Design for a Machine used for Superfinishing the Internal Surfaces of Gears that are Components of a Gearbox of a Truck

Transcription

1 Design for a Machine used for Superfinishing the Internal Surfaces of Gears that are Components of a Gearbox of a Truck BADEA LEPADATESCU 1) VALENTIN DITU ) ANISOR NEDELCU 3) 1), ), 3) Transilvania University of Brasov, Faculty of Technological Engineering and Industrial Management, B-dul Eroilor nr.9, Brasov ROMANIA lepadatescu@unitbv.ro, cobuzatu@unitbv.ro, a.nedelcu@unitbv.ro Abstract:- In the paper is presented a machine tool that is used to accomplish the surface quality that is required for the internal surfaces of gears that are components of a gearbox of a truck. As is known in a gearbox of a truck are many gears that are mounted on a needle bearings. For this reason, the internal surfaces of these gears need to have a very high surface quality to work properly. The machine that is presented in the paper was designed to realize the entire requirement regarding the surface quality for all the types and sizes of gears that are in the truck gearbox. Key-Words: - surface finish, reliability, gear, high production, load bearing capacity 1 Introduction In many instances, superior workpiece quality in regard to load bearing capacity, efficiency, smoothness of running, operational safety, and last but not least, longevity, requires superior surface finishing of these workpieces. By logical extension, this means continuous adaptation and optimization of existing production processes. The superfinishing process gives to workpieces as called final touch, being an economical machining operation and tipically the last and therefore the qualitydetermining process, that makes it more important. Some of the advantages of using superfinishing process are presented below: - High flexibility; - Low noise volume; - Low energy costs; - Low initial investment; - Low tool costs; - Less friction; - Short processing time. The superfinishing process allows the targeted influencing of the following parameters: - Reduction of surface peak-to-valleys and increase of material contacta rea to over 90%, due to the plateau like surface structures; - Improvment of roundness, creation of microgeometries with particular applications; - Optimization of tribological properties through criss-crossinf finishing marks. Superfinishing removes the amorphous structure of the material, or soft skin. This layer is usually to 8 µm thick and is created by high temperature generates by the grinding wheel. It enables the user to achieve virtually any surface texture parameter, because only the roughness peaks are removed. The geometry of the workpiece remains unchanged. The main advantage of this method is consistent finish over the entire surface. Superfinish improves the bearing ratio resulting in greatly improved wear resistance. Stock removal is typically in the order of a few microns. The achievable surface finish quality is comparable to levels reached only by honing or lapping. Superfinishing process is a very clean process, because coolant or grinding emulsion is used of honing oils like Stone grinding. Recycling and waste disposal are simplified. This process is suitable for any material that could also be finished with geometrically undefined blades. In addition to the most diverse metal alloys and grades, other materials can also be finished, such as ceramics, plastics, non-ferrous metals as well as coatings, such as tungsten carbide, chromium, or copper. After the process of superfinishing the workpiece surface has a tightly controlled cross-hatch patter, obtained by the interaction of three interrelated motions. These motion are the oscillation of the stone, rotary movement of the workpiece and pressure of the abrasive tool on the workpiece. During the superfinishing process, parts pass through several distinc phases. When the abrasive tool makes initial contact with the part, dull grains fracture or ISBN:

2 pull away from the matrix to produce a new cutting surface. As the tool self dresses, relatively large amounts of stock removal phase, abrasive grains begin to dull, while surface irregularities and geometry continue to improve. This results in a cross-hatced surface free of irregularities and amorphous material. Machine to superfinish the internal surfaces of the gears In this paper is presented a machine to superfinish the internal surfaces of the gears which are components of a gearbox of the truck. It is known that in the gearbox of the truck are a lot of gears with different diameters that are used as the intermédiate gears, without transmitting the torque, only to transmit the rotary motion to other shafts. For this reason, these gears have the internal surfaces smoothly and these surfaces need to have a very high surface finish in the values of roughness between 0,4-0, µm R a. The previous process is grinding and the last machining process is superfinishing that gives the final dimension and roughness for these internal surfaces. These gears from the gearbox have an internal diameters between Ø mm and the width between 0-50 mm. One of these gears is shown in Fig.1. Fig.1 Gear with internal surface obtained after the process of superfinishing. To can machining all these types of gears was designed a machine that is presented in the sketch of Fig.. In this figure the workpiece (4) is held in jaws (3) and has a rotational motion through the machine gearbox (1). The superfinishing head has a oscillation movement with the amplitude of 1-3 mm and a frequency of 1500cd/min. These oscillation movement is realized by the motor (8) and the mechanism (7). It is used a plunge process when the workpiece is held and rotated, while the superfinishing multistone (the superfinishing stones are between 3-6, according with the internal diameter of the workpiece) makes contact with the internal surfaces of the part. During the superfinishing process were used abrasive stones with silicone carbide, which is a combination of pure white quartz, petroleum coke, sawdust and salt in an electric furnace. To achieve the desired surface finish was used abrasive materials with fine grit sizes between 400 and 100 on the FEPA scale. The time of machining was between seconds, depending on the size of part diameter. ISBN:

3 Fig. Sketch of the superfinishing machine. One of the important problem that must be solved was to design a device that can be hold and center the workpiece in those three jaws. For this reason were realized for every size of workpiece a special device as can be seen in Fig.3. This device has as a body a ring (6) where are fixed by screws three small parts (4) with two balls (3) on each. This device allows to center the part and to transmit the rotational movement that is needed during the machining process. Fig.3 Device to hold the workpiece in the superfinishing machine. ISBN:

4 3 Factors that influence the workpiece surface finish To obtain the surface finish for the workpiece is needed to take into consideration the next main factors: - the pressure of the abrasive stone over the worpiece surface; - the grain size of the abrasive stone; - the cutting speed during machining process. During the tests was used the superfinishing machine that is shown in Fig.4. This machine was build to superfinish all the range of the gears from the gearbox of a truck and is used because we need to know the optim process parameters for each of the workpiece type. Fig.4 The superfinishing machine used in machining internal surfaces of the gears. 3.1 The influence of the abrasive stone pressure on the part surface finish In Fig.5 is shown the graph of the influence of the abrasive stone on the part surface finish when was used a cutting speed of 15 m/min and an abrasive stone with grain size of 600. It can be seen that if is used a pressure of the abrasive stone on the part surface finish more than Pa, is possible to obtain the better surface quality of the part in the same processing time as with smaller presuure. The dependence between part the surface finish and pressure of the abrasive stone on the part surface is shown by equation(1): R a = 0, t 0, t + 0, (1) with an error compared with the tests results of: E r = 1, ISBN:

5 R a [ m] 1,6 1,4 1, 1,0 0,8 II I I: p=15.10 I-p=0,5x Pa MPa II-p=1,3x10 3 II: p=5.10mpa -4 III-p=,5x10 3MPa III: p= v=0m/min Pa gain size =400 V=15 m/min 0,6 0,4 III 0, t(s) Fig.5 The influence of the abrasive stone pressure on the part surface finish. 3. The influence of the grain size on the part surface finish The dependence between the surface finish and the abrasive grain size is shown in Fig.6. It was used two type of abrasive stones, with grain size of 600 and 100, maintaining the cutting speed at a value of 15 m/min and a pressure of stone on the part surface of Pa. It can be seen that in case of using abrsive stone with grain size of 100 the surface finish is with better quality for the same time of processing. Usually, two types of grain size is often used in the superfinishing machines that can have simultaneously semifinishing and finishing stations during machining. Based on mathematical programs was obtained the value of surface roughness R a according with the garin size of abrasive stone: R a = 7,6178 (grain size) -0,558 () with an error compared with the experimental values of: E r = 7, Ra [ m] 1,6 1,4 1, 1,0 I I-gain I: grain size size II-gain size II: grain size 100 v=5m/min V=15 m/min p=,5x10 3MPa P= Pa 0,8 0,6 II A 0,4 0, B Fig.6 The dependence between abrasive grain size and part surface finish. t(s) ISBN:

