Polycarbonate (PC) is a linear aromatic polyester with density 1.18-1.22 g/cm³, notched Izod impact strength of 600-900 J/m, and a heat deflection temperature of roughly 130°C rising about 10°C with glass-fibre reinforcement [S4].
For mold and die shops, these numbers define the operating envelope: PC tooling is specified where impact resistance, optical clarity, and dimensional stability outweigh the need for steel-class hardness or the abrasive-wear life of P20 or H13 tool steels [S1][S4].
Where PC Molds Fit vs Steel Molds
Polycarbonate is one of the five major engineering plastics and the fastest-growing general-purpose engineering resin, used for short-run injection molds, prototype tooling, and Class A surface verification where the part material itself is also PC [S4]. A Shenzhen-based moldmaker producing PC auto-mirror housings lists polycarbonate as both the mold feedstock and the part material, with mold service life quoted at 50,000,000 shots for die-steel-cored tools handling HDPE [S3].
Steel-cored PC inserts target a different niche: the mold base is hardened die steel, the cavity or insert is machined or cast PC, and the part is molded in the same resin for prototype colour and shrinkage studies [S1]. This is consistent with PC's role as a prototype-bridge material rather than a production-steel replacement: carbon-steel molds for ABS office dustbins are still offered on the same supplier list [S3].
Core Specs That Drive Mold-Material Selection
The four PC properties that determine whether it is fit for a given mold or die application are impact strength, heat deflection temperature, mould shrinkage, and hydrolysis resistance [S4]. Notched Izod of 600-900 J/m puts PC at the top of the engineering-plastic impact table, with flexural modulus above 2400 MPa and creep rate below 100°C load that remains low [S4].
HDT of 130°C un-filled rises about 10°C with glass-fibre loading, and the UL temperature index of glass-fibre-reinforced grades reaches 120-140°C, which is the upper limit for sustained molding-duty thermal exposure [S4]. Mould shrinkage is low and dimensional stability is good, which is why PC is also the resin of choice for the molded part when optical clarity (light transmittance approaching glass) is required [S4].
PC's main weaknesses in a mold context are poor hydrolysis resistance, notch sensitivity, and limited scratch and chemical resistance; it yellows under long UV exposure and is not rated for repeated high-pressure steam service [S4]. It is also not suitable for abrasive-glass-filled compounds, and its wear resistance sits in the lower-middle band versus most engineering plastics, so PC tooling frequently receives a surface treatment such as aluminium or silver plating when used in mirror-housing or reflector production [S3][S4].
PC Grades Available to Tool Shops
Commercial PC grades map directly to the failure modes a mold or die will see in service: antistatic, conductive, glass-fibre reinforced flame-retardant, UV-stabilised, food-grade, and chemically resistant variants are all standard catalogue lines [S4]. For mold and die use, glass-fibre reinforced grades are the practical default because they lift HDT, raise modulus, and cut creep; UV-stabilised grades are picked when the tool or the part is stored or operated under sunlight [S4].
Standard unmodified PC carries an inherent UL94 V-2 flammability rating without additives, and flame-retardant grades reach UL94 V-0 with the right filler package [S4]. Dielectric constant of 3.0-3.2 and arc resistance of 120 s make unmodified PC a credible insulator for any electrical-function insert, but neither figure substitutes for steel hardness in a high-pressure injection cavity.
Process Settings and Molding Window
PC processes on standard injection or extrusion equipment, and the molding window is the same as for any amorphous engineering resin: melt temperature in the upper range of the machine, mold temperatures held to deliver amorphous clarity, and shot size matched to machine barrel capacity [S4]. Tool-and-die shops that run both steel and PC inserts typically keep 30-ton to 730-ton presses on the floor, with shot weights from a fraction of an ounce to several pounds, which covers nearly all PC prototype tooling jobs [S1].
For die-cast (metal-casting) tooling, the working principle is different: liquid metal fills a movable cavity under low-then-high velocity, and the die applies forging pressure during solidification to close shrinkage porosity and break the as-cast grain, which lifts the mechanical properties of the casting relative to a static gravity pour [S2]. Polycarbonate does not enter that picture directly, but it is increasingly used as a pattern or short-run die for low-melting alloys, where its 130°C HDT is more than adequate and its impact strength allows the pattern to survive handling [S2][S4].
Comparison: PC vs Steel vs Aluminum vs Epoxy Tooling
PC tooling competes against three classes of benchmark: hardened die steel (P20, H13, S136), aluminium alloys (7075, QC-10), and cast-epoxy or sprayed-metal prototype tooling. Against die steel, PC loses on wear life and on upper temperature ceiling (130°C HDT vs 600°C for H13) but wins on machining time, optical polish for transparent parts, and per-cavity cost for prototype runs below about 5000 shots [S1][S4].
Against aluminium, PC is closer in thermal limit (aluminium tools top out around 180°C with the right treatment) but PC delivers higher impact strength and better dimensional stability, while aluminium still wins on thermal conductivity and on cycle time for high-volume production [S4]. Against cast epoxy, PC is harder, more dimensionally stable, and orders of magnitude higher in impact strength, but epoxy tools are still cheaper for one-off layup or prepreg masters [S4]. The right pick is therefore a function of shot count, surface finish, and the temperature the tool will see, not of one spec line.
Standards, Certification, and Sourcing Signals
Quality-system baseline for PC mold production is ISO 9001, with the Shenzhen auto-mirror program cited as ISO 9001:2008-certified, an older revision that is still in circulation among Chinese mold exporters [S3]. Tool-steel molds for engineering plastics such as HDPE are quoted with 50,000,000-shot life on hardened die-steel cavities, which is the benchmark PC tooling rarely matches but is sometimes specified to emulate in prototype [S3].
For part-side material compliance, PC's inherent UL94 V-2 flammability rating, dielectric constant 3.0-3.2, and arc resistance 120 s are the published reference values for any electrical-insert design [S4]. For a deeper read on the resin side, see the polycarbonate encyclopedia entry, and for tool-frame engineering the casting mold and mold base pages cover the steel-side envelope that any PC insert sits inside.
For a complementary read on selecting the same resin family in a different working envelope, see the aerospace PC grades, specs, and cabin compliance reference.