GB2642481A

GB2642481A - Grinding tool

Info

Publication number: GB2642481A
Application number: GB2410000.0A
Authority: GB
Inventors: Richards Mark; Bate Kevin; Philpot John; Unuvar Kadir
Original assignee: Tyrolit Uk Ltd; Jaguar Land Rover Ltd
Current assignee: Tyrolit Uk Ltd; Jaguar Land Rover Ltd
Priority date: 2024-07-10
Filing date: 2024-07-10
Publication date: 2026-01-14
Also published as: GB202410000D0

Abstract

A grinding tool 1 is used for grinding first and second features on a cylindrical wall. The tool comprises a shaft 26 having a longitudinal axis of rotation 11, and first 23 and second 24 grinding locations which are spaced apart along the axis of rotation. Each grinding location is annular and supports a grinding ring 5, 6. Each ring can comprise an abrasive coating, such as a layer of diamond grit. The shaft can include a coolant passage system with coolant outlets 61, 71 in the grinding rings. A method of performing grinding operations on a cylinder bore comprises feeding the shaft into the bore and bringing the first grinding ring into contact with a bottom end portion of the bore while maintaining a separation between the second grinding ring and the bore. The shaft is rotated so that the first grinding ring performs an undercut operation on the bore. The second griding ring is then brought into contact with a top end portion of the bore while separating the first grinding ring from being in contact with the bore. The shaft is again rotated and the second grinding ring performs an upper chamfering operation on the bore.

Description

[0001] Grinding Tool The present invention relates to a grinding tool for grinding an engine block or, more generally, a metal workpiece having a cylindrical surface

[0002] Backgrounda

[0003] For many years, engine blocks have been machined on multi-axis machining centres which perform multiple machining operations such as drilling, thread tapping and milling. An engine block is mounted on a fixturing whilst the machining operations are performed, and the individual tools are mounted on HSK spindle adaptors and are stored in a tool changer (magazine) until they are needed. A tool is removed from the magazine, used to perform its operation, and returned to its position in the magazine In an engine block, the cylinder bores may be spray coated. Where a cylinder bore needs to be machined, such as to form a chamfer, a cutting tool is used, and the cutting tool needs to cut through the (relatively hard) spray coating and cut into the underlying (relatively soft) base material. The base material may be aluminium if the engine block has been cast in aluminium material. The cutting tool has to apply a force which is large enough to cut through the spray coating, and this large force may cause vibration and deflection of the cutting tool. As a result, the cutting tool may have a low tool life, the cycle time may be longer than is desirable, and the final quality of the end product may be lower than is desirable. A low tool life and a long cycle time are undesirable because they increase the overall manufacturing cost.

[0004] The spray coating may be an ultra-hard thermically sprayed coating, and the large transfer of energy into the coating during the cutting operation (turning or milling) may weaken the bond to the underlying base material (the aluminium of the engine block).

[0005] Summary

[0006] According to an aspect of the present invention, there is provided a grinding tool for grinding first and second features which are spaced apart along a longitudinal axis of a cylindrical wall, the grinding tool comprising: a shaft having a longitudinal axis of rotation and first and second grinding locations which are spaced apart along the longitudinal axis of rotation; wherein: the first grinding location is annular and supports a first grinding ring; and the second grinding location is annular and supports a second grinding ring.

[0007] The cylindrical wall may be a cylinder bore of an engine block, and the cylinder bore may have a spray coating. The first and second features that are to be machined may be at respectively the bottom end and top end of the cylinder bore and involve machining through the spray coating and into an underlying base material.

[0008] By replacing the previously-used cutting operations (using carbide milling or hobbing cutters) and instead using grinding operations, it is possible to machine a bi-metal structure (of a relatively-hard coating on a relatively-soft base material) without the machining (the grinding) causing the coating to lift away from the base material.

[0009] The grinding tool has a longer tool life (approximately 50% longer) than the cutting tool that it supersedes, and the grinding tool also has a shorter (faster) cycle time (approximately 50% shorter).

[0010] The first and second grinding rings may each comprise an abrasive coating, such as a layer of diamond grit. The coating may be galvanically connected to the base material of the shaft. The coating may be an electro-plated coating wherein an electro-plated metal (such as nickel) encapsulates a particulate abrasive (such as diamond grit) The shaft may include a coolant passage system which has coolant outlets in the first and second grinding rings.

[0011] The shaft may have a proximal end and a distal end. The first grinding location may be at the distal end, and the second grinding location may be at the proximal end.

