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Round nut caulking process optimization and crack elimination

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Round nut caulking process optimization and crack elimination

  1. 1. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 1 Chapter 1 COMPANY PROFILE 1.1Bosch India Bosch India a member of Bosch group of companies, Germany. Founded in 1951 then known as MICO pioneered the manufacture of auto spark plugs and diesel fuel injection equipment in India. Access to the international technology of Bosch, with a conscious commitment to quality of its more than 10,000 employees has made MICO the largest manufacturer of diesel fuel injection equipment in the country and one of the world’s largest. In addition, MICO manufactures industrial equipment, auto-electrical, hydraulic gear pumps for tractor applications, electric power tools, packaging machines and Blaupunkt car multimedia systems. An all-India network of more than 4,000 authorized representations ensures widespread availability of both products and after-sales service. From 2007 onwards MICO was called as Bosch India Ltd with a rich history of 125 years. All round the world, the Bosch name stands for competence and product diversity in the following sectors: automotive equipment, power tools and accessories, thermo- technology, household appliances, communication, automation and packaging machines. The “Workshop for Precision Engineering and Electrical Engineering” that Robert Bosch founded in Stuttgart, Germany, in 1886 has grown in the course of more than 100 years to become a global player.
  2. 2. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 2 Worldwide, the Bosch group has 221,000 employees today. It has around 250 subsidiaries and associated companies in over 50 countries and a total of 227 manufacturing sites. There are 18,500 scientists, engineers and technicians engaged in R&D. As a result, Bosch applies for over 2,000 patents each year. This places the Company at the top in the entire automotive industry. In India, the Bosch group has about 18000 employees, and in business year 2007 achieved total consolidated revenue of over Rs 57000 million. Bosch has grown phenomenally in India, way back since 1922 when the Illies Company established a Bosch agency in he then British India. The founding of Bosch Ltd. In 1951 spurred off an accelerated growth in the automotive segment which has not stopped till date. Bosch has strong and voracious presence in the country today at numerous locations in diverse industry segments-both automotive and non-automotive. In India, the Bosch Group is comprised of following companies • Bosch Ltd (formerly ‘Motor Industries Co. Ltd.) • Robert Bosch Engineering and Business Solutions Ltd. • Bosch Chassis Systems India Ltd. • Bosch Rexroth India Ltd.
  3. 3. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 3 Since the first in-line fuel injection pump was produced by Bosch in 1927, countless numbers of them have reliably kept diesel engines in motion. These “classics of diesel fuel- injection technology” are still in use today on a large numbers of engines. Their particular strengths are their durability and ease of maintenance. Bosch Limited is the flagship of the Bosch Group subsidiaries in India. Founded in 1951, the company is India's largest auto component manufacturer and also one of the largest Indo - German company in India. The Bosch Group holds close to 70-% stake in Bosch Limited. The Company is headquartered in Bangalore with manufacturing facilities spread across the country in five different locations. The plants are TS 16949 and ISO 14001 certified. The company has excellent R&D and manufacturing capabilities with access to state of-the-art technology from Bosch. Its strong local competencies, combined with its global strengths, have given the company market leadership in most of the segment it operates in. Bosch Limited manufactures and trades in the following three major business sectors • Automotive Technology Business divisions: Diesel and Gasoline Fuel Injection Systems, Blaupunkt Car Multimedia Systems, Auto Electrical and Accessories, Starters and Motors, Energy and Body Systems. • Industrial Technology Business divisions: Packaging Machines, Special Purpose Machines • Consumer Goods and Building Technology Business divisions: Power Tools, Security Systems
  4. 4. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 4 1.2 Milestones 1951 - Establishment of the company 1953 construction of the first factory building at Bangalore 1954 - Manufacture of spark plugs, single-cylinder diesel fuel injection pumps. 1955 - Manufacture of elements and delivery valves. 1956 - Manufacture of multi-cylinder diesel fuel injection pumps. 1972 - Manufacture of nozzles and nozzle-holders at Nasik Pilot Plant. 1974 - Production begins at Nasik Plant. 1981 - Manufacture of special purpose machines and tools. 1986 - Manufacturing of VE Distributor pump. 1990 - Naganathapura Plant inaugurated. 1991 - MICO becomes the Bosch Global Development Centre for single-cylinder diesel fuel injection pumps. 1992 - Marketing of automotive accessories. ISO 9001 certified for all the three plants. 1993 - Manufacture of Bosch electrical power tools. 1994 - Manufacture of packaging machines. 1995 - MICO becomes the Bosch Global Development Centre for a range of multi-cylinder diesel fuel injection pumps. 1996 - Blaupunkt car audio system launched. 1997 - QS 9000 certification for Bangalore, Nasik and Naganathapura Plant. 1998 - 20 millionth single-cylinder pump produced.
