By Oleg Raykis
Today there exist a number of technologies for additive manufacturing of components.
The two most prominent types utilizing lasers for generating parts out of metals are either powder bed based solutions or direct energy deposition, often referred to as laser metal deposition. As a company Laserline focuses mainly on the second type. Depending on the application it allows you to produce larger part sizes with higher productivity (deposition rates and therefore higher productivity) due to the fact of not being limited by the size of the building chamber as it would be in the case of a powder bed machine. It is also much faster in many cases.
Laserline identified four main application areas for AM in which we operate and be described based on examples in this article. Those areas include, besides generating complete parts by terms of additive manufacturing, also repair welding application or hybrid machines – a combination of conventional machining and laser technology the fourth main application area would be providing functional areas on conventionally manufactured parts.
Additive manufacturing technology allows generating shapes and structures in a single production step with little material loss, post machining and tool wear (near-net-shape manufacturing). Thereby you can use material in powder or wire form. The advantage of using wire is that you will have a 100% material utilization; the compromise on the other hand might be the directional dependency when you supply the wire laterally and not coaxial. Pic. 1 shows an example of a free form application as a rocket nozzle demonstrator part made out of Inconel 625.
Pic.1 Free form powder AM of a rocket nozzle demonstrator (Source: Fraunhofer CLA)
The part was done without any type of process control. Another interesting example of AM with Titanium is shown in Pic.2.
Pic. 2 Ti64 powder AM with closed loop process control (Source: Fraunhofer CLA)
Compared to the rocket nozzle, process control was used when producing the demonstrator part in pic.2. The camera based system (in this case E-MAqS) is capable of measuring the size and temperature of the melt pool. Furthermore it can give feedback to the laser source and adjust the laser power accordingly to maintain the desired size of the melt pool. This in turn ensures consistent reproducible part build ups with no defects.
Another very interesting and promising approach is to integrate the laser source into machine tools. There are several hybrid machine tool concepts being developed; one of them is the combination of additive and subtractive tools which achieves a new level of manufacturing. One example is the merger of a laser with a 5-axis milling machine. The integrated diode laser deposits the powdered metal layer by layer, generating a solid, fully dense metal part. The following milling operations directly finish machines surfaces in areas necessary, without changing setup.
Pic.3 An example of a conventional milling machine with integrated AM technology (Source: DMG Mori-Seiki)
This flexible switch between laser and mill also allows the machining finish of areas, which would be impossible to reach on the final component. Designs with undercuts, internal geometries and overhangs without support structure are no problem. The manufacturing of completely new structures and designs are now possible. All weldable metals, which are available in powder form, can be used, for example steel, nickel and cobalt alloys as well as titanium, bronze or brass.
A third important field of AM from our perspective are repair welding applications. Probably the most prominent and widely industrially utilized are the repairs of turbine blades. Turbine blades in steam engines, especially in the first two rows, experience a lot of wear through erosion. Instead of replacing the whole part it is possible to repair the worn area by putting a couple of layers (mostly nickel / cobalt based super alloys) and machine them down to the finished surface, see Pic.4.
Pic.4 Turbine blade repair (Source: Fraunhofer ILT)
This remanufacturing procedure saves up to 90% of material and energy cost compared to manufacturing a new blade. Even though turbine blades are the most prominent example of laser repair welding a wide variety of other parts can be restored using the procedure, e.g. worm shafts, helical gears, molds, etc. to name a few. When speaking about additive manufacturing most people have the production of complete parts in mind. This doesn’t always have to be the case. Often it makes more sense from an economic standpoint to add to a conventionally (and relatively inexpensively) produced part functional areas where they are needed. Pic. 5 shows one such example.
Pic. 5 Extruder barrel demonstrator (Source: Fraunhofer CLA)
In this case 100 lbs. of hard and wear resistant Stellite 21 powder material was deposited on a metal pipe base structure to form the extruder thread. One further example of it can be functional layers on drill bits where sensors need to be shielded from magnetic interference. By creating heat resistant layers out of non-magnetic materials it is possible to place those sensors.Through a clever combination of the usage of conventional and additive manufacturing technologies it is possible to produce advanced parts without increasing the cost.