How to use metal 3D printing to manufacture gears in transmission systems?

1. Choosing the right material: how to balance cost and performance
Metal 3D printing gears need to be made of a material that balances mechanical capabilities, processing characteristics, and cost. The most common materials right now are stainless steel, titanium alloy, aluminium alloy, and high-performance alloy steel. These materials have the following properties and can be used in the following situations:
Stainless steel, like 316L
It offers good resistance to corrosion and moderate strength, making it a good choice for entry-level applications including food processing and chemical equipment that need to be resistant to corrosion. A certain medical device company uses 316L stainless steel 3D printed micro gear sets, which cut the number of parts from 12 to 3 while still meeting the ISO 13485 standard. This also cuts assembly time by 70%.
Titanium alloy, like TC4, is the best choice in the aircraft industry since it is light (4.5g/cm³) and has a high specific strength (tensile strength ≥ 900MPa). Boeing has cut the weight of its satellite antenna drive system by 40% by 3D printing titanium alloy planetary gears. They also used topology optimisation design to make the gears last for more than 100,000 cycles.
Aluminium alloys, such AlSi10Mg, are very popular in the consumer electronics and automotive industries because they are easy to work with and cheap (approximately one-third the price of titanium alloys). A certain new energy vehicle maker employs 3D printing using aluminium alloy to make gearbox gears. By optimising the internal lattice structure, the gears' weight is cut by 35%, the noise is cut by 5dB, and the cost of each component is cut by 22% compared to typical forging methods.
You can get hardness exceeding HRC45 by using precipitation hardening treatment on high-performance alloy steel like 17-4PH. This makes it good for industrial gears that have to handle a lot of weight. AddiTec and Amorphology worked together to make a 6-inch diameter strain wave gear flexible wire that is 3D printed with 17-4PH steel. This cuts down on material use by 65% and production costs by 58%, while still keeping the zero backlash properties.
2. Design optimisation: going from geometric limits to functional integration
The physical properties of subtractive techniques constrain traditional gear design. On the other hand, 3D printing technology uses topology optimisation and biomimetic design to deeply integrate structure and function.
Control of involute tooth profile that is exact
The precision of the tooth profile parameters affects how well involute gears mesh. CAD software like Fusion 360 has a built-in gear generator that can automatically figure out important numbers like pitch diameter, pressure angle (typically 20 °), modulus, and more. This makes sure that the gearbox error of 3D printed gears is 0.01mm. Through parametric design, a certain company that makes industrial robots has increased the gearbox efficiency of 3D printed harmonic reducer gears from 82% to 91%.
New use of conformal cooling water circuit
Traditional gear cooling uses oil baths or sprays from the outside. 3D printing technology, on the other hand, may make complicated waterways inside the gear, such spirals and trees. Siemens Energy has made gas turbine gears' surface temperatures more even by 25% and their thermal fatigue life three times longer by designing internal cooling water circuits.
Lightweight Lattice Structure Breakthrough
Lattice design can cut down on weight a lot while keeping strength. One company that makes aeroplane engines employs 3D printed honeycomb gear cores to make gears with a diameter of 200mm 40% lighter. They also use topology optimisation to cut the stress concentration factor by 60%.
3. The printing process: a double assurance of speed and accuracy
The main steps in metal 3D printing gears are selective laser melting (SLM) and directed energy deposition (DED). Here are their technical details and the situations in which they can be used:
The SLM process: Putting into action micrometer-level accuracy
SLM technology employs a powerful laser to melt metal powder one layer at a time, making precision moulds with a layer thickness of 0.02–0.1 mm and a surface roughness of Ra ≤ 3.2 μ m. The Platinum BLT-S1500 is a 32-laser collaborative scanning system that can print numerous gears at once in a forming chamber with a diameter of 1.5 meters. This cuts the time it takes to print one item by 80% compared to previous methods.
DED process: making big gears cheaply
DED technique uses a laser or arc to directly deposit metal wire or powder into shape. It works well for large gears with a diameter of more than 500 mm. You may use AddiTec's Meltio Engine laser head with CNC machines to do "printing milling" all in one go. A company that makes gearboxes for wind turbines utilises DED technology to print planetary gears that are 1.2m in diameter. This increases the amount of material used from 15% in traditional forging to 85%, and it cuts down on the time needed for further processing by 70% through mixed manufacturing.
Multi-material printing: a new way to grade functionality
With DED technology's dual line powder feeding system, you can get a gradient distribution of material qualities in the same gear. Amorphology's bimetallic gear has a tooth surface made of high-hardness martensitic stainless steel (HRC35) and a core made of high-toughness austenitic stainless steel. This makes the gear both wear- and impact-resistant, and it lasts three times longer than a gear made of just one material.
4. Post-processing: going from printed parts to working parts
Metal 3D printed gears need to go through extra steps like heat treatment, precision machining, and surface strengthening to match the strict standards of the gearbox system.
Heat treatment: get rid of leftover stress and make the mechanical performance better
To get rid of interlayer stress and improve the grain structure, 3D printed gears usually need stress relief annealing (holding at 500–600 °C for 2–4 hours) and solution treatment (quenching at 1050–1100 °C). Through heat treatment technology, a particular company that makes car transmissions has raised the tensile strength of 3D printed aluminium alloy gears from 320MPa to 380MPa and the elongation rate from 8% to 12%.
Precision machining: controlling tolerances down to the micrometre level
3D printed gears can be accurate to IT8-IT9 levels at first, although the gearbox system usually needs tolerances of IT6-IT7 levels. The five-axis linkage CNC milling machine can make precise cuts on the surfaces of gear teeth, with a tooth profile error of less than 0.005mm and a tooth orientation error of less than 0.003mm. A maker of high-precision machine tools has lowered the noise level of 3D printed gears from 75dB to 62dB using a "printing milling" approach.
Strengthening the surface: making it more resistant to wear and corrosion
Laser cladding technology may put coatings made of tungsten carbide (WC) or nickel-based alloys on the surface of gears, making them as hard as HRC60 or higher. A certain company that makes mining equipment put laser cladding technology on 3D printed gears. This made untreated gears last five times longer and reduced wear by 80% in muddy conditions.
5. Industrial Practice: From testing prototypes to making a lot of them
Steel 3D printed gears have gone from being used in labs to being used in factories. Some common examples are:
the field of aerospace
Airbus A380 planes use 3D printed titanium alloy gears in their landing gear system. The number of parts is cut down from 27 to 5, the weight is cut down by 45%, and the surface temperature of the gears is cut down by 30 °C thanks to the construction of an internal cooling water circuit. This makes the landing gear much more reliable.
Field of robotics
The UR5 collaborative robot from Universal Robots has 3D printed aluminium alloy harmonic reducer gears that cut down on joint loads by 30% because they are so light. Biomimetic tooth design also reduces the transmission error from 0.5 arc minutes to 0.2 arc minutes, which makes the robot more accurate while it works.
Field of energy equipment
State Power Investment Corporation's fourth generation nuclear power steam generator gearbox gear is made of 3D-printed nickel-based alloy material. The design of a conformal cooling water circuit makes the heat transfer efficiency 92%. Blockchain technology makes it possible to trace powder materials throughout their entire life cycle, which keeps nuclear power equipment secure.