The UK is a land of many legends, one of which tells the story of two imps sent by Satan to northern England to do dreadful things. They are said to have wreaked particular havoc in Lincoln Cathedral, where the two imps knocked over tables and chairs, and even threw things at an angel. The angel then turned one of the imps into stone – and you can still see the imp’s grotesque face on one of the cathedral’s columns today. Every child in the region around Lincoln knows the Lincoln imp, not least due to the fact that it adorns the emblem of the local soccer club.
Rebirth of an Imp
The 1923 Ruston B2 that had been parked for decades at the plant site of the gas turbine manufacturer in Lincoln was basically a wreck. The vintage vehicle was missing important parts, which made it impossible to restore. These parts, however, have now been reproduced by Siemens’ Materials Solutions subsidiary using 3D printing technology. The project that led to these reproductions demonstrates the possibilities offered by additive manufacturing of spare parts and components.
It also sits atop the radiator grilles of the cars that were built in Lincoln by the industrial equipment manufacturer Ruston & Hornsby between 1919 and 1924. The production of military equipment at Ruston & Hornsby came to a halt after World War I. Construction of engines for tractors and locomotives couldn’t compensate for the loss of income, so Ruston & Hornsby decided to add automobiles to their product range. However, the sedans that Ruston & Hornsby’s Chief Engineer, Edward Boughton, designed on the basis of the high standards of the armaments industry were too heavy. These days, we’d say they were over-engineered. Ruston & Hornsby was also unable to set up an efficient mass production system, which means the manual work needed to produce the cars made them very expensive. Only 1,500 people purchased a vehicle, and many of them were officials at embassies in the UK. Only a few models remain in existence today, including two that are nicknamed Gin and Tonic. These cars have stood on the Ruston factory grounds in Lincoln since the 1960s.
The Case of the Missing Imp
Unlike Gin, Tonic – which was built in 1923 and exported to Australia – was a true wreck. Geoffrey de Freitas, a British MP from 1950–1961, came across the car while Down Under. He brought it back to England in the 1960s and gave it to Ruston. The plan was to have company apprentices restore it. However, important parts had been damaged or were missing. The steering housing was broken, for example – and of all things, the imp on top of the radiator grille was gone. By that time, the design drawings had all disappeared, making it prohibitively expensive to produce individual components by casting.
But in 2003, restoration efforts were given new hope when Siemens acquired Ruston with a view to expanding its portfolio to include small gas turbines – a field in which Ruston has been a leader in Europe since the 1960s. Gas turbines are still manufactured in Lincoln today, and when Siemens acquired Ruston, it also took possession of the two vintage vehicles. Still, nothing could be found to replace Tonic’s steering housing or its imp, so restoration plans were put on hold again, until, in 2016, Siemens acquired Materials Solutions. The Worcester (UK)-based company specializes in additive manufacturing and produces gas turbine parts for Siemens, as well as components for the aerospace industry – and even for automotive racing teams. Materials Solutions General Manager Phil Hatherley heard about the vintage cars. “We offered to reproduce the steering housing and the imp using metal and 3D printing technology,” he explains.
Printing with Stainless Steel
Hatherley’s vision has been fulfilled. The steering housing has been reproduced, and the mischievous Lincoln imp once again sits atop Tonic’s radiator grille. It took five days just to print the steering housing, as the component, which weighs several kilograms, was printed layer by layer using type 316 stainless steel. In this process, a laser melts metal powder – and for a fraction of a second the metal liquefies and bonds with the metal layer below. Each layer is only 20 micrometers thick.
It also took several days to prepare for the printing process. First of all, since there were no design drawings, the housing had to be scanned from all sides using cameras, although the scanning itself only took a few minutes. However, before the component could be scanned, broken-off pieces had to be reassembled. Missing areas were then filled into the 3D model on a computer using Siemens NX CAD software. Engineers also scanned Gin’s imp to recreate the imp for Tonic. This reverse engineering procedure is not only used to restore vintage cars; it’s also suitable for industrial sectors that experience bottlenecks in the supply of spare parts for old machines whose design drawings can no longer be found. In this manner, 3D printing can be used to manufacture spare parts whenever they’re required, which eliminates the need for expensive tooling, warehousing and logistics, and also makes spare part management faster and more efficient.
Vast Potential Follow-up processing took even longer. Technicians carefully removed the supporting structure needed to produce overhanging parts in the metal printer. Because the housing is large and has a complex shape, stresses build up in the materials as the metal layers are printed. These stresses can be reduced by heat treatment in a vacuum furnace.
Gin – the A1 model built in 1920 and equipped with a 2.6 liter engine with an output of 15.9 bhp – participated in the 2018 vintage care race at the Cadwell Park racing circuit in Lincolnshire. Tonic could theoretically be taken for a spin as well; the problem is it needs a new windshield, a new soft top, and new upholstery. Nevertheless, it won’t be long until the impressive Ruston B2 model (3.3 liter engine, 20 bhp) is also tearing up the circuit in vintage car races. Says Hatherley: “As nostalgic as our effort to restore these two vehicles may seem, Tonic also shows just how much potential additive manufacturing offers for the future of spare parts logistics in many industries.”