Quality Control Methods

By AMREP | Posted on January 10, 2025

Broadly speaking, the quality control process has three steps: the specification of what is wanted, the production of things to satisfy the specification and the inspection of the things produced to see if they satisfy the specification. And highly successful companies share a common trait: the consistent use of proven quality control methods that ensure operational excellence, efficiency, and reliability.

• 11 Different Quality Control Methods
• Types of Quality Control Methods
• Techniques of Quality Control
• Partnering for Excellence in Quality Control

11 Different Quality Control Methods

1. Inspection

Inspection is one of the most traditional and simplest quality control methods. It involves visually checking raw materials, in-process items, and finished products. Inspectors look for defects, inconsistencies, or deviations from specifications. Only approved materials and products proceed to the next stage. This method helps identify problems early and ensures only quality items reach customers.

Practical Application

SPC helps companies like Boeing maintain tight tolerances on components used in aircraft. By applying SPC, manufacturers can identify small defects or variations in parts early, preventing costly errors or delays in production.

For example, a slight deviation in metal thickness could compromise safety, so SPC is critical in ensuring consistency and quality control during assembly.

2. Statistical Process Control (SPC)

SPC uses statistical tools to monitor and control a process. SPC helps to identify variations, by collecting data from different production stages. Control charts track these variations and highlight any out-of-control conditions. If the process goes beyond the acceptable limits, corrective action is taken immediately. This method is effective in maintaining consistent quality over time.

Practical Application

Companies like Honda use a combination of manual and automated inspection methods to ensure the vehicles' exterior and interior components meet high standards. Robots and cameras detect visual defects, such as paint imperfections, while quality inspectors manually check functional components like brakes and engines to ensure safety and reliability.

3. Sampling

Sampling involves selecting a random sample of products for testing. Instead of inspecting every item, a small portion is chosen for quality tests. These tests ensure that products meet specifications without slowing down production. If a sample fails, further investigation is conducted. Sampling is efficient and reduces the time spent on quality checks.

Practical Application

In the textile industry, acceptance sampling is applied to manage large orders of fabric. For instance, a company producing bulk orders of clothing might only inspect a small portion of fabric rolls for defects, rather than checking every roll. By sampling, the company saves time and resources but still ensures the bulk product meets quality standards, reducing the risk of producing defective goods.

4. Automated Testing

Automated testing uses machines to perform repetitive tests on products. These machines check various parameters such as strength, size, and alignment. Automated testing ensures consistency and accuracy. Any product that fails to meet standards is flagged for further action. This method speeds up the quality control process and minimizes human error.

Practical Application

Automated testing is used in warehouses to check the quality of products like electronics. Machines test parameters such as battery life or screen quality. If products fail, they are flagged for rework or rejection, ensuring only high-quality items are shipped. This speeds up quality control and minimizes human error.

5. Employee Training

Employee training plays a key role in quality control. Workers must understand the company’s quality standards and know how to spot defects. Regular training sessions help employees stay updated on new quality practices. Skilled workers can identify issues early, reducing defects and improving product quality.

Practical Application

Employee training is essential for ensuring that workers understand quality control procedures, safety standards, and equipment usage. For example, warehouse staff are trained to properly handle inventory, use automated systems, and identify defective products. This training improves operational efficiency, reduces errors, and enhances safety, ensuring that quality standards are consistently met throughout the supply chain.

6. Root Cause Analysis

When a defect occurs, it’s important to find out why it happened. Root cause analysis is the process of identifying the underlying issue causing defects. It involves analyzing production lines, materials, and procedures. Once the root cause is found, corrective measures are taken to prevent future issues. This method helps eliminate recurring problems.

Practical Application

Root Cause Analysis (RCA) is used to investigate recurring issues, such as delays in shipments or inventory discrepancies. For example, if a company experiences frequent stockouts, RCA can identify the underlying cause, such as supplier delays or poor demand forecasting. By addressing the root cause, such as improving supplier relationships or adjusting inventory management practices, the company can prevent future issues and enhance overall supply chain efficiency.

7. Preventive Maintenance

Preventive maintenance ensures machines are in good working condition. Routine checks and repairs are scheduled to avoid unexpected breakdowns. This method helps prevent equipment failure, which can lead to defects in products. Well-maintained machines run efficiently and produce high-quality products consistently.

