Optimization of Generation Gear Grinding Process

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Optimization of Generation Gear Grinding Process

Ankit V Gujrathi1

Integrated Product Development Engineer, Sanjeev Auto Parts Manufacturers Pvt. Ltd, Maharashtra, India.

Abhijit Wagp

Abhijeet Dalvi2

Integrated Product Development Engineer, Sanjeev Auto Parts Manufacturers Pvt. Ltd, Maharashtra, India.

Integrated Product Development Engineer, Sanjeev Auto Parts Manufacturers Pvt. Ltd, Maharashtra, India.

Abstract One of the main challenges in generation gear grinding is the establishment of an optimized grinding process. The objective of this paper was to design a more productive grinding process through the reduction in grinding time for a specific machine, in this case, LCS 380 Liebherr Machine. This paper presents the study carried by swapping to the precision shaped grinding (Cubitron II) wheels and altering the process parameters thereby optimizing the process. The relationship of the cutting parameters such as the cutting speed and the axial feed has been studied and their results have been recorded and measured in terms of the Maximum Material Removal Rate, Specific Material Removal Rate, and the Theoretical Average Chip Thickness. The impact of these test results on the output per hour and cycle time of the process has also been investigated. Finally, the quality of the process and validation of all material properties has been done.

KeywordsProcess optimization; Maximum Material Removal Rate; Specific Material Removal Rate; Theoretical Average Chip Thickness; Cubitrom II

  1. INTRODUCTION:-

    With an increase in the demand of a stringent gear quality to enhance the life of gear box and to reduce the noise level, the continuous generation grinding process has gained much demand [2]. This process uses a threaded grinding wheel (abrasive material) and a diamond dresser as cutting tools for the grinding process. Although this process has been a well- established process, only limited scientific knowledge of the process exists [1]. Grinding is an abrasive machining process which uses a grinding wheel as a cutting tool. It is suited for machining of hardened parts. Each grain of grinding wheel acts as a single point cutting tool and removes material in the form of tiny chips. It employs the use of the abrasive wheel in controlled contact with a workpiece. The cutting modes in grinding process correspond to heat dissipation. Since this energy is not consumed for chip formation but also by friction and the penetrated and plastically deformed workpiece, the heat is distributed in varies ways depending on the interaction on the tool and the workpiece. The different zones shown in the fig below correspond to the various zones such as 1-elastic deformation, 2-elastic and plastic deformation, and 3-elastic and plastic deformation and chip formation [11]. When an excess of heat is transferred to the workpiece and the critical

    temperature is reached, the thermal overload can cause various surface undulations, the major of them being the grinding burn.

    Fig.1 Stages of material deformation during formation of chips

    Till date, grinding was considered as a process where machining takes place with the help of geometrically unspecified cutting edges, as specified in DIN 8580. But with the new Precision-Shaped abrasive Grains (PSG) developed by 3M, grinding with geometrically defined cutting edges is possible. The PSG wheels, also known as Cubitron II wheels, generate a free-flowing chip during grinding similar to that in milling, but much finer. These chips no longer clog up the grinding wheel thereby preventing the loss in cutting ability of the grinding wheel and reducing the risk of grinding burn with better profile accuracy [9], [11].

    Fig. 2- Less material deformation and lateral build up

    Each individual ceramic of the Cubitron II wheels are identical in size and are precisely formed triangles of sintered aluminum oxide. The heat generated is dissipated directly through chips, hence minimizing the risk of thermal damage [10]. While dressing these PSGs break as minute triangular shaped particles compared to the irregular pattern of regular ceramic wheels. This results in an improved dressing cycle and reduces the load on dresser [9], [11].

    Fig. 3 Dressing of standard ceramics and PSG wheel

  2. PROBLEM IDENTIFICATION

    Fig. 4 Essential variables influencing the grinding process

    As the grinding process is dynamic, even a slightest of unbalance cutting force can alter the working temperature and result in grinding burn or create a parasitic or ghost frequency, which severely deteriorates the gear life [7]. Improper gear grinding results in following issues-

    • Grinding burn- It is the interaction between the abrasive grains of the grinding wheel and the flank of workpiece [3]. At the onset of grinding burn, the grinding forces and the rate of wheel wear increases abruptly, thereby deteriorating the surface finish of the gear flank [4].It generates a re-hardened zone near to the surface and a softened, tempered zone beneath it [4],[12].

    • Variation in profile and lead accuracy- Due to contacting conditions for continuous gear grinding, changing cutting forces can result in an unfavorable process dynamics and deviation in lead and profile accuracy [1].

