Quality #01: How to Create and Use a QC Process Chart (QC工程表)
1. What is a QC工程表? (What is a quality control process chart?)
A quality control process chart (QC工程表) is a tool for managing the production process. By using this form to consolidate the control characteristics and control standards at each process step, you can grasp both the quality management methods and the quality status of the product.
According to the definition of the Japanese Society for Quality Control (JSQC), a quality control process chart is defined as follows: "A chart that summarizes, in diagram form, the entire chain of processes for producing or supplying a product/service, showing who, when, where, controls what and how at each stage of that process."
In English the quality control process chart is called a "Quality Control Chart", meaning a chart for managing quality. In this chart, the characteristics to be controlled and the control methods are recorded for each process step, from the moment incoming materials arrive until the product is shipped out.
This chart is also called a "QC process diagram (QC工程図)" and is an important process management tool widely used by many companies in the manufacturing industry.
2. The role of the quality control process chart (QC工程表)
The QC工程表 plays an important role in maintaining and improving product quality during production. Specifically, its roles include:
Clarifying the quality management method at each production step. → Helps operators and inspectors clearly understand what needs to be controlled and inspected.
Standardizing quality standards and inspection methods. → Minimizes differences in judgment between different employees.
Increasing transparency in the production process. → Makes it easy to trace information when a quality incident occurs.
Serving as an important reference when training new employees. → Supports fast and accurate training on how to inspect and manage.
Serving as a basis for improving the production process. → By analyzing the data from the chart, you can detect weak points and propose improvement plans.
3. The main items in a quality control process chart (QC工程表)
I will explain the content of the quality control process chart (QC工程表) using a template (Figure 1) that can be downloaded from this website.
① Process flow symbols (process symbols)
The quality control process chart (QC工程表) is used not only internally within a company to manage quality, improve operations and train employees, but can also be used to explain the company's quality management system to external partners.
The symbols in the process diagram are specified by the JIS Z8206 standard, and when these symbols are used, customers can also easily understand the content.
Table 1 below presents the basic process diagram symbols.
② Process name
A "process" is the "work" performed by machine or by hand in the factory when producing a product. In this item, you record the names of the processes in the chain, such as receiving materials, machining, assembly, inspection, packaging, shipping, etc. (Examples: soldering, screw tightening, screw-tightening inspection, etc.)
③ Control items
In the Control items section, you record the control characteristics and control standards.
Control characteristics are the factors that express the state of the product as the result of each process.
Control standards are the standards set to meet customer requirements. Usually, to guarantee quality, these standards are set stricter than the customer's requirements to account for variation in the production and inspection process.
④ Control method
In the Control method section, you clearly state the specific way each control item is managed.
To guarantee quality, the chart must be designed so that you can easily see who is controlling what, when, with which tools and under what conditions at each process step.
By clarifying the measurement method, measurement frequency, the person measuring and the person responsible, you can minimize differences in how individuals manage the process.
An example of how to fill in a quality control process chart (QC工程表)
A quality control process chart (QC工程表) with the items mentioned above will look like the figure below.
4. The QC process chart (QC工程表) and the standard work instruction (作業標準書)
Both the quality control process chart (QC工程表) and the standard work instruction (作業標準書) are documents commonly used at the production site. The QC工程表 expresses the items related to quality.
The standard work instruction clearly states the steps for performing the work, the important points to note while working, and the tools to be used, in an easy-to-understand way.
The QC工程表 is the basis for building the standard work instruction. The method of performing work at each step is consolidated into a standard procedure in order to satisfy the control items and standards in the QC工程表. Workers then perform the work according to that standard procedure to ensure the work follows the standard.
If you compare the differences between the QC工程表 and the standard work instruction, it looks like Table 2 below.
That concludes the explanation of the basic knowledge of the QC process chart, as well as how to create and use it. I hope this will be a useful reference for individuals/companies promoting QC activities.
Checklist for deploying the QC工程表 in a factory
- Clearly define each process step, and that step's inputs and outputs.
- Record control items in measurable language, avoiding vague entries like "visual inspection".
- Clarify the judgment standard: on what dimension, limit, master sample or reference photo the OK/NG decision is based.
- Record the inspection frequency: 100%, by lot, by time or by product quantity.
- Determine who is responsible for recording, confirming and handling any abnormality found.
- Link the QC工程表 with the 作業標準書, the check sheet and the traceability record so that no document says something different.
A good QC chart is not just for submitting to the customer. It must help the site understand "what to control, how, when and who is responsible".
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