Selective laser melting 3D-printed engine is 20 percent lighter
Germany — Using selective laser melting, a research project has designed an internal combustion engine that is 21 percent lighter. In addition, a new design achieved better cooling characteristics and a more efficient oil circulation system.
In the “Leichtbau Motor” (lightweight engine) research project — “Leimot” for short — a consortium of science and industry has produced an internal combustion engine using a laser melting process, saving almost 21 percent in weight. In addition, the efficiency of the cooling system and the oil circuit was increased.
The focus was on the cylinder head and crankcase of a modern two-liter large-bore diesel engine. Instead of being produced by aluminum casting, as was previously the case, the two components were manufactured using a selective laser melting process. The aluminum alloy AlSi10Mg was used as the powdered starting material. These additively manufactured assemblies are around 21 percent lighter.
3D-printed cylinder head saves 2.3 kg in weight
The redesigned cylinder head saves 2.3 kg in weight, or 22 percent compared with the original component. To achieve this, it was necessary to specifically reinforce the areas subjected to high mechanical stress: This is because combustion primarily involves bending loads, while torsional loads occur in the overall engine structure. The best ratio of weight saving and rigidity is the combination of a double-T beam (IPB) and an integrated, closed drawer.
The exhaust duct could be 3D printed directly with thermal insulation using additive manufacturing. As a result, the exhaust gas post-treatment systems heat up more quickly. The turbine inlet temperature and thus the efficiency of the turbocharger also increase.
Crankcase saves 5.1 kg in weight
For weight and stiffness reasons, the crankcase was designed as a short skirt with an aluminum bedplate. The replacement of the steel bearing caps with the bedplate was made possible by the friction-reduced main bearing diameters of the basic diesel engine. With the redesigned crankcase including the bedplate, the weight was reduced by 5.1 kg compared to the original component.
The bulkheads of the crankcase were fitted with open, horizontal load structures, which are stiffened at suitable points by a cross-rib composite. Additional reinforcement is provided by two weight-reduced connecting tubes in the area of the balancer shafts. Based on topology analyses, low-load zones were optimized by lattice structures and cavities.
The side covers of the crankcase are now made of glass fiber-reinforced phenolic resin and are therefore around 15 percent lighter.
New cooling system with individual cooling lines in the cylinder head
The new cross-flow cooling system makes it possible to lower cylinder temperatures in a targeted manner and at the same time reduce the amount of water required. One main design difference is the use of individual cooling lines in the cylinder head to replace the large-volume water jacket. This reduces temperatures in the combustion chamber by up to 40 percent. And despite 40 percent less coolant used, the wall temperatures are significantly lower than those of the reference engine. As a result, both the warm-up phase after a cold start can be shortened and the drive power of the water pump reduced.
Less pressure loss thanks to improved oil circuit
Further advantages during cold starts and normal operation are provided by the improved oil circuit. The optimization measures include a new type of line routing — bends replace sharp deflections – and changes in cross-section. Together, these measures reduced pressure loss in the cylinder head and crankcase by 22 percent. An inverted siphon prevents the oil from draining when the engine is at a standstill. As a result, the appropriate oil pressure for the valve train is available more quickly after engine startup, and hollow bulkheads can be used for the oil returns.