How to judge the quality of a workshop’s assembly line?
The key is to prevent errors from happening.
What is “error proofing”?
Poka-YOKE is called POKA-YOKE in Japanese and Error Proof or Fool Proof in English.
Why is Japanese mentioned here? Friends who work in the automotive industry or manufacturing industry must know or have heard of the Toyota Production System (TPS) of Toyota Motor Corporation.
The concept of POKA-YOKE was first coined by Shingo Shingo, a Japanese quality management expert and founder of the TOYOTA Production System, and developed into a tool to achieve zero defects and ultimately eliminate quality inspection.
Literally, poka-yoke means preventing errors from happening. To truly understand poka-yoke, let’s first look at “errors” and why they happen.
“Errors” cause deviations from expectations, which may eventually lead to defects, and a large part of the reason is that people are negligent, unconscious, etc.
In the manufacturing industry, our biggest concern is the occurrence of product defects. “Man, machine, material, method, environment” can all contribute to defects.
Human errors are inevitable and cannot be completely avoided. These errors can also impact machines, materials, methods, environment, and measurements, as people’s emotions are not always stable and can lead to mistakes such as using the wrong material.
As a result, the concept of “error prevention” emerged, with a significant focus on combating human errors. We generally don’t discuss equipment and material errors in the same context.
1. What are the causes of human errors?
Forgetting, misinterpretation, misidentification, beginner mistakes, deliberate mistakes, careless mistakes, complacency errors, errors due to lack of standards, unintentional mistakes, and deliberate mistakes.
1. Forgetting: When we are not focused on something, we are likely to forget it.
2. Understanding errors: We often interpret new information based on our past experiences.
3. Identification errors: Errors can occur if we look too quickly, don’t see clearly, or don’t pay close attention.
4. Novice errors: Mistakes caused by lack of experience; for example, new employees generally make more mistakes than experienced employees.
5. Intentional errors: Errors made by choosing not to follow certain rules at a specific time, such as running a red light.
6. Inadvertent errors: Mistakes caused by absent-mindedness, for instance, unconsciously crossing the street without noticing the red light.
7. Inertia errors: Errors resulting from slow judgment or action, such as braking too slowly.
8. Errors caused by lack of standards: Without rules, there will be disorder.
9. Accidental errors: Mistakes resulting from unforeseen situations, like a sudden failure of certain inspection equipment.
10. Deliberate Error: Intentional human error, which is a negative trait.
2. What consequences do these errors bring to production?
There are many examples of errors that occur during the production process.
No matter what parts are produced, these errors may bring the following consequences to production:
a. Missing a process
b. Operation error
c. Workpiece setting error
d. Missing parts
e. Using the wrong part
f. Workpiece processing error
g. Misoperation
h. Adjustment error
i. Improper equipment parameters
j. Improper fixture
If the cause and consequence of the error are linked, we get the following figure.
After analyzing the causes and consequences, we should start to solve them.
3. Countermeasures and ideas for error prevention
For a long time, major companies have relied on “training and punishment” as the primary measures to prevent human errors. Operators underwent extensive training, and managers emphasized the importance of being serious, hard-working, and quality-conscious. When errors occurred, wages and bonuses were often deducted as a form of punishment. However, it is challenging to entirely eliminate errors caused by human negligence or forgetfulness. Therefore, the error prevention method of “training and punishment” has not been entirely successful. The new error prevention method, POKA-YOKE, involves using specific equipment or methods to help operators easily detect defects during operation or prevent defects after operating errors. This allows operators to self-check and makes errors more apparent.
Before starting, it is still necessary to emphasize several principles of error prevention:
1. Avoid adding to the workload of operators to ensure smooth operations.
2. Consider costs and avoid pursuing expensive things without considering their actual effectiveness.
3. Provide real-time feedback whenever possible.
4. Ten major error prevention principles and their applications
From methodology to execution, we have 10 major error prevention principles and their applications.
1. Root elimination principle
The causes of errors will be eliminated from the root to avoid errors.
The picture above is a plastic panel of a gear mechanism.
A bulge and groove are deliberately designed on the panel and base to avoid the situation where the plastic panel is installed upside down from the design level.
2. Safety principle
Two or more actions must be performed together or in sequence to complete the work.
Many workers involved in stamping operations fail to remove their hands or fingers in time during the stamping process, which can lead to serious injuries. The image above illustrates that the stamping equipment will only function when both hands simultaneously press the button. By adding protective grating underneath the mold, an extra layer of safety can be provided, offering double protection.
3. Automatic principle
Use various optical, electrical, mechanical, and chemical principles to control or prompt specific actions to prevent errors.
If the installation is not in place, the sensor will transmit the signal to the terminal and issue a reminder in the form of a whistle, flashing light, and vibration.
4. Compliance principle
By verifying the consistency of the action, errors can be avoided. This example closely resembles the root-cutting principle. The screw cover is intended to snap on one side and extend on the other; the corresponding body is also designed to have one high and one low side and can only be installed in one direction.
5. Sequential principle
To avoid reversing the order or process of work, you can arrange it in the order of numbers.
The above is a barcode that will be printed only after passing the inspection. By first inspecting and then issuing the barcode, we can avoid missing the inspection process.
6. Isolation principle
Separate different areas to protect certain areas and avoid errors.
The image above depicts the laser weakening equipment for the instrument panel. This equipment will automatically detect the actual output status of the process. If it is found to be unqualified, the product will not be removed and will be placed in a separate area designated for unqualified machined products.
7. Copy principle
If the same work needs to be done more than twice, it is completed by “copying.”
The picture above displays both the left and right custom cnc parts of the windshield. They are designed identically, not mirrored. Through continuous optimization, the number of parts has been reduced, making it easier to manage and reducing the possibility of errors.
8. Layer principle
To avoid doing different tasks incorrectly, try to distinguish them.
There are differences in details between high-end and low-end parts, which is convenient for operators to distinguish and assemble later.
9. Warning principle
If an abnormal phenomenon occurs, a warning can be indicated by obvious signs or sound and light. This is commonly used in cars. For instance, when the speed is too high or the seat belt is not fastened, an alarm will be triggered (with a light and voice reminder).
10. Mitigation principle
Use various methods to reduce the damage caused by errors.
The cardboard separators are changed to blister tray packaging, and protective pads are added between layers to prevent paint from bumping.
If we do not pay attention to error prevention on the production line of the CNC production workshop, it will also lead to irreversible and serious consequences:
If a CNC machine is not properly calibrated, it may produce parts that do not meet the specified dimensions, leading to defective products that cannot be used or sold.
Errors in the cnc manufacturing process can result in wasted materials and the need for rework, significantly increasing production costs.
If a critical error is discovered late in the production process, it can cause significant delays as the faulty parts need to be remade, disrupting the entire production schedule.
Safety Hazards:
Improperly machined parts can pose safety risks if they are used in critical applications, such as aerospace or automotive components, potentially leading to accidents or failures.
Damage to Equipment:
Errors in programming or setup can cause collisions between the machine tool and the workpiece, damaging expensive CNC equipment and leading to costly repairs and downtime.
Reputation Damage:
Consistently producing low-quality or defective cnc parts can damage a company’s reputation, leading to loss of customers and business opportunities.
Post time: May-29-2024