Applying FMEA in the knitting process


Diploma Thesis, 2006
130 Pages, Grade: 1,7

Excerpt

TABLE OF CONTENTS

1 INTRODUCTION
1.1 Diploma Thesis
1.2 The Company

2 FMEA (FAILURE MODE AND EFFECT ANALYSIS)
2.1 Background
2.2 Types of FMEA
2.3 Fundamental ideas of FMEA – why conduct FMEA
2.4 Process FMEA

3 PERFORMING A PROCESS FMEA
3.1 Defining a TEAM
3.2 Bill of materials (BOM)
3.3 Organization in the productive area
3.3.1 Production process of the knitting department
3.3.2 Workstation functions within the process
3.4 Defect overview
3.5 Cause-Effect-Diagrams
3.6 Detected defects January-August 2005
3.7 Detected defects in the working process
3.8 Risk evaluation
3.8.1 Severity (SEV)
3.8.2 Occurrence (OCC)
3.8.3 Detection (DET)
3.8.4 Risk Priority Number (RPN)
3.9 Arrangements and solutions
3.10 Checking the process – action taken to reduce the defects
3.10.1 Which checkups are already planned?
3.10.2 RPN new calculation
3.11 FMEA form

4 CONCLUSION

5 REFERENCES

6 APPENDIX
6.1 Handbook FMEA
6.2 Complete FMEA form

LIST OF TABLES

Table 1: BOM

Table 2: Defect overview

Table 3: Detected defects 2005, January-August

Table 4: Detected defects according to the process functions

Table 5: Evaluation of severity (SEV)

Table 6: Severity of defects

Table 7: Evaluation of occurrence (OCC)

Table 8: Occurrence of defects

Table 9: Evaluation of detection (DET)

Table 10: Detection of defects

Table 11: RPN of defects

Table 12: Pareto Diagram

Table 13: Solutions of defects

Table 14: Comparison of defects 2005

Table 15: Recalculation of the evaluation of occurrence (OCC)

Table 16: Comparison of RPN

LIST OF FIGURES

Figure 1: FMEA Model

Figure 2: Fundamental ideas of FMEA

Figure 3: Brainstorming

Figure 4: The FMEA Process Map

Figure 5: Production Process 1

Figure 6: Production Process 2

Figure 7: Cause-Effect-Diagram: Barré

Figure 8: Cause-Effect-Diagram: Vertical line

Figure 9: Cause-Effect-Diagram: Pinholes

Figure 10: Cause-Effect-Diagram: Centerline

Figure 11: Cause-Effect-Diagram: Lycra thin end

Figure 12: Cause-Effect-Diagram: Pull-out yarn

Figure 13: Cause-Effect-Diagram: Dropped stitch

Figure 14: Cause-Effect-Diagram: Motes

Figure 15: Cause-Effect-Diagram: Stop marks

Figure 16: Cause-Effect-Diagram: Spandex pulling

Figure 17: Cause-Effect-Diagram: Holes

Figure 18: Cause-Effect-Diagram: Stripes

Figure 19: Cause-Effect-Diagram: Flat appearance

Figure 20: Cause-Effect-Diagram: Contaminated yarn

Figure 21: Cause-Effect-Diagram: Needle breaking the filament

Figure 22: Cause-Effect-Diagram: Heavy Barré

Figure 23: Cause-Effect-Diagram: Spots

Figure 24: Cause-Effect-Diagram: Horizontal broken filament

Figure 25: Diagram: Defects January-August 2005

Figure 26: Pareto Diagram

Figure 27: Diagram: Defects August 2005

Figure 28: Diagram: Defects October 2005

Figure 29: Diagram: Defects December 2005

LIST OF ABBREVIATIONS

illustration not visible in this excerpt

LIST OF IMPORTANT VOCABULARY[1]

Specific words used in the FMEA-process, which are not explained during this thesis.

