Introduction: The Importance of Screw Fastening in Manufacturing and the Urgency of Defect Reduction

In modern manufacturing, screw fastening plays an absolutely fundamental role in ensuring product safety and reliability. It forms the backbone of products across various industries, from automotive, home appliances, and medical devices to aerospace, and is a critical factor influencing their function and performance. However, if a defect occurs in this screw fastening, the impact can be immense.

When defective products occur, companies incur not only direct costs such as rework, scrap, and repairs, but also immeasurable losses in the form of product recalls, customer complaint handling, and damage to brand image. According to estimates by the Ministry of Economy, Trade and Industry (METI), the annual loss due to defective products in the manufacturing industry in Japan alone is said to reach several trillion yen (approximately 5 trillion yen annually). Furthermore, fastening components often account for an average of 5% to 15% of product costs, and their quality directly impacts the overall cost and reliability of the product. One study reported that approximately 15% of product recall causes are related to fastening defects, clearly demonstrating their importance.

Against this backdrop, stabilizing screw fastening quality is an urgent challenge that goes beyond mere cost reduction, directly enhancing a company’s competitiveness. Ohta Vietnam provides high-precision fastening solutions to address the quality challenges faced by manufacturing sites in Vietnam, strongly supporting our customers in defect reduction and productivity improvement.

Problems Caused by Screw Fastening Defects and Their Root Causes

Screw fastening defects directly lead to problems such as product malfunction, reduced safety, and shortened lifespan. For example, fastening defects in critical safety parts of automobiles can lead to serious accidents. In the case of medical devices, they could potentially cause life-threatening situations for patients. These issues can escalate into recalls and large-scale complaints, severely damaging a company’s credibility and resulting in enormous economic losses. Product accidents caused by fastening defects can amount to hundreds annually in specific industries (e.g., automotive parts).

The main causes of screw fastening defects are diverse, but include the following:

• Insufficient or excessive tightening torque (the force used to turn a screw): Deviating from the specified torque can result in insufficient clamping force or damage to screws and components. Experimental data shows that if tightening torque deviates by ±20% from the specified value, fastening reliability can decrease by more than 50%.
• Insufficient axial force (the tensile force generated when a screw is tightened): Even if the tightening torque is appropriate, axial force can be insufficient due to variations in friction coefficient, among other factors.
• Foreign material contamination: Foreign objects caught in the screw threads or seating surfaces can lead to unstable clamping force.
• Component precision defects: Variations in the dimensions or material of screws and fastened components can hinder stable fastening.
• Operator skill differences: In manual tightening, fastening quality can vary depending on the experience and skill of individual operators.
• Incorrect tightening sequence: When tightening multiple screws, failing to follow the correct sequence can cause component distortion or uneven clamping force.

Particularly in Vietnamese manufacturing sites, challenges such as a shortage of skilled workers, insufficient adherence to standardized operating procedures, and aging equipment can manifest as fastening defects due to human and equipment factors. It is not uncommon for the repair and replacement cost per defective product to reach 3 to 10 times the manufacturing cost.

Fundamentals of Management for Achieving Stable Screw Fastening Quality: Torque and Axial Force

To stabilize screw fastening quality, a deep understanding of its mechanism and appropriate management are essential. The purpose of screw fastening is to generate axial force between components, thereby securing them through friction. This axial force is the most critical factor determining a product’s functional integrity and its resistance to vibration and impact.

Commonly employed is torque management. This method aims to indirectly secure axial force by tightening screws to a specified torque value. However, the relationship between torque and axial force is significantly influenced by variable factors such as the friction coefficient of the screw threads and seating surfaces. For instance, the friction coefficient can vary greatly depending on the presence of lubricants, surface treatment, material, and temperature. Consequently, even when tightening with the same torque value, the actual axial force generated can show significant variations. The impact of tightening torque variation on axial force is substantial; even a ±10% torque variation can lead to an axial force variation of more than ±30%.

In contrast, axial force management offers the advantage of achieving more stable fastening quality by directly measuring or estimating and controlling axial force. However, direct measurement of axial force requires specialized sensors and equipment, making it difficult to implement on all manufacturing lines due to cost and complexity. Therefore, understanding the relationship between torque, axial force, and tightening angle (the angle through which the screw is turned), and managing these factors in combination, becomes crucial. For example, by simultaneously monitoring torque and tightening angle, it is possible to detect variations in the friction coefficient and estimate axial force more accurately. Research has shown that maintaining an appropriate axial force range can improve product fatigue life by 20% to 50%.

Appropriate screw selection (material, diameter, pitch, etc.) during the fastening design phase and consideration of tightening conditions (torque value, tightening sequence, tightening speed, etc.) are also fundamental for ensuring stable quality. Calibration of tightening torque wrenches is recommended at least every 3 to 6 months, based on JIS B 4653, and regular maintenance is indispensable.

Advanced Technologies for Improving Screw Fastening Quality and Their Practical Application

To improve screw fastening quality and reduce defects, the adoption of advanced technologies and practical management methods is essential.

