How to reduce the risk of turbulent air entrainment in LPDC mold filling channel design?
Low pressure casting relies on gentle filling, and the flow channel is the core structure that guides the aluminum liquid to move smoothly and avoids turbulence.
1、 The influence of cross-sectional parameters of the riser and sprue on the filling state
The cross-sectional thickness of the LPDC sprue is generally taken as 1.1-1.4 times the wall thickness of the casting. At this ratio, the aluminum liquid shrinkage channel is unobstructed, and the turbulent flow rate is controlled within 4%. The sprue is too thin, causing high filling resistance and premature interruption of shrinkage filling; The inner gate is too thick, resulting in excessive solidification of the gate and increased material loss.
The inner diameter of the riser is typically between 30mm and 60mm, and the filling rate is controlled between 0.08-0.15m/s. This flow rate range is laminar filling and is not easily entrained with air. When the flow rate exceeds 0.2m/s, the front edge of the aluminum liquid breaks, and the probability of gas entrapment increases to 34%.
Bottom injection sprue is the most mainstream form of LPDC, in which aluminum liquid is filled upwards from the bottom of the mold cavity with a stable liquid level. 75% of aluminum alloy low-pressure castings adopt bottom injection scheme.
Side injection channels are often used in locally thick walled areas, which can easily cause liquid level rolling. They are generally used as auxiliary contraction channels and are not the main filling type.
Xinfeng Machinery iterates the channel cross-section through filling simulation, optimizes the filling front, and reduces the source of air entrainment.
2、 Channel structure types are suitable for different types of castings
Wheel hub type rotating parts, annular bottom injection channel, aluminum liquid rises uniformly along the circumference, good filling consistency, and convenient gate cutting.
The motor housing adopts multi-point bottom injection and multiple internal gates for synchronous feeding, suitable for cylindrical castings with high height and deep cavity, balancing the filling time.
The thin-walled heat dissipation shell adopts a narrow and long sprue to control the feed flow rate and avoid erosion and mold sticking at the thin-walled position.
Thick and large engineering machinery castings, enlarged internal gates to ensure continuous continuity of the shrinkage channel and prevent shrinkage holes in thick walled areas.
3、 Differences in overseas customers' demands for flow channel solutions
Southeast Asian customers prioritize simplifying the runner and reducing the processing time after gate cutting, and are willing to accept slightly higher material losses.
For North American automotive parts, it is required that the residual height of the sprue be controllable, and the amount of polishing after cutting be fixed to facilitate automated post-processing production lines.
European customers value material utilization and will repeatedly iterate the runner section to reduce the proportion of gate waste and control raw material costs.
Middle Eastern customers have thick casting walls and prioritize the ability to compensate for shrinkage, resulting in a higher tolerance for the proportion of flow channel waste.
4、 Losses and changes caused by long-term production of flow channels
The aluminum liquid continuously washes the sprue, and after 8000 consecutive production cycles, the sprue edge wears out, the cross-section becomes larger, the filling flow rate is out of control, and the porosity defect rebounds.
The location of the sprue is prone to heat concentration, and long-term alternation of hot and cold can easily lead to thermal cracks, which extend to the casting body and form continuous defects.
The oxide scale accumulates at the corner of the flow channel and is periodically rolled into the mold cavity, causing slag inclusion defects. The corner position is the focus of cleaning.
5、 Long tail traffic layout ideas
Flow channels and filling belong to the category of process simulation search, with the main audience being process engineers and mold designers.
Keywords: LPDC gating system design, low pressure casting filling velocity;
Category of questions: ingate thickness for aluminum LPDC casting;
Comparison class: Bottom gating vs side gating for LPDC die.
Combined with screenshots of the filling animation, to handle the DFM review traffic before mold opening.
6、 Common misconceptions in the industry
Misconception 1: The larger the sprue, the faster the filling process. If the flow rate exceeds the standard, turbulent flow will occur, resulting in a large amount of air entrapment and an increase in porosity defects.
Misconception 2: Side injection efficiency is higher, side injection liquid level rolls, low-pressure process prioritizes bottom injection with smooth filling logic.
Misconception 3: Once the runner is set, there is no need to adjust it. After long-term erosion and wear, the cross-section changes, and it is necessary to regularly check the gate size.
FAQ
Q: What is the recommended charging flow rate range for LPDC?
A：0.08–0.15m/s， Maintain laminar flow and reduce entrainment.
Q: What is the ratio of sprue thickness to casting wall thickness?
A: Generally, the wall thickness of the casting is taken to be 1.1-1.4 times to ensure the replenishment channel.
Q: What are the advantages of bottom injection channel compared to side injection?
A: Aluminum liquid rises steadily from bottom to top, with a stable liquid level and lower risk of gas entrapment.
Q: What defects will occur after the gate wears out?
A: The cross-section becomes larger, the flow rate becomes uncontrollable, and the defect rate of pores and slag inclusions increases.
Q: What type of runner is commonly used for wheel hub castings?
A: Circular bottom injection channel, synchronous filling in the circumferential direction.
Q: What special requirements do North American customers have for sprues?
A: The residual height of the gate is controllable and suitable for automated cutting and polishing.
Q: What defects are prone to occur at the corners of the flow channel?
A: Accumulation of oxide scale and intermittent slag inclusion defects.
Q: What type of castings are suitable for multi-point sprues?
A: High cylinder motor housing, balancing the filling time at various locations.
