Abstract:
A process for manufacturing a single-piece bladed disk, including: using an abrasive water jet to cut a block of material, so as to create blade preforms extending radially outwards from a disk, while keeping material forming a connecting mechanism between at least two directly consecutive blade preforms, the connecting mechanism being at a radial spacing from the disk; then removing the connecting mechanism; then milling the blade preforms.

Description:
TECHNICAL DOMAIN 
     This invention relates in general to the manufacturing of single-piece blisks, preferably for an aircraft turbine engine. 
     STATE OF PRIOR ART 
     A single-piece bladed disk, also called a blisk, can be made using an abrasive water jet to cut a material block in a first step, followed by one or more milling steps. 
     The use of a cutting step using an abrasive water jet prior to milling can considerably reduce the manufacturing times and costs in comparison with a process based solely on milling. This is particularly due to the fact that such a manufacturing process requires removal of about 75% of the material in the original block to make the blisk. The removal of a large part of this material by cutting with an abrasive jet can reduce production times and also limits wear of milling machines. 
     Nevertheless, this process cannot be considered to be fully optimised. The presence of deformations and vibrations of the blades during this process is a disadvantage, that becomes particularly severe for long blades. Low advance rates are necessary to limit the consequences of these deformations and vibrations on the quality of the blisk produced, thus slowing production. Vibrations and longer manufacturing times also increase tool wear that has a negative impact on production costs. 
     SUMMARY OF THE INVENTION 
     Therefore, the purpose of the invention is to at least partly remedy the above-mentioned disadvantages of embodiments according to prior art. 
     To achieve this, the object of the invention is a process for manufacturing a single-piece blisk, comprising:
         a step in which an abrasive water jet is used to cut a block of material so as to create blade preforms extending radially outwards from a disk while keeping material to form the connecting means between at least two directly consecutive blade preforms, said connecting means being at a radial spacing from said disk; then   a step to remove said connecting means; then   a step to mill blade preforms.       

     The invention is thus remarkable in that during the cutting step using an abrasive water jet, it creates connecting means between at least two blade preforms, and preferably between all these blade preforms. This can strongly limit or even eradicate deformations and vibrations of blades while they are being manufactured, since they remain fixed to each other mechanically by material in the initial block. 
     This specific feature means that the different tools can be used at high advance rates thus reducing production times, without jeopardising the quality of the finished blisk. Furthermore, the reduction of production times and the reduction of blade vibrations during manufacturing slow tool wear, which advantageously limits production costs. 
     Preferably, the cutting step using an abrasive water jet is done such that said connecting means join more than three blade preforms to each other, preferably directly consecutive to each other. However, it would be possible to envisage several sets of directly consecutive preforms connected to each other, but with the sets not connected to each other. In any case, regardless of the needs encountered, the number of blade preforms fixed to each other by connecting means and the arrangement of these connecting means on the preforms, may be adapted. 
     According to one preferred embodiment, the cutting step using an abrasive water jet is done such that said connecting means approximately form a ring, preferably centred on the axis of the disk. This ring preferably extends around 360° and is possibly interrupted by the blade preforms that it connects together. However as mentioned above, this ring is not necessarily completely closed, in other words it may not connect all directly consecutive preforms. 
     However, the cutting step using an abrasive water jet is preferably made such that said ring connects all blade preforms to each other, and each preform will subsequently form one blade of the blisk. In this case, it will preferably be arranged such that the cutting step using an abrasive water jet is done with said ring connecting the tips of the blade preforms to each other. The ring then forms a peripheral annular portion of the cutout block with the preforms of the blades extending radially inwards from this ring, towards the disk. 
     Nevertheless, one alternative solution could be to carry out the cutting step using an abrasive water jet such that said ring connects said blade preforms together at a radially inwards distance from their tips. For example in this case, it would be possible for the ring to connect the preforms to each other at approximately mid-length. 
     Note that the two solutions proposed above can be combined, namely a peripheral support ring and an inner support ring radially inwards from the peripheral ring can both be provided. More generally, when a peripheral support ring is provided, additional connecting means between blade preforms can be provided, not necessarily in ring form, without going outside the scope of the invention. 
     The material forming the connecting means is preferably kept until the end of the abrasive water jet cutting step. It is then removed only during a later step in the blisk manufacturing process. 
     Note in this respect that the step to mill blade preforms is done so as to obtain profiled blade blanks, this step preferably being followed by a milling step to finish blade blanks so as to obtain blades to the final profile. 
     Obviously, other conventional steps can be used in the process according to the invention, such as:
         turning of the material block before the cutting step using an abrasive water jet;   polishing and/or shot blasting of the blades after the finishing step;   cutting blades to length;   and balancing of the blisk.       

     Preferably, the diameter of said single-piece blisk is greater than or equal to 800 mm. In this respect, note that the presence of connecting means holding the blades together during manufacturing makes it possible to manufacture large diameter blisks with long blades since the blade deformations and vibrations are reduced or even eliminated. Preferably, the minimum length of the blades is 150 mm. 
