The causes of errors can basically be classified into three categories, namely human reasons, method reasons and equipment reasons. Among them, human errors account for a large proportion. This is something that many quality scholars and company management have recognized very early.
For a long time, the main measure used by major companies to prevent human errors is "training and punishment", that is, extensive training for operators, and managers often advise operators to work more seriously and hard. Indeed, through training , can avoid a considerable number of human errors, such as errors caused by unfamiliarity with the process/operation, lack of work experience, and lack of appropriate operation guidance. However, errors caused by human negligence, forgetfulness, etc. are difficult to prevent.
Therefore, manufacturing companies have extensive and urgent needs for error-proofing technology. The concept of "error-proofing" is of great practical significance to product design and manufacturing process design. Many factories in Japan use a large number of very simple and practical error-proofing devices and will After hundreds of repeated applications and long-term persistence day after day, a quality miracle occurred: the number of defective parts per million (PPM) dropped to single digits or even zero, and product quality improved significantly.
This article mainly introduces the five methods and five principles of error prevention.
01 Technical application of error-proofing devices on equipment
In the manufacturing process of auto parts, the technical applications of error-proofing devices on equipment mainly include the following categories:
(1) Qualitative error-proofing Through image recognition technology, photoelectric , limit, proximity switch logic control technology, etc. to complete error prevention, such as:
- instant photo comparison: to distinguish whether the direction of assembly parts is correct; sensor induction detection: machining automatic line according to the appearance of different product models changes, the sensor will feed back the sensed information to the subsequent processing processes, so that the subsequent processes can call the corresponding processing procedures and implement the corresponding processing content;
- Hard probe: detects different models of parts and implements different assembly or processing Process, such as using a probe to detect the shape of the part, implementing different assemblies, such as using a hard probe to detect the cylinder bore, distinguishing 3.0L or 3.4L cylinder block;
- guide stop: distinguishing the conveying guide of the part;
- grating error-proofing: controls whether the workpiece is placed in place through the detection and control of the grating;
- fixture error-proofing: controls whether the assembly parts are placed in place on the fixture to prevent errors.
(2) quantitative error-proofing achieves the purpose of error-proofing through measurement probe induction or gas-to-electric conversion measurement technology (gas flow converted into electricity) , such as: ruby probe detection data feedback: detection through ruby probe The inner diameter of the pressed valve seat ring is used to distinguish whether the part is a 3.0L or 3.1L auto parts cylinder head ;
leakage test: online testing of auto parts such as cylinder heads, cylinder oil passages and water passages, etc., to control leakage The parts flow into the next process; on-line inspection tool diameter measurement: This is widely used in the station after boring and reaming in the machining automatic line, achieving 100% control of the emergence of unqualified products; torque control: automotive parts such as many bolts The degree of tightening of the fixation is controlled by a torque gun.
02 Poka-proofing of materials
Poka-proofing of workpiece holding equipment: Poka-proofing technology is implemented for the finished product holding, and the placement is directional, preventing the workpieces from colliding with each other, and ensuring the surface quality of the processed parts; color mark error-proofing: The racks for holding parts in the assembly area use color coding to prevent mistakes.
03 Manual error proofing
(1) Establish standard operation SOS: For example, finished products, products to be processed, products to be processed, material waste, work waste and other off-line parts during processing must be immediately hung up according to the handling specifications of various types of parts. Color identification labels, tool settings for normal use durability, error-proofing devices to establish TPM, PM maintenance systems, etc.;
(3) Workpiece visual inspection and measurement Poka-yoke: Operators visually inspect and measure the workpiece during processing according to the inspection frequency and defects in the blank itself, remove the unqualified workpieces, and take them offline at this station.
Levels of poka-yoke technology
According to the effect of poka-yoke, poka-yoke technology can be divided into the following three levels:
(1) Poka-yoke without manufacturing defects, that is, it is impossible to create bad parts, and the number of parts that may be damaged is zero ;
(2) Poka-yoke that does not pass defects, that is, it is impossible to pass bad parts to the next work station;
(3) Poka-yoke that does not accept defects, that is, subsequent work stations do not accept bad parts.
The ideal state of error-proofing technology is error-proofing that does not create defects. This is the most active, economical, predictable and error-preventing control technology. For example, error-proofing such as probe detection, guide limit, and sensor induction before processing can achieve the goal of avoiding manufacturing defects.
Verification of the error-proofing device
When using a new error-proofing device, the functional accuracy must be verified to prevent error rates. It can only be used if it has passed the verification of PPAP (Production Part Approval Process) method.
Verification of the error-proofing system
The normal operation of the error-proofing system is a process of implementation, verification, and maintenance. In its application, it must be ensured:
(1) Confirm that the error-proofing system is operating normally. In actual production, the error-proofing device must be inspected regularly Maintenance and verification. For example: for leakage detection of cylinder blocks and cylinder heads, the leakage testing machine must verify and verify the leakage of workpieces every day; similarly, various error-proofing devices on the production line need to undergo regular maintenance and verification to confirm that the error-proofing function operates correctly. .
(2) Confirm that human factors are under control
For the verification process of the error-proofing system, the verification inspection records must be archived. If there are errors, necessary measures must be taken for standardized corrections; the operator who implements error-proofing verification must ensure that the operator After training and training content records have been archived; ensure that the error-proofing system achieves the expected inspection capabilities, and the verification process is effectively under control according to the plan.
04 Five types of error prevention methods and five principles
There are 5 types of error prevention methods:
Failure - safety device, sensor amplification, redundancy, countdown and special inspection, control device.
is introduced as follows:
1. failure-safety device (Fail-safe devices)
interlocking sequence: ensures that the next operation cannot start before the previous operation is successfully completed;
early warning and interruption: will appear during the process Activated when the execution situation occurs; all completion signal: will be activated after all remedial measures are completed;
anti-fool workpiece clamping device : ensures that part of the work can only be fixed in one position;
limit mechanical device : is used to ensure that tools cannot exceed a certain position or number.
2. sensor amplification: is used to enhance human vision, hearing, smell, touch, taste and muscle strength, such as: optical amplification, multiple visual and auditory signals, remote control to monitor dangerous processes, and the use of pictures instead of text, etc.
3. redundant : used as an additional measure to ensure quality.
Multiple confirmation codes : For example, barcodes and color codes to prevent product confusion
Redundant measures and approvals : Two people are required to work independently;
Audit review and inspection procedures: Assurance plans are tracked;
Verification design : Utilize special designs, such as viewing holes, to determine whether a product or process is performing satisfactorily;
composite test bench : can inspect many characteristics, such as those that occur on high-speed production lines.
4. Countdown
organizes the process of reading out data and information to keep wrong procedures in parallel to check each step, such as spacecraft launch. It is also effectively used in surgical operations and welding.
5. Special inspection and control device : such as a computer checking credit accounts, invalid accounts are rejected, and timely feedback is provided.
has 5 error prevention principles:
Elimination (Elimination) : Eliminate possible errors in the process and products are redesigned;
Replacement (Replacement) : It is a change into a more reliable process;
Simplify (Facilitation): makes the process operation simpler and more reliable;
Detection (Detection): allows errors to be discovered before the next step;
eases (Mitigation): will make errors The impact is reduced to a minimum.
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