[0012] The coolant passage system may comprise an axial passage running from the proximal end towards the distal end of the shaft, and a first set of radial passages running from the axial passage to the first grinding location and to a first set of the coolant outlets, and a second set of radial passages running from the axial passage to the second grinding location and to a second set of the coolant outlets The axial passage may be a central axial passage located on the longitudinal axis of rotation of the shaft.

[0013] When grinding, the supply of a coolant fluid to a grinding location assists the grinding operation. The coolant fluid may provide lubrication to the surface that is undergoing the grinding operation and may remove (carry away) the ground-away (abraded) material. The coolant passage system may be configured to supply the coolant fluid to the grinding locations at a relatively high pressure and at a relatively low volumetric flow rate. The diameter of the coolant outlets may be configured to achieve this.

[0014] The first set of coolant outlets may have an outlet diameter which is less than an outlet diameter of the second set of coolant outlets The first grinding ring may have an outer diameter and an inner diameter. The second grinding ring may have an outer diameter and an inner diameter, and the outer diameter of the second grinding ring is greater than the outer diameter of the first grinding ring.

[0015] The inner diameter of the second grinding ring may be greater than the outer diameter of the first grinding ring.

[0016] The first and second grinding locations may be separated by a central shaft portion which has a shaft diameter which is smaller than the inner diameter of the first grinding ring and the inner diameter of the second grinding ring. This may assist in preventing the part of the shaft which is between the first and second grinding locations from making unwanted contact with (clashing with) the cylindrical wall during the grinding of the first and second features of the cylindrical wall.

[0017] The length of the central shaft portion may be at least 50% (60%, 70%, 80% or 90%) of the separation distance between the first and second grinding locations The first grinding ring may be configured for performing a lower chamfering operation and/or an undercut operation. Correspondingly, the first feature of the cylindrical wall may comprise a lower chamfer and/or an undercut.

[0018] The first grinding ring may include a first annular portion which is cylindrical and which is configured for performing the undercut operation The first grinding ring may include a second annular portion which is conically tapered and which is angled towards the second grinding ring and the second annular portion of the first grinding ring may be configured for performing the lower chamfering operation.

[0019] The second annular portion of the first grinding ring may be an edge portion.

[0020] The first annular portion of the first grinding ring may be contiguous with the second annular portion of the first grinding ring.

[0021] The second grinding ring may be configured for performing an upper chamfering operation and/or a spotfacing operation. Correspondingly, the second feature of the cylindrical wall may comprise an upper chamfer and/or a spotfaced surface.

[0022] The second grinding ring may include a first annular portion which is conically tapered and which is angled towards the first grinding ring and the first annular portion of the second grinding ring may be configured for performing the upper chamfering operation.

[0023] The second grinding ring may include a second annular portion which is perpendicular to the longitudinal axis of rotation of the shaft and which is configured for performing the spotfacing operation.

[0024] The first annular portion of the second grinding ring may be an edge portion.

[0025] The second annular portion of the second grinding ring may be contiguous with the first annular portion of the second grinding ring.

[0026] An HSK holder may be connected to a proximal-end connecting portion of the shaft. Thus, the tool may be made compatible with existing tool magazines which are configured to accept any tool which has a standard design of HSK holder.

[0027] The HSK holder and the shaft may be of a unitary construction (a monobloc) According to an aspect of the present invention, there is provided a multi-axis machining centre comprising a tool magazine containing a grinding tool which is in accordance with the present invention. The machining centre may be a 5-axis machining centre The machining centre may have a rotary drive which is configured to accept a standard design of HSK holder. Thus, each of the different tools which have the standard design of HSK holder and which are stored in the tool magazine may, when needed to be used, be fitted onto the rotary drive According to an aspect of the present invention, there is provided a method of performing grinding operations on a cylinder bore, the method comprising: providing a grinding tool which comprises a shaft having a longitudinal axis of rotation and first and second grinding locations which are spaced apart along the longitudinal axis of rotation, with the first grinding location being annular and supporting a first grinding ring, and with the second grinding location being annular and supporting a second grinding ring; feeding the shaft of the grinding tool into the cylinder bore and bringing the first grinding ring into contact with a bottom end portion of the cylinder bore whilst maintaining a separation between the second grinding ring and the cylinder bore; rotating the shaft of the grinding tool so that the first grinding ring performs an undercut operation and grinds an annular undercut at the bottom end portion of the cylinder bore; bringing the second grinding ring into contact with a top end portion of the cylinder bore whilst separating the first grinding ring from being in contact with the cylinder bore; and rotating the shaft of the grinding tool so that the second grinding ring performs an upper chamfering operation and grinds an annular upper chamfer at the top end portion of the cylinder bore.

