There’s a gap between a design that looks finished and a design that’s actually ready to be moulded, and it catches a lot of product teams out. The CAD model is approved, the dimensions are locked, the part does what it’s supposed to do, and yet the first thing a moulder does when it lands on their desk is start flagging problems. That’s exactly what a DFM checklist for injection moulding is for: a design for manufacture (DFM) review that checks the design against what injection moulding can and can’t do well, before you commit to steel. Understanding what it actually checks for can save a project weeks and a fair amount of money.

Why “finished” and “ready to mould” aren’t the same thing

Injection moulding is a manufacturing process in which molten plastic is injected under pressure into a prA part can be functionally correct and still be a headache to manufacture. DFM looks at the design purely through the lens of what injection moulding can and can’t do well, separate from whether the part works as intended.

The reason this matters comes down to timing. Change something at the CAD stage and it costs you an afternoon of engineering time. Change it after the tool’s been cut and you’re looking at re-machining steel, adding inserts, or occasionally starting the tool over. A design review before tooling is committed is, frankly, the cheapest insurance you’ll ever buy on a project.

What a review actually looks for

• Wall thickness. Uneven walls are behind a huge share of moulding defects. Thick sections cool slower than thin ones, and that mismatch is what causes warpage and sink marks. Keep the wall thickness as even as you can across the part, and if it has to change, let it taper rather than step.
• Draft angles. Every face that runs parallel to how the tool opens needs a bit of draft, usually a degree or two at minimum, so the part actually releases from the tool instead of dragging or scuffing. Textured surfaces want more draft than smooth ones. This is probably the single most common thing missing from early CAD, because a part with zero draft looks completely fine on screen. The problem only shows up the moment someone tries to mould it.
• Ribs instead of thick sections. If a part needs more strength, the first instinct is usually to make the wall thicker. Don’t. Use a rib instead. A thick solid section cools unevenly and tends to leave a sink mark right on the opposite face, whereas a rib gets you the stiffness without dragging that problem along with it, as long as it’s kept to roughly half the thickness of the wall it sits on.
• Radii on internal corners. A sharp internal corner is a stress concentration waiting to fail, and it doesn’t help the material flow through the tool either. Round it off wherever the part allows it.
• Where the gate and parting line sit. Both leave a mark on the part, the gate a small witness mark, the parting line a fine seam. Worth deciding early where that can live, ideally somewhere non-cosmetic, rather than leaving it to whoever cuts the tool to decide.
• Undercuts. Snap fits and clips are all doable, but each one usually means a side action or a lifter in the tool, which adds cost. Nothing wrong with including them if they earn their place, just don’t let them turn up as a surprise on the quote.
• Tolerances. Only tighten a tolerance where the part genuinely needs it, a mating face or a seal, say. Tightening everything by default adds cost for no real benefit and makes the part harder to hold in production.
• Material. Tooling is built around how a specific material shrinks as it cools, so the material needs to be locked in, not provisional, before the tool is cut. Swap it out afterwards and there’s a real chance the part stops holding tolerance.

Why a good reviewer beats a checklist

A list like the one above is a decent starting point, but it only gets you so far. What a good design review actually does is apply judgement to the part in front of it. A missing draft angle on a hidden internal rib is a non-issue. The same missing draft angle on a large cosmetic panel is a real problem. A checklist can’t tell you which is which; someone who’s moulded a few thousand parts can.

This is really the point of getting a moulder involved before the design is finished rather than after: reviewing for mouldability, tolerance risk, and material fit while changes are still free to make.

What skipping it costs

Projects that skip a proper review rarely fail outright. What usually happens is slower and more annoying: a first-article part that’s just outside tolerance, a tool that needs reworking to add draft or fix a sink mark, a launch that slips two or three weeks because of something that was entirely avoidable. None of it looks dramatic on its own. Add it up and it’s almost always more expensive than the review would have been.

How Naiad guides you from start to finish

Getting a design review done is one thing. Getting it done in a way that actually moves a project forward is another, and that’s really where we try to add value beyond just handing back a list of issues.

It starts before you’ve even sent anything over. If you’re not sure what stage your design needs to be at, or what to include, we’ll talk you through it rather than leaving you to guess. Some customers come to us with a finished CAD model, others with a rough concept and a sense of what the part needs to do. Both are fine starting points.

The review comes back as a conversation, not just a report. Where something needs changing, we’ll explain why it matters for that specific part, in that material, at that volume, rather than just flagging it against a generic rule. A missing draft angle on a cosmetic panel gets explained differently to the same issue on a hidden rib, because the consequence is different, and you shouldn’t have to guess which one actually matters.

If the design needs more than a review can fix, we don’t just hand it back. Where a project needs proper design or engineering input, reshaping a concept, running FEA, developing something closer to a finished part, we can pull in that capability through IDC rather than leaving you to find a separate consultancy and coordinate between two suppliers yourself.

Once the design’s ready, nothing changes hands. The same team that reviewed the part carries it through tooling and into production, so nothing gets lost in a handover and you’re not re-explaining the project to someone new halfway through.

That continuity is really the point of doing it this way: one point of contact, from a rough idea through to a part coming off the tool.

Getting a review done

Send over a STEP file, or whatever CAD format you’re working in, along with your expected material and rough annual volume, and a 2D drawing if there are tolerances that really matter. Do it before the tool’s committed, while changes are still cheap, and that’s really the whole point of doing it at this stage rather than the next one.