Method for producing a die insert

Abstract: A method of producing a marking on diamond, pearl, precious or semi-precious stone. For producing the marking, the region on the surface to be marked is irradiated with an ArF excimer laser whose output beam is passed through a mask which defines the marking. Identification or security marks may be created. The same process can be used to produce strong and durable extrusion dies having irregular cross sections, and cross sections which vary with depth through the die material.

Description: BACKGROUND OF THE INVENTION a. Field of the Invention The invention relates to a method for manufacturing a die insert for use in an extrusion die according to the generic portion of claim 1, and a die produced by the method. Such a method is known from JP-A-58086924. This document discloses a thin plate-like diamond sintering body covered with a substance for reflecting 80% or more of laser light. A circular area of the sintering body is not covered by the reflecting substance, whereby laser light directed onto the surface of the sintering body will only impinge within the circular area onto the body whilst laser light impinging onto the reflecting substance will be reflected. The invention relates to treating a die insert made of very hard materials, in particular, diamonds, or other similar hard material and having a complete cross-section of the extrusion opening, for example, die inserts used in spinnerets, die assemblies for extruding wires, glass or synthetic fibers, with an ultraviolet laser energy source. It is also known to employ lasers for producing extrusion openings in die inserts used in extrusion die assemblies. Using lasers for producing extrusion openings is disclosed, e.g., in U.S. Patents 4,703,672 and 4,534,934. It is the object of the invention to provide a method of producing die inserts having a complex cross-section of the extrusion openings thereof and corresponding die inserts. A further object is to provide a method of producing die inserts with which such cumbersome operations of treating the extrusion passages such as finishing, polishing, de-burring and the like are eliminated or significantly reduced and corresponding die inserts. The above object can be achieved with a method having the features of claim 1 and a die insert having the features of claim 5. Advantageous developements are set forth in the dependent claims. One method according to the invention involves subjecting a diamond a pulsed source of laser energy in the ultraviolet region of the spectrum. A preferred source of energy is an excimer laser. Excimer lasers are pulsed gas-discharge lasers. In these lasers, a gas mixture (for example, argon and fluorine) is energetically charged and, upon sufficient charging, is caused to produce an intense emission of pulsed laser energy. Excimer lasers are conventionally used to produce a pulse or a plurality of pulses at wavelengths ranging from approximately 193 nanometers (nm), or 0.193 microns, to about 351 nm, depending on the particular raregas-halide excimer produced. Argon fluorine excimers produce laser energy at 193 nm. For radiation at this wavelength, the depth of penetration into pure diamond is very minimal. While diamond is highly energy transmissive across a broad wavelength spectrum, pure diamond has particularly low transmissivity, low reflectivity and high absorption at about 193 nm, which corresponds to nearly the cutoff frequency of the crystal. For this reason, the excimer laser energy is taken up in a particularly thin surface layer which is rapidly brought to a high temperature. A thin layer of material in the range of from several angstroms to several microns is in this way vaporized from the surface by each pulse, or alternatively may be partially graphitized by each pulse of the excimer laser. Vaporization of material serves to protect the stone from overheating because of the high energy of sublimation for diamond carbon. It is known by those skilled in the art that diamonds are rarely "pure" crystals. Instead, impurities in the form of nitrogen atoms substituted into the crystal structure exist in almost every stone. The cutoff frequency of a given diamond increases with increasing presence of nitrogen impurities, and may range as high as 300 nm. Therefore, while the preferred embodiment is described in terms of use of an ArF excimer laser, other lasers may be suitably employed, wherein laser. energy having wavelengths ranging from under 200 nm to about 300 nm can be provided. These include, in the ultraviolet range, krypton fluorine excimers (248 nm). The most effective laser wavelength for a given stone will always depend on the purity of that diamond. Thus, it will be understood the "about 193 nm" as used herein is meant to embrace a range sufficient to include the