Metals in Manufacturing
Aluminum, stainless steel, zinc, and magnesium — when plastic is not enough, metal is the answer. Each one machines, casts, and finishes differently.
Metal parts carry the weight of the product — literally and perceptually. A metal housing communicates durability and quality that plastic cannot match. Metal structural components handle loads that would deform any polymer. But metal is more expensive to tool, more expensive to produce, and heavier to ship.
For hardware founders, metal selection is a balancing act: strength vs. weight, machinability vs. cost, corrosion resistance vs. finish options. Understanding the four main metal families that dominate consumer product manufacturing will help you make the right call before the first CNC program runs.
6061 aluminum is the default for machined parts. It machines fast, anodizes beautifully, welds well, and resists corrosion. It is used for camera bodies, drone frames, laptop cases, and nearly every CNC-machined consumer product. Tensile strength: ~310 MPa. The downside: it is not as strong as 7075 and cannot match the surface hardness of steel.
7075 aluminum is the high-strength option — roughly twice as strong as 6061. It is used in aerospace components, high-end bicycle parts, and anywhere weight matters but strength is critical. It machines well but is more expensive than 6061 and has lower corrosion resistance. It does not anodize as evenly. Only spec 7075 if you genuinely need the strength.
304 stainless steel is the corrosion-resistant workhorse. It is used for kitchen equipment, medical devices, outdoor hardware, and anything that touches food or water. 316 stainless adds molybdenum for even better corrosion resistance — worth the upgrade for marine environments. Stainless is harder to machine than aluminum and roughly 3x heavier. Laser cutting and stamping are often cheaper than CNC for sheet metal stainless parts.
Zinc (as Zamak or ZA alloys) is for die casting. It casts at lower temperatures than aluminum, fills thin walls beautifully, and takes chrome plating or powder coating well. It is used for zipper pulls, belt buckles, decorative hardware, and small structural components. Zinc is roughly 2.5x denser than aluminum — consider weight in your design. Magnesium alloys offer even lighter weight but are harder to cast and more expensive.
Metal sourcing mistakes
Specifying the wrong aluminum alloy for anodizing
6061 anodizes evenly. 7075 produces a duller, less consistent finish. Die-cast aluminum can be porous and may not anodize at all. Match your alloy to your finishing goal.
Ignoring galvanic corrosion
When aluminum and stainless steel touch in the presence of moisture, the aluminum corrodes. Use insulating washers, coatings, or match material pairs.
Designing thin walls for die casting
Zinc can fill walls as thin as 0.5 mm. Aluminum die casting needs at least 1.0–1.5 mm. If your CAD has thin-wall features designed for plastic, they will not survive translation to metal.
Forgetting that metal weighs more than plastic
A part designed in ABS weighs 2.8x more in aluminum and 8x more in zinc. Shipping costs, structural loads, and user experience all change. Calculate weight before committing.
What founders should remember
6061 aluminum is the default metal choice
Unless you have a specific need for stainless, zinc, or a different alloy, spec 6061. Every CNC shop stocks it and knows how to machine and finish it.
Surface finish determines alloy and process
Anodizing, powder coating, electroplating, and bead blasting each work best with specific materials. Decide your finish first, then choose the material that supports it.
CNC vs. die casting is a volume question
Under ~200 units, CNC is cheaper (no tooling). Above ~500 units, die casting amortizes the tooling cost and becomes cheaper per part. The crossover depends on part complexity.