Analysis of Effect of Ball and Roller Burnishing Processes on Surface Roughness on EN8 Steel

Analysis of Effect of Ball and Roller Burnishing Processes on Surface Roughness on EN8 Steel

Mr. N. M. Qureshi Mr. Vaibhav B. Patil, Mr. Basavaraj D. Teli, Assistant Professor (Mechanical Engineering) Miss. Radhika S. Mohite and Miss. Sonal S. Patil

1. Y. Patil College of Engineering and Technology, Dist-Kolhapur, Maharashtra, India.

   Abstract – This experimental study focuses on effect of various parameters and optimization of burnishing processes on surface finish of EN8 material during burnishing operation. In industry area use various surface finishing operations such as lapping, honing, etc. which is removal of the material from its surface. In the present experimentation, ball and roller burnishing processes which is plastic deformation are used with varying machining parameters to achieve the desirable surface finish. The experiment is carried out on the CNC machine of a particular job of EN8 material. By use of the Taguchi methodology optimum machining parameters obtained gives improved surface finish.

   Keywords- Surface Finish, Ball and Roller Burnishing process, Taguchi Methodology.

   1. INTRODUCTION

      In this cold-working method, a large contact pressure is exerted on the surface of the work piece by a smooth roller or a ball burnishing tool to cause plastic deformation of surface irregularities without removing the material. The high burnishing pressure exceeding the yield strength causes roughness peaks to flow towards the valleys which suppress all the texture of the rough surface, resulting in smoother surfaces [1]. The burnishing process produces a good surface finish, increases dimensional and shape accuracy, enhances surface hardness and also induces residual compressive stresses at the metallic surface layers [2]. This method can be carried out using conventional machines, such as lathe machine. On account of its high productivity, it also saves more on production costs than other conventional processes such as super finishing, honing and grinding. Moreover, the burnished surface has a high wear resistance and better fatigue life [2].

      The figure 1 shows the actual mechanism of burnishing process of plastic deformation with the movement of burnishing tool over the work piece. By use of the Taguchi methodology the burnishing parameters are analysed and optimisation to achieve considerable surface finish [6].

      Figure 1: The mechanism of burnishing process

      BE MECHANICAL, Department of Mechanical Engineering; D. Y. Patil College of Engineering and Technology, Dist-Kolhapur, Maharashtra, India.

   2. BENEFITS OF BURNISHING PROCESS Burnishing process can provide the following

      benefits especially as following,

      1. Polished surface finish

      2. Dimensional Consistency and accuracy

      3. Minimize the reworks and rejections

      4. More utilization of machining capabilities

      5. No chip accumulation

   3. THE EFFECT OF VARIOUS BURNISHING PARAMETERS ON SURFACE ROUGHNESS

      1. Depth of Penetration

         As increase in the depth of Penetration results increase in burnishing force, the roughness value decreases up to a certain point and then starts to increase. The force at that point is termed the optimum force and optimum depth of penetration. It depends on various factors: material being burnished, burnishing speed, ball diameter, pre-machined surface finish, feed-rate and frequency of oscillation [3].

      2. Feed-rate

         The height of the irregularities and hence the transverse surface roughness is determined by the feed-rate of the ball which is in the general range of 0.1 to 0.2 mm/rev. The figure 2 shows a smaller feed-rate f2 gives irregularities of lower height p, and hence better surface finish. The use of feed-rate is dependent on other factors such as ball diameter, burnishing speed and depth of penetration. With a larger ball diameter, the feed-rate can be increased as the factors have opposite effects on the surface irregularities. Figure 2 shows the height of the irregularities (shaded area) formed by varying the feed-rate [3].

         Figure 2: Effect of feed-rate on the surface roughness

      3. Burnishing speed

         As the speed increases the surface roughness start to decreases due to increases in compressive deforming force and the stability of burnishing tool at high speed. But up to a certain value of speed then it starts to decrease.

      4. Number of burnishing passes

         When number of passes is used more, more surface irregularities are suppress into the valley which reduce the surface roughness, but the number of passes must be optimum to avoid increase in machining cycle time.

      5. Burnishing tool size

      The height of irregularities is inversely proportional to tool contact size used as more contact area between work piece and tool. Thus, as the burnishing tool size increases surface finish improves [3].

   4. WORK PIECE MATERIAL AND ITS PROPERTIES

      EN8 also known as 080M40 unalloyed medium carbon steel. It is a medium strength steel, and has good tensile strength.

      1. EN-8 Steel (080M40) Specifications

         Table I

         Chemical Composition (In Percentages)

         C	Mn	Si	P	S
         0.35-0.45	0.60	0.35	0.015	0.015-0.6

      2. Mechanical Properties

         • Hardness = 201 to 255 BHN.

         • Yield stress = 465 MPa.

         • Max Stress = 700 to 850 MPa.

         • Tensile Stress = 550 MPa.

         • Elongation % = 16.

         • Length of each compartment= 40mm.

         • Diameter= 30mm.

         • Number of trial compartments for each process= 16.

   5. TOOL MATERIAL AND PROPERTIES

      Figure 3: The roller burnishing tool

      Figure 4: The ball burnishing tool

      Parts used for tool assembly are

      1. Ball bearing:

         • Hardness of bearing of outer case= 700 BHN.

         • Surface roughness value= 0.12 micron.

         • Inner diameter= 20 mm.

         • Outer diameter= 42 mm.

         • Face width= 12 mm.

      2. Roller holder

      3. Cylindrical pin

      4. Side bush, Allen screw for holding bearing in the tool at exact center [9] [12].

         Table II

         Chemical composition of ball bearing (In percentage)

         C	Cr	Mn	Si	Ni
         1.05	0.13	0.05	0.03	0.018

         • Ball hardness= 771 BHN.

