Connect the boss to an outside wall or support it with gussets to add stability rather than making the boss wall thicker.
Draft is the angle (taper) added to the sides of a part to make it easier to remove (eject) from the mold.
"My part has sink marks on a flat surface." Fix: The opposite side has a thick rib or boss. Hollow out the back side or reduce rib thickness.
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: Limit the rib height to a maximum of 3 times the nominal wall thickness. injection molding part design for dummiespdf exclusive
Several software tools can help you design and optimize your parts for injection molding. Some popular options include:
Sharp internal corners act as stress concentrators. When the part is dropped or put under load, mechanical stress focuses on that sharp point, making it the most likely place for a crack to start. Sharp corners also restrict the smooth flow of molten plastic during injection, leading to air traps or incomplete fills. Design Guidelines
Try to eliminate undercuts by redesigning the feature to be molded in the direct line of pull (opening/closing of the mold). Holes and Slots
Convert thick solid areas into hollow structures with a constant wall thickness. Connect the boss to an outside wall or
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Bosses are cylindrical features used to accept screws or pins during product assembly.
The wall thickness of the boss should not exceed 60% of the main component wall thickness to prevent sink marks on the exterior face.
Minimum Draft: 0.5 degrees is the bare minimum.Standard Practice: 1.5 to 2 degrees is ideal for most applications.Textured Surfaces: If your part has a leather or sandblast texture, you may need 3 to 5 degrees of draft to prevent the texture from scratching during ejection. The Power of Ribs Hollow out the back side or reduce rib thickness
An undercut is any feature that prevents the part from being ejected from a simple two-piece mold (e.g., holes, threads, snaps, or protrusions on the side).
Like ribs, they shouldn't be too thick. Keep the wall thickness of the boss consistent with the surrounding area to prevent sink. Use gussets for added strength instead of making the boss wall thicker. Radii and Fillets (Rounded Corners)
Do all vertical walls have at least 0.5 to 2.0 degrees of draft?
: Authoritative samplings that cover the basic machine mechanics and design mindsets are available from Wiley Catalog Images .