RICOH manufacturing DX Practical Lab
What is visual inspection?
The causes of defective products and 6 countermeasures.
Visual inspection are inspections carried on by human workers, to detect manufacturing mistakes. Visual inspections are necessary to prevent product defects from being missed, but many people may be wondering what exactly are the types of visual inspections and what kind of work is involved.
This article will therefore explain in detail the types of visual inspections, causes of missed defects, and countermeasures.
“Visual inspection“ refers to the process of examining a product with human eyes and intelligence. With the introduction of the latest technologies such as AI and IoT, inspections by machines and cameras are becoming more and more common in manufacturing plants.
Nevertheless, these technologies do not guarantee perfect inspections when it comes to detecting fine scratches, printing errors, or contamination of foreign substances. In these cases, it becomes necessary to introduce human workers to conduct a visual inspection.
Since detecting scratches, colors, and different parts can be extremely hard to automate, it is important to examine them thoroughly through visual inspection.
There are various types of visual inspections. Here is a detailed explanation of each type of visual inspection: in-line inspection, off-line inspection, total inspection, and sampling inspection.
Inline inspections are inspections that are incorporated into the manufacturing line to check for defective product during the production process. The advantage of this inspection is that it can be performed without stopping the flow of the production line, since the condition of the product is checked during the manufacturing process. This inspection is fast and suitable for total inspections; however, it is time-consuming and costly in terms of preparing the equipment and staffing.
Off-line inspection is performed in a process separate from the production line and has the advantage of being even more precise than an in-line inspection. In addition to being suitable for spot checks, another major advantage of off-line inspection is that it does not involve a flow of work, allowing more time for inspections. However, it is not suitable for total inspection. In addition, the skill of inspectors tends to vary, and labor costs can be high.
A total inspection involves examining all manufactured parts and products. Especially for products such as food and medical products that must not carry any defects or deficiencies, a total inspection is conducted for a reliable quality. Although the quality of all parts and products can be guaranteed and the risk of outflow of defective products can be reduced, the disadvantage of this inspection is that it requires significant labor and time, and it is not suitable for testing fracture or endurance.
Sampling inspection is a method where a random product is selected as a sample from a massive group of target products to be inspected. Since a pass/fail decision is made on a lot-by-lot basis, the time and effort required to prevent defective items may be minimized. In addition, since multiple items can be inspected in this method, it is also suitable for destructive inspections and endurance inspections. However, it does not guarantee the quality of all products perfectly as it only inspects sampled items. This leads to the disadvantage of missing a certain number of defects.
What specific tasks are included in a visual inspection? This part outlines the processes of visual inspection.
Shape and structure inspections are usually performed immediately after the assembly process. It is also mainly performed on functionality-oriented products to ensure that parts are not made with a shape or structure that differs from the standard specifications.
The reason to why the shape and structure inspection is conducted after the assembly is because products with wrong shapes and structures may be produced due to human errors or malfunctions in equipment in the production line.
In a production line that includes manual jobs, there is a risk of parts with substandard shapes and structures being produced due to human errors. It is common for defects in shape and structure to not be covered by warranty, so it is crucial for the manufacturer to inspect them thoroughly.
Surface inspection examines the surface of a product for scratches, chips, or discoloration. In most cases, this inspection is performed by companies that manufacture plastic products, components, and electrical appliances.
Plastic products and parts tend to get scratched easily depending on how they are handled, so it is necessary to conduct a detailed inspection. Some products are inspected in a fairly fine level of detail, to the point that the surface shape is checked to the nearest 0.1 mm.
The final inspection is a crucial last visual check of product quality. This inspection is generally performed at the end of the production line to ensure that there are no problems, before the product is released to the market, and to examine the overall quality of the product. This inspection includes the checking of the final condition, the scratches, and any other operational defects.
Conducting thorough inspections in this step is crucial, as neglecting final inspections could lead to defective products entering the market causing a damage in the company’s public trust. Furthermore, items that are found to have failed the final inspection will be discarded as a defective product.
So why do defects get missed during visual inspection? We have picked up four main causes for this.
In a manufacturing site where the inspection environment is not well maintained, there is a risk of missing defects due to inadequate inspections. An example of an unmaintained inspection environment could include areas without proper lighting. As mentioned above, visual inspection is an inspection in which products are checked by human eyes, so it is necessary to create an environment in which inspections can be performed properly.
Visual inspections, which are performed by human eyes, require careful management of the inspectors' mental and physical condition. If inspectors are fatigued, they are more likely to overlook defects, resulting in the outflow of defective products. To prevent inspectors from being burdened by their physical and mental conditions, it is important to listen to the workers regularly, and to create an appropriate inspection environment by introducing systems that enable speedy inspections and so on.
