METHOD OF AND APPARATUS FOR PROCESSING WORKPIECES BY USING SAND BLASTING UNIT

Abstract: A method of and an apparatus for processing, for example, chamfering by using a sand blasting unit a workpiece having both a surface to be processed and a surface not to be processed which are close to each other. A workpiece (W) fixed to a holder (2) on a turntable (1) is transferred to a processing position (P₁) by moving the turntable (1). An ejection nozzle (3) or (4) is directed to a surface (f₁) to be processed of the workpiece (W), while an ejection nozzle (5) is directed to a surface (f₂) not to be processed thereof. A fluid, such as air is supplied to the ejection nozzle (5), and grain-containing air to the nozzle (3) or (4). The fluid ejected from the ejection nozzle (5) prevents the grain from impinging upon the surface (f₂) not to be processed.

Description: This invention relates to apparatus for and a method of processing a workpiece W by causing a flow of abrasive grains to impinge against the first surface portion of the workpiece f₁ to produce abrasion thereof, and causing a flow of pressurised fluid to inhibit the flow of abrasive grains from producing abrasion of a second surface portion f₂ of the workpiece. Chamfering of an end edge Wa of a relatively small workpiece W, such as one shown in Fig. 1, and a peripheral edge Wc of a bore Wb therein, has conventionally been performed by a hand process, utilizing a thread-like abrasive tape. However, such method has disadvantages that it is troublesome, time-consuming and inefficient. It might be thought that an automated process utilizing sandblasting could be used in which abrasive grains comprised of, for example, silica sand, chilled cast iron or the like would be caused strongly to impinge against a surface of the workpiece to be processed. However, in the case of a head for a video signal recording and reproducing apparatus for example, the workpiece W has a surface f₂ requiring a mirror finish adjacent surfaces f₁ to be processed by the sandblasting, and there would be a fear that the abrasive grains of the sandblasting would also impinge against the mirror surface f₂ and degrade it. For this reasons conventional sandblasting could not be adopted for processing of the workpiece W. DE-A-2 846 737 representing the closest prior art discloses a sandblasting method in which the end of an electrical cable is stripped by inserting it into a generally tubular container and directing an abrasive particulate flow parallel to the surface of the cable through the tube to produce abrasion of the cable surface. A portion of the cable surface is protected from abrasion by an air flow generally tangential to the cable. FR-A-1 229 156 discloses a chemical cleaning process for semiconductors in which a jet of chemical cleaning liquid is directed obliquely at a first portion of a semiconductor workpiece and a second portion is shielded by an obliquely direct gas flow. In accordance with the present invention a flow of abrasive grains is directed at the first surface portion of the workpiece in a direction extending perpendicularly to a plane including the first surface portion, and said flow of pressurised fluid is fed directly at the second surface portion in a direction extending perpendicularly to a plane including said second surface portion. Features and advantages of the invention will be more fully understood by reference to an embodiment thereof which will now be described in conjunction with the accompanying drawings in which: Figure 1 is a perspective view of an example of a workpiece; Figure 2 is a schematic view of an arrangement of a processing apparatus in accordance with the invention; Figure 3 is a side elevational view of a portion of the apparatus of Figure 2, illustrating a position relationship between a rotary table 1 and a jet nozzle 5; Figure 4 is a perspective view of a support structure for injection nozzles 3 and 4 in the apparatus of Figure 2; Figure 5 is a perspective view of the apparatus of Figure 2; and Figure 6 is a cross-sectional view of an air blowing unit 27 in the apparatus of Figure 2. Figures 2 and 3 show an example of a basic structure of a processing apparatus in accordance with the present invention. In Figures 2 and 3, B is a base on which a rotary table 1 is disposed. An outer peripheral portion of the rotary table 1 is provided with four holders 2 equidistantly spaced from each other, objects W (as a matter of convenience, the object shown in Figure 1 is regarded as a workpiece) can be respectively held by the holders 2 and be intermittently transferred one by one to a processing station P₁. In this case, the rotary table 1 is driven by a motor 1a and is stopped by means of a limit switch or the like not shown, when the table is rotated to a predetermined position. The above-described processing station P₁, has disposed thereat two injection nozzles 3 and 4 and a single jet nozzle 