INTERNAL PEENING TECHNICS - VARITY AND DESIGN

Transcription

1 International Conference on Short Peening and Blast Cleaning INTERNAL PEENING TECHNICS - VARITY AND DESIGN R. G. Bosshard ANVIL DEVELOPMENTS, CH-8604 Volketswil-Switzerland ABSTRACT Following is a condensed description of various internal peening equipment arrangements. Also included is a principle information about small diameter peening technique which covers the range between 2.4 to 4.0 mm. For the major range of application, bore sizes 1 5 to 50 mm, instructions for optimization of nozzle design is presented. Detailed information is given how to develop and design a nozzle based on practical trials and tests. KEYWORDS Internal peening, Internal peening nozzle, internal blasting nozzle, peening lances. INTRODUCTION Mainly the aircraft industry needs the processes of shotpeening on various parts. Again many of this parts require a peening treatment inside holes or inside cylinders. A "hole" in connection with peening or blasting does not necessarily mean a cylindrical straight bore, it can also be a slot or any profile as common e.g. Fig. 1 Holes,,A" to,, H" Specified for peening 62

2 on compressor disks or drive shafts. The main component of a landing gear, see Fig.1, is a representative sample. For such purposes at least 3 different peening techniques are common on the base of air driven acceleration. For bores over e.g mm dia, conventional arrangements with straight nozzles can be possible. The most common range is between around 4.0 and 60 mm and can be treated with internally axial moving and rotating lances, with an additional satellite movement even up to 1 20 mm and more. Normally due to shape and size of the workpiece, it is not possible to rotate it, instead the nozzle gear must perform at least the rotation required. The 6 to 20 mm range can also be treated with the ricochet technique. The technically minimal 2.3 to 4.0 mm range, extremely important e.g. for oil holes is an expert job and needs special equipment and technique. Often it depends on the machinery that is available and also production and economical considerations determine the way how to do such jobs. A major problem with mainly the small size nozzles is, to get the necessary high intensity required by the particular specifications. Due to geometrical and physical facts, this can become quite an expert job. DIRECTLY WORKING INTERNAL WORKING NOZZLE ARRANGEMENTS Here the target axis is identical to the nozzle axis. The shot acceleration will take place in normal way inside the straight Fig. 2 A standard nozzle outfit with Fig. 3 A special arrangement outfit with a a 25 mm hose Inside a 250 mm bore 13 mm hose inside a 120 mm bore 63

3 nozzle. But as the impact angle in ordinary manner should be around 90, the bore to be treated must have a size of e.g. 250 mm when working with standard shotpeening equipment, Fig.2. It could go down to around 1 20 mm if small size nozzle with special clamp unit gets installed, Fig.3. TYPICAL COMMON SIZE PEENING LANCE ARRANGEMENTS This technique is the most widely used principle. The idea is, to use soma sort of a pipe with a specially shaped nozzle tip at the end, so that the media flow gets deflected and finally hits the wall of the bore to be treated. Fig.4. The end tip normally has one Ol..Jtlet orifice, but it is possible to have two or even more in some cases. In peening generally, the maximum intensity is Principle Lance Measurements: a Media hose internal diameter d Usable length of lance ( f Media acceleration length 1 l b Orifice diameter 11 Deflection angle ( g Media acceleration length 2 l c Lance external diameter Fig.4 A common internal lance achieved when observing an impact angle of around 90. Inside bores, this normally is not possible and moreover not advisable as enough room and distance must be reserved to the media flowing off. In addition, the shot energy inside the nozzle gets reduced when designing a sharp bent and this energy then is already lost for the effective peening job. The common lance principle can have numerous variations not only in the design of the nozzle tip, but also the variations when applying e.g. for high pressure bottles, heat exchanger pipes, plungers, landing gears and many_ more. Here the lance can rotate, thus requiring a rotary transmission lead through. Additionally it Cqn move longitudinal reciprocating, or the workpiece can do this; or movements can 64

4 be mixed. The modern technique uses an e.g. 6-axis robot equipped with a nozzle rotator. So the workpiece can be placed in a simple manner inside a peening cabin and the robot is capable to move the lance exactly as required. VARIATIONS OF INTERNAL PEENING PROCESSES Such a possibility can be the so called ricochet technique. For this, it is necessary that both sides of the hole have ample space for mechanical gear. Typical examples are turbine engine disks. Here the straight nozzle works against an opposite placed cone. So the shot gets deflected and directed to the wall of the hole. Fig.5. For short bores it can be sufficient to keep the nozzle in a t! Fig. 5 Two variations with ricochet principle a)deflectormo~ngon~ b) Deflector and nozzle coupled fixed distance to the bore entrance an.d to move the cone longitudinal only. For longer bores it might be necessary to move the nozzle simultaneously with the cone, with well experimented distance for highest efficiency. PEENING LANCE ARRANGEMENTS FOR SMALLEST DIAMETERS The most common size for round steel shot as used in industry is S-110, according specifications in the range between 0.30 to 0.60 mm diameter. The rarely used and also commonly finest 65

