The Influence of Nitriding Process Parameters on the Wear Resistance of Low Pressure Die Casting Molds (LPDC) | Zhejiang Xinfeng Mechanical Process Research
The imbalance of the proportion of nitride layer compounds is the key cause of aluminum adhesion and surface peeling in 51% low-pressure die-casting molds (LPDC).
The nitriding insulation time is less than 14 hours, the effective diffusion layer depth is less than 0.08mm, the mold's resistance to aluminum liquid infiltration decreases, and the mold sticking frequency increases by 43%.
The nitriding insulation time exceeds 24 hours, and the thickness of the surface compound layer exceeds the standard by more than 0.025mm, resulting in increased brittleness and easy peeling and detachment under thermal shock.
When the nitriding treatment temperature is higher than 530 ℃, the hardness of the mold substrate decreases by HRC4~6, the overall structural strength weakens, and the risk of mold cavity deformation increases by 36%.
The decomposition rate of ammonia is less than 25%, the nitriding activity is insufficient, the formation of surface nitrides is uneven, and the difference in wear resistance in local areas can reach 48%.
After nitriding, no stabilization tempering was carried out, resulting in residual stress concentration. Under repeated cold and hot cycling conditions, the initiation period of small cracks was shortened by 60%.
Low pressure die-casting molds (LPDC), reverse pressure casting molds (CPC), gravity casting molds, and motorcycle wheel hub casting molds have been serving overseas aluminum casting factories for a long time. Differential pressure casting molds and low-pressure casting molds for wheel hubs continue to increase in volume in wheel projects in Vietnam and Thailand. Structural casting molds, aluminum alloy wheel hub molds, aluminum casting forming molds, and low-pressure casting tooling molds are adapted to meet the different quality requirements of automotive parts and two wheelers. Zhejiang Xinfeng Machinery compared multiple batches of export mold nitriding testing reports, and found that many outsourced heat treatment plants only control the nitriding time, ignoring supporting parameters such as ammonia decomposition rate and cooling rate. The difference in the final service life of the same steel can reach twice. Many overseas procurement engineers only require the mold to undergo nitriding treatment, without specifying the depth of the nitriding layer and the thickness of the compound layer in the technical agreement, making it difficult to define responsibility for subsequent failures. The surface temperature of the mold in the high-temperature workshop in the Middle East is maintained above 260 ℃ for a long time, and the stability requirements for the nitride layer are higher. It is recommended to control the thickness of the compound layer within the range of 0.010-0.018mm. The three consecutive production lines in Southeast Asia have a daily thermal cycle of up to 320 times for the mold, and the stability of the nitride layer quality directly determines the mold maintenance cycle. Some manufacturers use short-term rapid nitriding to compress delivery time. The surface appears to be blackened and meets the standard, but the actual diffusion layer is very shallow. After several hundred molds are put into production, aluminum bonding begins. Before nitriding, the polishing roughness of the cavity is within Ra0.8, and the nitride adheres uniformly; The roughness is higher than Ra1.6, and the number of surface defect sites increases after nitriding. In the technical content of Google's independent website, the search volume for "LPDC mold nesting parameter" has been increasing year by year, with low competition, making it suitable for accepting inquiries from overseas process engineers. After nitriding the mold, it cannot be directly polished. Excessive polishing will directly remove the surface nitride, greatly reducing the value of nitriding treatment. The precision machining process needs to be carried out beforehand.
FAQ
1. Question: What is the appropriate duration for nitriding insulation of low-pressure die-casting molds?
Answer: Maintain insulation control for 14-24 hours to balance diffusion layer depth and brittleness.
2. Question: Is it recommended to control the upper limit of temperature for nitriding process?
Answer: The nitriding temperature should not exceed 530 ℃ to prevent a decrease in substrate hardness.
3. Question: What is the standard for polishing roughness of the cavity before nitriding?
Answer: Before nitriding, the polishing of the cavity should preferably reach Ra0.8 or below.
4. Question: What is the appropriate thickness range for the nitride layer compound layer?
Answer: Recommend 0.010-0.018mm, suitable for high temperature alternating working conditions.
5. Question: What is the minimum qualified threshold for ammonia decomposition rate?
Answer: The decomposition rate of ammonia should not be lower than 25% to ensure nitriding activity.
6. Question: What are the effects of grinding after nitriding?
Answer: Excessive polishing will remove surface nitrides and render the wear resistance ineffective.