[0028] When grinding the annular undercut, the shaft of the grinding tool may rotate whilst the longitudinal axis of rotation of the shaft undergoes circular interpolation inside the cylinder bore.

[0029] When grinding the annular upper chamfer, the shaft of the grinding tool may rotate whilst the longitudinal axis of rotation of the shaft undergoes circular interpolation inside the cylinder bore.

[0030] The longitudinal axis of the grinding tool may follow an orbital path whilst the grinding tool rotates.

[0031] The separation between the first and second grinding rings may be greater than the separation between the annular undercut and the annular upper chamfer, preferably 2% to 10% greater, more preferably 1% to 5% greater.

[0032] After the grinding of the annular undercut, the grinding tool may index radially inwards away from the annular undercut towards a longitudinal centre line of the cylinder bore. The shaft of the grinding tool may be fed further into the cylinder bore so as to bring the second grinding ring into contact with a deck face which is at the top end portion of the cylinder bore and which is perpendicular to the longitudinal centre line of the cylinder bore. The grinding of the annular upper chamfer by the second grinding ring may be performed so that the annular upper chamfer is created between the deck face and the cylinder bore.

[0033] The extent to which the shaft of the grinding tool is fed further into the cylinder bore is dependent on the separation between the first and second grinding rings relative to the separation between the annular undercut and the annular upper chamfer. If the first-mentioned separation is only slightly greater than the second-mentioned separation, the shaft of the grinding tool will only need to be fed slightly further into the cylinder bore. If the shaft of the grinding tool is only fed slightly further into the cylinder bore, it becomes easier to avoid the possibility of the first grinding ring (which is no longer in contact with the annular undercut) being advanced so far further that it comes into unwanted contact with structure (of the engine block) which is beyond the bottom end portion of the cylinder bore.

[0034] During the grinding of the annular upper chamfer, the second grinding ring may also perform a spotfacing operation on the deck face around the cylinder bore During the grinding of the annular undercut at the bottom end portion of the cylinder bore, the first grinding ring may also perform a lower chamfering operation and grind an annular lower chamfer at the bottom end portion of the cylinder bore at a position above the annular undercut.

[0035] The cylinder bore may have a spray coating at least at the positions where the undercut operation and the upper chamfering operation are performed. The spray coating may be present on the entire cylinder bore between the top and bottom end portions of the cylinder bore.

[0036] The cylinder bore may be a spray-coated cylinder bore in an engine block which is a casting of a metal which is softer than the spray-coating of the cylinder bore. The metal may be aluminium The grinding operations that are performed on the cylinder bore may serve to fill any porosity left in the aluminium of the engine block at the top and bottom end portions of the cylinder bore as a result of the casting process The method of the present invention may incorporate features described in relation to the grinding tool of the present invention, and vice versa.

[0037] Brief description of the drawings

[0038] Some embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which:-Fig. 1 is a side view of a first embodiment of a grinding tool in accordance with the present 25 invention Fig. 2 shows the grinding tool of Fig. 1 when inserted into a cylinder bore of an engine block, wherein the grinding tool is positioned for performing a grinding step of grinding an undercut and a lower chamfer.

[0039] Fig. 3 is an enlarged view of part of Fig. 2 and shows the undercut and the lower chamfer.

[0040] Fig. 4 shows the grinding tool of Fig. 1 when inserted further into the cylinder bore of the engine block, wherein the grinding tool is positioned for performing a later grinding step of grinding an upper chamfer and performing a spotfacing operation Figs. 5A and 5B are enlarged views of parts of Fig. 4. Fig. 5A shows the upper chamfer and the spotfacing. Fig. 5B shows how, during this grinding step, the grinding tool is clear of the previously-ground undercut and lower chamfer.

[0041] Fig. 6 is a longitudinal cross-sectional view of a second embodiment of a grinding tool in accordance with the present invention. Figs. 6A and 6B are enlarged views of part of Fig. 6, wherein Fig. 6A shows the second grinding ring and Fig. 6B shows the first grinding ring.

[0042] Fig. 7 is an exploded front perspective view of the grinding tool of Fig. 6.

[0043] Fig 8 is a front perspective view of a third embodiment of a grinding tool in accordance with the present invention.

[0044] Fig. 9 is a rear perspective view of the grinding tool of Fig. 8.

[0045] Fig. 10 is an exploded front perspective view of the grinding tool of Fig. 8.

