How to reduce casting deformation in LPDC mold ejection system layout?

How to reduce casting deformation in LPDC mold ejection system layout?
The stress during the cooling shrinkage process of low-pressure casting is complex, and the layout of the ejection system directly determines the dimensional stability of the finished product.

1、 Quantitative relationship between the density of top pole arrangement and casting deformation
It is recommended to control the center distance of the top pole at 70-110mm, and evenly distribute the top force. Under this scheme, the defect rate of casting plane warping can be controlled within 3.5%. When the spacing exceeds 130mm, local stress concentration occurs, and the probability of thin plate shell warping increases to 29%. The flange and thick walled hot joint positions have a large cooling shrinkage and stronger clamping force. Additional top rods need to be increased by 30% to counteract the clamping force caused by shrinkage. Thin walled heat dissipation shell, with a wall thickness of less than 3mm, the diameter of the top rod should not be too large. Priority should be given to using small top rods with diameters ranging from 6 to 8 to avoid top penetration and top concavity. The safe distance between the top pole and the edge of the product is 5-8mm. If it is too close to the edge, it is prone to edge breakage, and if it is too far from the center, it will experience uneven stress. Xinfeng Machinery synchronously conducts force analysis on the top out during the simulation phase to avoid single point stress concentration.

2、 Applicable working conditions for different roof structures
The single planar top rod structure has the lowest cost and is suitable for wheel hubs and simple disk components. It is easy to maintain and 80% of standardized LPDC molds adopt this solution. The overall top plate ejection is suitable for large-area thin-walled shells, with uniform stress and low deformation risk, but the increase in mold thickness leads to a 28% increase in processing costs. The inclined top structure is used for small internal reverse buckles, with limited travel and suitable for shallow reverse buckles. Long term production of inclined tops causes rapid wear and requires regular grinding. The composite structure of oil cylinder core pulling and ejection is used for complex multi buckle shells, with high difficulty in synchronous action control, and is mostly used for high-end new energy orders.

3、 Differences in preference for top out structures among overseas customers
Southeast Asian customers prefer simple top rod solutions with universal accessories and convenient local maintenance. 79% of inquiries reject the markup caused by complex top plate structures. North American automotive shell customers require that the ejector mark be controlled on the non assembly surface, and the position of the ejector pin must be locked during the DFM stage audit. European customers value the synchronization of the ejection action and require hydraulic circuits with synchronous valves to reduce the distortion and deformation caused by asynchronous ejection. Middle Eastern construction machinery castings have thick walls and strong clamping force, and priority is given to increasing the height of the top rod. They have a high tolerance for the appearance of top marks.

4、 The attenuation law of long-term operation of the ejection system
The gap between the top rod and the guide sleeve is worn, and after continuous production of 15000 molds, the gap becomes larger, the top rod is skewed, and there is an increase in indentation and concave defects. The ejection speed is too fast, the casting has not been fully cooled, the rigidity is insufficient, and it is easily deformed by ejection. It is recommended to control the ejection speed at 20-40mm/s. After the wear of the nitride layer on the surface of the top rod, the aluminum material is prone to stick to the rod, and each time it is pushed out, it pulls and pulls the surface of the casting, forming periodic surface defects.

5、 Layout ideas for long tail keywords
Top out and deformation belong to the pain points of mass production stability, suitable for process engineers and foundry workshop supervisors. Keywords: LPDC mold ejector pin layout, low pressure casting part warp control; Question class: How to reduce casting deformation in LPDC; Comparison category: ejector plate vs ejector pins for aluminum housing. Paired with a force diagram, it can handle search traffic for troubleshooting.

6、 Common misconceptions in the industry
Misconception 1: The more top rods there are, the less likely it is to deform. Having too many top rods increases the difficulty of sealing the parting surface, which can lead to burrs and increase processing costs. Misconception 2: The faster the ejection speed, the higher the production efficiency. When the casting temperature is too high, high-speed ejection will result in insufficient rigidity and a sharp increase in deformation risk. Misconception 3: The top pole can be arranged arbitrarily, but there is a huge difference in stress between the hot section and the thin-walled area, which requires targeted and differentiated arrangement.

FAQ
Q: What is the recommended distance between the conventional centers of LPDC top poles? A：70–110mm， The hot spot position should be appropriately encrypted to disperse the top force. Q: What is the appropriate diameter for the thin-walled shell top rod? A: Priority should be given to small top rods with a diameter of 6 to 8 within a wall thickness of 3mm to prevent piercing. Q: What is the recommended ejection speed range? A：20–40mm/s， Use lower speed for castings with high temperature. Q: What are the advantages of top plate protrusion compared to loose top rods? A: Uniform force distribution, lower risk of warping of thin plate shells, and higher mold cost. Q: What defects can be caused by the wear of the top rod? A: The top rod is skewed and stuck with aluminum, resulting in indentation and periodic surface strain. Q: What are the requirements of North American customers for the position of the top pole? A: Top marks should be placed in non assembly and non visible areas as much as possible. Q: What kind of inverted buckle is suitable for sloping tops? A: Small stroke, shallow inverted buckle structure, deep inverted buckle priority slider core pulling. Q: What is the safe distance between the top pole and the edge of the product? A：5–8mm， Balancing stress and preventing edge damage of castings.