Improvement Case Study: Enhanced Cooling Efficiency Through Mold Cooling Pipe Cleaning

Introduction

Mold cooling efficiency is a critical factor influencing product quality and cycle time in injection molding. Particularly in recent years, the use of molds featuring 3D cooling channels has increased to accommodate complex product geometries, leading to issues with poor cooling due to scale and rust deposits within the channels. This article presents a case study of cooling channel cleaning performed on a production mold, detailing the specific improvements implemented and their effects.

Background: The Spread of 3D Cooling Piping and the Emergence of Problems

The mold featured in this article utilised extremely fine 3D cooling pipes, approximately φ1.5mm in diameter, necessitated by the need to accommodate tight spaces. Prolonged storage of the mold after molding led to the accumulation of scale and rust within the cooling pipes. This caused a significant reduction in water flow, resulting in a substantial decrease in cooling efficiency. Consequently, issues arose, including an increase in molding defects and extended cycle times.

Solution implemented: Water Reamer

To address this challenge, a dedicated cleaning device, the “Water Reamer”, was introduced. This device possesses the following characteristics:Non-disassembly cleaning possible: Molds can be cleaned without disassembly, significantly reducing labour requirements

4-hour cleaning process + 2-hour drying process: Completed in a relatively short timeframe

Flow meter compatibility: Enables numerical management of water flow rates before and after cleaning, visualising maintenance effectiveness

Formation of anti-rust coating: Contributes to preventing rust recurrence after cleaning

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Case Study 1: Joint Product Mold (3D Piping, φ1.5mm)

This mold, manufactured in 2017, had been used for over 120,000 shots and featured fine 3D cooling piping in the slide section. The flow rate prior to cleaning was extremely low at 0.2 L/min. Due to inadequate cooling, molding defects occurred frequently.

Cleaning results :Flow rate: Increased from 0.2 L/min to 0.5 L/min

Status: Restored to a level enabling continuous molding

This cleaning avoided the need for mold remanufacturing (costing approximately ¥450,000), resulting in significant cost savings.

Case Study 2: Case Product Mold (Cooling Pipe, φ2mm)

A mold manufactured in 2012 with over 600,000 shots molded. It utilised a cooling pipe with a total length of 130mm. Prior to cleaning, the flow rate was 0.3L/min. Voids (hollow defects) occurred in the inner ribs, necessitating a cycle time extension to 70 seconds to manage the issue.

Cleaning results:

• Flow rate: Increased from 0.3 L/min to 0.6 L/min

  
  

  Cycle time: Reduced from 70 seconds to 63 seconds

  
  

  Defect rate: Improved to zero voids

  
  

  Calculated improvement effect equivalent to ¥378,000 per annum based on 9,000 shots per month.

  
  

  Case Study 3: Case Product Mold (Baffle Cooling/Rust)

  
  

  An older mold manufactured in 2005 with 700,000 shots, employing a baffle cooling system. It required 1 hour 30 minutes to reach operating temperature, and 8 shots were discarded per cycle due to weight defects.

  Additionally, the molded parts exhibited cooling lines, likely caused by insufficient cooling.

Cleaning Results

Flow rate: Increased from 0.2 L/min to 1.1 L/min

Heating time: Reduced from 90 minutes to 60 minutes

Discarded shots: Reduced from 8 to 3

Product weight: Increased by 1 g (within tolerance)

Defective items: 100 per month × ¥130 × 12 months = ¥156,000 equivalent. Adding reduced heating times and fewer scrap shots, the total annual improvement effect amounted to approximately ¥630,000 equivalent.

Results and Overall Effect

Combining the improvement effects from these three cases, the estimated annual cost benefit is approximately ¥1,058,400. Notably, comparison photographs before and after cleaning clearly show piping that was densely covered in rust, resembling a stalactite cave, transformed into a clean, black state post-cleaning.

Future Prospects and Operational Integration

Where manual cleaning using drills or rods was previously standard, the introduction of the water reamer enables maintenance without disassembly. Furthermore, quantitative recording via flow meters facilitates the creation of maintenance records that visualise mold degradation trends.

Furthermore, its application to new molds is expected to prevent scale and rust formation, thereby extending mold life and contributing to stable operation.

Summary

Cleaning mold cooling pipes is not merely routine maintenance; it is a strategic improvement activity directly linked to product quality and production efficiency. The cleaning method using the Water Reamer introduced here is an effective technique capable of handling difficult-to-clean areas such as 3D cooling pipes. It is likely to become an important piece of equipment in future injection molding operations.