Solving a Visible Parting Line on a Complex Spray-Coated Silicone Keycap
Parting lines are a normal part of silicone molding. But when a keycap is going to be spray-coated and laser-etched, even a small parting line on the visible surface can make the finished part look unacceptable. Recently, we ran into exactly this problem with a custom silicone keycap—and it led to a complete mold redesign. (Chicarubber)
The Challenge: A Difficult Undercut Shape
The keycap had an unusual structure. One key was very tall, with a wide top and a narrow middle. In cross-section, it looked like an undercut or a hook shape.
Because of that shape, our first thought was that the part could not be demolded normally. To solve it, we split the center plate. The part could be molded, but the split left a visible seam—a parting line—right across the surface. The customer saw it immediately and said it looked bad. They asked us to improve it.
Rethinking the Demolding Problem
We took another look at the product structure. Yes, the top was larger than the middle, which created an undercut. But the center of the part was hollow. That changed everything.
Because silicone is flexible, the hollow center allowed the part to compress and deform during demolding. Instead of splitting the mold, we could force the part off the core. The undercut was not impossible to release—it just needed a different mold design.
The Second Mold Design: One-Piece Center Plate
For the second sample, we opened a one-piece center plate. This design wrapped the entire product, leaving only the top exposed in the upper mold. The result was a much cleaner visible surface.
When the customer compared the two versions, they preferred the second one. They asked us to modify the first design to match it.
We discussed the first mold with our mold makers. Even if we made the mold tighter and more compact, the parting line would still exist on the surface. Tightening the mold would not eliminate the root cause. So we made the decision to rebuild the center plate and re-sample for customer approval.
Why This Matters for Spray-Coated and Laser-Etched Keycaps
This keycap required spray coating and laser etching. Both processes make surface quality even more critical.
A visible parting line can:
- Interrupt the spray coating and create an uneven look
- Show up as a rough line after laser etching
- Make the keycap feel less premium
- Cause rejections even if the part functions correctly
For silicone keycaps with printed, sprayed, or laser-etched graphics, the mold design must protect the visible surface. The parting line should be placed where it will not be seen—or eliminated entirely through a better demolding strategy.
What We Learned
This project reinforced a few important lessons:
- Do not assume an undercut cannot be demolded. Flexible silicone can often be force-demolded if the geometry allows deformation.
- A hollow center can be an advantage. It gives the part room to compress during release.
- A split mold is not always the best answer. It may solve demolding, but it can create visible parting lines.
- A one-piece center plate can produce a cleaner visible surface. When designed correctly, it can wrap the part and leave only the top exposed.
- Compare samples before committing. The customer’s feedback helped confirm the better design direction.
Final Thoughts
For custom silicone keycaps, especially spray-coated and laser-etched ones, surface appearance matters as much as function. A visible parting line can ruin an otherwise good part. (Chicarubber)
If you are working on a complex silicone keycap with undercuts, hollow sections, or difficult demolding requirements, the right mold design can make the difference. Sometimes the best solution is not to tighten the old mold—but to redesign it.
Looking for custom silicone keycaps with clean surfaces, reliable demolding, and consistent spray coating or laser etching? Contact us to discuss your project.
Solving a Visible Parting Line on a Complex Spray-Coated Silicone Keycap
If you need to customize silicone products, please contact us at chicarubber