[0046] Fig. 11 is an exploded front perspective view of the grinding tool of Fig. 8 wherein the exploded components are shown more-separated than in Fig. 10.

[0047] Fig. 12 is front perspective view of the grinding tool of Fig. 8 wherein the grinding tool is shown in longitudinal cross-section.

[0048] Fig. 13 a longitudinal cross-sectional view of the grinding tool of Fig. 8.

[0049] Fig. 14 is a front perspective view of the second grinding ring of the grinding tool of Fig. 8.

[0050] Fig. 15 is a front perspective view of the first grinding ring of the grinding tool of Fig. 8. Fig. 16 is a rear perspective view of the first grinding ring of the grinding tool of Fig. 8. Fig. 17 is a rear perspective view of the second grinding ring of the grinding tool of Fig. 8. Fig. 18 is a side view of the second grinding ring of the grinding tool of Fig. 8.

[0051] While the invention is susceptible to various modifications and alternative forms, some embodiments are shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the drawings and detailed description of these embodiments are not intended to limit the invention to the particular forms disclosed. In addition, although individual embodiments may have been discussed, the invention is intended to cover combinations of those embodiments. The invention covers all modifications, equivalents and alternatives falling within the spirit and the scope of the present invention as defined by the appended claims.

[0052] Deserintion of some embodiments A first embodiment of grinding tool will now be described with reference to Figs. Ito 5.

[0053] The grinding tool 1 comprises a shaft 2 and an HSK holder 3. The HSK holder 3 has a standard design which allows it to plug into a rotary drive 4 of a machining centre. The rotary drive 4 is depicted in dashed line in Fig. 1 but is not depicted in the other Figures for reasons of clarity.

[0054] The body of the shaft 2 and the HSK holder 3 are made of steel as an integral single body (a 15 monobloc). An example of the steel that may be used is Steel 42CrMoS4V (42CrMoS4 +QT) Material 1.7227.

[0055] The shaft 2 and the 1-15K holder 3 are rotatable around a longitudinal axis of rotation 11 of the tool 1. The shaft 2 and the HSK holder 3 may be driven to rotate around the axis 11 by the rotary drive 4.

[0056] The shaft 2 has a distal end 21 and a proximal end 22. A first annular grinding location 23 is located at the distal end 21, and a second annular grinding location 24 is located at the proximal end 22. A first grinding ring 5 is electro-plated as an abrasive layer onto the steel body at the first grinding location 23, and a second grinding ring 6 is electro-plated as an abrasive layer onto the steel body at the second grinding location 24. In relation to the el ectro-plating to form the grinding rings, the steel body of the shaft 2 is submerged in an electrolyte (with masking applied to the areas of the steel body other than the first and second grinding locations 23, 24) such that nickel is deposited at the first and second grinding locations 23, 24 whilst encapsulating a particulate abrasive in the form of man-made (synthetic) diamond crystals (so-called diamond grit). In this way, the abrasive is adhered to (galvanically connected to) the steel body of the shaft 2 at the first and second grinding locations 23, 24 to form abrasive coatings or layers The shaft 2 includes a nose portion 25 in front of the first grinding ring 5, a central shaft portion 26 between the first and second grinding rings 5, 6 and a proximal-end connecting portion 27 which is to the rear of the second grinding ring 6 and which serves to connect the rear end of the shaft 2 to the front end of the HSK holder 3.

[0057] The first grinding ring 5 has an outer diameter DI and an inner diameter D2. The second grinding ring 6 has an outer diameter D3 and an inner diameter D4. The outer diameter D3 is greater than the outer diameter Dl. In some embodiments, the inner diameter D4 may also be greater than the outer diameter Dl.

[0058] The central shaft portion 26 has a shaft diameter D5, and the shaft diameter D5 is less than the inner diameters D2, D4.

[0059] The first grinding ring 5 incorporates grooves 51 which are circumferentially uniformly spaced apart around the periphery of the first grinding ring 5 and which are aligned with the longitudinal direction of the rotational axis 11 of the grinding tool 1. Each groove 51 incorporates, at the base of the groove, two coolant outlets 71.

[0060] The second grinding ring 6 incorporates L-shaped grooves 61 which are circumferentially uniformly spaced apart around the periphery of the second grinding ring 6. Each groove 61 incorporates, at the base of the groove, a single coolant outlet 72.