cutoff frequency of any given stone, i.e., from about 190 nm to about 300 nm. The diamond is irradiated through a mask Such masks can be mounted on or in front of the diamond. The spacing of the mask from the diamond surface is not critical because of the parallel radiation beam produced by an excimer laser, unless reduction optics are also employed, in which case the position of the mask is necessarily important. Masks may also be fabricated with areas having different transmissivities to laser energy at the desired wavelength, yielding marks with areas of differentiated contrast selected from a generated gray scale. Another beneficial aspect of the invention resides in the ability to modify or change the mask pattern between laser pulses, or between groups of pulses, so as to "animate" a sequence of patterns on the material to be irradiated. In the case of irradiating diamond, because the laser energy vaporizes a certain thickness of material with each pulse or group of pulses, an extrusion die having a bore of axially varying cross-sectional shape may be obtained. For example, a pyramidal hole has been created through a section of diamond. A spiralling hole may easily be created as well as a limitless number of differently shaped holes. With the use of appropriate optical elements, it is also possible to create other highly complex, three-dimensional shapes in a diamond crystal. It is still more advantageous to image the mask on a surface of the diamond through optical means which passes ultraviolet radiation, e.g., sapphire or fused quartz or fused silica. If the image to be produced is first reduced, a high energy density is obtained on the surface of the diamond and therefore a lesser number of pulses or a reduced output capacity of the laser is required. Another improvement in performance is obtained with the use of a beam homogenizer before the mask, as is well known to those skilled in the art. As noted above, some diamonds may be more advantageously marked according to the invention by using KrF, XeCl or XeF lasers. Alternatively, any laser source capable of delivering sufficient energy at the appropriate wavelength would suffice. As it has already been. indicated the excimer laser can also be used for producing extremely fine complex patterns in the production of diamond plate extrusion dies such as for use in extruding metal wire, glass fiber or synthetic fibers. By repetitively pulsing the excimer laser, thin diamond plates may be essentially "drilled" with the resulting hole in the form of the mask, after reduction. This permits creation of fabrics having new and as yet unappreciated qualities. For example, fibers having uniquely high nap could be produced and then woven into new materials having applications such as filters, substrates or insulators. A particularly advantageous use of the invention is the creation of fibers, such as extruded glass fibers, having cross sections which possess great strength for their weight. For example, high resolution I-beam cross sectioned fibers may be obtained which, when blow-molded or otherwise formed into solid shapes, would have extraordinary strength characteristics for their size and weight. Almost any cross-section could be obtained for an extruded material, at extremely high resolution of surface features. Moreover, the die could be "drilled" in the direction of greatest strength of the diamond. Particularly strong and durable dies are thus obtainable according to the basic principles of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described with reference to the accompanying drawings wherein: Fig. 1 is a partially schematic view of an arrangement for producing a complex cross-sectional extrusion opening in a die insert made of a hard mineral; Figs. 2a-2c are plan views of hard mineral die inserts showing various complex cross-sections of extrusion openings; and Figs. 3a-3c are plan views of masks for producing extrusion openings shown in Figs. 2a-2c. DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION The methods of the present invention will be discussed as applied to forming extrusion openings in die inserts. Figure 1 generally illustrates an arrangement 10' for producing die inserts. A conventional argon fluorine excimer laser 11' provides pulsed laser energy for use in the methods of the invention. Such excimer lasers are commonly available from a number of commercial sources. One such supplier is Lambda Physik Inc., a West German company having offices in Acton, Massachusetts, which sells such lasers.under the designations "LPX 100" and "LPX 200" Series. Another such supplier is Questek, Inc. of Billerica, Massachusetts which markets an excimer laser under the designation "Series 2000". The argon fluorine excimer laser 11 produces a laser output 12' at 193 nm wavelength having a flat-top