         • Ball surface roughness= 0.12 micron.

   6. METHODOLOGY

   7. EXPERIMENTAL SET UP

      The experiment is carried out on CNC Machine. The set-up is as shown in figure 6 and 7.

      Figure 5: Photograph of CNC Machine

      Table III

      CNC Machine specifications

      The experiment is performed on CNC machine on each compartments of work piece with the different parameters as shown in figure 6 and 7. Total L16 experimental runs were carried out as shown in table IV.

      Figure 6: Ball burnishing process on CNC Machine

      Figure 7: Roller burnishing process on CNC Machine

      • Total number of trial taken for each process = 16.

      • Trial compartment diameter 30 mm and 40 mm length.

      Table IV

      Machining Parameters and their levels for Ball Burnishing and Roller Burnishing Processes

      Parameters	Level 1	Level 2	Level 3	Level 4
      Speed (rpm)	200	500	800	1100
      Feed (mm/rev)	0.05	0.3	0.7	1
      Depth of Penetration (mm)	0.2	0.3	0.4	0.5
      Number of passes	1	2	3	4

      The Experiments are performed as per Taguchi methodology with L16 orthogonal array created in Minitab- 17 software. The range of the burnishing parameters used in this experiment shown in Table V and Table VI.

   8. WORK PIECE AFTER BURNISHING

      Figure 8: Burnished work piece

      The surface roughness of burnished work piece is measured by use of Mitutoyo Surface Roughness Tester SG 210 as shown in figure 9 and Table V and VI shows the Roughness Average (Ra) value of Roller burnishing and Ball burnishing process respectively.

      Figure 9: Photograph of Surface Roughness testing set up

      Table V: Ra value for Roller Burnished components:

      Sr. No.	Speed (rpm)	Feed (mm/rev)	DOP (mm)	NOP	Surface Roughness Ra (micron)
      1	200	0.05	0.2	1	1.219
      2	200	0.30	0.3	2	1.574
      3	200	0.70	0.4	3	1.472
      4	200	1.00	0.5	4	1.216
      5	500	0.05	0.3	3	1.259
      6	500	0.30	0.2	4	1.475
      7	500	0.70	0.5	1	1.614
      8	500	1.00	0.4	2	1.174
      9	800	0.05	0.4	4	0.207
      10	800	0.30	0.5	3	0.400
      11	800	0.70	0.2	2	0.387
      12	800	1.00	0.3	1	0.502
      13	1100	0.05	0.5	2	0.114
      14	1100	0.30	0.4	1	0.241
      15	1100	0.70	0.3	4	0.429
      16	1100	1.00	0.2	3	2.533

      Table VI: Ra value for Ball Burnished components:

      Sr. No.	Speed (rpm)	Feed (mm/rev)	DOP (mm)	NOP	Surface Roughness Ra (micron)
      1	200	0.05	0.2	1	1.916
      2	200	0.30	0.3	2	0.618
      3	200	0.70	0.4	3	1.112
      4	200	1.00	0.5	4	0.918
      5	500	0.05	0.3	3	0.162
      6	500	0.30	0.2	4	0.343
      7	500	0.70	0.5	1	1.002
      8	500	1.00	0.4	2	1.588
      9	800	0.05	0.4	4	0.770
      10	800	0.30	0.5	3	1.405
      11	800	0.70	0.2	2	1.598
      12	800	1.00	0.3	1	1.180
      13	1100	0.05	0.5	2	0.490
      14	1100	0.30	0.4	1	0.639
      15	1100	0.70	0.3	4	1.082
      16	1100	1.00	0.2	3	1.225

      *DOP: Depth of Penetration, NOP: Number of Passes

   9. TAGUCHI ANALYSIS

      The experimental results are transferred to a mean to mean ratio with the criteria smaller-the-better is used to determine the surface quality by use of minitab-17 software. The response table of the analysis as shown in Table VII and VIII and corresponding graph of main effect for means for same.

      Table VII

      Response table for means for Roller Burnishing:

      Level	Speed	Feed	DOP	NOP
      1	1.3703	0.6997	1.6535	0.8940
      2	1.3805	0.9225	0.9410	1.0622
      3	0.6240	1.2255	0.7735	1.4160
      4	0.8293	1.3562	0.8360	0.8317
      Delta	0.7565	0.6565	0.8800	0.5843
      Rank	2	3	1	4

      Figure 10: Main Effect Plot for Means

      Table VIII

      Response table for means for Ball Burnishing:

      Level	Speed	Feed	DOP	NOP
      1	1.1410	0.8350	1.2705	1.1843
      2	0.7738	0.7512	0.7605	1.0740
      3	1.2382	1.1985	1.0273	0.9760
      4	0.8595	1.2277	0.9543	0.7783
      Delta	0.4645	0.4765	0.5100	0.4060
      Rank	3	2	1	4

      Figure 11: Main Effect Plot for Means

   10. CONCLUSIONS

In this experimentation, the burnishing speed, feed, depth of penetration & number of passes these all factors are optimized by using TAGUCHI Methodology.

Experimented results at predicted optimum level for Roller Burnishing from figure 10:

Speed	Feed	DOP	NOP
800	0.05	0.40	4

Experimented results at predicted optimum level for Ball Burnishing figure 11:

Speed	Feed	DOP	NOP
500	0.30	0.30	4

REFERENCES

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3. N. H. Loh and S. C. Tam, Effects of ball burnishing parameters on surface finish A literature survey and discussion, Precision Engineering 0141635, 9/88/040215 © 1988 Butterworth & Co (Publishers).

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