Fathom Digital Manufacturing Corp. is combining with a special-purpose acquisition company to go public in a deal that values the 3-D printing firm at about $1.4 billion, the companies said.

Based in Hartland, Wis., Fathom uses digital manufacturing techniques to quickly make prototypes and complex manufacturing parts for its customers. Fathom says it helps blue-chip companies innovate and solve operational challenges.

The company is merging with the SPAC Altimar Acquisition Corp. II. The Wall Street Journal previously reported the two sides were nearing a deal.

Fathom is one of several attempting to tap into a booming market for 3-D printed products, with more companies across industries seeking to simplify supply chains, bring down costs and minimize their environmental footprints.

“We allow our customers to accelerate innovation,” Fathom CEO Ryan Martin said. “We become their secret sauce when it comes to product development.”

Owned by the private-equity firm Core Industrial Partners, Fathom joins many 3-D printing companies going public through SPACs. Desktop Metal Inc. went public via a SPAC backed by the same investment firm—HPS Investment Partners LLC—that backs Altimar. Other companies in the space to recently unveil so-called blank-check deals include Velo3D Inc., Markforged and Shapeways.

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With investors excited about the industry’s growth potential, many of these companies are drawing lofty valuations and raising large sums through their SPAC deals. Fathom is expected to generate about $425 million in cash proceeds through its merger from the $345 million held by the SPAC and a $80 million private investment in public equity, or PIPE.

Fathom has several manufacturing facilities across the U.S. and hopes to differentiate itself from early-stage companies going public via SPACs by touting its existing business. Fathom posted about $150 million in sales in its 2020 fiscal year.

Also called a blank-check company, a SPAC is a shell firm that lists on a stock exchange with the sole purpose of merging with another firm to take it public. SPAC deals have emerged as a popular alternative to a traditional initial public offering in the past 18 months, partly because they allow companies such as 3-D printing firms to make business projections, which an IPO wouldn’t allow.

SPAC executives say the deals are accelerating growth for disruptive companies, while skeptics contend that they disproportionately benefit insiders who are granted unique incentives.

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Altimar raised $345 million in February and is one of several SPACs backed by HPS. One of them took Desktop Metal public late last year, while another combined with Owl Rock Capital Partners LP and Dyal Capital Partners to create Blue Owl Capital Inc.

SPACs have raised a record of roughly $115 billion this year, according to data provider SPAC Research. Issuance, however, has slowed in recent months, as shares of some popular companies that merged with SPACs struggle and regulators increase their scrutiny of the sector.

Shares of Desktop Metal and the blank-check companies taking other 3-D printing companies public have struggled in recent months as have other publicly traded names in the space such as 3D Systems and ExOne Co.

Still, some investors remain confident several companies will grow rapidly in the years ahead as more customers use smart technology in their industrial processes.

“This has to happen for so many different macro reasons,” Altimar CEO Tom Wasserman said. “There are going to be a number of winners in the space.”

Write to Amrith Ramkumar at amrith.ramkumar@wsj.com