Insufficient training of inspectors can lead to overlooking defects. Visual inspections tend to vary from inspector to inspector, and even if new inspectors are hired, it takes time and money to train them until they become full-fledged inspectors. In addition, an increasing number of companies are hiring foreign technical intern trainees, but the disadvantage of the time and effort required to train them due to cultural and language differences is a major issue.
Lack of manpower is another reason why defects are missed during visual inspections. When there is a shortage of labor, the workload on a single inspector increase, placing a heavy mental and physical burden on the inspector. This leads to a vicious cycle of increased workload, increased mental and physical discomfort, and inability to perform accurate inspections.
Based on the causes of missed defects in visual inspections, here we will consider countermeasures to prevent missed defects.
The following seven points can be cited as the main countermeasures.
Let us explain in detail what each of the above means.
First, it is necessary to review whether the environment for visual inspections is in place. Since visual inspections are performed through eyes, it is advisable to pay attention to the lighting facilities.
Check the inspection environment to make sure that it is appropriately lighten, not too bright and not too dark. If you are not sure how much illumination or brightness should be used, it is recommended to refer to the factory illumination standards defined in the JIS standard.
Although an increasing number of companies are increasing inspection speed to improve work efficiency, it is also important not to place too much emphasis on speed.
If you focus solely on inspection speed, the quality of inspections will deteriorate, and defects may be easily overlooked. The key is how to conduct visual inspections efficiently without lowering the quality of inspections.
To reduce the burden on inspectors, allow frequent breaks. If you are performing visual inspections continuously for a long period of time, eye strain will naturally reduce the worker’s concentration, allowing them to pass on defective products.
We recommend you allow a break of 10 to 15 minutes every two hours. It is also important to create an environment in which you can immediately assist the worker in the event of a sudden illness or other vacancy.
Creating a written standard in advance is another way to prevent defects from being overlooked. A written standard describes inspection criteria such as work content, defect items, measurement methods, etc., to prevent quality variations.
Clarifying the inspection standards helps ensure uniform quality. Whenever additions or updates to the written standards occur, they should be shared with all inspectors.
One way to prevent missing defective items and improve work efficiency is to create samples. Creating samples is one way to prevent missing defective items and improve work efficiency. It is advisable to prepare samples to objectively determine which items are good and which are not.
In particular, the limit sample, a sample on the borderline between good and defective products, is an important criterion for judgment when you are in doubt about whether a product is acceptable or not in terms of quality. Since judgment may be influenced by one's physical condition or preconceptions at the time, preparing samples will ensure that the quality of the product remains constant and is not influenced by one's physical condition or preconceptions.
One measure to prevent defects from being missed during visual inspections is to implement a quality control system. A quality control system supports the improvement of product and service quality.
For example, by importing inspection-related data directly from inspection equipment into a quality control system, data input errors and falsification of results can be prevented. Since visual inspection is a human-centered process, human error inevitably occurs. The major advantage of introducing a quality control system is to cover this with specialized equipment and IT systems.
In addition to preventing human error, a quality control system can also easily correct additions and changes to inspection items, leading to improved work efficiency.
For your reference, we have picked up some recommended quality control systems below.
RICOH SC-10A
RICOH SC-10A work support camera system is an image recognition camera that automatically checks the assembly status of similar parts, missing items, and correct work order during the assembly process. It records all images of work results, including serial numbers of parts and actual work time. In addition to preventing defects from being missed, it can also be used for work analysis and traceability since it collects both assembly results and performance results in real time.
RICOH SC-20
RICOH SC-20 work inspection camera inspects for work errors in the assembly process, allowing quality to be checked in real time during the work, and allows batch inspections after the work is completed. It can be easily installed without the need of a PC, making it easy for enterprises to start digital inspections. This system is recommended for companies in which visual inspections inevitably result in omissions or inconsistent quality.
Visual inspections, in which products are checked for defects with the worker’s eyes, are easily affected by the inspector's physical condition, preconceptions, and the inspection environment, making it easy for human error to occur, such as missing defects. There are various measures that can be taken to prevent defects from being missed, such as improving the inspection environment, giving inspectors adequate rest, and preparing standards and samples.
If you want to improve work efficiency and prevent defects from being passed on, we recommend the introduction of RICOH’S quality control system which assists visual inspections. RICOH offers the “Work Inspection Camera RICOH SC-20” to assist visual inspection, so please check it out.