  5. 5. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 5 1999 – Inauguration of Jaipur plant and manufacture of Blaupunkt car audio systems in India. 2000 - Inauguration of Mico Application centre (MAC), Bangalore plant adjudged “All India Best Establishment” for the 25th time, Manufacture of one-millionth auto electrical unit at Naganathapura Plant and QS 9000v certification for Jaipur Plant. 2001 - Launch of Terra-25 packaging machine. 2002 - Production of 25-millionth single-cylinder pump, launch off first Bosch Car Service outlet, ISO 9001:2000 certification for industrial equipment packaging technology and power tools divisions and ISO 14001 (Environmental Management System) certification for Bangalore Plant. 2003 - Production of 10-millionth inline-A pump, TSI6949 certification for all Mico Plants, ISO 9001:2000 certification for car multimedia division and Blaupunkt crosses the 100,000 mark of car radios that have been sold since its inception. 2004 - ISO 14001:1996 certification for Environmental Management System for all the plants, Launch of BVK2000A-World’s fastest candy wrapping machine, Launch of Terra 40 packaging machine, introduction of capsule packaging as an anti-spurious measure for elements, nozzle and delivery valves and launch of ‘Plena Voice Alarm System’ by Bosch security Systems for emergency evacuation. 2006 - Launch of Bosch brand at Auto Expo 2006 Inauguration of the Common Rail Pump manufacturing facility at Bangalore 2007 - Inauguration of the Common Rail Injector manufacturing facility at Nasik Verna. Goa Plant inaugurated for Bosch Packaging Technology Announcement to change company’s’ name from Motor Industries Company Limited to Bosch Limited. Thus migrating the brand name MICO to BOSCH. 2008 -Company name changed from Motor Industries Company Limited to Bosch Limited 2009 - Won NDTV Car & Bike Award for Auto Component Manufacturer of the Year.
  6. 6. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 6 1.3 Quality Principles a) We want satisfied customers. That is why the highest quality of our products and service is one of our major corporate objectives. This also applies to the quality of the work carried out in our name by our trading partners, and in their sales and organizations. b) The customer is the judge of our quality. His or her verdict on our products service is decisive. c) Our quality goal is always “zero defects” or “100% quality”. d) Not only do our customers assess the quality of our products, but also the quality of our services. Deliveries must be on time. e) Enquiries, offers, samples and complaints must all be dealt promptly. It is imperative that agreed deadlines be met. f) Each employee in the company contributes towards achieving our quality Member of the Board- to ensure that their work is the highest standard. Anyone who identifies a problem which may jeopardize quality, but does not have the authority to remedy he must report the matter immediately to his superior. g) All work must be without defects from the very beginning. The not only improves quality, but also reduces costs. Quality increases cost effectiveness. h) The quality of our products also depends upon the quality of sourced parts. Demand the highest quality from suppliers, and support them in adhering to our mutual quality goals. i) Even when painstaking care has been taken, defects can occasionally happen. This is why we have introduced numerous proven methods and procedures to identify defects at an early stage. j) Ensuring that quality goals are achieved is an important management duty. When assessing the performance of our employees, particular emphasis is placed on the quality of their work
  7. 7. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 7 1.4 Customers Worldwide
  8. 8. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 8 Chapter 2 DIESEL ENGINE AND COLD STARTING 2.1 Diesel Engine The diesel engine also known as a compression-ignition engine is an internal combustion engine that uses the heat of compression to initiate ignition and burn the fuel that has been injected into the combustion chamber. This contrasts with spark-ignition engines such as a petrol engine or gas engine, which use a spark plug to ignite an air-fuel mixture. Fig 2.1 a v-8 diesel engine 2.1.1 Function Diesel engines are self-igniting, or in other words the injected fuel ignites without an ignition spark being necessary. The work cycle is triggered in three stages: 1. Pure air is sucked in first. 2. This air is compressed to 30–55 bar – heating it up to 700–900 °C. 3. Diesel fuel is injected into the combustion chamber. The high temperature of the compressed air triggers self-ignition, the interior pressure rises and the engine performs its work. Compared to gasoline engines, self-igniters require more elaborate injection systems and engine structures. The first diesel engines were not particularly comfortable or fast drive units. When cold, the hard combustion sequence made them very loud. They were characterized by a higher performance weight, a lower performance per liter of capacity and poorer acceleration behavior. All of these disadvantages have been eradicated by continual development of the injection technology and the glow plugs. Diesel is now regarded as an equal or better drive source.
