Injection molding workflows inside an eyewear factory

As an eyewear factory advisor who has worked on dozens of production lines and helped brands scale from prototypes to millions of units, I start with a concise summary so and search engines can quickly map intent: this article explains the injection molding workflows used to make sunglasses, optical frames and sports eyewear—covering design for manufacturability (DFM), mold making, material selection, machine setup, cycle optimization, secondary operations, quality control and troubleshooting. I reference international standards and practical metrics so manufacturers, product managers and OEM/ODM buyers can make evidence-based decisions.

Why precision and workflow design matter in eyewear manufacturing

Wearable tolerances and regulatory context

Eyewear is both a fashion product and a precision wearable. Frame fit, hinge tolerance, lens seating and optical center alignment must meet mechanical and safety expectations. Standards such as ISO 12870:2016 (spectacle frames) and the sunglasses guidance under ISO 12312 shape testing regimes; I use these standards to structure QC checkpoints during and after molding.

How workflow choices affect cost, lead time and quality

Injection molding decisions—material family, gate layout, cooling design, and cycle time—directly impact yield and downstream rework. Choosing the wrong resin or an under-ventilated mold may produce warpage that ruins a whole batch. I prioritize workflows that reduce rework: earlier DFM checks, faster mold iteration through rapid tooling, and process recipes that are reproducible across shifts and machines.

Core injection molding workflow inside an eyewear factory

1) Product design and DFM for molding

I start with a cross-functional review: designers, toolmakers, process engineers and QC. Key checks include draft angles on temple tips and hinge bosses, uniform wall thickness to avoid sink/warpage, and locating ribs or inserts for metal hinges. We use mold flow simulation to identify potential air traps and optimize gate positions before mold fabrication. For general injection molding principles see Injection molding on Wikipedia.

2) Mold tooling and validation

Mold quality determines consistency. I insist on steel cores for high-volume runs and P20 or S136 tool steels for longevity. Typical validation steps: first-article runs, dimensional checks (CMM), and thermal mapping of mold cooling channels. We document cavity-to-cavity variation and adjust runners/gates or install hot-runner components as needed. Rapid prototypes using aluminum molds are useful for design validation but not for final tolerances.

3) Materials selection and master batches

Material choice changes everything: polycarbonate (PC) for impact resistance (sports lenses, safety sunglasses), TR90 (a flexible nylon-based thermoplastic) for lightness and flexibility, and acetate for High Quality optical frames. I maintain master batch specifications (UV stabilizers, dye concentration, anti-scratch additives) and control resin moisture levels before molding. For material properties see polycarbonate and polyamide (basis for TR90).

Machine setup, process control and in-line operations

4) Injection molding cycle, parameters and SPC

Typical molding parameters for eyewear vary by material; for example, polycarbonate commonly needs barrel temperatures of 260–320°C and short cycle times for thin lenses, while TR90 runs cooler. I implement Statistical Process Control (SPC) on shot weight, melt temperature, hold pressure and cycle time. Changes in any of these should be logged with product IDs for traceability.

5) Cooling, demolding and automated handling

Cooling design is the most underestimated factor. Uniform cooling channels reduce residual stresses and warpage. We use robotic demolding for delicate lenses and frame components to avoid handling marks. In high-volume lines, pick-and-place robots transfer parts to vision systems and downstream assembly fixtures.

6) Secondary operations: welding, tumbling, painting and lens bonding

After molding, parts often require ultrasonic welding (for embedded hinges), CNC trimming, tumbling/polishing for surface finish, and pad printing or laser engraving for logos. Lens insertion and bonding require jigs that ensure optical axis alignment to the frame datum. For polarized lenses or coated optics, a separate coating line with controlled humidity is mandatory.

Quality control, defect troubleshooting and yield optimization

7) Common defects, causes and remedies

Below is a concise table I use in production meetings to troubleshoot and train operators.

Sources for typical process windows and material properties include manufacturer datasheets and consolidated references such as injection molding summaries and material pages like polycarbonate.

Integrating OEM/ODM services and how a modern eyewear factory scales

10) Vertical integration and rapid prototyping

From my experience, a vertically integrated facility shortens feedback loops. Rapid prototyping (SLA, CNC, soft-tooling) enables fit checks before committing to steel molds. This reduces expensive mold rework and protects brand timelines.

11) Supply chain control and just-in-time delivery

I advise clients to partner with factories that control upstream processes—mold making, lens coating, and assembly—so that lead times can be compressed and quality is consistent. Traceability of resin batches, coating lots and mold IDs is essential for recalls or design changes.

