Intro
As a product engineer who has just entered the industry or has been working for a few years, do you often feel that once you finish the 3D drawings, you can throw them to the mold factory, wait for them to make a DFM report and raise questions, and then modify the drawings according to their opinions, and that’s considered completing the “interoperability”?
If you think like that, you’re probably already on the verge of falling into a trap.
Looking back on my more than ten years of experience in product design and development, I’ve mentored many newcomers and dealt with numerous mold factories. Today, I want to discuss this topic again: how product engineers and mold factories should collaborate to truly excel in Design for Manufacturing (DFM) rather than just making it a formality.
1 Don’t treat DFM reports like “someone else’s homework”
Many newcomers to mold manufacturing companies are overwhelmed when they receive dozens of pages of DFM reports. These reports are filled with parting lines , gates , ejector pin arrangements , and a bunch of incomprehensible mold flow analysis screenshots. They might think, “Aren’t these technical details the mold factory should be handling? I just need the product’s function, appearance, and dimensions to be correct.”
This idea is the biggest misconception.
Contents
| Item | Page | Item | Page |
|---|---|---|---|
| Revision History | 2 | Draft Analysis (Slider / Lifter) | 22 |
| Contents | 3 | Deflection | 23 |
| Product Information | 4 | Welding Line | 24 |
| Tooling Information | 5 | Venting Position | 25 |
| Gate Type / Location | 6 | Tooling EJ System | 26 |
| Tooling Layout / Gate Type / Location | 7–8 | Stress Mark Analysis | 27 |
| Parting Surface / Line | 9 | Logo Insert (Whether Inserted) | 28 |
| Slider Parting Line | 10 | R Angle Review | 29–30 |
| Lifter Parting Line | 11 | Plastic Thick & Thin Areas | 31 |
| Insert Parting Line | 12–13 | Remarks / Open Issues | 32 |
| Parting Line Step | 14 | Marking | 33 |
| Cooling System | 15–19 | Assembly / Interference | 34 |
| Draft Analysis (Cavity / Core) | 20–21 | The End | 35 |
A DFM report is not simply a one-sided “technical disclosure” from the mold manufacturer; rather, it’s a shared technical language and operational roadmap for both parties. Based on their manufacturing experience, the mold manufacturer tells you, “With your current design, I might encounter certain problems, and the product might have certain defects.” But ultimately, only you truly know whether these “problems” will occur or whether you can accept these “defects.”
For example, the report says that the root of a certain rib is too thick, and mold flow analysis shows that it’s likely to shrink. The mold manufacturer suggests reducing the amount of material used. If you simply reply “Modify as suggested,” you’re in a passive position. You need to make your own judgment:
What is the purpose of this rib? Is it for decoration or to increase strength?
If the amount of glue is reduced, will the strength be insufficient?
If slight shrinkage marks are permissible here, how much will they affect the appearance? Is it on a Grade A surface?
Are there any alternative structural solutions, such as adding a crater to reduce glue content?
For Example: Injection Molding Defect Analysis: Proper Boss Design
Mold factories understand “how molds are made,” while you understand “why the structure is designed this way.” If you don’t tell them the “why,” they can only offer advice in the safest and most conventional way, which may result in sacrificing some of your design intentions. In the end, the mold is made, and the product can be produced, but it may not be the “ideal design state” you initially wanted.
PART 2 The key to a smooth fit: Eliminate problems at the drawing stage
I’ve witnessed too many tragedies where major problems only surfaced during the T1 trial molding. Missing an undercut meant adding sliders to the mold, increasing costs by tens of thousands and delaying delivery by a month; an improperly designed wall thickness caused severe shrinkage across the entire surface, resulting in an unacceptable appearance and requiring major mold modifications…
True “smooth collaboration” hinges on “advance planning” and “anticipation.” Before the product’s 3D data is finalized but before the mold-making instructions are sent, one or more rounds of informal, in-depth communication and coordination should take place with the mold factory.
You should proactively do these things:
Drawing with a “mold-making mindset” : When drawing each reinforcing rib, each snap-fit position, and each boss pillar, you should mentally consider: “Will this part be easy to demold? Will the ejector pins be easy to place? Will there be shrinkage?” The most basic principles, such as draft angle, uniform wall thickness, and avoiding sharp corners, are fundamental skills; have you considered them all? You can’t expect the mold factory to optimize everything for you later. For example, the basic design principles repeatedly emphasized in books like “Product Structure Design Example Tutorial” and “Product Design Guide for Manufacturing and Assembly,” which are frequently read when you first enter the industry, such as “Simplifying Mold Structure” and “Avoiding Undercuts,” must be checked by you first.
