8 Must Checklist Items in a DFM Report

1. Draft angle analysis

The report should check that all side walls, ribs, columns and surfaces have enough draft angles in the mold opening direction.

Insufficient draft angle may lead to product sticking, drag mark, eject mark, part deformation, and even increased wear of the mold core. For ordinary glossy surfaces, 1°–2° is often used as a preliminary evaluation range, but it cannot be used as a fixed standard for all products. The actual angle should be determined based on the plastic material, product depth, surface requirements and shrinkage characteristics.

The darker the grain, the greater the draft angle usually required. If the appearance requirements limit the draft angle, the DFM report should clearly indicate the possible risks rather than simply stating “mold can be opened”.

2. Analysis of Wall Thickness Uniformity

Variations in wall thickness affect plastic flow, packing, and cooling. Excessively thick sections easily cause sink marks, bubbles, or internal voids, while sections that are too thin may lead to short shots, the need for higher injection pressure, or insufficient structural strength.

There is no single “ideal” wall thickness applicable to all plastics, it depends on factors such as material flow characteristics, product dimensions, flow length, structural strength requirements, and intended application. The 1.5–3.0 mm range is for common products.

In DFM, any significant, abrupt changes in wall thickness should be highlighted. Suggestions including coring out material, incorporating gradual transitions, adding fillets, or strategically placing reinforcing ribs can be provided.

3. Gate Location and Filling Feasibility

The DFM report should specify the recommended gate location, type, and quantity, while also analyzing the flow path of the plastic from the gate to the extremities of the part when neccessary.

Improper gate selection can lead to weld lines appearing in load-bearing areas or on visible surfaces; it may also cause issues such as trapped air, jetting, uneven packing pressure, and dimensional instability. Some of these problems can be solved by adjusting molding parameters, but if the issue comes from an incorrect gate location often cannot be resolved through injection parameters adjustments alone.

For large, thin wall, multi-gated, or geometrically complex products, mold-flow analysis should be used to verify the filling balance, weld line placement, clamping force, and pressure distribution. Performing filling simulations for complex parts at the early stage of development is beneficial for design optimization.

4. Parting Lines, Undercuts, and Mold Structure

The DFM report should clearly indicate the proposed parting lines and identify any undercuts, side holes, or snap-fits that would affect the moldability.

If the mold requires slides, lifters, or removable inserts / pins, the DFM analysis should specify the orientation and expected travel distance of these components. For undercuts that serve no functional purpose, the primary discussion should focus on if the product design can be modified to eliminate it to avoide no-needed complex structure.

Complex molds are not inherently undesirable; however, every additional moving mechanism typically increases manufacturing costs, maintenance requirements, and long-term production risks.

5. Ejection System and Manufacturing Feasibility

DFM should consider sufficient and well-balanced ejection points for the part. Ejector pins should not be concentrated in areas such as thin-walled sections, deep ribs, visible cosmetic surfaces, or places easy to cause deformation; otherwise, issues like eject marks (“whitening”), raised areas, warping, or obvious ejector pin marks may occur.

For parts with deep cavities or large surface areas, it may be necessary to use larger ejector pins, sleeves, lifters, or stripper plates to distribute the ejection force. Furthermore, it is essential to verify if features such as deep, narrow slots, sharp corners, excessively small radius, or exceptionally deep ribs are actually feasible to do machining.

Just because a structure can be modeled in 3D software,but it does not mean that it can be produced cost-effectively and stably.

6. Cooling System and Risk of Deformation

The mold cooling system is frequently overlooked, yet it directly impacts the molding cycle, dimensional stability, and the risk of product deformation.

DFM should identify areas with thick wall sections, deep cores, and locations where routing cooling channels is difficult. If the cooling rates across different parts of a product is big, it can lead to uneven shrinkage and warpage. For critical products, it is insufficient just examining the product structure, what a must-check is to evaluate whether the mold provides adequate space for an effective cooling system.

7. Venting and Air Trap Risks

As plastics enter the mold cavity, the air must be expelled in a timely manner. DFM analysis could also help identify the final areas to be filled, the ends of deep ribs, weld lines, and potential locations for air trap. It can recommend the inclusion of appropriate venting—for instance, along the parting line or near inserts and ejector pins.

Inadequate venting can lead to issues such as burning (scorch marks), short shots, reduced weld line strength, and dimensional instability. Simply increasing the injection pressure or speed may, in some cases, exacerbate these problems.

So, sometimes, venting analysis should be evaluated in conjunction with gate placement and the filling sequence.

8. Shrinkage, Tolerances, and Dimensional Stability

The DFM report should specify the material grade, anticipated shrinkage, and critical dimensional requirements. Plastic shrinkage is not a fixed value, it is influenced by factors such as product geometry, wall thickness, gate location, mold temperature, melt temperature, and holding pressure conditions.

A DFM analysis should check tolerances for critical functional dimensions and non-critical dimensions, and check if the specified tolerances align with the capabilities of the chosen material and manufacturing process. Imposing overly strict tolerances on all dimensions does not necessarily improve product quality; instead, it may lead to increased costs for mold adjustments, inspection, and production.

A high-quality DFM report should go beyond merely listing issues—it should identify potential risk areas, explain the underlying causes, outline the impact on quality, propose solutions, and highlight items requiring client confirmation.

Before the manufacture of an plastic injection mold, the product team’s primary concern should not be whether the mold can be built, but rather whether it can consistently and reliably produce parts that meet all functional and cosmetic requirements over the long term. This is the true value of a DFM review.

SPM has over 15 years experience of helping customers to analyze their product design and realized their design to final real products. If you have neew project, maybe we can talk?