5. The injection nozzles 3 and 4 are provided for strongly blasting abrasive grains delivered from a tank 7 through pipes 8 and 9 by compressed air provided by an operation of an air compressor 6, against the surface to be processed f₁ of the object W. Since, in the case of the object W shown in Figure 1 there are two surfaces f₁ to be processed in back to back relation, the nozzles 3 and 4 are mounted on a slider 10, as shown in Figure 4, in such a manner that tips of the respective nozzles face toward each other. The arrangement is such that the nozzles 3 and 4 are axially moved by the movement of the slider 10 by a motor 11 in such a manner that when one of the injection nozzles 3 moves perpendicularly toward one of the surfaces to be processed f₁ of the object W at the processing station P₁, the other injection nozzle 4 moves away from the other surface to be processed f₁, and, when the injection nozzle 4 moves toward the surface to be processed f₁ facing thereto, the other injection nozzle 3 moves away from the other surface to be processed f₁. As shown in Figure 4, the slider 10 is supported by the base B, for example, through a supporting member A. The jet nozzle 5 is provided for strongly blowing exclusion fluid such as air for excluding the abrasive grains, against the surface not to be processed f₂ of the object W. Since the surface not to be processed f₂ is formed by an upper surface of the object W, the nozzle 5 is disposed above the rotary table 1, as shown in Figure 2, so as to extend perpendicularly to the surface not be processed f₂ of the object W at the processing station P₁, and the nozzle 5 is connected to a support source 31 of the exclusion fluid through a pipe 13 and a valve 30. In addition to the two nozzles 3 and 4, the slider 10 has thereon a suction unit 14 which is in communication with a dust collection device 16 through a pipe 15. The dust collecting device 16 draws the abrasive grains having processed the object W and dust generated upon the processing through the suction unit 14, to separate the abrasive grains from the dust, to thereby purify the air which is discharged to the atmosphere by a blower 17. The dust collecting device 16 is connected to the tank 7 through a communication duct 19 having provided therein a damper 18 so as to be able to return the recovered abrasive grains to the tank 7. The above described pipes 8, 9 and 15 have respectively provided therein valves 20, 21 and 22, the pipe 8 and the pipe 15 are connected to each other by a bypass tube 24 having provided therein a valve 23, at the side of the above described valve 20 adjacent the tank 7 and at the side of the valve 22 adjacent the dust collecting device 16. Accordingly, with this arrangement, the abrasive grains are injected from the two injection nozzles 3 and 4 by the simultaneous opening of the valve 20 and the two valves 21 and 29, the abrasive grains are injected against the surface to be processed f₁ from any one of the injection nozzles 3 and 4 by the opening of only one of the two valves 21 and 29 to enable the processing, and during the interruption of the processing, the closing of the valve 20 and the opening of the valve 23 allow the abrasive grains to be recirculated in the order of the tank 7 - pipe 8 - bypass tube 24 - pipe 15 - dust collecting device 16 - communication duct 19 - tank 7, to maintain the abrasive grains in a fluent condition, so that it is possible to stably supply the abrasive grains to the injection nozzles 3 and 4, rapidly simultaneously with the start of the processing. A stop station P2 subsequent to the processing station P1 of the above described rotary table 1 has arranged thereat blowing nozzles 25 and 25 for blowing clean air against the object W having the processing completed, to remove, from the object W, dust such as the abrasive grains adhering thereon. The blowing nozzles 25 and 25, the injection nozzles 3 and 4, the jet nozzle 5 and the suction unit 14 are covered by a cover 26, as shown in Figure 5, which cooperates with an approximate half of the rotary table 1 to form a single, large processing chamber, so that the dust generated by these components is prevented from scattering to the outside, but is drawn into the dust collecting device 16. As shown in Figues 5 and 6, an air blowing unit 27 is provided, at a feeding-in side of the cover 26 at which the object W having not yet been processed is fed thereinto, for forming an air-curtain at the feeding-in side, and brushes 28 are provided at a feeding-out side thereof for the object W having been processed, so that the object W is freely capable of being fed in and out of the interior of the cover 26, and the interior and exterior of the cover 26 are shielded from each other. In the above described arrangement, the motors 1a and 11, valves 20 to 23, 29 and 30 are controlled by a controller 40. A processing method of the object by means of the sandblasting