     Preferably, the thickness of said single-piece blisk is greater than or equal to 100 mm. Nevertheless, it may be of the order of 160 mm or even more due to the potentially high performances that can be achieved by the abrasive water jet cutting technique. This thickness is approximately equal to the distance along the blisk axis covered by each blade, between the leading edge and the trailing edge. 
     Preferably, the blades of the single-piece blisk are twisted, the angle of twist varying up to 45° or even more. 
     Preferably, said material block used is made of titanium or a titanium alloy. 
     Preferably, said single-piece blisk is a single-piece blisk for an aircraft turbine engine. 
     Even more preferably, said single-piece blisk is a single-piece blisk for a turbine or compressor rotor in an aircraft turbine engine. 
     Other advantages and characteristics of the invention will become clear after reading the following detailed and non-limitative description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       This description will be made with reference to the appended drawings among which; 
         FIG. 1  shows a perspective partial view of a single-piece blisk for a turbine engine that can be obtained by implementing the manufacturing process according to this invention; and 
         FIGS. 2   a  to  2   e  represent views diagrammatically showing the single-piece blisk at different steps in its manufacturing process, when the blisk is made according to one of the preferred embodiments. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Firstly with reference to  FIG. 1 , the figure shows a single-piece blisk  1  to be obtained by the use of a manufacturing process according to this invention. It is preferably intended to form part of a compressor or turbine rotor for an aircraft turbine engine. 
     The single-piece blisk, hereinafter referred to as a blisk that is to be obtained using the process according to this invention is large, in other words its diameter is greater than or equal to 800 mm, the length of its blades  2  is not less than 150 mm and the thickness &lt;&lt;e&gt;&gt; of its disk  4  is greater than or equal to 130 mm. Furthermore, the blades supported by the disk  4  with its central axis  5  are strongly twisted with an angle of twist up to or even more than 45°. For information, this angle is equal to the fictitious angle between the root  6  and the tip  8  of a specific blade  2 , according to conventional practice. 
     A preferred embodiment of the process for manufacturing the blisk  1  will now be described with reference to  FIGS. 2   a  to  2   e.    
     Firstly, a first turning step is performed on a block of material made of titanium alloy, also called a &lt;&lt;single-piece blank&gt;&gt; and preferably pre-machined, to machine this block for example to within 1 mm of its final dimensions. 
     The next step consists of cutting the solid block using an abrasive water jet so as to form the blade preforms. 
     This is done using a very high pressure (for example 3000 bars) and very high precision water jet cutting machine (for example a 6-axis machine). The very high water pressure transports the abrasive optimising its cutting effect on the material. The water jet is created in a known manner using a diamond or sapphire nozzle. There is also a mixing chamber used to add abrasive such as sand. A focussing gun homogenises the water and sand, focussing sand on the zone to be cut. 
     This abrasive jet cutting technique enables a large material removal rate and good repeatability. It is thus perfectly suitable for removing material so as to create inter-blade spaces through the entire thickness &lt;&lt;e&gt;&gt; of the material block along its axis  5 . 
     This is illustrated in  FIG. 2   a  that shows the top part of the material block  100  after the abrasive water jet cutting step is complete. Therefore this block comprises blade preforms  102  extending radially from disk  4 , in other words orthogonal to the central axis  5 . In general, the cutout is made within the thickness of the block  100  so as to form inter-blade spaces  110  between directly consecutive blade preforms  102  in the circumferential direction. 
     It is also done so as to form the connection means between the preforms  102 , in this case taking the form of a ring  112  centred on the axis  5  and preferably connecting all tips  108  of the blade preforms  102 . Thus, the ring  112  forms a peripheral annular portion of the cutout block  100 , and consequently creates an external radial delimitation of the inter-blade spaces  110  that is kept until the cutting step is complete. 
     This abrasive water jet cutting step can be implemented by making a first cutting operation to remove a first piece of material that twists or has a spiral shape along the radial direction from the disk, followed by a second cutting operation to remove a second smaller volume of material, that also twists or has a spiral shape along the radial direction. 
     More precisely, the left part of the diagrammatic view contained in  FIG. 2   b  shows that the first cutting operation will cut out a first piece of material  114  extending through the entire thickness of the block  100  along its axis  5 . This is done by moving the axis of the focussing gun  116  along a closed line  118  shown in the lower part of  FIG. 2   a , initiated from the root  4  and extending along the radial direction to near the outer radial end of the block but without reaching it so as to form the ring, the line  118  then following this ring in the circumferential direction before changing to the radially inwards direction again to reach the root  4 , and then following this root back to its initial point. 
     During its path along the above-mentioned line  118 , the axis of the gun  116  moves by an appropriate additional movement relative to the axis  5  that preferably remains fixed, this additional movement essentially consisting of the axis of the gun pivoting about the radial direction and forming a first piece  114  with a generally twisted shape along the radial direction. More generally, note that the path followed by the gun  116  relative to the axis  5  is a so-called 5-axis path obtained by two simultaneous rotations. The first piece  114  is preferably removed manually by the operator as shown diagrammatically in the central part of  FIG. 2   b . As can be seen on this figure that shows a typical section perpendicular to the radial direction, the piece  114  is in the form of a quadrilateral for which the two opposite sides along the thickness of the block pass very close to the two directly consecutive blades  2  that will be obtained once the process is complete. 
