Optimization of demoulding stability of PU self-bonded leather parts: reducing surface pitting and strain

# PU self-skinning demoulding stability case: two weeks to reduce poor appearance and extend the mold cleaning cycle

# Project overview

• Industry/Scenario: PU self-skinning foam parts (automotive interior)
• Production method: Single shift continuous production
• Core Goal: Reduce corner pitting and minor strains, improve batch consistency and reduce mold cleaning pauses

# Initial questions

There are three typical problems that customers encounter during continuous production:

1. Pits and small strains appear concentrated in the corner area
2. Appearance consistency fluctuates between batches, increasing the pressure for rework judgment
3. Mold contamination accumulates quickly and the frequency of mold cleaning is relatively high.

# Live baseline (before optimization)

• Defective appearance rate: about 4.5%~5.8%
• Mold cleaning cycle: Clean approximately every 60 to 80 molds
• Stability performance: The back section has obvious lift, and the consistency between shifts is insufficient.

Statistical caliber: daily production line reports for a single shift for two consecutive weeks, based on the customer’s current appearance criteria.

# Diagnostic Process (Days 1-3)

Check the consistency of the process first, and then compare the formula/dosage:

1. Check the spray distance, spray angle and overlap rate to check the coverage uniformity
2. Record the changes in defect distribution at different mold temperature stages
3. Comparing the residue and demoulding boundary under changing dilution ratios
4. Unify the mold cleaning baseline before evaluating material parameters to avoid interference from dirty molds

Diagnostic Conclusion

• The main contradiction is the fluctuation of the spray window and dilution ratio, rather than simple material failure.
• The original window tolerance is narrow and can easily amplify into appearance defects under continuous beats.

# Implementation Plan (Days 4-10)

• Option A (Process Priority): Fixed spray window (spray distance/angle/overlap rate)
• Option B (Dilution Synergy): Control the dilution ratio within the executable range
• Plan C (Maintenance forward): Change to preventive mold cleaning within the beat

Establish SOP simultaneously:

• Confirmation of the first item in each shift (key inspection in corner areas)
• Random inspection of coverage and appearance defects every 2 hours
• Abnormal troubleshooting sequence: Spray → Mold temperature → Mold cleaning → Dilution ratio

# Two-week results (trial production stage)

• Defective appearance rate: reduced from about 4.5% to 5.8% to 2.0% to 2.9%
• Mold cleaning cycle: increased from every 60~80 molds to every 100~130 molds
• Consistency performance: The fluctuations in the later period have significantly converged, and the proportion of rework has decreased.

# Reusable experience

1. In the PU self-skinning scenario, first control the spraying consistency, and then talk about dilution optimization to make the improvement more stable.
2. Corner defects are usually window boundary problems, and hard pressing through “spraying” is not recommended.
3. Evaluation using the dual indicators of “appearance defective rate + mold cleaning cycle” is closer to the true cost

# Applicable boundary description

The results of this case are based on the current mold status, temperature and humidity conditions and rhythm. Under different foaming densities, component geometry and appearance standards, it is recommended to verify the sample first and then scale up the entire line.

# Consulting advice

Mold temperature range, spraying method, dilution ratio and defect distribution can be provided, and we can provide a practical initial process window suggestion.