  9. 9. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 9 2.2 Cold Starting A cold start is an attempt to start a vehicle's engine when it is cold, relative to its normal Operating temperature, often due to normal cold weather. A Cold Start situation is commonplace, as weather conditions in most Climates will naturally be lower temperature than typical operating temperature of an engine. 2.2.1 Causes of cold start More effort is needed to turn over a cold engine for multiple reasons: • The engine compression is higher as the lack of heat makes ignition more difficult • Low temperatures cause engine oil to become more viscous, making it more difficult to circulate. • Air becomes denser the cooler it is. This affects the air-fuel ratio, which in turn affects the flammability of the mixture. 2.2.2 Solution to cold start In order to ensure that the start does not take an inordinate period of time or may indeed be impossible at lower temperatures, aids are used to support the cold start. They compensate the poorer starting conditions and initiate the punctual and even ignition for stable combustion. One component of the cold start support is the glow plug. Thermal energy, generated by electricity, flows into the combustion chamber to create the ideal ignition conditions for the injected fuel. If an engine has a divided combustion chamber, it is indispensable as a cold start aid in order to ensure starts in frequent temperature ranges of 10- 30 °C. Due to the considerable deterioration of the start quality at temperatures below freezing point, the glow plug is also used for diesel engines with direct injection.
  10. 10. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 10 Chapter 3 GLOW PLUG AND ITS ASSEMBLY SEQUENCE 3.1 Product description Diesel engines, unlike petrol engines which rely on a spark to ignite the air-fuel mixture, function due to the auto-ignition of diesel fuel when subjected to high pressures. Under high pressure, the temperature of the diesel fuel increases to a point where the fuel self-combusts. In cold weather however, this temperature is not always achieved and glow plugs assist by heating the air-fuel mixture to assist in cold starting. Heating unit is the major contributor for heat generation whereas the housing provides means of holding the heating unit very firmly on the engine cylinder as shown in figure. 3.1.1 Purpose: Diesel engines have spontaneous ignition, which means that the injected fuel does not require a spark to ignite it. The high temperature, which occurs as a result of compressing intake air, is sufficient to ignite the fuel. However, in cold conditions, more energy is required to help ignition at start because both the intake air and the engine itself are colder and compression and pumping losses are higher too. Therefore, in diesel engines, glow plugs are a key factor for every cold start. At low ambient temperatures they heat the combustion chamber sufficiently to allow stable combustion conditions for the injected fuel. The 'glow pencil' (rod-like heating element) of the glow plug (which fits in the cylinder head) protrudes into the glow chamber or pre-combustion chamber. It is most effective when positioned on the edge of the mixing vortex. If it protrudes too far into the combustion chamber, it impedes the preparation and formation of an ignitable fuel/air mixture.
