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A case study on the abrasive surface finishing of aluminum flat sheet
Wear 258 (2005) 13–17
A case study on the abrasive surface finishing of aluminum flat sheet Pradip K. Saha∗ The Boeing Company, MC 19-FT, P.O. Box 3707, Seattle, WA 98124-2207, USA Received 22 December 2003; received in revised form 18 March 2004; accepted 24 March 2004 Available online 8 October 2004
Abstract A case study of a unidirectional abrasive metal removal process applied on aluminum flat sheet in manufacturing processes is presented. A series of tests were conducted using belt type abrasive media of varying equivalent grit sizes on both bare and clad aluminum flat sheet. Samples were processed through each media in the longitudinal, transverse and angular orientations with respect to the rolling direction to quantify and qualify the metal surface as well as the abrasive media. In clad aluminum, a layer of pure aluminum metallurgically bonded to a substrate by rolling process, is used for appearance and corrosion resistance in aircraft component applications. An optical microscope was used to investigate the relationship between the equivalent grit sizes of the abrasive media and the maximum penetration depth into the clad layer after the directional abrasive process. Measurements of groove depths on the edges of the 2024 clad aluminum sheet samples were conducted after processing through abrasive belt media of equivalent abrasive grit sizes, varying from 180 to 320. It was found that any abrasive belt media with equivalent grit size below 320 may be inappropriate to process clad aluminum sheet due to penetration of the abrasive into the clad layer which can expose the substrate aluminum alloy to the atmosphere. © 2004 Elsevier B.V. All rights reserved. Keywords: Tribology; Abrasive media; Clad aluminum; Groove depth
1. Introduction In recent years, Tribology has received increasing attention by industry to explain the interrelation between friction and wear principles and practices [1]. Without this science, an abrasive metal removal process would be impossible to characterize/quantify when the surfaces are in relative motion. In order to study and have a better understanding of wear, it is essential to recognize several mechanisms of wear. Burwell [2] made an excellent survey and listed four mechanisms including adhesive wear, abrasive wear, corrosive wear and surface fatigue. Schey [3] provided a useful review of the wear process in metal forming operations. Abrasive wear covers generally two types of situations. In both cases wear occurs by the plowing-out of softer material of a given volume by the harder indenters of an abrasive surface. In the first instance a rough, harder abrasive surface slides against a softer metal ∗
Tel.: +1 206 655 0360; fax: +1 206 662 0453. E-mail address: [email protected].
0043-1648/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.wear.2004.03.023
surface. In the second case abrasion is caused by loose hard particles sliding between the rubbing abrasive and metal surfaces. Kalpakjian [4] also provided an excellent review of abrasive processes and finishing operations. The size of an abrasive grain (grit) is identified by a number. The smaller the grain size, the larger the number is. A given surface is scored only if it is softer than the abrasive. It is therefore not surprising that resistance to abrasive wear is a function of a material’s hardness. Many investigators have confirmed that hardness is the most important parameter in abrasive wear. Kruschov [5] plotted resistance to wear against hardness for a range of annealed pure metals, obtaining a linear relationship. He also found that prior workhardening of the pure metals had no effect on the wear rate. Richardson [6] has shown that if wear resistance is studied as a function of the ratio of the hardness between the metal surface and the hardness of the abrasive, then the wear resistance increases rapidly as the ratio becomes greater than 0.8. The process of removing burrs as an undesirable projection of material resulting from a cutting, forming, blanking
14
P.K. Saha / Wear 258 (2005) 13–17
due to a material’s critical purpose of application. An optical microscope was used to investigate the maximum penetration of abrasives into the clad layer after the directional abrasive process, since the stylus of a typical surface profilometer can not reach the bottom of the abraded groove (valley) due to its finite size.
