Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Aluminum & Mild Steel Load Question *NEW Member*

  1. May 3, 2010 #1
    I have a question regarding what material type and thickness could support a given load most cost effectively. Weight of the part will also be a factor in the cost due to the wacked out freight charges these days.

    I have no idea where to locate the information that I need or a formula so that I can figure it out myself. I am not a engineer by trade but I am a quick study.

    I am trying to make a couple of support stands for a machine. I already have all of the drawings done and now I just need to pick out the correct material for the job. Also I have considered revising the design but in all honesty this is the best way all things considered and I do mean all things (Shipping size, shipping weight, packing etc....)

    I would like to know the following regarding aluminum and mild steel:

    NOTE: The stands are 24" tall for scaling purposes

    Based on the attached picture, which is more suitable, Mild steel or aluminum? Also what thickness would each need to be in order to support the said load?

    Any and all help would be greatly appreciated
     

    Attached Files:

  2. jcsd
  3. May 3, 2010 #2

    Astronuc

    User Avatar
    Staff Emeritus
    Science Advisor

    One can find material properties here.

    http://www.matweb.com/search/MaterialGroupSearch.aspx

    Probably mild steel would be the way to go, as opposed to Al. Depending on the Al alloy, one would have to make a thicker part from Al than from steel in order to acheive the same marging to yield strength.

    There is also the matter of geometric design, e.g., type of a channel/column, as well as the base. The supporting system might be a like a cradle of some kind.
     
  4. May 5, 2010 #3

    Mech_Engineer

    User Avatar
    Science Advisor
    Gold Member

    Not true, mild steel just doesn't have the strength of high strength aluminum alloys and it weighs more to boot.

    Aluminum 6061-T6 or 7075-T6 has a very good strength to weight ratio compared to mild steel. Mild steel like A36 has a yield strength of about 36 ksi, while Al 6061-T6 has a yield strength of about 35-40 ksi and only 34% the density of A36 steel (this means a part made out of aluminum would weigh 34% that of an A36 steel part of the same strength). Al 7075-T6 has a yield strength of 73 ksi and 36% the density of A36, making it even stronger.
     
  5. May 5, 2010 #4
    That was my understanding in a nutshell but I wanted to verify it before I began trying to select the correct material that will support the vertical load (Static Load?) and the lateral forces (Term?) that are due to the 10deg Outward Brake on each leg that were put there for stability reasons.

    Since I do not have a formal education in this field I am going to need to know a few simple things as well as how to calculate and/or search for the solution/answers myself in the future. I am not expecting a teaching lesson or anything, I would mearly like to know the basics and anything else you all are willing to teach to a sponge. lol

    So I need to know how to locate as well as identify the proper material, in aluminum or mild steel, to support the load in the configuration that was in my attached drawing.

    Also, what would be the answer for Mild Steel and Aluminum?

    Any further help would be great. Again I am a newb here but I am ready and willing to learn whatever you got.

    Thanks again
     
  6. May 6, 2010 #5

    Astronuc

    User Avatar
    Staff Emeritus
    Science Advisor

    I wasn't thinking of high strength Al alloys, but more along the lines of comparable low strength Al alloys, like 1100, since the OP was comparing it to relatively low strength mild steels.

    Consider:

    Al alloy 1100 composition

    Code (Text):
    Al        99 min
    Cu        0.05 - 0.2
    Mn        0.05 max
    Rem Each  0.05 max
    Rem Tot   0.15 max
    Si+Fe     0.95 max
    Zn        0.1 max
    H14 Temper -320F, YS ~20 ksi, UTS ~30 ksi
    but Temper at 68F, YS = 17 ksi, UTS = 18 ksi

    Comparison of common Al-alloys
    http://www.precisionsheetmetal.com/home/materials.htm#Aluminum%20Alloy%20Comparison [Broken]

    http://www.makeitfrom.com/data/?material=6061_Alum&type=Basic_Mechanical

    Composition of Al 7075
    (Source: http://asm.matweb.com/search/SpecificMaterial.asp?bassnum=MA7075T6)
    Code (Text):
    Al         87.1 - 91.4  
    Zn         5.1 - 6.1  
    Mg         2.1 - 2.9  
    Si Max     0.4  
    Cr         0.18 - 0.28  
    Cu         1.2 - 2  
    Fe Max     0.5
    Mn Max     0.3  
    Other, ea  0.05 Max    
    Other, tot 0.15 Max  
    Ti Max     0.2
    And the T6 temper imparts considerable strength as stated above.

