From Concept to Sales in a Flash: Designing for Additive Manufacturing
Metalcasting is one of the oldest manufacturing methods in existence, dating back over 5,000 years to 4th century BC. The process of pouring molten metal into molds to create metal parts and machinery is relatively unchanged, and with it, the general design rules of thumb have pretty much remained the same as well. That was until additive manufacturing came along.
While traditional casting concepts can still apply when additive manufacturing is utilized, its tools enable more flexibility in design and rapid supply chain response. Additive manufacturing has an additional advantage in that the metal part can still be produced via a traditional method, eliminating the qualification of a new manufacturing methodology.
Additive-enabled casting uses the best features of additive manufacturing and traditional casting to produce complex metal parts cost effectively. Essentially, industrial 3D printing can produce the molds, cores and patterns for casting metal parts, using nearly any castable metal. This approach eliminates the need for permanent tooling and allows for complex parts to be manufactured immediately.
The method is viable for first prototypes right through to large annual production volumes. For example, with additive manufacturing, there is no need for prototype tooling in the early stages of a new product design as the designer can prototype several variations on a design rapidly and with no additional cost.
Additive-enabled casting is also suitable for many casting processes, from small investment castings, such as jewelry, to mid-sized V-process parts, to large sand castings.
Let’s explore a little further how eliminating tooling can speed up the response of the foundry. By eliminating the need for tooling in the sand casting process, the tool doesn’t need to be removed from the molded sand, so no draft is required in the as-cast design. This results in a casting closer to the net shape of the final part. Because these kinds of molds are typically produced by the binder jetting process (also called sand binder jetting), the biggest design limitation is ensuring a way to remove sand out of a mold cavity. By eliminating tooling, undercut and overhanging features are also possible. One of the other big restrictions of traditional sand cast tooling is limiting the placement of the parting line between the cope (upper tool) and drag (lower tool), because tooling has to be removable from the cavity. This allows the designer using printed casting molds to move the parting line to a less important area of the part or make it easier to remove any flash.
For even more complex or more difficult castings, binder-jetted casting molds make it easy to incorporate cheek or side molds to the cavity design, add alignment and assembly features, add gas vents at precise locations to reduce porosity or add gating or runner features to better control metal flow into the mold—all of which can improve casting quality and reduce cost.
Table 1 highlights how designing or modifying for additive manufacturing enable the designer to increase complexity of the design while reducing cost and improving quality of the resulting casting.
Taking a look at cores and the casting design, additional design factors can be considered (Table 2). Traditionally, cores have similar tooling requirements to the mold, and complex cores need to be produced as several pieces that are later assembled by hand and glued together. By printing this core, the assembly steps and variation in that assembly are reduced. This enables better control of the cavity during the casting process and could potentially lead to a reduction in metal section thickness because of a reduced tolerance stackup. Again, the designer also has the freedom to incorporate more complexity into the design without sacrificing cost or speed to market.
For fragile, large or complex cores, 3D sand printing also enables the addition of features that can simplify assembly, such as a handle that is removed before casting, or improve shipping, such as a mounting point or shipping box, from the place of printing to where the part is cast. One additional bonus of printed sand tools is they can be recycled in the foundry sand reclamation system instead of generating trash in the form of dunnage for shipping.
The U.S. patent application US20180339334 in Figure 1 helps illustrate the previous considerations. This design shows a highly engineered, lightweight engine casting that would not be producible by casting tool methods. The design integrates what would traditionally be separate cores for exhaust ports, intake ports, water jacket and cylinders into one 3D-printed piece. In addition, the design incorporates features to aid assembly in the foundry, as well as gas vents to improve casting quality.
Even with all the above considerations, why hasn’t additive manufacturing been adopted industrywide into the casting process? It comes down to the fundamentals. Finding these additive manufacturing sweet spots requires awareness from engineering and sourcing teams to know how to best apply these techniques. Robust design- and modify-for-manufacturing training can help your team identify opportunities to apply this method to cores and molds, and it can also help determine when it is not the right method to use. Ultimately, investing in additive manufacturing can save substantial time and money.
What was good in 4 BC can be great in 2021. Additive manufacturing enables design freedoms never thought possible in metal casting. It is time to design the future of the industry.
Ask your foundry and foundry service provider what they are doing and how they can help; many are actively working on 3D-printing projects to improve their operations. Or join the American Foundry Society where the Additive Manufacturing Division members would be happy to help you along in your AM journey. CS