beam profile (in horizontal cross-section) which propagates in a parallel beam path, when such laser 11' is provided with appropriate conventional resonator optics as is known. The output beam 12' is directed to pass through a mask 23' having a cross-section corresponding to the cross-section of the extrusion opening of the die insert. A portion of the laser radiation is stopped by the mask 23' and only in those regions which correspond to the form of the desired opening is the radiation of the laser allowed to pass through the mask. Of course, the die inserts can be made of a hard material other than diamond, i.e., such as sapphire and the like, as explained hereinabove. After passing through the mask, the beam is directed to reduction optics 24', which may be a suitable reduction lens insuring obtaining an extrusion opening of a predetermined size. The reduction lens 24' focuses on the beam on the die insert 51 which may be similar to the die insert (5) shown in U.S. patent No. 3,114,966. The insert 51 is supported in an appropriate mounting 52. The extrusion opening in the die insert 51 is formed with an appropriate number of energy pulses which would depend on the output energy of the selected excimer laser and the thickness of insert itself. Figures 2a-2c show several examples of two-dimensional cross-sections of extrusion openings obtainable with the arrangement according to the invention, and Figs. 3a-3c show masks used in the arrangement of Fig. 1 to obtain extrusion openings of shapes shown in Figs. 2a-2c. The masks shown in Figs. 3a-3c have cut-out areas corresponding to cross-sections of extrusion openings of the die inserts shown in Figs. 2a-2c. Although so illustrated, the extrusion openings need not have only geometric shapes or regular patterns. Any irregular shape which may be formed on the mask may be used to form a corresponding planar extrusion opening. Moreover, complex three-dimensional extrusion openings are possible according to the present invention. By creating a sequence of masks to be positioned between the laser energy source and the workpiece, with the successive cut-out or unmasked areas becoming smaller in at least one direction, an opening is created whose cross section varies in the extruding direction. The use of the methods described herein to produce any of a limitless number of extrusion dies in this manner is contemplated by the inventors, even though the results obtainable by actual extrusion of various materials is bounded only by the imagination of the person creating the series or sequence of masks.

Claims: A method of manufacturing a die insert (51) for use in an extrusion die, the die insert having a die extrusion opening therethrough, comprising the steps of: providing a source (11') of ultraviolet laser energy having an output; positioning a mask (23') having a cut-out area corresponding to a cross-section of the die extrusion opening, between the output of said source (11') of ultraviolet laser energy and the die insert; and directing a beam from the output through said mask (23') onto said die insert (51) for producing the extrusion opening therein, characterized by said output having a wavelength of less than 300 nm. The method of claim 1, further comprising the steps of: positioning a second mask having a different cut-out area corresponding to a second cross-section of the die extrusion opening between the output of said source (11') of ultraviolet laser energy and the die insert (51); and directing a beam from the output through said second mask onto said die insert (51) for producing the extrusion opening therein, wherein the cross-section of die extrusion opening varies in the direction in which material is to be extruded. The method of claim 1, further comprising the step of positioning a reduction lens (24') between said mask (23') and the die insert (51). The method of anyone of the preceding claims, wherein said die insert (51) is constituted of diamond. A die for extruding fibers, wires, filaments and the like having a complex many sided cross-section, comprising: a die insert (51) made of diamond, having an extrusion opening with a cross-section corresponding to the complex cross-section of the fiber, wire, filament and the like, the die insert (51) being produced by directing an ultraviolet laser bean having a wavelength of less than 300 nanometers onto the die insert (51) through a mask (23') having a cut-out area corresponding to the cross-section of the extrusion opening and positioned between the ultraviolet laser source (11') and the die insert (51).

Inventors: ALEV NECIP, WINSTON RONALD H, ALEV, NECIP, WINSTON, RONALD H.
Applicants: WINSTON HARRY SA, HARRY WINSTON S.A.
Application year: 1991
Main classification: B23K26
IPC codes: B23K26, B44B7, B28D5, B41M5, G01N21, B29C47, A44C11, A44C17, D01D4