     Following on from the above, each removal of a first piece  114  forms the surface of two directly consecutive blade preforms  102 . Preferably, the first step is to cut out all the first pieces  114 , the number of which depends on the number of blades to be provided in the blisk, and these pieces  114  are then removed manually before starting the second cutting operation. 
     This second operation is done such that the shape of the resulting blade preforms is as close as possible to the twisted shape with inverted curvature of the final blades which is difficult to approach with a single cut since the abrasive water jet passes through the block in an approximately straight line, although the blade sections are curved. 
     The right part of the diagrammatic view contained in  FIG. 2   b  shows that the second cutting operation will cut out a second piece of material  120  that extends over only part of the thickness of the block  100 , in other words over only part of the thickness of the radial elements  122  formed by removal of the first pieces  114 . The piece  120  also extends only along a radial portion of its associated element  122 , namely it extends starting from the root without reaching the ring, as can be seen in  FIG. 2   a.    
     This is done by moving the focussing gun  116  along a radial line  124 , a portion of which is shown in  FIG. 2   a . This line is initiated from the root  4  and therefore extends approximately radially without reaching the ring  112  that appeared during removal of the first pieces  114 . For example, line  124  through which the abrasive water jet passes is at approximately mid-thickness of the radial elements  122  and it stops beyond the radial mid-height of these elements. 
     During its path along the above-mentioned line  124 , the axis of the gun  116  is driven by an appropriate additional movement relative to the axis  5  that preferably remains fixed, this additional movement essentially involving pivoting of the axis of the gun about the radial direction, and forming a second piece  120  with a twisted shape along the radial direction. More generally, note that the path followed by the gun  116  relative to the axis  5  is a so-called 5-axis path obtained by two simultaneous rotations. This second piece  120 , once completely separated from the root  5  by the abrasive water jet, preferably separates by itself without assistance by the operator, as shown diagrammatically in the right part of  FIG. 2   b.    
     In this respect, note that the gun  116  moves not only along the approximately radial line  124 , but also along a circular portion (not shown) of a line extending from the inner radial end of the line  124  along the root  4  to completely separate the piece  120  from the root. 
     As can be seen in  FIG. 2   b  that shows an arbitrary section perpendicular to the radial direction, the piece  120  is in the form of a triangle of which one of the sides passes as close as possible to the blade  2  that will be obtained from the radial element  122  concerned once the process is complete. 
     Once all the second pieces  120  have been removed, all that remains of the block are the blade preforms  102  attached to each other at their tips  108  by the ring  112 . The abrasive water jet cutting step is then complete. 
     In this preferred embodiment, the process continues with a step in which the ring  112  connecting the blade preforms  112  is removed. This step is done in any manner that an expert in the subject considers appropriate, such as wire cutting or milling. In this respect,  FIG. 2   c  schematically shows separation of the ring  112  from the rest of the block  100 , by breakage of the link between this ring  112  and the preform tips  108 . Once all these approximately circumferential breaks  128  have been obtained, the ring may be effectively extracted from the block by relative displacement along axis  5  of the block. The ring  112  is then considered to be eliminated. Alternately, the ring  112  could be removed simply by eliminating portions of this ring located between the preforms  102 , the other portions located at the radial end of these preforms then being kept, for example so as to form part of the tips of the blades at a later stage. The required breaks are then no longer approximately circumferential like the breaks  128  in  FIG. 2   c , but are approximately radial and still within the thickness of the block. 
     The next step is to mill the blade preforms  102  so as to obtain profiled blade blanks  202 . In other words, the purpose of this step, for example done using a 5-axis milling machine, is to remove the material remaining on the blade preforms  102  to approach the final dimensions, for example within 0.6 mm. 
     In this case, the preforms  102  are preferably machined one by one and each forms a profiled blade blank  202 , as shown in  FIG. 2   d.    
     Another milling step is then done and is called the finishing step to mill the blades  2  to achieve their final profile from the blanks  202 . The tooling used enables more precise machining to obtain the final dimensions, therefore obtaining blades  2  as shown in the right part of  FIG. 2   e.    
     At this stage of the process, the remaining volume of material is less than 25% of the volume of this block just before initiation of the abrasive water jet cutting step, namely just after the above-mentioned turning step. 
     The process may also be continued by one or several conventional steps including a polishing step for example by manual fitting or tribofinishing, a shot blasting step, a blade cutting to length step and/or a blisk balancing step. 
     Although the embodiment mentioned above was described with a support ring  112  formed at the blade tips, it could equally well be formed at a more central part of these blades, radially inwards from the tips. 
     Obviously, an expert in the subject could make various modifications to the invention as described above, solely as non-limitative examples.