Examplary Failure Modes and Effects Analysis (FMEA) of a Flashlight

Table of Contents

1. Table of Contents

2. Introduction of FMEA
a. History
b. General Facts and Benefits
c. Types
d. Method Description

3. Preparing the Content for FMEA
a. Product Structure
b. Structural Tree
c. Functions
d. Functional Tree
e. Possible Failures
f. Malfunction Tree
g. Failure Trees

4. FMEA Form

5. Pareto Analysis

2. Table of Figures

Figure 1: Flashlight Components of Sublevel 1

Figure 2: Structural Tree

Figure 3: Functional Tree

Figure 4: Malfunction Tree

Figure 5: Failure Tree 1

Figure 6: Failure Tree 2

Figure 7: Failure Tree 3

Figure 8: FMEA Form

Figure 9: Pareto Table

Figure 10: RPN % - Pareto Chart

3. Introduction of FMEA

a. History

FMEA was developed in the 1960 during a NASA project and formerly mainly used in cutting edge aerospace projects in order to avoid quality problems to occur. The method was standardized in Germany in 1980 named “Failure Effect Analysis” originally. Since it first was not used in production engineering, its deployment and modification especially for this industry sectors has been triggered by the introduction of quality system guideline by Ford during the late 1980s. The original method was extended in the sense of improving the needs of the automotive industry and its scope changed to a system FMEA for products and processes. The main modification appeared to be the introduction of risk priority number (RPN). The RPN provides an indication of the urgency of the various failure modes to the developing company. Thus it can provide guidance when searching for improvement. Three indicators mainly determine the value of the RPN: likelihood of occurrence, significance of the effects of the failure, likelihood that it will be detected.

b. General Facts and Benefits

FMEA is the short term for “Failure Mode and Effects Analysis”. According to ISO 9004-1 “risk assessment should be undertaken to assess the potential for, and the effect of, possible failures or faults in products or processes” and FMEA is considered to be a suitable method to this purpose. The benefit of a FMEA is to identify reveal potential faults during the development phase of products or new production methods already. Appropriate action to avoid failures to occur can already be implemented at the planning stage. Therefore, FMEA uncovers the correlations between faults and factors that influence quality in a systematic manner. The knowledge about these correlations can be very valuable for companies and should be made available within the company in order to take quality harming aspects into account as early as possible. Adjustments to hinder quality problems and other failures from occurring can save a lot of money and also customers’ credit to the company. A sustainable and sophisticated FMEA system provides a source of experience acquired from previous solutions - empirical knowledge which in other ways hardly can be kept over times. Originally FEMA intended to “record and systematically evaluate information relating to the reliability, safety and maintenance of a system through inductive analysis of types of failures sustained by all of the components and of their effects”. All effort going along with the maxim that a minimum number of possible of failure modes leads to a faultless product. Further benefits of FMEA are:

- Reduces process development time and costs
- Documents and tracks risk reduction activities
- Helps to identify critical-to-quality characteristics
- Helps increase customer satisfaction and safety

The method of FMEA is closely related to quantitative methods such as Fault-Tree Analysis and incident-sequence analysis.

c. Types

Various types of FMEAs can be found like e. g. Design FMEA, Process FMEA and System FMEA. Differences between the mainly origin form associated objective during the planning phase, when the FMEA is drawn up. The System FMEA is conducted concerning the work schedule of manufacturing – revealing the potential failures inherent in the design from the point of production.

d. Method Description

1) Organizational Preparation for FMEA

The first step is to define the parts or processes which are needed for the FMEA. After the team is defined, responsible persons are assigned to the team. Furthermore, a project schedule is implemented.

2) Preparing the subject of FMEA

In this step, the systematically structure of the task needs to be described in a detailed way to ensure a smooth process. The FMEA task are assigned to the team members.

3) Conducting the analysis

The conducted analysis contains potential faults, causes and effects of faults and potential risks.

4) Evaluating the analysis results

In this step, measures are identified to eliminate the weaknesses of the product. Applied methods are design modifications, detection methods and damage limitation methods.

5) Following up deadlines and checking effectiveness

The final step of FMEA is to make the measures effective and control that the tasks are done before the deadlines. If it is necessary to conduct a new risk assessment, new measures need to be planned.

4. Preparing the Content for FMEA

a. Product Structure

Before the final FMEA sheet can be filled out the required data needs to be prepared. In our case, we need to organize the components of the flashlight into a graphic to get a structured overview of the components. The more detailed the preparation steps are done the easier it is in the end to put the values into the FMEA form. A convenient way to do this is to use a tree graphic to divide the components using several structural levels. To be able to conduct a reliable FMEA analysis all single components need to be listed. By disassembling the flashlight, the single parts could be described and analysed:

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Figure 1: Flashlight Components of Sublevel 1

The components of the flashlight can be structured into 3 sublevels. Above the components of sublevel 1 are shown which namely are Central Part, Battery Case, Reflector Unit, Tail Cap and LED Unit. The idea is to get more and more specific with each additional sublevel. The last sublevel of the structural tree should represent all single, not dividable components. For example, the Reflector Unit can be further divided into Reflector and Lens. The Tail Cap is assembled out of a Switch, Electrical Spring and O- Ring. The Battery Case and 3xAA 1.5V Batteries represent sublevel 3 of the Energy Unit. The LED Unit can be divided into LED, Electrical Spring and Solder Joint. Since the Central Part is just a shell with threads on both sides, it can not be further divided.

b. Structural Tree

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Figure 2: Structural Tree

c. Functions

For all the determined elements of the systems and the subsystems several functions are defined. For this reason, the structural tree is extended to the functional tree. In the following chapter a short description of each function and sub function shall be given.

Main function

- The flash light has to deliver a light beam which has to be light enough to bright dark spots accurately. The brightness of the beam should be stable and constant over time.

Functions of Sublevel 1

- The reflector part has to protect the parts it contains which are the lens and the reflector itself. Furthermore, it has to ensure a stable connection to the middle part.
- The middle part has the function to connect the reflector part and the tail cap. Furthermore, it has to protect the energy unit which is located in its interior.
- The tail cap has to enclose its inner parts. These inner parts are the O-ring and the switch. Its main function is the connection of the push mechanics through the switch use and the corresponding electrical components.
- The energy unit has to provide the energy of the batteries it stores.
- The LED unit fixates the components it contains. The main function is the emission of the light beam delivered by the LED.

Functions of Sublevel 2

- The lens has to protect the LED. Furthermore, the light beam should be able to pass the LED.
- The reflector has to ensure that the light beam is stable through its mirrored surface. Additionally, it also protects the LED.
- The O-ring has to protect the sensitive electrical components and mechanics against environmental influences.
- The switch has to open or close the electrical circuit.
- The spring of the tail cap has to ensure the electrical connection between the energy unit and the tail cap.
- The battery case guarantees a stable fixation of the batteries.
- The batteries themselves have to provide neither higher nor lower as 1.5V each.
- The LED has to transfer electricity in to light.
- The spring of the LED has to ensure the electrical connection between the energy unit and the LED.
- The solder joint should work as a mechanical fixation of the LED unit.

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