    One has to look at the form of the parts. If made of Al-alloy, would the frame parts be extruded or rolled, and then welded? How or when would the temper be done? One has to consider the entire production route.


    If we're considering any Al-alloy, particularly high strength Al alloys, then why restrict ourselves to mild steel. Why not consider 1040, or 4140 or 4340, or some HSLA?

    1018 Mild (low-carbon) steel
    Ultimate Tensile Strength, psi 63,800
    Yield Strength, psi 53,700

    ASTM A513 alloys 1020 - 1026 Mild (low-carbon) steel
    Ultimate Tensile Strength, psi 87,000
    Yield Strength, psi 72,000

    1028 steel has roughly the same YS and UTS as 1026 steel.

    Some sites comparing selection of Al alloys vs Steel
    Strength of Aluminum vs Strength of Steel
    http://www.kastenmarine.com/alumVSsteel.htm

    Comparing Al, CroMo steel, Carbon Steel
    http://www.ihpva.org/Projects/PracticalInnovations/materials.html (not official)
    http://www.americanmachinetools.com/tensile_strength.htm

    But then

    Steel Alloy 1040
    Code (Text):
                                          YS(ksi) UTS(ksi)
    Annealed   (@ 1450 deg F)              51.3     75.3
    Normalized (@ 1650 deg F)              54.3     85.5
    Hot rolled                             60.0     90.0
    Oil-quenched & tempered (@ 600 deg F)  86.0    113.0
    https://www.efunda.com/materials/al...ow_prop=uts&Page_Title=Carbon Steel AISI 1040

    Code (Text):
    Steel Alloy 4140
    Annealed   (@ 1500 deg F)              60.5     95.0
    Normalized (@ 1600 deg F)              95.0    148.0
    Oil-quenched & tempered (@ 600 deg F) 208.0    238.0
                             
    Steel Alloy 4340
    Annealed (@ 1500 deg F)                68.5    108.0
    Normalized (@ 1600 deg F)             125.0    185.5
    Oil-quenched & tempered (@ 600 deg F) 230.0    250.0
     
    Last edited by a moderator: May 4, 2017
  7. May 6, 2010 #6
    Am I correct in assuming that this stand is a transit stand, not a long term mounting for a machine in use?

    Can I also ask about the fixing down design? I would advise you to check this aspect carefully as substantial shock loads can develop during transit.
     
  8. May 6, 2010 #7

    Astronuc

    User Avatar
    Staff Emeritus
    Science Advisor

    This is a key aspect of design. Anything in transit must be designed to take dynamic/transient/impact loads that might be experienced during transport/transit. These are well above static loads.

    Nuclear fuel designers must consider 4g axial and 6g transverse accelerations, which are well above loads expected in service, but could be expected in a transport mishap.

    Ideally a material has quite a separation between YS and UTS. Usually the operating stresses are well below YS - i.e., no plastic deformation allowed. If YS is exceeded, the part/system may be unusuable and must be scrapped.
     
  9. May 6, 2010 #8
    WOW! That is what I am talking about! Thank you both very much! Please allow me some time to review all of the information, all of which is very relevant to me having a proper grasp on how to figure this out in the future.

    Thank you again for talking your valuable time to help me with this and to teach me the basics!

    I will follow up soon.
     
  10. May 6, 2010 #9
    a little side note:

    The stands are for servicing only, so the load will remain static.

    I am assuming that the material that I need for this load will not fall under the "sheet metal" category due to the needed thickness, is that correct?

    If so then what category should I be looking in where the material is large enough to cut out these parts with a water jet?

    I figured I would give you some more details to help with the proper material selection.

    -The max load the stands will see is 1000lbs each and on the 4000lb machines we will be able to use 1 on each of the 4 corners.

    -The drawing does not look exactly like the final stand but for material selection I think it should be good enough


    Also, lets also say that I removed the bend, what thickness and type of aluminum and mild steel would be appropriate for this application with the given static load remaining the same?

    Thanks
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook