[ Additive Manufacturing ]
[ Additive Manufacturing ]
Fraction of pieces having given value
investment cast 17-4 PH to 3DEO printed 17-4 PH , we perform a tensile test . In one study , researchers measured the effects of casting porosity on the tensile behavior of investment cast 17-4 PH stainless steel . Figure 1 displays examples of engineering stress-strain curves from investment cast 17-4PH stainless steel in the H925 and H1100 conditions . As we can see quite clearly , the strain to failure varies significantly , primarily due to the effects of internal voids – or the inconsistency of material porosity present in these investment cast parts . Some tests in this study exhibited failure strains ( engineering strain ) that would not meet commercial specification requirements for castings ; 6 and 10 % for H925 and H100 , respectively , AMS 5355 ( Ref 1 ). When compared to 3DEO ’ s printing process , which results in similar levels of porosity , however consistent structural porosity , the stress-strain curve not only yielded superior results than that of investment casting , but as you can see in this image , the results are near-identical in performance . In addition , the effect of casting porosity on the mechanical behavior of investment cast 17-4PH stainless steel was studied . It stated that : “ Interdendritic porosity , formed during solidification and shrinkage of the alloy , reduces the yield strength and ultimate tensile strength roughly in proportion to the reduction in load bearing crosssection . The effects of casting porosity on ductility (% strain , % reduction in area ) are more severe , in agreement with research on other alloy systems . In this study , 10 % porosity reduced the ductility of 17-4PH stainless steel by
property ( strength , elongation , etc .) Figure 5 . Variability in a property cast components leads to a distribution of property values .
almost 80 % for the high-strength H925 condition . Tensile testing at -10C ( 263 K ) further reduces the alloy ductility with and without pores present . In the lower strength H1100 condition , the ductility is higher than the H925 condition , as expected , and somewhat less sensitive to porosity .” This is represented in the below tables . As you can see in Figure 3 . ( C = casting ), the minimum tensile strength for H900 is 1241 MPa . As compared to 3DEO ’ s printed 17-4 PH , which surpasses the industry standard for MPIF , when heat treated at H900 , it is already surpassing the tensile strength of investment casting at 1300 MPa . Bringing this into actual customer stories , a number of 3DEO ’ s aviation and aerospace customers have reported greater than 60 % failure in the nondestructive testing ( NDT ) process for investment cast parts due to poor material quality and inconsistencies part-to-part . As one could imagine , this adds a lot of additional , and often unexpected , costs and extra work .
Areal fraction comparison Fracture-related mechanical properties ( ductility , strength , toughness , etc .) of cast alloys are sensitive to both averages and extrema of microstructural attributes . What we see repeatedly with investment castings is that even if several pieces of the same component are cast by using the same exact process and average process parameters , as well as the same average alloy chemistry , they still may not result in the same fracture-related mechanical properties , despite having the same average microstructure . These inconsistencies are represented here in Figure 5 .
On the other hand , with 3DEO , because our printing and sintering process holds much uniformity in material properties component-by-component , the quantitative fractography is nearly identical between parts .
Design and manufacturing considerations In addition to the material and mechanical property comparisons between investment casting and 3DEO , there are a number of additional benefits that customers get from adopting their manufacturing processes to additive manufacturing . Additive manufacturing is praised for its ability to accommodate unique geometries and angles difficult to create using other manufacturing methods . When looking at the needs of aviation and aerospace customers , where additive manufacturing shines in design and part functionality includes :
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Internal channels
•• No drill-and-plug operations
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Gradual curves for less pressure drop
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Burr-free junctions between channels
•• Powder-free process
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Captive features , straight / undrafted / overhung surfaces
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Webs , holes , tabs , gussets , slots , and hooks difficult to ensure in molding
With investment casting , total cost of parts can be deceptively difficult to calculate . In order to understand total cost , you have to consider all costs associated with a supplier , especially location / transportation requirements , secondary processes or post-operations necessary , yield loss due to low quality , and more .
Increased speed to market Speed to parts can make the difference between you hitting or missing your quarterly numbers . Likewise , slower than expected deliveries can mean you ’ ve disappointed your customer by missing your own deadlines . When things go wrong with investment casting , it can take weeks or months to get back on track . Meanwhile your customers continue to be disappointed about something that is out of your control . If parts aren ’ t to spec , they can require costly mold modifications , reworking or maintenance .
References available on request .
66 Stainless Steel World September 2023 www . stainless-steel-world . net