Hold a pre-DFM meeting:
Don’t just send emails. Invite the mold project manager and design engineers for a video conference or a visit in person. Share your screen, facing the 3D model, and explain your design intent: “This surface is a Class A appearance surface, and there can’t be any creases”; “How many Newtons of pull-in force does this clip need to withstand?”; “This hole needs to precisely mate with another part, with a tolerance of ±0.1mm.” At the same time, guide them to raise concerns: “Based on your experience, will this deep cavity venting be difficult?”; “Will this slender structure deform during ejection?”
Make good use of the powerful tool “Calligraphy Flow Analysis (CAE) : Don’t treat it as a tool for mold manufacturers to show off their skills or to complete a task. It’s a scientific reference for your joint decision-making. When the mold manufacturer presents you with analysis charts showing filling time, weld line location, air pockets, cooling, and warpage, you should review them together:
Are the weld lines located on the exterior surface or in critical stress areas? If so, can they be corrected by adjusting…
Can you avoid this by adjusting the gate location (managed by the mold manufacturer) or optimizing the product wall thickness (managed by you)?
Is the trapped air located in a corner? Do you need to add venting to the mold or add a small venting rib to the product?
What is the trend of warping and deformation ? Will it affect subsequent assembly? Is pre-deformation compensation necessary on the mold?
This process is like a war simulation. By simulating the production process on a computer, all conceivable problems are exposed, and solutions are discussed collaboratively. This is far less costly than discovering problems in an already produced mold and then “operating” on it.
PART 3 Pay close attention to every detail and take responsibility for your design
The blueprints are frozen, the molds are being manufactured, and you think you can finally relax? No, a huge challenge awaits you.
When key stages of mold processing are completed, such as high-speed milling of the parting surface, assembly of the slider and ejector mechanism, and processing of the cooling water system, it is essential to require the mold factory to provide regular photo or video feedback. You should care about the “growth process” of the mold as you would care for your own child.
You must be present for the T0/T1 trial molding ! This isn’t a matter of trust, but a matter of responsibility. Only by personally seeing the first batch of samples, touching and measuring them, can you make the most direct judgment.
How serious are the shrinkage marks in that area you were worried about before ? Are they an acceptable “mark” or an unacceptable “defect”?
Once assembled, does it feel right ? Is the “click” sound of the clips clear and smooth?
When several parts are assembled together, are the step differences and gaps within an acceptable range?
At this point, you, the mold maker, and the injection molding engineer are all comrades in arms. If there are problems with the sample, don’t blame each other; instead, gather around the machine and let the data speak for itself . Is it a problem with the process parameters (temperature, pressure, speed)? Or is it a problem with the mold (insufficient polishing, poor venting)? Or is it an inherent flaw in your product design (such as significant variations in wall thickness)?
An excellent engineer must be able to identify the root cause of a problem and lead the solution. If it can be solved by adjusting the process, let the process be adjusted; if the mold needs polishing or repair of the venting grooves, then clearly request the mold factory to do so; if it is indeed a design defect, such as insufficient strength requiring the addition of glue, then it must be acknowledged decisively and revised drawings should be provided as soon as possible.
PART 4 Why is this to safeguard your own designs?
Finally, to answer the question in the title: Why should product engineers be so “meddlesome” and deeply involved in DFM?
Because you are ultimately responsible for the product . The mold factory delivers a mold that can be produced, while you deliver a successful product that meets functional, performance, appearance, and cost requirements .
A well-designed mold ensures smooth production, a high yield rate, and stable mass production of your products, minimizing after-sales issues. You’ll be synonymous with “reliable” in the company. Conversely, a poorly designed mold leads to constant repairs and modifications, causing production setbacks and low yield rates. Even if the initial drawings are beautiful, the project will fail, and you’ll likely end up taking the blame.
Design Maker (DFM) is an essential course for your transformation from a “blueprint designer” to a “product implementer .” It requires you to not only understand design specifications, but also material properties, molding processes, and mold making. This experience of “outsmarting” and working closely with mold manufacturers will become your most valuable asset.
So stop passively waiting for DFM reports . Be proactive, bring your thoughts and questions, get involved early, and engage in in-depth communication . Treat the mold factory as your R&D partner, not just a simple processing supplier. Your goals are aligned: to produce the best products with the highest efficiency and lowest cost .
This path may be a bit tiring at first, but once you get the hang of it, you’ll gradually discover that your control over product design is stronger than you ever imagined.
The above is for you, who are growing and learning.