5 shot is the S-70, 0.20 to 0.40 mm. (13'000 pellets/g[1 ]). Peening equipment design engineers recommend to have orifice dias not smaller then 3 times of the pellet size. Therefore the smallest inside dia of a media line can have _3 x 0.40 = 1.2 mm. Working with a wall thickness of e.g. 0.4 mm for a lance, the outside dia will reach 2.0 mm. With thinking of at least one pellet size clearance between nozzle and bore size, holes should be bigger then clearance = 3.0mm. Now with a trick it is possible to peen bores down to 2.4 mm. The special equipment of a peening machine manufacturer[2] works as follows: Fig. 6 Peening of minimal size holes 2.4 mm (baiker) principle) a) The nozzle gets positioned just outside the bore. b) Peening is performed with only nozzle rotation, no axial movement for this operation. This will bring the bore entrance, normally designed with a radius, to the intensity level required. c) Interruption of the peening process and moving the nozzle into the bore. Continuation of peening process with rotation and axial movement. Now the pellets leave the specially designed nozzle tip under a specific angle and will hit the surface of the hole. Ricocheted from the wall of the hole, the 66

6 pellets will move away from the nozzle thus securing that no pellets will be found in the too narrow area between nozzle and bore. Utmost care has to be taken, not to move outside with the nozzle. In such a fatal case it might happen, that pellets got jammed between bore entrance area and nozzle. This is a frequently used operation on oil holes of e.g. turbine compressor shafts. Consequently the corresponding intensity test procedure had to be developed. NOZZLE DESIGN PRACTICE Certainly the shot flow and all related characteristic could be computer modeled. But this will be quite a job and will be a task for future development. For the design and application engineer the following key facts are the base of all studies: Diameter of hole to be treated Length of hole Area to be treated as part of the length Pocket hole or through hole Situation of hole in reference to workpiece Shot size specified Intensity required Testing facilities Additionally for commercial application: Available peening machine equipment Production rate Cost optimization Approval EXPERIMENTAL INTERNAL NOZZLE OUTFIT To optimize the geometry of internal nozzles, a special developer kit is suggested. Fig. 7 This outfit allows in a simple way to find the best geometry together with manufacturing possibilities. The device consist of a standard shaft, a pipe insert and the actual orifice unit split in two parts for simple machining. Material could be mild steel as test runs can be a matter of e.g. a few 67

7 Fig. 6 Peening of minimal size holes minutes. The cylindrical internal liner, responsible for the first stage media acceleration,.can be of different shapes, Fig.8, and certainly the ideas for the end tip Fig.9 are unlimited. The testing evaluation of the performance of such new creations need some effort. Simple tests with abrasive technique[3] will show the intensity distribution according the relative position of the test area versus orifice outlet. Also the peak of the intensity can be determined in thi-s simple way. Figures about the intensity can be worked out with the help of ALMEN-Strips in a special arrangement[4] or eventually with the rather uncommon ALMEN Round[5], either following the routine test principle or working with a simulative rig. The development is done in two principle steps: a) Evaluation ~nd testing of the specific nozzle in respect of peening performance. b) Transformation of evaluated geometry into a producible device. Partly there is a linear scaling possible. So if the optimal shape has been found, it can be adapted to the necessary size within 68

8 certain limits. Also the mechanical details and manufacturing possibif ities have to be studied together with the decision for the materials to be used. But it is to say that such a high tech nozzle can safe a considerable amount of production t ime, energy and therefore safe money. I I I c Fig. 8 Lance Passage area variations CONCLUSION Fig. 9 The deflection device in various geometries Internal. peening is only a small field in the art of peening and blasting. There are many standard solutions and daily new challenges call for the engineers. Also the continuous development in material makes it possible to redesign equipment of the past and to replace it with innovations of today for tomorrow. REFERENCES 1. PEENING REFERENCE MANUAL Electronics. Inc., 5th Ed./ Vol. II, page S.Baiker, "Multi-purpose CNC Shot Peening Plant", ICSP-6, page R.G.Bosshard, "Development of Peening/Blasting Nozzles", MET AL FINISHING NEWS, Vol.1, Dec "BA-100 Almen Strip Holder", METAL FINISHING NEWS, Vol.1, Dec.2000, page 8 5. R.G.Bosshard, "Online Monitoring with Almen-Rounds", ICSP +.BC1, 1996 Bhopal 69