[0061] The first grinding ring 5 includes a first annular portion 52 which is cylindrical and which is configured for performing an undercut operation. The first grinding ring 5 also includes a second annular portion 53 which is conically tapered and which is angled towards (faces towards) the second grinding ring 6 and the second annular portion 53 is configured for performing a lower chamfering operation. The second annular portion 53 is an edge portion and the first annular portion 52 is contiguous with the second annular portion 53 Each groove 51 is located primarily in the first annular portion 52 and has a front end which extends to the front end of the first annular portion 52 and a rear end which breaks into the front end of the second annular portion 53.

[0062] The second grinding ring 6 includes a first annular portion 62 which is conically tapered and which is angled towards (faces towards) the first grinding ring 5 and the first annular portion 62 is configured for performing an upper chamfering operation. The second grinding ring 6 also includes a second annular portion 63 which is perpendicular to the longitudinal axis of rotation 11 and which is configured for performing a spotfacing operation. The first annular portion 62 is an edge portion and the second annular portion 63 is contiguous with the first annular portion 62.

[0063] For each groove 61, part of the groove is located on the first annular portion 62 and is generally aligned with the longitudinal direction of the rotational axis 11 of the grinding tool 1 and has a front end which extends to the front end of the first annular portion 62 The coolant outlet 72 is contained in this part of the groove. The other part of the groove 61 is located on the second annular portion 63 and extends generally radially outwards to the outer circumferential edge of the second annular portion 63 with a (slight) spiral twist relative to the rotational axis 11.

[0064] Figs. 2 to 5 show how the grinding tool 1 of Fig. 1 may be used to perform grinding operations on a cylinder bore 81 of an engine block 8. The body of the engine block 8 is cast aluminium, and the aluminium forms a relatively-soft base material for a relatively-hard spray coating which lines the inside of the cylinder bore 81 from a top-end portion 82 to a bottom-end portion 83 of the cylinder bore 81. The spray coating 84 may be applied in a vacuum by feeding a wire to a spray tool which melts the wire to form a spray which is sprayed at high pressure onto the cylinder bore 81 as the spray tool follows a spiral track down from the top to the bottom of the cylinder bore 81. The wire may be in accordance with ISO 14919:2015-5.3-1,6-1 which is the ISO standard that covers different types of wire suitable for thermal spray coating. The hardness range of the spray coating may be between 400-550 HVO 1.

[0065] The cylindrical wall of the cylinder bore 81 has a longitudinal axis (a centre line) 85. At the start of the sequence of steps for performing grinding operations on the cylinder bore 81, the grinding tool 1 is positioned above the engine block 8 with its rotational axis 11 aligned with the centre line 85 of the cylinder bore 81. The tool 1 descends into Os fed into) the cylinder bore 81 along the centre line 85 until the first grinding ring 5 is level with the bottom-end portion 83. The tool 1 then indexes radially outwards to bring the first grinding ring 5 into contact with the spray coating 84 at the bottom of the cylinder bore 81. This positioning is shown in Fig. 2. As can be seen from Fig. 2, the second grinding ring 6 is clear of the engine block 8.

[0066] The tool 1 rotates about its rotational axis 11 (in response to being rotated by the rotary drive 4) whilst the rotational axis 11 is moved in a circular orbital path around the centre line 85 so that the tool 1 undergoes circular interpolation inside the cylinder bore 81. The first grinding ring 5 performs a grinding operation and grinds an undercut 86 and a lower chamfer 87 into the bottom-end portion 83. The undercut 86 and the lower chamfer 87 are more easily seen in the enlarged view of Fig. 3.

[0067] The undercut 86 is ground by the first annular portion 52 of the first grinding ring 5. The lower chamfer 87 is ground by the second annular portion 53 of the first grinding ring 5. Coolant is discharged from the coolant outlets 71 and carries away the abraded material of the spray coating 84 and the underlying metal of the body of the engine block 8.

[0068] The grinding operation performed by the first grinding ring 5, by grinding through the spray coating material and some of the underlying metal at the bottom end of the cylinder bore, forms a neat, finished bottom edge to the spray coating of the cylinder bore whilst also creating a clearance undercut at the bottom of the cylinder bore.

[0069] The tool 1 then indexes radially inwards to move the rotational axis 11 towards the centre line 85 of the cylinder bore 81. The tool 1 is then fed further into the cylinder bore 81 until the second grinding ring 6 is in contact with the top-end portion 82 of the cylinder bore 81, as shown in Fig. 4 and in the enlarged view of Fig. 5A.

[0070] As can be seen from Fig. 4 and from the enlarged view of Fig. 5B, the first grinding ring 5 has dropped down away from the bottom-end portion 83 and is no longer in contact with the engine block 8.

