What is the printing performance of 316L stainless steel commonly used in mold manufacturing?

1. Properties of the material: 316L stainless steel (UNS S31603/EN 1.4404) is a type of low-carbon austenitic stainless steel that has corrosion resistance and toughness at high temperatures. Its key components include 16% to 18% chromium, 10% to 14% nickel, and 2% to 3% molybdenum. Adding molybdenum makes the material far more resistant to pitting and crevice corrosion, especially in places with chloride ions. In these places, its corrosion resistance is more than three times that of regular 304 stainless steel. 316L stainless steel can resist seawater erosion for a long time, which means that marine engineering moulds made from it will last 2 to 3 times longer than moulds made from other materials.
Also, the austenitic structure of 316L stainless steel makes it very robust at high temperatures. Its tensile strength can still stay above 400MPa at 600 °C, which is far higher than the 200MPa threshold of regular mould steel. This feature makes it perfect for moulds used in die-casting and thermoforming at high temperatures. The die-casting mould for the battery pack housing of new energy cars, for instance, can handle the impact of aluminium liquid at 400 °C. A single mould can last for more than 80,000 uses, which is 40% longer than typical H13 steel moulds.
2. Printing process: using several technological paths to fulfil the needs of making moulds
There are three major ways to 3D print 316L stainless steel: selective laser melting (SLM), direct metal laser sintering (DMLS), and binder jetting. Each has its own technical features and uses:
SLM method uses a high-energy density laser to melt layers of 15–53 μ m spherical powder. This makes parts with a density of 99.5% or higher. Its main benefit is that it can print complicated conformal cooling channels, which greatly increase the cooling effectiveness of moulds. For instance, in big automobile panel moulds, SLM-printed conformal water channels make the temperature of the mould more even, going from ± 15 °C to ± 3 °C, which cuts the cycle time by 35%.
DMLS technology: uses a laser with a lower energy density to partially melt powder that is 20 to 63 μ m thick. This is good for printing big structural parts. The fact that it can make lightweight moulds with honeycomb lattice structures within is what makes it so special. This makes the moulds lighter without losing strength. In aircraft engine blade moulds, for instance, the dot matrix structure produced by DMLS cuts the weight of the mould by 40% and the stiffness by only 10%.
Adhesive spraying technology: Use an inkjet head to spray adhesive on top of each other to bond 45–150 μm powder. Then, degreasing and sintering it will make it stronger. This technique can print at a speed of up to 500cm³/h, which is fast enough for making mould blanks on a big scale. For instance, while making moulds for consumer electronics cases, adhesive spraying technology cuts the time it takes to make a blank from 7 days to 2 days and cuts the cost of each item by 60%.
3. How well it works: A good mix of accuracy, strength, and resistance to corrosion
Accuracy of dimensions: The dimensional precision of 316L stainless steel 3D printing can be as low as ± 0.05mm (for sizes between 100mm and 100mm), and the surface roughness Ra is < 3.2 μm. It is possible to make precise moulds of complex cavities by improving the design of the support structure and the printing settings. For instance, SLM printed titanium alloy dental crown moulds used to make medical implant moulds are accurate to within ± 0.02mm, which is what is needed for clinical implants.
Physical properties: After being heated, 316L stainless steel printed parts can withstand a tensile strength of 650MPa, a yield strength of 480MPa, and an elongation rate of 30%. The tiny equiaxed grain structure that 3D printing creates makes it 15% stronger against fatigue than other forging materials. After cryogenic treatment, the fatigue life of DMLS printed moulds used for semiconductor packing rose from 50,000 cycles to 120,000 cycles.
316L stainless steel printed parts can withstand corrosion better than typical casting materials. In a 3.5% NaCl solution, the pitting potential of 316L stainless steel parts reaches +320mV (SCE), which is 80mV greater than traditional casting materials. The uniform and dense oxide film that forms during the printing process gives it an edge in terms of corrosion resistance. 316L stainless steel can withstand strong corrosive gases that are released when fluoroplastics break down for a long time. The mould life is eight times longer than that of DC53 mould steel.
4. Use in business: From making prototypes to making a lot of them
Field of aerospace: For making a certain type of engine turbine disc forging die, SLM technology was used to print 316L stainless steel moulds that were 1.2 tonnes lighter and 680 kg heavier, while making them 25% stiffer. The mould cavity's size change is less than 0.02mm after 5000 thermal cycles of testing, which meets aviation grade precision standards.
Industry of new energy vehicles: DMLS technology prints moulds that combine conformal cooling water pipes and lattice support structures. This makes the temperature of the mould more even by 40% and lowers the amount of warping in the result from 0.5% to 0.15%. The mould is being used on a wide scale, with an annual output of 100,000 sets.
In the field of medical devices: The combination of adhesive spraying technology and CNC precise machining allows for quick changes to titanium alloy acetabular cup moulds used to make orthopaedic implant moulds. The time it takes to go from design to finished product has been cut from 45 days to 7 days, which has cut the cost of each unit by 70%.