2. Materials and test methods
Fig. 1. Test part preparation.
or shearing processes is commonly known as deburring. The need to deburr blanks prior to forming depends on the operations to be performed on the blanks, and on the end use of the formed parts. The SME handbook [7] gives an overview of mechanical and abrasive finishing processes including polishing abrasives with their standard grain sizes for various applications. Quantifying and qualifying the abraded surface is an important consideration from the application point of view. Most of the previous research explored the abrasive process characteristics and mechanism by using surface roughness profiles. Surface profiles did not adequately characterize the behavior of abrasive cutting edges acting against a sheet surface to remove material during the process. Yamaguchi and Shinmura [8] examined the microscopic changes produced in the abraded surface texture. In addition to the surface roughness measurements, they used atomic force and scanning electron microscopy to characterize the abrasive metal removal process. In the present study, the interaction between different abrasive belt type media and aluminum flat sheet (both bare and clad) was investigated to determine the best possible abrasive media for unidirectional abrasive machines to process the material. A series of surface roughness measurements were conducted to study the surface finish of aluminum flat sheet after the abrasive process. Direct surface roughness measurements on aluminum clad sheet using a surface profilometer may not be sufficient to qualify and quantify the surface condition,
Fig. 2. Kinematics of unidirectional abrasive process.
The materials used in these tests were 2024-T3 and 6013T4 aluminum flat sheet of three different thicknesses including; 0.040 in. (1.016 mm), 0.063 in. (1.6002 mm) and 0.100 in. (2.54 mm). Both bare and clad sheets of 2024-T3 alloy were used in the test plan. The sheet materials had unidirectional typical mill finishes (surface textures as conformed by the cold rolls textures to the rolling direction). Test parts were blanked as shown in Fig. 1 for abrasive finishing in three different directions (longitudinal, transverse and angular at 45◦ ) with respect to the rolling direction. The rectangular test parts (longitudinal and transverse) were typically 3 in. (76 mm) wide by 6 in. (152 mm) long whereas the squared shaped test parts (angular) were typically 6 in. (152 mm) on each side. Abrasive belts of three different grit sizes (180–320) were used to finish both bare and clad aluminum flat sheets. Fig. 2 shows the operating principles and the kinematics of the belt-driven unidirectional abrasive machine used in the case study to process aluminum flat sheet. An aluminum workpiece with initial thickness (t1 ) is fed into the gap (g), between the abrasive belt and the conveyor that is moving with a velocity (VC ). At the grinding interface, the linear velocity of the belt, VA (DN) is acting in the same direction as the conveyor movement, where N is the revolution of pulley of diameter D. The belt frame is subjected to the induced pressure (P), which is caused by the
Fig. 3. Tribology in clad sheet processing.
P.K. Saha / Wear 258 (2005) 13–17
15
Fig. 4. Typical profilometer traces before and after unidirectional abrasive process on 2024-T3 bare flat sheet (a) original mill finish surface (Ra = 25 in. = 0.635 m), (measured perpendicular to the rolling direction); (b) after abrasive process (Ra = 55 in. = 1.397 m) (grit size 240), (measured perpendicular to the abrasive direction).
difference between the workpiece original thickness (t1 ) and gap (g). Finally, the work-piece is dragged against the friction force (F) through the belt frame with a relative velocity (VW ) and abraded to the final thickness (t2 ). More thickness variation may occur if the applied pressure P is kept higher to remove more material from the abraded surface. As the flat sheet enters into the gap between the abrasive and the conveyer belts, the surface finish of the top side
Fig. 5. Variations in surface roughness on a flat sheet after abrasive processing in three different directions (a) 6013-T4 (gage 0.100 in. (2.54 mm)); (b) 2024-T3 (gage 0.100 in. (2.54 mm)).
Fig. 6. Maximum groove depth comparison of clad 2024-T3 sheet of thickness 0.063 in. (1.6002 mm) (a) 2024-T3 clad sheet processed with abrasive belt of grit size 320; (b) 2024-T3 clad sheet processed with abrasive belt of grit size 240; (c) another example of 2024-T3 clad sheet processed with abrasive belt of grit size 240 (reproducible).
