Mercury Marine

Mercury Marine is using Atlas molded polystyrene in a metal casting process known as lost-foam casting.

Mercury Marine was founded in 1939 in a small Wisconsin machine shop and has since grown into the largest builder of marine propulsion systems in the world. Number one on the water, Mercury Marine’s history of constant improvement in marine engine technology sets the standard for reliable, trouble-free performance, superior power and torque, low emissions, and low fuel consumption. A leader in innovation, Mercury Marine revolutionized the four-stroke marine engine marketplace.

By the 1990s, Mercury Marine was using molded polystyrene to fabricate specific components of their engines in a process known as lost-foam casting. Up until that point, they had been purchasing the polystyrene they were using from a Canadian vendor and wanted a dual-source pool of resources. In searching for a second material supplier, their objective was twofold: strengthen the supply chain and form a partnership with another molded polystyrene vendor that could help Mercury innovate and push the envelope in what they were designing, fabricating, and achieving.

Atlas Molded Products is proud of our 20+ year relationship with Mercury Marine. Based on a mutual interest in continually improving processes, products, and performance, like Mercury Marine’s engines themselves, this relationship has been about reaching beyond the edge of innovation since the start.


Mercury Marine is using molded polystyrene in a metal casting process known as lost-foam casting. This is a type of evaporative-pattern casting like investment casting except that it incorporates molded polystyrene rather than wax to take advantage of polymer foam’s low-boiling point. The process begins by making an aluminum mold to strict geometric specifications. The foam pattern is produced in the die during the molding process, whereby the pre-expanded beads of polystyrene are introduced into the preheated mold at low pressure. Steam is then introduced into the mold causing the polystyrene to expand and fuse within the heated aluminum mold.

Once the foam segments are complete, the segments are mechanically or robotically assembled to form the final pattern. The pattern is dipped into a ceramic slurry, covering the foam in a hard shell capable of withstanding the intense heat of the next phase. The ceramic coated patterns are then placed in a vessel where foundry sand is introduced and compacted around the entire cluster of patterns. The ceramic mold, with the molded polystyrene foam inside, is then filled with molten aluminum. This liquid aluminum is poured into the mold at temperatures of more than 1,400 degrees, immediately disintegrating the molded polystyrene in the middle to take the shape of the finished part. The molded piece then goes to a quencher, where it is rapidly cooled and the metal hardens before being sent for milling, grinding, or possibly machining, if needed.

Since molded polystyrene is approximately 98 percent air, the process of completely disintegrating the foam within the mold’s core is virtually instantaneous, hence the name Lost Foam. This process is easier than working with a wax mold, which leaves a residue that must be removed from each finished part.

Among the many challenges in developing foam molds that precisely articulate every detail and geometry of the fully finished part, the absolute certainty of the finished form is the most significant. As these parts are being incorporated in the larger power train, and exhaust systems, even the smallest variation in size, shape, or detail will make a component unusable.

As Mercury Marine considered possible molded polystyrene manufacturers to join their vendor pool in the late 1990s, beyond product certainty, their secondary considerations were vendor proximity and willingness and capability to support the product innovation process.


Atlas Molded Products enters the equation as a most proud partner. This relationship now extends into its fourth decade of mutual success with innovation as the foundation of everything this team has done together. This program began as a fledgling opportunity for Atlas to prove ourselves in the highly specialized niche market of lost foam foundry. This is a technically demanding field that takes advantage of molded polystyrene’s dimensional stability, which allows intensely intricate engineered parts to be mass-produced from a single foam form.

Over an initial ramp-up and test run phase of three full years, Atlas worked side-by-side with Mercury Marine’s design and engineering team to review design specifications and build a reliable QA/QC program capable of meeting wall thicknesses as small as 5 mm with tight dimensional and location tolerances.. Molded polystyrene’s clean, smooth face gives cast pieces cleaner, tighter surfaces with limited disruption. Molded polystyrene also allows a mold to account for multiple segments, bifurcated passageways, and other combined castings that reduce machining and assembly costs in the finished part.

The program started with a single part - a simple heavy cylinder head known affectionately as the Brick Head. Over the years, Atlas has perfected the processes of molding, handling, and assembling the foam segments through strict geometric tolerancing, controlling foam density, testing adhesives, managing glue lines, and understanding down-the-line assembly process to improve efficiency. Today, we are producing more than 20 different SKUs for Mercury Marine with wall thickness as thin as 3 millimeters in targeted locations, which is about 40% thinner than where we started 23 years ago.

A key component of our success has been the continual, weekly meeting between Atlas and Mercury Marine’s engineering and manufacturing departments. Our best solutions evolve from a continual insistence on proactively managing quality concerns, design changes, and assembly challenges collaboratively to improve performance while saving time and money in manufacturing and assembly.

When dealing with a lost foam foundry process, clients are relying on near net shape castings working exactly as planned with no room for error. To achieve this, Atlas Molded Products values the partnership and processes that lead to perfection-level performance beyond all else. In OEM parts manufacturing, the ultimate measure of success is a successful product launch.


Lost foam casting is a uniquely challenging, ultra-specialized area of molded polystyrene production that facilitates manufacturing of an endless array of OEM parts for Mercury Marine and many other industry-leading, household names across America and around the world. Operating from the edge of innovation, Atlas Molded Products takes tremendous pride in the relationships we build. We enjoy dissecting challenges, pushing ourselves, our technology, and our products to the highest levels of performance and we can only do that through partnership with our clients.

Lost Cast