Suitability of Stiffened Sheet Metal as Against a Plate Metal in Fabrication Works: A scientific approach towards metal craft work

Download Full-Text PDF Cite this Publication

Text Only Version

Suitability of Stiffened Sheet Metal as Against a Plate Metal in Fabrication Works: A scientific approach towards metal craft work

Subramanya D. Sanbhat

Fabrication Technology & Erection Engineering Department Fr. Agnel Polytechnic, Vashi

Navi Mumbai, India

AbstractThis paper is an attempt to deduce on the economical selection of a plate versus sheet metal for use in fabrication works. The method adopted is theory and practical applications of the principles of Strength of Materials (SOM) to a plate, a sheet metal and a stiffened sheet metal. The results confirmed that in spite of less rigidity due to less thickness; sheet metal strength could be enhanced considerably as against the strength of a thick plate by appropriately applying the principles of stiffening. This ability of increasing the strength/weight ratio by stiffening sheet metals helps in cost control on the shop floor.

KeywordsDeduce, Plate, Sheet metal, SOM, Stiffening

  1. INTRODUCTION

    Material

    Elastic Moduls, E

    MN/m2

    Density, r

    Kg/m3

    Tensile Stiffness Index, Ew= E/r MNm/kg

    Bending Stiffness Index,

    Sw= Ew/12.r2 Nm7/kg3

    Steel

    210000

    7800

    25

    0,03

    CF

    composites

    200000

    2000

    100

    2,00

    Paper

    15600

    700

    22

    3,70

    Material

    Elastic Moduls, E

    MN/m2

    Density, r

    Kg/m3

    Tensile Stiffness Index, Ew= E/r MNm/kg

    Bending Stiffness Index,

    Sw= Ew/12.r2 Nm7/kg3

    Steel

    210000

    7800

    25

    0,03

    CF

    composites

    200000

    2000

    100

    2,00

    Paper

    15600

    700

    22

    3,70

    The basic principle of stiffening can be illustrated by supporting a tumbler of water on a piece of note paper bridging two other tumblers as shown in the Fig. 1 and Fig. 2 below. From the figures it is clear that a sheet metal panel will not support a very great load due to the thinness of the material. A metal plate of the same surface area will support a fairly substantial load because of its extra thickness. But, although the metal plate is much more rigid than the sheet metal panel, this rigidity is obtained at the expense of considerable additional weight. Therefore, more the weight, more the rigidity and as per the prevailing market cost rate per kg, more would be the cost.

    Original piece of note paper corrugated by folding

    Figure 2. Note paper stiffened by corrugation

    Strength/weight ratio is an important factor in the fabrication industry and by stiffening the sheet metal in an appropriate manner, it is possible to produce a multiplicity of light fabrications which are very rigid and strong. The comparative parameters as from [1], to justify the above illustration for stiffening using a corrugated note paper in lieu of a sheet metal are as shown in Table 1. below.

    TABLE 1. COMPARISON OF STEEL AND NOTE PAPER

    Note paper

    Empty tumblers

    Figure 1. Note paper

    Tumbler of water

    1. Literature Review

      The following conclusions reviewed from [2] [14] on the sheet metals types, alternative materials, fabrication processes, methods for stiffening sheet metal components, etc. are compiled in the Table 2 to be utilized for defining the objectives of this paper.

      TABLE 2. METHODS OF STIFFENING

      Pros

      Cons

      Remarks

      A.

      Plate component

      More rigidity More stiffness

      More weight More cost

      Not economical

      B.

      Less weight

      Less rigidity

      Not

      Sheet

      Less cost

      Less stiffness

      economical

      component

      unless used

      used as it is

      in proper

      (without

      orientation

      stiffening)

      with respect

      to applied

      load

      C.

      Less weight

      Additional

      Economical

      Sheet

      Less cost

      cost of

      but subject to

      component

      More rigidity

      fabrication or

      conditions in

      fabricated (less

      More stiffness

      changeover to composite

      fabrication process used

      thickness)

      materials

      (Refer Figure

      5.)

      D.

