ADDITIVE MANUFACTURING PREPRESS

Industrial SLS & MJF 3D Printing Powder Evacuation & Vector Prepress Guide

Powder bed fusion additive manufacturing technologies like Selective Laser Sintering (SLS) and HP Multi Jet Fusion (MJF) build components without dedicated support structures by using the surrounding un-sintered polymer powder bed as a natural support. When lightweighting parts through internal hollowing, engineers must design calibrated escape holes and account for volumetric polymer shrinkage.

1. Powder Evacuation Hydraulics

Trapped un-sintered powder inside closed cavities increases component weight and risks thermal sink deformation. The minimum escape port diameter $D_{\text{escape}}$ scales with internal hollow volume $V$ and the number of ports $N$ via $D_{\text{escape}} \ge \max(3.5\text{ mm}, 1.8 \cdot (V/N)^{1/3})$. Positioning two escape holes on opposing geometric faces creates a pressurized pneumatic flow circuit during post-processing blasting, reducing depowdering cycle times by over 70%.

2. Engineering Specifications & Tolerances

3. 2D Slicing & Direct Vector CAM Checklist

• Consistent Boundary Winding: Slicing engines require outer perimeters oriented clockwise (CW) and internal hollow holes oriented counter-clockwise (CCW) to prevent inverted solid void infill.
• Thermal Mass Balancing: Avoid abrupt transitions between thick solid blocks (> 15mm) and thin walls (< 1.0mm) to prevent uneven cooling shrinkage sink marks.
• Living Hinge Grain: Orient living hinges parallel to the build platform (XY plane) for maximum fatigue life (> 50,000 flex cycles).