Mathematical Methods and Optimization Techniques in Engineering
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 2) ANISOR NEDELCU3) 1), 2), 3)Transilvania University of Brasov, Faculty of Technological Engineering and Industrial Management, B dul Eroilor nr.29, Brasov ROMANIA [email protected], [email protected], [email protected]
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 8 m thick and is created by high temperature regard to load bearing capacity, efficiency, generates by the grinding wheel. It enables the user smoothness of running, operational safety, and last to achieve virtually any surface texture parameter, but not least, longevity, requires superior surface because only the roughness peaks are removed. The finishing of these workpieces. By logical extension, geometry of the workpiece remains unchanged. this means continuous adaptation and optimization of The main advantage of this method is consistent existing production processes. The superfinishing finish over the entire surface. Superfinish improves process gives to workpieces as called “final touch”, the bearing ratio resulting in greatly improved wear being an economical machining operation and resistance. Stock removal is typically in the order of tipically the last and therefore the quality a few microns. The achievable surface finish quality determining process, that makes it more important. is comparable to levels reached only by honing or Some of the advantages of using superfinishing lapping. Superfinishing process is a very clean process are presented below: process, because coolant or grinding emulsion is used High flexibility; of honing oils like Stone grinding. Recycling and Low noise volume; waste disposal are simplified. Low energy costs; This process is suitable for any material that could Low initial investment; also be finished with geometrically undefined blades. Low tool costs; In addition to the most diverse metal alloys and Less friction; grades, other materials can also be finished, such as Short processing time. ceramics, plastics, non ferrous metals as well as The superfinishing process allows the targeted coatings, such as tungsten carbide , chromium, or influencing of the following parameters: copper. Reduction of surface peak to valleys and After the process of superfinishing the workpiece increase of material contacta rea to over 90%, due to surface has a tightly controlled cross hatch patter, the plateau like surface structures; obtained by the interaction of three interrelated Improvment of roundness, creation of motions. These motion are the oscillation of the microgeometries with particular applications; stone, rotary movement of the workpiece and Optimization of tribological properties through pressure of the abrasive tool on the workpiece. criss crossinf finishing marks. During the superfinishing process, parts pass through Superfinishing removes the amorphous structure of several distinc phases. When the abrasive tool makes the material, or ‘soft skin”. This layer is usually 2 to initial contact with the part, dull grains fracture or
ISBN: 978-960-474-339-1 171 Mathematical Methods and Optimization Techniques in Engineering
pull away from the matrix to produce a new cutting gearbox of the truck are a lot of gears with different surface. As the tool “self dresses”, relatively large diameters that are used as the intermédiate gears, amounts of stock removal phase, abrasive grains without transmitting the torque, only to transmit the begin to dull, while surface irregularities and rotary motion to other shafts. For this reason, these geometry continue to improve. This results in a gears have the internal surfaces smoothly and these cross hatced surface free of irregularities and surfaces need to have a very high surface finish in the amorphous material. values of roughness between 0,4 0,2 m Ra. The previous process is grinding and the last machining process is superfinishing that gives the final 2 Machine to superfinish the internal dimension and roughness for these internal surfaces. These gears from the gearbox have an internal surfaces of the gears diameters between Ø 35 110 mm and the width In this paper is presented a machine to superfinish the between 20 50 mm. One of these gears is shown in internal surfaces of the gears which are components Fig.1. of a gearbox of the truck. It is known that in the
Fig.1 Gear with internal surface obtained after the process of superfinishing.
To can machining all these types of gears was with the internal diameter of the workpiece) makes designed a machine that is presented in the sketch of contact with the internal surfaces of the part. During Fig.2. In this figure the workpiece (4) is held in jaws the superfinishing process were used abrasive stones (3) and has a rotational motion through the machine with silicone carbide, which is a combination of pure gearbox (1). The superfinishing head has a oscillation white quartz, petroleum coke, sawdust and salt in an movement with the amplitude of 1 3 mm and a electric furnace. frequency of 1500cd/min. These oscillation To achieve the desired surface finish was used movement is realized by the motor (8) and the abrasive materials with fine grit sizes between 400 mechanism (7). and 1200 on the FEPA scale. It is used a plunge process when the workpiece is The time of machining was between 30 40 seconds, held and rotated, while the superfinishing multistone depending on the size of part diameter. (the superfinishing stones are between 3 6, according
ISBN: 978-960-474-339-1 172 Mathematical Methods and Optimization Techniques in Engineering
Fig.2 Sketch of the superfinishing machine.
One of the important problem that must be solved This device has as a body a ring (6) where are fixed was to design a device that can be hold and center the by screws three small parts (4) with two balls (3) on workpiece in those three jaws. For this reason were each. This device allows to center the part and to realized for every size of workpiece a special device transmit the rotational movement that is needed as can be seen in Fig.3. during the machining process.
Fig.3 Device to hold the workpiece in the superfinishing machine.