      More weight

      Additional

      Economical

      Sheet

      More cost

      cost of

      but subject to

      component fabricated (medium

      More rigidity More stiffness

      fabrication or changeover to composite

      conditions in fabrication process used.

      thickness

      materials

      (Refer Figure

      but less

      6.)

      than for a

      plate)

      E.

      Less weight

      Additional

      Economical

      Web

      Less cost

      cost of

      but subject to

      stiffeners

      More rigidity

      fabrication or

      conditions in

      (structural sections)

      More stiffness

      changeover to composite

      fabrication process used.

      materials

      (Refer Figure

      7.)

    2. Objective

    Study of the stiffening methods by applying the principles of Strength of Materials and hence conclude their suitability for fabrication in metal craft works with relevant illustrations that depict;

    • Improved strength and rigidity for the intended function

    • Safe edge for handling

    • Aesthetic look for marketing

  2. RESULTS AND DISCUSSION

    First method: Utilize the existing geometry available to improve strength but by employing a different orientation and same loading as shown in Fig. 3 and the comparison of the deflection parameter for both the cases is as shown in Table 3.

    Figure 3. Stiffening using change in orientation

    TABLE 3. COMPARISON OF TWO ORIENTATIONS FOR LOADING

    /tr>

    Sr. No s.

    Variables

    Assumed values

    Deflection

    y*10-6mm

    Moment of Inertia I

    1

    Loading perpendicul ar to L*W

    L=

    50mm, B=

    15mm, W=

    20mm, E=2*105

    N/mm2, P= 10N

    9.26

    14062.5mm4

    2

    Loading perpendicul ar to B*W

    0.02

    156250mm4

    Thus, the second position with a higher Moment of Inertia results in a lesser amount of downward deflection. The results so obtained may be deduced that the deflection of a component under a load reduces when the extreme fibers of the component lies far away from the neutral axis. The more farther the distance more is the ability to sustain any bending load. This obviously implies that any plate material having considerable thickness with respect to other dimensions is able to withstand bending loads very easily unlike a sheet metal. But, the fabricability of a sheet metal to be folded, joined by bolts, rivets, adhesives, etc. enables the above condition to be achieved as shown in Fig. 4.

    Figure 4. Principle of stiffening

    The above method of corrugation of the note paper (analogous to a sheet metal) helps to separate the extreme fibers to lie much more beyond the neutral axis as compared to before the corrugation. This is similar to a plate metal which also has its extreme fibers far away from the neutral axis. So, stiffening obtained improves strength with less weight as compared to a similar plate with similar strength but more weight as seen from Table 4. below.

    TABLE 4. COMPARATIVE STIFFNESS FOR CORRUGATED SHEET

    METAL

    Sandwich panel

    Load applied (kN)

    Total deformation (mm)

    Stiffness (kN/mm)

    Total weight (N)

    3 curve

    13.5

    0.215

    62.79

    161.7

    4 curve

    13.5

    0.042

    321.43

    168.7

    (Source: IJERT, Vol. 1 Issue 8, October 2012)

    Hence, for a given length and height of the structure, increasing the number of curved waves (3 waves to 4 waves) the strength increases effectively. For increase of 4% weight, the strength is increased to 66% and increase in stiffness to 80.47%. Hence, from the above discussion when the number of curved waves increases to infinity (i.e. manifests as a solid plate) the tremendous increase in strength, stiffness and weight are evident.

    Second method: In this method, the same reasoning as in the First method is achieved by adopting fabrication methods on the sheet metal by folding/hem (single and/or double), punching a lightening hole, etc. Consider a single fold given to the sheet metal on all the four sides to attain strength and rigidity in both planes of bending as in Fig. 5. Now applying the principles of strength of materials we have the comparative figures in favor of the fold as in Table 5.

    Figure 5. Stiffening by fold

    Sr. Nos.

    Variables

    Assumed values

    Deflection

    y mm

    Moment of Inertia

    I

    1

    Loading perpendicular

    t= 2mm, W=

    0.0099

    53.33

    mm4

    to W*t

    80mm

    (W= 80mm)

    (50mm

    2

    Loading perpendicular

    after

    0.0025*10-2

    5102.39

    mm4

    folding),

    Sr. Nos.

