How to set the LPDC charging pressure curve and match the boosting rate and holding time with the casting?
Low pressure casting relies on the pressure inside the crucible to push the aluminum liquid up, and the pressure curve is the core of the process; Excessive pressure rise leads to air entrainment, while excessive pressure rise leads to cooling and isolation at the front edge; Insufficient pressure maintenance and insufficient shrinkage, excessive pressure maintenance and stuck mold on the gate.
1、 Quantitative parameters for pressure segmentation
Rising section: The pressure rise rate is 0.8-1.5kPa/s, and the aluminum liquid rises smoothly into the rising pipe to avoid rolling and rolling slag on the liquid surface; Raising the liquid pressure only requires lifting the aluminum liquid to the gate, without rushing into the mold cavity.
Filling section: pressure rise rate of 0.3-0.8kPa/s, with a lower limit for thin-walled shells and an upper limit for thick walled components; At this stage, the aluminum liquid slowly fills the mold cavity to maintain laminar flow and reduce turbulent air entrainment.
Crust section: After filling is completed, stabilize the pressure for 3-8s to allow the surface of the casting to form a solidified shell first, preventing bulging and deformation during the pressure holding stage.
Pressure holding section: The pressure holding is 15-30kPa, and the holding time is determined by the solidification time of the hot spot, usually 20-60s; the holding must be continued until the gate is completely solidified, and the pressure relief and contraction are interrupted in advance.
Pressure relief section: Slowly release pressure after the gate solidifies, with a pressure relief rate of 2-4 kPa/s, to prevent negative pressure from sucking air into the alumina liquid inside the crucible.
During the trial molding stage of Xinfeng Machinery, the standard pressure curve is output and synchronized with the equipment engineer to provide the curing process parameters.
2、 Differences in curves of different casting types
Thin walled new energy shell: slow down the filling rate by 0.3-0.5kPa/s, prolong the filling time, and avoid front cooling and cold isolation; The holding time is moderate.
Wheel hub rotating parts: Filling rate 0.5-0.8kPa/s, symmetrical filling stability, holding pressure for 25-40s.
Thick walled construction machinery castings: The holding pressure is 22-30kPa higher, and the holding time is extended by 40-60s to ensure thick walled shrinkage.
Small thin-walled components: The overall curve is shortened, the holding time is shortened, and excessive adhesion of the gate is avoided.
3、 Differences in pressure curve control for overseas customers
Most factories in Southeast Asia manually adjust the pressure, relying on the experience of operators. The curve is not fixed, and the parameters fluctuate greatly between batches, resulting in significant fluctuations in defects.
Tier 1 in North America, the rate, pressure, and time of each segment of the pressure curve are all written into the control plan, and the curve is automatically stored. Abnormal curves are automatically locked and traceable.
European customers adopt closed-loop pressure control, with pressure curve and mold temperature linked, and automatic adjustment of pressure rise rate for temperature changes, resulting in higher process stability.
Middle East thick walled castings, with redundant amplification of parameters during the pressure holding stage, to prevent insufficient shrinkage caused by furnace temperature fluctuations and aluminum liquid temperature drops.
4、 Defects corresponding to abnormal curve parameters
Rapid filling and pressure rise → turbulent air entrainment, dispersed porosity and slag inclusion in castings;
Slow pressure rise during filling → Cooling at the front edge of the aluminum liquid, resulting in thin-walled cold insulation, flow patterns, and insufficient pouring;
Insufficient holding time → Pressure relief occurs before the gate solidifies, resulting in loose thick walled shrinkage cavities;
The holding time is too long → the gate solidifies and firmly sticks to the gate sleeve, causing the gate to tear and the casting to deform when ejected;
Rapid pressure relief → negative pressure suction of crucible, oxidation of aluminum liquid, and increased slag inclusion.
5、 Long tail traffic layout ideas
Pressure curve, filling rate, and holding time belong to the special topic of process curve, aimed at process engineers and equipment debugging personnel.
keywords LPDC pressure curve setting、low pressure casting filling rate and dwell time；
Problem class: Pressure rise rate for thin wall LPDC casting;
Comparative category: manual pressure control vs automatic curve control LPDC.
Suitable for process debugging and automation production line upgrade pages.
6、 Common misconceptions in the industry
Misconception 1: The higher the pressure, the faster the filling process, and the better. High speed pressure directly disrupts laminar flow, resulting in a large amount of trapped gas and slag.
Misconception 2: The longer the pressure is maintained, the denser the casting becomes. If the pressure exceeds the solidification time of the gate, it will only increase the risk of gate sticking and tearing.
Misconception 3: A set of curves is applicable to all working conditions, and the curves need to be adjusted synchronously due to changes in aluminum liquid temperature and mold temperature.
FAQ
Q: What is the recommended boost rate for the charging section?
A：0.3–0.8kPa/s， Thin walled shell adopts low speed.
Q: What is the standard range for maintaining pressure?
A：15–30kPa。
Q: What are the cut-off conditions for maintaining the core pressure?
A: The gate can only be depressurized after it has completely solidified.
Q: What is the function of the liquid lifting section?
A: Lift the aluminum liquid smoothly to the gate position without rushing into the mold cavity.
Q: Is it harmful to release pressure too quickly?
A: Negative pressure suction in the crucible causes oxidation of the aluminum liquid, leading to the rise of slag inclusions.
Q: North American pressure curve control?
A: Segmented parameter solidification, curve storage traceability, abnormal machine locking.
Q: How to adjust the pressure holding of thick walled castings?
A: Increase the holding pressure and extend the holding time.
Q: What is the function of the crust segment?
A: The surface layer should solidify first to prevent deformation caused by pressure holding and bulging.
