Aug 31, 2026Technical Case Studies

Why 2D Drawings Are Not Enough for Injection Molding DFM | A Real RFQ Story

A real engineering RFQ shows why 2D drawings can start an injection molding review, but 3D CAD is often essential for reliable DFM, tooling and cost optimization.

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When a Good Cost-Down Idea Is Still the Wrong DFM Solution

Recently, we received a very detailed RFQ through www.jeancen.com from an Australian engineering company.
It was the kind of inquiry mold makers like to receive.
The customer had already prepared 2D drawings, product photos, several product sizes, and a clear list of requirements.
The part was a large plastic component intended for outdoor use in a construction environment.
The customer was already thinking beyond simply “making it in plastic.”
They were asking about:
  • impact resistance;
  • UV resistance for Australian outdoor conditions;
  • flexibility in certain fixing areas;
  • low weight;
  • lower material consumption;
  • simple and economical tooling;
  • fast molding cycles;
  • storage and shipping efficiency;
  • possible flame-retardant requirements;
  • tooling cost;
  • part weight;
  • production cost;
  • T1 timing;
  • mold life;
  • packaging and container loading.
In other words, this was not really a request for a mold quotation.
It was a request for an engineering and manufacturing solution.
And that created an important question for us:
How much should a mold supplier promise when the customer has detailed 2D drawings, but no 3D CAD?


The Temptation Is to Quote First

When a serious RFQ arrives, there is always pressure to respond quickly.
The customer may already be speaking with several suppliers.
Another factory may send a tooling price tomorrow.
Another may send a part price the same day.
So it is tempting to take the 2D drawing, make several assumptions and return a number as quickly as possible.
But a fast number is not always a useful number.
From the drawings, we could understand the general product size, its use environment, many visible features, and the customer's cost targets.
Our engineer could also start considering possible material directions.
For this particular application, modified PP and modified HDPE with UV and possible flame-retardant additives were identified as initial directions for further evaluation.
But there was something we could not reliably calculate:
the actual molded part.
Without the complete 3D geometry, we did not yet have enough information to confidently determine the exact volume, weight, full wall-thickness distribution, rib structure, and all of the mold-forming details.
And those details affect almost everything that comes later.


Why Part Weight Is More Than a Number on a Quotation

For many injection molding projects, part weight directly affects material cost.
But in this case, the material itself also required additional consideration because of outdoor exposure and possible flame-retardant requirements.
To obtain a meaningful material quotation, we first needed a reasonable estimate of how much material each part would actually consume.
That sounds simple.
But for a large plastic part with holes, ribs, edges, and structural features, estimating weight from a front-view drawing can easily create false accuracy.
And once the weight is wrong:
material cost is wrong;
the part quotation is wrong;
cycle assumptions may be wrong;
and sometimes even the press selection is wrong.
So we asked the customer for the 3D STEP files.
Not because we wanted more paperwork.
Because we wanted the quotation to be based on the product that would actually be molded.


2D Drawings Can Start a DFM Review. They Cannot Always Finish It.

A good 2D drawing is extremely useful.
It can tell an experienced mold engineer a lot.
It can reveal obvious size issues, hole patterns, certain thicknesses, general product architecture, and areas that deserve attention.
It is enough to start asking engineering questions.
But complete DFM normally requires more.
For example:

Wall thickness

Is the wall truly uniform?
Are there local heavy sections hidden behind the visible surface?

Ribs and structural features

Are ribs helping stiffness efficiently, or creating unnecessary material and sink risk?

Warpage

Will one area cool and shrink differently from another?
For a large molded component, this becomes increasingly important.

Gating

Where should the plastic enter the cavity?
How far must it flow?
Would multiple gates or a different feed strategy be necessary?

Cooling

Can the mold remove heat evenly enough to maintain dimensional stability and reasonable cycle time?

Ejection

Can a large, relatively thin component leave the mold without distortion or damage?

Tool construction

Which areas should remain integral in the mold?
Which areas, if any, should use replaceable inserts for machining or maintenance reasons?
These are not questions we like to leave until T0.
Jeancen's engineering approach is to identify as many of these risks as possible before steel is cut, because solving a problem in CAD or mold design is usually much easier than discovering it after the first trial.


We Kept Thinking Even Without the 3D

The customer had not yet provided the 3D data, but our engineer continued reviewing the information that was available.
One question kept coming up:
Could the total tooling investment be reduced?
The customer had several different product lengths.
Instead of automatically assuming that every size required a completely separate large mold, we explored whether a smaller product could be redesigned so identical pieces could connect together to form some of the larger sizes.
On paper, the idea had several potential advantages:
  • fewer large molds;
  • lower initial tooling investment;
  • smaller molded components;
  • potentially easier handling;
  • potentially lower manufacturing risk.
We prepared a simple preliminary concept and sent it to the customer.
The customer replied that the idea would not work for their application.
And that answer was useful.