6 3.3 The influence of the cutting sped on the part surface finish Cutting speed has an important influence on the part surface finish specially on the machine tools with two stations of machining: semifinishing and finishing. For the finishing station the cutting speed Ra [ m] 1,6 1,4 1, 1,0 0,8 0,6 0,4 0, I II III is bigger which ensure obtaining a high surface quality of the part after processing. It was used a pressure of abrasive stone on the part surface during machining of Pa. Fig.7 shows this dependence between the cutting speed and part surface finish. I: v=0 m.min I-F=daN/cm s II: v=15 m/min II-F=1,5daN/cm s III: III-F=1daN/cm v=10 m/min s P= Pa gain size = t[sec] Fig.7 The dependence between the part surface finish and cutting speed. The value of surface roughness depending on the cutting speed is giving by the equation: R a = 0,0006 (3) Fs - 0, F s + 0,47486 with an error compared with test results of E r =, Conclusions The superfinishing machine that was presented is usefully to machining process of all types of gears that are component of a gearbox of a truck. The device of holding worpieces ensures a good centering and its simple construction gives flexibility when is changing the oart to be machined. This operation is the last in the operations plan and ensure a good roughness for internal surfaces of the gears. By this process is reduced wear, energy consumption and leads to savings in service and maintenance costs. Using application of artificial neuron network for modeling and analysis, we can predict and obtain the best process parameters of superfinishing technology for Fs each type of workpiece material and size References: [1] Yordanova S., Assenov V. and Z. Nedic. Application of Artificial Neural Networks for Linearising Control of а Non-Linear Plant, Proceedings of the 3rd Japan-Australia-New Zealand Joint Seminar JANZS 004, Auckland, New Zealand, Jan. -3, 004, pp V [] Yordanova S. and R. Tzeneva. Application of Neural Networks for Analysis in Bolted Busbar Ra Connections of New Design, Proc. of the XLIII Int. Sc. IEEE Conf. on Information, Communication and Energy Systems and ISBN:

7 Technologies ICEST 08, Serbia, Niš, 5-7 June, 008, ISBN , pp [3] Wasserman P.D. Neural Computing. Theory and Practice. ANZA Research, Inc. Van Nosrand Reinold, N.Y., 199. [4] Demuth H., M. Beale. Neural Network Toolbox for Use with MATLAB. Users Guide. The Mathworks Inc., [5] Yordanova S., A. Todorov. Investigation on Some Applications of Neural Networks in Control of Plants with Variable Parameters. In: Problems of engineering cybernetics and robotics, No47, BAS, 1998, pages [6] Yordanova S. Investigations on Neural Networks Flowrate Control. Proceedings of the WSES/MIUE/HNA Int. Conf. Mathematics & Computers in Mechanical Engineering 99 (session Computer Aided Metrology), Florida Keys, 5-9 July, 1999, ISBN: [7] Haykin S., Neural Networks: A Comprehensive Foundation. nd Edition, Prentice Hall, ISBN [8] Farago, F. T., Abrasive Methods Engineering, Vol.1, 1976, New York: Industrial Press. [9] Borokowski, J., and A. Szymanski., Uses of Abrasives and Abrasive Tools. Chichester, Eng,: Ellis Horwood, 199. [10] King, R. I., and R.S. Hahn., Handbook of Modern grinding Technology. New York: Chapman and hall/methuen [11] McKee, R.L., Machining with Abrasives. New York: Van Nostrad Reihold, 198. [1] Lepadatescu, B, Dumitrascu, A.E., Enescu, I., Nedelcu, A. Research regarding the improvment of workpieces surface finish by machining through superfinishing process. In : Proceedings of the 4 th International Conference on Manufacturing Engineering Quality and Production Systems, Barcelona, Spania, Septembrie 011., pag , ISBN: [13] W. W. Thierheimer, N., łane, D. C. Thierheimer - Tehnical system to controlling of suspension with direction, în Annals of DAAAM for 009 & Proceedings of 0th DAAAM World Symposium, Included in ISI/SCI Web of Science and Web of Knowledge, 5-8 November 009, ISSN , pp , Vienna, Austria. [14] Lepadatescu, B., Fota, A., Nedelcu, A., Buzatu, C., Dumitrascu, A.E., Enescu, I. Flexible Superfinishing Modules used in SME (Small and medium Enterprises). In: Proceedings of the 8 th WSEAS International Conference on SIGNAL PROCESSING, ROBOTICS and AUTOMATION (ISPRA 09), Cambridge, UK, February 1-3, 009; pag.86-90, ISSN: , ISBN: ISBN: