4 “Marks” on Your Injection Molded Sample — Normal or a Quality Issue? A Must-Read for Procurement

What Are Injection Mold Marks? The Factory Says They’re Normal

Understanding injection mold marks is essential for procurement.When procurement receives injection molded samples, a closer look often reveals:

Several small circular dots on the back of the product;

A thin line running along the edge;

A slightly discolored or uneven area near the injection point.

The first reaction is usually: “Is this a quality defect?”

In fact, these 4 types of marks are nearly unavoidable on every injection molded product. They are structural byproducts of the injection molding process itself — not defects, but normal process characteristics. However, if design and mold planning are done poorly, these marks will appear in the wrong places, affecting appearance and function.

This article breaks down all 4 marks clearly, so you have more confidence when inspecting goods, approving samples, and communicating with factories.

1. Ejector Pin Marks: Those Small Circles on the Back of the Product
What Does an Ejector Pin Do?
After the plastic cools and solidifies inside the mold, it needs to be “pushed out.” This ejection action is performed by ejector pins.
Ejector pins are thin cylindrical rods embedded in the mold. After the product cools, they apply force to push the product out of the mold cavity.

Since the ejector pins are in direct contact with the product, they leave behind circular ejector pin marks on the product surface — typically slight protrusions or depressions that are visible to the naked eye, can be felt by touch, and cannot be completely eliminated.

What Procurement Should Focus On: Where Are the Ejector Pin Marks?
Ejector pin marks themselves are not the problem. The problem is when ejector pin marks appear on visible exterior surfaces.

Proper mold design should prioritize placing ejector pins:

On the back, interior, or other non-appearance surfaces;

Near ribs or other structural positions;

On flat, evenly supported areas — avoid placing them on rounded corners, sharp edges, or steep slopes.

When inspecting goods, procurement can directly ask the factory: Are the ejector pin mark locations away from the product’s front face and customer-visible surfaces? If not, adjustments should be requested during the sampling stage — not discovered after mass production has begun.

Real Case: Poor Ejector Pin Placement Led to an Entire Batch Being Returned
A procurement officer sourcing consumer electronics components received the first samples, felt everything looked fine, and immediately arranged mass production.
The end customer then complained: visible circular ejector pin marks on the product’s front face did not meet appearance standards, and requested a full batch rework.
Upon investigation, it turned out that no clear requirements for ejector pin placement were stated during sampling. For ease of ejection, the factory placed the pins on the flattest area of the product’s front surface.
Reworking the mold and rerunning production wasted a full round of time and cost.

2. Gate Marks: The “Scar” Left by the Injection Point
What Is a Gate? Why Does It Leave a Mark?
During injection molding, molten plastic travels from the injection machine through the runner system and enters the mold cavity through an opening called a “gate.”
After cooling and demolding, the gate location leaves behind a connection point mark. Even after manual trimming, it cannot be made perfectly flush — this is the gate mark (injection point mark).

Gate Location Design Directly Affects Product Appearance and Function
Gate location selection must balance multiple factors simultaneously:

Appearance: Gate marks should be placed on non-appearance surfaces or inconspicuous locations — avoid placing them in the center of the product’s front face;

Function: Gate location must account for even filling of the cavity — unbalanced filling can lead to warping and deformation;

Assembly: Gate marks must not protrude above the surface, as this can interfere with assembly. A recessed gate design is typically used so residual material doesn’t extend beyond the product surface;

Ease of removal: Is it easy to trim the gate after molding? Will the removal process cause secondary damage to the product surface?

A poorly planned gate location can, at best, affect appearance — and at worst, cause warping and dimensional instability.

Questions Procurement Can Ask the Factory Before Sampling
Where is the gate planned to be located? Is it away from the appearance surface?

Is a cold runner or hot runner system being used? Hot runners reduce gate marks but increase mold costs;

Is there a risk of weld lines? (Where two streams of molten plastic meet, a weld line forms — affecting both appearance and structural strength)

3. Parting Line: The “Seam” Along the Product Edge
How Does a Parting Line Form?
An injection mold consists of two halves — the core and the cavity. The product is formed while both halves are closed together, then ejected after the mold opens.
The line where the two mold halves meet is the parting line.

After the product is formed, a visible line or slight step remains at the parting line location — a structural characteristic that cannot be completely eliminated through processing.
A real-world analogy: just like a waffle made in a two-part mold, there will always be an imprint around the seam where the two halves joined.

What Happens When the Parting Line Is in the Wrong Place?
On a prominent front surface: appearance quality is directly compromised — high-end consumer product clients are especially sensitive to this;

Crossing a critical dimension area: slight misalignment on either side of the parting line due to mold manufacturing tolerances can affect dimensional accuracy;

On an assembly mating surface: even a minor parting line step can affect the fit precision and sealing effectiveness between two components.

What Good Parting Line Design Looks Like
Run the parting line along product corners or edges so it “hides” in less noticeable locations;

When the appearance surface has a prominent texture (grain/stipple), the texture can visually minimize the parting line;

Critical dimension areas and customer-visible front surfaces are the two locations the parting line must avoid.

When approving first samples, procurement should specifically inspect whether the parting line location meets appearance and functional requirements — not just verify that the overall shape matches the drawing.

4. Draft Angle (Demolding Taper): Invisible but Highly Impactful
What Is a Draft Angle?
When an injection molded product is ejected from the mold, friction occurs between the product’s side walls and the mold surface.
If the side walls are completely vertical (0 degrees), demolding resistance is very high. At best, this causes surface scratches; at worst, the product cannot be ejected at all — potentially damaging the mold.

A draft angle is a small taper built into the product’s side walls to allow smoother demolding. This angle is typically between 0.5 and 3 degrees — barely visible to the naked eye, but with a significant impact on production stability.

What Problems Occur When the Draft Angle Is Insufficient?
Visible scratch marks or stress whitening on the demolding surface, affecting appearance;

Ejector pins need to apply excessive force to push the product out, causing ejector pin deformation marks on the product;

In severe cases, the product becomes completely stuck inside the mold, making normal mass production impossible;

Accelerated mold wear, significantly shortening mold life.

Basic Draft Angle Principles Procurement Should Understand
The deeper the product (e.g., deep boxes, deep cylinders), the larger the draft angle required;

Basic rule: maintain at least 1 degree of draft angle; when the surface has texture (grain), the draft angle needs to be increased accordingly;

Both the inside and outside walls need draft angles — not just the outer walls;

If a customer’s drawing has areas with 0-degree vertical walls, the factory’s engineer should proactively raise this for evaluation before mold cutting — not wait until problems emerge during trial molding.

4 Inspection Questions Procurement Can Use Directly When Approving Samples
Next time you receive injection molded samples, use these 4 checkpoints for a quick review:

Ejector Pin Marks: Where are they located? Do they appear on the product’s front face or customer-visible surface? Is the size within an acceptable range?

Gate Marks: Is the injection point located on a non-appearance surface? Does any residual material protrude above the product surface?

Parting Line: Does the parting line avoid the product’s front face and critical dimension areas? Is there any visible misalignment or step?

Draft Angle: Are there any scratch marks on the demolding surface? Is there any deformation or ejector pin depression at the ejection locations?

Getting clear answers to these 4 questions during the sampling stage will eliminate a large volume of rework and disputes during mass production.

Contact Rayleap Plastic
If you are currently:

Preparing to cut a new mold and want to plan ejector pin locations, gate positions, parting lines, and draft angles correctly from the design stage;

Holding a sample and unsure whether certain marks are normal process characteristics or actual quality issues;

Send your drawings or sample photos to Rayleap’s engineering team. We can help you:

Review structure before mold cutting to proactively avoid location risks for all 4 types of marks;

Assist with sample evaluation: identify which marks are normal process characteristics and which require factory correction;

Provide specific mold optimization recommendations — not just a generic “no problem.”

Contact Us:

Whatsapp: 86-13715466102

Email: zeng@rayleap.com

Website: rayleap.com

Plan the locations of these 4 marks properly from the start — your appearance quality and production consistency will be far more stable

To learn more about how injection molding works, read our complete guide to theiinjection molding process