How to Design for Ductile Iron: Tips for Engineers and OEMs
Designing a new component isn’t just about function; it’s about designing for manufacturability, performance, and cost-efficiency. When it comes to ductile iron castings, smart design up front can reduce production time, cut costs, and extend the life of your parts.
At Farrar Corporation, we’ve spent decades working with engineers and OEMs to optimize castings from concept to finished component. Whether you’re designing from scratch or converting a weldment or steel part to ductile iron, here are key design tips to keep in mind.
1) Prioritize Uniform Wall Thickness
Inconsistent wall thickness is one of the most common challenges in casting design. Thick-to-thin transitions can cause uneven cooling, which may lead to shrinkage, porosity, or internal stress.
Best practices:
- Keep wall sections as uniform as possible
- Avoid abrupt changes in thickness
- Use generous radii or tapers when transitions are necessary
Why it matters: Uniform cooling improves casting soundness, dimensional stability, and reduces the need for costly machining allowances.
2) Include Proper Draft Angles
A draft angle is the slight taper applied to vertical surfaces of a casting to allow for easy pattern removal from the mold.
Best practices:
- 3° draft on external walls
- Slightly more for internal walls or deep pockets
Why it matters: Proper draft minimizes the risk of mold damage and improves repeatability, especially in automated molding lines like our 20″ x 24″ Roberts Sinto systems.
3) Simplify Core Requirements Where Possible
Cores are used to create hollow sections or undercuts, but they add complexity, cost, and risk to any casting.
Best practices:
- Eliminate unnecessary cored sections
- Use open pockets or redesigned geometry instead of deep cores
- Consult with your foundry early for core feasibility
Why it matters: Reducing core use lowers the chance of core shift, improves structural integrity, and speeds up production.
4) Use Generous Radii and Fillets
Sharp corners can act as stress concentrators and may also disrupt metal flow in the mold.
Best practices:
- Use 1/8″ minimum inside radius (or more if wall thickness allows)
- Add fillets between intersecting features or surfaces
Why it matters: Smooth transitions reduce stress cracking, improve metal fill, and enhance fatigue performance.
5) Know Your Minimum Section Limits
Ductile iron flows well but still has practical limits for wall thickness. Too thin, and you risk incomplete filling or structural weakness.
Best practices:
- Aim for a minimum section thickness of 0.300″
- Allow more for larger parts or complex core layouts
Why it matters: Staying within the recommended thickness ensures reliable casting integrity and prevents costly defects or part failure.
6) Design for Machining Efficiency
If your casting will be machined, be intentional with machining stock, datum surfaces, and access points.
Best practices:
- Provide flat, stable mounting surfaces
- Avoid hard-to-reach internal features
- Consider how part orientation will affect fixturing
Why it matters: Farrar provides in-house CNC machining and assembly, and optimized designs reduce cycle time, tool wear, and post-processing costs.
7) Leverage Your Foundry Partner Early
The best way to avoid design pitfalls is to involve your foundry early in the development cycle. At Farrar, we collaborate with engineering teams to review part geometry, suggest improvements, and flag risk factors, long before tooling is built.
Why it matters: Early involvement can lead to:
- Lighter, stronger parts
- Faster prototyping and tooling turnaround
- Lower total cost of ownership
Partnering with Farrar = Better Castings by Design
Designing for ductile iron isn’t just about what’s possible; it’s about what’s efficient, manufacturable, and reliable. By working with a foundry that understands the nuances of casting, machining, and heat treating, you ensure your parts perform well from mold to machine.
Farrar’s engineers bring hands-on expertise to casting design, pattern engineering, and production tooling, giving you a true value-added partner every step of the way.
Have a part in development?
Let’s connect early to ensure it’s designed for success. Give us a call or request a quote today!
