Method for manufacturing a sintered body

Abstract

A method for manufacturing a sintered body having one or more hard constituents in a metallic binder phase, the method including the steps of forming a green body from a powder composition including at least the one or more hard constituents, the metallic binder phase, and an organic binder system, forming a pattern in a surface of the green body such as to provide a tag enabling individual identification of the green body, and sintering the green body with the tag to form a sintered body having a smaller volume than the green body. The pattern is formed such that the tag is readable after the sintering operation.

Claims

1. A method for manufacturing a sintered body having one or more hard constituents in a form of a metal carbide with the general composition (Ti, Nb, Ta, W)C or combinations thereof, or in form of metal carbonitrides, in a metallic binder phase, the method comprising: forming a green body from a powder composition including at least the one or more hard constituents, the metallic binder phase, and an organic binder system; forming a pattern in a surface of the green body to provide a tag enabling individual identification of the green body, wherein forming the pattern comprises using a laser to selectively burn off the organic binder system with a marking speed of 500-3000 mm/s, thereby forming indentions in the surface; and sintering the green body with the tag to form a sintered body having a smaller volume than the green body, wherein the pattern is formed such that the tag is readable after the sintering operation.

2. The method according to claim 1, wherein the tag is in the form of a data matrix code.

3. The method according to claim 1, wherein the tag includes a plurality of first modules and a plurality of second modules, the first and second modules being of equal module size, each of the plurality of first modules being level with a surface of the green body surrounding the tag, and each of the plurality of second modules including an indentation with respect to said surface, and wherein forming the pattern includes selectively forming the indentations.

4. The method according to claim 3, wherein forming the pattern includes adapting an intended size of the indentations such that, after sintering of the green body, a contrast is achieved between neighbouring first and second modules.

5. The method according to claim 4, wherein adapting the intended size includes setting the intended size to a smaller value than the module size.

6. The method according to claim 1, further comprising storing and retrieving data relating to the manufacturing of the sintered body in a central database.

7. The method according claim 1, further comprising post-sintering processing of the sintered body, wherein the pattern is formed such that the tag is readable after the post-sintering processing.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the invention will in the following be described by means of example with reference to the appended drawings, in which:

(2) FIG. 1 is a flow chart illustrating a method according to an embodiment of the invention,

(3) FIG. 2a shows an example of a data matrix code,

(4) FIG. 2b is a scanning electron microscopy image of a part of a tag formed on a green body according to an embodiment of the invention,

(5) FIG. 2c is a magnification of the tag shown in FIG. 2b,

(6) FIG. 2d is a magnification of the tag shown in FIG. 2b,

(7) FIG. 3a is a scanning electron microscopy image of a part of the tag in FIG. 2b-2d after sintering,

(8) FIG. 3b is a magnification of the tag shown in FIG. 3a,

(9) FIG. 4a is a scanning electron microscopy image of a part of the tag in FIG. 3a-3b after applying a CVD coating,

(10) FIG. 4b is a magnification of the tag shown in FIG. 4a,

(11) FIG. 5 shows a green body according to an embodiment of the invention, and

(12) FIG. 6 shows a sintered body according to an embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

(13) A method for manufacturing a sintered body according to an embodiment of the invention is schematically illustrated in the flow chart of FIG. 1. The sintered body is made of, or substantially made of, a material comprising one or more hard constituents in a metallic binder phase. Examples of such materials include cermet, polycrystalline cubic boron nitride and cemented carbide (hard metal). The hard constituents may be tungsten carbide (WC), or another metal carbide with the general composition (Ti, Nb, Ta, W)C, or combinations thereof. The hard constituents may also include metal carbonitrides such as Ti(C, N). The metallic binder phase may be Co, Ni or Fe, or combinations thereof. For example, the material may be a tungsten carbide (WC) based hard metal, or a titanium carbonitride based hard metal. The method comprises the following steps: (a) Forming a green body from a powder composition comprising at least the one or more hard constituents, the metallic binder phase, and an organic binder system. The green body may be formed using e.g. extrusion, powder injection moulding (PIM), multiaxial or uniaxial pressing, or additive manufacturing. The organic binder systems are selected depending on the method of forming the green body. For example, a method of forming a green body using PIM or extrusion is described in EP1510590, in which the organic binder system consists of poly(ethylene-co-vinylacetate) and a (Polyethylene)-blend-(Poly(oxy-1,2-ethanediyl), .alpha.-hydro.-omega.-hydroxy)-based wax. Another organic binder system for PIM or extrusion comprising olefinic polymers, waxes and petroleum jelly is described in WO2010096003. For multiaxial or uniaxial pressing, e.g. a poly(ethylene glycol) organic binder system may be used. (b) Forming a pattern in a surface of the green body such as to provide a tag enabling individual identification of the green body, wherein the tag is formed such that it will survive a subsequent sintering process and be readable after sintering. The pattern may preferably be formed using a laser programmed to selectively modify the surface by burning off the organic binder system, thereby forming indentations in the surface of the green body. The tag may be in the form of a data matrix code, consisting of a plurality of first type modules and second type modules of equal module size, each first type module being in level with the surface of the green body surrounding the tag, and each second type module comprising an indentation with respect to the surface of the green body. (c) Sintering the green body with the tag to form a sintered body having a smaller volume than the green body. The sintering operation is preferably a liquid phase sintering operation, i.e. a sintering operation in which the metallic binder phase melts and solid grains coexist with wetting liquid binder. In the case of cemented carbide, this means solid grains of tungsten carbide (WC) and liquid phase cobalt (Co). The sintering temperature should thus be above a temperature of at least 1250° C. for WC—Co based cemented carbide. The organic binder system is removed in connection with the sintering operation and/or in a separate process step before the sintering operation, such as in a catalytic process, by extraction in a solvent, and/or by thermal debinding at an elevated temperature below the sintering temperature, e.g. at around 500° C. (d) Optional post processing, e.g. providing a PVD and/or a CVD coating on a surface of the sintered body. The PVD or CVD coating may be provided so that the tag is covered and is sufficiently thin so that the tag is readable also after application of the coating. Post processing may also include grinding of cutting edges on the sintered body, as well as blasting or brushing of the surface of the cutting insert.

