GB2403445A

GB2403445A - A method of cutting material

Info

Publication number: GB2403445A
Application number: GB0315687A
Authority: GB
Inventors: Paula Mavis Spiller; Andrew Philip Bushnell
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 2003-07-04
Filing date: 2003-07-04
Publication date: 2005-01-05
Also published as: GB0315687D0

Abstract

A method of cutting material having a ductile state and a brittle state comprises creating a stress concentration path in the material, for example by creating one or more surface irregularities 16, 18 and 20 cooling the material, for example using a cryogenic coolant, to transfer it from the ductile state to the brittle state; and applying a force to the cooled material to divide the material.

Description

A Method of Cutting Material Embodiments of the present invention relate

to a method of cutting material and/or an article which has been cut in accordance with said method.

Numerous cutting techniques for separating or dividing material are available, including machining, laser cutting and abrasive water jet cutting. Machining and laser cutting can alter the material properties whilst abrasive water jet cutting can leave gritty deposits on the surfaces of the cut material. These effects may be undesirable.

According to a first aspect of the present invention, there is provided a method of cutting material having a ductile state and a brittle state, the method comprising: (a) creating a stress concentration path in the material; (b) cooling the material to transform it from the ductile state to the brittle state; and (c) applying a force to the cooled material to divide the material.

The separation or division of material into first and second portions is achieved by this method of cutting.

Step (a) may include creating a surface irregularity in the material e.g. a score line, or may include creating at least two surface irregularities e.g. a score line with a notch providing different levels of stress concentration.

Step (a) may include creating a first surface irregularity e.g. a notch to determine a location of crack initiation and creating a second surface irregularity e.g. a score line to determine a direction of crack propagation.

The material may have one or more surfaces and step (a) may include scoring the material to provide one or more score lines on one or more of said surfaces. Step (a) may include creating at least one notch in the material.

The or each notch may provide a first level of stress concentration and the or each score line may provide a second level of stress concentration. The or each notch may provide a higher level of stress concentration than the or each score line. The or each notch may determine the location of crack initiation and the or each score line may determine the direction of crack propagation.

Preferably, step (b) includes cooling the material using a cryogenic coolant. The cryogenic coolant may be liquid nitrogen or carbon dioxide.

The material may have a brittle transition temperature and step (b) may include cooling the material to a temperature substantially equal to, or less than, the brittle transition temperature to transform it from the ductile state to the brittle state.

The material may have a thickness and step (b) may include cooling the material to transform it from the ductile state to the brittle state through said thickness.

Steps (a) and (b) of the method may be performed simultaneously. Step (b) may comprise cooling the material along the stress concentration path, and directing cryogenic coolant onto the stress concentration path.

Step (c) may include applying a continuous force, or may alternatively include applying a cyclic force to cause crack propagation by fatigue.

The force applied in step (c) may cause the material to exceed its ultimate tensile strength along the stress concentration path, resulting in crack propagation and division of the material.

Step (a) may include providing an edge for supporting the material along the stress concentration path, which edge may be provided by a fulcrum.

The material may have first and second portions separated by the stress concentration path and step (c) may include applying a clamping arrangement to the first portion of the material and applying the force to the second portion of the material.

According to a second aspect of the present invention, there is provided an article comprising a material which has been cut in accordance with the method according to the first aspect of the present invention.

Embodiments of the present invention will now be described by way of example only, and with reference to the accompanying drawings, in which: Fig. 1 is a schematic illustration of a first method of cutting a sheet; Fig. 2 is a schematic illustration of a first method of applying a force F to the sheet of Fig. 1; Fig. 3 is a schematic illustration of a second method of applying a force F to the sheet of Fig. 1; Fig. 4 is a schematic illustration of a third method of applying a force F to the sheet of Fig. 1; Fig. 5 is a schematic illustration of a second method of cutting a sheet; Fig. 6 is a schematic illustration of a first method of cutting a block; and Fig. 7 is a schematic illustration of a second method of cutting a block.

Referring to the drawings, there is shown schematically a method of cutting material having a ductile state and a brittle state, the method comprising creating a stress concentration path in the material, which may include creating one or more surface irregularities; cooling the material to transform it from the ductile state to the brittle state; and applying a force to the cooled material to divide the material.

