A casting apparatus and process

Abstract

Casting apparatus which comprises a piston 14 arranged within a sleeve 12 and a mould 16 arranged on the piston sleeve 12, where a cavity in the mould 16 is positioned to receive metal injected from t

Description

A Casting Apparatus and Process Field of the Invention The invention relates to apparatus for casting and a process for casting, with a view to reducing defects in cast products. Background to the Invention When casting with liquid metal, it is desirable that the end product has as few defects as possible. Whilst some defects can be tolerated, and others can be repaired, there are a number of defects that cannot be tolerated. There are various ways in which defects can occur, one of which is gas porosity, which is the formation of gas bubbles within the casting and shrinkage porosity, the least tolerated, after it has cooled. This occurs because most liquid metals can hold dissolved gas, but the solid form of the same material cannot. Thus, gases may become trapped inside the metal, which significantly reduces the strength of the casting. One way in which gas porosity and poor grain structure, can be caused is through turbulence during the casting process. As with other liquids, pouring the molten metal into a receptacle causes turbulence, which can result in the introduction of gas into the liquid and, in turn, this can cause cavities to form in the casting and / or for metal oxides to form. A further problem caused by turbulence in casting is the erosion, or wearing away of the internal surface, of the mould. As such, it is paramount that turbulence during the casting process is avoided when increasing the product quality. A further cause of poor quality casting is pouring defects, which include misruns, where the metal does not fully fill the mould cavity, and cold shuts, where two fronts of liquid metal do not properly fuse. Both misruns and cold shuts can occur where the liquid metal enters the mould at the wrong flow rate for the mould, for example, where the mould narrows, but the flow rate is not adapted accordingly. Therefore, preventing defects 1s desirable in order to produce a good quality casting. Summary of the Invention Accordingly, the present invention is directed to a casting arrangement, comprising: a piston sleeve; a piston arranged within the piston sleeve; a driver to adjust the position of the piston within the piston sleeve; and a mould having a mould cavity, the mould being arranged upon the piston sleeve, the mould cavity positioned to receive material from the piston sleeve, when 1m use, wherein, the mould is arranged in such a manner that the orientation of the mould cavity, relative to the ground, can be adjusted, whilst the casting process is in operation. The arrangement of the present invention has a piston and sleeve, along with a driver to control the piston. A mould is positioned adjacent the piston sleeve to receive liquid metal from the piston sleeve and the driver is used to control the flow of liquid metal into the mould. In the present invention, the orientation of the mould can be adjusted to reduce turbulent flow of the metal into the mould. As will be appreciated by the skilled person, the present invention operates in a similar manner to the way in which one might attempt to reduce turbulence when pouring drinks; the receptacle is angled, relative to the ground, so that the liquid, in this case molten material, can pass along the internal surface of the receptacle, rather than dropping into the receptacle. The resulting flow produces less turbulence than traditional casting arrangements, because the ‘waterfalling’ of molten material is reduced by angling the section receiving molten material. Combined with the variable flow rate analysis set out herein, the system can be employed to produce a finished product with fewer defects than existing casting apparatus, methods and systems. It 1s preferable that the orientation of the mould cavity can be adjusted in at least two angles, or, degrees of freedom, for example, roll and pitch, although yaw adjustment may also be advantageous. By adjusting the angle of the mould and / or the mould cavity, relative to the ground, and preferably in at least two degrees of freedom, the mould can be adjusted in order to smooth the flow of the metal within the mould. Thus, the mould can be tilted so that rather than the metal falling into a cavity, the metal can run down the side of the mould, thereby reducing turbulence in the mould. The mould can be re-orientated according to the shape of the mould and the section into which the molten metal is entering. It will be appreciated that three, four or more degrees of freedom may be employed, depending on the requirements of the mould and the product to be cast. In one arrangement, a rotational element is provided to adjust the orientation of the mould cavity, and it may be that the rotational element is a gimbal. A gimbal, which is taken to be a pivoted support and permits rotation of an object around at least one axis, provides a convenient and compact arrangement for the rotation of the mould cavity. Thus, the gimbal can provide multi-axis rotation of the mould. The element for adjusting the orientation of the mould may be arranged between the piston sleeve and the mould so as to allow adjustment of the mould orientation relative to the piston sleeve. Rotation of the mould cavity, relative to the piston sleeve allows the piston sleeve to be kept in place, preferably mounted upon a firm surface, and the only mould to be moved. Thus, the mass that requires rotation is less than that of the