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In 2003, a revolutionary additive metal fabrication technology was introduced to the North American market called Direct Metal Laser Sintering (DMLS)1. Over the course of the past five years, this technology has gradually become better known to many companies with primary interest being the production of direct to metal parts versus inserts.

While some companies are successfully using DMLS to make tooling inserts, wide acceptance of the technology in the moldmaking industry has been elusive. In an effort to try and understand where the technology might fit in today’s mold building shops, Morris Technologies and Extreme Tool & Engineering partnered on a project to test the pros and cons of the DMLS technology compared to traditional toolmaking methodologies.

Figure 1. Part design; parts made. Figures courtesy of Morris Technologies
and Extreme Tool & Engineering.

Direct Metal Laser Sintering
DMLS is an additive technology that works by sintering very fine layers of metal powders layer-by-layer from the bottom up until the build is complete. The process begins by sintering a first layer of 20 micron powder onto a steel platform. The platform then lowers by 20 microns, a fresh layer of powder is swept over the previously sintered layer, and the next layer is sintered on top of the previously built one. A powerful 200W Yb-fibre laser is precisely controlled in the X and Y coordinates allowing for exceptional tolerances to be held (+/-0.001"/inch). The latest technology takes advantage of a dual spot laser allowing feature sizes as small as 0.203mm to be built. With a machine build envelope of 250 x 250 x 215mm, many medium to small parts and inserts are able to be constructed in hours and days versus days and weeks using traditional processes. Once started, the machine builds unattended, 24 hours a day. Parts and inserts that come out of the machine typically will go through a series of post steps including support removal, shot peening, machining and other steps as required.

DMLS Versus Traditional Moldmaking
As various companies consider using DMLS for tooling applications, one of the difficult-to-answer questions that continuously comes up is how does it compare to traditional moldmaking methodologies?

Traditional sources of information relied on those who were using the technology for various niche applications or work that has been done in Europe. Generally speaking, DMLS has always been a technology to consider where the core and cavity being investigated had a high level of complexity to it and where possibly conformal cooling lines might be of value.

With those broad guidelines, it has been difficult to fully understand the pros and cons of DMLS specific to mold inserts. In an attempt to try and gain a better understanding of where DMLS might be a solution to consider, Morris Technologies and Extreme Tool joined forces to do a comparison between the two methodologies.

Figure 2a. DMLS-designed cavity and core with conformal cooling lines.

Goal Setting
Goals and expectations for the project were selected including:

• The DMLS technology is successfully being used to create direct parts, but can it successfully be used to create mold cavities and cores?
• The goal was to independently build a relatively complex geometry using both traditional methodologies and the DMLS technology.
• We would evaluate and compare the leadtime differences between traditional and DMLS.
• We would evaluate and compare the cost differences between traditional and DMLS.
• We would compare the accuracy differences between the two approaches.
• We would try and determine what the limitations of the DMLS process might be and where opportunities to improve it might rest.

Process Steps
1. The first step in this process was the selection of a geometry that would represent where DMLS might ideally be used. Simple geometries where CNC machining is straight-forward are already known to not be a good fit for DMLS, thus our team opted to acknowledge this and focus on where we believe the comparison might be most appropriate.

Figure 2b.

The part selected had a combination of decent complexity and part size that would fit the DMLS technology well. From a complexity standpoint, the geometry needed to have a fair amount of EDM work associated with it in order for DMLS to be a competitive solution. With today’s high-speed CNC technologies and the current state of the DMLS technology, if the mold can be constructed solely via CNC, that is probably going to be the way to go. The size of the geometry was also important given the build envelope limitations of the DMLS process and the cost impact making inserts too large in DMLS (see Figure 1) .

2. The next step was to create the cavity and core blocks/split. The time to do this would be roughly equivalent in either approach; however, with the DMLS process there are important differences to take into consideration given how the process works.
For DMLS, minimizing the amount of material to sinter and the height of the inserts is of paramount importance to keep costs at a minimum. This is not a concern for traditional moldmaking.

Cost breakdown. Chart courtesy of Extreme Tool & Engineering.

For this experiment, we incorporateed conformal cooling lines to see what impact this might have on the cycle time of the tool. Conformal cooling lines, in the appropriate application, can greatly enhance the tool life and part quality plus reduce the cycle times of the tool tremendously. It is one of the primary advantages of DMLS over more traditional methods of constructing inserts (see Figures 2ab).

3. With both the traditional and DMLS designs completed, MTI and Extreme Tool began the construction of the inserts independent from one another. MTI built the inserts using CoCr MP1 alloy and did minimal processing on the inserts before sending to them to Extreme Tool. Post-build, the only processing MTI did on the inserts was to stress relieve them. Extreme Tool received the inserts and proceeded to finish them up for their tool. Meanwhile, Extreme Tool was independently working on the same tool, but using traditional CNC machining and EDM to create the cores and cavities.

Various issues were encountered by Extreme with the DMLS inserts including difficulty working with the CoCr material and tolerance variations. Although most of these issues would be resolved, this initial trial proved to add significant cost and leadtime to the DMLS inserts in order to correct the problem areas. After all work had been completed on the inserts, for this specific experiment, traditional toolmaking seemed to have both a cost and leadtime advantage over DMLS (see Chart 1).

Following are the challenges faced with the DMLS inserts:

• The scale from the stress relieving operation proved difficult to remove and did not allow for conduction of electricity, thus EDM corrective work on the inserts was not an option.
• The inserts, as supplied, had warpage of around 0.030". Originally, the intent was to use them as produced, however given the amount of warp on the shut-off surfaces, additional grinding was required to achieve the necessary flatness tolerances.
• Dimensionally there was enough variation that additional machining was required adding more time and cost that was unanticipated.
• The material hardness (40 Rc) coupled with the properties of CoCr made tapping very difficult even with carbide taps.
• The surface finish of the inserts required polishing using traditional methods.
• None of the ejector holes could be reamed with HSS tooling/reamers.

Given the above (see Figure 3), it might be tempting to jump to the conclusion that DMLS inserts are not a cost and time competitive solution for creating cores and cavities, it is important to keep two key items in mind:

1. This was an initial attempt to do a comparison between DMLS inserts and traditionally made inserts. The team believes substantial costs could be eliminated from the DMLS inserts if the design of the core and cavity is revamped to minimize sintering time. We purposefully created the inserts closer to a traditional block to see how it would compare, and it is clear that further optimization is required for DMLS inserts to remain cost and time competitive.
2. The Cobalt Chromium material is not the optimized alloy to use to make inserts. The only reason we used the CoCr material was due to the lack of availability of the alloy specifically meant for tooling inserts: Maraging Steel MS1. This alloy is now released and in theory should eliminate some of the warping issues along with the difficulty of post-work issues.

Figure 3. DMLS-produced cavity detail.

As such, MTI and Extreme are embarking on a second test to incorporate the various items learned here to see if DMLS is a technology able to compete with traditional methods of making inserts. There is a high degree of confidence that it will compete favorably.

Summary
Although on the surface this initial comparison between DMLS and traditional moldmaking methods would suggest that DMLS may not hold any major advantages, it is important to keep in mind that this is a specific case and an initial attempt at making a comparison. With the numerous opportunities to hone the process in, we believe there may very well be some compelling reasons to consider DMLS as a technology to leverage in many applications. Much will be learned after we incorporate the various changes in our second comparison and these findings will be the subject of a future article.

References
1Morris Technologies was the first company in North America to procure the technology and was targeting markets that would potentially benefit from the technology for direct parts as well as mold inserts.