The future of binder jetting in the automotive industry
Printing millions of pieces: The fight against sinter shrinkage and foundries.
1. Introduction: The race for the million units
Laser powder bed printing (PBF-LB) produces breathtaking rocket engines, but is often too expensive and too slow for large-scale production in the automotive industry (Volkswagen, Ford, BMW). If you want to produce a million water pump wheels per year, you need a change in technology. The key word is: Metal Binder Jetting (MBJ).
Companies like Desktop Metal, HP and ExOne are pushing binder jetting because it catapults 3D printing from the exclusive aerospace lab into the loud, driven halls of mass automotive production.
How does Metal Binder Jetting work?
MBJ does not use a laser! A layer of metal powder is applied, and an inkjet print head (similar to the one in the office) sprays microscopic drops of a liquid plastic binder (glue) exactly where the component is to be created. Layer by layer. The result is a delicate component made of metal dust that is only held together by adhesive (green part). It is extremely fast (printing an entire layer in seconds).
2. Sintering: Dust becomes solid metal
The green part from the MBJ printer is not yet a finished component (you can crush it with your fingers). It must be depowdered and pushed into a sintering furnace.
The plastic adhesive first burns in the oven at approx. 400 °C (debinding). Then the temperature is set to z. B. 1,300 °C increased (just below the melting point of the metal). The metal particles diffuse into each other and weld together. The result is a solid, almost 100% dense metal component that is often metallurgically better than a cast part.
3. The mathematical hurdle: sinter shrinkage
The oven process has a massive physical effect: shrinkage.
Because the burned adhesive leaves voids, the component often shrinks by 15 to 20% in all directions during sintering. Predicting this shrinkage is extremely difficult. Gravity causes overhanging roofs in the furnace to sink (sagging), and friction on the sinter plate hinders shrinkage at the bottom. The automotive industry requires tolerances in the tenth of a millimeter range. Advanced simulation software (Digital Twin) must therefore massively "pre-distort" the CAD model before printing (live sintering simulation) so that it shrinks exactly to the target size in the oven.
4. Support-free: The true strength of MBJ
In PBF laser printing, thick metal support structures consume enormous amounts of money and time. In binder jetting, the powder bed itself is the support. Since nothing is melted and nothing is warped, the loose powder supports the component perfectly. You can stack hundreds of small gears like chocolates in three dimensions throughout the entire installation space (3D nesting) - a gigantic productivity boost for the automotive industry.
5. Conclusion: The frontal attack on investment casting
Metal Binder Jetting is not yet ready for the extreme stresses of an aircraft turbine, but that is not the goal. MBJ attacks the market for classic metal investment casting and Metal Injection Molding (MIM). When the software finally masters sinter shrinkage, millions of complex gear parts, housings and hinges will come out of the inkjet printer cheaper than they could ever be cast.