mould and the piston sleeve together. Alternatively, or additionally, the rotational element is arranged beneath the piston sleeve such that the piston sleeve and the mould move together and relative to the floor. Whilst more power may be required to move the full arrangement, it may be desirable to do so, particularly as there is then a reduced risk of molten material leaking from between the piston sleeve and the mould. It is envisaged that where a rotational element is employed, the rotational element may be in the form of a planar surface that can be rotated in at least two, and possibly three, degrees of freedom. Thus, the whole piston and mould arrangement can be mounted upon a surface that can be tilted or rotated to allow the molten material to move smoothly into the desired location. The driver may be connected to the mould and / or to the piston sleeve to drive the mould towards the piston. Thus, the piston may be kept stationery and the sleeve driven over the piston to fill the mould. By driving the mould and / or the piston sleeve towards the piston, gravity and be used to reduce the power required to drive the arrangement. Additionally, the driver can be accurately controlled to ensure a smooth filling of the mould. It 1s advantageous that the top of the piston sleeve is provided with an arcuate profile and the inlet to the mould is provided with a corresponding arcuate profile such that the longitudinal axis of the mould can be rotationally adjusted in at least two degrees of freedom relative to the longitudinal axis of the piston sleeve. In such an arrangement, similar to a ball-joint, the molten material can pass though the top of the piston sleeve and into the mould. The driver may be connected to the mould or the mould sleeve. When the piston is fixed in place, the mould sleeve can be lowered over the piston, thereby forcing the molten material into the mould. An advantage of arranging the driver in such a manner is that gravity can assist with the movement of the mould towards the piston, thereby requiring less power or energy to cast the product. Alternatively, the driver may be attached to the piston and the piston sleeve held in place. The piston can then be moved within the sleeve to force molten material into the mould. The driver may be in the form of a robotic arm, but it could comprise a forklift, a pneumatic or hydraulic ram or another driving force. In one arrangement, the mould may be collected from a station by a robotic arm. The mould is then positioned over the piston sleeve, which contains the piston and molten metal, subsequent to which, the robotic arm can lower the mould onto the sleeve. The movement of the mould over the sleeve, with the assistance of gravity, can force the piston, which is fixed in place, to travel up the sleeve, which injects the material into the mould. Such an arrangement reduces the number of moving parts that would traditionally be used to push the piston upwards, thereby simplifying the casting process. A robotic arm can allow manufacture of several systems at once, increasing capacity for little additional cost of equipment. For example, a different mould can be collected by the robotic arm and a second cast undertaken either on the same piston or a second piston. This reduces the turnaround time. A robotic arm may also provide better angular control of the mould. The robotic arm can manipulate the position of the mould to turn, pivot or angle the mould, thereby allowing the turbulence within the mould to be reduced. The angular adjustment of the arrangements set out herein may be achieved by the use of hydraulics, for example hydraulic piston and cylinder systems to provide accurate adjustment of the mould, relative to the ground and / or the piston sleeve. The present invention extends to a casting process comprising the steps of: providing a casting arrangement as set out herein; analysing the internal volume of the mould and determining a variable flow rate and a variable orientation for casting a product in the mould; and casting a product using the casting arrangement and varying the flow rate and orientation of the mould. The internal volume of the mould can be analysed to determine the volume of molten material required to fill the mould at a constant flow rate. The flow rate can be adjusted by varying the movement of the piston within the piston sleeve. To that end, the driver can be adjusted to increase the displacement of molten material for larger cross-sectional areas within the mould, and the displacement can be decreased for narrower cross-sectional areas. Software can be used that takes the output from a simulation of the casting flow and solidification, breaks the proposed simulation into separate step, or slices across the mould, with those steps identifying the total volume of material required to fill any particular step, at any given point of the injection cycle. The speed of the piston can then be directed by the software to alter the injection velocity, thereby ensuing a constant fill speed throughout the changing volume of the mould. Whilst it may be advantageous for each step to have the same axial distance along the mould, it might be that the steps have varying ‘depths’ to accommodate the moulding process. Having a relatively constant flow rate of molten material entering the mould reduces turbulence in the casting process. Preferably, the analysis comprises a simulation of the casting flow and breaks the simulation into separate steps and then identifies the volume of material required to fill each of the steps at a point in the moulding process to determine the flow rate