While 3D sand printing has seen a drastic increase in use over the last five years, the technology is primarily used for small- to medium-scale  prototypes and high-mix, 少量的工具. 随着新技术的发展, the speed and scale of printing is believed to increase  exponentially. Two recent studies on 3D printing for metalcasting are shared.

Making Headway to High Speed Sand Printing 

杰瑞·泰尔, University of Northern Iowa (Cedar Falls, 爱荷华州); Nathaniel Bryant, IMERYS (Atlanta); Kip Woods, Emerson Process Management (Marshalltown, 爱荷华州)

在过去三年中，生产打印砂模和砂芯的公司数量以及使用该技术的公司数量翻了两番. 

The technology has allowed improvements in the casting process in several ways. The cost of hard tooling is eliminated. 传统的铸件是通过在正形状周围形成砂子，并通过无机矿物或化学聚合物在适当的位置粘合而产生的. 例如, 与单个铸件的价值相比，正面形状的模具非常昂贵，并且必须在铸件设计的生命周期内摊销. 如果没有足够的未来产量要求，这种高成本往往会阻碍铸件的使用, and the components are produced using subtractive methods. This subtractive method is costly and less capable of producing complex internal geometry, which in turn requires multiple machined components. This is neither cost effective nor without large amounts of energy consumed and waste generated. 金属铸造的增材制造消除了昂贵的工具，并允许更好地利用占地面积和资本资金, all while reducing the overall component cost and material waste, particularly for prototypes and very low volume work.

在金属铸造中采用增材制造的关键障碍是可能的生产率和随后的制造成本. 印刷模具和芯的成本可能比传统的模具和芯生产贵20-30倍, which can make it less cost effective for production volumes higher than a few dozen. 

这阻碍了它在高产量作业上的使用，而这些作业最有可能利用该技术并随后提高质量和竞争力. 由此产生的投资回报，铸造厂购买的设备往往比传统设备要长得多, putting it out of reach for small to medium size enterprises (SMEs), which comprise over 80% of operating U.S. 铸造厂. 目前的增材制造技术针对的是服务中心，在那里可以保持较高的利用率，并且可以从高价的3D设备中获益, 哪些因素决定了印刷砂的高成本. This has stagnated the industry, keeping it viable for only low production and prototype casting.

The next generation of equipment is already being conceived and will be produced by a U.S. domestic supplier of foundry equipment. 国内制造允许使用当地可用的部件，这些部件往往更容易获得，并且可以更快地响应机器维护和维修. Using domestic components also allows for a lower cost of equipment, 船舶消除, 和OEM的库存要求. 

The new printer will target the operating foundry, 而不是服务中心, and will allow the SME 铸造厂 to advance their technology. Consequently, they will become a more valuable part of the supply chain. The printing equipment being conceptualized will be designed for affordability, 促进短期投资回报, 并提供高操作速度，以便将该技术用于生产而不是原型. 这项技术将为生产既具有成本竞争力又利用增材制造技术所能提供的设计自由的铸造部件提供范式转变. 

In sand printing, the process starts and fails with the sand layer. 迭代创建过程必须在许多不同的环境条件下可重复，这些条件存在于中小型铸造厂中，以获得成功, all while trying to use the most cost-effective printing media available. The selection of sand media requires the understanding of how it will spread, 冲击打印分辨率, 以及长期的可重用性. 即使呋喃印刷部件的pH值和酸需求值相同，印刷介质的丝网分布的微小变化也会对最终印刷产生很大影响. 

北爱荷华大学(UNI)的研究人员进行了广泛的研究，以确定3D砂打印材料的最佳特性. 这些研究导致了许多区域可用材料的开发，这些材料既降低了砂印刷的成本，又扩大了其能力. 在扩展功能的同时降低运营成本的结果间接提高了行业采用率. 了解砂印所用材料的特性将有助于提高速度和效率, moving the technology from service centers to typical smaller business 铸造厂.

UNI先前的研究通过开发几种国内骨料来源，大大降低了3D砂打印的成本, bonding resins and printing methodology. 该大学正在继续与设备制造商合作，以改进设计并促进打印机的建造. 该设计将结合技术，使生产速度达到目前最佳技术的10倍. The speed increases will come from new high-speed print heads, advanced software and machine design improvements. 将研究设备设计的变化，以允许大幅面印刷和最大范围的材料使用, including environmentally friendly inorganic resins.

This paper can be read in its entirety at www.afsinc.org/2020 - 056. 

Producing Large-Scale Castings With 3D Sand Printing

安德鲁·H. 乔尔·派克. Busler和Alex R. 内田穆勒公司. (田纳西州的查塔努加)

大型无烘烤模具的图案传统上使用木材作为制造腔压痕的材料. This has posed challenges to producing consistent castings, as wood will swell and shrink due to different levels of temperature and humidity, leading to a phenomenon of dimensional seasonality. As polymers are typically more resistant to these effects, they have been used by patternmakers for some time; however, urethanes have usually been limited to small- and medium-sized work.

在过去的几年里, developments in 3D printing have scaled up both the size and speed of prints. 

To produce large-scale 3D printed parts effectively, two primary process steps are required: additive (printing) and subtractive (machining). 大型打印头主要基于塑料注射成型行业中常见的螺杆挤出机.

With the advent of large-scale 3D printing, there is now the possibility to replace wood patterns with plastic, increasing patterns’ strength and dimensional stability. 然而, the larger printers do not have the same resolution of smaller printers, which necessitates the need for CNC machining to net size.

When creating the print file for large-scale printing, the model needs to be larger than the target geometry to ensure adequate machine stock. Due to the intricacies of the different slicing software, this is a tricky step. 锥形壁尤其难以保持一致的机器库存和融合，并且通常需要对打印文件进行单独的层调整. 

Material properties also must be considered regarding managing the heat in the printed part. 必须仔细考虑打印细节，以提供抗开裂和尺寸稳定性. 每种材料都有一个独特的温度阈值，超过该阈值将导致材料降解，并在层之间分层. Time and heat management between layers is critical. 

在选材方面, large 3D printers use a pelletized polymer, 不同的聚合物具有不同的性质和加工参数，如熔化温度和压力. The application and properties of the different materials vary as widely as their compositions. 早期的开发主要集中在纤维填充的ABS塑料上，但更多的化合物正在成为可能. 

While 3D printing 100% of the tooling as a single piece may be technically feasible, it would not be economically prudent to do so. 就像小型3D打印一样, holding flatness over very large areas can be tricky, which would be detrimental to the parting line. 

Gating and runner systems can be printed as integral to the casting, especially when the casting layouts were simulated with various software. 然而, doing so would sacrifice flexibility and reparability. 有分开的门的, 跑步者, 滤波器输出, 渣的陷阱, or other features allows for them to be replaced as they age or wear. It also allows for changes without needing to separate them from an integral piece. 

3D printing will increase in use within the metalcasting industry, 随着更多的技术和技能可供使用，对“传统”模式制作的定义将继续改变. More research is needed into this area, 特别是在耐磨性方面, behavior and durability of the different materials.