Practical Application

Preventive maintenance is used to ensure that equipment, such as forklifts, conveyor belts, and automated sorting systems, is regularly serviced to prevent breakdowns. For example, a warehouse may schedule routine checks on its conveyor system to identify wear and tear before it leads to a failure. This helps reduce unplanned downtime, extend the lifespan of equipment, and maintain smooth operations, improving overall efficiency and minimizing disruptions in the supply chain.

8. Six Sigma

Six Sigma is a data-driven method aimed at reducing defects and improving processes. It uses a set of tools to identify inefficiencies and errors in production. By analyzing data, teams can find solutions that improve product quality and process efficiency. Six Sigma helps companies achieve near-perfect products with minimal defects.

Practical Application

In the supply chain industry, a company may apply Six Sigma to streamline order fulfillment. By analyzing data on delays, errors in picking, and shipping mistakes, the company can identify inefficiencies in the process. Using Six Sigma tools, they implement changes such as optimized inventory management or better employee training, which leads to fewer mistakes, faster delivery times, and improved customer satisfaction.

9. Quality Audits

Quality audits involve reviewing company processes and products for compliance with quality standards. Internal or external auditors assess everything from raw materials to finished goods. The findings from audits lead to improvements in procedures and policies. Audits help ensure that quality control systems remain effective and up-to-date.

Practical Application

Quality audits are conducted to ensure that suppliers and internal processes comply with established standards. For example, a company may perform regular audits of its suppliers to verify that they meet quality standards for raw materials. The audit may include checking production records, inspecting facilities, and reviewing compliance with safety and environmental regulations.

10. Feedback Loops

Feedback loops are essential for continuous improvement. By collecting customer feedback, companies can identify areas for improvement. If customers report defects or issues, the company can investigate and take corrective action. Feedback helps adjust products and processes to better meet customer needs and expectations.

11. Taguchi method

The Taguchi Method of quality control is a statistical approach developed by Japanese engineer Genichi Taguchi. It is focused on improving the quality of products and processes by designing them to be robust and less sensitive to variations, even those that cannot be controlled. The primary objective of the Taguchi Method is to minimize variation and reduce defects, thereby improving the overall performance of a product.

Practical Application

Taguchi method is used to optimize product design and manufacturing processes. For example, a company may apply the Taguchi method to improve the packaging of fragile items. By experimenting with different materials, shapes, and cushioning techniques, the company can identify the most cost-effective packaging solution that minimizes damage during transit, ensuring product quality and reducing waste.

Must Read: Quality Control:Definition, Significance, and Methods

Types of Quality Control Methods

Quality control methods vary depending on the industry and product. Some industries rely on scientific measures, while others use more qualitative approaches. Generally, there are four main types of quality control: process control, acceptance sampling, control charts, and product quality control. Each type has its own unique application to ensure high-quality standards.

1. Process Control

Process control focuses on maintaining the consistency of manufacturing processes. It involves monitoring variables like temperature, pressure, and speed to ensure the production process stays within desired limits. This type of control minimizes variations and ensures the process remains stable.

2. Acceptance Sampling

Acceptance sampling is used to inspect a subset of products from a batch rather than the entire lot. It helps determine whether the entire batch meets quality standards. This method is efficient, especially when testing every unit is impractical, and allows businesses to manage risk effectively.

3. Control Charts

Control charts are statistical tools used to monitor process behavior over time. They track variations in a process to identify potential problems early. This type of control is essential for maintaining product consistency and ensuring that processes remain within set limits.

4. Product Quality Control

Product quality control directly inspects finished products to ensure they meet quality specifications. This type involves testing, examining, and evaluating products after production to detect defects. It's commonly used in industries like manufacturing and food production to guarantee that only high-quality items reach the customer.

Read More: Quality Assurance Vs Quality Control

Techniques of Quality Control

Effective quality control techniques are the backbone of any successful organization. By employing a variety of methods, businesses can identify defects early, streamline processes, and improve overall efficiency. Here are some of the key techniques that help maintain good quality:

1. Statistical Process Control (SPC)

Statistical Process Control (SPC) is a technique that uses statistical methods to monitor and control a process. By measuring variations in process data, SPC helps identify trends or issues that could lead to defects. Control charts are a key tool in SPC, as they visually represent process behavior over time. This allows operators to make real-time adjustments to maintain consistent quality.

2. Inspection

Inspection is the process of examining products for defects or deviations from specifications. This can be done manually or with automated systems. Visual inspection involves checking for obvious defects, while dimensional inspection measures physical attributes to ensure they meet design requirements. Functional testing checks whether the product works as intended. Inspection ensures that products meet quality standards before reaching customers.

