What is the defect rate in manufacturing? Explaining calculation methods, guidelines, and acceptable ranges

In manufacturing, the defect rate is a key numerical indicator for quality control.

A stable supply of high-quality products not only leads to increased customer satisfaction and earning the trust of the company, but also contributes greatly to cost reduction.

For example, in many factories that handle automobile parts, reducing the defect rate is one of the important goals.

Efficient management is essential because an increase in the defect rate directly leads to a decrease in customer satisfaction and an increase in costs. Proper inventory management can also reduce human error by workers, thereby lowering the defect rate.

In this article, we will explain the basics of defect rates in manufacturing, how to calculate them, and specific methods for reducing defect rates.

Please use this article as a reference and incorporate it into your daily work to reduce your defect rate.

What is defect rate?

The defect rate is an indicator that shows the proportion of defective products among all manufactured products. It is important data used to evaluate and improve product quality.

Officially known as the defect rate, it is an important indicator of quality control in the manufacturing industry. Therefore, by analyzing the causes of defective products based on data, it is possible to identify problems and implement improvement measures, aiming to improve product quality.

The importance of understanding defect rates

Understanding the defect rate leads to the following benefits:

• Improved customer satisfaction
• Improved corporate image
• Cost reduction
• Improving production efficiency

Reducing defect rates has various benefits for companies, and by providing a stable supply of high-quality products, companies can gain the trust of their customers and improve their corporate image.

In addition, excellent quality control makes it possible to reduce unnecessary costs such as rework and disposal.

Possible causes of defective products include poor quality parts and materials, design errors, and even the influence of conditions within the process. Therefore, it is necessary to firmly establish quality standards and constantly promote visualization.

Defective rates and other related quality indicators

PPM (Parts Per Million) is an indicator that shows the number of defective parts per million. It is mainly used in quality control and the manufacturing industry to express the defect rate in more detail.

Formula for converting percentage defective rate to PPM
PPM=Defect rate (%)×10,000

By using PPM, even slight differences in defect rates can be clearly understood, enabling more precise quality control.

Yield is an indicator that shows the percentage of acceptable products obtained in the final manufacturing process compared to the amount of raw materials and parts used.

For example, let's say that in the automobile manufacturing process, parts for 1,000 vehicles are input, and 800 of these are completed as acceptable products, then the yield is 80%.

Yield is an important indicator for assessing the efficiency of the entire manufacturing process.

If the yield rate is 80%, this means that 200 units' worth of parts will be defective. Possible causes of these defects include poor quality parts, mistakes in the assembly process, or even breakdowns in production equipment.

In order to improve yield, it is necessary to identify these factors and take measures to improve them.

It is important to maintain a high yield while keeping the defect rate low, and to achieve this, it is essential to develop equipment that utilizes IoT and automation technology.

How to calculate the defect rate

The defect rate is calculated using the following formula:

Defective rate (%)=(number of defective products / total number produced)x 100

For example, if 1,000 products are manufactured and 10 of them are defective, the defect rate is calculated as follows:

Defective rate (%) = (10 pieces / 1,000 pieces) x 100 = 1%

It is extremely difficult to completely eliminate defects in manufacturing, so it is common to set a realistic target value for the tolerance of the defect rate.

The standard deviation "σ" (sigma) is used as a guideline for the defect rate. Generally, the manufacturing industry aims for 3σ, but for products that affect human life, such as those in the medical, aviation, and automotive industries, the target is often 6σ.

For example, 3σ means that there should be less than three defective products per 1,000 manufactured units, while 6σ means that there should be three defective products per one million products.

Methods for reducing defect rates

The following methods are effective in reducing the defect rate:

• Product inspection before shipping
• Building an education system
• Strengthening the management system
• Organize your work environment
• Utilizing QC methods
• Implement a quality control system

Here we will introduce the following six methods in detail.

Product inspection before shipping

Pre-shipment product inspection offers many benefits, including increased customer satisfaction, brand protection, cost savings, and legal liability protection.

Even when it is practically difficult to inspect all products, it is possible to maintain quality control standards efficiently and effectively by conducting appropriate sampling inspections based on statistical methods.

Furthermore, the introduction of an automated inspection system that utilizes AI and IoT is expected to improve inspection efficiency, prevent human error, and improve quality control through data accumulation.

