Core and Cavity Modeling

USEFUL FOR COMPLEX MOLDED PARTS

• Approaches part modeling from a tooling perspective.
  • Uses 3 basic parts to create a final product
    • Core – the male part of a mold
    • Cavity – the female part of a mold
    • Part Body – the solid that the core and cavity act upon
  • This approach simplifies modeling irregular and complex geometries

DEFAULT COORDINATE SYSTEM DEFINES THE GLOBAL ZERO

• This is necessary when using the “Design in Place” approach.
  • All major components have the same Zero
  • Assembly placement is within parts by the relationship between the geometry and the Zero
    • Global Zero is not used for:
    • Assemblies that rely on constraints
  • Components shared between multiple assemblies, for instance screws

PART COORDINATE SYSTEM DEFINES THE LOCAL ZERO

• Create a Local Zero Coordinate System
  • • Defined by the Global Zero
    • Defines the position of geometry to Global Zero
    • May be offset or rotated
    • Define axis directions based on project conventions
  • Create Local Datum Planes
    • Based on Local Zero Coordinate System
    • Base of all part geometry
    • Name them after the axis that define them
  • Alternate Approach
    • Use skeleton geometry to define and control the part coordinate system and planes from the parent assembly

USE ONLY THE LOCAL DATUM PLANES

• HIDE THE GLOBAL DATUMS, FRONT, TOP, & RIGHT AND THE COORDINATE SYSTEM IN THE LAYERS AND SAVE THAT STATUS.
• DO NOT CREATE ANY LINKS TO GLOBAL DATUMS OR COORDINATE SYSTEMS!

DEFINE REFERENCE GEOMETRY FOR THE PART

• Points, Datum Planes, and Axis in Addition to the Local Zero features
  • Define major features of the part
    • Parting lines
    • Screw boss levels and locations
    • Interfaces to other parts
    • Screen center
• Alternate Approach
  • Use skeleton geometry to define and control the part coordinate system and planes from the parent assembly

CORE PART START

• Extrude a block from the parting line
• Make the block bigger than the final part will be
• Add the basic internal shape of the part to the block on the parting line side

CORE PART DETAILS

• Add draft and rounds to features as you go
• The earlier they are added, the better the chance of them working prope

CREATE COMPLEX FEATURES AS SEPARATE PARTS

Designing as a separate part has many advantages:

• Drafts and rounds are performed on a simpler part and are more likely to work
• Common features like bosses and snaps are easier to reuse in different parts
• It is easier to swap out or remove a feature from the part model
• Interactions between the feature and complex surfaces on the part are not part of the modeling process
• The resulting part model tree is much cleaner and easier to understand

ADD SECONDARY FEATURES TO CORE PART

• Cut the secondary features from the core part
• Add rounds and drafts to surfaces created by this operation

FINISH ADDING FEATURES TO THE CORE

• Cut features like ribs past the outside of the core
  • This will ensure that they conform with the contours of the housing without relying on complex surface operations or rib commands
• When the core is complete, create a publish geometry feature of the solid surfaces

CUT THE CORE FROM THE PART

• The part is a separate model
  • It starts out with a base block, just like the core did
  • Make the block slightly larger than the desired part in all directions
• Use the cutout from other model feature
  • Select the publish geometry feature from the core as the cutter
• Add any features that rely on surfaces resulting from the cutting operation

CUT THE CAVITY FROM THE PART

• Create the Cavity Part with the same techniques as the core part
  • The cavity base block extrudes to the opposite side of the parting line from the core
• Separate features between the core and cavity based on their draft direction
• Add any finishing features

WORKING WITH MULTI-PART MODELS

• In order to modify a subpart it must be in either the working directory or the path
• To change a subpart such as the core, right click on it in the model tree and select open base
• The main part must be regenerated before the changes to a subpart will appear
• In order to create a copy of a part in another location, open the part and all subparts and use the backup command