US 20010004581 A1
In a negative mould (1) closed by a lid (3), hard material abrasive grains (5) are nickel-attached to the peripheral inside surface. The negative mould (1) contains, in addition to the outside contour (4) of the tool to be manufactured, also the surfaces for the location bore (7) and the end face locations (7′) of the said tool. Subsequently the inner space of the negative mould (1) is completely filled with a casting mass (6) interspersed with solid particles (8) and the said mass allowed to harden. The mould (1) is removed by machining or etching. This process permits the inexpensive and economic manufacture of tools coated with hard material abrasive grains.
1. Tool for grinding, honing or cut-off grinding, or for the dressing of grinding, honing or other fine machining tools, the tool comprising a location bore (7) and end face location surfaces (7′) for attaching to a tool spindle or a tool mandrel, wherein an entire tool body including the location bore (7) and the end face location surfaces (7′) is composed of a hardened cast mass (6), in which at least on a periphery (4) hard material abrasive grains (5) are embedded.
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8. Process for the manufacture of a tool for grinding, honing, cut-off grinding or for dressing fine machining tools by means of a negative mould (1), a peripheral inside contour (4) of which is a negative of a peripheral outside contour of the tool, wherein the negative mould (1) used for manufacturing the tool is closed with a lid (3), wherein a thus formed hollow space not only contains the peripheral outside contour of the tool (2), but also the contours of its location bore and end faces, and wherein to form a tool body the entire hollow space of the negative mould (1) is filled with a casting mass (6) which is subsequently hardened.
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 Tools of which the working surfaces are provided with a layer of hard material abrasive grains, such as CBN or diamond, are being used more and more in many manufacturing fields as grinding, honing, cut-off grinding or dressing tools under the designation CBN grinding wheel or grinding worm, CBN honing stone, cut-off grinding disc, form or profile dressing roller, diamond dressing gear etc. Particularly in those applications where they are employed as profile grinding wheel, profile dressing roller or dressing gear, the demands made on the topological accuracy of their cutting (abrading) surface are high. Since a subsequent machining of the hard abrasive grain studded cutting surfaces is only possible to a limited extent and at great expenditure, such tools are often made by the so-called reversal process, the tool being built up - starting with an exactly made negative mould - from the outside, i.e. the peripheral hard material abrasive grain layer, inwards to the tool-locating bore.
 In DE 37 26 855 A1 the build-up of the tool and the tool manufacturing process is described using the example of a profile dressing roller. The manufacture of the metal ring with the hard material abrasive grains on its periphery is actually not presented in this document. It concerns a well known process, however. The ring is formed by galvanically embedding the hard abrasive grains lying on the peripheral inner wall of the negative mould in nickel. Into this ring a basic body is inserted made preferably of hardened steel with an exactly machined bore and locating end face, which serves to attach the tool to the tool spindle. After exactly centering the basic body relative to the center of the negative mould by means of a suitable device, the outer metal ring carrying the hard abrasive grains is connected to the basic body to form one unit by cast filling the intermediate space with a low temperature melting metal, e.g. a bismuth-tin alloy, or a naturally hardening pourable plastic, pure or interspersed with solid particles. In the case of very stringent accuracy requirements it is often necessary to trim grind the bore and the end location face of the basic body after casting, before removing the negative mould, in order to assure the specified radial and axial trueness of the tool cutting surface relative to the tool spindle.
 With the reversal process employed today, very accurate tools can be made. The numerous manufacturing operations and the long bath times for the nickel-embedding of the hard abrasive grains result in long manufacturing times, however, and high manufacturing costs which limit the economic efficiency of the processes in which they are currently used.
 The objective of the present invention is to provide for the described application a tool and a process for its manufacture, which permit shorter manufacturing times and lower manufacturing costs. In accordance with the invention, this task is fulfilled with a tool and a manufacturing process featuring the characteristics according to the patent claims.
 Hereby, whilst retaining the high accuracy of form and radial and axial trueness of the tool used for fine machining such as grinding and honing and for the dressing of grinding wheels, grinding worms and honing stones, the manufacturing time and manufacturing costs are according to the invention lowered, in that the hard material abrasive grains applied to the inner wall of the negative mould are not completely embedded in a galvanically produced nickel layer, but after only a brief period of nickel-attaching are bonded in a naturally hardening cast mass, to which solid particles of metal, glass, carbon fibres, minerals or other suitable materials can be added, and in that the space between the peripheral inner wall and the inner contour of the negative mould forming the location seating and the location end face is filled with a cast mass, whereby the manufacturing expenditure for the tool is additionally reduced by an amount equivalent to the manufacture, the exact positioning and the casting of a metallic basic body.
