mini project
TRANSCRIPT
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A Study on Quality Control of Components in the Workshop
A MINI PROJECT WORK
Submitted in fulfilment of the award of degree of Bachelor of Technology
In
AERONAUTICAL ENGINEERING
Submitted by
G Lokesh 11951A2111
M Ram Kishore Singh 11951A2120
E Shashank Sai 11951A2128
J Uday Kumar 11951A2135
Under the supervision of
K.Anirudh Asst.Professor
April, 2015.
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Department of Aeronautical Engineering
CERTIFICATE
This is to certify that the work embodies in this dissertation entitled ‘A Study on Quality Control of Components in the Workshop’ being submitted by
G Lokesh 11951A2111
M Ram Kishore Singh 11951A2120
E ShashankSai 11951A2128
J Uday Kumar 11951A2135
For partial fulfillment of the requirement for the award of Bachelor of Technology in Aeronautical Engineering discipline to Institute of Aeronautical Engineering, Dundigal, Hyderabad, Telangana State, during the academic year 2014-2015 is a record of bonafide piece of work, undertaken by him the supervision of the undersigned.
Approved and Supervised by
Signature K.Anirudh
Department of Aeronautical Engineering, Asst.Professor
Forwarded by
V V S Haranadh Prasad Dr A. Barai Dean Academics Department of Aeronautical Engineering IARE, Hyderabad IARE, Hyderabad
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Department of Aeronautical Engineering
DECLARATION
We G Lokesh, M Ram Kishore Singh, E Shashank Sai, and J Uday Kumar are students of ‘Bachelor of Technology in Aeronautical Engineering’, session: 2014 – 15, Institute of Aeronautical Engineering, Dundigal, Hyderabad, Telangana state, hereby declare that the work presented in this project entitled ‘ A Study on Quality Control of Components in the Workshop'is the outcome of our own bonafide work and is correct to the best of our knowledge and this work has been undertaken taking care of engineering ethics. It contains neither material previously published or written by another person nor material which has been accepted for the award of any other degree or diploma of the university or other institute of higher learning, except where due acknowledgement has been made in the text.
G Lokesh 11951A2111
M Ram Kishore Singh 11951A2120
E ShashankSai 11951A2128
J Uday Kumar 11951A2135
Date:
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ACKNOWLEDGEMENT
The mini project entiltled "A STUDY ON QUALITY CONTROL OF COMPONENTS IN THE WORKSHOP" is the sum of total efforts of our batch. It is our duty to bring forward each and everyone who is directly or indirectly in relation with the project and without whom it would have been demanding task for its structure to be developed.
We express our sincere thanks to the Principal Dr.G.POSHAL garu of "INSTITUTE OF AERONAUTICAL ENGINEERING" for allowing us to carry out our mini project work.
We gratefully acknowledge Assc PROF.Y.B.SUDHIR SASTRY (HoD Dept. of AERONAUTICAL ENGINEERING ), for his encouragement, continous support and advice during the course of our mini project.
We express our honest gratitude to Sri N.V.S.RAMCHANDRA RAO, Dy.Manager,Small parts Division (production MT-2 shop) for spending his valuable time and suggestions, guidance made by him at various stages of this work done at "HMT MACHINE TOOLS LIMITED - PRAGA DIVISION".
Finally we sincerely thank all the members who were helpful directly in the completion of our mini project. Our heartfelt thanks to all the employees , who spent their valuable time during our training sessions in explaining all the intricacies involved in the system processes and being patient in answering all our queries.
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ABSTRACT
Quality control of components manufactured in an engineering workshop. We hereby try forward the methods of checking various items, many in the shop floor at different stages of operation, as well as final inspection after complete manufacture of the items.
Quality control is a process through which a manufacturer seeks to ensure that product quality is maintained or improved and manufacturing errors are reduced or eliminated. Quality control requires the manufacturer to create an environment in which both management and employees strive for perfection. This is done by training personnel, creating benchmarks for product quality, and testing products to check for significant variations.
A major aspect of quality control is the establishment of well-defined controls. These controls help standardize both production and quality issues. Limiting room for error by specifying which production activities are to be completed by which personnel reduces the chance that employees will be involved in tasks for which they do not have adequate training. We have included the quality checking procedures for different components of machines present in the shop floor. The following are made use of during quality control of a machine component at the shop floor:
• The machine components • The instruments meant for the usage during the quality control phase at the shop floor. • In general, all the measurements taken in the above contexts will be recorded in standard
formats.
Examples:
• Part operation up to finishing stage. • Standard test charts for certification of the machines, accessories & mountings.
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List of Contents
Sl No. NAME Page No. 1 CHAPTER 1- Company Profile
1.1 Introduction 1.2 Quality management system
5 7 7
2 CHAPTER 2- Quality Control in HMT 2.1 Introduction 2.2 Motivation 2.3 Objective 2.4 Limitations
8 8 8 9 9
3 CHAPTER 3- Quality Standards at HMT 3.1 Introduction 3.2 Quality management system of ISO 9000 3.2.1 9000C Standards for Aerospace quality management system
10 10 10 12
4 CHAPTER 4- Quality Control Equipment Used In HMT. 4.1 Vernier Calipers 4.2 Micro meter 4.3 Bore indicator 4.4 Height indicator 4.5 Universal hardness tester 4.6 Surface finish tester 4.7 Profile projector 4.8 Universal microscope 4.9 Plug gauges 4.10 Rollers 4.11 Sample micrometers
18 18 18 21 21 22 22 23 24 24 25 25
5 CHAPTER 5- Quality Inspection in HMT 5.1 Definition 5.2 Origins of quality inspection 5.3 Important of quality of inspection 5.4 Evolution of quality inspection 5.5 Types of quality inspection
26 26 26 26 26 27
6 CHAPTER 6- Quality Inspection Design in HMT 6.1 Introduction 6.2 Product design 6.3 Product manufacturing
28 28 28
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6.4 Quality inspection of design process in HMT 6.5 Taguchi design level 6.6 Quality inspection Stages
29 29 31 32
7 CHAPTER 7- Failures 7.1 Facture 7.2 Fatigue 7.3 Stages in fatigue failure 7.4 Creep
35 35 38 39 40
8 CHAPTER 8- Inspection of components in HMT 8.1 Inspection of Bearings 8.2 Inspection of Couplings 8.3 Inspection of Gears
42 42 51 53
9 CHAPTER 9- Quality assurance in HMT and Quality improvement
55
10 CHAPTER 10- Heat treatment in HMT 10.1 Annealing 10.2 Hardening and Tempering 10.3 Harden ability 10.3 Surface Hardening 10.5 Carburizing
56 56 57 57 57 57
11 Conclusion 58
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LIST OF FIGURES
FIGURE No.
NAME PAGE No.
2.1 Quality Approval 3 4.1 Vernier callipers 5 4.2 Micrometer 7 4.3 Different types of micrometer 8 4.4 Bore indicators 9 4.5 Flange indicators 10 4.6 Grove micrometer 11 4.7 Bore indicator 12 4.8 Height gauges 12 4.9 Universal hardness tester 15 4.10 Surface finish tester 16 4.11 Profile projector 18 4.12 Ring gauge 19 4.13 Rollers 20 4.14 Sample micrometer 21 6.1 Traditional approach to design process 22 6.2 Typical shape of the design iterations 23 7.1 Macroscopic image of ductile fracture 25 7.2 Microscopic image of ductile fracture 25 7.3 Macroscopic image of brittle fracture 26 7.4 Microscopic image of brittle fracture 28 7.5 Macroscopic image of fatigue 29 7.6 Microscopic image of fatigue 31 7.7 S-N Curve 31 8.1 Types of Bearings 32 8.2 Bearing isometric view 32 8.3 Bearing 2D view 34 8.4 Bearing 3D view 37 8.5 Universal Coupling (isometric view) 38 8.6 Universal Coupling 2D 39 8.7 Universal Coupling 3D (a) 39 8.8 Universal Coupling 3D (b) 39 8.9 Spur gear 2D 40 8.10 Spur gear 3D 40 8.11 Multi gearing 40
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LIST OF TABLES
Table No. Name Page No. 7.1 Ductile vs Brittle curve 37
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CHAPTER 1
COMPANY PROFILE
Praga is one of the leading machine tool manufacturing units in India. Established in 1943, Praga's products are well known in the field of machine tools. The company is organised in two divisions- viz. the machine tool and CNC division which pulsates with the activities of employees , turning out a wide range of products. The two divisions equipped with modern facilities for design, development and manufacture of machine tools, are manned by qualified personnel with proven record of technical knowledge and exquisite craftsmanship acquired over a period of years.
MANUFACTURERS OF:
• Surface Grinding Machines • Cutter & Tool Grinding Machines • Thread Rolling Machines • Spline Rolling Machines • Pulley Forming Machines • Tube Finning Machines • Milling Machines • Horizontal Machining Centres • CNC Lathe Machines • CNC Milling Machines • CNC Surface Grinding Machines • CNC Cutter & Tool Grinding Machines • Praga is also manufacturer of Customer Tooling for the above
MACHINERY LIKE:
• Jigs & Fixtures • Mountings • Accessories • Tooling for the above mentioned cold forming processes
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Praga is collaborated with some of the world famous companies like Jones & Shipman of U.K, Gambian of France, and George Fischer of Switzerland, Mitsubishi Heavy Industries of Japan and Keiyo Seiki of Japan. The collaborations have culminated in Praga producing standards.
