Real-Time Position Feedback for Die Casting Machine Clamping

Clamp-position feedback on a die-casting machine must work stably for long periods in an environment of high-temperature radiation, oil mist, mould-release vapour and severe shock together. Clamp position determines mould seating and the build-up of clamping force; shot-side displacement is used to calculate the plunger speed curve and the intensification switch point. Magnetostrictive displacement sensors, with absolute-position output and non-contact measurement, are a common replacement on die-casting machines for external long-stroke magnetostrictive and potentiometer-type feedback; the key is to distinguish mounting form and protection class by measuring point, not to use one model throughout.

Two classes of position measuring point on a die-casting machine

The first is clamp open/close stroke: the moving platen travels a long stroke, and the end position determines mould seating and clamping-force build-up; absolute position with retention on power loss is required, so that homing is not repeated at every power-up. The second is shot-plunger stroke: the stroke is shorter but the speed is extremely high; the controller needs the plunger speed curve by differentiating displacement, to judge the slow-shot to fast-shot switch and the intensification point. The second class demands a far higher update rate than the first; if the sample period cannot keep up, the speed curve is smoothed through the critical inflections and process analysis loses meaning.

Site constraints on clamp-position feedback

The reality of a die-casting shop: high mould-surface temperature, continuous radiant heat on nearby parts; vapour and oil mist driven onto the machine when mould-release is sprayed; continuous vibration from clamp shock and shot recoil. The corresponding selection constraints are three — ambient temperature must be checked against the sensor’s operating-temperature range, not storage temperature (the distinction is in Operating Temperature vs. Storage Temperature); protection class at least IP67, with IP69K recommended near the spray zone; vibration and shock ratings must cover shot recoil. Temperature also introduces zero and span drift through change of waveguide sonic velocity; compensation logic for high-temperature duty is in Do Sensors Need Warm-Up? Self-Heating, Thermal Equilibrium and the Real Magnitude of Temperature Effects.

Measuring-point selection comparison

Choosing in-cylinder versus external

Clamp and shot cylinders on die-casting machines are mostly high-pressure systems. An in-cylinder type puts the rod in the piston-rod bore, so the rod is not exposed to spray and flying metal, with better life and reliability; the cost is that the piston rod must be deep-bored to specification (minimum bore generally ≥12.7 mm) and the pressure rating must cover system peak pressure (by series: Series 16/16R is 350 bar working / 530 bar peak, Series 17/17EX is 350/600 bar, Series 19 in-cylinder is 300/600 bar). An external type is convenient to retrofit without touching the cylinder, suited to in-service machines, but the rod needs a guard and must be kept off the spray and splash path. In-cylinder products include Series 16 cylinder-integrated and Series 17 hydraulic-cylinder integrated; the overall hydraulic closed-loop selection approach is in Why Choose Magnetostrictive Sensing for Hydraulic Cylinder Position Control. Another scene of clamp-position coordination with temperature control (rubber vulcanising presses) is in Rubber Vulcanising Presses: Coordinating Clamping Position with Temperature Control.

Signals and process-data acquisition

Shot-curve analysis needs displacement, speed and pressure aligned on the same time axis. If the controller uses analog acquisition, match A/D sample rate to sensor update rate; the slower of the two sets the curve resolving power. With a fieldbus type (for example CANopen, EtherCAT), distributed clocks can be used for multi-axis synchronous sampling, reducing inter-channel time offset; configuration points are in How to Connect Magnetostrictive Displacement Sensors to a Fieldbus. If the reading jumps at the instant of the shot, it is often related to strong electromagnetic interference or incorrect shield earthing; the troubleshooting order is in Troubleshooting Magnetostrictive Displacement Sensors.