WO2021161332A1

WO2021161332A1 - System and method for developing uni-layer brazed grinding wheels by placing grit in a pre-defined array

Info

Publication number: WO2021161332A1
Application number: PCT/IN2021/050115
Authority: WO
Inventors: Amitava Ghosh; Prithviraj Mukhopadhyay; D Raghava SIMHAN
Original assignee: INDIAN INSTITUTE OF TECHNOLOGY MADRAS (IIT Madras)
Priority date: 2020-02-11
Filing date: 2021-02-04
Publication date: 2021-08-19

Abstract

A system and method for developing uni-layered brazed grinding wheels by placing cBN/Diamond abrasive grits in a pre-defined array using pick-drop-place (PDP) technique, as discussed in greater detail herein. The system and method provides an approach for manufacturing uni-layer brazed cBN/Diamond grinding wheel in a convenient and precise way of transferring individual cBN/Diamond grits from source to substrate surface with good control on grit protrusion height from the wheel base surface, prevent clustering of grits, and offers a high flexibility in adopting any predefined pattern for arranging diamond grits without using any template.

Description

DESCRIPTION

SYSTEM AND METHOD FOR DEVELOPING UNI-LAYER BRAZED GRINDING WHEELS BY PLACING GRIT IN A PRE-DEFINED

ARRAY

TECHNICAL FIELD

[0001 ] The present invention generally relates to abrasive tools and methods for developing the same. The present invention is additionally related to methods for placing micro-sized cBN/Diamond abrasive grits in a predefined geometric array on active curved surface of the grinding wheel. The present invention also relates to pick-drop-place (PDP) attachment in conjunction with two high resolution linear tables for producing patterned cBN/Diamond grinding wheels. The present invention in particular relates to a system and method for developing uni-layered brazed grinding wheels by placing cBN/Diamond abrasive grits in a pre-defined array using pick-drop-place (PDP) technique.

BACKGROUND OF THE INVENTION [0002] Abrasive tools are popularly used in a wide range of industrial applications, such as for example, but not limited to, cutting, drilling, sawing etc. In particular, cBN/Diamond based abrasive tools are used in several machining applications due to the superior hardness of these abrasives. The tools are mostly used in machining other hard materials. Due to their high hardness, they are also known as superabrasives and such abrasive tools have high techno-commercial relevance. The use of superabrasive tools become indispensable in machining applications where other tools lack in hardness and durability. Moreover, the ability of the superabrasives to retain its sharpness under aggressive machining conditions have drawn the interest of tool manufacturing industries for using them to develop high-end cBN/Diamond grinding tools. Manufacturing of new generation cBN/Diamond grinding wheels require placing of cBN/Diamond abrasives uniformly over the periphery of the wheel hub in a uniform manner. [0003] In general, grinding refers to removal of material through micro-milling action exhibited by sharp abrasive grits. These abrasive grits are held together with a suitable binding agent in the form of a disc, known as grinding wheels. Conventional grinding wheels primarily use alumina and silicon carbide as abrasive grit material. However, the use of these wheels becomes difficult when it comes to machining of exotic non-ferrous super alloys. Interaction of either AI₂O₃ or SiC abrasives with non-ferrous hard material make grits blunt, reducing life of the tool. Hence, the use of superabrasive grinding wheels for machining non-ferrous materials becomes indispensable. Industrial grade engineered synthetic cBN/Diamond grits, are therefore, primarily used for developing wheels meant for grinding ferrous/non-ferrous materials.

[0004] Based on bond type, different variants of superabrasive wheels are available and range from resin to metal bonded grinding wheels. The ability of metal bonded system to retain abrasives for long machining duration makes them suitable for manufacturing wheels that are used under aggressive machining environment.

[0005] Manufacturing of metal bond type grinding wheels involve joining of cBN/Diamond abrasives to steel using either electroplating or brazing technology. However, lower protrusion height and weak bond developed at interface limits the scope of electroplating technology for manufacturing these wheels. On the other hand, formation of chemical bonds makes brazing process superior to electroplating technology.

[0006] Manufacturing of brazed diamond grinding wheel involves the application of filler on curved surface of the grinding tool. Filler alloys like Cu- Sn-Ti and Ag-Cu-Ti alloys are well known for chemically joining cBN/Diamond grits to metal substrate. The operation is subsequently followed by placement of cBN/Diamond grits in either random or systematic mode. The entire assembly is then heated to a temperature above the liquidus point of the filler material.

