Machine-Mold Harmony: How to Select the Right Injection Press
Introduction
Selecting the wrong injection machine leads to defects, inefficiency, or mold damage. Key factors include clamping force, shot size, and plasticizing capacity.
Selection Criteria
Clamping Force (Tonage)
Calculate based on projected part area (including runners):
Clamping Force (tons) = Projected Area (in²) × Pressure (psi) / 2000
Example: A 100 in² part at 5000 psi requires 250 tons.
Shot Size & Plasticizing Capacity
Ensure the machine’s shot size is 20–80% of its maximum capacity.
Small shots (<20%) cause inconsistent melt; oversized shots degrade material.
Screw Design
Use general-purpose screws for most materials; barrier screws for engineering plastics.
L/D ratio of 20:1 ideal for uniform melting.
Mold Size Compatibility
Check platen size, tie-bar spacing, and ejection stroke to fit the mold.
Advanced Considerations
Electric vs. Hydraulic Machines: Electric for precision (medical parts); hydraulic for large parts.
Multi-Cavity Molds: Ensure even melt distribution with hot-runner systems.
Case Study
A toy manufacturer reduced flash defects by 40% after switching to a 300-ton machine (previously 200 tons) for a multi-cavity ABS mold.
Conclusion
Audit machine specs against mold requirements during DFM. Partner with press suppliers to validate compatibility.