required per step to reduce defects in the finished product. It will be appreciated that other mathematical methods and / or models may be employed to achieve the analysis. Each step can be considered as a small distance along an axis of the mould and the volume of each step can then be calculated. For example, if each step is considered to be a millimetre along the axis of the mould, the flow rate of molten material required to provide a constant fill rate of the mould can be determined by calculating the cross-sectional volume for each millimetre step. Once the flow rate has been determined, the piston can be moved at the required variable speed to provide a smooth flow of molten material into the mould. An analysis of the internal shape and volume of the mould can be undertaken using software and running on a processor, such as a computing device or smartphone. The angular adjustment of the mould can be calculated during the analysis undertaken to determine the required flow rate. Thus, software may be employed to control the flow rate and the angular adjustment of the mould, so that the two are synchronised, thereby allowing the flow rate to match the position of the mould, or vice versa. This allows for a considerably less, and in some circumstances near zero, turbulent filling of the mould cavity, thereby reducing the risk of defects in the final product. Alternatively, the angular adjustment may be determined separately from the fill rate analysis. Advantageously, the casting arrangement is connected to an induction melting furnace and wherein, the induction melting furnace can provide molten metal to the casting arrangement. Rather than heat the metal and then cast using the molten material, the casting arrangement can be connected to, or can incorporate, an induction melting system or furnace. This allows the molten material to be transferred into the mould directly after melting, thereby reducing the risk of contamination and increasing the operator safety level. Furthermore, the volume of material required can be calculated and melted within, or adjacent, the arrangement, thereby reducing the risk of waste material and reducing transport of molten material. The invention extends to a casting system as set out herein that is employed to operate the casting system described herein. The system including the variable flow rates and the calculation of the volume steps, can be employed in operating the arrangements disclosed herein, including the pivotable mould, in order to cast a better quality product with fewer defects. Brief Description of the Drawings An embodiment of the invention will now be described, by way of example only, and with reference to the accompanying drawings, in which: Figure 1 shows a first arrangement of the present invention; Figures 2.1 and 2.2 show the arrangement of Figure 1 in different positions; Figure 3 shows a further arrangement of the present invention; Figures 4a to 4c shows the arrangement of Figure 3 in operation; Figure 5 shows an enlarged view of the piston and cylinder of the arrangement of the present invention; Figure 6 shows another arrangement of the present invention; and Figure 7 shows a portion of a piston and sleeve arrangement that can be used with the present invention. Detailed Description of Exemplary Embodiments Figure 1 shows an arrangement 10 comprising a piston sleeve 12, a piston 14 arranged within the piston sleeve 12 and a mould 16 positioned at an outlet of the piston sleeve 14. The piston sleeve 12 comprises an outer cylinder 18, which may be provided with integrated rapid induction coils 20 therein. The integrated induction coils 20 can be employed to melt metal within the piston sleeve 14 or to keep any molten metal therein in a molten state. An inner cylinder 22 is provided within the outer cylinder 18 and coaxial therewith. As more clearly shown in Figure 5, a piston head 24 is arranged within the inner cylinder 22, with the piston head 24 being connected to a first end of a piston shaft 26. A first side of a piston seal 28 is provided on the surface of the piston head, the piston seal 28 sealing the internal faces of the inner cylinder 22 to reduce the risk of material leaking around the piston head 24. On a second surface of the piston seal 28 is a piston seal protector 30 that reduces the risk of damage to the piston seal 28. The second end of the piston shaft 26 may be connected to a surface to hold the piston head in place, relative to the surface, or to a driver, such as a stepper motor, depending upon the system employed. Some arrangements will employ a fixed piston and other may employ a driven piston. Arranged between the piston sleeve 14 and the mould 16 is a mould interface 34. The mould 16 comprises an internal cavity 36 that will be filled with molten material during the casting process. Figure 2 shows the arrangement 10 of Figure 1, with a different mould 16 applied to the arrangement 10. The mould 16 in Figure two comprises three internal chambers 16a, 16b, 16c, all of which are in fluid communication with one another. In the arrangement 10 of Figure 2, the sleeve 12 and the piston 14 therein, along with the mould 16 are all able to be pivoted together, so that they move to an angle that is non- perpendicular with the ground. Thus, as shown in Figures 2.1 and 2.2, the arrangement 10 can be moved from a substantially vertical position, Figure 2.1, to an angle A, which is away from vertical, Figure 2.2. Detailed on the figures is the turbulence of the molten material that flows through the internal chambers 16a, 16b, 16c, as the mould 16 is filled. Where the base of the mould is