3. Sampling

Sampling involves inspecting a representative sample of a batch rather than the entire lot. This technique helps save time and resources. Various sampling methods, such as acceptance sampling or random sampling, are used to make quality decisions based on statistical probability. If the sample passes, the whole batch is accepted; if it fails, corrective actions are taken.

4. Six Sigma

Six Sigma is a data-driven technique focused on reducing defects to a level of fewer than 3.4 per million opportunities. It uses the DMAIC framework—Define, Measure, Analyze, Improve, and Control—to systematically improve processes. By identifying and removing sources of variability, Six Sigma aims to achieve near-perfect quality levels.

5. Failure Mode and Effect Analysis (FMEA)

FMEA is a technique for identifying potential failure modes in a product or process. It involves analyzing each step of the process to determine where failures could occur and assessing their impact. By prioritizing the most critical failure modes, companies can implement corrective actions to prevent defects before they happen.

6. Control Charts

Control charts are graphical tools used in SPC to monitor process stability. They display data points over time and indicate upper and lower control limits. Any data points outside these limits suggest that a process is out of control and may require adjustments. Control charts help track variations and maintain consistency in production.

7. Design of Experiments (DOE)

Design of Experiments (DOE) is a structured technique for testing multiple variables to determine their effect on product quality. By carefully planning experiments, DOE helps identify the optimal settings for process variables, minimizing defects and improving product quality. This technique allows for systematic testing of different combinations of factors to find the best performance.

8. Root Cause Analysis (RCA)

Root Cause Analysis (RCA) is a problem-solving technique used to identify the root causes of defects or quality issues. It goes beyond identifying symptoms and focuses on the underlying problems that contribute to defects. Techniques like the "5 Whys" and Fishbone diagrams are often used in RCA to explore potential causes and prevent future defects.

9. Pareto Analysis

Pareto Analysis is based on the Pareto Principle, which suggests that 80% of problems are caused by 20% of the factors. This technique helps prioritize the most common or impactful quality issues. By focusing on these high-priority factors, companies can achieve significant improvements in product quality with minimal effort.

10. Total Quality Management (TQM)

Total Quality Management (TQM) is a comprehensive approach to improving quality across all aspects of an organization. TQM involves all employees in quality improvement efforts, from top management to the shop floor. It emphasizes customer satisfaction, continuous improvement, and a strong commitment to quality in every process and product.

11. Benchmarking

Benchmarking involves comparing a company’s processes or products against industry leaders or best practices. By identifying gaps in performance, organizations can implement improvements to meet or exceed standards. Benchmarking helps companies understand where they stand in terms of quality and provides insights for enhancement.

12. Quality Function Deployment (QFD)

Quality Function Deployment (QFD) is a technique used to ensure that customer requirements are met in the design process. It translates customer needs (or "whats") into technical specifications (or "hows"). By focusing on customer satisfaction from the start, QFD helps create products that align with customer expectations and maintain high-quality standards.

13. Poka-Yoke (Mistake Proofing)

Poka-Yoke, also known as mistake-proofing, is a technique that aims to prevent errors in the production process. It involves designing processes, tools, or devices that either prevent mistakes from happening or make them immediately detectable. Poka-Yoke eliminates human errors and ensures that products meet quality standards consistently.

14. Andon System

The Andon system is a visual tool often seen in Toyota’s production lines. What’s particularly interesting about Andon is its cultural significance in Japan—it's not just a tool for reporting problems, but also an empowering signal for workers. It enables employees to stop the production line if they detect an issue, which fosters a strong sense of ownership and responsibility for quality at every stage of production.

15. Total Productive Maintenance (TPM)

Total Productive Maintenance (TPM) is a technique that focuses on maximizing the efficiency and reliability of equipment. By involving all employees in maintenance tasks, TPM aims to prevent equipment breakdowns and reduce downtime. This helps maintain consistent product quality by ensuring that machinery is always operating at peak performance.

Partnering for Excellence in Quality Control

At Amrep Inspect, we understand the importance of quality control methods in delivering superior products. We help businesses achieve consistent quality and stay ahead of industry standards using tried-and-true QC techniques. Trust AMREP Inspect to be your partner in ensuring top-notch quality control, every step of the way. OurQuality Inspection Services guarantee that your products meet the highest standards of excellence.

Contact us today to elevate your quality control standards with AMREP Inspect!