Praga has contributed to the development of the machine tool industry in the country and creation of a vast band of skilled technicians. Thus, Praga today is a name to reckon within the Machine tool Industry.
(
+
)
=
PRESENT STATUTES OF THE PRAGA TOOLS,
HYDERABAD MERGER OF
HMT- MACHINE TOOLS LIMITED
In complacency of the directories of government of India & BIFTR M/s Praga Tool Ltd, has merged with HMT Machine Tools Ltd. Bengaluru with effect from 13-06-2008 and all the merging formalities had been completed on 20-06-2009.
M/s Praga Tools Ltd had been renamed as HMT Machine Tools Limited (Praga Division Hyderabad) from the date onwards. All the policies, rules & regulations, guidelines and facilities are applicable to Praga employees as per the HMT Machine Tools Limited.
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1.1 INTRODUCTION The literature on quality management provides a broad range of definitions of quality. In particular, the literature notes that quality is a subjective term and that individuals and organizations have their own perceptions and definitions. However, the common theme or focus of each of these definitions reflects the need for the total characteristics and features of a product or service to satisfy a specified need or use. In terms of aeronautical information services and products, the word “quality” should communicate a high level of consistent performance, reliability and overall credibility in meeting and satisfying the aviation industry's identified needs. As individuals and organizations hold their own perception of what defines quality, there is obviously a need for a common understanding. ISO provides this in its definition of quality: the "degree to which a set of inherent characteristics fulfills requirements". "Requirement" signifies "need or expectation that is stated, generally implied or obligatory"; "inherent" signifies "quality is relative to what something should be and what it is, especially as a permanent characteristic". For example, the price of a product may be determined by the cost and profit margin of the supplier. It is an assigned and transient feature but is not necessarily related to the quality of the product. The most important aspect is that, at minimum, it meets specified requirements. Any feature or characteristic of a product or service that is needed to satisfy user needs or achieve fitness for use is a quality characteristic. When dealing with products, the characteristics are mostly technical, for example accessibility, availability, operability and durability, whereas service quality characteristics have a human dimension, for example waiting time, delivery time, accuracy and accessibility. These characteristics are measurable and consequently can be used to monitor the quality of the product or service. 1.2 QUALITY MANAGEMENT SYSTEM: QMS is a management system that directs and controls an organization with regard to quality. Activities generally include the following: a) Quality control b) Quality assurance c) Quality improvement The intent of the ISO 9000 QMS is to provide a management framework for the organization to comply with applicable requirements, control its processes and minimize their risk and ultimately satisfy customer needs and expectations.
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CHAPTER 2
QUALITY CONTROL IN HMT
2.1 INTRODUCTION
The components meant for assembly of various machines manufactured in the shop floor right from new material stage to finished stage.
As we go ahead with the manufacturing procedures it is customary to check the components as per the drawing specification and in some cases allowances for finishing process.
As the components are finished they would be taken up for final inspection after which the clearance (acceptance/rework/rejection) will be given by the quality control inspector. In case of acceptance the components will be dispatched to the components' stores or assembly or customer through appropriate documentation.
After all the components are assembled in various sub-assemblies of a machine; these sub-assemblies will be checked and certified by quality control inspector.
After the sub-assemblies are completed and certified by the quality control inspector, these will be assembled to complete the final assembly of the machine after which the machine will be checked as per standard test charts as recommended by ISI (ISO-9000 principles) or BIS.
In general, all the measurements taken in the above contexts will be recorded in standard formats.
2.2 MOTIVATION
Throughout the centuries, people have challenged to make their lives easier. One way to accomplish this was to invent tools that make the job less difficult. We know these tools as machines. The tools most of us think about when we hear the word 'machine' are actually a combination of two or more simple machines. We use simple machines everyday and are dependent on them in many aspects of our lives. You need a bottle opener to open a soft drink bottle. A furniture mover needs to bring a ramp usage to bring up heavy cabinet into the back of a truck. A carpenter needs hammer to separate two boards that have been nailed together incorrectly.
In the same way even for a machine to be manufactured for an industry there are certain machine manufacture techniques. These can be enhanced with proper approach in component designs and simplifying the manufacturing process. This manufacturing process includes the study of proper machining operations.
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2.3 OBJECTIVE
Defects experienced during construction are costly and preventable. However, inspection programs employed today cannot adequately detect and manage defects that occur on construction sites , as they are based on the measurements taken at specific locations and times, and are not integrated into the complete electronic models. Emerging sensing technologies and project modelling capabilities motivate the developments of a formalism that can be used for active quality control of construction sites. In this paper, we outline a process of acquiring and updating detailed designing information, identifying inspection goals, inspection planning, as-built data acquisition and analysis and defect detection and management 'quality control'.
2.4 LIMITATIONS
Even though our mini project subjects to a brief study on various machining processes, these operations are restricted only to the specified components and dimensions, the operational features vary accordingly with the required component design. However, these explain well how the operational techniques are being adopted in making a component more flexible for machinery. Our mini project is confined to the components that are being described here.
Fig 2.1 Quality Approval
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CHAPTER 3
QUALITY STANDARDS AT HMT
3.1 INTRODUCTION
The turbulent environment forces modern companies the constant search for the sources of competitive advantage. To succeed they should meet the needs and expectations of its clients, which requires the management to take appropriate action in respect of the quality of offered products.
In aviation quality is linked to the wide range of security issues and no other production industry raises such a big interest of observers, as the aviation industry does.
The purpose of this study is to present selected quality standards, on the basis of which the quality management systems are being built in the aerospace industry.
3.2 QUALITY MANAGEMENT SYSTEM IN THE CONTEXT OF ISO 9000 STANDARD
ISO standards from 9000 series belong to the group of international standards relating to implementation of the quality management system in organizations from different sectors diversified in respect of largeness. These standards are characterized by: versatility and elasticity in usage, compatibility with other standards, objectivity in relation to evaluation of quality system. Moreover, they were updated several times- amendments made in 2000 being the most significant.
Currently ISO 9000 family consists of:
− ISO 9000:2005 Quality management systems – Fundamentals and vocabulary.
− ISO 9001:2008 Quality management systems – Requirements.
−ISO 9004: 2009 Managing for the sustained success of an organization – A quality management approach.
− ISO 19011:2011 Guidelines for auditing management systems.
Preparation and implementation of the quality management system require a certain terminology, therefore ISO 9000:2005 standards include basic definitions and describe basic rules, on which a system should be based. These rules include:
- Defining the needs and expectations of clients,
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- Creating a vision and developing a policy which helps to put it into practice,
- Identifying primary and secondary processes, measuring and improving,
- Managing interrelated processes and activities,
- Constant research about new ways of improving the functioning of the organization and quality system
- Making decisions on a basis of gathered data and information,
- Establishing partner relations with clients
ISO 9000:2008 standard include requirements towards quality management system. They are divided into 5 chapters and relate to:
- general requirements towards system, which should be based on a systemic approach and developed as well as supervised documentation, which should consist of: quality policy, a quality manual, documented procedures and notes as well as other documents essential for effective management of processes
- management’s responsibility for: engagement in a creation of a system, determining requirements of organization clients, realization of the quality policy, planning processes, determining rights and responsibilities, reviewing of a management,
- managing of the organization’s resources including: human resources, infrastructure and work environment,
- managing of processes essential for realization of a product related to: clients, purchases, production or delivering services, supervision of the equipment for monitoring,
- doing measurements, analyses and improvements by: monitoring of client’s satisfaction, conducting internal audits, performing supervision over products, which do not meet requirements, conducting corrective and preventive activities
Only ISO 9001 standard is underlined to certificate a system that is to determine by the independent unit that the system is compatible with the standard’s requirements.
ISO 9004:2009 standard indicates recommendations for achieving permanent success in constantly changing environment. Presented recommendations emphasize a need to consider client’s and other parties interested in organization requirements and stress the importance of studying in the process of improvement.
8 The last standard: ISO 19011:2011 relates to problems connected with conducting audits and includes information concerning rules of auditing, managing programs of audits as well as guidelines for evaluation of competences of people engaged in realization of audits.
Quality management system built on a basis of requirements and recommendations included in ISO9000 standard can be implemented in every organization regardless of its profile of action. This system can be characterized as: “management system for leading an organization and its supervision in relation to quality”. Terms used in this definition mean:
- Management system: system for establishing organization’s aims and their realization,
- Quality: degree in which a group of inherent (permanent) properties fulfill the requirements
Implementation of a system should begin by establishing by the management of the organization its scope and field of implementation. It is relevant to conduct an analysis first and evaluate current status of management. Consecutive activities concentrate on identification of processes and preparing systemic documentation. It is also necessary to conduct trainings among employers and undertake corrective and preventive activities, which improve system.
