**2.1 Study about implementing the FMEA Process for a steel structures components assembly**

In **Figure 16**, the technical details of the components of the "Stator Housing" assembly are shown, which were considered for the FMEA Process research,

*Failure Analysis – Structural Health Monitoring of Structure and Infrastructure Components*

**Figure 15.** *The main advantages of applying FMEA for a company.*

respectively the welds used to make the housing are shown [20]. It is specified that the welds used to make the housing were considered very important.

The components of the "Stator housing" assembly shown in **Figure 16** are: 1 – support plate, 2 – flat bar, 3 – stiffening plate, 4 – flat bar, 5 – housing base, 6 – ring segment, 7 – front wall, 8.9 – ribs, 10 – shell, 11 – shell segment, 12 – intermediate wall, 13 – front wall, 14 – cable guide, 15 – reinforcement, 16 – pipe, and 17 – supporting bush.

**Figure 17** shows details of the elements of the assembly that will be considered in the FMEA study, respectively the welds used to make the housing.

**Figure 18** shows the positioning of the welded elements along the stator housing.

**Figure 16.** *Elements of assembly "Stator Housing" considered for the FMEA study.*

**Figure 17.** *Elements of the ensemble considered for the FMEA study.*

**Figure 18.**

*Positioning the welded elements on the stator housing assembly.*

Regardless of the product/manufacturing process to which the FMEA method is applied, the steps required to perform an FMEA Process analysis in order to obtain a "zero defect" production are those shown in **Figure 19**.

FMEA-Process analysis includes several stages: process/product analysis, process diagram determination, FMEA preparation, control plan development, statistical data analysis, document package update, FMEA team information, use of documentation made by FMEA application.

In general, the steps required to prepare an FMEA-Process analysis are as follows: planning and preparation, risk analysis, assessment and, subsequently, risk minimization. These steps are shown in **Figure 20**.

**Figure 21** shows the stages of the technological process of manufacturing the "Stator housing" assembly. The necessary operations and stages in the chronological order of their development are: qualitative inspection—material reception, CNC cutting, saw cutting, adjustment, semiautomatic cutting, saw cutting, parting off on guillotine, components adjustment, shell rolling and spot welding, rings rolling and spot welding, assembly and sharpening, ribs assembling and welding, welding and assembling, manual marking out and parting-off, final welding, final assembling, first sandblast cleaning, final adjustment, final sandblast cleaning, priming.

From **Figure 21** it can be observed on the left side of the figure the presence of the 6M: Man, Machine, Method, Measure, Mother Nature (Environment), Material.

The influence of each factor of the 6M on the quality of the product, as a result of a process (output) is shown in **Figure 22** [13].

The influence of the equipment on which the manufacturing process takes place is minimal, because the initial settings remain unchanged for a long time.

The influence of the human factor is remarkable, being on a higher class. Employees can be trained and motivated to perform, manage, and verify manufacturing processes and products; however, the mental factor related to their health or family problems cannot be quantified, producing inattention, lack of interest, etc.

**Figure 20.** *The stages of preparing the FMEA analysis.*

The most significant and uncontrollable influence has the environment (M Nature) in which the manufacturing processes take place, being included here is both the internal working environment of the company and the external business environment, the domestic and international economic market.

**Figure 23** shows the technological flow used to build the "Stator Housing" assembly.

The FMEA-process analysis was performed in order to improve the quality of the welded elements of the "Stator housing" assembly, this being partially shown in **Table 5**.

As it can be seen in **Table 5**, there are several operations that have a cumulative score for Severity, Occurrence, and Detection, respectively RPN major, of over 60 points. But the operations that could cause serious disruptions to the technological process are those with a high RPN of over 100 points (cells colored red as in **Table 5**), these being the following:

• when chamfering small surfaces, due to the low weld mechanical strength over time (Severity—point 8, Appearance—point 3, Detection—point 5), RPN is 120; it is recommended to purchase a chamfering machine;

**Figure 21.**

*The stages of the technological process of making the ensemble.*

**Figure 22.** *Process model and influencing factors.*


It was found that RPN decreased to zero and therefore achieved finished products with "zero defects," after taking the necessary steps to implement the recommendations for each operation with a high RPN.

**Figure 23.** *Process flow for the realization of the "Stator Housing."*




> **Table 5.**

*Aspects of FMEA-process analysis for "Stator Housing".*

**Figure 24.** *Diagram of RPN distribution.*

The RPN values in descending order for the assembly subjected to the FMEA analysis are represented in the diagram shown in **Figure 24**.

The risk prioritization figure (RPN) is obtained by multiplying the assessment factors established for Severity, Probability of Occurrence and Detection.

The maximum RPN value for the product in question was:

$$\mathbf{RPN} = \mathbf{8x4x5} = \mathbf{160} \tag{2}$$

This maximal value for RPN was obtained when chamfering on the entire length of the workpiece due to irregular shape of chamfering.

The solution that has been proposed for the correction of this defect was purchasing a chamfering machine, which significantly reduced the RPN value.

From the diagram shown in **Figure 24**, it may be noticed that measures are required for the defects that have RPN values greater than 120. Thus, for the "Stator housing" assembly, for the chamfering operation along the entire length of the part, due to the irregular shape of the chamfer, a low mechanical resistance of welding over time results (Severity – score 8, Appearance – score 4, Detection – score 5), RPN is 160 or, due to the quality of the weld bead, (Severity – score 5, Appearance – score 4, Detection – score 5), RPN is 100. For smaller dimensions and surfaces chamfering, the effect is low weld mechanical strength over time due to the small size of the chamfer (Severity – score 8, Appearance – score 3, Detection – score 5), RPN is 120.

