Metal additive manufacturing, or 3D metal printing, has received a lot of attention in the last several years. General Electric spent more than $1 billion to purchase Arcam and Concept Laser and formed a new division called GE Additive. They predict they will have manufactured more than 100,000 metal components for their own use by 2020 and will be generating more than $1 billion in additive manufacturing revenues by that same year.  Furthermore, they predict they will sell 10,000 metal printers in the next decade.

Desktop Metal, a startup formed by MIT professors, has received $115 million in funding from such corporations as GE, Caterpillar, BMW, and Lowes.

IDTechEx, a marketing research firm has predicted that the metal additive manufacturing market will reach $6.6 billion by 2026, about the same size as the U.S. investment casting market. 3Diligent, a metal printing service provider, claims metal 3D printing will shape the aerospace industry.

With press like this, it is no wonder that investment foundries are concerned about the potential loss of business to metal printing. Is metal printing likely to make investment casting obsolete?

Per numbers from the Investment Casting Institute, in 2016, investment casting was a $13.5 billion industry worldwide. In North America alone, the industry generated $5.8 billion worth of castings and employed several thousand people. The majority of the market is in high value-added components such as those used in aerospace, industrial gas turbine, and defense applications. North America has more than 180 investment foundries, all of whom are concerned about the impact metal printing may have on their business.

In the past few years, the number of manufacturers of metal additive manufacturing systems has ballooned from less than 10 to more than 30 and new ones seem to appear every month.  Some have forecast that metal printing will become the dominant method of creating metal parts. Will metal printing make investment casting obsolete?

In a recent study, investment foundries and metal printers were asked to quote 75 different scenarios covering a range of investment casting cases. Quoted prices were averaged for both investment cast and printed metal and in each case, the lowest cost method was determined. The analysis was then repeated assuming that metal printing prices declined to determine what ground metal printing may gain as costs come down.  

The results provide some insight to both metal printers and investment casters and can guide them on where to focus their efforts in the future.  

Methodology
There are many reasons that a manufacturer may choose a particular manufacturing process for a component. They may choose the method that provides the components in the shortest period of time, the method that provides the best metallurgical properties, or the method that provides the best surface finish.  Most often, however, manufacturers will choose the least expensive method that provides acceptable quality. The objective of the study was to find those situations where metal printing might be less expensive than investment casting.

Investment casting is used over a very wide range of manufacturing situations. It is used to create components ranging from fractions of an inch to several feet in dimension. It is used to create components with geometric complexity ranging from very simple to incredibly complex. Finally, it is used to make production volumes ranging from a single part to tens of thousands of parts.

Of course, the least expensive method in one situation may not be the least expensive in another. The potential scenarios in investment casting are many.  Scenarios vary with part size, part complexity, and production volumes.  

To cover the majority of the investment casting landscape, 75 different scenarios were defined consisting of three different part sizes, five different part complexities, and five production volumes.

Part sizes chosen were four inches, eight inches, and 16 inches. Clearly, investment casting is used to manufacture components both larger and smaller than this range, but this will cover the majority of the market.

Geometric complexities ranged from very simple to so complex they cannot likely be cast.  Geometry 1 is a simple dome illustrated in Figure 1.  The pattern could be created in a simple two-part mold with no side actions or inserts. Geometry 2, an open impeller illustrated in Figure 2, is a little more complex.  It still can be created in a two-part mold, but the vanes create a more complex casting situation. Geometry 3, a closed impeller illustrated in Figure 3, is a step up in complexity. It cannot be molded in a two-part mold. Creating wax patterns will require either soluble or ceramic cores, resulting in multiple tools and increased cost. Geometry 4, a drone frame, is another step up in complexity and is a geometry that cannot be molded.  Investment casting would require printed patterns. Geometry 5, another drone frame, is a lattice structure designed to minimize the weight of the casting.  The tight spacing of the lattice makes it unlikely that the pattern could be shelled without bridging. Even if it could be shelled, the thin web of the lattice would be difficult to fill. This geometry probably could only be created with metal printing.

Note that geometries 1, 2, and 3 are moldable and can be created using conventional investment casting, hybrid investment casting or metal printing. Geometry 4 is not moldable and therefore cannot be created using conventional investment casting. It can, however, be created using either hybrid investment casting or metal printing. Geometry 5 is neither moldable nor castable and can only be created using metal printing.