  11. 11. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 11 3.1.2 Working Principle: In older generation diesel engine car, unlike in gasoline engine car, the operator did not turn the key to the start position and had the engine running immediately. Instead, the operator turned the key to the on position. The glow plug rely switched on the glow plugs, and a light on the instrument cluster illuminated as shown in figure , this process is called preheating or glowing. If the car had been running very recently, or if the ambient temperature was hot, the wait to start light might not come on; in this case, the operator may proceed to turn the key to the start position and start the engine without having to wait. When internal sensor detect that the core of the engine block has reached a certain designated temperature, when a certain amount of time elapses, the glow plug relay switches off the wait to start light. A preheating cycle usually lasts for 2 to 5 seconds. The operator then proceeds to turn the key to start position, as in a gasoline engine. The glow plug relay switches off the glow plugs after the engine is running (or, in older cars, at the same time the “wait to start” light goes out). In some newer cars, glow plugs continue to operate for upto180 seconds after engine start to keep the engine within emission regulations, as combustion efficiency is greater. 3.1.3 Parts of a Glow plug: The above figure shows the complete design of element sheathed metal glow plug. The glow plug consists mainly of the plug body, the tubular heating element or glow tube (4) with the heating coil (1) and regulating coil (3) and the connecting bolt(7) . The tubular heating element consist of hot gas and corrosion resistant element sheath which encloses a filament surrounded by a compressed electrically insulating magnesium oxide powder(2) that conducts heat very well . During mechanical compression, the powder is pressed so tightly together that the coli rest as if it were cast in cement. This makes it so stable that the thin wires of the heating and regulating coil can permanently stand up to all oscillations. The filament is made up of two resistors in series, the heating coil and regulating coil. The heating coil is welded into the cap of the element sheath for grounding.
  12. 12. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 12 The regulating coil is in contact with terminal stud; its resistance is characterized by a large temperature co-efficient, which establishes the connection to vehicle electrical system. The non-corrosive glow tube is pressed gas tight into the housing (5). Additionally, the plug is sealed to the connecting point by an O-ring (8) or a plastic part. The glow plug takes the electrical energy from the battery. An electronic glow time control device deals with the control. The filament is made of high temperature resistance material (kanthal). A glow plug has a housing provided with an internal passage which is bounded by an inner circumferential surface and has an open front end. An elongated glow pin is carried by the housing rigid therewith and extends with radial clearance through the passage .a forward portion of the pin is located inwardly adjacent to the open front end of the passage and ignition of fuel takes places in the region of this forward front end portion. Round pin connected (10) provides connection between connecting bolt and vehicle connecting system 3.1.4 Characteristics of the glow plug: Shorter heating time: Glow plug must ensure a high temperature to support ignition in as short a time as possible and must maintain this temperature regardless of, or align it to suit, the ambient conditions. Compact form: Modern diesel engines with common rail or multi point fuel injection and 4- valve technology can offer only limited space , however, this means the space required by the glow plug must be minimized, which leads to very thin and long form Exact alignment to suit the combustion chamber: The glow plug must be protruded sufficiently into combustion chamber or pre chamber. This is the only way to provide the heat right where it is needed. It must not protrude too far into the combustion chamber also.
  13. 13. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 13 3.1.5 Functions: Strong current of 11v flows through the connecting bolt to the regulating coil and to the heating coil at the start of pre-heating. It heats up to the starting temperature (approx. 850°C) in 2-5 seconds and makes the heating zone glow. This raises the temperature of regulating coil even more, which was already hot due to electric current. In the start phase the glow spreads rapidly right up, close to the plug body after 2-5 seconds and temperature increases above (1000°C) and become constant. Consequently, electrical resistance rises and current is reduced to such an extent that glow tube cannot be damaged. This means that the glow plug cannot overheat. After the engine starts, in the after glow or post glow phase the glow plug continues to operate more than 180 seconds to improve the initial operation and to reduce blue smoke emission and combustion noise. The current draw and total heating output of glow plug decreases the temperature approaches steady state conditions. An alloy is used in the glow plug ; its resistance grows with temperature . This means that the regulating coil can be designed in such a way that it permits greater current to pass into the heating coil at the start, once the target temperature has been reached. This means that the start temperature is reached faster, and remains safely within the permitted range due to the rather controls. The phases of glow plug and the heating behavior of glow plug is shown below. Note: Rapiterm glow plugs operate with 7V High speed metal glow plug operates with 5V. Metal glow plug operates with 11V.
  14. 14. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 14 3.2 Introduction to Glow Plug Manufacturing Operations 3.2.1 Process Route: The figure below shows the process route of glow plug employed at the company. The phase 1 of process route is involved in the assembly of the heating unit and phase 2 for housing unit. A total of 260m2 space is occupied by two phases. The main project focus is based on the Caulking operation.