carried out by the above described processing apparatus will now be described. The object W which is a subject of the processing is loaded on the holder 2 at a station P of the rotary table 1, and is transferred to the processing station P₁ by the intermittent rotation of the rotary table 1. As one object W stops at the processing station P₁, the motor 11 is actuated to first cuase the injection nozzle 3 to move toward one of the surfaces to be processed f₁. As the injection nozzle 3 reaches a predetermined injection position, the air is discharged from the jet nozzle 5 toward the surface not to be processed f₂ of the object W, simultaneously therewith, the valves 20 and 21 associated with the injection nozzle 3 are opened, the valve 23 in the bypass tube 24 is closed, and the abrasive grains recirculated through a passage comprised of the tank 7, pipe 8, bypass tube 23, pipe 15, dust collecting device 16 and communication duct 16 are injected from the injection nozzle 3 toward the surface to be processed f₁ through the pipe 9 to process the surface. That is, the flash removal and the chamfering take place on the edges Wa and Wc at the side of the surface to be processed f₁. In this case, the air from the jet nozzle 5 is injected at a velocity (pressure) higher than that of the abrasive grains, so that after the impingement of the air against the surface not to be processed f₂, the air flows along the surface not to be processed f₂, to prevent the abrasive grains injected from the injection nozzle 3 from being brought into contact with the surface not to be processed f₂. When the processing of one of the surfaces to be processed f₁ has been completed in this manner, the valve 21 is closed and the valve 23 is opened so that the abrasive grains are recirculated as described above, and the motor 11 is actuated to move the injection nozzle 3 away from the surface to be processed f₁ on which the processing has been completed, and to move the other injection nozzle 4 toward the surface to be processed f₁ which has not yet been processed. As this has been completed, the valve 29 associated with the injection nozzle 4 is opened, and the valve 23 is closed, so that the abrasive grains are injected from the injection nozzle 4 to process the surface to be processed f₁ which has not yet been processed. When the processing of the two surfaces to be processed f₁ of one object W has been completed, the rotary table 1 is rotated so that a new object W attached at the station P is transferred to the processing station P₁, and the object W on which the processing has been completed is transferred to the subsequent station P₂. At the station P₂, the blowing nozzles 25 and 25 are actuated to blow the air against the processed object W to clean the same, and all of the air and the abrasive grains discharged within the cover 26, together with the dust collected into the dust collecting device 16 through the suction unit 14. The abrasive grains thus drawn into the dust collecting device 16 are separate from the dust and are returned to the tank 7 through the communication duct 19 for re-use in the processing. The processed object W from which the dust and abrasive grains are removed at the station P₂, is removed from the holder 2 at a station P₃. The illustrated processing apparatus utilised for the description of the present invention is merely an example, and does not limit the processing method of the present invention. It is to be appreciated that the abrasive grain exclusion performance of the exclusion fluid jetted from the jet nozzle 5 has an intimate relation to the velocity, specific gravity, particle size and the like of the abrasive grains injected from the injection nozzles 3 and 4, and although air is mainly utilised as the exclusion fluid jetted from the jet nozzle 5, it is possible to utilise liquid such as water. As described above, in the present invention, the abrasive grains impinge against the surface to be processed, which is located adjacent the surface not to be processed, and the exclusion fluid is blown against the surface not to be processed, to avoid the impingement of the abrasive grains on the surface which is not to be processed, and accordingly it is possible to process by sandblasting only the surface to the processed without damage of the surface not to be processed by the abrasive grains. In addition, since it is sufficient to provide a jetting system of the exclusion fluid which is similar in fluid jetting function to the sandblasting, there is also provided an advantage that the processing apparatus is simple in structure. From the foregoing it will be understood that the invention is very useful for processing where a chamfering takes place on a relatively small workpiece having a surface to be processed and a surface not to be processed which are located adjacent to each other, as is the case with a head for a video tape recorder, for example.