3.2.1 AS 9100C as the basis of the Aerospace Quality Management System
European Union has released some of the most important documents forming the basis for a kind of air law among the members of the design and production of the EU aviation products. The most important document is a regulation of the European Parliament and of the Council of the European Community No 216/2008 on common rules in the field of civil aviation and establishing a European aviation safety agency here in after referred to in the industry as the Basic Regulation. The document was modified, and the latest version was founded in January 2013, creating a regulation (EC) No 6/2013 (commission regulation (EU) no 6/2013).
This regulation approves two other documents of the European Commission, namely:-Commission Regulation (EC) 1702/2003 of 24 September 2003 laying down implementing rules for the certification of aircraft and related products, parts and appliances in terms of airworthiness and environmental protection, as well as for the certification of design and production organisation.
The purpose of the implementation of the Basic Regulation was to establish and maintain uniform and high level of civil security in the European Union as well as the protection of the environment. In addition, it aims to facilitate the free movement of persons, goods and services, the promotion of certification, while avoiding duplication of legislation. Dynamic development of the aviation industry has become a motivator to create standards for this
9 sector of the economy, which resulted in building the standards AS 9100 Quality Management Systems-Requirements for Aviation, Space and Defence Organizations. The purpose of this action was to achieve a significant improvement in the quality and safety, and reduce costs by analyzing the values.
So far the norm was two renewals to version AS 9100B (now outdated) and current AS 9100C. Aerospace quality standard AS 9100C relates to the quality management system (QMS) and the requirements for aerospace organization (Quality Management Systems - Requirements for Aviation, Space and Defence Organizations). Specifies requirements for a quality system for organizations that are facing the need to demonstrate its ability to provide the aviation product meeting the requirements of the customer. Assumes that the organization where this standard is implemented, aims to enhance customer satisfaction through the effective application of the system of systematically improved and ensuring compliance requirements with the statutory requirements and regulations.
In the framework of the AS 9100C are both ISO 9001: 2008 entries, as well as AS 9100B and topical additions necessary for aeronautical products. In addition, this standard places requirements for the quality management system for the aerospace industry in order to improve the quality and safety while reducing costs due to the elimination or reduction of the exceptional requirements of the organization and the pooling of these variability inherent expectations. AS 9100C, constructed on the basis of ISO9001: 2008 quality management system certification forms the basis of air companies, without which no organization could operate in the correct way. However, this is not the only one document to standardize the work of the organization. Technical standards SAE International shall inform that report AS 9100C is voluntary and used by organizations in order to develop the level of technical and engineering sciences. The organization should be identified and links are managed in such a way that any resources were used to transform input data into output. The advantage of this approach is to ensure that the current supervision of ties between the various processes in the system processes, as well as over their combination and mutual interaction.
All the requirements contained in the standard AS 9100C are general and are intended to be used by the aerospace organizations regardless of their size, type or product produced. If any of the requirements of the standards could not be met by the organization, then the discussion is recommended over the exclusion of such requirements. However, the exemption is not acceptable in the case of the company's efforts to obtain the certificate of conformity with this standard, unless exemptions apply. The realization of the product, and such exclusions do not affect the previous version of AS9100C standard. Organization's ability to deliver a product that satisfies the client's requirements and the requirements of applicable legislation.
Acquiring organizations parts, materials and assemblies and engaged in the resale of these products including products and buyers organizations to divide them into smaller parts for sale,
10 should apply in turn the standard developed by the International also AS9120 Aerospace Quality Group (IAQG). As mentioned above, the standard AS 9100 is constructed on the basis of ISO 9001, but complemented the content intended for aerospace organizations. Consequently, among the additions can be found among others. The new definition such as: key property risk, special requirements and critical elements and other content that in a shortened and selective are presented below.
According to the requirements of the standard AS 9100C quality management system should relate to the customer requirements and the requirements of legislative and legislative. All processes of the aerospace industry should be identified along with reciprocal links. In addition, the organization is obliged to determine the criteria and methods for the course and supervise processes, ensure the availability of information and resources necessary for these functions. Essential activities such as: monitoring, measurements, analyze processes and the implementation of the measures necessary to achieve the objectives and continuous improvement. Documentation requirements of the quality management system according to the AS 9100C are the same as in the case of ISO 9001. The highest leadership of the Aviation Organization should ensure the opportunity to measure the compliance of the product and the timeliness of deliveries, and take appropriate action in the event of not achieving planned results. In addition to the objectives relating to the quality of the product, which apply both in ISO 9001, as well as in the internal organization strategy, attention should be paid to aspects such as:
- Safety of the product and staff;
- Reliability, availability and the ability to operate;
- A bility to produce and control;
- The relevance of the components and materials used in the product;
- Selection and development of embedded software;
- Recycling and final disposal of the product at the end of the period of use.
In the area of project management, organization of traffic in order to meet the requirements for the allowable risk should plan and manage the implementation of the product in a way that is based on the structure and subject to supervision within the framework of the set of resources and schedules. In addition, the Organization has established air, deploy and lead risk management process under the relevant requirements. This process should include:-assigning responsibility for risk management;-to define criteria such as risk probability, consequences, the acceptability of the risk; -identification, implementation, and management of actions to minimize the risk of exceeding the criteria-admissibility of remaining risks after the debilitating action.
The company has established air, deploy and carry out the planning process and oversight of temporary and permanent transfer work. In addition, the requirements associated with the device must include the special requirements. In turn after delivery activities include among others. Operation is subject to the provisions of the warranty, contractual obligations, and
11 additional. At the same time the airline organizations are committed to planning, implementation and implementation of configuration management. The Organization, if appropriate, shall enter the Division of design and development work on the extracted steps. For each of these actions, in turn, should be referred to the task, the necessary resources, liability, the scope of the project and the input and output as well as constraints in the planning.
In the area of purchasing, an aerospace organization should be responsible for the quality of the purchased products or semi-finished products, also from the sources indicated by the client. A factor likely to apply when assessing suppliers are its quality data obtained from objective sources. Such organizations include processes and quality management systems certification bodies and Government agencies. The Organization should pay attention to the identification of the products along with outlining the respective releases of specifications and technical data. In addition, it is important to draw attention to the requirements for the design, testing, research, control, verification of the application of statistical techniques to the deliverable of the product and appropriate statements for approval by the Organization, as well as critical elements. Information about purchases should also include requirements for test samples. Requirements including the requirements should be provided in the supply chain and put to record. The right of access to all devices and objects associated with the device and all the relevant records must receive both the Organization as well as the client and the authorities at every level of the supply chain.
Review of the product by the customer at every level of the supply chain may not be for the proof of the effectiveness of quality control and should not exempt the organization from liability to provide acceptable product and comply with all applicable requirements. Verification activities, in turn, may include:
- To obtain objective evidence of product quality on the part of suppliers;
- Control and audit on suppliers;
- An overview of required documentation;
- Control devices on delivery;
- authorized supplier for verification or certification providers.
If the product is in turn released for use in the production in anticipation of the completion of all the required verification measures, should be identified and described so as to allow its withdrawal and replacement in case of not meeting the requirements. In the event of a transfer verification at the supplier, the Organization should determine the requirements for communication and to maintain the register of transfers.
Conditions of production surveillance shall include:
- The availability of information, which in the case of providers should include drawings, parts lists, processes and material standards;
- The availability of work instructions, which may include process diagrams, documentation of production and documentation control;
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- Use of proper equipment, specific equipment;
- Settlement during the manufacture of the products documented for all entries;
- involved in the manufacture and control of finished according to plan;
- Actions for the prevention, detection and removal of foreign objects;
- Monitoring and control of resources such as water, air, energy and chemical products joined in so far as they affect the quality of the product,
- Implementation of the quality criteria laid down in a clear and practical way through example: written standards, representative samples or illustrations;
In addition, the Organization should use a representative element of the first batch of a new part or Assembly in order to verify the manufacturing process, documentation and Instrumentation in terms of fulfilment of the requirements. These actions are often called control first. In turn, tools, equipment and software used to automate the monitoring and implementation process of the product must be validated before releasing into production and have supported. Information subject to monitoring in order to evaluate the customer satisfaction should include product, promptness, customer complaints and requests for corrective actions, but should not be limited to them. Aviation organizations should implement plans to improve client satisfaction, referring to shortcomings identified by the evaluation and assessing the effectiveness of their effects.
In determining the appropriate methods for monitoring and measurement of processes, it is desirable, that the Organization has taken into account the nature and extent of monitoring or measurement applied to each of its processes in relation to their impact on the conformity with the requirements for the product and the efficiency of the quality management system. In the event of non-compliance with the process, the Organization should take appropriate corrective actions, assess whether non- compliance process affects the non-conformity of the product, determine whether non-compliance process is limited to a particular case or can affect other processes or product and to identify and oversee the incompatible products. The monitoring and measurement of product was also expanded to include the requirement for the acceptance of measurement device, which should be documented and include acceptance criteria and/or rejection, the order of execution of measurements and tests the required records of the results of measurements and the required type of measuring instruments. If you turn from the organization is required to demonstrate the eligibility of the product, shall provide records that provide evidence of conformity of the product with the requirements of, and upon delivery of all documents should accompany the products
In the case of monitoring for illegal products, the Organization should protect the reporting process in time, and the actions taken to the effects or potential effects of the non-compliance of the product detected after delivery to the customer should be appropriate to the nature and importance of these effects. Therefore, the Organization should also take preventive measures to reduce the potential consequences of non-compliance for other products and processes. As presented above, the standard aviation AS9100C is the norm, but due to its nature as the necessity of taking care of safety and high quality of the products. On the safety use of aeronautical products is not only the staff, but also (and perhaps above all) organizations involved in designing, producing and renovation of aeronautical products affected by the standard presented. Quality management system based on the standard is complex but at the same time, QMS of AS9100C largely providing high quality equal to the high level of safety of aeronautical products.