    • Required surface roughness- One can define the characteristics of grinding wheels for optimal grinding process by keeping in mind the relation between the grit size of the wheel and the achievable surface roughness on gear [6].

    • Variation in case hardness- Abusive grinding of the workpiece leads to tempering of the gear and reduces surface hardness. Severe tempering often causes local re-hardening which in turn results in surface cracks [8].

    The impact of cutting speed and the axial speed have been studied so as to achieve a benchmarking result in Continuous Gear Grinding process. To achieve an optimal working condition, one needs to understand the relationship of grinding parameters like chip thickness, surface speed, specific material removal rate and the maximum material removal rate [2],[5], [10].

  3. EXPERIMENTATION

In order to study the impact of the process parameters on the grinding process, 5 components were selected as per the gear geometry and case depth requirement. All the components have been worked with the Cubitron II grade wheels manufacture by 3M. This experiment was carried out on Liebherr make LCS 380 Gear Grinding Machine (vc max= 63m/s) and conducted at K-96 plant, Gear Excellence Division, of Sanjeev Auto Parts Manufacturers Pvt. Ltd. with the help of 3M working program.

Fig.5 Geometric data of gears

Fig.6 Process parameters

  1. Maximum Material Removal Rate (Qmax) – It ascertains whether the performance potential of a given machine model has been fully used. It removes the chip volume in mm3 that can be removed in one second.

    Qmax= ((aemax*hev*ns*gg*fzmax*30)/cosß) hev=2.25*m

    ns- RPM of the Worm wheel

    gg- No. of starts of the grinding worm

    fzmax- Max axial feed rate of the workpiece (mm/rev) cosß- Cosine of helix angle

    Graph 1: Achieved max. material removal rate

  2. Specific Material Removal Rate (Qw)- It indicates how many mm3 one(1) mm wheel width removes per second (mm3/mm/sec).

    Qw= ae effective*vf ae effective= sinnax

    vf= ((z*zg*ns*sz)*60*cosß) z- No. of teeth on workpiece

    zg- No. of starts on grinding worm

    sz- radial feed in mm/rev of workpiece ax- Total depth of cut (mm)

    sinn sine of pressure angle

    Graph 2: Achieved specific mateial removal rate

  3. Theoretical Average Chip Thickness (hmom)- It is the most important parameter for the setting up and evaluation of all grinding processes. During the grinding process ships are compressed, pulled and/or welded together in a manner that cannot be established mathematically. The hmom together with the given parameters such as depth of cut ae, feed rate vw, and surface speed vc, corresponds to the resulting depth of penetration of the individual grain halfway to the arc of contact.

    hmom= (1000*Qw)/vc

    Qw- Specific material removal rate (mm3/mm/s) vc- – Surface speed of grinding worm

    Graph 3: Achieved theoritical chip thickness

  4. PROCESS VALIDATION-

  1. Gear accuracy-

    The components processed with the optimized parameters have been inspected on the Klingelnberg P40 machine and the results for the angular errors (fH and the fhß) have been shared. Furthermore, the results of standard deviation for profile (f*) and lead (fß*) have been studied and recorded. The standard deviation is the total displacement of the actual angular error caused during the grinding process. It gives an indication of the process variation and is a crucial parameter for establishing a stable process.

    Fig.7 Lead and profile graph of component 1324.304.021

    Graph 4: Variation in fH- left flank

    Graph 5: Variation in fH- right flank

    Graph 6: Variation in fHß- left flank

    Graph 7:Variation in fHß- right flank

  2. Surface roughness of flank- The surface roughness has been measured across the gear and along its face width. Their measuring data has been recorded and the achievable surface roughness is between 2.1-3.6µm.

  3. Nital Etching test- As the gear grinding process involves high contact between workpiece and wheel it is extensively sensitive to grinding burn, hence microethcing with dilute HNO3 is to be done.

    The following sequence illustrates the setup of the Nital Etching procedure carried out on Reischauer Nital Etching Equipment. The workpiece is immersed in a prescribed sequence in tanks containing different acid solutions and intermittent water tanks for cleaning and neutralizing. This procedure makes grinding burn visible.

    Fig.8 Sequence of grinding burn testing

    SANJEEV GROUP OF COMPANY

    Burn Test Procedure

    Sr.No.

    Process

    Solution

    Bath Temprature

    Process Time

    1

    Cleaning Of Component

    Biological Solution

    Room Temperature

    10 Sec – 15 Sec

    2

    Rinsing

    Warm Water

    35°C-45°C

    10 Sec – 15 Sec

    3

    Drying

    Dry Compressed Air

    10 Sec

    4

    Degreassing

    Potassium Hydroxide Amines

    Salt Of Organic Acids

    Room Temperature

    2 Min

    5

    Rinsing

    Warm Water

    35°C-45°C

    10 Sec – 15 Sec

    6

    Drying

    Dry Compressed Air

    10 Sec

    7

    Etching

    Denatured Ethyl Alcohol Nitric Acid 8% Vol.

