FMEA analysis

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FMEA analysis
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FMEA analysis (Failure Mode and Effect (Critical) Analysis - FMEA, FMECA) is a method of analyzing the causes and effects of defects, which was developed in the US in the 1950s. Its purpose was to prevent defects occurring in products already at the stage of the drawing board. Early error prevention was particularly important in the aerospace, aerospace and military industries. As shown by the analysis, 3/4 defects in production and use can be prevented at the design stage.

The method was declassified (as a military method), and then popularized in the US and Europe, as well as on other continents. First, it was used in high-tech industries, but later turned out to be of great benefit also in other sectors of the economy, including services (to detect threats exposing the client, e.g. to financial losses, inappropriate treatment.) However, it should be noted that for services, the Servqual method can give better results. Since the 1990s, FMEA has also been used as a tool for process improvement (not only manufacturing) as well as a simple risk management tool. This method is most often used in the production of highly complex products, e.g. in the automotive industry, but despite the passage of more than half a century since its development, FMEA is still finding new applications. The method can be easily computerized and used in semi-automatic mode using MRP / ERP systems.

The goals of the FMEA analysis are consistent with the principle of "continuous improvement". Thanks to the use of the FMEA method it is possible to subject the product or process to subsequent analyzes, and subsequently to introduce on the basis of the obtained results improvement measures (ie all kinds of corrections, new solutions) that will contribute to the effective elimination of the sources of defects. Analyzes can be carried out for whole products, individual components or construction elements of a given product, as well as for the entire technological process or any of its operations. Most often, however, the FMEA analysis concerns a product / construction or a production process.

The field of application of the FMEA method

  1. Product optimization
    • at the design stage - the best time for analysis, it is possible to achieve the best results thanks to the ease of making changes in the product located only on the drawing board (or rather in the computer),
    • before implementation for production - limited effects due to limitations imposed by the prepared product design. However, it is still better to use FMEA than not to use it.
    • later stages - very limited effects due to the fact that almost all parameters have already been determined. It is worth considering using FMEA before the next product update.
  2. Process optimization (process FMEA or PFMEA - Process FMEA)
    • implementation of a new process - a very good moment, but it happens very rarely in the company,
    • improvement of the existing process - a very good moment, because improvement of the process is not as limited as the improvement of the product.
  3. Risk management
    • as a simple method of identification and risk management. It may be sufficient for small and medium enterprises.

The basic stages of FMEA analysis

  1. Stage 1. Preparation
    • Defining the goals of the study
    • Creating a team
    • Determining the scope of the analysis
    • Functional decomposition
    • Collecting data
  2. Stage 2. Analysis
    • Qualitative analysis
    • Quantitative analysis
    • Piling corrective or preventive actions
    • Implementation of activities and their supervision

The most important steps are discussed below:

Determining the scope of the FMEA analysis

The scope of the analysis is crucial for the obtained results. If the analysis is limited to a few elements, it may not bring anything new. However, if the scope is too large, the analysis time and its cost will be very high. You probably do not need to analyze parts that are well known from previous products, unless they may be incompatible with new solutions. The level of decomposition should also be considered. Very deep decomposition is not always the right prospect for analysis, because it can override problems resulting from relationships between elements of the product.

Each analysis is carried out under defined conditions. The team should decide how to adopt the level of environmental variables, e.g. availability of nominal power, simultaneous number of defects (usually 1 at a time), availability of necessary resources at the entrance, the ability to receive process results.

Functional decomposition

The analyzed object should be divided into elements. In the case of a product, they are parts or even raw materials. In the case of a process, these are tasks. FMEA is a very detailed analysis, therefore it is necessary to divide the object into small parts. For each element, you should collect data on, among others:

  • the number of defects,
  • types of defects,
  • known problems (e.g. based on literature),
  • restrictions of use (e.g. temperature, humidity).

Qualitative analysis

Qualitative analysis focuses on possible defects, their causes and consequences:

  • defect - unfavorable condition of the tested element,
  • Cause - what must happen for the defect to occur. There may be many reasons for one drawback. They should be analyzed as separate cases.
  • the result - what will happen if the defect occurs (not the reason! - frequent error). There may be a number of short and long-term effects. Everyone should be analyzed separately.

