Why Does Your Silicone Product Manufacturer Insist on Design Changes?

Why Does Your Silicone Product Manufacturer Insist on Design Changes? The Undercut Problem Explained

How Undercuts Drive Up Tooling Costs, Kill Production Efficiency, and Challenge Every Silicone Product Manufacturer – and What You Can Do About It

Have you ever sent your part drawings to a silicone product manufacturer, only to have the first response come back not as a quotation, but as a request – “We need to revise this structure”?

You might be confused. Your design works perfectly for the function. So why the pushback? The answer often hides in one single word: undercut.

At FromRubber, a leading silicone product manufacturer with over 16 years of experience, we see this scenario daily. We specialize in custom silicone solutions – from prototyping to mass production – and we know that a seemingly small design feature can make or break your project’s cost, quality, and timeline. In this article, we’ll unpack the undercut dilemma, show you why it matters more than you think, and give you actionable strategies to save time and money while working with your silicone product manufacturer.

What Is an Undercut – and Why Is It the “Natural Enemy” of Molds?

In mold design, an undercut refers to any feature that is oriented perpendicular or opposite to the main parting direction, preventing the part from being directly ejected after mold opening. In plain terms, these are the features that “hook” onto the mold and keep the part stuck inside – such as internal recesses, side holes, snaps, hooks, or complex cavities.

Undercuts are not inherently “wrong” – some designs genuinely need them for mechanical functions. The real problem is that many designers never consider how their part will actually come out of the mold until the tooling shop points out that “this part cannot be smoothly mass-produced.”

From a silicone product manufacturer’s perspective, undercuts are classified into several types:

• External undercuts – features on the outside of the part that resist ejection.
• Internal undercuts – recesses or cavities inside the part that create suction or mechanical lock.
• Side undercuts – perpendicular features requiring side-action cores (slides).
• Complex geometries – combinations that demand multi-stage ejection.

Each type adds a layer of difficulty that directly affects tooling design, production speed, and final cost.

The Cascade Effect of Undercuts: From Tooling to Unit Price, Every Step Adds Cost

When your part contains numerous or deep undercuts, here is what your silicone product manufacturer faces:

1. Tooling complexity skyrockets

Rigid steel molds “hate” undercuts. To handle them, the mold must incorporate slides, lifters, and other moving components. Each undercut feature multiplies the complexity of the tool. A simple silicone part might cost a few thousand yuan for the mold, but once you add undercuts, multi-cavity layouts, or irregular curved surfaces, the mold cost can easily jump to tens of thousands of yuan – or even ¥120,000.

To put it in numbers: each undercut feature increases mold cost by 15%–40% and extends lead time by 2–4 weeks. A single undercut can add anywhere from $2,000 to $15,000 to your tooling expense.

2. Production efficiency plummets

Complex undercuts require elaborate ejection mechanisms, making the demolding process slow and cumbersome. Every added difficulty in demolding reduces tool life, extends cycle time, and increases scrap rates. Operators struggle with each shot – longer cycles, higher rejection rates, and more downtime.

For a high-volume project, a 10% increase in cycle time can translate to thousands of dollars in lost productivity over the product lifecycle.

3. Unit price climbs

Higher mold costs must be amortized into each part. Slower production and higher scrap are directly reflected in the piece price. Ultimately, every single cost increase gets passed straight back to you – the buyer.

At FromRubber, we always share a transparent cost breakdown, so our clients see exactly how design choices affect their bottom line.

Silicone Is Elastic – Doesn’t That Solve the Undercut Problem?

Some designers think: silicone is soft and flexible, so we can just pull it out of the mold, right?

There is some truth to this. Silicone does have an “elastic advantage” over rigid plastics – its inherent flexibility can allow forced demolding in cases of shallow undercuts. However, this is not a universal pass.

For deep undercuts, large-volume undercuts, or complex geometries, elasticity alone is insufficient. While vacuum casting of silicone molds can accommodate certain undercut shapes, deeper or more complex features often require additional tear strips or multiple mold sets. Even with flexible silicone tools, hard undercuts still demand specialized removal tools or extra process steps.

A real-world case: one factory received a transferred mold and found that demolding was extremely difficult – parts cracked, tore, and showed severe defects. The root cause? The product design had undercuts, but the mold was not engineered to handle them. The result – either the parts could not be produced at all, or they came out as scrap.