    Room Temperature

    2 Min 30 Sec – 2 Min 45 Sec

    8

    Rinsing

    Warm Water

    35°C-45°C

    10 Sec – 15 Sec

    9

    Drying

    Dry Compressed Air

    10 Sec

    10

    Bleaching

    Denatured Ethyl Alcohol Hydrocloric Acid 8% Vol.

    Room Temperature

    1 Min 30 Sec – 1 Min 45 Sec

    11

    Rinsing

    Warm Water

    35°C-45°C

    10 Sec – 15 Sec

    12

    Cleaning

    Isopropenol

    10 Sec

    13

    Drying

    Dry Compressed Air

    10 Sec

    14

    Visual Inspection for Burn

    s

    The above procedure is in accordance with ZFN 5013 and ISO 14104. Grinding abuse becomes noticeable where a black colour shows the areas affected by the grinding abuse.

    Fig.8 Image of gear flank after grinding burn test

  4. Metallurgical inspection-

    The metallurgical inspection of the above components has been done and the data for parameters have been recorded. The testing of these parts has been done in the met-lab facility available at C4 plant of Sanjeev Auto parts.

    Fig.9 Metallurgical data results

    Graph 8: Comparison of before and actual cycle time

    Graph 9: Increase in the output per hour

    ACKNOWLEDGMENT

    Our sincere thanks to all the members of the K96 unit and C4 unit for their support in the study and experimentation. A special thanks to our HOD, Mr. Mangesh M. Kulkarni our manager Mr. VK Deshapnde Sir for their support and gratitude.

  5. RESULTS AND CONCLUSION

The material removal with each abrasive grain on grinding wheel surface is the fundamental of grinding. During grinding, rubbing and ploughing are uneffective in terms of material removal, only cutting action is ideal [11]. The above results conclude that the above conducted experiment has been successfully validated. The achievable Qmax, Qw and hmom with the use of Cubitron II wheels has substantially increased and has delivered successful results. The comparision of cycle time and ouput per hour, before and after conducting this experiment, have been shared herewith.

REFERENCES

  1. C. Brechera, M. Brumma and F. Hübnera, Approach for the Calculation of Cutting Forces in Generating Gear Grinding, 9th CIRP Procedia CIRP 33, pp. 287 292, 2015.

  2. B. Karpuschewski (1)*, H.-J. Knoche, M. Hipke, Gear finishing by abrasive processes, CIRP Annals – Manufacturing Technology 57, pp. 621640, 2008.

  3. F. Del Re1 · M. Dix2 · F. Tagliaferri3, Grinding burn on hardened steel: characterization of onset mechanisms by design of experiments, The International Journal of Advanced Manufacturing Technology, December 2018.

  4. R. Deiva Nathan, L. Vijayaraghavan, R. Krishnamurthy, In-process monitoring of grinding burn in the cylindrical grinding of steel, Journal of Materials Processing Technology 91, pp. 3742, 1999.

  5. K Mekala et al., Optimization Of Cylindrical Grinding Parameters Of Austenitic Stainless Steel Rods (Aisi 316) By Taguchi Method, International Journal of Mechanical Engineering & Robotics Research 2014, Vol. 3, No. 2, April 2014.

  6. Sergiu Mazuru, Serghei Scaticailov, and Ion Stingaci, Grinding of the gears with high depth Processing, MATEC Web of Conferences 112, November 2017.

  7. Handbook Gear Grinding 3M Abrasive Systems Division, USA, 2014.

  8. Rex Newman, Hard Finishing by Conventional Generating and Form Grinding, presented at the AGMA Gear manufacturing Symposiom, April 1-3, 1990.

  9. Walter Graf,Cubitron II: Presision-Shaped Grain (PSG) Turns the Concept of Gear Grinding Upside Down, May 2014.

  10. 3M Conventional Grinding Wheels catalogue, 2016.

  11. Xun Chen & Tahsin T. Öpöz, Effect of different parameters on grinding efficiency and its monitoring by acoustic emission, Production & Manufacturing Research Journal, VOL 4, NO-1,pp. 190208, 2016.

  12. Emma Domare, Generating gear grinding- An analysis of grinding parameters effect on gear tooth quality, Faculty of Health Science and Technology, Karlstads University, 2018.

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