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CHAPTER 4
QUALITY CONTROL EQUIPMENT USED IN HMT
4.1 VERNIER CALIPERS
Verniers are used for checking external and internal dimensions that are controlled within
±0.2mm and above. Gear tooth vernier is used for checking chordal thickness of bevel gears at
major diameter in its taper.
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Fig 4.1: Vernier callipers
4.2 MICROMETERS
Micrometers are used for checking dimensions of shafts and controlled within ±0.01 to ±0.05.
Fig4.2 Micrometer
Fig 4.3 Different types of micrometers
15 →Three point bore micrometer is used for checking bores of tolerance ±0.03 to ±0.08.
Fig 4.4 Bore micrometer scale
→ Flange micrometers are used for checking accurate dimensions on stepped faces. Pitch micrometers are used for checking effective diameters of threads.
Fig 4.5 Flange micrometer
→Groove micrometers are used for checking groove diameters of external grooves. For
checking groove diameters, we use inside calliper and an external micrometer.
16
Fig 4.6: Groove micrometer
4.3 BORE INDICATORS
Bore indicators are used for checking bores of tolerance ±0.001 to ±0.025.
Fig 4.7 Bore indicator
17 4.4 HEIGHT GUAGES
Height gauges are used for checking parallelisms, run outs, concentricity and so on. On surface
plate we use height master for comparing the heights or distances of holes, faces etc.
Fig 4.8 Height gauges
4.5 UNIVERSAL HARDNESS TESTER
Universal hardness tester is used for checking hardness of work pieces after we calibrate it by
cross checking with a master piece provided for this purpose.
Fig 4.9 Universal hardness tester
18 4.6 SURFACE FINISH TESTER
Surface finish tester is used for checking the surface finish of ground & tapped surfaces
after calibrating it on master piece.
→Sine bar is used for checking the accuracy of angles of tapered surfaces.
Fig 4.10 Surface finish tester
→Centimetre is used for checking the centre distances of two holes directly.
4.7 PROFILE PROJECTOR
Profile projector is used for checking the irregular contours of work pieces by comparing the
shadow magnified (by 10, 20, 50, 100 times) with a shadow graph drawn on transparent sheets
by design’s depth.
Fig 4.11 Profile projector
19 4.8 UNIVERSAL MICROSCOPE
Universal microscope is used for checking the threads, serration profiles by comparing them
with oculars containing ideal (error free) profiles duly printed on them.
4.9 PLUG GUAGES
Plug gauges are used for checking the lower and upper limits of holes. Similarly we use ring
gauges for calibrating bore indicators before we check work pieces with them.
Fig 4.11 Plug gauge
Fig 4.12: Ring gauge
20 4.10 ROLLERS
Pins or rollers are used for checking O.W.M on threads/serrations.
Fig 4.13 Rollers
4.11 SAMPLE MICROMETERS
Fig 4.14 Sample micrometers
These types of micrometers are used for the different sizes of the components depending on their ranges provided. Each micrometer consists of different ranges of which could be calculated using the specific kind of sample micrometers. They range from 25mm to 150mm.
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CHAPTER 5
QUALITY INSPECTION IN HMT
5.1 DEFNITION
Quality inspection are measures aimed at checking, measuring, or testing of one or more product characteristics and to relate the results to the requirements to confirm compliance. This task is usually performed by specialized personnel and does not fall within the responsibility of production workers. Products that don't comply with the specifications are rejected or returned to improve.
5.2 ORIGINS OF QUALITY INSPECTION
Quality inspection is one of the first stages of evolution of management. The origins of the quality inspection back to the late nineteenth and early twentieth century. In days of fast-growing industry, FW Taylor developed the rules of scientific management. Quality wasn't up to speed with rapidly increasing labour productivity. Often, the customer had to reckon with defective products. To alleviate customer frustration, this problem was solved by replacing the defective product with a new one. Conducting this type of procedure entailed generating considerable cost. To reduce the excessive cost escalation manufacturers, introduced the unknown to craft the position controller. The designated employee, through carried out inspections, made sure that the greatest possible number of good products leave the gate of the factory. This initial form of quality control based on the principle of quality by sorting
5.3 IMPORTANCE OF QUALITY INSPECTION
The key assumption relating to quality inspection is to adopt the principle that the ultimate controller is a client. The optimum form of quality inspection is the man who's aim is the best customer satisfaction. Quality inspection serves three main purposes:
1. Identification of the problem 2. Preventing its occurrence 3. Elimination of the problem
Effective quality inspection is dynamic, drawing attention to everything that is happening, searching and providing for the problems associated with product quality. Effective identification of the problem requires verification checks after each stage of production. One option is to check the delivered components before they are used in further manufacture. Second, the system of self-assessment by the workers.
5.4 EVOLUTION OF QUALITY INSPECTION
At the beginning, quality inspection mainly concerned on the control of postoperative or post-production control of production processes. Considering the quality inspection in a broader sense, one might say that it is perceived as an activity associated with a diagnosis of a selected aspect of product quality which informs about the partial quality, obtained at a given stage of the formation or operation of the device, and being compared with the declared quality such as product characteristics. At various stages of formation of the product the quality inspection takes different forms, and is implemented using different methods.
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5.5 TYPES OF QUALITY INSPECTION
• Quality inspection of product design - At the design stage, verification or validation phase - refers to assessing the status of compliance with the requirements enunciated by users or by the designers. The resulting quality of the design is essentially un-measurable and its evaluation is characterized by a considerable objectivity.
• Quality inspection of the design process - At this stage the task of inspection consists of checking whether accepted or held methods and means of production, can produce quality performance in accordance with the quality of design.
• Quality inspection in the production stage - Inspection used to determine the compatibility of the resulting quality of the product or fractional part of the documentation requirements contained in the design or technology.
• Thorough quality inspection - shall be carried out after completion of all stages of the production process. Final product and its compatibility with the standard design is subject of inspection.
• Inspection one hundred percent, - which consists of subjecting the inspection of all units produced. Due to time-consuming, this method is applied only to products manufactured individually or in small series.
• Statistical inspection - a lot of statistical inspection is assessed on the basis taken in a random sample. Therefore, this form of control is called a sample inspection. Depending on the size and frequency of sampling and the use of audit information to reverse effects on the production process, control may be statistical in nature
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CHAPTER 6
QUALITY INSPECTION OF PRODUCT DESIGN IN HMT
6.1 INTRODUCTION
Quality control starts at the point of product conception and is carried all the way through to the final design and manufacture of a product. Product defects and failures can be attributed to poorly designed product, a poorly designed manufacturing process and/or a poorly designed quality system. Separate engineering groups within a company are assigned to (1) design and develop products referred to as product design engineers, (2) design and develop the manufacturing processes referred to as industrial-manufacturing-process engineers and (3) design and develop the quality system referred to as quality control or quality assurance engineers. Some companies require their manufacturing and process engineers to function as quality control engineers as well which is usually the practice of smaller companies.
6.2 PRODUCT DESIGN
When a company designs a product for sale in the open marketplace, the engineers should use the engineering design sciences to design each component of the product. During the initial design phase, a prototype is made. The prototype should then be tested in the lab and in the field. These tests should determine functionality, safety, product durability and product life. If design problems become apparent during testing, a product redesign should be performed to eliminate the issue. Then product testing should resume. If the product is improperly designed and not thoroughly tested; design flaws could be the result, and the product could be unsafe and/or could fail. Failure may be catastrophic after a short period of use; the product could fail from use over a longer period of time or the product failure may be not performing according to the literature shipped with the product. The failure may or may not injure a customer depending on the type of product. The bottom line is that if a product has one or more design flaws and has not been properly tested before it is released for mass production, it will fail in some way at some point. The failure could be either from lack of performance, safety or durability.
In the world of engineering, good engineers use the engineering sciences to design products. In this endeavour, design problems must be worked out and solved by the engineer if the engineering science is available. A product must be designed to operate safely and must be designed and manufactured with a reliability that will ensure a long and trouble free life. But whether the science is available or not, functionality, performance, durability and safety issues must be solved, and whatever form the design solution takes under these conditions is called “Engineering”.
