A method and apparatus for injection molding. The injection molding machine includes a mold formed by a fixed mold half and a movable mold half cooperating with the fixed mold half for defining a mold cavity of the mold and a gate channel leading to the mold cavity. An injection piston is operatively associated with the mold cavity for pressing a melt via the gate channel into the mold cavity. A sensor device detects a melt front of the melt rising upstream of the mold cavity in a conveying direction of the melt at a predetermined detection height. The sensor device includes walls defining a measurement gap disposed at the detection height and extending transversely to the conveying direction of the melt. The measurement gap is at least partially penetrated by a fraction of the melt from the melt front when the melt front rises toward the mold cavity. A measuring device operatively associated with the measurement gap is responsive to a presence of the fraction of the melt in the measurement gap without directly contacting the melt and generates a measurement signal for controlling predetermined parameters of the machine.