Quality control is the set of activities, inspections, and methods used to verify that a product or process meets established requirements and specifications.
In the manufacturing industry, quality control helps detect deviations, reduce defects, and ensure that manufactured products meet defined industrial quality standards before reaching the customer.
To achieve this, controls can be carried out on raw materials, during the manufacturing process, or on the finished product.
In this article, we explain what quality control is, what its main types are, which tools are used, how it is carried out, and some examples of its application in the industry.
We will also look at how digitalization through a MES system can improve the management and traceability of quality controls.
What is quality control?
Quality control is the process by which a company verifies that its products, materials, and processes meet predefined quality requirements.
These requirements may relate to the dimensions of a part, the weight of a product, the temperature of a process, its physical or chemical characteristics, its performance, or any other specification established by the company, regulations, or the customer.
Control can be carried out through inspections, measurements, testing, sampling, checklists, or statistical tools such as Statistical Process Control (SPC).
Its objective is not only to detect defective products at the end of the manufacturing process. An effective quality control system makes it possible to identify deviations as early as possible, take action on the process, and prevent them from recurring.
What is quality control used for?
The main objectives of industrial quality control include:
- Ensuring that products meet specifications.
- Detecting defects and deviations during manufacturing.
- Reducing scrap, waste, and rework.
- Preventing non-conforming products from reaching the customer.
- Maintaining the stability of production processes.
- Improving product and process traceability.
- Obtaining data to analyze problems and drive continuous improvement.
For this reason, it should not be limited to a final inspection. In more advanced industrial environments, quality controls are integrated into the different stages of the production process.
Quality control vs. quality assurance: what is the difference?
Although they are related, quality control and quality assurance are not exactly the same.
| Quality Control | Quality Assurance |
|---|---|
| Checks products and processes. | Establishes processes to prevent problems. |
| Relies on inspections, measurements, and testing. | Relies on procedures, standards, and methodologies. |
| Detects deviations. | Aims to prevent them from occurring. |
| Has a primarily operational approach. | Has a preventive and systematic approach. |
In summary, quality control verifies that the results meet the requirements, while quality assurance focuses on creating the conditions necessary for those results to be consistent.
Types of quality control
There are different types of quality control depending on when and how the inspection is carried out. In manufacturing, the most common are the following.
Raw material quality control
This is carried out before materials, components, or raw materials are introduced into the production process. It may include checking:
- Dimensions.
- Weight.
- Physical or chemical characteristics.
- Visual condition.
- Supplier certificates.
- Compliance with purchasing specifications.
The objective is to prevent non-conforming materials from entering production and causing problems at later stages.
In-process quality control
In-process quality control is carried out during manufacturing. It is particularly important because it allows deviations to be detected before they affect a large volume of products.
Examples include checking dimensions during a machining process, monitoring temperature during a thermal operation, or verifying specific machine parameters.
This type of control makes it possible to take action on the process while production is underway.
Finished product quality control
This is carried out once manufacturing has been completed to verify that the product meets the requirements before it is released and delivered to the customer.
It may include visual inspections, functional tests, dimensional measurements, testing, or checks of labeling and packaging.
Although it is important, final inspection should not replace the controls carried out during the process. The earlier a deviation is detected, the lower its impact is likely to be.
Sampling quality control
Sampling quality control consists of inspecting a representative sample of a batch rather than checking every unit produced.
It helps reduce the time and resources required for inspections when 100% inspection is not necessary or feasible.
Methodologies such as AQL (Acceptable Quality Limit) are used in this area to establish sampling criteria and batch acceptance criteria.
Statistical Process Control (SPC)
SPC uses statistical methods to analyze the variability of a production process.
Unlike a one-time inspection, SPC makes it possible to monitor process performance over time and detect trends or changes that could lead to quality problems.
The tools used include control charts and capability indices such as Cp and Cpk.
Quality control tools
Quality control tools make it possible to collect, represent, and analyze data to detect problems, identify their causes, and monitor process stability.