 In the following an embodiment of the invention with respect to a profile dressing roller is explained in detail, referring to the drawings. These show:
FIG. 1 an axial section of the negative mould with profile dressing roller in accordance with the invention,
FIG. 2 an enlargement of the detail encircled in FIG. 1, and
FIG. 3 a variant of FIG. 2 with nickel-attached hard material abrasive grains.
 In the embodiment of the invention selected here, the negative mould 1 for the tool 2 is a pot-shaped metal body produced directly or by the reversal process, which is closed by a lid 3. In cross-section the inner contour of the negative mould 1 corresponds with the peripheral, end face and bore contour trace of the axial section through the tool. The bottom 11 of the hollow space of the negative mould 1, the enveloping surface 12 of the central cylindrical core 13 and the inner face 14 of the lid 3 are provided with an electrically insulating coating. In the closed inside space there are for example one or more annular electrodes 15, which are connected via an insulated conductor to one pole of a direct current source 17, the other pole of which is connected to the negative mould via the switch 16.
 Lying on the peripheral inner surface 4 of the negative mould 1 are the hard material abrasive grains 5. The inside space of the negative mould 1 is filled with a naturally hardening, pourable mass 6 interspersed with solid particles 8, which said mass bonds and supports the hard abrasive grains 5, and simultaneously forms the end face and bore of the tool location seating 7, 7′.
 The composition of the cast mass 6 and the nature and size of the added solid particles 8 are selected such that the strength, the heat resistibility and the hardening distortion are optimally appropriate to the loading or the accuracy demands on the tool. Suitable casting substances 6 are for example a 2-component synthetic resin and ceramics. The added particles 8 are preferably metal swarf, glass splinters, carborundum grains, ceramic particles or minerals such as silicates or borates of differing grain sizes and grain forms. By appropriately adapting the proportion of the solid particles 8, and their material, form, size and distribution relative to the synthetic cast mass, it is possible to optimally adjust the desired properties such as form stability, mechanical strength and temperature resistibility. By the use of differing sizes of particle, spaces between the larger particles can be filled by the smaller ones, producing a high form stability and strength. Suitable hard material abrasive grains 5 are for example diamond, CBN or carborundum grains. The holes 9, 10 serve to introduce the liquid casting mass 6 into the inner space of the negative mould 1.
 As first variant, which is mainly suitable for inexpensive hard abrasive grains, carborundum for instance, the abrasive grains 5 are fed in such quantities into the hollow space of the negative mould 1 rotating about its axis 18, that the abrasive grains 5 at least cover the entire inner surface 4 of the negative mould 1. The layer thickness will vary depending on the inner contour 4. The rotating negative mould 1 is subsequently filled with the liquid casting mass 6 via the holes 9, 10, the hollow space being for example evacuated beforehand. The cast mass is allowed to harden. For this variant the elements 15, 16, 17 are not required.
 In the case of expensive hard abrasive grains of diamond or CBN for example, the abrasive grains 5 are likewise introduced in the above quantities, and the mould 1 rotated about its axis 18. Then an electrolyte containing nickel is filled in through the holes 9, 10. The switch 16 is switched on, and the peripheral grains 5 are attached to the inner surface 4 by a thin nickel layer 19. Afterwards the lid 3 is opened, and all the abrasive grains 5, except the nickel-attached ones, are tipped out together with the electrolyte. The lid is closed again, and the casting material 6 poured in through the holes 9, 10 in the above manner. The rotation is not absolutely necessary for this operation.
 Instead of the nickel-attaching, this method can also be employed by previously applying a uniform coat of adhesive to the inside surface 4 of the negative mould 1.
 For the nickel-attaching of the abrasive grains 5 to the inner surface 4, in place of the electrolysis, a chemical precipitation of metals onto this inner surface 4 could also be considered.
 In order to avoid undesirable cavities in the tool body, and to bring the solid particles 8 added to the casting mass 6 into mutually stable contact, the filled negative mould 1 is centrifuged and/or vibrated, and/or subjected to vacuum.
 After the hardening of the cast mass 6 the negative mould is removed, by machining and etching away for example, so far that the locating bore 7 and the locating seatings 7′ on the face surfaces of the tool 2 are layed free. Any casting flashes at the feed head points of the cast mass 6 into the hollow space of the negative mould 1 are removed by machining. If required the locating bore 7 and the locating seatings 7′ are subsequently fine machined to the specified dimensions. Finally, the outer ring shaped rest of the mould 1 is removed.