• Introduction of Automated Fastening Equipment: Automated fastening using electric screwdrivers and robotic arms achieves significantly higher precision and repeatability compared to manual work. This eliminates quality variations caused by differences in operator skill and can substantially reduce defect rates. Numerous cases report a 20% to 50% reduction in defect rates after implementing automated fastening equipment. Furthermore, increased tightening speed also improves productivity.
• Real-time Monitoring and Data Management Systems with Torque/Axial Force Measurement Devices: Systems that measure and record torque and tightening angle in real-time during the fastening process and immediately detect anomalies are crucial for quality control. Centralized management and analysis of this data help in understanding quality trends, early problem detection, and root cause analysis. Some companies have seen an average productivity increase of 15% to 25% by implementing data management systems.
• Utilization of Poka-Yoke (Mistake-Proofing) Systems: Poka-Yoke systems, which prevent errors such as incorrect screw supply, wrong tightening position, or incorrect tightening sequence, fundamentally prevent defects from occurring. Examples include image recognition for screw type verification, sensor-based detection of tightening positions, and sequence control to enforce tightening order. Poka-Yoke systems have been proven to reduce human errors by more than 90%.
• Regular Equipment Calibration and Maintenance Plan: Tightening tools and measuring instruments lose accuracy with use. Regular calibration and maintenance are essential to ensure they operate in optimal condition at all times.
• Continuous Training and Skill Development Programs for Operators: Even with increasing automation, ultimate quality still depends on human oversight. Fostering operators with appropriate knowledge and skills forms the foundation for quality maintenance.

Ohta Vietnam offers high-precision fastening tools incorporating these advanced technologies. For example, our high-precision electric screwdrivers achieve torque accuracy within ±5%, contributing to stable fastening quality. We propose optimal solutions tailored to our customers’ manufacturing sites, achieving both defect reduction and productivity improvement.

Challenges in Screw Fastening Quality Management in Vietnamese Manufacturing and Ohta Vietnam’s Contribution

Vietnam’s manufacturing sector has seen remarkable growth in recent years, recording an average annual GDP growth rate of 6% to 7% over the past decade, with foreign direct investment (FDI) increasing by more than 10% annually. Many Japanese companies have expanded their operations, increasing Vietnam’s role as a production base for high-quality products. However, a challenge arises from the gap between the stringent quality standards demanded by Japanese companies and the local quality management systems.

Particularly in screw fastening, in addition to the human and equipment factors mentioned earlier, variations in component quality within the supply chain and a lack of specialized knowledge among local engineers can hinder quality stabilization. Furthermore, labor costs in Vietnam have risen by an average of more than 10% over the past five years, making the transition from labor-intensive production systems to more automated and labor-saving ones an urgent necessity.

Ohta Vietnam contributes by providing concrete solutions to these unique challenges faced by Vietnamese manufacturing.

• Provision of High-Precision Fastening Solutions: We provide high-precision electric screwdrivers, torque measurement devices, and automated fastening machines that meet Japanese quality standards, thereby achieving stable fastening quality.
• Technical Support and Consulting: Engineers with specialized knowledge offer technical support ranging from optimizing fastening design to setting on-site tightening conditions and troubleshooting. We analyze customers’ manufacturing processes and propose optimal quality management methods.
• Local Educational Support: We provide training programs for Vietnamese engineers and operators, supporting the improvement of their specialized knowledge and skills related to screw fastening. This promotes the establishment of autonomous quality management systems locally.
• Creation of Success Stories: Ohta Vietnam’s client companies have achieved an average defect rate improvement of 15% after implementing our solutions. Furthermore, the cost reduction effect from implementation can range from 10% to 20% across the entire production line.

Ohta Vietnam not only supplies products but also acts as a partner in solving customers’ quality challenges, supporting the sustainable growth of Vietnamese manufacturing.

Conclusion: Pursuing Sustainable Quality and Productivity

Managing screw fastening quality is fundamental to ensuring product quality and safety, and ultimately influences a company’s competitiveness. Defect reduction directly leads not only to short-term cost savings but also to long-term customer trust and enhanced brand value. In modern manufacturing, this quality management is not merely an inspection process; it requires a comprehensive review of the entire process, from design to manufacturing and maintenance, pursuing continuous improvement through technological innovation and data utilization.

By actively introducing advanced technologies such as automated fastening equipment, real-time monitoring systems, and Poka-Yoke, and combining them with operator skill enhancement, human errors can be minimized, achieving stable and high-precision fastening quality. The ROI (Return on Investment) for quality investment is generally said to yield a return of 3 to 5 dollars for every 1 dollar invested. With the advancement of smart factories over the next five years, a further defect rate reduction of 10% to 15% is expected, making investment in quality an indispensable strategy for the future of manufacturing.

Ohta Vietnam strongly supports the business growth of Vietnamese manufacturers by providing specialized knowledge, high-quality fastening tools, and extensive local support to address the quality challenges they face. As a partner committed to sustainable quality and productivity, please consult Ohta Vietnam.

Conclusion

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