The recommended improvement measure is the purchase of a chamfering machine, with the setting of the responsible department and the deadline for application. Following the application of the last measure, a risk assessment is carried out again. The main potential defects analyzed are: low mechanical strength of the weld; deformations; welding lines; large unevenness on chamfered surfaces; excessive weld convexity; high values of geometric deviations in excess of the prescribed tolerances; assembling errors; non-uniformity of the color of the part surface; cracks; air gaps; welding spatter, scratches.

The potential causes of the defects have been studied and improvement measures have been proposed. These include:


**Figure 25** shows a comparison between the actual process RFT (Right First Time) index for the number of landmarks inspected weekly, after applying the FMEA analysis, and the waiting level.

**Figure 25** shows that, after applying the FMEA Process for the Stator Housing assembly, at the weekly check, for Monday, from January to August 2014, the RFT index was always over 80%, and starting from week 21, it was located at 100%, far exceeding the proposed level of expectation of 50%.

In conclusion, by proper use of the analysis of FMEA Process expensive amendments of the assembly "Stator Housing" technological process could be avoided by

**Figure 25.** *Actual process RFT index for the number of assemblies inspected.* identifying potential defects, to avoid them, and also, by assessing risks and potential consequences of failures/defects [19].

The main potential defects that were analyzed were: low mechanical strength of the weld; deformations; weld line; large irregularities on the tapered surface; excessive convexity of the weld; high values of the geometric deviations exceeding the tolerances specified values; assembly errors; irregularity of the part surface nuance; cracks; bubbles; weld spatter, scratches.

Potential causes of defects were studied and, after that, improvements were proposed. These include: implementation and tracking preventive maintenance program; preparation and specific compliance for welding; purchase of specialized setting and reception table for workpieces; buying a chamfering machine; changing welding system with automatic welding system purchasing a humidity measuring device and its uses rectification and verification of table assembly; purchase of special chisels for cleaning weld splashes; operators monitoring by monitoring nonconformities operators and their regular training

### **2.2 Research about implementing FMEA Process for a Packing Shaft**

A study on the application of FMEA Process analysis was performed for the packing axis shown in **Figure 26** [21].

**Figure 27** shows the execution drawing of the packing shaft, where there also appear the sections with risk factors prone to.

**Figure 28** presents the process flow of the shaft, with the operations and stages necessary to achieve the benchmark, in chronological order of their development.

In **Figure 29**, the method of estimating the effects of each process and the influences on the final product is presented [20].

The FMEA Process analysis for the packing shaft was performed by a team of experts from the company.

**Table 6** shows the beginning of the table completed after the accomplishment of the analysis.

It was found that there are several operations that have a cumulative score for Severity, Occurrence and Detection, respectively the major RPN risk coefficient of over 90 points.

There are operations that lead to serious disruptions of the technological process, with a high RPN, of more than 100 points (cells colored red, as in **Table 6**), these being the following:

**Figure 26.** *Packing shaft.*

**Figure 27.** *Execution drawing of the packing shaft.*

• for cutting-off operation, when the semi-finished product shows arrow curvature due to deviation from coaxiality because of large successive temperature variations (Severity – score 5, Appearance – score 3, Detection – score 10), so RPN is 150, it is recommended to have material certification from the supplier.

#### **Figure 28.**

*Process flow of packing shaft subjected to FMEA analysis.*

**Figure 29.**

*Method for establishing the influences that occur during technological process [20].*


It is specified that the abbreviation OTD, which appears in **Table 6** means "on time delivery."

The highest density of risks of occurrence of defects with major result on the product are signaled in the parting-off phases of the semi-finished product, but the highest value of RPN = 250 is recorded in the turning operation, when the milled and drilled shaft does not comply with the documentation, the shaft may be rejected or reclassified due to human error, respectively the operator is trained but does not comply with the manufacturing process.

When recommending measures to improve the process, in order to completely reduce the RPN, the following were considered:

• requesting the material certificate from the supplier;


The RPN values in order of their appearance are presented in the diagram in the **Figure 30** [21].

It can be seen from diagram 30 that the operations with major risk, respectively those with an RPN> 100 appear in the first stages of the shaft processing process, respectively at cutting and turning, a fact also found in **Table 6**.

In **Figure 31**, the RPN values in descending order of parts subjected to FMEA analysis are represented.

After taking the necessary measures to implement the recommendations for each operation with a high RPN, it decreased to zero, which led to the obtaining of finished products with "zero defects."

**Figure 30.** *The RPN values in order of their appearance [20].*

The main potential defects analyzed were: deviation from coaxiality due to large successive temperature variations, mounting of the shaft made of a material other than the one mentioned by the specification, milled and drilled shaft is not in accordance with the documentation, shaft reshaping, reclassifying or rejecting, part dimensions damage.

The potential causes of the defects have been determined and improvement measures have been proposed, including:


After the application of these measures, a new risk assessment was carried out, finding that the target of having a production with "zero defects" was reached.

Timely use of FMEA-Process analysis can avoid costly changes to the technological process of making the product "packaging tree" by identifying potential defects, avoiding them, and assessing the risks and potential consequences of defects and obtaining "zero defects" as target products [21].





**Figure 31.** *Diagram of RPN distribution [20].*
