GB2118085A

GB2118085A - Method and apparatus for the deformation of workpieces

Info

Publication number: GB2118085A
Application number: GB08309203A
Authority: GB
Inventors: Klaus Peter Hornauer; Helmut Reccius
Original assignee: Individual
Current assignee: Individual
Priority date: 1982-04-15
Filing date: 1983-04-05
Publication date: 1983-10-26
Also published as: FR2525139B1; GB8309203D0; DE3213896A1; FR2525139A1; GB2118085B

Abstract

This invention relates to a method of an apparatus for the deformation by shotblasting of the surfaces of workpieces in which the surface of the workpiece which is to be treated is subjected to the impact of shot particles of generally spherical form in free flight. In accordance with the invention and in order to reduce friction and heat generation a layer of liquid (51) is formed between the shot (13) and the surface of the workpiece (3). The liquid used to form said liquid layer (51) may also be used to provide acceleration for the ball-shot (13). <IMAGE>

Description

SPECIFICATION Method and apparatus for the deformation of workpieces The present invention relates to a method of an apparatus for the deformation by shot-blasting of the surfaces of workpieces made of materials which are capable of being elastically and plastically deformed, in particular by the application of shot particles of generally spherical form of suitable diameters and of suitable hardness for impact deformation, said particles having a smooth surface and being accelerated in free flight so as to deform the workpiece by means of their kinetic energy in the sense of a localised displacement of material, a layer of liquid being formed between the shot particles and the work surface to which they are applied through which layer the shot penetrates into the surface layer of the workpiece.

It has been known for a long time to treat workpieces surfaces, particularly metal surfaces, by blasting with solid particles for the purpose of removing impurities, for example residues of casting moulds, or flash-and-burr-formations, and also for de-scaling or like purposes.

In such operations the solid particles are accelerated in an airjet delivered by means of suitable apparatus through a nozzle impelling them under relatively high pressure towards the workpiece surface to be treated.

For propelling the solid particles it is also known to prepare a slurry of particles in a liquid and to add this to the airjet which, due to the form of the particles generates friction on application to the worksurface which favours deburring, for example, as well as producing an impact effect between the solid particles and the treated surface.

The treatment of workpiece surfaces by means of a carrier medium containing solid particles is also used for the purpose of achieving a consolidation or strengthening of the treated workpiece due to structural compacting. It is known for this purpose to impel shot or balls of hardened steel, glass or ceramic material against the work surface by means of an accelerating airjet.

It is also known to blast the surfaces of paneltype workpieces with hardened steel shot for the purpose of their deformation, the steel shot being accelerated, e.g. in free fall, to the required impact velocity by means of an air jet or by impeller wheels.

According to current knowledge the deformation which is obtainable by the unilateral application of shot blasting particles to the surface of a panel-type work-piece is due to the fact that the shot bodies release their kinetic energy on impingement on the work surface and the usable energy is converted into deformation work in a superficial layer of the workpiece.

As the shot particles penetrate into the surface of the workpiece the material is displaced sideways; the layer of material beneath the deformed layer opposes expansion of the plastic zone of the influenced layer which generates tensile strain in the interior of the workpiece and compression stress in the influenced zone. The desired magnitude of deformation (curvature or radiussing of the workpiece) is obtained by controlling the plastic elongation in the influenced surface layer by means of the process parameters, for example shot velocity.

It was frequently found that workpieces which were treated by the shotblasting method, besides acquiring the desired curvature or radiussed deformation, display a greater degree of insensitivity in respect of stress corrosion and have improved fatigue strength behaviour.

If reproduceable deformation conditions are to be achieved by application of the known shotblasting process it is necessary to take into account a number of characteristic data regarding the material, the workpiece and also the shot particles. Such data are, for example, the measurements and the hardness as well as the shape or form of the shot particles, the intensity of the blasting jet, the diameter of the jet or beam of shot and of the associated nozzle orifice in the blasting apparatus and/or the distance between the blasting nozzle and the treated work surface.

Another important aspect is avoidance of surface damage in the form of scratching, scoring or the like caused by the penetration of the shot particles into the work surface, because the bottom of the impact notch or indentation may well penetrate through the zone of plastic deformation into the zone therebeneath which is in tension. In that event there is a danger of permanent fracture.

