniumbased carbonitride alloy, so called cermet, or ceramics. The milling cutter (if high speed steel or cemented carbide) or the inserts are preferably coated with at least one thin layer of wear resistant material with in itself known CVD-and PVD-methods such as TiC, TiN and/or Al 2 O 3 . A thin layer of diamond is particularly suitable. The total thickness of the layer is <20 µm, preferably 2-10 µm. For making larger openings a milling cutter with the design shown in fig 3 and 4 is particularly suitable. It consists of a milling body 10 equipped with thereto removable inserts 11. The inserts 11 are in the shown case provided with a central hole 12 through the insert, wherein a threaded locking pin (not shown) is inserted to clamp the insert. When machining the milling cutter rotates counterclockwise in fig 4 whereby the side surface of the insert 13 forms the clearance face of the cutting edge 14 and the edge surface 15 forms the rake face of the cutting edge. A number of inserts 11 are at the shown embodiment arranged in a spiral path in the 10 longitudinal direction of the milling body. Four such spiral paths are uniformly distributed around the circumference of the milling body 10.

Claims: Method of machining and shaping a through opening in a fiber reinforced composite material (1) with damagefree edges by a machining operation whereby one rotation symmetrical milling body (3) is brought into engagement with said composite material by partly rotating around its own axis (5), comprising the steps of A) providing said body in the shape of a drilling endmill with smaller diameter than the finished opening having a body defining a longitudinal axis of rotation, and a plurality of cutting edges disposed uniformly on an outer periphery of said body, extending generally spirally about said axis of rotation, B) forming a initial hole (2) in the composite by rotating said endmill and bringing said endmill into cutting engagement with said composite material, said axis of rotation oriented substantially perpendicular to a longitudinal direction of reinforcement fibers disposed at a edge of said initial hole, said edge of said initial opening having damages or defects (6) possessing a radial spread; thereafter C) moving said endmill along said edge of said initial hole while rotating said endmill about said axis of rotation, with said axis of rotation offset radially from a center axis of said initial hole and with said cutting edges in contact with said edge of said initial hole so as to enlarge said initial hole into a finished opening, the size and/or geometry of the finished opening differing significantly from that of the initial hole; and D) performing step C to remove a amount of said composite wherein a lower limit of said removed amount is defined by said radial spread of said damages or defects. Method according to claim 1, characterized in that the milling body (3) is equipped with inserts (11) of cemented carbide. Method according to claim 1, characterized in that the milling body (3) is equipped with inserts (11) of ceramics. Method according to any of the claims 2-3, characterized in that the inserts (11) are coated with at least one thin layer of wear resistant material. Method according to claim 4, characterized in that the inserts are coated with at least one thin layer of diamond.

Inventors: THELIN ANDERS, THELIN, ANDERS
Applicants: SANDVIK AB, SANDVIK AKTIEBOLAG
Application year: 1993
Main classification: B23C3
IPC codes: B23C3, B23C5