How to avoid shrinkage, looseness, and difficult removal of gate residue in LPDC gate design and replenishment channels?
The sprue is the core channel for low-pressure casting aluminum liquid to enter the mold cavity and also undertake shrinkage filling. Many engineers only focus on smooth filling and ignore the solidification sequence of the sprue; The gate solidifies in advance, and even with high pressure, it cannot be replenished, resulting in continuous looseness in the thick walled area.
1、 Quantitative standards for gate section, thickness, transition, and position
A356 conventional bottom gate thickness: 0.8-1.2 times the casting wall thickness; Take 1.0-1.2 times for thick walled hot joints and 0.8 times for thin-walled parts to ensure that the sprue solidifies later than the casting body.
Gate width: matched according to the filling flow rate, the cross-sectional area of a single gate is generally 15% -25% of the total cross-sectional area of the mold cavity; The cross-section is too small, the filling resistance is high, and the contraction channel is closed prematurely; The cross-section is too large, the pouring material is thick, and the cutting and polishing costs are high.
Transition fillet R3-R6 between gate and casting body, sharp corner transition is prohibited; The sharp corners cool quickly and easily form a cold gap, while cutting the sprue can easily lead to breakage and damage to the casting body.
Gate length control 8-15mm; excessive heat storage difference, premature solidification; Too short, aluminum liquid flushes the mold cavity, causing erosion and sticking of aluminum.
Multi point gate layout, balanced flow rate of each gate, to avoid individual gates solidifying first and local isolated hot spots.
Xinfeng Machinery conducts DFM filling and solidification simulation to predict the solidification timing of the gate and prioritize making the gate the final solidification area.
2、 Gate cooling, pressure holding matching, and post-treatment plan
The cooling water channel in the gate area is separately controlled, and the gate cannot be forcefully cooled; Strong cooling will directly cause the sprue to solidify first, the shrinkage channel to be cut off, and the hot spot to become loose.
The holding pressure and holding time must match the solidification window of the sprue: before the sprue completely solidifies, the pressure must be effectively transmitted to the hot spot of the casting; Continuing to maintain pressure after the gate solidifies will not yield any benefits, but will only increase the stress on the mold.
Machining removal of sprue scheme: Reserve clamping platform and process breakpoint, with breakpoint thickness controlled at 2-3mm, for easy sawing and punching, reducing grinding workload.
The appearance of the sprue should avoid visible surfaces and be prioritized for placement on flanges and non appearance machined reference surfaces.
3、 Differences in Gate Solutions for Overseas Customers
Southeast Asian customers generally have larger sprues, relying on long-term pressure maintenance to compensate for insufficient shrinkage. In the later stage, manual polishing of sprue marks is required, and the appearance requirements are relaxed.
The size and solidification timing of the sprue for North American automotive pressure parts are included in the simulation report. The residual height of the sprue has clear tolerances, and it is not allowed to damage the body by grinding. The punching and cutting fixtures must be developed synchronously.
European customers tend to prefer narrow and long slow cooling gates, pursuing stable sequential solidification and relying on gate shrinkage instead of simply relying on high-pressure holding to reduce mold fatigue.
Large scale thick walled castings in the Middle East adopt large section annular gates, with dispersed filling flow rates and extensive shrinkage to avoid isolated hot spots.
4、 Gate Failure Defect Chain
The thickness of the sprue is too small and it is strongly cooled → the sprue solidifies first → the shrinkage channel is closed → the hot spot shrinkage hole is loose;
Transition at the sharp corner of the gate → rapid cooling of the aluminum liquid at the front edge → cold isolation at the root of the gate;
The gate section is too large → the gate material is thick, the cutting and polishing time is high, and it is easy to cause edge breakage and damage;
The gate is arranged on the exterior surface, and the polishing marks cannot be eliminated, resulting in poor appearance.
5、 Long tail traffic layout ideas
Low pressure casting gate, shrink fit gate, and gate solidification timing, aimed at process, simulation, and mold engineers.
keywords LPDC gate design feeding channel、low pressure casting gate solidification sequence；
Question class: Gate Thickness Ratio for A356 Low Pressure Casting;
Comparison category: Single gate vs Multi gate for LPDC aluminum casting.
Suitable for filling and shrinking DFM themed pages.
6、 Common misconceptions in the industry
Misconception 1: The larger the gate, the better the shrinkage. If the gate is too large, the filling flow rate will be out of control, and the cost of gate removal will skyrocket.
Misconception 2: The gate position can be placed arbitrarily, and the gate cannot be placed far away from the hot spot, forming an isolated hot spot.
Misconception 3: Strengthen cooling in the sprue area to accelerate production pace, and directly cut off the shrinkage channel due to strong sprue cooling.
FAQ
Q: What is the recommended ratio of gate thickness to casting wall thickness?
A: The wall thickness of the casting is 0.8-1.2 times.
Q: What is the standard length of the sprue?
A：8–15mm。
Q: Gate transition fillet?
A：R3–R6， Avoid sharp corners.
Q: Why can't the sprue be forcefully cooled?
A: Prevent premature solidification of the gate and interruption of shrinkage.
Q: What are the core requirements for multi-point gating?
A: The flow rate of each gate is balanced, and the solidification timing is consistent.
Q: North American pressure parts gate control?
A: Simulate and verify the solidification timing, and control the residual tolerance of the gate.
Q: What is the thickness of the sprue breakpoint?
A：2–3mm， Convenient for punching and sawing.
Q: What are the consequences of premature solidification of the sprue?
A: The holding pressure cannot be transmitted to the hot spot, resulting in shrinkage porosity.
