Sheet metal materials and processing guide

Material selection in sheet metal is a trade between four variables: cost, corrosion resistance, formability and finish. SPHC is hot-rolled mild steel, the cheapest option, with a rougher surface that suits structural parts where appearance does not matter. SPCC is cold-rolled, giving a better surface for painted or visible parts at a higher price. SECC is electro-galvanised cold-rolled steel, which adds corrosion resistance without the cost of stainless and is the usual choice for enclosures and chassis. SUS304 stainless resists corrosion without coating and is standard for outdoor and food-contact products, at several times the material cost and with more difficult forming. Aluminium is light and corrosion resistant but needs different cutting parameters and work-hardens with repeated bending.

Four things, in descending order of impact. Material cost dominates on thicker or stainless parts, and it is set by the nesting efficiency of your part on the sheet, not by its own area. Cutting time is driven by total path length and by thickness, so a part with many small holes can cost more to cut than a larger plain one. Piercing count matters separately, because each internal cutout starts with a pierce that takes noticeably longer than the cut itself. Secondary operations, deburring, forming and finishing, then add to the base cost. A design change that reduces hole count or improves nesting often saves more than negotiating the rate does.