A Cheaper Mold Is Not Automatically a Better Solution

This is probably the most important lesson from the whole inquiry.
From a manufacturing point of view, an idea may look clever.
It may reduce the number of molds.
It may simplify production.
It may even save money.
But if it changes how the customer needs to install, use, or approve the product, then it may be the wrong solution.
That is why good DFM is not simply:
“How do we make this easier to mold?”
It is:
“How do we make this easier and more economical to mold without losing what the product is supposed to do?”
The customer's real-world constraints come first.
Installation method matters.
Structural requirements matter.
Safety requirements matter.
Service conditions matter.
And sometimes a design feature that looks unnecessary to the mold maker exists for a reason that is not visible in the CAD model.
Good engineering begins by finding out which requirements can change — and which ones cannot.


This Is Also Why We Still Wanted the 3D CAD

After the modular idea was rejected, we did not try to convince the customer that our idea was better.
We dropped it.
Instead, we offered to continue reviewing the customer's original one-piece design.
That is where the 3D CAD becomes especially valuable.
With the complete model, an experienced mold engineer can start looking for cost reductions within the customer's original design intent rather than changing the way the product works.
For example:
  • Can material be removed from low-load areas?
  • Can ribs provide stiffness more efficiently than extra wall thickness?
  • Are there local heavy sections that can be cored out?
  • Can the mold structure be simplified?
  • Can difficult machining areas be redesigned?
  • Can gating or cooling be improved?
  • Can warpage risk be reduced before tooling starts?
  • Can the design be made easier to eject and maintain in production?
These are the kinds of changes that often create real manufacturing value.
Not redesign for the sake of redesign.


“Can You Quote From 2D?”

Customers sometimes ask this question.
The answer is:
Sometimes, yes — for an initial budget.
But there is a difference between a preliminary budget and a manufacturing quotation that a project should rely on.
For a relatively simple part with clear dimensions and an established material, a supplier may be able to provide an early estimate from 2D information.
For a large or structurally complex molded component, especially where weight, material, warpage, mold construction, and production economics matter, the 3D model becomes much more important.
A responsible supplier should tell you which assumptions are being made.
The number should not look more certain than the engineering information behind it.


What If the 3D CAD Is Confidential?

This is also understandable.
For many customers, the 3D CAD contains far more intellectual property than a PDF drawing or product photo.
That should not be treated casually.
If confidentiality is the reason a customer is reluctant to release CAD files, an NDA can be signed before the files are shared.
It is also not always necessary to send an entire product family immediately.
For an initial manufacturing review, one representative part can sometimes be enough to begin the discussion.
The important thing is that both sides understand what information is available and what conclusions can reasonably be made from it.


What We Took Away From This Inquiry

We do not know whether this particular project will eventually move forward with us.
That is normal.
Not every engineering discussion becomes an order.
But the inquiry was still valuable because it reinforced something we see repeatedly in tooling projects:
Good DFM is not about showing how many changes an engineer can make.
It is about knowing:
what needs to change;
what should not change;
what can already be concluded;
and where more information is needed before making a promise.
Sometimes the most professional answer to a customer is not:
“Yes, we can quote everything today.”
Sometimes it is:
“We can already see several directions, but we need the 3D data before telling you which one is actually right.”
That may take a little longer at the beginning.
But it is usually much cheaper than discovering the wrong assumption after the mold has already been built.


Have a Similar Injection Molding Project?

If you have:
  • a product idea;
  • 2D drawings;
  • early-stage CAD;
  • an existing plastic part that needs cost reduction;
  • or a 3D model that needs DFM before tooling,
Jeancen Mold can review the project from a tooling and injection-molding perspective before steel cutting.
Our work focuses on connecting product structure, DFM, mold design, T0/T1 validation, and stable injection molding production, rather than treating each step as a separate activity. This engineering-first positioning is consistent with Jeancen's documented product-development and DFM workflow.
You can start with one part.
Project enquiries: www.jeancen.com
If your 3D CAD is confidential, we are also open to reviewing an NDA before receiving the files.


Confidentiality note

This article is based on a real recent manufacturing inquiry. The customer's identity, drawings, dimensions, volumes, and other identifiable project details have been intentionally omitted or generalized to protect confidentiality.