By using 3D sand printing, 2/3 of the normal costs could be saved.
CASE STUDY BORO FOUNDRY - SUPERHEATER HEAD
How 3D printing and sand casting are influencing modern spare parts production
UK foundry Boro Foundry Ltd uses 3D printed sand moulds to produce spare parts. For a historic steam locomotive, Boro manufactured a new superheater head based on the original design drawing from the 1950s. By using 3D sand printing, the foundry was able to save 2/3 of the costs compared to conventional production and reduce the assembly time of the mould package from over 14 hours to just 3.5 hours. Projects like this impressively demonstrate the advantages that additive manufacturing offers for spare parts production - both in economic and design terms.
The steam engine was the first major milestone in industrialisation. However, the steam locomotive is at least as symbolic in this context. For the first time it was possible to transport people and goods over long distances without the use of horses. Today, many of these former drivers of industrialisation are still in use in the UK, both on the country's main lines and regularly on private heritage railways.
Obsolete, costly and inefficient
UK-based Tyseley Locomotive Works is a specialist restoration and maintenance centre for historic steam locomotives. In early 2022, Tyseley Locomotive Works received advice from the University of Warwick's WMG group to consider printed moulds and subsequently commissioned Boro Foundry to manufacture a new superheater head for one of their steam locomotives. Sam Edwards is director of sales and business development at Boro Foundry and led the project on the foundry side. "Superheaters play a crucial role in the operation of steam locomotives. They are used to heat the steam sent from the boiler to the cylinders to temperatures well above the saturation temperature of the steam," explains Sam.
In this case, the boiler produces steam at a temperature of 202 °C, and the superheater raises the temperature to as high as 340 °C. This increases the energy (enthalpy) contained in the steam, which can then be used to meaningfully increase the work done in the locomotive's cylinders. In addition, superheating minimises the condensation that can occur as the steam expands in the cylinders, reducing the risk of damage that can be caused by excessive condensate.
"Precision and quality were clearly paramount on this project; after all, the old component had worked perfectly for several decades until it was no longer fit for purpose," says Edwards. "Although superheaters have been used in the locomotive industry for many decades, the original manufacturing process has become outdated, costly and inefficient."
3D printing sets the course
This is because the original part contains a series of holes (56 in total) through which steam is directed during operation. These holes make the casting process much more difficult. The biggest challenge is the core, which is inserted into the mould to integrate the cavities or holes into the casting. Originally, the core was supported by clamps, bolts and the use of core plugs to keep it statically in position during casting. However, the risk and likelihood of the core moving during casting is significant. Unevenly thick and thin wall sections and additional downstream machining would be the result. An inspection of the original part revealed that this may have been the cause of localised thinning, leading to the original head being withdrawn from service.
"Quotes for a conventionally manufactured mould package, including pattern making, would have cost up to £34,000. We also estimated that the mould would take around 14 hours to assemble," said Edwards. "All of this, combined with the risk that the part would end up defective or, in the worst case, completely unusable, prompted us to look for an alternative manufacturing solution. We found it in voxeljet's 3D sand printing." Edwards continues.
Future-oriented, cost-efficient and innovative
The original design drawing was no longer available and therefore had to be redrawn by a Tyseley engineer. This drawing was then converted into a 3D model by Stafford Road Design and optimised for 3D printing. Boro Foundry worked with engineering firm Cerve Ltd to develop a mould set consisting of just three mould parts and a core. The moulds were produced at the voxeljet On Demand Printing Center near Munich.
The technology used for this is the Binder Jetting 3D printing process: Like most additive manufacturing processes, binder jetting is based on digital CAD files. These are broken down by the printing software into wafer-thin layers, each of which represents a cross-section of the object. Then the printing process begins: a recoater applies a micrometre-thin layer of the powder material to be printed, in this case quartz sand (average grain size: 140 µm), onto a building platform.
Then the print head moves over the build platform and selectively applies a binder to the areas that represent the cross-section of the object to be printed. Now the build platform lowers by exactly one layer thickness and the recoater applies a new layer of sand, which the print head selectively binds again. These process steps are repeated until the object is completely printed and can be unpacked from the box.
Thanks to 3D sand printing, Boro was able to reduce the assembly time for the mould to 3.5 hours and the total cost to just over a third of the quotes for traditional mould and pattern making.
Unlike the original part, Boro also chose to print the mould including the 56 holes on the underside of the part.
Although the 3D-printed mould also ran the risk of the core breaking away and floating up due to the casting pressure, Boro was able to fix the core and mould with bolts by integrating recesses for bolt connections directly into the CAD file or printed mould.
Before the actual casting, Boro simulated the casting process to design a gating system that reduced the casting pressure and the associated risk of erosion or movement of the core. In addition, the simulation helped predict the gas rise during casting and reduce the risk of gas entrapment. Boro then cast about 550 kg of iron at about 1330 °C. The new superheater for Tyseley Locomotive Works measures 1300 mm x 600 mm x 400 mm and weighs 406 kg.
"A particularly pleasing result with real added value was that all 56 remained free, eliminating the need for subsequent drilling, which in turn saved time and money at the end of the day," Edwards concludes. "Innovation was the key to success here. The use of 3D modelling, casting simulation and 3D sand printing significantly improved overall quality, time and cost. We have achieved overwhelming success with the application of these new technologies. This paves the way for a brighter future when it comes to manufacturing parts like this superheater header and offers the prospect of even larger and more complex castings for such applications."
