Since moulds have been expensive to manufacture, they were usually only used in massproduction where thousands of parts were being produced. Typical moulds are constructed from hardened steel, pre-hardened steel, aluminium,and/or beryllium-copper alloy.:176 The choice of material to build a mould from is primarily one of economics; in general, steel mouldscost more to construct, but their longer lifespan will offset the high erinitial cost over a higher number of parts made before wearing out.Pre-hardened steel mouldsare less wear-resistant and are used for lower volume requirements or largercomponents; their typical steel hardness is 38–45 on the Rockwell-C scale.Hardened steel moulds are heat treated after machining; these are by far superior in terms of wearresistance and lifespan. Typical hardness ranges between 50 and 60 Rockwell-C(HRC). Aluminiummouldscan cost substantially less, and when designed and machined with modern computerisedequipment can be economical for mouldingtens or even hundreds of thousands of parts. Beryllium copper is used in areasof the mouldthat require fast heat removal or areas that see the most shear heat generated.:176 Themouldscan be manufactured either by CNC machining or by using electricaldischarge machining processes.