[0007] Manufacturing of superior quality brazed cBN/Diamond grinding tool requires precise positioning of abrasive grits in regular pattern. Brazed cBN/Diamond grinding wheels consisting abrasive grits arranged in random manner causes an uneven distribution of cutting forces during grinding, leading to an ineffective machining operation. A very few prior arts have presented the method of manufacturing and developing uni-layer grinding tools with an attempt to arrange cBN/Diamond grits in a regular pattern. [0008] US 6,679,243 B2 discloses a method of distributing diamond particles in a predefined manner on a matrix support material. The method involves the use of a template having a plurality of apertures corresponding to predetermined pattern. The diamond particles are sprinkled over the top surface of the template, and the apertures get filled with the particles. The particles are then pressed into the matrix support material and subsequently the template is removed. In another prior art, EP 1 208 945 Bl, a method of producing abrasive tools is disclosed. The disclosure presents a method wherein a suitable adhesive is applied on the surface of the substrate over which diamond grits get brazed. The size of the adhesive droplet was adjusted through modification of the diameter of the discharge nozzle. The adhesive was micro-dozed at certain desired locations and the grits were sprinkled over it. The sprinkled grits that come in contact with the adhesive droplets stick and remain adhered to the substrate. The non-adhered grits are thereafter removed. One major drawback of such technique is that if the abrasive particles are smaller in size, clustering of grits might occur at different locations. Another prior invention, US 2012/0192499 Al, discusses about the method of placing abrasive grits using a transfer plate. However, the process involves the use of an adhesive that might weaken the joint strength after brazing the grits.

[0009] Based on the foregoing study, a need therefore exists for an improved method of manufacturing uni-layer brazed cBN/Diamond grinding wheel which offers a convenient and precise way of transferring individual cBN/Diamond grits from source to substrate surface with good control on grit protrusion height from the wheel base surface, preventing clustering of grits and offering high flexibility in adopting any pattern of arranging diamond grits without the use of any predefined template. Also, a need exists for an improved system and method for developing uni-layered brazed grinding wheels by placing cBN/Diamond abrasive grits in a pre-defined array. Therefore, the inventors have come up with a pick-drop-place (PDP) technique, discussed below in greater detail, as a solution to the aforementioned concerns.

SUMMARY OF THE INVENTION

[00010] The following summary is provided to facilitate an understanding of some of the innovative features unique to the disclosed embodiment and is not intended to be a full description. A full appreciation of the various aspects of the embodiments disclosed herein can be gained by taking the entire specification, claims, drawings, and abstract as a whole.

[00011 ] One aspect of the disclosed embodiment is to provide for an improved superabrasive tool for a wide range of industrial applications.

[00012] It is another aspect of the disclosed embodiment to provide for an improved method for manufacturing uni-layer brazed cBN/Diamond grinding wheel which offers a convenient and precise way of transferring individual cBN/Diamond grits from source to substrate surface with good control on grit protrusion height from the wheel base surface, prevent clustering of grits, and offers a high flexibility in adopting any pattern for arranging diamond grits without the use of any predefined template.

[00013] It is further aspect of the disclosed embodiment to provide for an improved system and method for developing uni-layered brazed grinding wheels by placing cBN/Diamond abrasive grits in a pre-defined array using pick-drop- place (PDP) technique, as discussed in greater detail herein.

[00014] The aforementioned aspects and other objectives and advantages can now be achieved as described herein. A system and method for developing uni layered brazed grinding wheels by placing cBN/Diamond abrasive grits in a pre defined array using pick-drop-place (PDP) technique, is disclosed herein. Two incremental type-high resolution linear stage drives (1,2) that are used for precisely planting plurality of cBN/Diamond abrasives on a curved periphery (3) of the grinding wheel substrate (4) wherein the grinding wheel substrate (4) was machined out of a steel blank. Note that the proposed invention uses a single crystal synthetic diamond grits of mesh size 60/70 for developing the single layer diamond grinding wheel. The surface of the steel hub was covered with a thin layer of eutectic silver-copper alloy containing 2-5 wt% of TiH₂ as filler material before placing the diamond grits over the periphery of the wheel. The pick-drop- place setup consists of a digital camera (5) and a piezoelectric sensor (6) for precisely monitoring the placement of grits over the wheel periphery. The sensor (6) was further connected to a charge amplifier (7) possessing high sensitivity and resolution wherein the output of the charge amplifier (7) is monitored using a digital oscilloscope (8). The grits were placed on the periphery of the grinding wheel with a load value varying in between 0.8 N to 1 N using a load measuring sensor (6) in order to ensure that the grits are protruded out of the bond level at a uniform height.

