How to effectively conduct PFMEA cause analysis?

Date：2022-06-10 15:55:00Views：940

The failure cause analysis method shall identify all process characteristics and all variation sources of process characteristics in the cause analysis. However, the reasons for PFMEA in most factories are "illegal operation, failure to operate according to the operation instructions, new employees, operational errors, lack of training, lack of staff skills, poor raw materials, equipment damage, etc." while the preventive measures are "four major strengthening", "strengthening training, strengthening control, strengthening inspection and strengthening management".

How to effectively conduct PFMEA cause analysis? It should be carried out from the following aspects:

1. The accuracy and status of hardware facilities, including the accuracy and status of equipment, tooling, molds, cutters, tools, etc. for example, if the cutters are worn in the processing process, it is impossible for the equipment not to deteriorate or wear, the service frequency should be counted for life management, and the accuracy measurement can also be carried out regularly to detect the degree of accuracy decline. Generally, it can be carried out through predictive maintenance, but attention should be paid, We generally assume that the material design of the tool is reasonable, and do not consider the excessive wear caused by the poor material of the tool, which should be considered by the equipment MFMEA; The status of the equipment shall maintain the basic conditions of the equipment, such as oil pipe blockage, oil leakage, etc., which shall be controlled through preventive maintenance such as cleaning, refueling, fastening, etc. The initial failure of the equipment is poor design, not considered by PFMEA. It is more considered to be poor operation, poor spot inspection and poor deterioration. The accuracy and status of the equipment are improved through preventive and predictive maintenance.

2. Dynamic process parameters, such as voltage, current, temperature, etc., are generally controlled through program processing. For example, temperature 390 ℃± 10 ℃, 390 ℃ is the setting parameter, and ± 10 ℃ is the display fluctuation. The first step is process design, and the parameter selection is determined through experience or DOE experimental design. The second step is process control, and the alarm or shutdown is given after equipment detection exceeds the tolerance. At present, many equipment do not need parameter setting, The set procedures (voltage, current, temperature, etc.) can be introduced into production. Employees only need to adjust the correct procedures in their daily operation, so as to reduce human errors. Of course, the more advanced equipment has a self-learning function. When the process parameters are close to the upper and lower limits, they will automatically adjust, and self-learn and optimize the process parameters according to the qualified status of the products, such as the rolling process in the steel plant.

3. Static process parameters refer to the parameters that will not change during processing after setting in the production process. For example, if the speed of the grinding wheel on the grinder will not change after setting, they do not need to be considered as a variation source. The speed and time of the equipment will be managed in the process design as a static process. If the injection molding holding time is 3 seconds (s), the tolerance cannot be met, or the injection molding holding time is set at 2~3 seconds (s).

4. Auxiliary variables and auxiliary system status, such as clamping tooling hydraulic pressure, cutting fluid pressure, temperature, cleanliness, etc., are the conditions for the normal operation of the equipment. They are generally controlled in the daily spot inspection of the equipment. For example, the air pressure is 0.5~0.7mpa, which is controlled within a certain range through the air pressure regulating valve. Therefore, it cannot be written as 0.6 ± 0.1MPa. Of course, it does not rule out that some equipment can set the air pressure, which will become a dynamic process.

5. Operation essentials: do not take the operator's knowledge and skills as parameters or reasons, but rather record the operator's possible errors, and of course, do not take strengthening training as a preventive measure. For example, when screwing, the reason is not "illegal operation", but "the torque gun is not vertical". We believe that it is normal for people to make mistakes. Obviously, only "training and punishment" can not solve the problem. Therefore, the error prevention method is adopted in the process design. For different operational errors, tangible error prevention, orderly error prevention, counting error prevention and information enhanced error prevention can be selected. Do not take lack of training, new employees and unskilled employees as the reasons for PFMEA. It is a systematic reason. If employees of a factory go to work without training, they will die.

6. Environmental variables, such as ambient temperature, humidity and air cleanliness, are generally controlled through infrastructure. Don't forget that the positioning and identification of 5S are also very important. For example, if you take the wrong material, the failure is due to the lack of identification and location.

7. The characteristics of incoming products, such as machining allowance, positioning hole / surface accuracy, material metallography / hardness / humidity (water content), etc., are generally transferred to the previous process for control. However, in the process of processing, the problems in the line side storage process must be considered, such as the material deformation caused by the lack of protection in the packaging box.