24 6.3 PRODUCT MANUFACTURING
Most products are made up of one or more components. Depending on a component and its material, the product is manufactured using a specific process. This process could be made up of tooling and dies, material handling and holding fixtures, high precision high volume multi-axis machining and turning centres, high pressure injection molding machines, punch or forming presses, roll formers, finely detailed electronic manufacturing etc. These components must then be transported from one operation to the other by conveying, by pick and place robots or by forklift utilizing palletized containers. Once each component part of the product has been manufactured, the components must then be assembled into a complete and functional unit. This can be performed manually by hand or using automated processes via robots and other automatic assembly machines. The final assembly must then be inspected for proper function. And finally it must be packaged and shipped to the end user. In any one of these operations, the product or its components can be made incorrectly or damaged in some way. If a defect is mistakenly manufactured into the product and is not discovered through inspection, then functionality, performance or safety issues could surface at some point. For example, if a jagged edge is machined onto a component by mistake, it could cut the end user. If a shaft that is designed to experience torsional stresses is mistakenly manufactured in a machining operation leaving an undesirable tool mark on the circumference of the shaft, this tool mark would become a stress riser and cause the shaft to fail catastrophically in service due to fatigue. It is important for a company to properly inspect components and assemblies for manufacturing defects before the product reaches the end user to avoid performance issues or a catastrophic failure that could lead to a personal injury.
6.4 QUALITY INSPECTION OF DESIGN PROCESS IN HMT Fig 6.1 Traditional approach to design process as a feedback system with cycle operation
Major disadvantages of the previous (classical) approach:
• Tends to drop into cycle operation, repeating the testing/design phases • Optimizes exclusively the design process output
System Design
Testing
User Requirements
(Inputs)
Product or Process Design (outputs)
25 • Weak relations between the System Design and the Testing steps – occurrence of a so
called “over the wall problem solving” • Strong influence of mentality of the manpower involved.
Fig 6.2 Typical shape of the design iterations
To extinguish the negative phenomenon leads to Taguchis’ approach to design process:
Core properties of the Taguchis’ method:
A general design criterion (objective function) drives the design process, which should be clearly defined as:
1. Variance (scatter) minimization within the design process leads to minimization of the variance also in the resulting process → tool to improve quality.
2. Pushing the mean value of the designed process output towards the required value as much as possible.
3. Efforts to conduct possibly environment-independent design (could also be derived from experiments in the design phase of the process)
Taguchi’s method is a 3-level procedure consisting of:
Due Date No. of Design Changes
Months
Jap.
U.S.
20-‐24 14-‐7 3-‐1 3
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6.5 TAGUCHI DESIGN LEVELS
Level 1: System design
Integrating scientific state of the art about the task solution, existing technologies, previous experiences, etc. → leads to development/selection of basic alternatives to the design for the end-user (also called as “mapping function”)
Level 2: Parameter design
• Selection and tuning of nominal parameter values of the chosen method for the designed system
• Optimization and tuning of previously chosen parameters with respect to the final sensitivity of the designed system to input variations (noise) - close to classical sensitivity analysis. (e.g. .varying quality of assembly parts, raw material input, etc.).
• High importance of a design-phase experiment for identification of such parameters and sensitivities.
System Design
Tolerance Design
User Requirements
(Inputs)
Product or Process Design (outputs)
Parameter Design
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Level 3: Tolerance design
Identification and selective reduction of parameter tolerances (optimization) to achieve minimal quality loss while decreasing price of the designed process (e.g. using less expensive parts, materials, less qualified manpower, etc.)
6.6 QUALITY INSPECTION IN PRODUCTION STAGE IN HMT
Conduct an inspection during production:
The ideal timing actually depends on the product type and the experience of the factory. But a few rules of thumb can be followed for 80% of consumer goods, if these conditions are true:
• The factory is used to making this kind of product involving this level of complexity, • The cycle time to get the first finished products out of the lines is no more than 10 days.
In such cases, the below sketch is applicable:
Process Output
Control Factors
(System internal parameters)
Process Inputs + Noise
(parts, manpower, raw materials, market, etc.)
Designed Process
System Sensitivity Analysis
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There are two dangers to avoid:
Checking too early
The very first products that get off the lines are not representative of average quality (they are usually worse). And the factory needs to have time for their internal QC, or they will claim that “of course, they would not ship this kind of defects.”And if you think you can inspect products that have gone through a few processes but are not finished, you’d better be sure you can find quality issues this way. It depends on the type of products, but inspection firms usually don’t have the expertise to do that.
Checking too late
Most factories in Asia produce in very large batches–this is why finished products often do not appear before one or two weeks into production (and sometimes more).If the buyer waits until 50% of the products are finished, it is likely that another 30% are already being processed. If quality issues are found at that stage, they might already be present on 80% of the order.
Checked during production:
Naturally, the inspector verifies that production is taking place in the workshop. He can also ask for the updated production planning.
An inspection during production can be failed for three reasons:
1. Non-conformity to specs:
All the relevant aspects of the product (quantity, components, assembly, aesthetics, function, size, labeling…) are controlled, based on the buyer’s requirements.
2. Too many visual defects:
Based on the sampling plan, the inspector selects and checks some products, and then he compares the number of defects to the AQL limits.
3. Failed on-site test(s):
Some simple tests can be done by the inspector in the factory, instead of sending samples to a laboratory.
29 Limits of an inspection during production:
First, it is not enough in itself. A factory might identify some problems, hide them away from the inspector, and then ship them out. This is why an inspection during production should be followed by a final random inspection, to confirm average quality.
Second, for sensitive projects, the factory might need some guidance from the beginning of production. This is the work of a technician capable of setting up processes as required.
Third, in certain cases production takes place on multiple lines or even in multiple factories. One inspector will not be able to get an idea of average quality in one day. He should stay for longer and monitor both production schedule and quality.
Fourth, very often labeling and packing cannot be checked properly.
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CHAPTER 7
FAILURES
Failure of materials may have huge costs. Causes included improper materials selection or processing, the improper design of components, and improper use.
7.1 FRACTURE
FUNDAMENTALS OF FRACTURE:
Fracture is a form of failure where the material separates in pieces due to stress, at temperatures below the melting point. The fracture is termed ductile or brittle depending on whether the elongation is large or small.
Steps in fracture (response to stress):
• track formation • track propagation
Ductile Fracture:Stages of ductile fracture
• Initial necking • small cavity formation (microvoids) • void growth (ellipsoid) by coalescence into a crack • fast crack propagation around neck. Shear strain at 45o • final shear fracture (cup and cone)
The interior surface is fibrous, irregular, which signify plastic deformation.
Fig 7.1 Macroscopic image of Ductile fracture
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Fig 7.2 Microscopic image of Ductile fracture
Brittle Fracture:
There is no appreciable deformation, and crack propagation is very fast. In most brittle materials, crack propagation (by bond breaking) is along specific crystallographic planes (cleavage planes). This type of fracture is trans-granular (through grains) producing grainy texture (or faceted texture) when cleavage direction changes from grain to grain. In some materials, fracture is inter-granular.
Fig 7.3 Macroscopic image of brittle fracture
Fig 7.4 Microscopic view of brittle fracture
32 Table 7.1 Ductile vs. brittle fracture
Ductile Brittle
Deformation Extensive Little
track propagation slow, needs stress Fast
type of materials most metals (not too cold) ceramics, ice, cold metals
Warning permanent elongation None
strain energy Higher Lower
fractured surface Rough Smoother
Necking Yes No
Principles of Fracture Mechanics
Fracture occurs due to stress concentration at flaws, like surface scratches, voids, etc. If a is the length of the void and ρ the radius of curvature, the enhanced stress near the flaw is:
σm ≈ 2 σ0 (a/ρ)1/2 (7.1)
where σ0 is the applied macroscopic stress. Note that a is 1/2 the length of the flaw, not the full length for an internal flaw, but the full length for a surface flaw. The stress concentration factor is:
Kt = σm/σ0 ≈ 2 (a/ρ)1/2 (7.2)
Because of this enhancement, flaws with small radius of curvature are called stress raiser.
Impact Fracture Testing
Normalized tests, like the Charpy and Izod tests measure the impact energy required to fracture a notched specimen with a hammer mounted on a pendulum. The energy is measured by the change in potential energy (height) of the pendulum. This energy is called notch toughness.
Ductile to brittle transition occurs in materials when the temperature is dropped below a transition temperature. Alloying usually increases the ductile-brittle transition temperature. For ceramics, this type of transition occurs at much higher temperatures than for metals.
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7.2 FATIGUE
Fatigue is the catastrophic failure due to dynamic (fluctuating) stresses. It can happen in bridges, airplanes, machine components, etc. The characteristics are:
• Long period of cyclic strain. • Most usual (90%) of metallic failures. • Brittle-like even in ductile metals, with little plastic deformation. • Occurs in stages involving the initiation and propagation of cracks.
Fig 7.5 Macroscopic image of Fatigue
Fig 7.6 Microscopic image of Fatigue
Cyclic Stresses
These are characterized by maximum, minimum and mean stress, stress amplitude and stress ratio.
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Fig 7.7 S—N Curve
Fatigue limit (endurance limit) occurs for some materials (like some ferrous and Ti allows). In this case, the S—N curve becomes horizontal at large N. This means that there is a maximum stress amplitude (the fatigue limit) below which the material never fails, no matter how large the number of cycles is.
For other materials (e.g., non-ferrous) the S—N curve continues to fall with N.
Failure by fatigue shows substantial variability.
Failure at low loads is in the elastic strain regime, requires a large number of cycles (typ. 104 to 105). At high loads (plastic regime), one has low-cycle fatigue (N < 104 - 105 cycles).
