Abstract:
A composite cast tool is cast in one continuous piece, partly of steel and partly of grey iron, so that an interconnection zone is formed between the steel and the grey iron. The steel portion forms the working component of the tool, for example a cutting edge, and the grey iron portion forms the body component of the tool. The steel portion and the grey iron portion have projections or walls extending towards one another. The interconnection zone is located in the region of union between these walls and is planar.

Description:
The present application is the U.S. national stage of International Application PCT/SE2009/000123, filed Mar. 5, 2009, which claimed priority to Swedish Application 0800521-7, filed Mar. 6, 2008, both of which are incorporated by reference. 
     BACKGROUND AND SUMMARY 
     The present invention relates to a composite cast tool which is cast in one continuous piece and which has at least one first portion which comprises the working component of the tool and which is manufactured from steel, and one second portion which comprises the body component of the tool and which is manufactured from grey cast iron, there being at least one interconnection zone between the steel and the grey iron. 
     In the manufacture of tools for sheet metalworking, such as cutting, hole making, bending or other shaping operations, it has long generally been the practice to separately manufacture a tool body by casting it from grey iron. This tool body has then been provided with a number of working components, for example steel cutters. 
     The tool body produced by casting has often required heat treatment after the casting operation, this being followed by machining in order to realise the requisite seats, guide shafts and bolt holes etc. for securing the steel cutters, but also to make possible fixing of the tool in a machine. 
     In the production of the working component or components, for example the steel cutters, the point of departure has often previously been bar material, the working components being machined to the correct form, provided with apertures for fixing bolts, guide shafts and the like, thereafter, heat treatment takes, followed by machining, for example grinding. 
     Producing a tool in the above-outlined manner is an extremely time-consuming operation and often determines itself the time consumption which is needed for the new production of different products. 
     WO 03/041895 A1 discloses a composite cast tool, as well as a method of its manufacture. According to this publication, the tool is cast in a single mould, which is thus charged with both the steel melt and the grey iron melt. During the casting of these materials, an interface or interconnection zone is formed. 
     In the prior art technology according to the above-mentioned publication, major problems have been encountered as regards the positioning and formation of the interface or interconnection zone between the two materials. This has had a negative effect on mechanical strength in and around the interconnection zone. 
     Further, it has not been possible according to the prior art technology to control in an accurate manner the temperature throughout the entire interconnection zone, which has had as a consequence that major temperature variations have occurred and resultant problems in the mechanical strength of the interconnection zone. 
     It is desirable to design the tool intimated by way of introduction such that the interface or interconnection zone between the steel and the grey iron may be accurately positionally determined. It is also desirable to design the tool so that it may be possible to ensure good control of the temperature at the interconnection zone. 
     According to an aspect of the present invention, a tool is characterised in that the first portion includes at least one projection or one wall which extends towards the body component, that the second portion includes at least one projection or one wall which extends towards the working component, corresponding projections or walls on the first and second portions being united with one another at the interconnection zone, and that the interconnection zone is substantially planar. 
    
    
     
       BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS 
       The present invention will now be described in greater detail hereinbelow, with reference to the accompanying Drawings. In the accompanying Drawings: 
         FIG. 1  is a cross section through a mould for manufacturing the tool according to the present invention; 
         FIG. 2  is a perspective view of a tool which is inverted in relation to the position on its manufacture; 
         FIG. 3  is a part of the tool according to  FIG. 2 , all working components manufactured from steel having been removed; 
         FIG. 4  is a cross section through a tool in the region of the interconnection zone; 
         FIG. 5  is a cross section through an alternative tool in the region of the interconnection zone; and 
         FIG. 6  is a view corresponding to that of  FIGS. 4 and 5 , but showing an additional alternative tool. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  schematically shows a cross section through a mould for casting of the tool according to the present invention. The mould has a first mould cavity section  1  and a second mould cavity section  2 , where the first mould cavity section  1  is intended for the casting of steel, while the second mould cavity section  2  is intended for the casting of grey iron. Reference numeral  3  relates to a casting box or flask, while reference numeral  4  relates to casting sand placed in the casting box. The mould has an ingate or sprue  5  for steel and another ingate or sprue  6  for the grey iron. The ingate system for the steel extends at least partly to a position down below the first mould cavity section  1 , for which reason the steel will be cast in a direction from beneath and upwards. Between the two mould cavity sections  1  and  2 , there is a dividing plane  7  which represents the intended position for an interconnection zone between the steel and the grey iron. The dividing plane  7  is planar and in the casting position of the mould is disposed horizontally. The interconnection zone will, if the present invention is correctly reduced into practice, have an approximate thickness of 1 to 2.5 mm. 
     The component or components  10  of the tool that are cast in steel, hence in the first mould cavity section or sections  1 , are intended to constitute the working component or components of the tool, while that component  11  of the tool which is cast in the second mould cavity section  2  in grey iron, is intended to constitute a body component for the tool. How many working components the tool has may vary from a single component and upwards to quite a considerable number. 
     The steel component  10  cast in the first mould cavity section  1  includes at least one projection or one wall  8  which extends upwards towards the body component (the component manufactured from grey iron). Correspondingly, the second component  11  of the tool, i.e. the portion cast manufactured from grey iron, has one wall or projection  9  which extends in a direction downwards towards the working component of the tool or its working components. The width or thickness of these projections or walls  8 ,  9 , in the region of the dividing plane  7  must be the same throughout the entire length of the projection or the wall, and, in one practical version, may lie in the order of magnitude of between 50 and 150 mm. Large or abrupt thickness changes in the walls  8  and  9  must not occur in the proximity of the dividing plane  7 . If a plurality of projections or walls is used in a tool, all must have substantially the same thickness. The height of these walls  8  and  9  must be of the same order of magnitude as or be larger than the width or thickness, but never less than 30 to 40 mm 2 . 
       FIGS. 2 and 3  are inverted compared with  FIG. 1 , hence that which faces upwards in  FIGS. 2 and 3  is turned to face downwards in  FIG. 1 . 
       FIG. 2  shows in perspective a tool with eight first portions  10  manufactured from steel and one second portion  11  manufactured from grey iron. It will also be apparent from  FIG. 2  that the portions  10  manufactured from steel have projections or walls  8  which, in  FIG. 2 , are located lowermost, thus are turned to face towards the second portion  11 . Correspondingly, it will be apparent that the second portion  11  has, in a manner analogous with the first portions  10 , upwards directed walls or projections  9  which are thus turned to face towards the first portions manufactured from steel. The ideal position for the interconnection zone between the two materials is indicated by the dividing plane  7 . 
     In  FIG. 3 , which corresponds to  FIG. 2  but where all portions  10  of the tool manufactured from steel have been ‘omitted’, the formation of the walls or projections  9  of the second portion  11  directed towards the working components are more clearly apparent. It is also apparent that the dividing plane  7  is planar and that the walls  9  are in principle of even thickness throughout their entire length. 
     It will also be apparent from  FIG. 3  that the walls  9  of the second portion  11  merge in a much large cross-sectional area, at least at certain parts of the tool, and indicated by reference numeral  12 . The position of this area change  12  is however located a safe distance (&lt;approx. 40 mm 2 ) from the intended position of the interconnection zone, i.e. the dividing plane  7 . 
     As was mentioned above, the steel is cast from beneath in the first mould cavity section  1 . The casting of the steel is terminated when the upper defining surface of the steel has reached up to the position of the dividing plane  7 . Thereafter, there is a pause in the casting process. During this pause, the temperature in the first portion  10  will fall most rapidly in the lower parts in  FIG. 1  and last at the dividing plane  7 . Only when the temperature of the steel portion  10  has fallen to a first level corresponding to the liquidus temperature of the steel minus approx. 30-150° C., most often for example 1440-1330° C., at the dividing plane, will the casting procedure be continued with casting of the grey iron at a second temperature, which corresponds to the liquidus temperature of the grey iron plus 100-150° C., for example 1320° C. 
     According to the present invention, it is important that the temperature in the steel portion  10  in the dividing plane be as uniform as possible throughout the entire surface of the dividing plane. This is the reason for the uniform thickness formation of both of the walls  8  and  9 . 
       FIG. 4  shows a partial section through a tool in the region of the dividing plane  7 . The steel portion  10  has, in the illustrated example, been formed with a cutting edge  13  in its lower end in the Figure. 
     In order to ensure that the temperature, in terms of time, falls last in the steel portion  10  at the level of the dividing plane  7 , the steel portion  10  has been given a wall thickness that is slightly tapering in a direction away from the dividing plane  7 . This is illustrated by the added circles which have a size which increases in a direction from beneath and upwards. This formation is favourable for controlling the temperature reduction in the steel portion, but also implies that possible sinkages will be at the dividing plane  7 . 
       FIG. 5  shows a slightly modified embodiment of a double cutting tool with double cutting edges  13 . Also in this embodiment, the thickness in the steel portion  10  declines a direction away from the dividing plane  7  in order, as is intimated by the added circles, to be least in the region at the cutting edges  13 . 
       FIG. 6  shows a slightly modified embodiment where the steel portion  10  has two cutting edges  13  and two walls  8  directed towards the grey iron portion  11 . Also in this embodiment, the wall thickness of the steel portion  10  declines in a direction away from the dividing plane  7  and is at its least at the maximum distance therefrom. This relationship is clearly apparent from the circles written into the steel portion  10 . 
     The tapering wedge shape downwards, which the steel portions  10  have in the casting position below the dividing plane, i.e. the intended interconnection zone, has not be disclosed in  FIGS. 4 to 6  but should lie in the range of between 5 and 30°.