The set: defect + cause + effect creates a failure mode. All information should be recorded in the table (see examples below).

FMEA analysis - quantitative

Quantitative analysis refers to three variables:

  • (P) Probability of occurrence (related to the cause of the defect)
  • (D) Difficulty of detection (related to the disadvantage itself)
  • (S) Meaning of effect (related to effect)

The product of these three variables gives the overall result of the analyzed set \(R = P \cdot D \cdot S\)

Each variable is evaluated on a scale of 1 to 10, with 10 being the maximum. These variables, however, are not clearly defined and require individual approach each time. A company using FMEA should define its own evaluation tables that will help in assigning evaluations. An example of such a table is below:

Evaluation of the significance of the defect effect

Evaluation Evaluation criteria
1

Small damage that can not cause any real effect in the operation of the device or system, nor can it affect the technological process or assembly operations

2,3

a small defect causing only slight customer dissatisfaction that is likely to have a slight deterioration in the operation of the device or system; slight modifications may be necessary in the technological or assembly process

4,5,6

damage that causes some customer dissatisfaction. The customer experiences discomfort or is upset with this damage (e.g. the engine does not light for a long time, the compressor breaks down, the window is not tight). The customer notices deterioration of the device or subsystem operation. It may cause unplanned processing, repair or damage to the equipment

7,8

a high degree of customer dissatisfaction caused by the nature of such damage as an inoperative vehicle or its subsystems. The damage does not affect the safe operation of the product or applicable regulations. May cause serious disturbances in subsequent technological or assembly operations, requires major modifications or poses a threat to the machine operator in the machining or assembly process

9,10

damage violates operational safety or applicable regulations

Corrective or preventive actions in FMEA

There are three possible directions for improvement:

  • reducing the likelihood
  • improved detection of defects
  • reduction of the significance of the effect.

The choice depends on the type and complexity of the defect and the product. Success is closely related to the experience and competence of team members using the method. While implementing corrective or preventive actions in FMEA, it should be remembered that they should be constantly supervised and their effects should be verified by the FMEA method.

An example of FMEA analysis of a product

FMEA analysis for a PC computer

Element Defect Effect Cause P S D R Corrective action
system unit system does not load computer does not work wrong system program 3 10 9 270 program exchange
monitor wrong colors green and red not available incorrect graphics card 2 3 2 12 check the card and replace
hard disk drive unreadable loss of data bad disk installation 4 8 10 320 installation of the correct drive
keyboard 4 2 5 40 blocking impossible transmission of data incorrect connection 4 2 5 40 keyboard test, connections check
printer printout errors print can not be read damage to the driver 6 3 3 54 replacement of the controller
Disk drive read errors can not store data dirty drive or drive mechanism 3 5 2 30 cleaning mechanism or disk replacement
expansion card expansion card error unused card options badly connected card 7 1 8 56 testing connections, proper connection after the test

The example given is very simplified and in practice would have to be significantly extended. With a few dozen or even several hundred potential disadvantages, it is useful to use the Pareto method to identify those that should be removed at the earliest.

FMEA analysis for a bath mixer with a shower

Element Defect Effect Cause P S D R Corrective action
body leak leaked bad cast, micropores 5 10 4 200 battery replacement
wrong threads mounting difficulties poor machine positioning 3 1 1 3 body replacement
head punching spilling the bathroom too small thread 2 10 8 160 head replacement
leakage leakage bad gasket 3 8 6 144 gasket replacement
spout crooked mounted unsightly appearance faulty installation 7 3 1 21 re-assembly
shower switch hampered switching excessive effort too hard gasket 8 5 3 120 change gasket
incomplete switching water spills out of the spout and spraying at the same time incorrect installation 6 4 4 96 re-assembly
hose unraveling unsightly appearance "break" hose 3 6 3 54 hose replacement
leakag leakage curves hose clip 3 7 8 168 hose replacement

As a result of the analysis, it was found that the most serious of the mentioned disadvantages are: micropores in the body of the battery, leaks in the hoses, knocking out the heads and their leaks, and impeded switching on the spray. Further work should focus on minimizing the likelihood of these problems occurring.

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