Plastic Injection Part Design with Ribs and Bosses

Ribs are often used to add strength and stiffness to plastic parts in critical areas or geometric designs where thin walls exist.  This makes the part stronger with added support but can also cause sink marks on the exterior side of the part, where the rib comes together to meet the main wall in the part design.  When using ribs to add support, remember the general rule that the rib should not be more than 60% of the wall thickness.  Adding ribs to an injection mold design will increase costs, and may require EDM processes.  

Working with an experienced injection mold manufacturer will give you the best value for your investment.  Skilled journeyman mold makers and experienced injection mold design engineers will have the best knowledge of where to place ribs for added support and how this will affect the tool design, and the cost.

Mold making companies today can provide you with a two-dimensional computer aided design to show you exactly how your injection mold will produce the required plastic part, and alert you to any problematic areas ahead of time.  

Bosses are a very common feature in many plastic parts, and comes from the word emboss, which means a raised stamp or design, standing out on the surface.   Bosses that are designed with too thick dimensions can cause sink marks similar to the use of ribs.  Utilizing the proper ratio of ribs to bosses a molder can reduce or eliminate unsightly sink marks caused by either feature.  

Ribs used to connect boss areas to a side wall can add strength while avoiding sink marks.  Sharp corners are another area where excessive stress can concentrate and adding small radii feature in this area can strengthen the corner and reduce excessive stress.

Michiana Global Mold is a full-service mold design and construction company, with vast experience in all types of molds.  We offer an ISO registered Quality System, state-of-the-art domestic mold building facility with off-shore partner, and decades of experience with precision, complex tooling.  Contact us today for a FREE design consultation and to speak with one of our highly skilled design engineers.