What should be included in a DFM checklist?
A robust DFM checklist must bridge the gap between part design and tool manufacturing. It should include critical audits for nominal wall thickness, draft angles, rib-to-wall ratios, gate locations, ejector pin placement, and parting line visibility. Additionally, it must evaluate material-specific risks like shrinkage anisotropy.
What draft angle is recommended for textured surfaces?
Standard surfaces require 1° to 1.5°, but textured faces demand more "breathing room." The golden rule is to provide a base of 1.5° plus an additional 1° of draft for every 0.0254mm (0.001 inch) of texture depth. Insufficient draft leads to "drag marks," requiring expensive mold polishing and re-texturing.
What rib thickness ratio prevents sink marks?
To avoid unsightly depressions on aesthetic surfaces, internal ribs should typically be designed at 50% to 60% of the nominal wall thickness (0.5t to 0.6t). For high-shrinkage materials like Polypropylene, this ratio may need to drop to 40%. Excessive rib thickness creates a "heat reservoir" that pulls the surface inward during cooling.
Where should weld lines be avoided?
Weld lines are not just cosmetic flaws; they are structural notches. They must be avoided in A-surfaces (aesthetic faces), sealing lands (where gaskets sit), and high-stress features like snap-fits or screw bosses. If flow fronts meet at less than 135°, molecular entanglement is poor, significantly reducing local strength.
How do you identify thin steel risk?
Thin steel risk occurs whenever mold geometry becomes fragile. Check for any steel sections or "blades" in the mold that are thinner than 0.8mm. Narrow slots, closely spaced holes, or sharp shutoffs create cantilevered steel that fatigues under cyclic injection pressures. These areas should be converted to modular inserts.
What is “steel-safe” design?
"Steel-safe" is a conservative manufacturing strategy where the mold is intentionally left with "extra metal." For example, you machine a mold pin slightly smaller than the target hole. It is easy to "remove steel" (making the plastic feature larger) later via grinding, but "adding steel" requires expensive welding.
What closure evidence is acceptable?
Closure evidence must be verifiable and documented. Acceptable evidence includes updated CAD models reflecting agreed-upon changes, revised 2D drawings with relaxed tolerances, or Moldflow re-simulation reports proving that air traps or sink marks have been mitigated. A simple "email promise" is rarely sufficient.
When should you run a steel-cut gate?
The "Steel-Cut Readiness Gate" is triggered only once the 3D data is frozen, all high-risk DFM items are closed or formally accepted, the tooling concept (gates/cooling) is approved, and a quality inspection plan is defined. Cutting steel prematurely is the primary cause of major project budget overruns.
Can you use this for overmolding/inserts?
Absolutely, but the focus shifts toward interfacial integrity. For overmolding, you must check for mechanical retention features (like knurling), verify the Coefficient of Thermal Expansion (CTE) mismatch to prevent cracking, and ensure the mold has adequate sealing lands to prevent plastic leakage into functional areas.
How to convert checklist rows into action items?
Every "Fail" or "Risk" row must be assigned an Owner (Design or Tooling), a Target Date, and a Tracking ID. In a web-based DFM tool, these rows should sync directly to a project management system like Jira or Asana, ensuring no technical risk is left unaddressed.