At FromRubber, we have successfully rescued many such projects by redesigning the mold structure and suggesting minor part modifications that eliminated the need for complex slides, saving our clients up to 40% in tooling costs.

So, What Can You Do? Modify Early, Modify Smart

Since undercuts bring so many problems, the solution is straightforward: change them if you can, and do it as early as possible.

1. Perform a DFM (Design for Manufacturability) review at the concept stage

Professional engineers will thoroughly analyze your drawings before tooling starts and provide a DFM report covering mold structure, part dimensions, demolding feasibility, and more. Eighty percent of success is determined at the design stage. Modifying a geometry on the drawing board costs virtually nothing; making the same change after the mold is cut costs real money and precious time.

FromRubber offers a complimentary DFM analysis for every new project, helping you identify potential undercut issues before they become costly mistakes.

2. Optimize the geometry – eliminate unnecessary undercuts

Engage your silicone product manufacturer in early discussions to identify which design features can be simplified or even split into multiple components to avoid undercuts altogether. Many undercuts are in fact avoidable – designers simply overlook the hidden cost until it's too late.

For example, changing a side hole to a through-hole, or adding a small split line, can completely eliminate the need for side-action cores.

3. Design adequate draft angles

If undercuts are truly unavoidable, at least ensure the part can release as smoothly as possible. For silicone parts, a draft angle of 1°–3° is generally recommended. For deep cavities or micro-features, consider increasing the draft to 3°–5°. Do not underestimate these few degrees – a small adjustment in draft angle, parting line location, or forced-demolding strategy can have a tremendous impact on final product quality.

4. Consider material shrinkage and mold design compensation

Silicone shrinks after curing, typically between 2% and 4% depending on the compound. This shrinkage can actually help release the part from certain undercuts, but it must be precisely calculated. A knowledgeable silicone product manufacturer like FromRubber uses advanced simulation tools to predict shrinkage and adjust the mold geometry accordingly, often turning a problematic undercut into a manageable feature.

Why FromRubber Stands Out as Your Trusted Silicone Product Manufacturer

With over 16 years in the industry, FromRubber has accumulated deep expertise in handling complex silicone designs. We have successfully delivered more than 8,000 mold projects and served over 2,300 clients across various industries – from medical devices and automotive to consumer electronics and home appliances.

Our engineering team specializes in Design for Manufacturability – we don't just build molds; we partner with you to refine your design so that it is optimized for production without sacrificing functionality. We offer:

• Free DFM review – catch undercut issues before tooling starts.
• In-house tooling – full control over quality and lead time.
• Flexible production – from low-volume prototypes to high-volume mass production.
• Material expertise – we recommend the best silicone compound for your application, considering hardness, tear strength, and elongation.

We understand that every project is unique. Our iterative approach ensures that we test and validate the mold design through simulation and sample runs, so you get perfect parts right from the start.

Real Success: How We Saved a Client 35% on Tooling by Eliminating Undercuts

A European medical device manufacturer approached us with a silicone housing design that featured multiple internal undercuts for snap-fit connections. Their previous silicone product manufacturer quoted them an exorbitant price due to the complex slide mechanisms required.

Our team reviewed the design and proposed several modifications: we changed the snap-fit geometry to a simpler cantilever design, added a small draft angle on the internal ribs, and split the part into two components that could be assembled later. The result? The mold cost dropped by 35%, cycle time reduced by 20%, and the client enjoyed a much more robust production process with near-zero scrap.

This is the power of early collaboration with an experienced silicone product manufacturer.

Closing Thoughts: Undercuts Are Not Forbidden – But You Must Think Ahead

Undercuts are not the enemy – some product functions genuinely require them. The real issue is that many designers never ask the fundamental question: “How will this part actually come out of the tool?”

By the time your silicone product manufacturer reviews the drawings and sees too many undercuts, too-deep recesses, and impossible demolding, you are left with only two options: either change the design, or pay more and wait longer. Ultimately, you – the buyer – end up footing the bill for that unasked question.

So next time your silicone product manufacturer asks you to modify a structure, don't assume they're being difficult. They are not trying to make your life harder – they are trying to save you from a much bigger pitfall.

Change it if you can. And do it as early as possible.