[0071] Again, the tool 1 rotates about its rotational axis 11 (in response to being rotated by the rotary drive 4) whilst the rotational axis 11 is moved in a circular orbital path around the centre line so that the tool 1 undergoes circular interpolation inside the cylinder bore 81. The second grinding ring 6 performs a grinding operation and grinds an upper chamfer 88 and a spotfaced surface 89 at the top-end portion 82. The upper chamfer 88 and the spotfaced surface 89 are shown in the enlarged view of Fig. 5A. The spotfaced surface 89 is produced on a deck face 810 around the top end of the cylinder bore 81.

[0072] The upper chamfer 88 is ground by the first annular portion 62 of the second grinding ring 6. The spotfaced surface 89 is ground by the second annular portion 63 of the second grinding ring 6. Coolant is discharged from the coolant outlets 72 and carries away the abraded material of the spray coating 84 and the underlying metal of the body of the engine block 8.

[0073] The grinding operation performed by the second grinding ring 6, by grinding through the spray coating material and some of the underlying metal at the top end of the cylinder bore, forms a neat, finished top edge to the spray coating of the cylinder bore whilst also creating a spotfaced surface around the top of the cylinder bore.

[0074] The tool I then indexes radially inwards to move the rotational axis ii back into alignment with the centre line 85 of the cylinder bore 81. The tool 1 is then withdrawn from the cylinder bore 81 and may be returned to the tool magazine (not shown) of the machining centre.

[0075] By using grinding operations, it is possible to machine a bi-metal structure (of a relatively-hard spray coating on a relatively-soft base material of the engine block) without the machining (the grinding) causing the coating to lift away from the base material.

[0076] The grinding tool has a longer tool life (approximately 50% longer) than the cutting tool that it supersedes, and the grinding tool also has a shorter (faster) cycle time (approximately 50% shorter).

[0077] Because the central shaft portion 26 has a shaft diameter along its entire length which is smaller than the inner diameter D2 of the first grinding rings and the inner diameter D4 of the second grinding ring 6, the part of the shaft which is between the first and second grinding rings is prevented from making unwanted contact with (clashing with) the cylindrical wall of the cylinder bore 81 during the grinding of the features 86, 87, 88 and 89. As may be seen in Fig. 2 and Fig. 4, the shaft 2 remains clear of the cylinder bore 81 during the grinding operations.

[0078] This beneficial effect may be maximised by making the length Li of the uniform-diameter main portion 261 of the central shaft portion 26 a large percentage of the separation distance between the first and second grinding rings 5, 6. For example, the length Li may be at least 85% (more preferably, at least 90%) of the separation distance between the first and second grinding rings.

[0079] Additionally, the length of the central shaft portion 26 is only slightly longer than the separation distance between the upper chamfer 88 and the lower chamfer 87. This minimises the axial movement required of the shaft 2 when moving from the first grinding operation configuration (Fig. 2) to the second grinding operation configuration (Fig. 4).

[0080] A second embodiment of grinding tool is shown in Figs. 6 and 7. The second embodiment is generally similar to the first embodiment.

[0081] In the exploded view which is Fig. 7, the first and second grinding rings 5, 6 are shown separated from the main body of the shaft 2, as if the grinding rings are separately manufactured before being mounted on the main body of the shaft 2. The depiction in Fig. 7 is merely for ease of visual depiction and to assist the reader in understanding the shape of the grinding rings. As explained in the context of the first embodiment, the first and second grinding rings 5, 6 are abrasive layers which are deposited in-situ by means of electro-plating.

[0082] The longitudinal cross-sectional view of Fig. 6 shows more detail of a coolant passage system 7 that ends at the coolant outlets 71_, 72 (not visible in Fig. 6, but see instead Figs. 1 to 5) where the coolant is discharged during the grinding operations performed by the first and second grinding rings 5, 6. The coolant passage system 7 includes a central axial passage 73 which extends from the rear end of the HSK holder 3 to the front end of the shaft 2 where the passage is closed by a screw-threaded plug 28.

[0083] As will be explained in more detail in relation to the third embodiment, a first set of radial passages extends from the central axial passage 73 to the coolant outlets 71. A second set of radial passages extends from the central axial passage 73 to the coolant outlets 72.

[0084] Thus, overall, in the coolant passage system, during a grinding operation, coolant may flow axially along the central axial passage 73 and then flow radially along the radial passages and then exit from the coolant outlets 71, 72. The coolant outlets 71 may have an outlet diameter which is less than an outlet diameter of the coolant outlets 72.