substantially parallel with the floor, and the mould cavity 16 is oriented accordingly, the turbulence in the molten material 1 passing between the internal cavities 16a to 16¢ is much greater than the turbulence in the molten material 2, when the mould 16 is in the tilted position. The turbulence created by molten material moving between cavities in the mould 16 can be significantly reduced by ‘tilting’ the mould 16 away from the intended vertical orientation, as demonstrated by the turbulence 1 being greater than turbulence 2. The turbulence shown in Figure 2.2 is significantly reduced as the molten material does not ‘drop’ between the cavities 16a, 16b, 16c, but slides down the internal surfaces. The arrangement of Figure 2 may be created by mounting the piston sleeve 12 and piston 14 on a pivotable or moveable surface. The mould 16 should be securely mounted upon the piston sleeve 12 to ensure that it stays in place, relative to the piston sleeve 12. A driver (not shown) may be connected to the piston 14 to drive it within the piston sleeve 12, or the mould 16 and / or the piston sleeve may be connected to a driver, so that the piston 14 can remain fixed and the piston sleeve 12 can be moved relative thereto. In the arrangement shown in Figures 3 and 4, the piston sleeve 12 and the piston arrangement is the same as that of Figures 1 and 2; however, the interface between the piston sleeve 12 and the mould 16 is different. In this embodiment, the arrangement 40 is such that the top of the piston sleeve 12 has an arcuate external surface profile 42 and the inlet 44 to the mould cavity 16 has a corresponding arcuate internal profile 46. The external profile may be hemispherical and the internal profile provided with a corresponding hemispherical profile. Thus, the piston sleeve 12 is received into the mould 16 in a similar manner to a ball-and- socket joint, thereby allowing the mould 16 to be rotated on top of the piston sleeve 12, as displayed in Figures 4b and 4c. As shown in Figures 4, to operate the arrangement 40, the piston 14 is retracted in the piston sleeve 12 and molten metal 50, or metal particulate, such as metal pellets, is placed into the piston sleeve. The induction coils, where present, are employed to keep the metal 50 in a molten state within the piston sleeve 12. The mould 16 is placed on top of the piston sleeve 12, with the internally concave, or female, profile 46 of the mould 16 receiving the externally convex, or male, profile 42 of the piston sleeve 12. Thus, the two parts are mounted together, with the mould inlet 44 being in fluid communication with the internal cavity of the piston sleeve 12. It will be appreciated that seal elements may be applied to the joint to reduce the risk of leaks. As the piston 14 is moved within the piston sleeve 12 towards the mould 16, the molten metal 50 is pushed towards the mould 16 and enters therein. The orientation of the mould 16, relative to the top of the piston sleeve 12 can be adjusted by rotating the mould 16 by moving the mould 16 on top of the piston sleeve 12, which is enabled by the matching profiles. The movement of the piston can be varied and adjusted to ensure a constant fill rate for the mould 16, taking into account the dimensions of the cross-section of the mould 16 during the filling process. This enables the mould 16 to be filled at a steady rate and at an angle that will reduce the turbulence in the mould 16, compared with existing systems. Figure 6 shows a cross-sectional view of a casting arrangement 60 that employs a gimbal. In the arrangement 60, the junction between the top of the piston sleeve 12 and the mould is provided with a gimbal joint mould interface 62 arrangement therebetween. In this arrangement, the piston sleeve 12 is provided with a conical top profile 64 having an outlet 66 therein, through which the molten material can be dispensed by movement of the piston 14 within the piston sleeve 12. The mould interface 62 sits atop the conical top section 64 and can pivot in two or three degrees of freedom. The mould is then mounted on the mould interface 62, so that it can be tilted with the mould interface 62. In operation, molten material is forced through the outlet 66 of the piston sleeve 12 by the piston 14. The molten material passes through an aperture 68 in the mould interface 62 and into the mould mounted thereupon. Thus, the angle of the mould, relative to the piston sleeve 12, can be adjusted to reduce turbulence within the mould cavity during the casting process. Figure 7 shows a sectional view of a further arrangement 70 in which a piston 14 is provided within a piston sleeve 12. The piston sleeve 12 is provided with an outer cylinder 18 that comprises induction coils 20 and an inner sleeve 22 is provided within the outer cylinder 18, with the inner cylinder 22 housing the piston 14. The piston 14 has a piston head 24 and, as with Figure 5, a piston seal 28 and a piston seal protector 30 are provided on the piston head 24. At the top of the piston sleeve 12 is a three-dimensional pivot table 72. The pivot table 72 has an aperture 74 therein to allow the flow of molten material therethrough and the table is able to pivot, or move, in three planes. The mould (not shown) is affixed to the pivot table 72 and so the pitch, roll and yaw of the mould can all be adjusted by the pivot table. The angular adjustment of the mould may also allow the mould to be rotated to assist with the removal of any trapped air, so that it can escape from the mould. One or more features of an embodiment set out herein may be incorporated into a different embodiment of the invention.

