The wall thickness of the boss should be 50% to 60% of the main wall thickness.
Apply a minimum of 0.5 to 1 degree of draft angle to the sides of the ribs. 4. Radii and Fillets: Avoid Sharp Corners Sharp corners are the enemy of strong plastic parts. Why Radii Matter
: Instead of making a part thicker for strength, add ribs (thin support walls) or bosses (points for fasteners).
: This is the most vital rule. Maintaining consistent thickness (ideally < 5mm) prevents defects like "sink marks" and "warpage" caused by uneven cooling. Draft Angles : You must include a taper—usually at least
Will the part require ? Share public link injection molding part design for dummiespdf exclusive
A draft angle is a slight taper applied to the vertical walls of your part. This allows the part to "break free" from the mold surface as soon as the mold opens.
The thickness of the boss should be kept similar to the wall thickness, and gussets (small supports) should be used for added strength rather than just making the base thicker. 3. Dealing with Complex Features
Do all vertical walls feature a minimum of 1 to 2 degrees of draft?
The single most important rule in injection molding design is to keep wall thicknesses as uniform as possible. Why It Matters The wall thickness of the boss should be
[Pellets Feed] -> [Melting & Mixing] -> [High-Pressure Injection] -> [Cooling] -> [Part Ejection]
Designing for injection molding is a balancing act between aesthetics, strength, and manufacturability. By focusing on uniform wall thickness, adding sufficient draft, and using ribs instead of bulk, you can design parts that are cheaper to make and higher in quality.
"Injection Molding Part Design For Dummies," by Thom Tremblay and Protolabs, outlines key design principles such as uniform wall thickness, draft angles, and proper rib/boss design to ensure efficient, defect-free production. The guide provides a four-step overview of the molding process—clamping, injection, cooling, and ejection—tailored for engineers and designers. Access the PDF directly at design-technology-tutor.com .
Note: Always consult with your injection molding manufacturer early in the design phase. They can provide specific material data and DFM feedback that can save you tens of thousands of dollars in tooling modifications. Radii and Fillets: Avoid Sharp Corners Sharp corners
The radius of an outside corner should be equal to the inside radius plus the wall thickness. This ensures that the wall thickness remains perfectly uniform around the bend. 6. Design Around the Parting Line and Undercuts
angle to the mold), it will scrape against the mold during ejection, causing friction, damage to the part, and potential jamming.
This guide serves as your essential handbook for injection molding part design for dummies , breaking down complex engineering principles into actionable rules and insights. Let’s dive deep into the world of moldability.