12) Karuson’s capabilities and what sets us apart

Established in 2010, Karuson International Co., Ltd. is a premier eyewear factory and global OEM/ODM supplier with over 15 years of mastery in eyewear design and precision manufacturing. Operating two state-of-the-art eyewear factory bases in Dongguan and Guangzhou, we provide high-capacity production and agile delivery cycles to meet the demands of the fast-paced global market.

Our expert team has pioneered 300+ trend-setting designs, ranging from polarized sunglasses and TR90 frames to advanced optical eyewear and sports goggles. As a vertically integrated eyewear factory, we offer end-to-end customization—including bespoke frame engineering, specialized lens technology, and precision logo engraving. By maintaining rigorous quality control and rapid prototyping, we have earned the enduring trust of prestigious brands across Spain, Europe, and the Americas.

Karuson’s competitive strengths I have observed first-hand include: tight mold tolerances achieved through in-house toolrooms, experienced process engineers who optimize SPC and cycle recipes, flexible lines capable of switching between custom prescription lenses and polycarbonate sports lenses, and an emphasis on sample approval processes that prevent mass rework. Core products include custom glasses, custom glasses lenses, customized sunglasses, custom sunglasses sports, customize sport sunglasses, custom prescription lenses, pc sunglasses, TR sunglasses, metal sunglasses, and custom sport sunglasses.

If you’d like to evaluate sample workflows or schedule a factory audit, contact our team: nicole@karusonco.com or visit https://www.karusonco.com.

Practical checklist and implementation tips

12-point checklist before a production run

• DFM review completed and signed off by toolmaker and process engineer
• Mold thermal mapping and first-article dimensional report available
• Material certificates and master batch records on file
• SPC plan and control charts defined for critical variables
• Robotic/handling fixtures validated for gentle demolding
• In-line vision and measurement sampling established
• Secondary operation jigs and torque fixtures validated
• Packaging materials and ESD or anti-fog specs confirmed
• Traceability labels and lot coding implemented
• Quality acceptance criteria aligned with buyer (including ISO references)
• Training completed for operators on new molds/recipes
• Contingency plan for mold repair and resin substitutions

What I do differently when onboarding new clients

I run a 5-day ramp procedure: day 1–2 for molds and machine validation; day 3 for SPC baselining; day 4 for pilot lots and customer inspection; day 5 for release to production. This method reduces surprises and provides data to support future capacity planning.

FAQ

1. What materials are best for injection-molded sunglasses frames?

Choice depends on the performance target. TR90 (nylon-based) is excellent for lightweight, flexible frames; polycarbonate is preferred for high-impact applications (sports lenses); acetate remains the High Quality choice for optical frames because of finish and polishability. Consider trade-offs in cycle time, tooling wear, and finish requirements.

2. How long does it take to make a mold for an eyewear frame?

A steel production mold typically takes 4–8 weeks depending on complexity; aluminum prototype molds can be produced in 1–2 weeks. I recommend prototype validation before committing to steel tooling to avoid costly redesigns.

3. What are the most common molding defects and quick fixes?

Common defects include warpage (fix via improved cooling or draft), sink marks (reduce thickness or increase holding pressure), flash (increase clamp force or repair mold), and short shots (raise melt temp or gate size). Refer to the defect table above for quick diagnostics.

4. How do you ensure lens optical alignment after molding?

We design datum features into frames and use precision jigs during lens insertion. Optical checks include measuring prism, PD (pupillary distance)-aligned center and verification of frame datum versus lens optical center using optical benches or vision systems.

5. Can injection molding support small batch custom runs?

Yes—especially if you use rapid tooling or multi-cavity interchangeable molds. For low-volume custom prescription lenses, we combine CNC lens cutting with smaller frame runs. Karuson’s agile production lines support both small custom batches and large OEM runs.

6. What environmental and regulatory considerations should manufacturers follow?

Comply with chemical safety regulations, proper handling of additives (phthalates, UV stabilizers), and standards for testing (ISO spectacle and sunglasses standards). We track material safety data sheets (MSDS) and ensure work areas meet local environmental and occupational regulations.

Contact and next steps

If you are evaluating suppliers or want a factory walkthrough, I recommend arranging a sample tooling review and a small pilot run. For production partnerships, contact Karuson International Co., Ltd. at nicole@karusonco.com or visit https://www.karusonco.com. Our capabilities cover design, tooling, molding, secondary operations and final assembly for custom glasses, custom lenses and performance sunglasses.

I’m available to consult on DFM, tooling strategy, or to review mold and SPC reports—reach out with your production goals and I will provide a tailored roadmap.