[0085] The supply of the coolant fluid to the grinding locations assists the grinding operations. The coolant fluid provides lubrication to the surface that is undergoing the grinding operation and removes (carries away) the ground-away (abraded) material. The coolant passage system is configured to supply the coolant fluid to the grinding locations at a relatively high pressure and at a relatively low volumetric flow rate. This is achieved by selecting the size and the different diameters of the coolant outlets 71, 72 Fig. 6A shows more detail of the second grinding ring 6 and how it includes, at the rear of the grinding ring, a third annular portion 64 in the shape of a lip Fig. 6B shows more detail of the first grinding ring 5 and how it includes, at the front of the grinding ring, a third annular portion 54 in the shape of a lip The lip portions 54, 64 are non-functional in the sense that, during the grinding operations, they do not contribute to the grinding away of material of the engine block.

[0086] A difference between the first and second embodiments is that, in the second embodiment of grinding tool, the proximal-end connecting portion 27A of the second embodiment is of increased diameter and has a diameter that matches the outer diameter D3 of the second grinding ring 6.

[0087] A third embodiment of grinding tool is shown in Figs. 8 to 18. The third embodiment is generally similar to the first embodiment In the third embodiment, the HSK holder 3A has smaller diametrical dimensions than in the first embodiment.

[0088] In the third embodiment, Figs. 12 and 13 show the entrances to the first set of radial passages 74 of the coolant passage system 7 and the entrances to the second set of radial passages 75 of the coolant passage system 7 Compared with the first embodiment of grinding tool, the third embodiment has modified grooves in the first grinding ring 5. In the third embodiment, the grooves 51A are helically orientated relative to the longitudinal axis of rotation 11 of the grinding tool, instead of being parallel to the rotational axis I. The helical configuration may improve the flow of the coolant during the grinding operation performed by the first grinding ring 5 of the third embodiment.

[0089] The improved flow may assist with removing the aluminium chips resulting from the grinding of the engine block so that the chips are removed before they can "weld" themselves to the abrasive surface of the first grinding ring 5 and thereby degrade the grinding performance of the first grinding ring 5. Also, a helical groove has a greater surface area for dispensing coolant during grinding, compared to a longitudinally-aligned groove There has been provided a grinding tool which has a shaft with first and second grinding rings which are spaced apart along a longitudinal axis of rotation of the shaft. The shaft may be fed into a cylinder bore of an engine block so as to bring the first grinding ring into contact with a bottom end portion of the cylinder bore whilst maintaining a separation between the second grinding ring and the cylinder bore. The shaft may be rotated and the first grinding ring grinds a first annular feature at the bottom end portion of the cylinder bore. The shaft may then be fed further into the cylinder bore so as to bring the second grinding ring into contact with a top end portion of the cylinder bore whilst separating the first grinding ring from being in contact with the cylinder bore. The shaft may be rotated so that the second grinding ring grinds a second annular feature at the top end portion of the cylinder bore.

Claims

1. CLAIMS1 A grinding tool for grinding first and second features which are spaced apart along a longitudinal axis of a cylindrical wall, the grinding tool comprising: a shaft having a longitudinal axis of rotation and first and second grinding locations which are spaced apart along the longitudinal axis of rotation; wherein: the first grinding location is annular and supports a first grinding ring.; and the second grinding location is annular and supports a second grinding ring.

2. A grinding tool according to claim 1, wherein the first and second grinding rings each comprise an abrasive coating, preferably a layer of diamond grit

3. A grinding tool according to claim 1 or 2, wherein the shaft includes a coolant passage system which has coolant outlets in the first and second grinding rings.

4 A grinding tool according to any preceding claim, wherein: the shaft has a proximal end and a distal end; the first grinding location is at the distal end; and the second grinding location is at the proximal end.

A grinding tool according to any preceding claim, wherein: the first grinding ring has an outer diameter and an inner diameter; the second grinding ring has an outer diameter and an inner diameter; and the outer diameter of the second grinding ring is greater than the outer diameter of the first grinding ring.

6. A grinding tool according to claim 5, wherein the inner diameter of the second grinding ring is greater than the outer diameter of the first grinding ring.

7. A grinding tool according to any preceding claim, wherein the first and second grinding locations are separated by a central shaft portion which has a shaft diameter which is smaller than the inner diameter of the first grinding ring and the inner diameter of the second grinding ring

8. A grinding tool according to any preceding claim, wherein the first grinding ring is configured for performing a lower chamfering operation and/or an undercut operation.