    Variables

    Assumed values

    Deflection

    y mm

    Moment of Inertia

    I

    1

    Loading perpendicular

    t= 2mm, W=

    0.0099

    53.33

    mm4

    to W*t

    80mm

    (W= 80mm)

    (50mm

    2

    Loading perpendicular

    after

    0.0025*10-2

    5102.39

    mm4

    folding),

    TABLE 5. COMPARISON OF TWO ORIENTATIONS FOR LOADING

    to W*t

    (W= 50mm)

    E=2*105

    N/mm2, P= 10N

    2

    Loading perpendicular to L*t (Assume, L= W= 50mm)

    0.0025*10-2

    5102.39

    mm4

    Third method: In this method, applicable for thicknesses that disable the sheet metals to undergo folding and/or bending operations, the above reasoning is again achieved by applying stiffeners/reinforcements at the required locations to attain strength and rigidity in both planes of bending as in Fig. 6 and comparative figures in favor for the same as in Table 6. The necessary stiffeners may be fabricated separately and then assembled by means of rivets or bolted joints.

    Figure 6. Stiffening by hem or applied stiffener

    TABLE 6. COMPARISON OF TWO ORIENTATIONS FOR LOADING

    Sr. No s.

    Variables

    Assumed values

    Deflection

    y mm

    Moment of Inertia

    I

    1

    Loading perpendicular

    t= 2mm, W= 80mm

    0.0099

    53.33

    mm4

    to W*t

    (50mm

    (W= 80mm)

    after

    2

    Loading perpendicular to W*t

    folding), E=2*105

    N/mm2,

    0.064*10-2

    203.33

    mm4

    (W= 50mm)

    P= 10N

    2

    Loading perpendicular

    0.064*10-2

    203.33

    mm4

    to L*t

    (Assume, L=

    W= 50mm)

    Another category in this method involves stiffening of structural sections, especially I sections/columns/beams with added stiffeners which may be conceptualized as a combination of I – section and a rectangular solid beam as in Fig. 7 and then compared as shown in Table 7.

    Little

    depth Web

    Sideways movement (Thrust)

  3. CONCLUSION

Fabrication works make use of plate and sheet metals. The various fabrication processes involved are marking/measuring, cutting, folding/bending, rolling, presswork, joining, cleaning/painting. Depending upon the end use/application of the fabricated component an evaluation of the strength of stiffened sheet metal in terms of reduced deflection subjected to a point load as against a plate material helps offset the associated disadvantages of sheet metal. This implies that the cost of employing the appropriate stiffening operation (material & labor cost) ought to be less than cost of the plate material. This again implies that the stiffening operation ought to be as simple as possible. Some illustrations from [5] for the same are as given below to complete the objectives of the paper.

Greater depth

Web

Stiffening methods for small thickness are labor intensive and involves manual interventions as shown in Fig. 8 below.

Sideways movement (Thrust)

Figure 7. Web stiffening

TABLE 7. COMPARISON OF STRUCTURAL SECTION

Pros

Cons

Remarks

Rectang ular beam

Good strength Good rigidity

High weight High cost

Not economical

I – beam

Good strength Good rigidity

Low weight Low cost Unsuitable for sideways thrust

Uneconomical for eccentric loadings

Web

Good

Medium

Section

stiffened

strength

weight and

combination of

I – beam

Good

cost

rectangular beam

rigidity

subjected to

and I beam

Suitable

for

conditions in

giving a greater

sideways thrust

fabrication process

value of moment of inertia at the

sections of

stiffener for the

entire span of the I

– beam

Pros

Cons

Remarks

Rectang ular beam

Good strength Good rigidity

High weight High cost

Not economical

I – beam

Good strength Good rigidity

Low weight Low cost Unsuitable for sideways thrust

Uneconomical for eccentric loadings

Web

Good

Medium

Section

stiffened

strength

weight and

combination of

I – beam

Good

cost

rectangular beam

rigidity

subjected to

and I beam

Suitable

for

conditions in

giving a greater

sideways thrust

fabrication process

value of moment of inertia at the

sections of

stiffener for the

entire span of the I

– beam

ALTERNATIVES

  1. Folds/Hems

  2. Diamond break Figure 8. Sheet component fabricated (less thickness)

Stiffening methods for more thickness are also labor intensive and involves manual/ machine interventions as seen in the Fig. 9 and Fig. 10 (for structural sections) below.

  1. Circular component stiffening (before or after rolling)

    1. Large panel stiffening

  2. Stiffening thick sheet metals

    Figure 9. Sheet component fabricated (medium to less than plate thickness)

    1. Welded joints

    2. I- beam of plates bolted/riveted Figure 10. Methods of web stiffening

Stiffening a flange is done when a single fillet weld has to be used, the other side being inaccessible for welding and if otherwise this single weld would be subjected to bending as shown in the Fig. 11 below.

  1. Stiffening for welded flanged connection

  2. Stiffening of welded connection between two I-section members Figure 11. Stiffening with gusset plates

REFERENCES

  1. Monica Ek, G̦ran Gellerstedt, Gunnar Henriksson, Paper Chemistry and Technology, Volume 4, Walter de Gruyter GmbH & Co. KG, Germany, 2009, pp. 1 Р57

  2. Roger Timings, Basic Fabrication and Welding Engineering, 1st edition,

    Newness Publ. (Imprint of Elsevier), 2008, pp. 328, 329, 356, 359 361

  3. Support Materials, Basic Principles of Fabricated Component Design: Manufacture and Test Methods (Higher), Higher Still Publ. 1999. pp. 24

    26

  4. Kenyon Pitman, Basic Fabrication and Welding Engineering, 1st edition,

    Pitman Publ., 1979, pp. 157 180

  5. FJM Smith, Basic Fabrication and Welding Engineering, 1st edition,

    Longman Publ., 1975, pp. 258 264, 270 271

  6. Joshi & Mahajan, Process Equipment Design, 1st edition, Macmillan Publ., 1996

  7. Hazra and Choudhari, Workshop Technology, Vol 1 & 2, 11th edition,

    Media Promoters & Publ., 1997

  8. S.Ramamrutham and R. Narayan, Strength of Materials, 11thedition. 1993, pp. 124 160, 252 370, 418 – 566

  9. Rex Miller and Thomas J. Morrisey, Metal Technology, 1st edition,

    Howard W. Sams & Co., Inc. Publ., 1975, pp. 120 145

  10. Edwin P. Anderson, Audels Sheet Metal Workers Handy Book, 1st edition, D. B Taraporewala Sons & Co., Pvi. Ltd. Book Publ., 1990

  11. Karoly Jarmai and Jozsef Farkas , Design, Fabrication and Economy of Metal Structures: International Conference Proceedings 2013, Miskolc, Hungary, April 24 26 2013, Springer Science & Business Media Publ., pp. 17 22, 29 36, 145 150

  12. Taylan Altan and A. Erman Tekkayya, Sheet Metal Forming Fundamentals, 1st edition, ASM International (USA), 2012, pp. 5 23, 39 43, 73 86, 91 93, 129 144, 203 – 211

  13. Lanier Bryan Keith, Study in the Improvement in Strength and Stiffness Capacity of Steel Multi-sided Monopole Utilizing Carbon Fiber Reinforced Polymers as a Retrofitting Mechanism Retrieved from; http://www.ce.ncsu.edu/srizkal/linked_files/Study_in_the_Improvement

    _in_Strength_and_Stiffness.pdf

  14. A.Gopichand, Dr.G.Krishnaiah, B.Mahesh Krishna, Dr.Diwakar Reddy.V, A.V.N.L.Sharma, Design And Analysis Of Corrugated Steel Sandwich Structures Using Ansys Workbench, International Journal of Engineering Research & Technology (IJERT), Vol. 1 Issue 8, October 2012

Leave a Reply

Your email address will not be published. Required fields are marked *