Controlled Pressure Casting for Submerged Member Force Management
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Solution Overview
Problem
Conventional high pressure die casting faces challenges in managing forces on submerged members due to pressure imbalances and inefficiencies in air removal and heat transfer, especially as the die cavity fills and solidifies, requiring high hydraulic pressures and additional mechanisms to prevent movement and ensure filling.
Innovation Solution
The method involves applying a main pressure to force molten metal into mold cavities and using auxiliary pressures to densify the casting, with sensors monitoring cavity filling to activate auxiliary pressure sources, reducing the need for high main pressure and enabling efficient filling and solidification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high pressure is applied to the hydraulic shot cylinder to fill the die cavity, then the die cavity fills with molten aluminium, but the forces on submerged members become very high and difficult to manage
Solution Approach 1:
The pressure application is segmented into two distinct phases: initial cavity filling pressure and subsequent densification pressure. The system separates the function of filling (performed at lower pressure) from the function of densification (performed at higher pressure after filling), thereby avoiding the need to apply high pressure during the vulnerable filling stage when submerged members are exposed to unbalanced forces
Solution Approach 2:
The die cavity is filled with molten aluminium first at lower pressure before the densification phase begins. This preliminary filling action ensures that the cavity is completely filled and submerged members are positioned correctly before any high pressure is applied, preventing force imbalances during the critical filling stage
2Reliability
If pressure is intensified after filling to reduce entrapped air and increase heat transfer, then air removal and heat transfer improve, but the pressure fails to reach material within cavities after in-gates freeze-off
Solution Approach 1:
The densification pressure is applied preliminarily, immediately after cavity filling but before the in-gates freeze-off. This timing ensures that pressure can be effectively transmitted to the molten metal within the cavities to expel entrapped air and establish thermal contact, avoiding the problem of pressure failure that occurs when gates solidify first
Solution Approach 2:
The pressure application is maintained continuously during the critical period from cavity filling through densification, ensuring uninterrupted pressure transmission to the molten metal. This continuous pressure action prevents air entrapment and maintains thermal contact throughout the solidification process, rather than interrupting pressure after filling
3Reliability
If high hydraulic pressure is used to ensure complete filling, then filling reliability improves, but machine tonnage and hydraulic cylinder size increase
Solution Approach 1:
The pressure application is segmented into two distinct phases: initial cavity filling pressure and subsequent densification pressure. The system separates the function of filling (performed at lower pressure) from the function of densification (performed at higher pressure after filling), thereby avoiding the need to apply high pressure during the vulnerable filling stage
Solution Approach 2:
The densification function is extracted from the main filling operation and performed as a separate subsequent step. By removing the densification requirement from the initial filling phase, the system can use lower pressure during filling, reducing machine tonnage requirements while still achieving complete filling and proper densification
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces the required machine tonnage, allows for smaller hydraulic cylinders, and maintains pressure effectively throughout the solidification process, enhancing casting quality and efficiency by minimizing pressure on the molten metal and reducing machine size requirements.
Implementation Method 1
applying a first auxiliary pressure to the molten metal in the first mold cavity... to densify the casting formed in the first mold cavity
Implementation Method 2
the pressure applied to the hydraulic shot cylinder is typically increased... to reduce the volume of entrapped air and increase the rate of heat transfer
Data Source
AI summary
A method of forming metal castings includes positioning a first end of a structural member in a first mold cavity and a second end of the structural member in a second mold cavity. The first and second mold cavities are fluidly coupled to a reservoir of molten metal. A main pressure is applied to the molten metal in the reservoir to force the molten metal into the first and second mold cavities. First and second auxiliary pressures are applied to the first and second mold cavities to densify the castings formed in the first and second mold cavities. Another method for casting includes maintaining a main pressure at or less than an initial, mold-filling pressure after the first and second mold cavities have been filled. Additionally, a method for detecting whether a first mold cavity is sufficiently filled with molten metal includes monitoring a moveable element.