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P.K. Saha / Wear 258 (2005) 13–17
of the material conforms to the size and distribution of indenters on the belt due to their plowing action against the softer workpiece material with the applied pressure P on the belt assembly. In the case of the clad aluminum flat sheet material, there is a definite layer (about 5% of the total sheet thickness) of nearly pure aluminum bonded metallurgically on the substrate (2024-T3). This clad material is produced in the rolling mill for the purpose of improved corrosion resistance and a shinier more visually appealing finish. Direct surface roughness measurements on clad sheet using a surface profilometer may not be sufficient to qualify and quantify the surface condition due to the critical purpose of this material’s application. In roughness measurements, the diamond stylus could trace up to a certain depth within any groove (valley) due to the finite size of the stylus as shown in Fig. 3. However, under no circumstances, should the clad layer allowed to be penetrated by the abrasive particles. To find the maximum groove depth, especially in clad material, an optical microscopic analysis was performed for all the different processing combinations. In the microscopic measurements, the maximum groove depths as well as distribution of groove depths were compared for different abrasive grades. Also compared were new and used abrasive belts as used in the case study.
3. Results and discussion 3.1. Bare Sheet Fig. 4(a) and (b) show some typical profilometer traces from the bare flat sheet test parts of 2024-T3 before and after abrasive processing. Fig. 4(a) is typical of traces produced from the original surface of the flat sheet as received from the rolling mill, while Fig. 4(b) shows the surface after an abrasive process, (both in the rolling direction, and measured perpendicular to the abrasive direction). Fig. 5(a) and (b) show the variations in arithmetic mean value roughness (Ra) of the test parts as a function of equivalent grit size of three different abrasive grades, for two different alloys, and for three different abrasive directions. Typically, the roughness measured at 45◦ to the rolling direction was found to be much lower than that measured perpendicular to the longitudinal or transverse directions. The original (mill) surface of the test pieces has a profile which resembles a series of peaks and valleys extending lengthwise in the rolling direction. If the abrasive belt interacts with this surface in a direction parallel to the rolling direction, the compliant abrasive belt can force the abrasive particles to penetrate to the full depth of the mill finished valleys between the peaks. This effectively allows the abrasive
Fig. 7. Maximum groove depth comparison of 2024-T3 clad sheet thickness 0.063 in. (1.6002 mm) (a) 2024-T3 clad sheet processed with abrasive belts of grit size 320 (new); (b) another example of 2024-T3 clad sheet with abrasive belts of grit size 320 (new); (c) 2024-T3 clad sheet processed with abrasive belts of grit size 320 (used).
P.K. Saha / Wear 258 (2005) 13–17
belt to deepen these valleys, thereby resulting in a larger measured difference between the peaks and valleys. This effect is lessened somewhat when processing in the angular direction (45 ± 10◦ ) due to the act of shaving off the peaks from the original rolled finished material, while not inducing as much deepening of the mill finished valleys. In turn, the measured difference (roughness) will also be less. 3.2. Clad sheet A series of similar roughness measurements were performed on clad sheet material to quantify the surface finish. The measurements showed that the roughness values of the abraded clad material surface using the same abrasive grade were higher than those of the bare material of the same 2024T3 alloy. This may be due to the softer surface of the clad layer of nearly pure aluminum. To quantify and qualify the clad integrity, after abrasive processing simple optical microscopic methods were used to measure the groove depth of the clad flat sheet test parts. A series of microscopic mountings were made per Fig. 3(b) to study various aspects of the abrasive processing including belts of different grit sizes varying from 180 to 320 and new and old belts of same kind. Groove depths on 2024-T3 clad sheet of 0.063 in. (1.6002 mm) were measured for each of the various abrasives grades. Fig. 6 shows the comparison of the maximum groove (wear) depth within the clad thickness on 2024-T3 sheet due to the application of different grit size belts from the same manufacturer; varying from very fine to medium grade. Fig. 6(b) shows that the groove depth has compromised the clad thickness. Figs. 6(b) and (c) show the reproducibility of the maximum groove depth using the same belt in two different test parts. Fig. 6(c) shows that clad thickness is about to be compromised. Fig. 7 shows the comparison of maximum groove (wear) depth within the clad thickness on 2024-T3 sheet for two different belt conditions (brand new and used). Under the same abrasive conditions, the new belt shows more metal removal compared to that of the used belt. Figs. 7(a) and (b) show the reproducibility of maximum groove depth using the same new belt on two different test parts.
