How to control the process parameters of LPDC mold nitriding treatment?

How to control the process parameters of LPDC mold nitriding treatment?

Nitriding is the mainstream surface strengthening process for improving the wear resistance and aluminum adhesion resistance of LPDC mold cavities.

1、 Quantitative relationship between nitride layer thickness, hardness, and service life

The effective hardening layer of gas nitriding is commonly in the range of 0.08-0.12mm. In this range, the anti stick aluminum and wear resistance of the mold are improved by about 30%, while the toughness is sufficient and not easy to peel off. The hardened layer is less than 0.06mm, and the wear resistance gain is limited. After 2000 production cycles, the surface effect rapidly deteriorates.
When the hardened layer exceeds 0.15mm, the brittleness of the nitride layer increases, and under thermal shock, it peels off and debris enters the mold cavity, forming slag inclusion defects in the casting. The failure probability increases to 27%.
After nitriding, the surface hardness is HV900-1100, and the substrate maintains HRC44-48. However, if the substrate hardness is insufficient, the nitride layer loses support and is more prone to cracking.
Compared to gas nitriding, ion nitriding shortens the nitriding time by 40%, improves the uniformity of the infiltration layer, and stabilizes the nitriding effect at blind holes and deep grooves, with a premium of about 18%.
Xinfeng Machinery matches the corresponding nitriding process plan based on the customer's planned annual output.

2、 Pre treatment requirements for molds before and after nitriding

The recommended surface roughness for precision machining before nitriding is Ra ≤ 0.8 μ m. Surface knife marks and scratches will become stress concentration points for nitriding, and cracks will preferentially appear.
Before nitriding, stress relief tempering must be carried out. If the residual stress of precision machining is not released, the stress will be released during the nitriding heating process, and the cavity size will shift by 0.02-0.04mm.
The area with sealing surface and matching positioning surface needs to be shielded and protected. Nitriding will change the surface size and affect the bonding accuracy of the parting surface.

3、 Customer preferences for nitriding processes in different markets

Most mass production factories in Southeast Asia use conventional gas nitriding, which has lower costs and mature local heat treatment facilities. About 74% of inquiries do not specify ion nitriding.
North American automotive supporting customers require a nitriding process report, infiltration layer testing data, and a hardened layer thickness tolerance within ± 0.02mm.
Priority is given to ion nitriding for high-end European orders, with better uniformity of nitriding for complex deep cavity and fine rib molds, reducing early aluminum adhesion defects.
Middle Eastern construction machinery molds have large fluctuations in production pace and place greater emphasis on the stability of the nitride layer to avoid frequent polishing and repair of the mold cavity.

4、 Taboos for the use of nitriding molds

The nitride layer is not resistant to strong mechanical polishing. Hard sandpaper and grinding wheel polishing will directly remove the hardened layer, resulting in zero wear resistance. Repair can only be done by re nitriding.
If the local temperature of the mold exceeds 620 ℃ for a long time, the nitride layer will undergo tempering softening, the hardness will rapidly decrease, and the problem of aluminum adhesion will recur.
Nitriding cannot repair existing hot cracks, and cracks will continue to extend after nitriding. Molds with cracks must be welded and polished before nitriding.

5、 Layout ideas for long tail keywords

Nitriding and surface treatment belong to the category of process matching search, suitable for procurement and heat treatment engineers.
Keywords: LPDC mold nitriding process, nitride layer thickness for low pressure die;
Question class: Gas Nitriding vs Plasma Nitriding for Casting Mold;
Tutorial class: How to Prevent Nitride Layer Peeling.
Paired with metallographic infiltration layer detection sample, undertake process comparison flow rate.

6、 Common misconceptions in the industry

Misconception 1: The thicker the nitride layer, the longer the lifespan. If the infiltration layer is too thick, it will become brittle and peel off under cold and hot impacts, leading to casting defects.
Misconception 2: Nitriding can repair cavity cracks, but it cannot eliminate cracks and instead allows them to further propagate.
Misconception 3: After nitriding, there is no need to control the mold temperature. Continuous high temperature can cause the nitriding layer to soften and fail during tempering.

 FAQ

Q: What is the recommended thickness for the nitride layer of LPDC molds?
A：0.08–0.12mm， Balancing wear resistance and peel resistance.
Q: What are the advantages of ion nitriding compared to gas nitriding?
A: Uniform infiltration layer, better effect of deep cavity fine reinforcement position, and shorter processing cycle.
Q: Why is it necessary to relieve stress before nitriding?
A: To avoid stress release caused by heat treatment and temperature rise, resulting in cavity size deviation.
Q: What is the maximum temperature tolerance of the nitride layer?
A: Long term working conditions should not exceed 620 ℃, otherwise the surface will soften due to tempering.
Q: Why should the mating surface be shielded after nitriding?
A: Nitriding changes the surface size, which can damage the fitting accuracy of the parting and positioning surfaces.
Q: Can the nitride layer be remedied if it is polished off?
A: It needs to be re polished, cleaned, and the entire mold needs to be nitrided again.
Q: What content does the North American customer nitriding report include?
A: Record of infiltration layer thickness, surface hardness, and metallographic examination.
Q: Is nitriding suitable for trial mold production?
A: There are few trial molds, generally no nitriding, and mass production molds are prioritized for nitriding.