Shot bodies or particles with an irregular, e.g.

polygonal or rough surface, such as for example sand particles which are normally used in sand blasting for cleaning purposes, are not suitable for this application. Furthermore, the application in impact deforming operations requires impact- or shot particles with a specified minimum size and a specific hardness.

it is the aim of the present invention to provide an improvement in respect of material properties in workpieces shaped by shot-blast-deformation, particularly in respect of reduced sensitivity to stress - corrosion and in respect of fatigue~ strength behaviour.

It is further the aim of the invention to provide an improvement in shot-blast-deformation plant in respect of reduced noise generation and dust pollution and also in respect of a simplified outlay of apparatus in combination with a substantial, reduction in the energy costs required to operate the plant.

According to the invention the said aims are achieved due to the fact that the acceleration of the spherical shot is obtained by means of a liquid which is pressurised for this purpose. With the aid of the method according to this invention for impact-deformation of panel-type workpiecès it is possible, by means of the layer of liquid which is formed between the shot particles and the work surface, to achieve an improvement in the physical properties of the work material additionally to the improvements which are achievable by impact deformation.

The introduction of the liquid prevents the generation of high temperatures in the surface layer of the workpiece which could otherwise arise in the course of the shotblasting process at the points where the shot particles hit the work surface, for example due to friction caused by a rough work surface, or by an oblique impingement of the shot particles on said work surface, or by a spin component in the movement of the particles.

The generation of unduly high temperatures at the points of impingement on the workpiece may give rise to precipitation phemomena in the microstructure of the work material, or to a phase transformation with deleterious effects in respect of fatigue strength and stress corrosion.

In the absence of a layer of liquid the deformation blows may set up inherent residual strains in the region of the bottoms of the notches or indentations created by particle impact. Such residual strains result from the flow-inhibiting effect of friction between work and shot particles during impact.

According to a further attractive development of the invention, another essential characteristic resides in that the liquid for forming the said layer is delivered under pressure through a slot blasting apparatus with acceleration and propulsion of the shot towards the work surface. Thus the liquid is used, on the one hand, to form the liquid layer on the surface of the workpiece and, on the other hand, simultaneously for the acceleration of the shot particles for impingement on the workpiece surface. By comparison with the use of compressed air for shot propulsion the use of a liquid propellant achieves a decrease in respect of the flow velocity of the pressure medium needed to achieve the required shot acceleration or in the length of the acceleration path of the shot particles.

The slower flow velocity of the liquid affords a considerable economy in primary energy.

Moreover, the layer of liquid which spreads over at least a major part of the workpiece surface during the deformation process absorbs or attenuates the vibrations which occur in the workpiece and thus achieves a very considerable noise suppression result. The slower flow velocites of the liquid in the system also help to reduce noise generation. In addition to this the liquid prevents dust formation which is quite unavoidable in shotblasting deformation processes without liquid.

With the aid of the process according to this invention and the construction of associated plant and apparatus for the execution of this process it is considerably easier to produce special nozzle- or jet shapes, for example broad- or flatbeam shapes, or intermittent blasting jets.

A further characteristic aspect of the present invention resides in the construction and arrangement of the apparatus for applying the process, in that a housing of the shotblasting apparatus which was disclosed in US-PS 23 69 576 and in which the liquid feed is connected to an annular space into which extends a ballshot feed pipe concentric therewith is developed further by arranging for the outlet orifice of said pipe to enter into the interior space of the housing in the region of a constricted section of the housing interior.

Due to the arrangement according to this invention an ejector effect is produced in the region of this constricted section of the housing interior by means of the pressure-fed liquid in respect of the shot particles which are fed in free fall through the shot feed and a certain suction effect is effective inside the shot feed pipe.

The accompanying drawings illustrate one example of an apparatus or plant for the application of a method according to this invention. This embodiment is hereinafter more particularly described.

In the drawings Figure 1 is a schematic representation of a deforming plant in association with the example of an apparatus according to this invention, and Figure 2 is a schematised cross section, enlarged by comparison with Figure 1, of the shotblasting apparatus seen in Figure 1.

As will be obserbed from Figure 1, the deforming plant 1 shown therein comprises a fluid-tight container 2 in the interior of which are accommodated the shotblasting apparatus 9 with associated adjusting means and associated feed and conveyor means for liquid and ball shot, as well as the work support for the workpiece to be treated.

In detail, the workpiece carries reference number 3 and the work support, generally indicated at 4, consists of leg or stand parts 5' and a work support plate 5. Above the work support 4 and the workpiece 3 a track- and guide rail 8 extends horizontally across the container width and the shotblasting apparatus 9 is slidable along said rail.