All five geometry files were sized so that the major dimension was four inches (101.4mm). To create the eight- and 16-inch (203mm and 406mm) sizes, the files were scaled by a factor of 2 and 4.

Five levels of production volume were used; 1, 10, 100, 1,000 and 10,000 copies.

These values of three major variables define a manufacturing space that includes the majority of the investment casting industry.

Several investment foundries were asked to quote each of the combinations of part complexity, part size, and production volumes. They were asked to quote both conventional investment casting and hybrid investment casting using printed patterns. Material to be quoted was 17-4 stainless steel.

Seven foundries responded to the request. Pricing is typically considered very proprietary information and the requested information would provide a great deal of information about the foundry’s pricing strategy.  To minimize their fears about competitors obtaining access to their pricing, the author signed non-disclosure agreements, agreed not to disclose their identities, and only provided summary information (mean, median, maximum and minimum pricing) on each of the 75 scenarios.

For the conventional investment casting quotes, participants were asked to estimate the cost of tooling rather than actually seeking bids from tooling suppliers.
Printed pattern suppliers were asked to quote the same scenarios. The quoted prices were averaged for each pattern printing method and those averages were supplied to foundries for use in quoting hybrid investment casting prices. The foundries were asked to use the prices for whichever printing technology they were most comfortable with. Twelve printed pattern suppliers responded to the inquiries.

Several companies who provide metal printing services were also asked to quote printed metal components for the same scenarios and metal.  Three metal printing suppliers responded to the inquiry.  

Printed pattern suppliers and printed metal suppliers were provided the same level of confidentiality as the foundries.

For each scenario, all prices for conventional investment casting were averaged, as were the hybrid investment casting and metal printing prices.  In each scenario, the lowest price was identified.

Figure 6 illustrates the lowest prices for the 25 scenarios for 4-inch (101mm) components.  In those scenarios colored green, conventional investment casting with molded wax patterns was the least expensive method of manufacture.  As expected, it is the least expensive method for all higher production volumes that can be done with conventional investment casting, as shown by those squares colored green.

In those scenarios colored red, hybrid investment casting with printed patterns was the least expensive method of manufacture. For simpler geometries 1 and 2, the hybrid investment casting was least expensive for only very low quantities of 10 or less. Hybrid investment casting is least expensive up to 100 copies for geometry 3, which has a significantly higher tooling cost. For geometry 4, which can only be done with printed patterns or printed metal, hybrid investment casting is the least expensive for quantities of 10 or more.

Metal printing is the least expensive option for quantity 1 of geometry 4 and for all of geometry 5, which can only be done with printed metal. Figure 7 illustrates the lowest prices for the 25 scenarios for the 8-inch (203mm) components. Very little has changed from the pricing for 4-inch (101mm) components.  Quantity 100 of geometry three is now least expensive with conventional investment casting and quantity 1 of geometry 4 is now least expensive with hybrid investment casting.
Figure 8 illustrates the lowest prices for the 25 scenarios for the 16-inch (406mm) parts. The only change is that printed metal is not the least expensive method for any of the 16-inch (406mm) part scenarios. None of the metal printers contributing were able to build parts that large.  Consequently, those parts are not currently manufacturable.

Observations
From these results, several observations can be made:
•    At current pricing, metal printing will not take market share from conventional investment casting.
•    At current pricing, metal printing provides a lower cost of manufacture than hybrid investment casting only for small un-moldable parts.
•    At current pricing, hybrid investment casting will be less expensive than metal printing castable but un-moldable for all but single quantities of the smallest part.

There is no doubt that over time, the cost of metal printing will come down. The number of manufacturers of metal printers is increasing rapidly, increasing competition and putting pressure on prices.  In addition, as the number of printers sold increases, economies of scale will reduce manufacturing costs. Also, we may well see new printing technologies introduced that will lower costs.  If metal printing costs come down, will it become a lower cost alternative for part of the investment casting landscape?

To answer that question, the average metal printing prices were reduced by 50%. All 75 scenarios were then re-examined to determine the lowest cost method for each. That analysis was repeated for price reductions of 75% and 90%. The results are shown in Figure 9.