9. A grinding tool according to claim 8, wherein the first grinding ring includes a first annular portion which is cylindrical and which is configured for performing the undercut operation.

10 A grinding tool according to claim 8 or 9, wherein the first grinding ring includes a second annular portion which is conically tapered and which is angled towards the second grinding ring and the second annular portion of the first grinding ring is configured for performing the lower chamfering operation.

11 A grinding tool according to claim 9 and claim 10, wherein the second annular portion of the first grinding ring is an edge portion and the first annular portion of the first grinding ring is contiguous with the second annular portion of the first grinding ring

12. A grinding tool according to any preceding claim, wherein the second grinding ring is configured for performing an upper chamfering operation and/or a spotfacing operation.

13 A grinding tool according to claim 12, wherein the second grinding ring includes a first annular portion which is conically tapered and which is angled towards the first grinding ring and the first annular portion of the second grinding ring is configured for performing the upper chamfering operation.

14. A grinding tool according to claim 12 or 13, wherein the second grinding ring includes a second annular portion which is perpendicular to the longitudinal axis of rotation of the shaft and which is configured for performing the spotfacing operation.

15. A grinding tool according to claim 13 and claim 14, wherein the first annular portion of the second grinding ring is an edge portion and the second annular portion of the second grinding ring is contiguous with the first annular portion of the second grinding ring.

16. A grinding tool according to any preceding claim, wherein an HSK holder is connected to a proximal-end connecting portion of the shaft

17. A multi-axis machining centre comprising a tool magazine containing a grinding tool according to any one of claims Ito 16.

18. A method of performing grinding operations on a cylinder bore, the method comprising: providing a grinding tool which comprises a shaft having a longitudinal axis of rotation and first and second grinding locations which are spaced apart along the longitudinal axis of rotation, with the first grinding location being annular and supporting a first grinding ring, and with the second grinding location being annular and supporting a second grinding ring; feeding the shaft of the grinding tool into the cylinder bore and bringing the first grinding ring into contact with a bottom end portion of the cylinder bore whilst maintaining a separation between the second grinding ring and the cylinder bore, rotating the shaft of the grinding tool so that the first grinding ring performs an undercut operation and grinds an annular undercut at the bottom end portion of the cylinder bore; bringing the second grinding ring into contact with a top end portion of the cylinder bore whilst separating the first grinding ring from being in contact with the cylinder bore; and rotating the shaft of the grinding tool so that the second grinding ring performs an upper chamfering operation and grinds an annular upper chamfer at the top end portion of the cylinder bore.

19. A method according to claim 18, wherein: when grinding the annular undercut, the shaft of the grinding tool rotates whilst the longitudinal axis of rotation of the shaft undergoes circular interpolation inside the cylinder bore; and when grinding the annular upper chamfer, the shaft of the grinding tool rotates whilst the longitudinal axis of rotation of the shaft undergoes circular interpolation inside the cylinder bore.

20. A method according to claim 18 or 19, wherein the separation between the first and second grinding rings is greater than the separation between the annular undercut and the annular upper chamfer, preferably 2% to 10% greater, more preferably 1% to 5% greater.

21. A method according to any one of claims 18 to 20, wherein: after the grinding of the annular undercut, the grinding tool indexes radially inwards away from the annular undercut towards a longitudinal centre line of the cylinder bore; the shaft of the grinding tool is fed further into the cylinder bore so as to bring the second grinding ring into contact with a deck face which is at the top end portion of the cylinder bore and which is perpendicular to the longitudinal centre line of the cylinder bore; and the grinding of the annular upper chamfer by the second grinding ring is performed so that the annular upper chamfer is created between the deck face and the cylinder bore.

22. A method according to claim 21, wherein: during the grinding of the annular upper chamfer, the second grinding ring also performs a spotfacing operation on the deck face around the cylinder bore.

23. A method according to any one of claims 18 to 22, wherein: during the grinding of the annular undercut at the bottom end portion of the cylinder bore, the first grinding ring also performs a lower chamfering operation and grinds an annular lower chamfer at the bottom end portion of the cylinder bore at a position above the annular undercut.

24. A method according to any one of claims 18 to 23, wherein: the cylinder bore has a spray coating at least at the positions where the undercut operation and the upper chamfering operation are performed.

25. A method according to any one of claims 18 to 24, wherein the cylinder bore is a spray-coated cylinder bore in an engine block which is a casting of metal which is softer than the spray coating of the cylinder bore, and preferably the metal is aluminium.