It's completely understandable that shares of 3-D printer makers rallied on Tuesday following news General Electric (GE) - Get Report is buying two of their peers. The purchases are a big vote of confidence for 3-D printing by one of the world's largest companies, and raise the potential for other firms to counter GE by making their own 3-D printing acquisitions.

Still, printer makers might be a little nervous that such a big name is entering the space. Particularly since GE's move is the latest in a string of noteworthy entries over the last few years.

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GE is buying Arcam AB and SLM Solutions, two European makers of additive manufacturing systems used to create metal objects for industries such as aerospace, healthcare, energy and automotive, for a combined $1.4 billion. The companies produced $142 million in revenue last year between them.

GE forecasts Arcam and SLM will underpin an additive manufacturing business that will produce $1 billion in annual sales by 2020, and also drive $3 billion to $5 billion in cost savings over the next decade by allowing it to avoid buying printers from third parties.

Nonetheless, the news fueled M&A hopes for 3-D printer makers 3D Systems (DDD) - Get Report, Stratasys (SSYS) - Get Report, ExOne (XONE) - Get Report and Voxeljet (VJET) - Get Report, and resulted in them posting gains ranging from 3.8% to 5.8% on Monday. Belgian 3-D printing software/services provider Materialise (MTLS) - Get Report rose 7.9%.

GE is no stranger to 3-D printing. It already has 300-plus 3-D printing machines in operation, and predicts its Aviation unit will have manufactured 100,000 additive parts by 2020. Gas turbine and jet engine parts are among the 3-D printed items the conglomerate has produced.

Arcam and SLM's focus on metal printing meshes well with a lot of GE's existing 3-D printing efforts. But it also limits their overlap with the aforementioned printer makers. Citi analyst Kenneth Wong observes Stratasys "has zero exposure" to metal printing outside of its on-demand parts manufacturing business, and that 3D Systems' exposure, which stems from its 2013 acquisition of France's Phenix Systems, accounts for "a small proportion" of its sales mix.

He also notes Voxeljet's print process involves sand and plastic materials, while adding many of their clients' end-use applications involve metal. ExOne's systems use both metal and non-metal materials.

Piper Jaffray's Troy Jensen points out Arcam and SLM are two of the world's four biggest metal printing firms, and declares GE has "positioned itself as a clear leader in the space." He adds the deal "brought much needed validation to the 3D printing industry," whose sales have been hurt badly over the last year by excess capacity at many industrial clients.

But while GE's 3-D printer business is focused on metal for now, the company plans to "extend [its] line of additive manufacturing equipment and products."

Moreover, GE is the second Fortune 500 company to enter the 3-D printing space this year. In May, HP Inc. (HPQ) - Get Reportunveiled its Jet Fusion printing line, while making big performance and cost-reduction claims. HP's printers only print black plastic for now, but support for more colors and materials is promised.

Many startups have also entered the market in recent years. The list includes Carbon3D, whose printing process relies on light and oxygen and is said to print items 25 to 100 times faster than conventional methods. It also includes Xjet, which claims its liquid metal printing process is much cheaper than existing powder-based metal printing solutions.

Research firm Wohlers Associates estimates 62 companies sold industrial-grade additive manufacturing systems in 2015, up from 49 in 2014 and 31 in 2011. GE and HP should be on the list of 2016 sellers, and other industrial and/or tech giants could join it in the years to come.