Cause – The reason why a particular element of a design or process results in a failure mode

Critical Characteristics – Product characteristics that potentially affect customer safety and / or non-compliance with government regulations thus requiring special controls to ensure 100% compliance with the specification

Current Controls – Any organised screening mechanism (person, thing, process or design) that prevents the Failure Cause from occurring, or detects the Failure Cause or Failure Mode and precludes it from reaching the customer

Customer – Any person and / or process that utilizes the product along the chain of processing and may be adversely by a product failure

Detection Ranking – The assignment of a numerical ranking to the perceived likelihood that the current controls (design and / or process) will detect a failure’s cause or its failure mode prior to the product reaching the customer

Effect – An adverse consequence that the customer might experience

Failure Mode – The way in which a product or process failure manifests itself to the customers

Function – Any intended purpose of a product or process

Greige goods – Knitted goods after leaving the machine and before being dyed / finished; unfinished material

ISO 9000 – International quality standards for product design, manufacture, and distribution

Occurrence Ranking – The assignment of a numerical ranking to the perceived likelihood of a failure cause happening during the intended life and use of a product

Poka Yoke – Japanese phrase for “error proof” – a quality improvement strategy emphasising preventing defects at their source by making changes, which prevent the defect from occurring

QS-9000 – Automotive sector-specific quality requirements

Ruggedization – Making a design or process stronger and more resistant to wear, abuse, and failure

Scour – To wash with soap

Severity Ranking – The assignment of a numerical ranking to a failure’s effect on the customer

Wale – In knitted fabrics, series of loops lying lengthwise in the fabric and knitted by a single needle

1 INTRODUCTION

The quality of products and processes in the textile industry is very important. Until today the methods, which are used to analyse and prevent failure modes and effects, are still simple procedures in the textile industry. Methods for predicting quality assurance are still not very common. The FMEA (Failure Mode and Effect Analysis) is an important strategy to analyse and prevent potential failures and defects in quality assurance. In other industries like the automotive industry the FMEA is already an important analysis in the quality management and indispensable for the production process. The idea of preventing and avoiding failures or defects before the manufacturing procedure is becoming also an important aspect in the textile industry. Therefore the FMEA is starting to play a decisive role in the textile production.[2]

The FMEA process analyses and evaluates the risks in order to detect and prevent the failures and defects. It also requests the knowledge –based background of the team members. The knowledge of the experts in different areas of the process is documented in form of manuals and an advantage to reduce the failures and defects. The orientation of the FMEA team provides with internal communication and increases the comprehension in several problems. Safe products and processes can improve the development and the production procedure. Conducting FMEA after the product development does not consider the costs and benefits of the process.

The FMEA method requests consistent realization. It is to be mentioned that the improvements are not visible immediately. To conduct an effective FMEA, the Company has to integrate the FMEA in the daily process flow.[3]

1.1 Diploma Thesis

The idea of this thesis “APPLYING FMEA IN THE KNITTING PROCESS” was developed during the first month while getting familiar with the production process of the knitting department. By the time of knowing the process and the most known defects during manufacturing, the author developed the idea of a strategy to apply FMEA (Failure Mode and Effective Analysis) in the knitting process. FMEA was still not well known for analysing and preventing potential failures or defects during the manufacturing process. In order to get a better idea of how to apply the FMEA in the knitting process, the production engineers and the quality department agreed in some discussions that were taken. The author was in charge of developing an overview of the complete FMEA process in order to know the importance and the procedure of performing an FMEA. The general idea of this project was to realize and define the basics of FMEA according to the most important steps for developing an FMEA by showing examples of the knitting department. These steps should be shown in form of flow charts and examples in order to give an easier understanding of the procedure. All team members of the FMEA should study the handbook. The purpose of applying this thesis into the production process of the knitting department is to improve the quality of the knitting production by reducing the potential failures and defects. The knitting department can provide a higher quality standard for their customers.

The FMEA should be integrated in the daily process to provide an effective FMEA.

