LPDC mold aluminum welding repair process specification, how to avoid crack recurrence after welding?
The most commonly used repair method for hot cracks, dents, and pressure damage on the sealing tape in the mold cavity is argon arc welding. However, improper welding repair can lead to repeated crack recurrence, making it increasingly difficult to use.
1、 Quantitative standards for welding material selection and pre weld groove treatment
H13 mold welding repair should prioritize the use of H13 hot work mold steel welding materials of the same material, matched with the thermal expansion coefficient of the base material, and the post weld thermal fatigue performance is closest to the substrate; Using ordinary carbon steel welding materials, the expansion of the welding area and the base material is not consistent, and cracking is inevitable under cold and hot shock.
Before welding and repairing cracks, a groove must be made with a bottom radius of R ≥ 1.5mm. Sharp edged grooves will form stress points, which can quickly cause cracking again after welding; Extend the crack end outward by 2-3mm and create a crack stop hole to prevent the crack from spreading during welding.
Polish the groove clean, remove the nitride layer, oil stains, and residual release agent. If the nitride layer remains in the groove, porosity and brittle structure will be generated during welding, and the brittleness of the weld area will significantly increase.
Preheating temperature is 250-350 ℃, with a lower limit for small parts and an upper limit for large and heavy templates to reduce welding temperature differences and post weld stress.
The Xinfeng Machinery Mold Repair Operation Manual requires mandatory pre inspection of groove, crack hole, and preheating.
2、 Layered welding and post weld heat treatment process
Multi layer and multi pass welding, with each layer welded, knocking slag, and waiting for the temperature to drop to around 200 ℃ before welding the next layer. It is not allowed to weld thick layers at once, as the stress concentration in thick layer welding is severe.
Insulation and slow cooling after welding, direct air cooling and rapid cooling are not allowed; After cooling to room temperature, arrange stress relief tempering at 520-560 ℃ to eliminate welding stress.
If the cavity needs to be nitrided in the future, the welding repair area must be polished flat, and after tempering is completed, it can be nitrided as a whole; The nitride layer will be damaged by the arc, and the welding area cannot retain the original nitride effect.
It is recommended to control the thickness of a single weld overlay within 3mm. If it exceeds the thickness, multiple welds and intermediate stress relief should be carried out to avoid accumulated stress.
3、 Differences in welding repair control requirements for overseas customers
On site welding in Southeast Asian factories is relatively flexible, with many only polishing and welding without tempering, suitable for low requirement and low-cost castings.
For North American automotive parts molds, the welding position, welding material, preheating, and tempering parameters must be recorded for each welding repair, and any changes must be recorded in the mold history. Customers have the right to refuse on-site welding repairs without records.
European customers limit the number of welding repairs. If the same position is welded more than 3 times, it will directly determine that the mold life has expired. It is recommended to open a new mold to avoid the risk of batch failure.
Middle Eastern construction machinery molds have thick and large templates, requiring a large amount of welding and repair work. The customer accepts standardized welding and repair, but requires post weld inspection to confirm that there are no cracks.
4、 Typical manifestations of welding repair failure
After welding and polishing, the surface looks intact. After several hundred molds were put into production, arc-shaped cracks appeared at the edge of the welding area. The root cause is the lack of crack stopping holes, sharp corner grooves, and preheating.
Pores and looseness in the welding area: Poor cleaning of the groove, residual nitride layer, and oil stains.
The aluminum adhesion in the welding area is more severe than that of the base metal: the welding material is incorrect, there is no tempering after welding, the metallographic structure is abnormal, and the hardness is uneven.
5、 Long tail traffic layout ideas
Welding repair, argon arc welding, and mold crack repair belong to the after-sales flow of mold repair, targeting mold repair technicians and procurement.
keywords LPDC mold welding repair specification、H13 die crack welding for low pressure casting；
Problem class: Best welding rod for H13 LPDC mold repair;
Tutorial class: How to stop re cracking after mold welding.
Suitable for the mold maintenance service page, accepting inquiries for stock mold maintenance.
6、 Common misconceptions in the industry
Misconception 1: Welding to cover the crack will fix it, but if the crack tip is not stopped, the welding stress will accumulate, and the crack will continue to extend towards the base material.
Misconception 2: Choose welding materials randomly. The difference in thermal expansion coefficient between carbon steel welding materials and H13 welding materials is significant, and repeated thermal shock will inevitably lead to cracking.
Misconception 3: The faster the welding is completed, the higher the cooling hardness. Rapid cooling will generate huge welding stress, high brittleness in the welding area, and easy cracking.
FAQ
Q: What welding material is preferred for H13 mold welding repair?
A: Specialized welding material for H13 hot work die steel of the same series.
Q: Why do we need to drill a crack stop hole before welding repair?
A: Prevent cracks from continuing to propagate towards the base metal during the welding process.
Q: Recommended preheating temperature for welding repair?
A: 250-350 ℃, upper limit for large items.
Q: What procedures must be carried out after welding?
A: Slow cooling+stress relief tempering to release welding stress.
Q: How many times is it recommended to weld the same position at most?
A: The industry generally controls within 3 times, and European customers have strict control.
Q: What is the minimum requirement for R at the bottom of the groove?
A：≥1.5mm， Eliminate stress spikes.
Q: Do we need to re nitride the nitride cavity after welding repair?
A: The nitride layer in the welding area is damaged and needs to be re nitrided after repair.
Q: What are the key points of welding repair control for North American customers?
A: Complete record of welding repair history, with traceable parameters.