4. Conclusions The abrasive wear process on aluminum flat sheet is dependent on the type, size and distribution pattern of the grit of the belt. The roughness measured on the abraded surface
17
perpendicular to the angular direction was found to be much lower than that measured perpendicular to the longitudinal or transverse directions. The interaction between an abrasive belt and the aluminum sheet may vary in a complicated manner when the clad sheet is processed using different equivalent grit sized abrasive media. An optical microscope was used to investigate the relationship between the equivalent grit sizes of the abrasive media and the maximum penetration depth into the clad layer after the directional abrasive process. Groove depth measurements on the edge of sheet thickness were conducted with 2024 clad aluminum flat sheet after processing through abrasive belt media of equivalent abrasive grit sizes (varying 180–320). It was found that any abrasive belt media with equivalent grit size below 320 may be inappropriate to process clad aluminum sheet due to the potential for penetration of abrasive into the clad layer resulting in exposure of the substrate aluminum alloy to the atmosphere. A new abrasive belt removes more material than a belt which has been under use for some period of time. This loss of abrasiveness happens because the media loses some high peak abrasive particles during the abrasive process.
Acknowledgements The author wishes to express his thanks to Mr. Victor Ledesma for performing the microscopic analysis of the test parts. The author would also like to thank Mr. Billy Small for his valuable suggestions and comments.
References [1] J. Halling, Principles of Tribology, Macmillan Education Limited, London, 1978. [2] J.T. Burwell, Survey of possible wear mechanisms, Wear 1 (1957) 119–141. [3] J.A. Schey, Tribology in Metal Working, ASM, Metals Park, OH, 1983. [4] S. Kalpakjian, Manufacturing Engineering and Technology, AddisonWesley, 1992. [5] M.M. Kruschov, Resistance of metals to wear by abrasion; related to hardness, Instn. Mech. Engrs. Conf. Lubrication and Wear, London, 1957, pp. 655–659. [6] R.C.D. Richardson, The wear of metals by relatively soft abrasives, Wear 11 (1968) 245–275. [7] C. Wick, R.F. Veilleux, Tool and Manufacturing Engineers Handbook, vol. III, Society of Manufacturing Engineers (SME), 1985. [8] H. Yamaguchi, T. Shinmura, Study of the surface modification resulting from an internal magnetic abrasive finishing process, Wear 225–229 (1999).
A case study on the abrasive surface finishing of aluminum flat sheet Pradip K. Saha∗ The Boeing Company, MC 19-FT, P.O. Box 3707, Seattle, WA 98124-2207, USA Received 22 December 2003; received in revised form 18 March 2004; accepted 24 March 2004 Available online 8 October 2004
Abstract A case study of a unidirectional abrasive metal removal process applied on aluminum flat sheet in manufacturing processes is presented. A series of tests were conducted using belt type abrasive media of varying equivalent grit sizes on both bare and clad aluminum flat sheet. Samples were processed through each media in the longitudinal, transverse and angular orientations with respect to the rolling direction to quantify and qualify the metal surface as well as the abrasive media. In clad aluminum, a layer of pure aluminum metallurgically bonded to a substrate by rolling process, is used for appearance and corrosion resistance in aircraft component applications. An optical microscope was used to investigate the relationship between the equivalent grit sizes of the abrasive media and the maximum penetration depth into the clad layer after the directional abrasive process. Measurements of groove depths on the edges of the 2024 clad aluminum sheet samples were conducted after processing through abrasive belt media of equivalent abrasive grit sizes, varying from 180 to 320. It was found that any abrasive belt media with equivalent grit size below 320 may be inappropriate to process clad aluminum sheet due to penetration of the abrasive into the clad layer which can expose the substrate aluminum alloy to the atmosphere. © 2004 Elsevier B.V. All rights reserved. Keywords: Tribology; Abrasive media; Clad aluminum; Groove depth
1. Introduction In recent years, Tribology has received increasing attention by industry to explain the interrelation between friction and wear principles and practices [1]. Without this science, an abrasive metal removal process would be impossible to characterize/quantify when the surfaces are in relative motion. In order to study and have a better understanding of wear, it is essential to recognize several mechanisms of wear. Burwell [2] made an excellent survey and listed four mechanisms including adhesive wear, abrasive wear, corrosive wear and surface fatigue. Schey [3] provided a useful review of the wear process in metal forming operations. Abrasive wear covers generally two types of situations. In both cases wear occurs by the plowing-out of softer material of a given volume by the harder indenters of an abrasive surface. In the first instance a rough, harder abrasive surface slides against a softer metal ∗
Tel.: +1 206 655 0360; fax: +1 206 662 0453. E-mail address: [email protected].