7.3 STAGES IN FATIGUE FAILURE
I. Crack initiation at high stress points (stress raisers)
II. Propagation (incremental in each cycle)
III. Final failure by fracture
Nfinal = Ninitiation + Npropagation (7.3)
Stage I – Crack initiation:
• slow • along crystallographic planes of high shear stress
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• flat and featureless fatigue surface
Stage II – propagation:
Crack propagates by repetitive plastic blunting and sharpening of the crack tip.
Factors That Affect Fatigue Life
• Mean stress (lower fatigue life with increasing σmean). • Surface defects (scratches, sharp transitions and edges). Solution: • Polish to remove machining flaws • Add residual compressive stress (e.g., by shot peening.) • Case harden, by carburizing, nitriding (exposing to appropriate gas at high temperature)
Environmental Effects
• Thermal cycling causes expansion and contraction, hence thermal stress, if component is restrained. Solution:
o Eliminate restraint by design o Use materials with low thermal expansion coefficients.
• Corrosion fatigue. Chemical reactions induced pits which act as stress raisers. Corrosion also enhances crack propagation. Solutions:
o Decrease corrosiveness of medium, if possible. o Add protective surface coating. o Add residual compressive stresses.
7.4 CREEP
Creep is the time-varying plastic deformation of a material stressed at high temperatures. Examples: turbine blades, steam generators. Keys are the time dependence of the strain and the high temperature.
Generalized Creep Behaviour
At a constant stress, the strain increases initially fast with time (primary or transient deformation), then increases more slowly in the secondary region at a steady rate (creep rate). Finally the strain increases fast and leads to failure in the tertiary region. Characteristics:
36
• Creep rate: dε/dt • Time of failure.
Stress and Temperature Effects
Creep becomes more pronounced at higher temperatures. There is essentially no creep at temperatures below 40% of the melting point.
Creep increases at higher applied stresses.
The behaviour can be characterized by the following expression, where K, n and Qc are constants for a given material:
dε/dt = K σn exp(-Qc/RT)
These are needed for turbines in jet engines, hypersonic airplanes, nuclear reactors, etc. The important factors are a high melting temperature, a high elastic modulus and large grain size (the latter is opposite to what is desirable in low-temperature materials).
Some creep resistant materials are stainless steels, refractory metal alloys (containing elements of high melting point, like Nb, Mo, W, Ta), and superalloys (based on Co, Ni, Fe.)
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CHAPTER 8
INSPECTION OF COMPONENTS IN HMT
8.1 BEARINGS
This Leaflet gives information on the uses of the various types of ball and roller bearings, and general guidance on installation, maintenance and inspection. Methods of assessing wear are described, but the appropriate aircraft manual should be consulted for the amount of play or clearance permitted, in any installation in which rolling bearings are used.
Types of bearings and their uses
Bearings are broadly classified by the type of rolling element used in their construction. Ball bearings employ steel balls which rotate in grooves raceways, whilst roller bearings utilise cylindrical, tapered or spherical operation under continuous rotary or oscillatory conditions, but, whilst ball bearings and tapered roller bearings accept both radial and axial loads, other types of roller bearings accept mainly radial loads. The following paragraphs amplify the uses of the various types of bearings, and examples are shown in Figure.
Fig 8.1 Types of bearings
Caged bearings
Caged bearings are in general use for engine applications and in equipment with rotational speeds in excess of approximately100 rev/min. Most other bearings on an aircraft are intended for oscillating or slow rotation conditions and do not have a cage; they are generally shielded or sealed and pre-packed with grease, but some have re-lubrication facilities.
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Ball bearings
These bearings may be divided into four main groups, namely radial, angular contact, thrust and instrument precision bearings.
Radial Bearings:
This is the most common type of rolling bearing and is found in all forms of transmission assemblies such as shafts, gears and control-rod end fittings. The bearings are manufactured with the balls in either single or double rows, rigid for normal applications, or self-aligning for positions where accurate alignment cannot be maintained. Such bearings may also be provided with metal shields or synthetic rubber seals to prevent the ingress of foreign matter and retain the lubricant, and with a circlip groove or flange for retention purposes. The balls are often retained in a cage, but in some cases filling slots in the inner and outer rings permit individual insertion of the balls, thus allowing a larger number of balls to be used and giving the bearing a greater radial load capacity; however, axial loads are limited due to the presence of the raceway interruptions.
Angular Contact Bearings:
These bearings are capable of accepting radial loads, and axial loads in one direction. The outer ring is recessed on one side to allow the ball and cage assembly to be filled, thus enabling more balls to be used and the cage o be in one piece. The axial loading capacity of an angular contact bearing depends to a large extent on the contact angle. To achieve the contact angle large radial internal clearances are usually employed; the standards of clearance specified for radial bearings.
(i) In applications where axial loads will always be in one direction, a single angular contact bearing may be used, but where axial loads vary in direction on opposed pair of bearings is often used, and adjusted to maintain the required axial clearance.
(ii) A particular type of angular contact bearing, known as a duplex bearing, is fitted with a split inner or outer ring, and is designed to take axial loads in either direction. The balls make contact with two separate raceways in each ring, and one essential condition of operation is that the bearing should never run unloaded.
The bearings are not adjustable, and radial loads should always be lighter than axial loads. This is a most efficient form of thrust bearing and is not speed limited as is the washer type described below.
Thrust Bearings:
Thrust bearings are designed for axial loading only, and are normally used in conjunction with a roller bearing or radial ball bearing. The balls are retained in a cage and run between washers
39 having either flat or grooved raceways. Centrifugal loading on the balls has on adverse effect on the bearings and they are therefore, most suitable for carrying heavy loads at low speeds.
Instrument Precision Bearings:
These bearings are used mainly in instrument and communication equipment, and are manufactured to a high degree of accuracy and finish. They are generally of the radial bearing type without filling slots, although other types are obtainable. Tolerances quoted in BS 3469 for instrument precision bearings are closer than those quoted in BS 292 for standard ball and roller bearings, and only three classes of radial internal clearance are specified. BS 3469 also contains details of test procedures for instrument precision bearings.
Roller bearings
Roller bearings may be divided into three main groups, according to whether they have cylindrical, spherical or tapered rollers.
Cylindrical Roller Bearings:
These bearings are capable of carrying greater radial loads than ball bearings of similar external dimensions, due to the greater contact area of the rolling elements. Bearings with ribs on both rings will also carry light, intermittent, axial loads.
(i) The type of cylindrical roller bearing most commonly used is that in which the diameter and length of the rollers are equal, and standard sizes within this type are listed in BS292. Bearings having rollers of a length greater than their diameter are also used for special applications.
(ii) A different kind of bearing in this category is the needle roller bearing, in which the length of the rollers is several times greater than their diameter. These bearings are designed for pure radial loads and are often used in locations whether the movement is oscillatory rather than rotary, such as universal couplings and control-rod ends. Needle bearings are particularly useful in locations whether space is limited, and are often supplied as a cage and roller assembly, the shaft of the components acting controlled to the standards specified by the bearing manufacturer. These bearings are particularly susceptible to the effects of misalignment and lack of lubricant, and may also be subject to brinelling, due to the lack of rotational movement. "Brinelling" is indentation of the surface of a material, resembling the indentations formed during a Brinell hardness test.
Tapered Roller Bearing:
These bearings are designed so that the axes of the roller form an angle with the shaft axis. They are capable of accepting simultaneous radial loads and axial load in one direction, the proportions of the loads determining the taper angle. Tapered roller bearings are often mounted
40 back to back in pairs, and adjusted against each other to obtain a working clearance. Because the axial load on the rollers results in rubbing contact on the cone rib, careful lubrication is essential, particularly at high speeds.
Spherical Roller Bearings:
A spherical roller bearing may have one or two rows of rollers which run in a spherical raceway in the outer ring, thus enabling the bearing to accept a minor degree of misalignment between opposite bearings. The bearing is capable of withstanding heavy radial loads, and moderate axial loads from either direction.
Radial internal clearance
Radial ball bearings and cylindrical roller bearings are manufactured with various amounts of radial internal clearance. Standard bearings are available in four grades of fit, namely Group2, Normal Group, Group3 and Group4, while instrument precision bearings are supplied in the first three groups only. Bearings are usually marked in some way to indicate the class of fit, a system of dots, circles or letters often being used. It is important that replacement bearings are of the same standard.
• Group 2 bearings have the smallest radial internal clearance and are normally used in precision work whether minimum axial and radial movement is required. These bearings should not be used where operating conditions, such a high temperatures, would reduce internal clearances, and are not suitable for use as thrust bearings or for high speed.
• Normal Group bearings are used for most general applications where only one ring is a interference fit and where no appreciable transfer of heat to the bearing is likely to occur.
• Group 3 bearings have a greater radial internal clearance than Normal Group bearings and are used where both rings are an interference fit, or where one ring is an interference fit and some transfer of heat must be accepted. They are also used for high speeds and where axial loading predominates.
• Group 4 bearings have the largest radial internal clearance; they are used where both rings are an interference fit, and the transfer of heat reduces internal clearances.
