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MEC 1012
Design Communication II

MEC 1012 Assignments

MEC 1012 - Assignment 4
Adaptivity, Weldments,
and Casting/Molding
Due in lab week 7

Design a functional mechanical assembly (in metric units) that includes several types of adaptivity, a weldment, and a cast or molded part. Also, demonstrate use of orthographics to view your design (check sections). Assignment 5 will ask you to produce the set of working drawings and track revisions.
If you'd like some inspiration, consider using this press concept.

 

Checklist: (hit links for details)
  1. Illustration Highlighting Adaptivity by:
    1. Algebraic Equation
      1. Model Parameters
      2. User Parameters
      3. Linked Parameters
      4. Embeded Parameters
    2. Projection
    3. Assembly Constraint
    4. Derived Part or Assembly
  2. Weldment
  3. Cast or Molded Part
  4. Check Sections
  5. Metric units?
Related Links

Details

  1. Illustration Highlighting Adaptivity - Make sure it's clear exactly where you have demonstrated what. Consider using a .idw sheet with a labeled view of your assembly or provide a labeled sketch (example)

    1. Algebraic Equation - a relationship that uses variables .Inventor calls its variables 'parameters' and allows you to call on the current value of a parameter by including the name of the parameter in an equation (ex. d0=10in, or Wall=2mm, or Length= 2*Width)
      1. Model Parameters - These are created when you add general dimensions and features to the model (named by default d0, d1 etc.). 
      2. User Parameters - These are predetermined numbers/algebraic equations independent of features. These are best for values used repeatedly such as draft, wall thickness and so on.
      3. Linked Parameters -These are laid out on a spreadsheet (Excel) and then  linked to the model.  A value change in the spreadsheet is immediately reflected in the model. This is a permanent relationship so the spreadsheet MUST reside in the workgroup folder. (Or the path must be designated in the project file.)
        How to set up the spreadsheet:
        1. Use A1 to label the purpose of the spreadsheet.
        2. Add column labels in a lower row.
        3. Use column A  to add parameter names.
        4. Place values and units in the following columns.
        When linking or embedding the spreadsheet you MUST designate the first cell which has the label for the first row of values. (In the example A5)
      4. Embeded Parameters - These are initially laid out on a spreadsheet (Excel) and then pulled into the model. The link is then severed to the spreadsheet. Subsequent changes to the original spreadsheet will NOT be reflected in the model. Instead changes must be made to the embedded spreadsheet.

    2. Projection - In sketch mode use 'project geometry' to project an existing edge (from the same or a different part)  into the sketch. The line in the sketch will adapt to changes in the edge that was projected.

    3. Assembly Constraint - By leaving some aspect of a part unspecified (like leaving out a length dimension in a sketch),  that part can be made to adapt to other parts in an assembly based on assembly constraints.  For example, a block (with length unspecified)  could be placed inside a box and mated to opposite inside walls of the box.  The dimensions of the box would then drive the block. You must have the sketch as well as the feature and part designated as adaptive.
      This capability is active when you see the swirling arrow symbol:

    4. Derived Part or Assembly - This allows you to use an existing part as the base for a new part. It allows you to scale an existing part and/or create a mirror image of the original. You cannot modify the derived features, but you can add new features. If you change the parent model these changes will be reflected in the derived part. Derived parts also allow you to make working drawings at various stages of manufacturing (for example, you can show machining features that are added after welding or casting by deriving the final part from a weldment or part that models the cast features. Consider checking out a how to article on deriving a weldment for specification of post-weld machining. You can also use basic sketch geometry for a derived part to drive several parts.

  2. Weldment - This is an assembly mode (under the application menu) that allows you to add welds to your parts. If this is an intermediate step in your manufacturing process you will need to use "save copy as" to create a copy of the model before welding. There will be drawings done at this point for the fabricators. Then  you will add the welds using the specialized commands:
    Prepartions
    Here you add chamfers for the welding bead
    Welds  
    You designate the surfaces that touch the bead
    Machining
    These are post-welding processes that finish the welding stage
    All of these processes can be specified (dimensioned) on the new .idw's that can now be generated specifically for these processes.

  3. Cast or Molded Part - In casting (metals) or injection molding (plastics), molten (liquid) material is forced into a hollow space between shaped pieces of steel (the mold).

    Definitions
    :
    Draft
    Taper that allows part to release from mold                                       
    Cavity
    Primarily Concave on steel/ convex on part
    (the outside cosmetic surface)

    Core
    Primarily Convex on steel/ concave on part
    (the inside where the knockouts show)

    Parting Line  
    Boundary between Cavity & Core

    Specifications for casting:
    Cavity Draft
    5 degrees min
    Core Draft
    1 degree min
    Wall Thickness
    2.5 mm
    Rib Thickness
    Max 60% of Wall Thickness (1.5 mm),  Min 1 mm

    Specifications for injection molding:
    Cavity Draft
    2 degrees min
    Core Draft
    .5 degree min
    Wall Thickness
    2 mm
    Rib Thickness
    Max 60% of Wall Thickness (1.2 mm),  Min .5 mm

  4. Check Sections - Use a .idw sheet with section views to see critical aspects of your design more clearly.  Is your draft tapered the right way? Are your ribs too thick?
For further explanations do not hesitate to use “help” both locally and at the Autodesk web site. Also, there are numerous samples in the application that can be very useful in using a new series of commands.
For your pleasure there is a gear blank available at V:/MEC/1012/Templates & Blocks. It is based on a spreadsheet. You may copy it to your folder and modify it there. Also, you are encouraged to use standard parts from the library or from various sites off the web.
Please send us any other good sites you find so we can add to this list:

Related Links: (use the Back button to return to this page)
  1. Here is a .pdf of various configurations of circlips 
  2. Apex Fasteners for mechanical designers
  3. More fasteners
  4. Multiple sites for gears of all types
  5. Bearings & Bushings
  6. Thomas Register-The BIBLE of builders of things mechanical
  7. An example of A to Z in new product development
  8. More fasteners BUT check out the engineering knowledge base
  9. Autodesk Tutorials and How To Articles 
  10. efunda Tap Drill Chart - ex. H drill for free fit clearance on 1/4-20 
Developed by Mary Waldo and Paul Johnson
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