0043-1648/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.wear.2004.03.023
surface. In the second case abrasion is caused by loose hard particles sliding between the rubbing abrasive and metal surfaces. Kalpakjian [4] also provided an excellent review of abrasive processes and finishing operations. The size of an abrasive grain (grit) is identified by a number. The smaller the grain size, the larger the number is. A given surface is scored only if it is softer than the abrasive. It is therefore not surprising that resistance to abrasive wear is a function of a material’s hardness. Many investigators have confirmed that hardness is the most important parameter in abrasive wear. Kruschov [5] plotted resistance to wear against hardness for a range of annealed pure metals, obtaining a linear relationship. He also found that prior workhardening of the pure metals had no effect on the wear rate. Richardson [6] has shown that if wear resistance is studied as a function of the ratio of the hardness between the metal surface and the hardness of the abrasive, then the wear resistance increases rapidly as the ratio becomes greater than 0.8. The process of removing burrs as an undesirable projection of material resulting from a cutting, forming, blanking
14
P.K. Saha / Wear 258 (2005) 13–17
due to a material’s critical purpose of application. An optical microscope was used to investigate the maximum penetration of abrasives into the clad layer after the directional abrasive process, since the stylus of a typical surface profilometer can not reach the bottom of the abraded groove (valley) due to its finite size.
2. Materials and test methods
Fig. 1. Test part preparation.
or shearing processes is commonly known as deburring. The need to deburr blanks prior to forming depends on the operations to be performed on the blanks, and on the end use of the formed parts. The SME handbook [7] gives an overview of mechanical and abrasive finishing processes including polishing abrasives with their standard grain sizes for various applications. Quantifying and qualifying the abraded surface is an important consideration from the application point of view. Most of the previous research explored the abrasive process characteristics and mechanism by using surface roughness profiles. Surface profiles did not adequately characterize the behavior of abrasive cutting edges acting against a sheet surface to remove material during the process. Yamaguchi and Shinmura [8] examined the microscopic changes produced in the abraded surface texture. In addition to the surface roughness measurements, they used atomic force and scanning electron microscopy to characterize the abrasive metal removal process. In the present study, the interaction between different abrasive belt type media and aluminum flat sheet (both bare and clad) was investigated to determine the best possible abrasive media for unidirectional abrasive machines to process the material. A series of surface roughness measurements were conducted to study the surface finish of aluminum flat sheet after the abrasive process. Direct surface roughness measurements on aluminum clad sheet using a surface profilometer may not be sufficient to qualify and quantify the surface condition,
Fig. 2. Kinematics of unidirectional abrasive process.
The materials used in these tests were 2024-T3 and 6013T4 aluminum flat sheet of three different thicknesses including; 0.040 in. (1.016 mm), 0.063 in. (1.6002 mm) and 0.100 in. (2.54 mm). Both bare and clad sheets of 2024-T3 alloy were used in the test plan. The sheet materials had unidirectional typical mill finishes (surface textures as conformed by the cold rolls textures to the rolling direction). Test parts were blanked as shown in Fig. 1 for abrasive finishing in three different directions (longitudinal, transverse and angular at 45◦ ) with respect to the rolling direction. The rectangular test parts (longitudinal and transverse) were typically 3 in. (76 mm) wide by 6 in. (152 mm) long whereas the squared shaped test parts (angular) were typically 6 in. (152 mm) on each side. Abrasive belts of three different grit sizes (180–320) were used to finish both bare and clad aluminum flat sheets. Fig. 2 shows the operating principles and the kinematics of the belt-driven unidirectional abrasive machine used in the case study to process aluminum flat sheet. An aluminum workpiece with initial thickness (t1 ) is fed into the gap (g), between the abrasive belt and the conveyor that is moving with a velocity (VC ). At the grinding interface, the linear velocity of the belt, VA (DN) is acting in the same direction as the conveyor movement, where N is the revolution of pulley of diameter D. The belt frame is subjected to the induced pressure (P), which is caused by the
Fig. 3. Tribology in clad sheet processing.
