19 Tips for Additive Manufacturing Design

A Modern Casting Staff Report
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The days of mere conjecture, experimentation and hypothetical theories have segued in to real world examples and experience for 3-D printing sand molds. No longer merely an emerging technology, 3-D printing has become a bona fide tool in the manufacturer’s workshop. While research and development continues, the library of successful production case studies grows, and industry experts have begun to learn a few best practices to share among peers.

At the AFS Additive Manufacturing for Metalcasting Conference in October 2016, several of these experts dispense advice on what they have learned in designing cast components for this evolving technology. Here, Modern Casting shares 19 of those lessons.

Start Up Front
1. Perform your design and casting simulations up front, even though it adds time. Simulate the casting process as soon as possible, make it a priority and get as close to perfect as you can, given the time limitations of the customer.
—David Weiss, Eck Industries

2. The design phase is the most critical aspect of a component’s life. Many manufacturing and performance issues created at this stage have a long term impact on product cost. An integrated approach using computer based technology not only reduces lead time, it also improves the design. Technologies that assist creating samples quickly will help maximize the evaluation time and decisions made during this critical phase.
—Tom Prucha, MetalMorphisis

3. It only takes a few hours to print a mold but engineering and development time are the most important aspects of producing useable structural castings and that usually takes more than a few days.

Design Nuts and Bolts
4. All the tools normally used to produce premium structural castings can be used with additive manufacturing techniques: chills, insulated sleeves, different sand types.

5. In additive manufacturing, casting orientation depends on the build-up direction (z-axis) vs. the parting plane in conventional sand casting.
—Jiten Shah, PDA LLC

6. Additive manufacturing opens unique design freedoms. Fillets and radii are always possible, machining a relief area can be incorporated easily, no draft requirements leads to lower weight, and cores can be eliminated where used due to back draft.

7. Isolated hot spots can be fed with spot risers.

8. Bottom gating is possible for uniform filling with the least turbulence.

9. Designers don’t have to account for core split lines, flash or veins. There is flexibility with the placement of feeding aids such as chills, risers, filters, gates, in-gates, and zircon facing cores.

Calculating Cost
10. Factor reasonable risk into the price.

11. Hybrid approaches can be utilized for time and/or cost savings. This means conventional patterns used with 3-D printed cores. For 1,000 parts or higher, hybrid is more cost effective than 3-D sand printing for parts with a complexity factor of 56 or higher.
—Brett Connor, Youngstown State University

12. When patternmaking requires expensive tooling, 3-D sand printing is advantageous for low quantity production of molds and cores, even for low complexity parts. The cost advantage depends on sand printing production costs.

13. For some highly complex parts, 3-D sand printing may be cost effective even if tooling exists already or part quantities are high, especially in situations where cores can be consolidated. With 20% fabrication cost reduction, sand printing is effective for parts with a complexity factor of 45 or higher.

Marrying Additive to Production
14. Remember that when prototyping for production, there is more freedom in additive manufacturing than in standard production techniques.

15. The design process must account for additive manufacturing all the way from concept to pouring, including the removal and handling of cores and molds. Cores greater than 80 lbs. require attachment points for crane removal. Dual purpose all thread slot allows lifting with straps by crane. Handholds reduce mold weight, allowing easier removal and allow for easier placement.

16. It’s time to unlearn standard flask sizes, common height copes and drags. Don’t be a square. 3-D printed molds can be contoured around the shape of the casting, saving printing time and mold material.
—Mark Lamoncha, Humtown Products

17. But still use common sense. You must have a parting line to clean internal cavities. The entire mold or mold pieces must fit in the printer. Safe handling practices must be considered.

18. Printed sand’s strongest advantage is reduced lead time. There is no need to manufacture tooling, part development can be at infancy stage, package designs (partings) are unconstrained, and there is more freedom in gating strategy.
—Dave Rittmeyer, Hoosier Pattern

Closing Note
19. So which process is best? All of them: conventional tooling, printed sand, or machined sand. In order to optimize printed mold designs, you need to learn how to apply each option or combination of options for the most cost effective and/or fastest way to produce your sand casting.

Machined sand might need draft. The tooling will limit fillet sizes. You must be able to see what needs machined. Normally this method is not suitable for a core. On the plus side, there is no need for tooling, it’s fast, any sand with or without additive can be used, and large molds normally are cheaper than printed sand.

In conventional tooling, draft is needed. The more complexity or tooling needed, the longer the lead times will be, but any sand—with or without an additive—can be used and it may be the most economical route depending on complexity, quantity and size.

3-D printed sand carries the need to be able to remove unbound sand, and consumables are limited. But no draft is needed, you are able to combine multiple cores into a single core and print complex geometry, and lead times are short.

The tips shared in this article were taken from presentations given at the AFS Additive Manufacturing for Metal Casting Conference held October 3-6, 2016, in Novi, Michigan.

A functional machined casting for a rear housing in a dual clutch transmission was produced in three weeks using 3-D printed sand technology. This enabled the customer to evaluate several designs quickly and achieve short time-to-market.