Diamond Turning vs. Molding for Freeform Optics 

Choosing the Right Path for Freeform Optics

When developing freeform optical components, one of the most important decisions is selecting the right manufacturing method. Diamond turning (SPDT) and injection molding are the two dominant approaches, and each comes with clear strengths and limitations. At Yighen Ultra Precision, we support both processes, helping customers transition from freeform optics prototyping to high-volume production without compromising precision or yield.

⚙️ Diamond Turning (SPDT) Freeform Optics

Diamond turning freeform optics—also known as SPDT machining—is the preferred solution for rapid prototyping and small-batch production. Using ultra-precision lathes and 5-axis freeform machining systems, Yighen achieves:

• Surface roughness (Ra): as low as 2–5 nm

• Form accuracy (PV): ≤0.1–0.2 µm typical

• Flexibility: can handle plastics, metals (Ni-P, Al, Cu), and selected infrared crystals (CaF₂, MgF₂)

• Speed: prototypes delivered in 3–10 days; 48–72h rush options available

SPDT is ideal for optical masters, pilot runs, or high-value systems where precision outweighs cost. Since the process directly follows CAD/CAM toolpaths, it is also the most effective way to validate a freeform optics design before investing in tooling.

🧩 Injection Molding Freeform Optics

When scalability is the priority, injection molding freeform optics offers unmatched efficiency. Once a mold insert is prepared, thousands of parts can be replicated with consistent quality and low unit cost. Yighen’s molding workflow integrates error-compensation algorithms to correct shrinkage and warpage, ensuring:

• Form accuracy: PV 0.2–0.5 µm after compensation

• Surface roughness: Ra 5–10 nm achievable with high-grade optical plastics (PMMA, PC, ZEONEX, TOPAS)

• Batch size: from 1,000 to 100,000+ parts

• Unit economics: high upfront tooling investment, but dramatically lower cost per lens in volume

This makes molding the method of choice for AR/VR, automotive HUD, and consumer electronics applications where weight, cost, and scalability matter most.

🔍 Why the Choice Matters

The decision between SPDT freeform optics machining and injection molding freeform optics often comes down to:

• Quantity required – Is this a single prototype or a 50k-unit program?

• Material selection – Do you need optical plastics, glass, or metal mirrors?

• Tolerance & MTF targets – Can 0.2 µm PV be acceptable, or is ≤0.1 µm mandatory?

• Timeline – Do you need results in days, or are you planning a production program months ahead?

Yighen’s engineers help customers navigate these trade-offs with real data, linking design intent directly to freeform optics manufacturing strategies.

⚖️ Side-by-Side Comparison

Choosing between diamond turning freeform optics and injection molding freeform optics depends on program requirements. The table below highlights their relative strengths:

💰 Total Cost of Ownership (TCO) – Batch Size vs Cost

This TCO comparison shows why many customers start with SPDT freeform optics machining for design validation, then transition to injection molding freeform optics when scaling. Yighen provides both paths under one workflow, ensuring a smooth handoff.

🔄 Hybrid Manufacturing Path

In practice, the best route is often a hybrid model:

1. Diamond turning to prototype freeform surfaces and qualify the optical design.

2. Use SPDT masters to fabricate mold inserts.

3. Apply error compensation algorithms to correct molding shrinkage.

4. Transition into freeform optics mass production for 10k+ parts.

This hybrid approach ensures both optical fidelity and volume economics.

📚 Case Study Examples

• AR Waveguide Input/Output Lens
  SPDT prototype delivered in 5 days; then converted to Ni-P mold insert. Injection-molded ZEONEX optics reached PV ≤0.25 µm after compensation, supporting 20k headset production.

• Automotive HUD Freeform Combiner
  Machined in glass with PV ≤0.2 µm; plastic replica molds used for high-volume HUD production. Compensation stabilized yield at ≥95% Cp/Cpk across multiple batches.

These case studies demonstrate how Yighen aligns prototyping with scalable production, avoiding costly redesigns.

📞 Work with Yighen

Whether you need a single SPDT freeform optics prototype or a 100k-unit injection molded freeform lens program, Yighen provides an integrated workflow from design to volume production.

👉 Contact Us | Download Freeform Optics Whitepaper
Or explore our Freeform Optics Machining & Manufacturing Services for the full picture.

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