P.K. Saha / Wear 258 (2005) 13–17
15
Fig. 4. Typical profilometer traces before and after unidirectional abrasive process on 2024-T3 bare flat sheet (a) original mill finish surface (Ra = 25 in. = 0.635 m), (measured perpendicular to the rolling direction); (b) after abrasive process (Ra = 55 in. = 1.397 m) (grit size 240), (measured perpendicular to the abrasive direction).
difference between the workpiece original thickness (t1 ) and gap (g). Finally, the work-piece is dragged against the friction force (F) through the belt frame with a relative velocity (VW ) and abraded to the final thickness (t2 ). More thickness variation may occur if the applied pressure P is kept higher to remove more material from the abraded surface. As the flat sheet enters into the gap between the abrasive and the conveyer belts, the surface finish of the top side
Fig. 5. Variations in surface roughness on a flat sheet after abrasive processing in three different directions (a) 6013-T4 (gage 0.100 in. (2.54 mm)); (b) 2024-T3 (gage 0.100 in. (2.54 mm)).
Fig. 6. Maximum groove depth comparison of clad 2024-T3 sheet of thickness 0.063 in. (1.6002 mm) (a) 2024-T3 clad sheet processed with abrasive belt of grit size 320; (b) 2024-T3 clad sheet processed with abrasive belt of grit size 240; (c) another example of 2024-T3 clad sheet processed with abrasive belt of grit size 240 (reproducible).
16
P.K. Saha / Wear 258 (2005) 13–17
of the material conforms to the size and distribution of indenters on the belt due to their plowing action against the softer workpiece material with the applied pressure P on the belt assembly. In the case of the clad aluminum flat sheet material, there is a definite layer (about 5% of the total sheet thickness) of nearly pure aluminum bonded metallurgically on the substrate (2024-T3). This clad material is produced in the rolling mill for the purpose of improved corrosion resistance and a shinier more visually appealing finish. Direct surface roughness measurements on clad sheet using a surface profilometer may not be sufficient to qualify and quantify the surface condition due to the critical purpose of this material’s application. In roughness measurements, the diamond stylus could trace up to a certain depth within any groove (valley) due to the finite size of the stylus as shown in Fig. 3. However, under no circumstances, should the clad layer allowed to be penetrated by the abrasive particles. To find the maximum groove depth, especially in clad material, an optical microscopic analysis was performed for all the different processing combinations. In the microscopic measurements, the maximum groove depths as well as distribution of groove depths were compared for different abrasive grades. Also compared were new and used abrasive belts as used in the case study.
3. Results and discussion 3.1. Bare Sheet Fig. 4(a) and (b) show some typical profilometer traces from the bare flat sheet test parts of 2024-T3 before and after abrasive processing. Fig. 4(a) is typical of traces produced from the original surface of the flat sheet as received from the rolling mill, while Fig. 4(b) shows the surface after an abrasive process, (both in the rolling direction, and measured perpendicular to the abrasive direction). Fig. 5(a) and (b) show the variations in arithmetic mean value roughness (Ra) of the test parts as a function of equivalent grit size of three different abrasive grades, for two different alloys, and for three different abrasive directions. Typically, the roughness measured at 45◦ to the rolling direction was found to be much lower than that measured perpendicular to the longitudinal or transverse directions. The original (mill) surface of the test pieces has a profile which resembles a series of peaks and valleys extending lengthwise in the rolling direction. If the abrasive belt interacts with this surface in a direction parallel to the rolling direction, the compliant abrasive belt can force the abrasive particles to penetrate to the full depth of the mill finished valleys between the peaks. This effectively allows the abrasive
Fig. 7. Maximum groove depth comparison of 2024-T3 clad sheet thickness 0.063 in. (1.6002 mm) (a) 2024-T3 clad sheet processed with abrasive belts of grit size 320 (new); (b) another example of 2024-T3 clad sheet with abrasive belts of grit size 320 (new); (c) 2024-T3 clad sheet processed with abrasive belts of grit size 320 (used).
