GB2191499A - Process for production of diamond-impregnated tools - Google Patents

Description

1 GB2191499A 1

SPECIFICATION

Process for production of abrasive diamond-! mpregnated tools The present invention relates generally to the field of manufacturing engineering and more 5 specifically, to the process for production of abrasive diamondimpregnated tools.

Tools produced according to the herein proposed process are intended to be used for machining of diamonds, glass, ceramics and other hard materials and they will find application in jewellery, optomechanical, and construction industries Known in the present state of the art is a process for production of diamond-impregnated 10 cutting disks involving the application of an oil-powder-diamond mixture onto the surface of a metallic disk, followed by charging the disk surface with the mixture using a hard-alloy element, such as a cast iron lap. As the impregnation process takes place, the hard-alloy element is loaded statically and rotated at a frequency from 2 to 40 s-1 (cf., e.g., a text-book -Processing of Raw Diamonds into Faceted Diamonds- by V.1. Epifanov et aL, 1982, "Vysshaya Shkola" 15 Publishers, Moscow, page 233, in Russian).

However, the aforementioned process is characterized by low production efficiency, since the charging operation takes from 20 to 30 minutes. Besides, this process fails to provide a high concentration of the diamond grains in the metallic disk body, or ensure their proper retention therein in the course of machining. This leads to low performance characteristics of the cutting 20 disks and too high a consumption of expensive rough diamonds.

The above-described process is impracticable for the production of thin abrasive disks whose thickness is comparable to the size of the diamond grains, on account of the deformation of the disks.

Another process for production of abrasive diamond-impregnated tools involves the application 25 of a layer of abrasive powder containing the diamond grains to a work- piece, followed by a pressing action produced by a hard-alloy punch all over the workpiece surface. The punch exerts a static load at a pressure within 400 to 500 MPa.

However, this process also fails to attain good adhesion binding between the diamond grains and the workpiece body because of inadequate impregnation. 30 Inasmuch as the embedding of the diamond grains occurs in the same direction as the application of the static load, it is unfeasible to impregnate the workpiece with the diamond grains in a concentration of over 40 vol.%. The above-said factors affect much adversely the performance characteristics of the tooling.

Besides, this process involves the use of power-consuming press-working equipment. 35 The present invention is aimed at the provision of a process for production of abrasive diamond-impregnated tools which would enable a high-efficiency production of abrasive tools featuring good performance characteristics.

The above-said object is accomplished due to the fact that in a process for production of abrasive diamond-impregnated tools consisting of the application of a layer of abrasive powder 40 containing the diamond grains to a workpiece, followed by an impact action produced by a hard alloy element on the applied layer with a view to impregnating it with the abrasive powder, according to the invention, the abrasive powder is impregnated by an impact impulse ranging from 200 to 800 kN.s against the hard-alloy element which spins at a frequency from 900 to 2500s---1. 45 Such a combined action on the workpiece provides most favourable conditions for the dia mond grains to be embedded in the workpiece in a most optimum way and be reliably secured therein. This makes it possible to produce thin tools, including cutoff tools as thin as 0.05 mm, the attainable diamond grain concentration being within 60 to 65 vol.%. Besides, tool life is extended by 40 to 45 per cent, higher stock removal rates are possible, e. g., a growth of 50 to 50 per cent is observed in cutting a diamond, and the efficiency to tool production is increased three- to fourfold.

It is expedient that the application of a layer of abrasive powder to a disk-shape workpiece be effected simultaneously with forming it into a spherical segment having a radius that is three to ten times its initial radius. 55 A combination of the shaping of the workpiece with the application of abrasive powder allows an optimum distribution of the diamond grains over the workpiece volume, which ensures a longer tool life.

It is also expedient that the use be made of an abrasive powder having the following composition (vol.%): 60 diamond grains 20 to 60 low-melting-point-metal up to 100, or a layer of abrasive powder containing the diamond grains be applied to a workpiece clad with 65 2 GB2191499A 2 a low-melting-point metal.

The incorporation of a low-melting-point metal in the mixture or use of a workpiece clad preliminarily with a low-melting-point metal, enables the contents of diamond grains ranging in size within 200 to 250 urn to be raised to a maximally possible concentration.

The herein proposed process occurs as follows. 5 The workpiece is coated with a layer of abrasive powder containing the diamond grains. A hard-alloy element, e.g., a tungsten carbide plate, is placed immediately above the abrasive powder layer and is rotated at a frequency from 900 to 2500 s-1. The opposite side of the workpiece is subjected to an impact impulse ranging from 200 to 800 kN-s applied all over the workpiece surface, whereby the latter is displaced at a very high speed towards the hard-alloy 10 element until a collision occurs.

As the workpiece is forced, by the action of the impact of the aforesaid magnitude, to thrust against the spinning hard-alloy element, the diamond grains run through intricate pathways to be charged into the workpiece body for a depth sufficient for their secure embedding. This ensures a higher diamond grain content in the tool, prevents grain spalling in the course of operation, 15 whereby tool performance is improved.

Besides, the short duration of the impact in conjunction with the reliable embedding of the diamond grains enhance the process efficiency.

The abrasive powder can be applied to the workpiece surface by free forming, by spraying or by screening, It is expedient that the abrasive powder be applied to a disk-shaped workpiece 20 simultaneously with forming it into a spherical segment having a radius that is three to ten times its initial radius. This enables the diamond grains to be firmly retained in the workpiece due to plastic flow of metal involved in the impregnation process.

If the value of the segment radius exceeds the upper of the limits mentioned hereinbefore, no substantial improvement of the tool performance characteristics is observed, and if it is less than 25 the lower limit, it becomes unfeasible to form the workpiece into a required shape with atten dant buckling.

The process permits the use of abrasive powders with grain sizes varying in a wide range, depending upon the designated purpose of the tool.

It is herein proposed that the use be made of an abrasive powder having the following 30 composition (vol.%):

diamond grains 20 to 60 low-melting-point-metal up to 100 35 As the structure of the tool material is being formed, the low-melting- point metal serves as a binding agent providing a proper adhesion for the diamond grains ranging in size within 200 to 250 urn.

A similar effect can be achieved through preliminary cladding of the workpiece surface with a low-melting-point metal. In this case, care should be taken that the cladding thickness be less 40 than half the minimum diamond grain size, since, if otherwise, the diamond grains fail to be adequately impregnated into the workpiece.

In what follows the herein proposed process will now be disclosed in detailed examples of embodiments thereof.

45 Example 1

Manufacturing of abrasive cutoff disks for cutting the diamond crystals. Steel disks, 80 mm in diameter and 0.08 mm thick, are used as blanks.

An abrasive powder with a grain size of 20/16 urn is uniformly spread over the workpiece surface using a glue. The workpiece is placed onto the face of an elastic polyurethane element 50 installed on a copper plate. Both the ealstic element and the plate are free to be displaced axially. A flat inductor of a magnetic pulse unit is fitted immediately adjacent to the copper plate.

A plate made of a WC-CO hard alloy is arranged above the workpiece surface and is spinned at a frequency from 900 to 2500 s-1. A capacitive charge integrator of the magnetic pulse unit discharges into the flat inductor, causing the elastic element and the copper plate to produce an 55 impact action on the workpiece. The impact magnitude is within 200 to 800 kN.s.

As a result of the collision of the workpiece and the hard-alloy plate, the diamond grains are impregnated into the workpiece and adhere thereto.

Table 1 given herebelow lists the performance characteristics of the manufactured abrasive cutoff disks in relation to the process parameters. 60 3 GB2191499A 3 Table 1

SDecifications Hard.-alloy plate ro- Impact magnitude, 5 tation frequency, kN-s, at a hard S-1.at an impact im- -alloy plate rot- pulse of 200 kN.s ation fre uency of 900 s- - 10 1500 2000 2500 200 400 600 800 Stock removal rate, mm2/h 34.1 35.2 35.4 37.5 35.2 38.3 38.9 15 Total cutti.nr,,,,, area, mm 2 43.2 45.6 45.9 41.9 42.2 4;.4 42.8 20 Relative rough diamond losses.

per cent 2.5 2.6 2.5 2.5 2.4 2.5 2.6 25 Example 2

Manufacturing of abrasive cutoff disks for cutting the diamond crystals. Bronze disks, 50 mm 30 in diameter and 0.05 mm thick, are used as blanks.

The abrasive powder is uniformly spread over the workpiece surface by the free forming method.

A polyurethane element carrying a workpiece is placed into a container incorporating a mov able copper plate. A hard-alloy plate whose surface is a concave shape of a radius from 150 to 35 500 mm. The copper plate is then subjected to a pulse magnetic field of a strength of

6.108A/m. As a result, the workpiece is shaped into a spherical segment, with attendant partial impregnation thereof with the diamond grains.

Further on, the spherical-shape plate is replaced with a flat hard-alloy plate that is rotated at a frequency of 1000 s 1, after which the copper plate is once agains subjected to the action of a 40 pulse magnetic field. The magnitude of an impact impulse imparted to the workpiece is 450 kN.s.

