DSG325 - Advanced parting lines and Part concavity and undercut strats

lecture 09 and 11

What is the rule of thumb for parting lines?

parting line doesn’t have to be planar

discontinuous parting lines change vertical level as they move along the part

What are some considerations for non-planar parting lines?

can be addressed with a counter lock which resists lateral movement

or symmetric manufacture of two parts at the same time

side thrust - pushes die halves laterally

What are some other considerations for parting lines?

keep material as close to parting line as possible (aka keep die pockets shallow

try to avoid thin sections and ribs

• thin areas cool faster, losing ductility and require more force to plastically deform

• reduces die life, part removal becomes more difficult

should the concave or convex side of a part face the moving platen?

concave face so that it shrinks/adheres to the side with the ejection pins

What is the mold strategy for core and cavity molds?

• all features on concave side of part created by mold B (moving)

• all features on convex side of part create mold A (stationary)

assuming a two part mold, you can expect to only ever find ejector pin marks on the ___ side of a part

concave

What are some ways to avoid undercut features in core and cavity mold design?

• avoid if functionally unnecessary

• parting line

• side - action

• inserts

• bump offs

• shut offs

How can parting lines be manipulated to avoid undercuts?

• move it up and down to “intersect” features that would otherwise be undercuts

• use a discontinuous parting line

  • required draft to be adjusted

What is a side action?

additional mold components that retract in a direction perpendicular to the main mold pull direction

which platen is a side action usually on?

stationary platen

How do bumpoffs work?

• relies on slight deformation of plastic part when ejected

• must be a smooth undercut feature with ramping geometry

• mold geometry can impact eject-ability of part

What are removable inserts?

additional mold components that are inserted into main mold by operator

plastic part forms around it and it is ejected with the part

must be removed by hand by an operator

How do shut offs work?

• part of first mold extends into other mold to reach under a feature that would otherwise be an undercut

• requires substantial draft angle for metal surfaces to slide past each other >3 degrees

which undercut strategy is this?

shut off

which undercut strategy is this?

side action

which undercut strategy is this?

removable mold inserts

which undercut strategy is this?

bumpoffs

which undercut strategy is this?

parting line manipulation