MIG-Welded Gearbox Casing

  1. GPillay New Member

    Messages:
    2
    Location:
    South Africa, KZN
    Good day,
    I hope you are well :)

    The *Please read before posting* was great motivation, so here's my shot in the dark...

    Background:
    I have a deadline fast approaching but this is more for my personal learning.
    Currently designing for a 3rd year machine design course. The (group) project brief requires a 2-stage reduction gearbox, shafts, gears and casing to be designed for marine applications. Steel plates were prescribed as the material for the casing. My concern is welding symbols. I am definitely not confident in my welding symbols which I've attached to this manufacturing drawing. The group has decided on an oil sump for gear lubrication.

    Question:
    It was suggested that all welds to the outer casing be full-penetration welds to ensure that the gearbox seals. I have indicated rather thick full-penetration welds across the breadth of the gearbox at the thick inner plates. The gearbox is covered by a thinner steel sheet bent around the gearbox and welded on. Is this the right approach to welding up the casing? Do these weld symbols make sense? Is the thickness realistic? If I give this to a MIG welder would they be happy to manufacture it?


    1.PNG 2.PNG



    Have a great day.
     
  2. barking mat

    barking mat Barking at Pigeons

    Messages:
    4,606
    Location:
    Brittany, The Arz Valley.
    I can't comment on the welding icons.

    But shouldn't it be attached to the bell housing of the motor?
     
    Mr Roo likes this.
  3. GPillay New Member

    Messages:
    2
    Location:
    South Africa, KZN
    Usually, I suppose. This is the supplied schematic and it appears that this is a second gearbox to the one attached to the bell housing of the motor.

    upload_2020-10-24_18-11-54.png
     
    barking mat likes this.
  4. bricol Member

    Messages:
    1,518
    N.Yorks, UK
    My usual get out is "fully welded all over" and "must be watertight" or "air tight to 5psi" . .
     
  5. Feet 'n Inches

    Feet 'n Inches Out of the rat-race at last

    Messages:
    363
    Location:
    Devon, GB
    Perhaps this link will help? The British standard for weld symbols is covered by this: BS EN 22553, would your college library have that info?
     
  6. Brad93

    Brad93 M J B Engineering

    Messages:
    10,386
    Location:
    Essex
    They’re specifying double bevel fillet welds. What’s the access to the inside. Back-gouging or grinding? Limits on distortion?
     
  7. Brad93

    Brad93 M J B Engineering

    Messages:
    10,386
    Location:
    Essex
    Also what’s 377? A number there, usually in brackets, would be the Welding process number.

    MAG is 135
     
  8. Brad93

    Brad93 M J B Engineering

    Messages:
    10,386
    Location:
    Essex
    +/- 0.1mm post welding can’t be held unless you want to invest a few thousand pounds in jig development and Procedure development.
     
  9. hobby_machinist Member

    Messages:
    56
    Location:
    Croatia
    +/- 0.1 might be tolerance between axis when bored out. If its welded within few mm id be happy because its not thin steel sheet that you can tack, re tack and beat till it fits
     
  10. Will! Member

    Messages:
    98
    Location:
    Derby - England
    I know I'll sound like a pedant but your dimensions are positioned a bit illogically. I've not identified all of them, because that would be doing your coursework for you, but here's some pointers.

    Where you've got 600 and 540 in grid reference C6, you would be better to keep the 600 and dimension the chamfers at the end instead, the same goes for 445 and 60 at the bottom of that view, go with 505 across the full width, then show the 60. Like you have with the 575 and 60 on the other drawing.

    You've put 390 twice on the one with 'wings', it's not wrong but it is bad practice to dimension the same feature twice.

    You've also missed the positional dimensions for the Ø11 holes.

    Move "M10 plug" to the bottom view, you're pointing at a feature that can't be seen (mention that it is "2x M10 plug", the same goes for the "8x Ø11 - 15 deep").

    Have a think about tolerances, the dimensions of your casing are not as important as the alignment between the internal holes for the bearings. You can probably +/-2mm or more on the outer casing, the bores for the shafts will have to be more like +/-0,1mm. Having these two tolerances allows the welder some breathing space to keep cost down, while constraining the machining (which you will do after welding, to get your accuracy back) to meet your function.

    Also have a look into Geometric Datums and Tolerances, it's a whole extra world of how to describe things on a drawing but you'll hit it in your first year of your career if you end up in design.

    Also, drop the bit about the sump lubrication from the drawing, the person manufacturing it has no interest in how you're lubricating your gearbox. If anything, this should be on an assembly drawing with the gears in - not in the housing drawing.

    Final note. Put "dimensions in mm" somewhere. Saves it being enormous :)

    Tactical edit: Get hold of a copy of "Manual of Engineering Drawing" by Simmons, Phelps and Maguire. It's served me extremely well.
     
  11. indy4x

    indy4x Forum Supporter

    Messages:
    1,835
    Location:
    Pontypool, South Wales. UK
    Just bought a copy based on your comments.

    Currently learning AutoCad at a local college, did Inventor last year but didn't finish due to Covid messing up the course. Wasn't overly happy with the level they were teaching at, it was all too rushed and ended up doing most of the learning myself

    Anyway, new college this year, it's only 1 evening a week and loads better but year 1 is AutoCAD and year 2 Inventor. I did O level engineering drawing but that was over 35yrs ago so forgotten lots, hopefully this will help get my head around standards while I battle on getting used to the vaguries of AutoCAD
     
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  12. Ged93 Member

    Messages:
    38
    Location:
    Italy
    Mmmm ... the drawing is a bit tricky and probably a builder/welder would not understand what you want , same with machining ( I'm not sure it can be machined also ) .

    Normally when you got a machined part like that it really helps to make 2 different drawings : one that shows the ' raw ' item without machining , including on dimensions the stock material necessary to reach machining tolerances and final dimensions , then a second type of drawing which gives dimensions necessary to machine the part . So imagine a classic workshop , you need to give informations to cutting department ( saw , plasma ,laser ) for every piece , then you need to tell to the welding/carpentry department how to assemble everything , then everything goes to machining department and they need to know what to do , big companies here work like that because it really helps to save time and money .

    I come from a technical/mechanical school and I remember that they never teach you an important thing ( my father told me this the first day of work with him ) : drawing is like language , we use language to speak with other persons because we want to tell something , if your language is incorrect , the others won't understand , the same happens with technical drawing : when you are making a drawing you must make sure that the others ( welding , machining , bending and so on ) will understand what your are ' talking about ' without errors or missunderstanding .

    It's pretty normal here to see technicians sending drawings to production and after 5-10 minutes you hear some blasfemies coming : missing dimensions ,tolerances , materials , quantities ... so funny
     
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