Patent GB-1397676-A (GB)
Title: Machine and method for cutting brittle materials
IPC: B28D5/04
Filed: 1973-11-30
Abstract: 1397676 Severing MOTOROLA Inc 30 Nov 1973 55642/73 Heading B3D A machine for cutting brittle material 64, such as semi-conductor devices, piezoelectric devices or crystals, comprises continuous wire supply means 10, take-up means 15 for used wire, a plurality of wire guides between said means and defining a cutting area 40, material mounting means 60 mounted above the cutting area for rigidly affixing pieces of material to be cut, the mounting means being vertically movable towards and away from the cutting area, and means for producing relative reciprocating movements between the wire and material in the cutting area. A relatively continuous flow of cutting mixture including fine particles of cutting material with a relatively constant average size and a fluid carrying agent is supported during the cutting operation. The wire supply means consists of a spool 12 driven by a motor 11, the wire being fed from the spool over pulleys 20, 21 to multi-groove pulleys 22, 23 mounted on a fixed part and a carriage 24, respectively. The wire then passes over pulleys 25, 26 to a pulley 27 through a means 30 for stripping cutting mixture from the wire and over multi-groove pulleys 36, 37, 38 which form a web 35 having a cutting area 40 between the pulleys 36, 37. Other cutting areas may be used between the pulleys 36, 38 or 37, 38. From the web, the wire passes over a pulley 45 in a further means 47 for stripping cutting mixture, pulleys 46, 48, multi groove pulleys 50, 51 on the carriage 24 and a fixed part, respectively, and pulleys 52, 53 leading to the take-up spool 17 which is driven by a motor 16. The wire is moved first in one direction and then the other to produce a sawing motion by reciprocation of the carriage 24 between positions determined by limit switches 55, 56, the wire also moving at a constant rate from spool 12 to spool 17. The piece of material 64 to be cut is mounted on the platform 63 of a block 62 movable along guides on a base 61 by a fluid cylinder 70 against the bias of a counterweight 65. The pressure of fluid supplied to the cylinder 70 is controlled so that the machine cuts at a constant rate. The cutting mixture, such as particles of silicon carbide or the like having a diameter of 22 microns and a fluid, such as glycerine and propylene glycol or water, the glycerine adding viscosity to the fluid so that particles adhere to the wire, is supplied to the cutting area 40 through nozzles 75, 76 from a source of say 5 gallons in a recirculating system whereby the machine can operate for some time without the particles reducing in size more then 1%, or from a source of unused slurry. A nozzle 81 supplies fresh water for washing the wire and piece 64 after the cutting operation. The stripping means 30 is similar to the stripping means 47 and as the wire moves towards the stripping means upon reciprocation of the carriage it is first subjected to a jet of gas from a slit 87 in a plenum 86 connected by a pipe 85 to a source of gas, such as air. A second jet is directed at the wire from a slit 90 in a plenum 89 connected by a conduit 88 to a source of gas. The wire then passes, by way of pulley 27 into a chamber 91 containing low viscosity fluid, such as water, and from the chamber past a jet from a plenum 94 for removing the low viscosity fluid. When the wire is travelling towards the cutting area, the jet from the slit 90 of the second plenum 89 removes the low viscosity fluid so that it does not reduce the viscosity of the cutting mixture.