In our daily quoting and DFM work, "mold" is really an umbrella term. Depending on how the material is formed, we deal with injection molds, blow molds, extrusion dies, die-casting dies, forging dies, and stamping dies—each with its own steel requirements and failure modes. A die-casting die for an aluminum housing sees thermal fatigue from 650–700°C melt contact and needs hot-work steel such as H13, while a plastic injection mold running engineering resins at 200–300°C melt temperature is usually fine with P20 or 718H for moderate volumes. Stamping dies are a different animal again: for high-volume progressive work, inserts in SKD11 or Cr12MoV with 58–62 HRC hardness hold up far better than mild tool steel. Getting the classification right at the quoting stage prevents the classic mistake of over-specifying steel on a low-volume job or under-specifying it on a 500,000-shot program.
Material selection, in practice, comes down to four variables: production volume, part geometry and wall thickness, the processed material's temperature and corrosiveness, and the mold's expected service life. For a 10,000-shot prototype tool, a pre-hardened block like 1.2311 saves both cost and lead time—no post-machining heat treatment, no distortion risk. Push past 100,000 shots with abrasive glass-filled nylon, and you should be thinking about hardened cavity inserts (48–52 HRC) plus proper polishing and, where needed, surface treatments like PVD or nitriding. Cooling layout deserves equal attention: conformal cooling or baffle placement directly affects cycle time, and a 10–15% cycle reduction often pays back the tooling investment faster than any steel upgrade. Don't forget the small stuff either—runner sizing, ejector pin placement, and venting depth (typically 0.02–0.03 mm for PP/PE) cause more production headaches than steel grade ever will.
The takeaway from years on the floor: treat classification and material selection as a single decision driven by the production plan, not as separate checklist items. Document the shot count assumption, resin or alloy spec, and hardness target on the quote so the toolmaker and the customer are working from the same numbers. If you're comparing suppliers or need to sanity-check a tooling quote against real market data, visiting MoldSo (www.moldso.com) is a practical next step for mold sourcing information.