In more detail, Fig. 1 illustrates schematically a first method of cutting a sheet 10 of material having an upper surface 12 and a lower surface 14. A stress concentration path is created by scoring the sheet 10 to create score lines 16, 18 respectively on the upper and lower surfaces 12, 14. The score lines 16, 18 define the location at which the material is to be divided or separated using the method into first and second portions 15a, 15b. The score line 18 is created on the lower surface 14 such that its position opposes the position of the score line 16 on the upper surface 12. Notches 20 may also be created in the sheet 10 at one or both ends of the score line 16 and/or the score line 18.

A fulcrum 21 is positioned along the lower surface of the sheet 10 and this provides an edge 21a for supporting the sheet 10 along the lower surface 14. The purpose of this edge 21a will be described below.

The sheet 10 is cooled using a cryogenic coolant, such as liquid nitrogen or solid phase carbon dioxide, and this is achieved by either placing the sheet 10 in a cooling chamber or by locally applying cryogenic coolant along the stress concentration path using a nozzle 22. In the latter case, the nozzle 22 is moved form a first edge A to a second edge B of the sheet 10 along the score line 16 on the upper surface 12.

Typically, when using a cooling chamber it is possible to cool the material to a temperature in the order of -150 C, whilst with localised cooling it is possible to cool the material to a temperature in the order of -100 C.

Whether cooled in a chamber or by using the nozzle 22 for localized coolant delivery, the sheet 10 is cooled so that it is transformed from the ductile state to the brittle state through its thickness. Typically, the material is cooled to a temperature in the order of 2 C below its brittle transition temperature.

A force is then applied to the sheet 10 to separate the first and second portions 15a, 15b. Fig. 2 illustrates schematically a force F applied to the upper surface 12 of each of the first and second portions 15a, 15b. The force F may be a continuous force or may be a cyclic force for subjecting the cooled sheet 10 to fatigue loading. In both cases, the edge 21a provides a reaction against the force F which causes a crack to propagate through the thickness of the sheet 10 between the score lines 16, 18, and/or between the first and second edges A, B. The notches 20 provide a higher level of stress concentration than the score lines 16, 18, and thus determine the location of crack initiation in the sheet 10.

Once a crack has been initiated, the score lines 16, 18 then determine the direction of crack propagation through the sheet 10.

Fig. 3 illustrates schematically a different method for applying a force to the cooled sheet 10. In this embodiment, force F is applied laterally to the first and second portions 15a, 15b of the sheet 10 on each side of the score line 16. This pulls apart the first and second portions 15a, 15b and causes a crack to propagate along the stress concentration path defined by the score lines 16, 18 and notches 20 between the first and second edges A, B. Due to the direction of application of the force F. it is not necessary in this embodiment to provide an edge 21a along the lower surface 14 of the sheet 10.

Fig. 4 illustrates schematically a further method for applying a force to the cooled sheet 10. In this embodiment, either a constant or cyclic force is applied locally along the stress concentration path defined by the score line 16, and this force is moved along the score line 16 between the first and second edges A, B of the sheet 10.

This method of force application induces a crack at the first edge A of the sheet 10 and causes it to propagate along the sheet 10 as the force F is being moved until it reaches the second edge B such that the first and second portions 15a, 15b become separated.

Referring now to Fig. 5, there is shown schematically a further method of cutting a sheet 30 to remove a circular portion of material from the sheet 30. In this method, a stress concentration path is created as described above by scoring the sheet 30 at corresponding positions on upper and lower surfaces 34, 36. This defines first and second portions 42, 44 on the sheet 30. The sheet 30 is then cooled either in a cooling chamber or using a nozzle as described above.

In this embodiment, the first portion 42 is either clamped or supported in position, and a force F is applied to the second portion 44 to separate it from the first portion 42. Force F is applied centrally to the second portion 44, or is evenly distributed across the upper surface of the second portion 44. Application of force F to the second portion 44 whilst the first portion 42 is supported causes a crack to propagate in the sheet 30 between the score lines on the upper and lower surfaces 34, 36 and hence separation of the second portion 44 from the first portion 42.

Fig. 6 illustrates schematically a method of cutting a block 50 of material. In this method, a stress concentration path is created by scoring four surfaces of the block to create a continuous score line 52 which defines first and second portions 54, 56 of the block 50 on either side of the score line 52.