Several observations can be made from these results:
•  If metal printing prices are reduced by 50%, there are no changes in the low-cost method for 8-inch (203mm) and 16-inch (406mm) parts. For 4-inch parts, metal printing becomes the lowest-cost method for single copies of all geometries and all quantities of geometries 4 and 5.
•    If metal printing prices are reduced by 75%, there are no changes in the low-cost method for 16-inch (406mm) parts. For 8-inch (203mm) parts, metal printing is the low-cost method only for geometry 5 and quantity 1 of geometry 4. Except for quantities 10 and 100 of geometry 3, metal printing is lower cost than hybrid investment casting for 4-inch (101mm) parts.
•    If metal printing prices are reduced by 90%, there are no changes in the low-cost method for 16-inch (406mm) parts. On 8-inch (203mm) parts, metal printing provides a lower cost than hybrid investment casting for quantities of 1 and 10 for all geometries except geometry 3.  Furthermore, it becomes less expensive than conventional investment casting for quantities of 100 of geometry 1. On 4-inch (101mm) parts, metal printing completely displaces hybrid investment casting and takes share from conventional investment casting.

But can metal printing prices really come down that much? It is tempting to assume the same kind of price reductions seen in consumer electronics. Consider the drop in prices of video cassette recorders or personal computers over the first 10 or 15 years of life. Based on that, a price reduction of 90% might be possible.

However, there are significant differences between metal printers and consumer electronics. First, the majority of the printer is mechanical and there have not been similar reductions in the cost of mechanical components. Even with production scaling from tens of units per year to thousands, it is doubtful that there would be reductions of more than 50%.  

Secondly, metal printers report that materials cost accounts for 10-15% of the cost of a printed part. Metal powder providers start with the same material that investment foundries would buy, and then add significant processing cost to convert it into powder of a uniform shape and size. As a result, the cost of materials for metal printers is significantly higher than for foundries. For example, a foundry will pay about $5 per pound for titanium ingots. The same alloy for metal printers cost about $150 per pound. Undoubtedly, that gap will narrow as the volume of powder sold increases, but it is extremely unlikely that it will come down by a factor of 10. Consequently, it is very unlikely that metal printing pricing will come down by 90%. In fact, a price reduction of 75% seems highly unlikely in view of the cost of materials. It is unlikely that prices will decline more than 50% in the foreseeable future.  

If metal printing pricing is reduced by no more than 50%, it becomes the low-cost method of manufacture only for single quantities of small parts, small un-moldable parts, and uncastable parts.

Conclusions
At current pricing, metal printing has no impact on the investment casting industry. Even if the price of metal printing falls by 50%, it will have no impact on the current conventional investment casting industry for parts four inches or larger.

While this study shows there is no immediate threat of metal printing making investment casting obsolete, there are other threats. In the past few years, there has been a great deal of development in topology-optimized or light-weighted components. Topology optimization is a method to minimize weight in a component while maintaining its strength and functionality. The optimized component may have such geometric complexity that it cannot be molded and therefore cannot be created using conventional investment casting. Such components can, however, be made using hybrid investment casting or metal printing, although at a higher cost.

For some industries, such as commercial aircraft and defense, the value of the lighter-weight component more than offsets the increased cost of manufacture.

There are now several commercially available tools for topology optimization and many of the components currently being investment cast likely could be replaced by optimized components which cannot be conventionally cast.

This study shows that hybrid investment casting can provide a less expensive means to create un-moldable but castable geometries than metal printing. However, hybrid investment casting is currently used only for prototype and very low volume components.

The industry will have to develop the capability to use hybrid investment casting on volume production runs. If they can’t or won’t, that business will fall to metal printing.

The push toward light-weighting and the development of topology optimization tools will significantly increase the demand for castings which cannot be molded using conventional wax pattern tooling (example Geometry 4) and can only be cast using hybrid investment casting. This increase in demand will be at the cost of demand for conventional investment castings.  It will be in the best interest of foundries to develop the capability to handle hybrid investment casting in production quantities, not just prototype. 

Click here to see this story as it appears in the July/August issue of Metal Casting Design & Purchasing