How to balance sealing, exhaust, and mold repair difficulty in LPDC mold parting surface selection?
The parting surface is the boundary between the moving and fixed molds, which not only needs to prevent the aluminum liquid from running and flying, but also reserves exhaust channels. It is the interface with the most trade-offs in mold design.
1、 Types of parting surfaces, sealing capabilities, and applicable castings
Flat parting surface processing is the simplest, with stable fitting and reliable sealing. It is the preferred choice for wheel hubs and circular rotating parts, and the processing cost is about 30% lower than that of parting surfaces; The disadvantage is that the complex shell cannot place the product in the optimal filling position.
The stepped parting surface is suitable for high and low drop shells, following the contour steps of the product. However, stress concentration occurs at the corner of the step, and repeated thermal shock can easily cause edge collapse. The corner R must be ≥ 1.5mm.
The curved surface follows the shape of the product, and the exhaust layout is closer to the gas accumulation position. Thin walled new energy shells are mostly used; The grinding workload is large, the mold closing and debugging cycle is prolonged, and the cost increases by about 40%.
Splicing type parting surface, disassembling complex curved surfaces into independent inlay blocks. If a single block is damaged, it can be replaced separately without the need for a complete repair template; However, there is a risk of aluminum leakage in the gaps between the inlays, and the gap between the inlays must be strictly controlled to be ≤ 0.015mm.
During the DFM evaluation of Xinfeng Machinery, priority is given to simplifying the parting surface. Under the premise of customer product tolerance, priority is given to flat parting to reduce the difficulty of mass production maintenance.
2、 Principles for dividing the width of the sealing tape on the parting surface and the exhaust zone
The width of the sealed pressure bearing strip is usually taken as 8-12mm. This area requires high hardness, grinding and bonding, to bear the locking pressure and prevent the aluminum liquid from escaping; Exhaust ducts are only arranged outside the sealing tape.
The sealing tape cannot continuously cover the entire parting surface, and an exhaust buffer zone needs to be reserved. The exhaust groove cannot penetrate the sealing tape, otherwise it will be squeezed and deformed during mold locking, resulting in continuous flying edges.
At the corner position of the casting contour, the sealing strip should have rounded corners for transition. The sharp corner sealing strip is prone to collapse under repeated mold locking impacts, and indentation occurs after 2000-3000 mold cycles.
The escape groove for the parting surface is arranged on the outside of the sealing belt to receive a small amount of spilled aluminum shavings, avoiding them from getting stuck on the sealing surface and causing mold damage.
3、 Differences in classification preferences among overseas customers
Southeast Asian customers prioritize flat parting, and it is easy to find maintenance fitters locally. Grinding and mold repair are simple, and 76% of inquiries reject the premium brought by complex conformal parting.
The contour of the parting surface of North American car shells must be clearly marked on the drawings, and the width and position of the sealing tape must be written in the PFMEA. It is not allowed to arbitrarily change the parting boundary on site later.
European customers prefer the inlay and parting structure, as the local damage to the cavity in the later stage requires separate replacement of the inlay block, without the need to return the entire mold to the factory, which shortens downtime.
Middle East thick walled engineering machinery castings, with high aluminum liquid pressure, widen the sealing band to 12-15mm, prioritize anti flying edges, and require flexibility in exhaust layout.
4、 Mass production failure mode of parting surface
Aluminum shavings are trapped on the parting surface, and after clamping and squeezing, pits are pressed out on the sealing tape. Subsequently, continuous aluminum leakage and flash will occur, and grinding and repair will consume the thickness of the sealing tape.
The hardness of the parting surface is insufficient, and plastic collapse occurs due to long-term mold locking impact. The collapsed position fails to fit properly, and the flying edge becomes larger and larger. The number of repairs is limited.
The grinding of the conformal surface is not in place, and some areas are in contact with the virtual position. The aluminum liquid preferentially escapes from the virtual position, forming intermittent flying edges, which takes a long time to debug.
5、 Long tail traffic layout ideas
The parting surface, sealing tape, and flash belong to DFM and defect search, targeting mold designers and process engineers.
keywords LPDC mold parting line design、low pressure casting mold flashing at parting surface；
Problem class: Sealing band width for LPDC partitioning surface;
Comparison class: flat parting line vs contoured parting line for casting die.
Suitable for DFM guide blog posts, undertaking pre mold solution consultation traffic.
6、 Common misconceptions in the industry
Misconception 1: The wider the sealing tape on the parting surface, the better. If the sealing tape is too wide, it will occupy the exhaust space and prevent gas from being discharged, resulting in an increase in porosity defects.
Misconception 2: The more closely the parting surface is fitted, the less exhaust is needed. There is no exhaust channel for complete sealing, the gas in the cavity is locked, and there are frequent air holes in thick walled areas.
Misconception 3: The gap between the inlay and parting is very small and will not allow aluminum to escape. The thermal expansion of the inlay block is inconsistent under cold and hot cycles, and the gap changes dynamically, which still poses a risk of aluminum leakage.
FAQ
Q: What is the standard width of LPDC parting surface sealing tape?
A：8–12mm， Thick walled high-pressure castings can be relaxed to 12-15mm.
Q: What are the advantages of flat parting surfaces?
A: Easy to process, convenient to grind, low cost of mold repair, commonly used for wheel hubs.
Q: What are the disadvantages of conformal surface classification?
A: The processing and grinding workload is large, and the mold closing and debugging cycle is longer.
Q: What are the requirements for controlling the gaps in inlay and parting?
A：≤0.015mm， Prevent aluminum from being blown down by alternating cold and heat.
Q: What is the recommended minimum turning angle R for the parting surface?
A：≥1.5mm， Avoid sharp corners collapsing.
Q: How to repair the compression injury on the parting surface?
A: After local welding, the sealing tape was re ground, and after multiple welding, the sealing tape failed.
Q: What is the function of the escape chute?
A: Containing spilled aluminum shavings to prevent them from damaging the sealing and bonding surfaces.
Q: What are the key control points for parting surfaces for North American customers?
A: The position of the parting line and the sealing tape should be written into the PFMEA and cannot be changed arbitrarily.
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