Die-Shot Monitor: Cavity Pressure Measurement
The pressure on the metal inside the cavity can not be measured using the hydraulic pressure because the conditions inside the cavity are completely different.
However, since the cavity is central to the Die Casting process, it is important to understand what is happening there.
With a Die-Shot system, you can now measure the actual pressure in the cavity, just the same as any other parameter.
Force Sensors
You do this by installing a special force sensor inside the ejector plate, behind an ejector pin. The pressure from the metal transmits through the ejector pin to the sensor. These sensors are very small yet extremely strong, and able to stand up to the forces and impacts in the ejector plate.
Another advantage of this system, is that it is quite easy to move the sensor to another ejector pin and measure the pressure in different region of the cavity.
A new view of the Die Casting process
Die-Shot gives you a completely new view of what is happening inside your die. It will show you that the actual pressure in some parts of the cavity is much less than indicated by the hydraulic pressure. This pressure loss is due to the restriction of the gate and the gradual soldification of the metal in the cavity.
Shrinkage Porosity Detection
Shrinkage porosity will form in those regions of the cavity where the pressure is low and the holding time of the pressure is short.
So now you have a tool which can be used to detect when the conditions for shrinkage porosity are present, which is particularly useful for Aluminium die castings.
Die-Shot enables you to view the hydraulic pressure on the metal on the same screen as up to three cavity pressure sensors. You can set target values for the pressure holding time of each sensor and warn you when it is too short.
Impact Pressure Measurement
The impact pressure at the point of cavity fill is the parameter related to the amount of flash on the part. You can now view the actual impact pressure inside the cavity and compare that to the impact pressure measured through the Hydraulic screen.
Intensification Pressure
When you look at the Hydraulic pressure screen for a cold chamber machine, you will see the rise in the pressure curve as the intensification pressure comes on. Whilst it might be comforting to see that the pressure has increased to say 70 MPa, in reality the pressure in the cavity will be much less. It is quite possible that in some regions of the cavity the intensification pressure may be only 10 to 15 MPa.
On the chart above, on the right of the screen, the blue line is the metal pressure at the plunger as measured in the hydraulic line. The pink line is the pressure inside the cavity, near the gate. As can be seen, it is much reduced. The yellow line is in the cavity away from the gate. It is not hard to see how low the pressure is here, and how quickly it drops away.