How to Read a Moldflow Report: A Buyer’s Field Guide

This is the practitioner’s read-the-report guide, organized around the four sections every Moldflow report should have and the specific numbers that determine whether you sign off or push back.

Section 1: Fill Analysis Results

The fill analysis section answers one question: will the part fill, and where will the flow fronts meet?

Fill time animation

The flow-front animation is the most important visual in the report. Watch it frame by frame. You’re looking for:

• Last-to-fill location. The last point to fill should be far from the gate. If it’s near the gate or under-filled, the simulation flagged a flow path problem the geometry needs to fix.
• Flow front symmetry. In a symmetric part with center gating, the flow fronts should reach the edges at the same time. Asymmetric flow indicates wall thickness imbalance, gate location off-center, or material flow anisotropy.
• Hesitation. If the animation shows the flow front pausing at a thin section before resuming, that’s hesitation — and it usually causes a short shot or weld line in production. Thicken the section or relocate the gate.

Injection pressure at switchover

The single number every Moldflow report buries on page 12 — and the one that matters most. This is the pressure the press needs to fill the part. If the simulation reports 18,000 psi and your production press maxes at 22,000 psi, you have only an 18% safety margin. Industry standard is 25-30% margin minimum. Below that, push back on the design or upgrade the press.

Predicted weld-line locations

Every weld line should be flagged on the report with both location and predicted strength (typically 60-90% of the bulk material strength). For each weld line:

• Is it on a cosmetic surface? If yes, gate location needs adjustment.
• Is it on a load-bearing feature? If yes, check the predicted strength against the applied stress.
• Is it acceptable as-is? Document the trade-off.

Section 2: Pack Analysis Results

The pack phase determines part dimensions, density, and residual stress. Two numbers matter:

Volumetric shrinkage at end-of-cycle

Most reports color-map shrinkage across the part. Look for:

• Uniform shrinkage: Good. The part shrinks predictably and warpage will be minimal.
• High-shrinkage zones (red): Either thick sections that need more pack pressure or under-packed regions caused by gate freeze-off. Both cause sink marks.
• Low-shrinkage zones (blue): Over-packed regions, often near the gate. Usually fine but can cause part stress that telegraphs as warp later.

Cavity pressure at part edges

The cavity pressure at the last-to-fill point should not drop below 30% of the gate pressure. Lower than that and you’ll see sink marks, dimensional shrinkage variation, and density gradients. The fix is usually pack pressure profile adjustment, not steel modification.

Section 3: Warp Analysis Results

Warp is the section buyers tend to skip because the visualization is the most confusing. Focus on three things:

Total displacement contour map

The contour map shows how much each region deviates from nominal geometry after the part cools. The number that matters: peak displacement on any controlled dimension. If your drawing calls out 0.15 mm tolerance and Moldflow predicts 0.31 mm peak warp, you have a problem — either the design needs symmetry fixes or you accept dimensional QC failures at the rate of ~30-50% of parts.

Warp source decomposition

Good reports break warp into three contributing causes: differential shrinkage (cooling-driven), orientation effects (fiber/molecular alignment), and corner effects (geometric). The breakdown tells you the fix:

• Cooling-driven warp: Add or rebalance cooling channels. Steel-side fix.
• Orientation warp: Change gate location or add a secondary gate to balance fiber flow. Design fix.
• Corner-effect warp: Reduce thickness transitions or add ribbing. Design fix.

Section 4: Cooling Analysis Results

The cooling section is where the simulation pays for itself on cycle time and dimensional stability.

Cooling time to ejection temperature

This is the minimum cycle time the part allows. The number the press operator will use to set the actual cycle. If Moldflow predicts 18 seconds and the production press is running at 12 seconds, the parts are coming out hotter than spec and dimensional stability is at risk.

Mold surface temperature uniformity

The temperature delta across the cavity surface should be under 5°C for normal parts, under 3°C for tight-tolerance parts. Larger deltas mean parts on the hot side are dimensionally different than parts on the cool side. The fix: add cooling channels in the hot zones or reroute existing channels.

Red Flags That Require Pushback to the Mold Maker

If you see any of these in the report, escalate before T1 sampling:

• Injection pressure margin below 20%
• Predicted warp exceeding any controlled dimension tolerance
• Weld line on a cosmetic surface where the drawing requires no defect
• Cooling time delta of more than 8 seconds between simulation and your target cycle time
• Cavity surface temperature delta exceeding 10°C
• Air-trap locations without vent provisions in the mold base design

Any of these means the design or tool needs a change. Catching them in the simulation phase costs hundreds. Catching them at T1 costs thousands. Catching them in production costs five figures.

What the Executive Summary Won’t Tell You

Executive summaries written by Moldflow service providers tend toward optimism — they want to deliver “passes simulation criteria” because that’s what clients want to hear. Read the underlying data. Specifically:

• The injection pressure number, not the qualitative “within press capability” statement.
• The peak warp number on every controlled dimension, not the average warp across the part.
• The weld-line locations on a 2D drawing overlay, not just the 3D animation.

FAQ

What injection pressure margin should I require?

25% minimum, 30% recommended. A 25% margin lets you tune pack profile without bottoming out the press. Below 20% and the press is the limiting factor on cycle and pack quality.

How accurate are Moldflow’s warp predictions?

For unfilled resins, typically within ±15% of measured warp at T1. For fiber-filled resins, ±25-30% — fiber orientation is harder to predict accurately. Use Moldflow warp data as directional, not absolute.

Should the report include a 2D overlay of weld lines on the drawing?

Yes, always ask for it. The 3D animation is dramatic but the 2D overlay on the drawing is what you’ll reference during T1 sample inspection.

How long should I keep a Moldflow report on file?

For the life of the tool plus 7 years (typical product-liability retention). When the tool needs a mid-life modification, the original Moldflow analysis is the baseline to compare against. We’ve referenced 6-year-old reports on production tools that were getting fiber-loading changes.