An injection assembly for a die-casting machine, comprising: - an injection piston controllable in translation to operate on molten cast metal in a machine die for which a desired speed (Vset) is defined during a metal injection step; - a main pressure chamber , upstream of the injection piston , for containing and pressurizing the fluid intended for the outward translation of the injection piston , wherein said main pressure chamber is further connected to an injection drain connected to the drain, along which an injection return drain valve operates; - a proportional injection delivery valve for feeding the fluid to a main inlet and from said main inlet to the main pressure chamber as a result of the opening of a main shut-off valve ; - a main back-pressure chamber , downstream of the tail end of the injection piston , connected to a return inlet for supplying pressurized fluid for the return translation of the injection piston , wherein the return inlet is connected upstream with a pump delivery , upstream of which a pump is located; - an injection return valve arranged between the delivery pump and the return inlet ; - a proportional injection drain valve for draining the fluid from the main back-pressure chamber , so that the action of the fluid in the main pressure chamber and the opposite action of the fluid in the main back-pressure chamber generate an outward thrust for the actuation in translation of the injection piston , controlled in opening according to a tuning speed (Vreg); - an auto-tuning injection valve opening system configured so that the opening of the injection valve during a predetermined die-casting cycle is tuned according to the tuning speed (Vreg), determined as a function of the difference between said predetermined desired speed (Vset) of the injection piston and an effective speed (Veff) of said injection piston detected for the previous die-casting cycle. - an injection piston controllable in translation to operate on molten cast metal in a machine die for which a desired speed (Vset) is defined during a metal injection step; - a main pressure chamber , upstream of the injection piston , for containing and pressurizing the fluid intended for the outward translation of the injection piston , wherein said main pressure chamber is further connected to an injection drain connected to the drain, along which an injection return drain valve operates; - a proportional injection delivery valve for feeding the fluid to a main inlet and from said main inlet to the main pressure chamber as a result of the opening of a main shut-off valve ; - a main back-pressure chamber , downstream of the tail end of the injection piston , connected to a return inlet for supplying pressurized fluid for the return translation of the injection piston , wherein the return inlet is connected upstream with a pump delivery , upstream of which a pump is located; - an injection return valve arranged between the delivery pump and the return inlet ; - a proportional injection drain valve for draining the fluid from the main back-pressure chamber , so that the action of the fluid in the main pressure chamber and the opposite action of the fluid in the main back-pressure chamber generate an outward thrust for the actuation in translation of the injection piston , controlled in opening according to a tuning speed (Vreg); - an auto-tuning injection valve opening system configured so that the opening of the injection valve during a predetermined die-casting cycle is tuned according to the tuning speed (Vreg), determined as a function of the difference between said predetermined desired speed (Vset) of the injection piston and an effective speed (Veff) of said injection piston detected for the previous die-casting cycle. <EOS>