[00015] A special attachment (9) can be used wherein multiple needles were fixed for planting more than one synthetic diamond grits in single attempt/instant. The spacing between the grits can be further reduced for obtaining a denser pattern wheel having grits arranged in a systematic array. A regular distribution of synthetic diamond grits will ensure that the load is uniformly distributed amongst all synthetic diamond grits during grinding operation. After the grits were placed uniformly over the top surface of the wheel substrate, the entire assembly was kept inside a furnace maintained under a vacuum level of 10⁷ Torr of vacuum level, and the entire assembly was heated to a temperature of 820 °C to 850 °C, depending on the weight percentage of TiH₂ added to the filler material.

[00016] The proposed invention uses PDP setup to ensure that all diamond abrasive grits are uniformly protruded out of the bond level. Additionally, the uniform spacing between synthetic diamond abrasive grits will ensure that the wheel can be used for long duration grinding operation with minimum or negligible scope of wheel loading.

BRIEF DESCRIPTION OF DRAWINGS [00017] The drawings shown here are for illustration purpose and the actual system will not be limited by the size, shape, and arrangement of components or number of components represented in the drawings.

[00018] FIG. 1 illustrates a graphical representation of a system 100 for developing uni-layered brazed grinding wheels by placing cBN/Diamond abrasive grits in a pre-defined array using pick-drop-place (PDP) technique, in accordance with the disclosed embodiments;

[00019] FIG. 2 illustrates a schematic representation of gripper system 200 consisting the suction/releaser head for placing diamond grits on the periphery of the grinding wheel, in accordance with the disclosed embodiments; and [00020] FIG. 3a and FIG. 3b illustrates an image 300 of single layer diamond grinding wheel in its as brazed condition and SEM image FIG. 3b showcasing the uniform distribution of diamond grits over the curved surface of the wheel hub respectively, in accordance with disclosed embodiments.

DETAILED DESCRIPTION

[00021] The particular values and configurations discussed in these non-limiting examples can be varied and are cited merely to illustrate at least one embodiment and are not intended to limit the scope thereof.

[00022] FIG. 1 illustrates a graphical representation of a system 100 for developing uni-layered brazed grinding wheels by placing cBN/Diamond abrasive grits in a pre-defined array using pick-drop-place (PDP) technique, in accordance with the disclosed embodiments. Two incremental type-high resolution linear stage drives (1,2) are used for precisely planting plurality of cBN/Diamond abrasives on curved periphery (3) of the grinding wheel substrate (4) that was machined out of a steel blank. It is to be noted that the proposed invention uses single-crystal synthetic diamond grits of mesh size 60/70 for developing the single layer diamond grinding wheel. The surface of the steel hub was covered with a thin layer of eutectic silver-copper alloy containing 2-5 wt% of TiH₂ as filler material before placing the diamond grits over the periphery of the wheel. The pick-drop-place setup consists of a digital camera (5) and a piezoelectric sensor (6) for precisely monitoring the placement of grits over the wheel periphery. The sensor (6) was further connected to a charge amplifier (7) possessing high sensitivity and resolution. The output of the charge amplifier (7) was monitored using a digital oscilloscope (8). The grits were placed on the periphery of the grinding wheel with a load value varying in between 0.8 N to 1 N using a load measuring sensor (6) in order to ensure that the grits are protruded out of the bond level at a uniform height.

[00023] A special attachment (9) can also be used wherein multiple needles were fixed for planting more than one diamond grits in single attempt/instant. The spacing between the grits can be further reduced for obtaining a dense patterned wheel having grits arranged in a systematic array. A regular distribution of synthetic diamond grits will ensure uniform distribution of cutting load amongst all diamond grits during grinding operation. After all grits were placed uniformly over top surface of the wheel substrate, the entire assembly was kept inside a furnace maintained under a vacuum level of 10⁷ Torr and heated to a temperature of 820 °C to 850 °C.

[00024] The proposed invention uses PDP setup to ensure that all diamond abrasive grits are uniformly protruded out of the bond level. Additionally, the uniform spacing between synthetic diamond abrasive grits will ensure that the wheel can be used for long duration grinding operation with minimum or negligible scope of wheel loading.

[00025] FIG. 2 illustrates a schematic representation of gripper system 200 consisting the suction/releaser head for placing diamond grits on the periphery of the grinding wheel, in accordance with the disclosed embodiments. The gripper system 200 comprises a suction/releaser head for placing the diamond grits precisely over the periphery of the grinding wheel. The suction/releaser head is connected to a rotary type vacuum pump and pneumatic supply system. With the help of a three-way control valve, the vacuum pump and pneumatic supply system is operated in an alternate manner.