The so-called 7 Basic Quality Tools are:
| Tool | What is it used for? |
|---|---|
| Check Sheet | Collecting data in a structured way. |
| Histogram | Analyzing data distribution. |
| Pareto Chart | Identifying and prioritizing the most frequent problems. |
| Ishikawa Diagram | Analyzing the possible causes of a problem. |
| Scatter Diagram | Analyzing the relationship between two variables. |
| Stratification | Separating data into different categories. |
| Control Chart | Monitoring process stability. |
These tools do not have to be used in isolation. For example, a company may use a check sheet to collect data, a Pareto chart to identify the most relevant problem, and an Ishikawa diagram to analyze its possible causes.
In addition to these tools, industrial environments use methodologies such as SPC, FMEA, the 5 Whys, 8D, root cause analysis, and sampling plans.
How is quality control carried out?
Although each production process requires specific controls, the quality control process generally follows a similar structure.
1. Define the quality requirements
First, it is necessary to establish what the product or process must meet. These requirements may come from internal specifications, drawings, regulations, or customer requirements.
2. Determine what needs to be controlled
The critical characteristics of the product or process are identified, such as dimensions, temperature, pressure, weight, composition, or performance.
3. Define how the control will be carried out
For each characteristic, the inspection method, measuring instrument, frequency, sample size, responsible person, and acceptance criteria are established.
These elements can be included in a quality control plan, which helps structure and standardize inspections.
4. Perform and record inspections
Controls are carried out according to the established criteria, and the results obtained are recorded.
5. Take action on deviations
If a result is outside the specifications, actions such as segregating the product, adjusting the process, opening a non-conformity, or performing a root cause analysis may be required.
6. Analyze the results
The data collected makes it possible to identify trends, recurring problems, and opportunities for improvement.
In this way, quality control becomes a source of information for improving the production process rather than simply an inspection activity.
What quality indicators are used to measure quality?
To determine whether a quality control system is working correctly, it is necessary to measure its results.
Some of the most widely used industrial quality KPIs include:
- Rejection rate.
- Scrap.
- Rework rate.
- First Pass Yield (FPY).
- First Time Quality (FTQ).
- Number of non-conformities.
- Customer complaints.
- Cp and Cpk indices.
- Cost of poor quality.
These indicators make it possible to identify trends and assess the impact of improvement actions.
Digitalized quality control: what does a MES bring to the table?
Quality control can be managed using paper documents, spreadsheets, and separate records. However, this approach makes it more difficult to centralize information and can increase the risk of manual errors.
A MES system makes it possible to digitize quality controls and connect their results with production.
The main applications of industrial quality control software such as MapexQM include:
- Defining and executing control plans.
- Digital recording of inspections and measurements.
- Checklist management.
- Traceability of results.
- Statistical process control.
- Non-conformity management.
- Analysis of quality indicators.
- Real-time access to information.
For example, a measurement taken during manufacturing can be linked to the production order, batch, machine, and time at which it was performed.
This provides a more comprehensive view of the process and makes it possible to act earlier on deviations, reducing the risk of generating large quantities of non-conforming products.
FAQs about quality control
What is the objective of quality control?
The objective of quality control is to verify that products and processes meet established requirements, detect deviations, and reduce the occurrence of defective products, rework, and waste.
What are the types of quality control?
The main types are raw material quality control, in-process quality control, finished product quality control, sampling quality control, and SPC.
What are the 7 quality control tools?
The seven basic quality tools are the check sheet, histogram, Pareto chart, Ishikawa diagram, scatter diagram, stratification, and control chart.
How is quality control carried out?
Quality control begins by defining the requirements that the product or process must meet. The characteristics that need to be controlled, the inspection method, frequency, and acceptance criteria are then determined. Finally, the results are recorded, deviations are managed, and the data is analyzed to improve the process.
What is the difference between quality control and quality assurance?
Quality control uses inspections, measurements, and testing to verify that results meet the requirements. Quality assurance takes a more preventive approach and aims to establish processes and standards that reduce the likelihood of problems occurring.
What is quality control in manufacturing?
It is the set of controls carried out on materials, processes, and products to ensure that manufacturing meets the established specifications and that deviations are detected and managed before they affect the customer.
How does a MES help with quality control?
A MES makes it possible to digitize inspections, record measurements, manage control plans, connect quality data with production, apply SPC, and improve the traceability of results. This enables faster, data-driven quality management.