EXAMPLES

Example 1

(14) A sintered body in the form of a cemented carbide (WC—Co) exchangeable tool head of a milling tool was produced using a method according to an embodiment of the invention. In step (a), a green body was formed using powder injection moulding with the above described organic binder system comprising olefinic polymers, waxes and petroleum jelly.

(15) In step (b), a pattern was formed on a surface of the green body to provide a tag in the form of a 12×12 data matrix code formed by a plurality of first type modules and second type modules of equal module size and of an approximately square shape. An example of such a data matrix code is shown in FIG. 2a. The first type modules were here formed by unmodified material in level with the surface of the green body surrounding the tag, and the second type modules were formed by indentations in the surface. The pattern was formed using a laser to selectively burn off the organic binder system and form the indentations. The laser used was a pulsed YAG laser operated with an output power of 20 W at 50 kHz, a pulse length of 250 ns and a marking speed of 3000 mm/s. 4 repetitions was used to create the pattern. Each module had a size of 0.25×0.25 mm.sup.2. The laser was programmed such that a black and white (B/W) ratio, or a degree of filling, was 75%, i.e. the laser was programmed to create each module with a frame having an area of 5-35% of the total module area, thus adapting an intended size of the indentations so that sufficient contrast would be achieved. The formed tag was found to provide sufficient contrast when read using a handheld Datalogic scanning equipment of model PowerScan PD9530. A series of electron microscopy images of the formed tag at increasing magnification is shown in FIGS. 2b-2d, showing the indentations (dark areas in FIGS. 2b-2c) formed by the laser. FIG. 2c shows a large magnification of an area within one of the indentations. A photography of the green body with the tag formed thereon is shown in FIG. 5.

(16) In step (c), the green body with the formed pattern was sintered according to known sintering process parameters at a temperature above the melting temperature of Co, with associated shrinkage. Prior to sintering, debinding was carried out by supercritical carbon dioxide extraction, followed by thermal debinding in connection with the sintering. After sintering, the tag on the resulting sintered body was still readable using the above mentioned scanning equipment. Scanning electron microscopy images of the tag on the sintered body are shown in FIGS. 3a-3b, wherein FIG. 3b shows a large magnification of an area within one of the indentations.

(17) In step (d) a CVD coating with a thickness of about 10 μm was applied on the sintered body. FIGS. 4a-b show scanning electron microscopy images of the tag after application of the coating, wherein FIG. 4b shows a large magnification of an area within one of the indentations. The tag was still readable after application of the coating.

Example 2

(18) A sintered body in the form of a cemented carbide (WC—Co) indexable cutting insert was produced using a method according to an embodiment of the invention. In step (a), a green body was formed using direct pressing, with a poly(ethylene glycol) organic binder system.

(19) In step (b), a pattern was formed on a surface of the green body to provide a tag as described in Example 1. The pulse length was 100 ns, the marking speed 500 mm/s, the power 20 W and the frequency 50 kHz. The pattern was formed using a single repetition with a B/W ratio of 95%. The formed tag was readable after creation using the same scanning equipment as in Example 1.

(20) In step (c), the green body was sintered using known sintering process parameters, with thermal debinding in connection with the sintering process. The tag was readable also after sintering. FIG. 6 shows a photography of the sintered cutting insert with the tag formed thereon.

(21) In step (d), a CVD coating was applied. The tag was still readable after application of the coating.

Example 3

(22) A sintered body in the form of a cemented carbide (WC—Co) exchangeable tool head of a milling tool was produced using a method according to an embodiment of the invention. In step (a), a green body was formed using powder injection moulding with the above described organic binder system comprising poly(ethylene-co-vinylacetate) and a (Polyethylene)-blend-(Poly(oxy-1,2-ethanediyl), .alpha.-hydro.-omega.-hydroxy)-based wax.

(23) In step (b), a pattern was formed on a surface of the green body to provide a tag as described in Example 1. The pulse length was 100 ns, the marking speed 500 mm/s, the power 20 W and the frequency 50 kHz. The pattern was formed using two repetitions with a B/W ratio of 75%. The formed tag was readable after creation using the same scanning equipment as in Example 1.

(24) In step (c), the green body was sintered using known sintering process parameters, with thermal debinding in connection with the sintering process. The tag was readable also after sintering.

(25) In step (d), a CVD coating was applied. The tag was still readable after application of the coating.

(26) In all the examples, the parameters used when creating the pattern may be varied. In step (a), the laser frequency may e.g. be varied within a range of 50-200 kHz, 1-6 repetitions may be used to create the pattern and the marking speed may e.g. be 500-3000 mm/s. The B/W ratio may e.g. be 65-95%. More than one pulse may preferably be used to form each module, such as at least 2×2 pulses or 3×3 pulses per module.

(27) The invention is of course not limited to the embodiments disclosed, but may be varied and modified within the scope of the following claims.