ISBN: 978-960-474-339-1 173 Mathematical Methods and Optimization Techniques in Engineering
3 Factors that influence the workpiece surface finish the cutting speed during machining process. To obtain the surface finish for the workpiece is During the tests was used the superfinishing machine needed to take into consideration the next main that is shown in Fig.4. This machine was build to factors: superfinish all the range of the gears from the the pressure of the abrasive stone over the worpiece gearbox of a truck and is used because we need to surface; know the optim process parameters for each of the the grain size of the abrasive stone; 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 The dependence between part the surface finish and In Fig.5 is shown the graph of the influence of the pressure of the abrasive stone on the part surface is abrasive stone on the part surface finish when was shown by equation(1): used a cutting speed of 15 m/min and an abrasive 2 stone with grain size of 600. It can be seen that if is Ra = 0, 00404∗ t – 0,036634∗ t + 0,937818 used a pressure of the abrasive stone on the part (1) surface finish more than 25.10 4 Pa, is possible to with an error compared with the tests results of: Er = obtain the better surface quality of the part in the 2 same processing time as with smaller presuure. 1, 24441∗ 10 .
ISBN: 978-960-474-339-1 174 Mathematical Methods and Optimization Techniques in Engineering
Ra [ m] 4 I p=0,5x10I: p=15.103 MPaPa 1,6 3 II p=1,3x10II: p=25.10 MPa 4 Pa 1,4 III p=2,5x10 3 MPa III: p=35.10 4 1,2 v=20m/minPa 1,0 I gain size =400 V=15 m/min 0,8 II 0,6 0,4 III 0,2
010 20 30 40 50 60 70 80 90 t(s)
Fig.5 The influence of the abrasive stone pressure on the part surface finish.
3.2 The influence of the grain size on the part simultaneously semifinishing and finishing stations surface finish during machining. The dependence between the surface finish and the Based on mathematical programs was obtained the abrasive grain size is shown in Fig.6. It was used two value of surface roughness Ra according with the type of abrasive stones, with grain size of 600 and garin size of abrasive stone: 1200, maintaining the cutting speed at a value of 15 0,558 m/min and a pressure of stone on the part surface of Ra = 7,622178∗ (grain size) 25.10 4 Pa. It can be seen that in case of using abrsive (2) stone with grain size of 1200 the surface finish is with better quality for the same time of processing. with an error compared with the experimental values 3 Usually, two types of grain size is often used in the of: Er = 7,8632∗ 10 . superfinishing machines that can have
Ra [ m] I gainI: grain size size 600 600 II gain size 600 1000 1,6 II: grain size 1200 1,4 v=25m/minV=15 m/min I p=2,5x10 3 MPa 1,2 P=25.10 4Pa 1,0 0,8 II 0,6 A 0,4 0,2 B
0 15 30 45 60 75 t(s) Fig.6 The dependence between abrasive grain size and part surface finish.
ISBN: 978-960-474-339-1 175 Mathematical Methods and Optimization Techniques in Engineering
3.3 The influence of the cutting sped on the is bigger which ensure obtaining a high surface part surface finish quality of the part after processing. It was used a pressure of abrasive stone on the part surface during 4 Cutting speed has an important influence on the part machining of 25.10 Pa. Fig.7 shows this surface finish specially on the machine tools with dependence between the cutting speed and part two stations of machining: semifinishing and surface finish. finishing. For the finishing station the cutting speed Ra [ m] I: v=20 m.min 2 I F=2daN/cms 1,6 II: v=15 m/min 2 II F=1,5daN/cms 1,4 III: v=10 m/min2 III F=1daN/cms 4 1,2 P=25.10 Pa gain size =600 1,0 III 0,8 0,6 I 0,4 II 0,2
5 10 15 20 25 30 35 40 45 50 t[sec] Fig.7 The dependence between the part surface finish and cutting speed.
The value of surface roughness depending on the The device of holding worpieces ensures a good cutting speed is giving by the equation: centering and its simple construction gives flexibility when is changing the oart to be machined. This 2 operation is the last in the operations plan and ensure Ra = 0,00026∗ Fs 0,006408∗ Fs + 0,474286 a good roughness for internal surfaces of the gears. (3) By this process is reduced wear, energy consumption
and leads to savings in service and maintenance with an error compared with test results of E = r costs. 2,5463∗ 10 3 . Using application of artificial neuron network for modeling and analysis, we can predict and obtain the
4 Conclusions best process parameters of superfinishing technology The superfinishing machine that was presented is for Fseach type of workpiece material and size usefully to machining process of all types of gears that are component of a gearbox of a truck.
V References:
[1] Yordanova S., Assenov V. and Z. Nedic. [2] Yordanova S. and R. Tzeneva. Application of Application of Artificial Neural Networks for Neural Networks for Analysis in Bolted Busbar Linearising Control of а Non Linear Plant, RaConnections of New Design, Proc. of the XLIII Proceedings of the 3rd Japan-Australia-New Int. Sc. IEEE Conf. on Information, Zealand Joint Seminar JANZS’2004, Auckland, Communication and Energy Systems and New Zealand, Jan. 22 23, 2004, pp.165 171.
ISBN: 978-960-474-339-1 176 Mathematical Methods and Optimization Techniques in Engineering
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