Case Study: Cost Reduction Through Mass Production and Elimination of the Deburring Process

Introduction

In the manufacturing industry, streamlining processes and optimizing mold cavity counts are critical improvement methods for achieving maximum results with limited resources. This article presents a case study of cost reduction achieved through improvements to the molding process for “Poppet Retainers,” implemented by the Sales Engineering Department of Sanko Gosei’s Auto Functions Business Unit.

This improvement initiative was centered on the following two key themes:

★ Revising the mold from a 4-cavity to an 8-cavity design (doubling the number of parts per mold)

★ Eliminating the product deburring process

As a result, we achieved cost reductions, improved productivity, and stabilized quality, yielding annual cost savings of approximately 750,000 yen.

Target Product: Poppet Retainer

This product is a plastic automotive component for which mass production began in late 2007.

The material used is **PET-GF35% (DuPont: RYNITE RE15022)**.

It is a component with extremely stringent requirements for dimensional accuracy and appearance.

Main Specifications

Projected Area: 9.0 cm²

Machine Model: TOYO Si180III (180-metric-ton injection molding machine)

Product Weight: 5.1 g/piece

Gate: Tunnel gate (3 points)

Drawing Requirement: Specifies “No flash”

Challenges: Aging of the 4-cavity mold and flash formation

As of 2019, more than 10 years after production began, the total number of shots had exceeded 700,000, and flash caused by mold wear had begun to become noticeable.

Burrs tended to form particularly in the “gaps between nested parts,” making it necessary to perform deburring on every single part. This resulted in additional labor hours, which directly led to reduced productivity and increased costs.

Improvement Measure 1: Elimination of the Deburring Process

Details of the Solution

By integrating the insert components of the mold, gaps between the inserts were eliminated.

As a result, burr formation was reduced, and the deburring process was completely eliminated.

Benefits

Stable surface quality

Cost reduction achieved by eliminating labor hours

Contributes to shorter lead times by eliminating secondary processing steps

Improvement Measure 2: Doubling the number of parts per mold from 4 to 8

Given the expectation of continued orders and customer requests for increased production capacity, we decided to upgrade the mold to an 8-cavity design.

Design Innovations

The products are arranged vertically in a 8-unit parallel configuration to fit within the 560 × 560 mm tie-bar spacing of the injection molding machine (Si180Ⅲ).

The injection molding machine remains the same as before (no capital investment required).

The diameters of the gates, runners, and spools were also optimized.

Improvement Measure 3: Shortening the Molding Cycle

Conventional molding cycle: 45 seconds; After improvement: 25.5 seconds (approx. 57%)

Key Points

• Optimize the diameter and layout of the spool runners

  Review mold cooling efficiency

  Molding conditions (mold temperature and resin temperature) follow the conventional settings; no readjustment is necessary

  
  

  Improvement Measure ④: Reduce resin consumption by lightening the runner system

Total weight of the old model (4-piece) runner and product: 53.3 g

The following changes were implemented for the new model:

　① Cut 15 mm off the spool

　② Removed unnecessary runner chucks

　③ Reduced runner diameter from φ5.2 to φ3.9

　④ Reduced the diameter of the second spool from φ4 to φ3

As a result, the total weight of the runners and products for the 8-piece configuration is 96.3 g,

which represents a reduction in resin usage of nearly 10 g compared to the total weight of 53.3 g × 2 = 106.6 g for the 4-piece configuration.

Summary of Improvement Effects

Item	Old（4pcs）	New（8pcs）	Effect
Deburring	Required	Not needed	Consistent Quality
Number of items	4pcs	8pcs	Double Productivity
Cycle Time	45sec	25.5sec	Reduced to 57%
Amount of Resin Used	37.5g／shot	73.2g／shot	Improved Efficiency

Conclusion

This case study is an example of an improvement initiative that “achieved significant cost reductions through the optimization of part count and mold structure.”

Particularly noteworthy are the following points:

・Utilization of existing equipment (molding machines) as-is

・Complete elimination of secondary processes through burr-free molding

・100% compliance with customer drawing requirements (burr-free)

These improvements offer benefits to both the production floor and the customer.

Going forward, it will be essential to continue efforts to maintain and enhance cost competitiveness by reviewing designs and processes without requiring significant additional investment in equipment. Manufacturing sites are expected to replicate these success stories across the board and use them to drive further improvement initiatives.