As plastic cools, it shrinks onto the core. If the side walls are perfectly vertical (zero draft), the part will lock onto the mold. Ejector pins will punch through it. Robots will tear it. The operator will curse your name.
: The outer diameter of a screw boss should be roughly 2x the inner screw hole diameter. 2. Mold Base Anatomy and Core/Cavity Split
You can design a perfect CAD model, but the plastic doesn't read CAD. It follows physics. Mold Flow Analysis (simulation software like Moldflow or Moldex3D) is no longer optional for complex parts.
: Limit height to less than 3 times the main wall thickness to prevent filling issues.
Gussets should support bosses, and the inner hole diameter should dictate a wall thickness around the boss of about 60% of the main wall. 2. Mold Base Anatomy and Steel Selection injection mold design guide
INCORRECT CORRECT | | | / \ | | Thick | | / Thin \ | | Wall | |/ Wall \| +-------------+ +-------------+ (Causes Sink) (Uniform Wall) Uniform Wall Thickness
Cooling channels should be placed from the mold surface.
I can provide specific adjustments for shrinkage, gating, and steel selection based on your application. Share public link
Automatically shear off from the part during ejection, reducing post-processing labor. As plastic cools, it shrinks onto the core
: The plastic in the runner freezes during every cycle and is ejected with the part as waste (or regrind). Fully round runners offer the best volume-to-surface-area ratio, minimizing pressure drop.
Do the ejector pins target structural areas to avoid punching through the part? If you want to tailor this further, tell me: What you are planning to mold? What is your target production volume ? Do you have a part drawing or rough geometry in mind?
The location and type of gate affect part appearance, weld lines, and packing pressure.
80% of the injection molding cycle is cooling time. Efficient cooling = lower cost per part. Robots will tear it
Use this Injection Mold Design Guide as your roadmap. Start with uniform walls, respect the draft, vent the air, and cool the steel. If you do that, you will turn molten resin into profitable parts consistently, predictably, and without headaches.
Every resin shrinks as it cools. You cannot cut a mold to the nominal part dimension.
Position the gate at the thickest section of the part. Never gate into a thin wall. The flow should move from thick to thin.
Before we look at specific features, we must adopt the mindset of the mold maker. An injection mold is a pressurized vessel. Typical melt pressures range from 10,000 to 30,000 PSI. Every design decision must answer one question: How does this affect melt flow and ejection?