The track rail 8 itself is mounted for horizontal sliding movement in a direction perpendicular to its length along supporting rails 12 arranged on the side walls of the container so that the blasting apparatus 9 can be displaced in a system of coordinates in a plane parallel to the work surface to be treated.

Below the work support plate 5 of the work support 4 there is provided a shot-return plane 14 which is inclined relative to the horizontal and has perforations 14' allowing the liquid to pass through. A liquid-return plane 15, likewise inclined relative to the horizontal is arranged below plane 14 in container 2.

The shot-return plane 14 adjoins a shot-returnchannel 17 which terminates in an opening leading into the reservoir of a ball feed device 18 which is pneumatically operated using compressed air to convey the shot balls 13. This ball feed device 18 is in constant communication via a flexible hosepipe 20 with a ball-shot storage container 21 of the shotblasting device 9. The liquid-return-plane 15 adjoins a liquid-returnchannel 15' into which extends the suction pipe 27 of a liquid feed device 26. Between the shotblasting device 9 and the liquid-feed device 26 there is a communication via a flexible hose 28.

The shotblasting device 9 shown in Figure 2 comprises a housing 30 in combination with an insert or liner part 31. The liner 31- comprises an upper portion 32 and an integrally connected cylindrical portion 33. The portion 32 is further integrally connected to a feedpipe part 34 for the ball-shot which is concentric with the inside wall of the housing interior, generally designated 35, and its discharge opening 34' is arranged inside this housing interior 35.

By means of the liner 32 and of housing part 30 and feedpipe 34 the interior space of the housing is split up into an annular space 35', a constricted section 36 and an expanding section 37. The feedpipe 34 for the ball-shot 13 termimates with its end orifice in the region of the constricted section 36 of the housing interior 35. The housing 30 has an outlet hole 38 at the bottom end and is provided with a guard ring 39. The annular space 35' communicates via bores 43' and annular chamber 42 as well as an orifice 43 with a. hose connection 44. The flexible hose 28 of the liquidfeed 26 is connected to part 44. Furthermore, the feedpipe 34 for feeding the ball-shot 13 communicates via connector pipe 45 with the shot- storage container 21. The flexible hose 20 of the ball-shot feed device 1 8 leads into this storage container 21.

In one embodiment of his apparatus jet nozzles 50 are connected via hose sections 28' to the pressure-feed device 26. A layer of liquid 51 on the work surface can be formed exclusively through, or by means of these nozzles 50 without any supply of liquid via the shot-blasting device 9. The supply of liquid may further be delivered through the nozzles 50 jointly with a liquid delivery via blasting device 9.

The above described system operates as follows: With the aid of the track rail 8 and supporting rails 12 and appropriately associated drive-and transmission means (not shown for the sake of greater simplicity or representation), the shotblasting device 9 with vertically or substantially vertically directed jets is adjustable in a plane parallel to the work surface. Additionally, further adjusting means may be provided (not shown) for varying the distance of the outlet orifice 38 of the blasting device 9 relative to the work surface.

In practical execution of deformation work, spherical shot particles 13 are sucked by means of the shot-feed device 18 from the associated storage container and fed through the flexible hosepipe 20 to reservoir 21 of the shotblasting device 9. The ball-shot 13 drops in free fall through connecting pipe 45 from the funnel-or hopper-type reservoir 21 into feed pipe 34.

Simultaneously with this process the liquid is fed to the shotblasting device 9 via flexible hosepipe 28 by means of the liquid feeder device 26. The liquid passes through hose connector 44, bore 43 and annular space 42, and through bores 43', into the annular chamber 35'. The liquid which is fed under pressure flows from annular chamber 35' through the constricted section 36 to section 37 of the interior housing space 35 in consequence of which the ball shot 13 which emerges in free fall at the opening 34' of feedpipe 34 is picked up by the flowing liquid and, accelerated by this pressure application, propelled against the work surface.

In the region of the constricted section 36 of the housing interior 35 an ejector effect builds up in respect of the outlet opening 34' of the feedpipe 34 which creates suction in pipe 34 and contributes to the acceleration of the ball-shot 13.

Section 37 serves to sustain liquid pressure and to guide the blasting jet or beam of ball-shot 13.