1.2 The Company

Textivisión, located in Tlalnepantla, Estado de Mexico, Mexico, is a textile company, which is specialised in knitting fabric specifically in synthetic fibres. The company was established in 1986.[4]

The main customers on the international market are USA, Canada, Europe and South America. Furthermore Textivisión is dealing with the national market. The entire production processes is obtain through international quality standards. The company disposes of a variety of machines for the knitting, dyeing, printing and finishing procedure. The protection of the environment is to be considered very seriously. Textivisión has been developed to one of the most important suppliers in the Mexican textile industry, especially in the fabrics, which include “spandex”. Taking consideration of the international market, Textivisión imports 20% (raw material) and exports 80% of their fabrics. The company is in co-operation of three manufacturing companies divided by areas:

- Milltex (knitting) 169 employees
- TTM (dyeing, finishing and printing) 232 employees
- SyPE (administration and personnel of the factory) 230 employees

2 FMEA (FAILURE MODE AND EFFECT ANALYSIS)

The FMEA (Failure mode and Effect Analysis) is a systematic method to analyse and rank the risks of the failures and to prevent them before the customer reaches the product.

The aim of the FMEA is to detect potential failures during the production planning and product development and to prevent them by realizing measurements to avoid the defects. Analysing evaluation to identify the failures or defects might operate first by using historical data, similar data for similar products, warranty data, customer complaints and other appropriate information. And the second is by working with inferential statistics, mathematical modelling, simulations, concurrent engineering and reliability engineering to define the failures or defects.[5]

The FMEA is also used to improve the quality of the existing products and to advance the quality control plans of developing new products. To improve and prevent failures the priorities of failures have to be defined by three components:

- Severity (SEV) effects of the failure
- Occurrence (OCC) frequency of the failure
- Detection (DET) ability to detect the failure before it reaches the customer[6]

To value the defects a numeric scale from 1 to 10 is used is a ranking table. The number 1 is the lowest and number 10 the highest risk rate.

The failures or defects are valued by the Risk Priority Number to define the priority of the defects. The RPN is a product of the severity, occurrence and detection. The number by itself is without any meaning because each FMEA has different meanings.

The failure or defect with the highest RPN has to be addressed first to solve the problem and reduce the defect. After the RPN is determined, then the risk evaluation of the defect begins by recommending action for the resolution. The risks are defined by minor, moderate, high and critical.

Any FMEA conducted properly and appropriately will provide the practitioner with useful information that can reduce the risk (work) load in the system, design, process, and service. This is because it is a logical and progressive potential failure analysis method (technique) that allows the task to be performed more effectively. FMEA is one of the most important early preventive actions in system, design, process, or service which will prevent failures and errors from occurring and reaching the customer.”[7]

The concept of applying an FMEA should compose:

- Cause-Effect-Diagrams
- Safety certifications
- Process / System improvement
- Extension of knowledge
- Documentation of Experiences
- Occurrence of customer satisfactions in relation to the effects of failures
- Defining warranty claims[8]

“A good FMEA

- Identifies known and potential failure modes
- Identifies the causes and effects of each failure mode
- Prioritises the identified failure modes according to the risk priority number (RPN) – the product of frequency of occurrence, severity, and detection
- Provides for problem follow-up and corrective action”[9]

illustration not visible in this excerpt

Figure 1: FMEA Model

Modified after: Dailey [2004], p. 8

Besides FMEA there are other variations like FMECA (Failure Mode and Effects and Critical Analysis) in the aerospace industry.

The difference to the FMEA is in its terms of failure rates and identification number in dubiousness.

An other characteristic is the reference of system in relation to application.

2.1 Background

The FMEA was developed and released in the United States Military Procedure MIL-std-1629 in November 1949 with the title:[10]

“Procedures for Performing a Failure Mode, Effects and Critically Analysis” to verify the failures within the production system. In the 1960s the FMEA was added from the NASA (American Space Effort) and part of the Apollo program. The concept of “Quality” is a very important tool together with “Security” in the area of aerospace, according to the safety and reliability of FMEA.

The extension of FMEA was created by the automobile industry, Company Ford in the 80s: Ford Motor Industry began to apply FMEA in the engineering production with the aim to improve the safety, quality and reliability of the products.

The Risk priority number (RPN) was developed because of the customer’s evaluations of failures, to give evidence about the strength and heaviness of the effects of the failures. It also should define which measures should be done urgently to advance or prevent the failures.

The result of these calculations was the FMEA form, which accrued in 1986.

By 1988 FMEA was applied in almost all big Automotive Companies.