Building an education system

In order to prevent defective products from being produced due to human error, it is essential to establish a training system for workers.

By creating a manual that clearly defines work procedures and conducting regular training, you can improve workers' skills and quality awareness.

It is also important not only to create a manual but also to review it regularly. Always be aware of the need for improvement, such as checking whether there are any problems with the current process, whether the correct information is included, and whether the content is easy for anyone to understand.

Strengthening the management system

Strengthening the quality control system in the manufacturing process will lead to a reduction in the defect rate caused by human error.

Specifically, it is important to regularly check the manufacturing process, take prompt action to correct any problems, and implement the PDCA cycle to continually improve quality.

By utilizing the PDCA cycle, we can continuously promote quality improvement.

Specifically, you should repeat the process of identifying current problems, creating an improvement plan (Plan), putting the plan into action (Do), evaluating the results (Check), and taking further measures to improve (Act). In this way, you can aim for continuous improvement.

Strengthening the management system is a pillar for maintaining and improving a company's competitiveness from a long-term perspective, and is also the foundation for gaining customer trust.

Organize your work environment

A clean and tidy work environment leads to improved work efficiency and the prevention of human error. In manufacturing sites, it is important to maintain a work environment based on the 5S principle.

5S is an acronym for the following five items:

• Organize
• Tidying up
• cleaning
• cleanliness
• Discipline

Organizing means discarding unnecessary items and keeping only what is necessary. This is the first important step in preventing material shortages and freeing up workspace in the factory.

Ordering involves placing items in a fixed location so that they are easy for anyone to understand and can be easily retrieved. Placing parts and other items in fixed locations will prevent dependency on one person and reduce the risk of poor maintenance.

Cleaning is required to keep the workplace clean at all times and remove sources of rubbish and dirt. A clean environment leads to reduced variation and quality defects, and will also influence the setting of productivity improvement goals.

Cleanliness means continually keeping things organized, tidy, and clean, and maintaining a comfortable environment at all times.Finally, discipline means developing the habit of following set rules and carrying out planned tasks properly.

Through these activities, you can create an efficient and organized work environment.

Utilizing QC methods

Utilizing QC methods is crucial in improving quality control.

QC (Quality Control) methods refer to a series of scientific methods that utilize objective numerical data to visualize and accurately understand the current state of the production process.

This method will enable you to quantitatively measure the performance of your production process and clearly see the current state of quality.

For example, quantifying the defect rate using a formula can lead to setting specific goals.

At manufacturing sites, various QC methods such as Pareto charts and fishbone diagrams are used to identify the causes of defective products, such as machine, material, and worker dependency, to prevent problems such as poor maintenance, and to develop effective countermeasures.

By introducing QC methods, quality control based on objective data will become possible rather than relying on subjective judgment, reducing quality variation and leading to the consideration of more efficient and effective improvement methods and improvement activities.

In many factories, including those in the automotive industry, QC methods are an essential element for standardizing and implementing thorough quality control.

A shortcut to improving quality is to refer to past success stories, consider QC methods that suit your company's objectives, and add them.

Understanding and properly utilizing the seven main QC techniques is key to quality control.

Implement a quality control system

A quality management system (QMS) is an organizational mechanism for maintaining and improving the quality of products and services.

By introducing a quality management system, you can clarify the responsibility system and business processes for product quality, and address quality management throughout your organization.

ISO9001 is the international standard for quality control systems, and many companies aim to obtain it.

Aiming to manufacture high-quality products by improving defect rates

In this article, we have explained everything from the basics of defect rates in manufacturing to how to calculate them, as well as specific methods for reducing defect rates.

In the manufacturing industry, the defect rate is an important indicator that affects product quality and the reliability of a company. An increase in the defect rate can have various negative effects on a company's activities, such as reduced customer satisfaction, increased costs, and a damaged brand image.

By introducing "i-Reporter," it becomes possible to detect defect rates early and plan improvement measures through real-time data analysis.

This will enable us to build an optimal production line and maintain a quality standard of 99.7%.The future trend in the manufacturing industry is likely to see the further adoption of IoT and AI technologies.
For more information about "i-Reporter," please click here.