The liquid which is provided for the acceleration of the ball-shot 13 impinges on the work surface jointly with the shot 13 and there forms a layer of liquid 51. This layer of liquid 51 is interposed between the shot 13 and the work surface when the former impinges or hits against the work surface and penetrates into the surface layers of the workpiece thus preventing, or at any rate substantially reducing friction between shot 13 and workpiece 3.

On completion of their deformation work the shot particles 13 are caught up on the ball-return-plane or tray 14 and roll into the return channel 17 which serves as a reservoir from which the ball-shot is once more picked up by suction applied by the ball-shot feeder device 1 8 for recycling through the ball-shot blasting device 9. Due to the provision of a deformation 14' in the inclined shot-return plane 14, the liquid which flows off the workpiece 3 and its work support 4 runs into the liquid-return tray, or plane 15, whence it is returned through the return channel 15' which serves as a liquid reservoir for recycling through the liquid feed device 26.

The liquid-feed, or conveyor device 26 may be adjustable in respect of pressure generation so that it is possible to vary the charge intensity of the ball-shot 13 within the shotblasting device 9 in accordance with given workpiece parameters, driving speed of device 9 and distance between delivery orifice 38 and work surface. The aforementioned liquid may comprise a liquid lubricant. Also non-liquid lubricants such as substances of solid or plastic consistency in colloidal form or dry lubricants may also be applied to the surface of the workpiece to be treated. Furthermore, the workpiece may be constantly immersed during the deformation process in a container filled with liquid, the surface being treated being submerged beneath the surface level of said liquid.

Claims

1. A method for the deformation by shotblasting of the surfaces of workpieces made of materials which are capable of being elastically and plastically deformed in particular by the application of shot particles of generally spherical form of suitable diameters and of suitable hardness for impact deformation, said particles having a smooth surface and being acclerated in free flight so as to deform the workpiece by means of their kinetic energy in the sense of a localised displacement of material, a layer of liquid being formed between the shot particles and the work surface to which they are applied through which layer the shot penetrates into the surface layer of the workpiece, characterised in that acceleration is imparted to the ball-shot by means of a liquid which is penetrated for this purpose.

2. A method according to Claim 1, characterised in that for the formation of the layer of liquid a liquid is delivered directly to the work surface by means of jet nozzles and/or through a shotblasting device.

3. A method according to Claim 1 or Claim 2 characterised in that the layer of liquid covers the whole, or approximately the whole, surface of the workpiece under treatment during the deformation process.

4. An apparatus for carrying out a method according to Claim 1 , in which there is a shotblasting device having a housing in which an annular space is provided adjacent to a liquid feed system, a shot-feed pipe extending concentrically into said annular space, characterised in that the outlet orifice of the shot-feed pipe leads into said annular space in the region of a constricted section formed in the latter.

5. An apparatus according to Claim 4, characterised in that the shot-feed pipe is arranged for feeding the ball-shot in vertically or approximately vertically directed free fall.

6. An apparatus acccording to Claim 4,.

characterised in that there is provided a fluid-tight container in which is mounted support means for the workpiece.

7. An apparatus according to Claim 6, characterised in that there is provided within said container beneath the workpiece support means a ball-shot-return plane which is inclined relative to the horizontal and provided with perforations for the liquid to pass therethrough, said shot-returnplane leading to a shot-feeder device.

8. An apparatus according to Claim 7, characterised in that a liquid-return plane which is inclined relative to the horizontal is provided beneath the ball-shot return plane.

9. A method according to Claim 1, characterised in that, for the formation of the layer of liquid, the workpiece is constantly immersed during the deformation process in a container filled with liquid, the work surface being submerged beneath the surface level of said l#iquid.

10. A method according to Claim 1, characterised in that the liquid is a liquid lubricant.

11. A method according to Claim 1, characterised in that non-liquid lubricants such as substances of solid or plastic consistency in colloidal form or dry lubricants are applied to the workpiece.

12. A method for the deformation by shotblasting of the surfaces of workpieces made of materials which are capable of being elastically and plastically deformed in particular by the application of shot particles of generally spherical form of suitable diameters and of suitable hardness for impact deformation, said particles having a smooth surface and being accelerated in free flight so as to deform the workpiece by means of their kinetic energy in the sense of a localised displacement of material, a layer of liquid being formed between the shot particles and the work surface to which they are applied through which layer the shot penetrates into the surface layer of the workpiece, substantially as hereinbefore described.

13. An apparatus for carrying out a method as claimed in Claim 12 and substantially as hereinbeforeaescribed with reference to and as shown in the accompanying drawings.