Lubrication
Adequate lubrication is essential for all types of rolling bearings. The purposes of the lubricant are to lubricate the areas of rubbing contact, e.g. between the rolling elements and the cage, to protect the bearing from corrosion, and to dissipate heat. For low rotational speeds, or for oscillating functions such as are found in a number or airframe applications, grease is a suitable lubricant; at high rotational speeds grease would generate excessive temperatures because of churning, and oil is more suitable. Because of the variety of uses to which rolling bearings are put, and the varying requirements of different locations, it is important that only those lubricants recommended in the approved Maintenance Manual should be used.
41
• External bearings on aircraft are often of the pre-packed, shielded or sealed types, and are usually packed with anti-freeze grease because of the low temperatures encountered; these bearings cannot normally be re-packed with grease, and when unserviceable must be rejected. Wheel bearings are normally tapered roller bearings, and should be re-packed with the correct grease when refitting the wheel (see Leaflet AL/3-19).
• Bearings fitted in engines and gearboxes are generally lubricated by oil spray, splash, mist, drip feed, or controlled level oil bath and loss of lubricant is prevented by the use of oil retaining devices such as labyrinth seals, felt or rubber washers, and oil throwers.
Installation of bearings
The majority of bearing failures are caused by faulty installation, unsatisfactory lubrication, or inadequate protection against the entry of liquids, dirt or grit. To obtain the maximum life from a bearing, therefore, great care must be exercised during installation and maintenance, and strict cleanliness must be maintained at all times.
• Where bearings carry axial loads only, the rings need only be a push fit in the housing or on the shaft, as appropriate, but bearings which carry radial loads must be installed with an interference fit between the revolving ring and its housing or shaft, otherwise creep or spin may take place and result in damage to both components. In instances where light alloy housings are used, the bearing may appear to be a loose fit during installation owing to the need to control bearing fit in the housing at the low temperatures experienced at high altitude.
• Before installation, a bearing should be checked to ensure that it is free form damage and corrosion, and that is rotates freely. In some cases bearings are packed with storage grease, which is unsuitable for service use and must be removed by washing in a suitable solvent as specified in paragraph. All open bearings should be lubricated with the specified oil or grease before installation.
• Bearings must be assembled the right way round, i.e. as specified in the appropriate drawing or manual, and should be seated squarely against the shoulders on shafts or housings so that raceways are at right angles to the shaft axis. Damage to the shoulders or bearing rings, or the presence of dirt, could prevent correct seating, impose uneven stress on the bearing and promote rapid wear. It is important, therefore, to ensure that there is no damage likely to prevent correct seating or the bearing rings, and that all mating surfaces are scrupulously clean.
• Bearings may often be installed using finger pressure only, but where one ring is an interference for(usually the rotating inner ring), an assembly tool or press should be used; in some instances it may also be necessary to freeze the shaft to heat the bearing in hot oil, depending on the degree of interference specified. If these tools are not available, the use of a soft steel or brass tube drift may be permitted in some instances; any force necessary must be applied only to the ring concerned, since force applied to the companion ring may result in damage to the rolling elements, or brinelling of the raceways.
42
• Retaining devices are used to prevent axial movements of the inner and outer rings of a bearing. Stationary outer rings are normally held in place by circlips or retaining plates, and shims are often used in conjunction with the latter to adjust the clearances in thrust or location bearings. Rotating inner rings are usually firmly held by means of a washer and nut on the shaft and, although the thread may be handed to prevent loosening during operation, care should be taken to ensure that the nut is securely locked to the shaft.
• On completion of assembly, the bearing housing should, where applicable, be lightly packed with grease to provide an adequate reserve of lubricant, and oil-lubricated bearings should be lightly lubricated with the appropriate oil. Excessive greasing should be avoided, however, since grease is expelled from the bearing as soon as it begins to rotate, and, if insufficient space is left, churning and overheating may occur, causing the grease to run out and the bearing to fail; as a rough guide, the bearing should be approximately one third full.
Maintenance of bearings
Ball and roller bearings, if properly lubricated and installed, have a long life and require little attention. Bearing failures may have serious results, however, and aircraft Maintenance Manuals and approved Maintenance Scheduled include inspections and, where applicable, lubrication instructions for all types of rolling bearings.
Lubrication:
Most bearings used in airframe applications are shielded or sealed to prevent the entry of dirt or fluids which adversely affect bearing life; these bearings cannot normally be re-greased, and must be replaced if it is evident that the lubricant has been washed out, or otherwise lost through failure of the seals or bearing wear. Grease nipples are provided for some open bearings so that the grease may be replenished at specified intervals, or when grease is lost through the use of solvents, paint strippers, detergents or de-icing fluid. Nipples should be wiped clean before applying the grease gun, to prevent the entry of dirt into the bearing. Grease forced into the bearing will displace the old grease, and any surplus exuding from the bearing should be wiped off with a clean lint-free cloth.
Inspection:
Ball and roller bearings are deliberately selected by aircraft and component designers, for use in installation where play or lost motion are unacceptable; wear or corrosion, once started, progress rapidly, and bearings showing evidence of these faults should be discarded. Frequent removal of bearings from shaft or housings may result in damage to either the bearing rings or mating surfaces, and for this reason a routine inspection of a bearing is normally carried out in in situ; wheel bearings, however, are normally inspected when the wheel is removed. If doubt exists as to the serviceability of a bearing, it should be removed, cleaned and inspected as described in paragraphs7, 8 and 9.
• It may not often be possible to examine the rolling elements and raceways while a bearing is in position, but it is usually possible to examine the rings externally for overheating, damage and corrosion, and to examine the cage for loose rivets and
43
damage, after removing surplus grease with a clean lint-free cloth. In all cases a bearing should be checked for wear as follows:-
(i) Actuate the moving parts slowly to check for smoothness of operation. Roughness may result from grit in the bearing or surface damage to the rolling elements or raceways, caused by corrosion or excessive wears.
(ii) Check for wear by moving the inner race or shaft in both axial and radial directions. The amount of clearance will depend to a large extent on the initial grade of fit of the bearing, but some wear will be acceptable with all classes of fit and may only be considered as unsatisfactory if it leads to excessive backlash in controls, or vibration during operation.
(iii) Check shielded bearings to ensure that there is no rubbing contact between the stationary and rotating components. Contract between the shield and inner ring is evidence of excessive wear in the bearing and could lead to contamination of the lubricant by particles of metal rubbed off the shield.
• With some bearings, creep or spinning or the races may occur and lead to damage to the shaft or outer ring housing. Where housing end covers or shaft nuts can be removed, these faults may be recognised by polishing of the ring faces.
• The internal condition of a bearing may sometimes be revealed by an examination of the lubricant exuding from the bearing. Metal particles reflect light, and give a rough feeling when the lubricant is rubbed into the palm of the hand.
• A problem frequently encountered with airframe bearings is moisture contamination, which may result in freezing and liability to operate a control in low temperature conditions. Every precaution should be taken to prevent the entry of liquids into bearings, and re-lubrication of open bearings is often specified after washing. During inspection, particular attention should be given to rust stains, which may be a good indication of the presence of moisture.
• The condition of landing wheel bearings on small aircraft, on which wheels are changed at infrequent intervals, may be checked by rocking and spinning the wheel. This check would normally be impractical and unnecessary on larger aircraft, since the wheels are changed more frequently in order to replace worn tyres.
Removal of bearings
Many roller bearings are made in two parts, which can be separated for claiming and inspection without removing the outer ring from its housing or the inner ring from its shaft; all that is necessary is partial dismantling of the associated components to allow the bearing to be inspected and rotated. When it is necessary to remove separated rings or complete bearings, care is necessary to ensure that they are not damaged. A suitable extractor should normally be used, but if this is not available, light hammer blows transmitted through the medium of a soft tubular drift may prove effective. Any force necessary should be applied to the ring concerned, since force applied to the companion ring may result in damage to the raceways and rolling elements. Force should not be applied to the ribs of a roller bearing as this may result in fracture or damage, which would necessitate the rejection of the bearing.
Cleaning bearings
44 Bearings to be cleaned for further examination should first be wiped free of all grease adhering to the outer surfaces; dry compressed air will assist in dislodging it from the cage and rolling elements, but the bearing should not be allowed to rotate.
• The bearings should then be soaked or swilled in whit spirit to remove any remaining grease or dirt. It is permissible to oscillate or turn the races slowly to ensure that all foreign matter has been removed, but the bearing should not be spun in this condition. Otherwise the working surfaces may become damaged due to the lack of lubrication.
• If a bearing cannot be completely cleaned by the above method, a forced jet of white spirit may be used to advantage. The jet may be obtained by fitting a pump to the washing tank, but an efficient filter must be provided.
• Jet cleaning can be considerably assisted if the bearing is mounted on a tapered mandrel so that the inner ring will remain stationary, whilst allowing the outer ring to revolve slowly as a result of the action of the fluid from the jet passing through the bearing.
• After cleaning, the bearing should be dried with clean, warm, dry compressed air, taking care to permit only very slow rotation, and lightly lubricated with oil to prevent corrosion. The bearing should be slowly rotated during oiling to ensure that all surfaces are covered.
