At the Inside 3-D Printing Conference held earlier this month in New York City, Terry Wohlers of Wohlers Associates, a leading 3-D printing industry insights firm, highlighted that while it's likely for 3-D printing to make up a greater percentage of the worldwide manufacturing base in the future, there will be major obstacles along the way. In particular, approaching 3-D printing from a manufacturing perspective hasn't been mastered yet -- and will likely take time to play out.

Currently, there are serious limitations with software being able to analyze a 3-D printing job beforehand to know whether support structures can be removed, or if metal powder can be removed from the inside of a hollow part afterward; how an object is oriented in the printer can literally sabotage an entire print job. 3D Systems (NYSE:DDD) and Arcam (NASDAQOTH:AMAVF) investors should acknowledge that it's likely going to take many years until major progress is made with these operational challenges.

Approaching 3D Systems and Arcam from a long-term time horizon will allow investors to temper their expectations to be more in line with a realistic view of the future of 3-D printing and the role it plays in manufacturing. Additionally, setting a long-term time horizon will increase the margin of safety associated with buying 3D Systems or Arcam at today's seemingly stretched valuations. The longer an investor holds 3D Systems or Arcam, the lower the long-term revenue growth rate to earn a positive return on investment is needed. Taking into account that the 3-D printing industry is expected to grow by about 19.3% a year for the foreseeable future, it's plausible that 3D Systems and Arcam will be able to sustain strong revenue growth in the years ahead, assuming their products and services remain competitive.

Ultimately, Wohlers is optimistic that these types of obstacles will work themselves out and 3-D printing will begin to make a bigger effect in the manufacturing world. How much money we're talking about in the future is anyone's guess, but Wohlers believes that 3-D printing could generate about $10.8 billion in revenues by 2021, a nearly fourfold increase from 2012 levels.

In the following video, 3-D printing specialist Steve Heller and industrials bureau chief Blake Bos discuss these obstacles that Wohlers highlighted during his keynote presentation.