The block 50 is cooled in a chamber so that it is transformed from the ductile state to the brittle state through its thickness, and a continuous force F is applied to the block 50 such that first and second components of the force act in opposite directions on the first and second portions 54, 56. This causes the first and second portions 54, 56 to shear and thus separate along the score line 52.

Fig. 7 illustrates schematically a further method of cutting a block 60. In this embodiment, the block 60 is scored to create a continuous score line 62 on three surfaces at a corner of the block, to define first and second portions 64, 66 on the block 60. Again, the block 60 is cooled to transform it to its brittle state and a clamping arrangement (not shown) is applied to the first portion 64 to secure it in position. An instantaneous force F is then applied to the second portion 66 which causes the first and second portions 64, 66 to shear along the score line 62 and thus separation of the second portion 66 from the first portion 64. ; In all of the above embodiments, the force F has a magnitude which causes the material to exceed its ultimate tensile strength. This will vary dependent on the material properties.

The application of the force to the cooled material causes a crack to propagate through the cooled material along the stress concentration path, or causes the cooled material to shear along the stress concentration path, and thus separate into first and second portions.

The method is particularly suited for cutting metals and in particular those used in aerospace applications, such as Steels, Titanium, Nickel Alloys, Magnesium or Aluminium. It is not however limited to use with these materials and can be used for cutting any material which experiences a ductile to brittle transition. The only materials which are known not to experience such a ductile to brittle transition are those having a Face Centre Cubic structure.

It should be noted that the features of the methods described above with reference to the drawings may be used in any combination.

Although embodiments of the present invention have been described in the preceding paragraphs with reference to various examples, it should be appreciated that various modifications to the examples given may be made without departing from the scope of the invention as claimed. For example, the method could be used to cut plastics material.

The stress concentration path may be created other than by scoring the material or creating notches. The material may be cooled other than by the use of cryogenic coolants.

Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon. - 9

Claims

Claims 1. A method of cutting material having a ductile state and a

brittle state, the method comprising: (a) creating a stress concentration path in the material; (b) cooling the material to transform it from the ductile state to the brittle states and (c) applying a force to the cooled material to divide the material.
2. A method according to claim 1, wherein step (a) includes creating a surface irregularity in the material.
3. A method according to claim 1 or claim 2, wherein step (a) includes creating at least two surface irregularities providing different levels of stress concentration.
4. A method according to any of the preceding claims, wherein step (a) includes creating a first surface irregularity to determine a location of crack initiation and creating a second surface irregularity to determine a direction of crack propagation.
5. A method according to any of the preceding claims, wherein the material has one or more surfaces and step (a) includes scoring the material to provide one or more score lines on one or more of said surfaces.
6. A method according to any of the preceding claims, wherein step (a) includes creating at least one notch in the material.
7. A method according to any of the preceding claims, wherein step (b) includes cooling the material using a cryogenic coolant.
8. A method according to claim 7, wherein the cryogenic coolant is liquid nitrogen or carbon dioxide.
9. A method according to any of the preceding claims, wherein steps (a) and (b) are performed simultaneously.
10. A method according to any of the preceding claims, wherein step (b) comprises cooling the material along the stress concentration path.
11. A method according to claim 10, wherein cryogenic coolant is directed onto the stress concentration path. -
12. A method according to any of the preceding claims, wherein step (c) includes applying a continuous force.
13. A method according to any of claims 1 to 11, wherein step (c) includes applying a cyclic force to cause crack propagation by fatigue.
14. A method according to any of the preceding claims, wherein step (a) includes providing an edge for supporting the material along the stress concentration path.
15. A method according to any of the preceding claims, wherein the material has first and second portions separated by the stress concentration path and step (c) includes applying a clamping arrangement to the first portion of the material and applying the force to the i second portion of the material.
16. An article comprising a material which has been cut in - accordance with the method as defined in any of the preceding claims.
17. A method of cutting material substantially as hereinbefore described with reference to and/or as shown in the accompanying drawings.
18. An article substantially as hereinbefore described with reference to and/or as shown in the accompanying drawings.
19. Any novel subject matter or combination including novel subject matter disclosed herein, whether or not within the scope of or relating to the same invention as any of the preceding claims.