[00026] As the rotary pump creates vacuum, the suction head grips the grit that needs to be placed on the periphery of the grinding wheel. The suction gripper in its next step is made to release the grit by activating the pneumatic supply and switching off the rotary vacuum pump.

[00027] In the system 100, vacuum-operated PDP setup is used for effective planting of the grits at desired location in co-ordinate-controlled manner over the curved surface of the grinding tool via use of both single and multiple needles for placing the grits. Use of multiple needles provides an additional benefit of placing more than one numbers of cBN/Diamond grits in single instant, without clustering. It is necessary to ensure that protrusion of cBN/Diamond grits from the surface of the steel substrate is uniform and 60% to 70% above the bond level. [00028] FIG. 3a and FIG. 3b illustrates an image 300 of single layer diamond grinding wheel in its as-brazed condition and SEM image 300 showcasing the uniform distribution of diamond grits over the curved surface of the wheel hub respectively, in accordance with the disclosed embodiments. One aspect of the disclosed embodiment is to provide a novel technique or method for manufacturing uni-layer cBN/Diamond grinding wheel having grits arranged in any desired/customized and systematic pattern. Another aspect of the disclosed embodiment is to provide a novel method for developing uniform patterned uni layer brazed grinding wheel which offers a convenient way to precisely transfer individual grits from source to substrate surface. Another benefit of using this method is that there will be a substantial reduction in the filler alloy consumption with good control on grit protrusion height from the bond level and flexibility in adopting any pattern.

[00029] The further aspect of the disclosed embodiment discusses the use of PDP attachment for placing cBN/Diamond grits in any predefined and desired pattern. Additionally, the setup will also aid in minimizing the filler alloy usage and ensure a uniform protrusion height of the grit from the bond level. The entire manufacturing process involves the use of an attachment for gripping of cBN/Diamond particle, an incremental type linear stage CNC drive for relocating and planting the grits precisely at the desired location over the curved surface of the diamond grinding tool. The present invention also proposes a novel methodology for implanting the grits at predefined position on specified substrate in a co-ordinate-controlled manner.

[00030] It will be appreciated that variations of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also that various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.

Claims

CLAIMS I/We CLAIM:

1. A system 100 for developing uni-layered brazed grinding wheels by placing cBN/Diamond abrasive grits in a pre-defined array using pick-drop-place (PDP) technique, comprising: at least two high resolution linear stage drives (1,2) that are used for precisely planting plurality of cBN/Diamond abrasives on curved periphery (3) of the grinding wheel substrate (4) that was machined out of a steel blank; a gripper system unit having a suction/releaser head for placing the diamond grits precisely over the periphery of the grinding wheel wherein the suction/releaser head is connected to a rotary type vacuum pump and pneumatic supply system. The vacuum pump and pneumatic supply system is operated in an alternate manner using a three-way control valve.

2. The system as claimed in claim 1 wherein the surface of the steel hub was covered with a thin layer of eutectic silver-copper alloy containing 2-5 wt% of T1H2 as filler material before placing diamond grits over the periphery of the wheel.

3. The system as claimed in claim 1, the pick-drop-place (PDP) comprises a digital camera (5) for precisely monitoring the placement of grits over the wheel periphery and a piezoelectric sensor (6) wherein the sensor (6) is connected to a charge amplifier (7) possessing high sensitivity and resolution and the output of the charge amplifier (7) is monitored using a digital oscilloscope (8).

4. The system as claimed in claim 1 wherein the grits are placed on the periphery of the grinding wheel with a load value varying in between 0.8 N to 1 N using a load measuring sensor (6) in order to ensure that the grits are protruded out of the bond level at a uniform height.

5. The system as claimed in claim 1 further comprising a special attachment (9) with multiple needles for planting more than one synthetic diamond grits in a single attempt/instant wherein the spacing between the grits can be further reduced for obtaining a denser patterned wheel having grits arranged in a systematic array.

6. The system as claimed in claim 6 wherein the entire assembly was kept inside a furnace, maintained under a vacuum level of 10⁷ Torr of vacuum level, and heated to a temperature of 820 °C to 850 °C, depending on the weight percentage of TiH₂ added to the filler material,

7. In the system as claimed in claim 1, the vacuum-operated PDP is used for effective planting of the grits at desired location with micron level precision over the curved surface of the grinding tool via use of both single and multiple-needles for placing the grits.

8. The system as claimed in claim 8; the use of multiple needles provides an additional benefit of placing more than one numbers of cBN/Diamond grits in single instant, without clustering.

9. The system as claimed in claim 1 wherein the protrusion of cBN/Diamond grits from the surface of the steel substrate is uniform and is 60% to 70% above the bond level.