Table 2 contains the performance characteristics of the manufactured abrasive cutoff disks in relation to the radius of the workpiece spherical segment.

4 GB2191499A 4 Table 2

Specifications Radius of workDiece spherical seg- 5 ment, mm 200 300 350 400 500 10 Stock removal rate, mm2/h 33.2 34.8 35.3 36.2 36.7 36.9 15 Total cutting area, mr.q 2 40.5 42.3 43.1 43.3 43.5 43.8 Relative rough 20 diamond losses.

per cent 2.6 2.5 2.5 2.4 2.4 2.4 25 Example 3 30

Manufacturing of abrasive cutoff disks for cutting the textolite sheets up to 40 mm thick.

Steel disks, 200 mm in diameter and 1.0 mm thick, are used as blanks.

A mixture consisting of diamond grains ranging in size from 315 to 250 urn and tin powder with a size of particles from 300 to 320 urn, is uniformly sprayed over the workpiece surface. A hard-alloy plate (WC-CO) is placed immediately adjacent to the layer of abrasive powder and is 35 rotated at a frequency of 1500 s-1. The opposite side of the workpiece is then subjected to an impact impulse of 650 kN-s produced by a hydraulic hammer installation.

As a result of the collision of the workpiece and the hard-alloy plate, the diamond grains are impregnated into the workpiece. Retention of the diamond grains in the workpiece is attained due to their embedding in the molten tin which serves as a solder. 40 Table 3 gives the performance characteristics of the manufactured abrasive disks in retation to the diamond grains-to-tin ratio, at a cutting speed of 60 m/s and feed rate of 0.6 mm per revolution.

45 Table 3

Specificat-ions The diamond grain content of mixture 50 (the base is tin), vol.

30 40 50 6o 55 Near resistance,.

mglm 2 0.41 0.55 Mo o.69 0.72 Total cutting 60 area, m 2 8020 8350 9126 9200 9280 65 GB2191499A 5 Example 4

Manufacturing of abrasive cutoff disks for cutting the textolite sheets up to 50 mm thick, Steel disks, 200 mm in diameter and 1.0 mm thick, are used as blanks. Initially, the blanks are clad with a layer of tin 18 urn thick. A mixture consisting of diamond powders with a grain 5 size of 400/250, a grain size of 63140, and tin powder (the mixture components are in the ratio 30:30:40, respectively) is applied to the workpiece surface. Further process operations are similar to those described hereinabove in Example 3.

Wear resistance of the manufactured disks is 0.83 M9/M2, and the cutting area is 9290 M2.

10 Example 5

Manufacturing of abrasive disks for cutting the diamond crystals. A diamond powder with a grain size of 50/40 urn is applied to a steel workpiece. A hardalloy plate (WC-CO) is placed immediately adjacent to the workpiece coated with the abrasive powder and is rotated at a frequency of 2200 s-1. The opposite side of the workpiece is subjected to an impact impulse of 15 750 kN.s produced by a pneumatic impact unit.

After a collision with the rotating plate, the subsurface layer of the workpiece becomes impregnated with diamond grains in a concentration up to 60 vol.%.

The manufacured tools provide a rate of stock removal in the cutting process within 1.9 to 2.0 mg/min. 20

Claims (5)

1. A process for production of abrasive diamond-impregnated tools consisting of the applica tion of a layer of abrasive powder containing the diamond grains to a workpiece, followed by its impregnation therein produced by subjecting the workpiece to an impact impulse ranging from 25 to 800 kN.s applied to said layer by a hard-alloy element which spins at a frequency from 900 to 2500 s-1.

2. A process as claimed in Claim 1 wherein charging a disk-shaped workpiece with abrasive powder is effected simultaneously with forming it into a spherical segment having a radius that is three to ten times its initial radius. 30

3. A process as claimed in Claims 1 and 2 wherein the use is made of an abrasive powder having the following composition (vol.%).

diamond grains 20 to 60 low-melting-point metal up to 100 35

4. A process as claimed in Claims 1 and 2 wherein a layer of abrasive powder containing the diamond grains is applied to a workpiece clad with a low-melting-point metal.

5. A process for production of diamond-impregnated tools as claimed in Claims 1 to 4 and substantially described herein and in examples 1 through 5. 40 Printed for Her Majesty's Stationery Office by Burgess & Son (Abingdon) Ltd, Dd 8991685, 1987. Published at The Patent Office, 25 Southampton Buildings, London, WC2A l AY, from which copies may be obtained.