Claims

Claims 1. A casting arrangement, comprising: a piston sleeve; a piston arranged within the piston sleeve; a driver to adjust the position of the piston within the piston sleeve; and a mould having a mould cavity, the mould being arranged upon the piston sleeve, the mould cavity positioned to receive material from the piston sleeve, when in use; wherein, the mould is arranged in such a manner that the orientation of the mould cavity, relative to the ground, can be adjusted, whilst the casting process is in operation.

2. A casting arrangement according to claim 1, wherein the orientation of the mould cavity can be adjusted in at least two degrees of freedom.

3. A casting arrangement according to claim 1 or claim 2, wherein a rotational element is provided to adjust the orientation of the mould cavity. 4, A casting arrangement according to claim 3, wherein the rotational element is a gimbal.

5. A casting arrangement according to claim 3 or claim 4, wherein the rotational element is arranged between the piston sleeve and the mould so as to allow adjustment of the mould orientation relative to the piston sleeve.

6. A casting arrangement according to claim 3 or claim 4, wherein the rotational element 1s arranged beneath the piston sleeve such that the piston sleeve and the mould move together and relative to the floor.

7. A casting arrangement according to any one of claims 3 to 6, wherein the rotational element is a planar surface that can be rotated.

8. A casting arrangement according to any preceding claim, wherein the driver is connected to the mould and / or to the piston sleeve to drive the mould towards the piston.

9. A casting arrangement according to claim 8, wherein the top of the piston sleeve is provided with an arcuate profile and the inlet to the mould is provided with a corresponding arcuate profile such that the longitudinal axis of the mould can be rotationally adjusted in at least two degrees of freedom relative to the longitudinal axis of the piston sleeve.

10. A casting process comprising the steps of: providing a casting arrangement according to any preceding claim; analysing the internal volume of the mould and determining a variable flow rate and a variable orientation for casting a product in the mould; and casting a product using the casting arrangement and varying the flow rate and orientation of the mould.

11. A casting process according to claim 10, wherein the analysis comprises a simulation of the casting flow and breaks the simulation into separate steps and then identifies the volume of material required to fill each of the steps at a point in the moulding process to determine the flow rate required per step to reduce defects in the finished product.

12. A casting system comprising the casting of any one of claims 1 to 9, wherein the casting arrangement is connected to an induction melting furnace and wherein, the induction melting furnace can provide molten metal to the casting arrangement.

13. A casting system according to claim 12, wherein the casting process of claims 10 or 11 1s employed to operate the casting system. Claims 1. A casting arrangement, comprising: a piston sleeve; a piston arranged within the piston sleeve; a driver to adjust the position of the piston relative to the piston sleeve; and a mould having a mould cavity, the mould being arranged upon the piston sleeve, the mould cavity positioned to receive material from the piston sleeve, when in use; wherein, the mould is arranged in such a manner that the orientation of the mould cavity, relative to the ground, can be adjusted, whilst the casting process is in operation, and wherein the orientation of the mould cavity can be adjusted in at least two degrees of freedom. 2 A casting arrangement according to claim 1, wherein a rotational element is provided to adjust the orientation of the mould cavity.

3. A casting arrangement according to claim 2, wherein the rotational element is a gimbal.

4. A casting arrangement according to claim 2 or claim 3, wherein the rotational element is arranged between the piston sleeve and the mould so as to allow adjustment of the mould orientation relative to the piston sleeve.

5. A casting arrangement according to claim 2 or claim 3, wherein the rotational element is arranged beneath the piston sleeve such that the piston sleeve and the mould move together and relative to the floor.

6. A casting arrangement according to any one of claims 2 to 5, wherein the rotational element is a planar surface that can be rotated.

7. A casting arrangement according to any preceding claim, wherein the driver is connected to the mould and / or to the piston sleeve to drive the mould towards the piston.

8. A casting arrangement according to claim 7, wherein the top of the piston sleeve is provided with an arcuate profile and the inlet to the mould is provided with a corresponding arcuate profile such that the longitudinal axis of the mould can be rotationally adjusted in at least two degrees of freedom relative to the longitudinal axis of the piston sleeve.

9. A casting process comprising the steps of’ providing a casting arrangement according to any preceding claim; analysing the internal volume of the mould and determining the volume of molten material required to fill the mould at a variable flow rate and a variable orientation for casting a product in the mould; and casting a product using the casting arrangement and varying the flow rate and orientation of the mould.

10. A casting process according to claim 9, wherein the analysis of the internal volume of the mould comprises a simulation of the casting flow and breaks the simulation into separate steps and then identifies the volume of material required to fill each of the steps at a point in the moulding process to determine the flow rate required per step to reduce defects in the finished product.

11. A casting system comprising the casting of any one of claims 1 to 8, wherein the casting arrangement is connected to an induction melting furnace and wherein, the induction melting furnace can provide molten metal to the casting arrangement.

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