Case Study: Gear Plate—Saving Lives Through Quality and Process Improvements

Introduction

At Sanko Gosei Philippines, we have been molding and shipping gear plates—a key component of instant cameras—at a high monthly production rate of 300,000 units. However, serious challenges had emerged in this production process, including frequent quality issues and an increasing workload on staff.

In this article, we will introduce the initiatives we undertook to simultaneously improve the quality of the gear plates and streamline the production process, thereby optimizing staffing levels (enhancing workforce efficiency).

Background of the Improvement

The gear plate is a component that holds the rotating parts inside the shutter button, and its dimensional accuracy and molding quality directly affect its functionality. Glass-fiber-reinforced polycarbonate was used for molding, and injection molding was performed using an 8-cavity mold on a Toshiba EC130S (130-metric-ton) molding machine.

Initially, this process required three operators per molding machine. Among the factory’s 39 molding machines, the gear plate was the only part that required a three-person crew. This resulted in reduced productivity and rising labor costs. The breakdown of the workload is as follows:

High-gate rework: 35 seconds

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• Test: 32 seconds

  

• Product Movement and Handling: 15 seconds

  

• Sorting by compartment and packing: 11 seconds

  

The cycle time per cycle (8 cells) was 93 seconds, significantly exceeding the machine cycle time (32 seconds). As a result, an inefficient situation persisted in which three people were required to operate even a single machine.

Improvement Goals and Structure

Our goal was clear.

• ・Reduce the cycle time to 28.8 seconds or less and achieve single-operator operation.

  
  

  ・Fundamentally eliminate high-gate defects.

  
  

  ・Bring all quality issues close to zero.

  
  

  To achieve these goals, a project team was formed. The plant manager, project leader, quality control, and production control worked together as one to conduct a thorough analysis and improvement of the production process.

  
  

  Identification and Analysis of Major Issues

  
  

  1. High-gate defects

“High gate” refers to a defect in which the gate portion of a molded part protrudes further than intended.

The investigation revealed a high occurrence rate of 71.25% out of 160 parts produced in 20 shots. The cause was found to be the holding pressure conditions and molding timing.

In molding tests conducted at a holding pressure of 0 MPa, although the high gate disappeared, sink marks occurred in all parts. Ultimately, by setting two-stage holding pressure conditions (first holding pressure: 85 MPa, second holding pressure: 45 MPa), we achieved zero defects.

2. Burden on the Inspection Process

Since workers were responsible for inspecting all 9 items, the inspection took 32 seconds. However, more than 80% of defects occurred only during startup, and production remained stable during mass production. By standardizing the startup procedure manual and switching to QA patrol inspections (every 3 hours), we narrowed the scope of the 100% inspection to 3 items and reduced the inspection time to 10 seconds.

3. Sorting by Compartment and Packaging

Although products were previously packed into trays or boxes by cabinet, complete separation could not be guaranteed in practice, requiring 100% inspection during sorting. After reviewing the purpose of the process, we determined that there was no benefit to separating the products by cabinet and discontinued this practice. This reduced the packing time from 11 seconds to 7 seconds.

4. Product Handling and Movement

We were wasting a significant amount of time moving products to the finished goods storage area, located 5 meters away, and performing operations that required a 90-degree turn. By redesigning the workflow, relocating the finished goods area, and removing the rework station, we reduced the operation time from 15 seconds to 10 seconds.

Results After Improvement

Through our improvement efforts, we achieved the following overall results:

High-gate defect rate: 71.25% → 0%

Inspection time: 32 seconds → 10 seconds (−22 seconds)

Cavity separation time: 11 seconds → 7 seconds (−4 seconds)

Transport time: 15 seconds → 10 seconds (−5 seconds)

Work takt time per cycle: 93 seconds → 27 seconds

As a result, the process now operates with ample margin even compared to the machine cycle time (30.5 seconds), allowing us to transition from a three-person staffing level to a one-person operation.

Cost Reduction and Monetary Benefits

The benefits of this improvement were significant in quantitative terms, yielding the following annual results:

Workforce Reduction (Elimination of 2 Positions): Approximately 21.6 million yen/year (Japanese rates)

Cycle Time Improvement: 130,000 yen/year

Space Efficiency (2.3 m² reduction): 40,000 yen/year

Reduction in Defect-Related Losses: Zero complaints, reduced rework costs

In total, we achieved annual cost savings of approximately 21.77 million yen.

The Significance of “Optimizing Workforce Utilization”

A key feature of this project was its focus on the concept of “optimizing workforce utilization”—which aims not only to reduce defects and shorten cycle times but also to maximize the utilization of human resources. By transitioning from a three-person team—which had been under heavy strain—to a system where stable production is possible with just one skilled operator, we enhanced the added value provided by our workforce and enabled the redeployment of personnel to other processes.

Future Developments

The know-how established in this project—specifically regarding “optimization of holding pressure conditions” and “standardization of operations”—can be applied horizontally to other molds with the same pin gate specifications. Furthermore, we plan to incorporate troubleshooting measures for mold startup into standard procedures and utilize them in future new mold development.

Summary

The gear plate quality and process improvement project adopted a multifaceted approach—covering equipment conditions, workflow, inspection standards, and holding pressure settings—and simultaneously achieved both quality stabilization and maximum efficiency. The greatest achievement was that this went beyond merely reducing the workload; it realized “human-centered optimization,” which leads to the effective utilization and growth of our workforce.

Moving forward, we will continue to expand similar improvements to other processes and promote greater efficiency across the entire production floor.