P.K. Saha / Wear 258 (2005) 13–17
belt to deepen these valleys, thereby resulting in a larger measured difference between the peaks and valleys. This effect is lessened somewhat when processing in the angular direction (45 ± 10◦ ) due to the act of shaving off the peaks from the original rolled finished material, while not inducing as much deepening of the mill finished valleys. In turn, the measured difference (roughness) will also be less. 3.2. Clad sheet A series of similar roughness measurements were performed on clad sheet material to quantify the surface finish. The measurements showed that the roughness values of the abraded clad material surface using the same abrasive grade were higher than those of the bare material of the same 2024T3 alloy. This may be due to the softer surface of the clad layer of nearly pure aluminum. To quantify and qualify the clad integrity, after abrasive processing simple optical microscopic methods were used to measure the groove depth of the clad flat sheet test parts. A series of microscopic mountings were made per Fig. 3(b) to study various aspects of the abrasive processing including belts of different grit sizes varying from 180 to 320 and new and old belts of same kind. Groove depths on 2024-T3 clad sheet of 0.063 in. (1.6002 mm) were measured for each of the various abrasives grades. Fig. 6 shows the comparison of the maximum groove (wear) depth within the clad thickness on 2024-T3 sheet due to the application of different grit size belts from the same manufacturer; varying from very fine to medium grade. Fig. 6(b) shows that the groove depth has compromised the clad thickness. Figs. 6(b) and (c) show the reproducibility of the maximum groove depth using the same belt in two different test parts. Fig. 6(c) shows that clad thickness is about to be compromised. Fig. 7 shows the comparison of maximum groove (wear) depth within the clad thickness on 2024-T3 sheet for two different belt conditions (brand new and used). Under the same abrasive conditions, the new belt shows more metal removal compared to that of the used belt. Figs. 7(a) and (b) show the reproducibility of maximum groove depth using the same new belt on two different test parts.
4. Conclusions The abrasive wear process on aluminum flat sheet is dependent on the type, size and distribution pattern of the grit of the belt. The roughness measured on the abraded surface
17
perpendicular to the angular direction was found to be much lower than that measured perpendicular to the longitudinal or transverse directions. The interaction between an abrasive belt and the aluminum sheet may vary in a complicated manner when the clad sheet is processed using different equivalent grit sized abrasive media. An optical microscope was used to investigate the relationship between the equivalent grit sizes of the abrasive media and the maximum penetration depth into the clad layer after the directional abrasive process. Groove depth measurements on the edge of sheet thickness were conducted with 2024 clad aluminum flat sheet after processing through abrasive belt media of equivalent abrasive grit sizes (varying 180–320). It was found that any abrasive belt media with equivalent grit size below 320 may be inappropriate to process clad aluminum sheet due to the potential for penetration of abrasive into the clad layer resulting in exposure of the substrate aluminum alloy to the atmosphere. A new abrasive belt removes more material than a belt which has been under use for some period of time. This loss of abrasiveness happens because the media loses some high peak abrasive particles during the abrasive process.
Acknowledgements The author wishes to express his thanks to Mr. Victor Ledesma for performing the microscopic analysis of the test parts. The author would also like to thank Mr. Billy Small for his valuable suggestions and comments.
References [1] J. Halling, Principles of Tribology, Macmillan Education Limited, London, 1978. [2] J.T. Burwell, Survey of possible wear mechanisms, Wear 1 (1957) 119–141. [3] J.A. Schey, Tribology in Metal Working, ASM, Metals Park, OH, 1983. [4] S. Kalpakjian, Manufacturing Engineering and Technology, AddisonWesley, 1992. [5] M.M. Kruschov, Resistance of metals to wear by abrasion; related to hardness, Instn. Mech. Engrs. Conf. Lubrication and Wear, London, 1957, pp. 655–659. [6] R.C.D. Richardson, The wear of metals by relatively soft abrasives, Wear 11 (1968) 245–275. [7] C. Wick, R.F. Veilleux, Tool and Manufacturing Engineers Handbook, vol. III, Society of Manufacturing Engineers (SME), 1985. [8] H. Yamaguchi, T. Shinmura, Study of the surface modification resulting from an internal magnetic abrasive finishing process, Wear 225–229 (1999).