Inspection after removal
After removal and clearing, bearings should be inspected for corrosion, pitting, fracture, chips, discoloration and excessive internal clearances. With self-aligning bearings or bearings having detachable rings, the condition of the rolling elements and raceways can be seen by swivelling the outer ring through 90 degrees or by separating the outer ring, as appropriate. With bearings having non-detachable rings, the raceways and balls or rollers are sometimes accessible for visual examination, but if not, their condition may be judged by holding the inner ring and oscillating the outer ring. Provided there is no foreign matter inside the bearing, any roughness will indicate internal damage.
• Slight corrosion on the outer surface of the rings is usually acceptable, provided that it does not prevent proper fit of the rings in housings or on shafts. Stating on the raceways or rolling elements may be acceptable on non-critical bearings, but deep pitting or scaling of the surface would not be acceptable on any types of bearings. Fracture, chips or damage to the rings, balls rollers or cage, would necessitate rejecting the bearing.
• If the rings show signs of creep or spinning, the outside and inside diameters of the bearing should be checked with a micrometer and plug gauge respectively. The shaft and housing should also be inspected for damage and wear, to ensure that a proper fit will be obtained when the bearing is replaced.
• The running smoothness of a bearing may be determined by mounting it on a shaft which is mechanically rotated at 500 to 1000 rev/min. With the shaft running and the bearing oiled, the outer ring should be held, and the smoothness and resistance should be determined by applying alternate axial and radial loads in either direction. The outer ring must be square to the shaft, or a false impression of toughness may result.
• Excessive wear in a bearing will result in large internal clearances, and a badly worm bearing will normally have been rejected following the initial inspection in situ.
45
• Axial clearance in a bearing is seldom quoted since it depends on the internal design of the particular bearing, but, where necessary, a rough guide to the radial internal clearance may be determined by mounting the inner ring on a shaft and measuring, with a dial test indicator, the average radial movement obtained at various angular positions of the outer ring. It is important that the outer ring moves in the same plane as the inner ring, or an incorrect reading will result.
Protection against corrosion
Bearings which have been found satisfactory and are to be re-used ,should be lubricated with oil or grease as appropriate, and reinstalled, bearings which are to be stored should be dipped in rust preventive oil wrapped in greaseproof paper and suitably boxed and labelled. Bearings should be stored horizontally, in a clean, dry atmosphere, and it is recommended that, after one year in storage, the bearings should be inspected for corrosion and re-protected.
Fig 8.2 Bearing isometric view
(a)
46
(b)
Fig 8.3: (a) Bearing 2D, (b) Bearing 3D
8.2 INSPECTION OF COUPLINGS
Couplings are used to join or connect two shafts in such a way that when both the shafts rotate, they act as one unit and transmit power from one shaft to other. These type of couplings are also known as shaft couplings. Shafts to be connected or coupled may have collinear axes, intersecting axes at a small distance.
Universal coupling is a rigid coupling that connects two shafts, whose axes intersect if extended. It consists of two forks which are keyed to the shafts. The two forks are pin joined to a central block, which has two arms at right angles to each other in the form of a cross. The angle between the shafts may be varied even while the shafts are rotating. Universal coupling is a non–aligned coupling. Generally non–aligned couplings are used to transmit power between two shafts which are not coaxial.
Classification
Classification of couplings can be made on the basis of rigid or flexible designs.
Rigid Couplings:
Illustrated by a flange coupling, compression coupling, or tapered-sleeve coupling. This type of coupling is suitable for low speeds, accurately aligned shafts.
Flexible Couplings:
Illustrated by Falk flexible coupling, Oldham coupling, gear type of flexible coupling, roller or silent chain coupling, etc.
Flexible couplings are used:
(a) To take care of a small amount of unintentional misalignment.
47 (b) To provide for “end float”, that is, axial movement of a shaft. (c) To alleviate sock by
Fig 8.4 Universal coupling (Isometric view)
Fig 8.5 Universal coupling 2D
Fig 8.6 Universal coupling 3D (a)
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Fig 8.7 Universal Coupling 3D (b)
8.3 INSPECTION OF GEARS
Gears are machine elements, which are used for power transmission between shafts, separated by small distance. Irrespective of the type, each gear is provided with projections called teeth and intermediate depressions called tooth spaces. While two gears are meshing, the teeth of one gear enter the spaces of the other. Thus, the drive is positive and when one gear rotates, the other also rotates, transmitting power from one shaft to the other.
Spur gears are the most common type of gears. They have straight teeth, and are mounted on parallel shafts. Sometimes, many spur gears are used at once to create very large gear reductions. Two spur gears in mesh known as spur gearing. In all gearings except worm gearing, the smaller of the two gears called the pinion and the larger one gear or gear wheel.
Fig 8.8 Spur gearing 2D
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Fig 8.9 Spur gearing 3D
Fig 8.10 Multi gearing
CHAPTER 9
QUALITY ASSURANCE IN HMT
Quality assurance is also a part of quality management but it is focused on providing confidence that quality requirements will be fulfilled. In other words, it pertains to all those planned and systematic actions necessary to provide adequate confidence that a product will satisfy the requirements for quality. This is a fundamental shift in concept from the reactive downstream approach of quality control by means of detection, to a proactive upstream approach that controls and manages the upstream activities to prevent problems from arising.
QUALITY IMPROVEMENT IN HMT
Quality improvement is another part of quality management that is focused on increasing the ability to fulfill quality requirements. It is not concerned with correcting errors but concerned with doing things better to improve system efficiency and effectiveness. ISO offers the PDCA cycle as a useful tool for continual improvement. The methodology applies to both high-level strategic processes and to simple operational activities.
50 Plan - Plan the improvement Do - Implement the improvement Check - Monitor and measure the results against policies, objectives and requirements Act - Take actions to continually improve the performance
PDCA Cycle
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CHAPTER 10
HEAT TREATMENT IN HMT
Heat treatment is generally applied to steels to impart specific mechanical
properties such as increased strength or toughness or wear resistance. Heat treatment is also
resorted to relieve internal stresses and to soften hard metals to improve machinability. Heat
treatment is essentially a process of heating the steels to a pre-determined temperature followed
by a controlled cooling at a pre-determined rate to obtain desired end results. The heat treatment
process can be classified into:
1. Recrystallization annealing which is employed to relieve internal stresses, reduce the
hardness and to increase the ductility of strain hardened metal. At first, upon an increase in the
heating temperature the elastic distortions of the crystal lattices are eliminated. At higher
temperature new grains for and begins to grow (recrystallization).
2. Full annealing which involves phase recrystallization and is achieved by heating alloys above
the temperature required for phase transformation. This is followed by slow cooling. Full
annealing substantially changes the physical and mechanical properties and refines a coarse
grained structure.
3. Quenching wherein hardening alloys are heated above the phase transformations temperature
and are then rapidly cooled (quenched).
4.Tempering involves the reheating of hardened of hardened steel to a temperature below that
required for phase transformation so as to bring it nearer to an equilibrium state.
10.1 ANNEALING
Annealing is the process necessary to obtain softness, improve machinability, increase
or restore ductility and toughness, relieve internal stresses, reduce structural non-homogeneity
and to prepare for subsequent heat treatment operations.
The Process consists of heating the metal to the required temperature depending upon
the carbon content and other alloying elements of the steel and then cooling in the furnace at a
slow rate. Most of the cast iron components are annealed at a low temperature before final
machining.
52 10.2 HARDENING AND TEMPERING
In this process steel is heated to predetermined temperature and then quenched in water,
oil or molten salt baths. Hardening followed by tempering is done to improve the mechanical
properties of steel. Tempering consists of reheating the hardened steels to a temperature below
lower critical values followed by cooling at a desired rate.
10.3 HARDENABILITY
It is defined as the capacity to develop a desired degree of hardness usually measured in
terms of depth of penetration. The higher the carbon content, the harder a steel will be after
hardening owing to a martensite structure.
10.4 SURFACE HARDENING
This is a selective heat treatment in which the surface layer of metal is hardened to a
certain depth whilst a relatively soft core is maintained. The principal purpose of surface
hardening is to increase the hardness and wear resistance of the surface. Surface hardening may
be accomplished with or without changing the chemical composition of the surface.
10.5 CARBURIZING
This is a process for saturating the surface layer of low carbon steels with carbon.
Several methods are employed for this purpose such as pack carburizing, gas carburizing and
liquid carburizing.
After carburizing, regardless of the process employed, the material is heat treated to produce
a hard surface resistant to wear. The heat treatment process for carburized parts consists of the
following:
a) Normalizing after carburizing at temperatures of 8800-9000 to improve the core structure of
the work which is over heated by carburizing.
b) Hardening at 750-8500to eliminate the effects of overheating and to impart a high hardness to
the carburized layer and
c) Tempering at 1500 to 1800
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CHAPTER 11
CONCLUSION
The summary of project have the literature survey, procurement of raw materials, machinery required for production, production process, and time estimation for manufacturing and feasibility studies. It becomes very important to check the latest arrivals in order to meet the industrial needs. Hence, we suppose our project could provide an intimate study regarding the basic manufacturing technologies and their processes for those who try to establish an unaccounted growth of their organisation.