Claims: A method of processing a workpiece (W) by causing a flow of abrasive grains to impinge against the first surface portion of the workpiece (f₁) to produce abrasion thereof, and causing a flow of pressurised fluid to inhibit the flow of abrasive grains from producing abrasion of a second surface portion (f₂) of the workpiece characterised in that said flow of abrasive grains is directed at the first surface portion of the workpiece in a direction extending perpendicularly to a plane including the first surface portion (f₁), and said flow of pressurised fluid is fed directly at the second surface portion (f₂) in a direction extending perpendicularly to a plane including said second surface portion. A method according to claim 1 wherein the workpiece includes first and second surface portions (f₁, f₂) that comprise respective planar surfaces arranged in a non-parallel to configuration. Apparatus for processing a workpiece (W) including first and second workpiece surface portions (f₁, f₂) comprising: abrasive grain supply means (7, 8); fluid supply means (31) for supplying pressurised fluid; means (3, 4, 9) for supplying a stream of pressurised fluid containing the abrasive grains to produce abrasion of said first surface portion (f₁); means (5) for directing a flow of the pressurised fluid such as to inhibit the flow of abrasive grains from producing abrasion of the second surface portion (f₂) of the workpiece; characterised in that said means (3, 4, 9) supplying said stream of pressurised fluid and abrasive grains comprises at least one nozzle for directing said flow of abrasive grains and fluid at the first surface portion (f₁) in a direction extending perpendicularly to a plane including said first surface portion; and said means (5) for supplying pressurised fluid to the second surface portion (f₂) is so arranged that the flow thereof is fed directly at the second surface portion in a direction extending perpendicularly to a plane including said second surface portion. Apparatus according to claim 3 wherein the workpiece includes said first and second surface portions in the form of planar surfaces (f₁, f₂) arranged in a non-parallel configuration. Apparatus according to claim 4 wherein said first and second planar surface portions are arranged orthogonally of one another. Processing apparatus according to any one of claims 3 to 5 further including vacuum generating means (17) and a suction port (14) for receiving abrasive grains after impingement thereof upon the workpiece. Apparatus according to claim 6 further including collecting means (16) connected between said vacuum generating means (17) and said suction port (14) for collecting abrasive grains. Apparatus according to claim 7 including means (18, 19) for supplying grains collected by said collecting means (16) to said supply means (7) whereby the abrasive grains are recirculated. Apparatus according to claim 8 further including a bypass passage (24) capable of being opened and closed and provided between a first abrasive grain path (8) disposed between said abrasive grain supply means (7) and said nozzle (3, 4) and a second abrasive grain path (15) extending between said suction port (14) and said vacuum generating means (17). Apparatus according to claim 9 including a first valve (21, 29) for controlling supply of said stream of pressurised fluid containing the abrasive grains to said nozzle (3, 4), a second valve (23) for opening and closing said bypass passage, and control means (40) for controlling the opening and closing of said first and second valves, said control means opening said first valve and closing said second valve when said workpiece (W) is processed, and when said workpiece is not processed, closing said first valve and opening said second valve.

Inventors: HAMADA, SHUJI, TANO, TERUO
Applicants: NIIGATA ENGINEERING CO., LTD.
Application year: 1985
Main classification: B24C1
IPC codes: B24C3, B24C1