In the Same year ISO 9000 (International Organization for Standardization) of business management standards developed.

The ISO was in charge that the organizations developed a significant Quality Management System in order to improve the Quality and satisfy the Customer needs and expectations. The QS 9000 can be compared with the ISO 9000 and is special for the automotive industry. It was developed by Daimler-Chrysler, Ford Company and the general Motors Cooperation developed QS 9000 in order to standardize the quality systems. The FMEA was used for advance quality control plans within the automotive industry.

In February 1993 the Automotive Industry Action Group (AIAG) and the American Society for Quality Control (ASQC) copyrighted the FMEA standards for the whole industry. The standards are approved and supported by the automotive industry: Ford, Daimler-Chrysler and general Motors Cooperation and presented in an FMEA Manual to provide general guidelines for preparing an FMEA.

Today the FMEA is used in plenty of areas in the industry and has become and important tool in the product and process industry.

Since 1996 there is a difference between System-FMEA of the product and of the process. A new FMEA form was presented in 1996.

2.2 Types of FMEA

The FMEA is divided into four different types of FMEA, depending on the time of inspection, inspection complexity and the inspection type: System-FMEA, Design-FMEA, Process-FMEA, Service-FMEA. The procedure is basically in all types similar.[11]

1. System FMEA

The System – FMEA is used to analyse systems and subsystems already in the design stage. The system also focuses on potential failure modes between the functions of the system caused by system deficiencies.

Co-operations are between:

- Different subsystems
- Customer-supplier
- Different works

2. Design FMEA

The Design – FMEA is used to analyse products before they are released to manufacturing. The FMEA focuses on failure modes caused by design deficiencies. The aim of the Design-FMEA is to eliminate the potential failures in the product development phase.

3. Process FMEA

The Process – FMEA is used to analyse manufacturing and assembly processes. The FMEA focuses on failure modes caused by process or assembly deficiencies. The aim of a systematic process flow is:

- Proof of following the quality measurements
- Optimal process flow
- Process reliability

4. Service FMEA

The Service – FMEA is used to analyse services before they reach the customer. The FMEA focuses on failure modes (tasks, errors, mistakes) caused by system or process deficiencies. The Benefits are:

- Priority stabilization for improvement actions
- Job flow
- Task deficiencies

For the knitting department the Process FMEA is the most important function because it analyses the potential failures and defects caused during the manufacturing process.

2.3 Fundamental ideas of FMEA – why conduct FMEA

The purpose of FMEA is to find the weak points in the production process and analyse the severity and evaluate the effects besides finding solutions and measurements to prevent the failures. The FMEA system is also able to improve the product or the process.

There are also other benefits of conducting FMEA:[12]

- Improves the quality, reliability and safety of the products
- Increases customer satisfaction
- Reduces product development time and costs
- Establishes a priority for design improvement actions
- Helps in the analysis of new manufacturing and/or assembly process
- Lists potential failures and identifies the relative amount of their effects
- Develops early criteria for manufacturing, process, assembly, and service
- Brings focus to product / process failure modes and their effect on reliability, producibility and the customer
- Provides a record of preventative action in design and/or process improvement
- Provides a list of critical and significant characteristics for production and quality planning
- Provides historical record for future product failure investigations
- Provides criteria on based prioritisation for design or process improvement
- Provides new ideas for future improvements in similar designs or processes

The most important rationale for conducting FMEA is to protect the consumer and producer.

illustration not visible in this excerpt

Figure 2: Fundamental ideas of FMEA

Modified after: Meier [2005], p.6

URL: http://www.fmeainfocentre.com/download/kunz_meier.pdf

2.4 Process FMEA

The process FMEA is a method to identify potential failures during the manufacturing process and provide corrective actions before the first production process starts. To avoid these failures it is necessary to find out the causes of the problems and present actions to correct the system before starting the first production. The first production run is always the most important one because it conducts samples for the customers and it is not an occasional prototype production. The change of designs is usually not the major event of this procedure.

For each failure in the system there has to be a specific methodology to prevent the problems or risks, which can arise. There are a variety of reasons to focus in identifying and analysing the problems such as customer requests, conditional improvement philosophy and competition.

The process FMEA is accomplished through the whole production process, including all series of steps, the product has to follow: labour, machine, method, material, measurement and environment considerations. Each of these steps has its own area of creating failures.

To conduct a process FMEA the most important elements are: human, materials, equipment, methods, environment that can be shown in a Cause-Effect-Diagram to analyse the defects.

The goal, purpose, and/or objective of the process FMEA is to define, demonstrate, and maximize engineering solutions in response to quality, reliability, maintainability, cost, and productivity as defined by the design FMEA and the customer.”[13]

The aims of process FMEA are:[14]

- Optimal process reliability
- Detection of keeping conditions
- Advancement of costing
- Environment protection/pollution control
- Work safety

The process FMEA must base its requirements on solid needs, wants and expectations of the customer.

Before starting to conduct a process FMEA, it is important to do a brainstorming within the team to analyse the advantages of the FMEA. The main reason for performing a FMEA in the knitting department is to improve the quality of the fabric and to prevent and decrease the defects and failures during the manufacturing process. The following chart shows a brainstorming for the advantages of the FMEA.

illustration not visible in this excerpt

Figure 3: Brainstorming

Modified after: Stamatis [1995], p. xxvii

3 PERFORMING A PROCESS FMEA

A process FMEA is defined by analysing certain functions within the production process to evaluate the potential failures. The defects will be evaluated by the Risk Priority Number (RPN). Therefore the rankings severity, occurrence and detection have to be calculated first.[15]

The FMEA Process Map lists the most important steps to conduct a process FMEA. There are 13 steps to follow to obtain acceptable results within the Team:

1. Create a detailed component list (Bill of Materials (BOM)) for the related product of the FMEA: This means a list of all the required materials, including sub-assemblies and supplies to produce the material/fabric.
2. Identify the complete production process and the detailed workstation functions.
3. Identify the failure modes: Defect overview of the complete process.
4. Describe the effects of each defect, using the Cause-Effect-Diagram.
5. Develop a Severity Ranking (SR) for each defect : Ranking table SEV.
6. Identify the causes of each defect, using the Cause-Effect-Diagram.
7. Develop an Occurrence Ranking (OR) for each defect: Ranking table OCC.
8. Identify the current control (detect the defects) in the production line.
9. Develop a Detection Ranking (DR) for each defect: Ranking table DET.
10. Calculate the Risk Priority Number (RPN) for each defect.
11. List the RPN from the highest ranking to the lowest in order to explore the most critical defect.
12. Set actions to correct, reduce or remove all defects according to the selected defect mode.
13. Recalculate RPN and continue taking action to reduce all defects.

[...]


[1] cp. Dailey [2004], p.2-4 Textiles Panamericanos [1995]

[2] cp. Reinecke /Schermbeck [1998]

[3] cp. http://www.itlocation.com/de/software/prd56770,,.htm [2004]

[4] cp. Texivisión, Gerencia de Recursos Humanos [2005]

[5] cp. Stamatis [1995], p. 25

[6] cp. Stamatis [1995], p. 180

[7] Stamatis [1995], p. 25

[8] cp. DGB-Band 13-11 [2004], p. 9

[9] Stamatis [1995], p. 26

[10] cp. http://www.theleanmachine.com/newsletters/December2003/FMEA.htm cp. Müller / Tietjen [2003]

[11] cp. Stamatis [1995], p. 46

[12] cp. Stamatis [1995], p. xxvi Dailey [2004], p. 6

[13] Stamatis [1995], p. 157

[14] cp. DGQ-Band13-11 [2004], p. 44

[15] cp. Dailey [2004], p. 15

Excerpt out of 130 pages

Details

Title
Applying FMEA in the knitting process
College
Albstadt-Sigmaringen University
Grade
1,7
Author
Year
2006
Pages
130
Catalog Number
V74302
ISBN (eBook)
9783638019958
File size
1754 KB
Language
English
Tags
Applying, FMEA
Quote paper
Inkeri Walser (Author), 2006, Applying FMEA in the knitting process, Munich, GRIN Verlag, https://www.grin.com/document/74302

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