  15. 15. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 15 3.2.2 Components of Glow Plug The heating unit of glow plug consists of four major components; Connector, Heating element, Tube and O-ring shown in figure. The assembly sequences of these components are explained further in this chapter. 1. Caulking: Caulking is one of several different processes to seal joints or seams in various structures and some types of piping. In this process the connector being in form of a pipe and the gap between the heating element and the connector is sealed by caulking process as shown in figure. The figure depth being 0.15 ± 0.05mm. 2. Tig Welding: The glow is TIG welded to the heating element as shown in figure after the caulking process. The parameters in this process are welding bead being 0.6mm, a resistance of 1800 ± 1500, current of 26-28 Amps and Argon gas 10-15 Lt/min as a shielding gas used in this process. 3. Oven: The main function of this process is to remove all the moistures caused from manual handling of the tig welding parts. In this process, both the tig welded components and the MgO powder is dried to 300°C for 10 minutes in drying oven. No chemical and mechanical properties changes in due course of heating time 4. MgO filling and O-ring Pressing: The aim of this process is to fill MgO powder in between the annular spaces of Nicrofer tube and connector for easy conduction of temperature. In this the collector and tube are held tightly by two fingers and stretched to specified length as shown in figure and vibrated for tight and uniform compaction of the powder, later the viton ring is inserted in and presses tightly between the connector and Nicrofer tube; this is done to prevent MgO from spilling.
  16. 16. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 16 5. Pre-Swaging: The main function of this process is to ensure MgO powder is within the tube. In this process, swaging i.e. reduction of the outer diameter of tube will take place. This reduction process is very critical for next process. The reduction in the diameter is the result of continuously rotating swaging dies on the stationary heating unit as shown in figure 6. Swaging: Multistage swaging process is the one of the most critical and core of heating unit. The name itself indicates Swaging of heating unit takes place at different levels under single machine. Swaging is one of the core process to of the heating unit. Swaging involves continuously rotating swaging hammers that will continuously hammers the part fed in the machine. For the swaging process to work efficiently the work parts remains stationary against the swaging dies. Swaging process results in the reduction in entire body diameter i.e. called as “Longitudinal strain” and also results in increase in total length of heating unit length called “Lateral stain”. 7. Facing: The main aim of this process is to cut the total length of heating unit after swaging to desired length as per customer requirements. Simple cutting and chamfering machine is dedicated to this process. 8. Thread Rolling: The main function of this process is to knurl the heating unit as per DIN 82 RGE 05 with 450 chamfer angle. This chamfer is necessary to hold the terminal cap as shown on parts of glow plug.
  17. 17. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 17 9. X-Ray Inspection: X-ray inspection is an Non Destructive technique where the glow plugs are placed on Acrylic Tray as shown in figure and the tray is placed inside a X-ray machine. After viewed with help of computer the L3 length is checked for rejections. The X-ray machine takes 10- 75 seconds to scan each Acrylic Tray assembly with glow plugs. 10. Visual Inspection: Visual inspection of glow plugs are checked for rust, crack and damage, O-ring projection(±) 1.0mm ,bulge burs and uniform weld cup on the tube 11. Assembly: Assembly mainly includes hydro pressure pressing (pressure 4-6 bar and load = 150 to 600kgf) of the housing onto the heating unit, gas tightness is used to check for leakages and mounting of the terminal cap. The housing is indicated in green color and terminal cap in brown as shown in figure.
  18. 18. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 18 3.2.3 Process Flow Chart of Glow Plug
  19. 19. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 19 Chapter 4 Round nut in glow plug 4.1 Round nut (rim nut) A round nut is a small flat piece of metal made of aluminum with a threaded hole. It is fastened onto connector pin of glow plug and it has a distinctive shape compared to the normal nuts which are typically square or hexagonal. The shape of the nut is similar to that of a pulley and it has a groove on its surface. The groove is such that the tip of caulking tool can fit into it. Fig 4.1(a) Side view Fig 4.1(b) Top view
  20. 20. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 20 4.1.1 Geometry of the Round Nut Fig 4.2 Drawing of the nut. Several types of glow plugs are being manufactured in Bosch; they differ from each other depending on the vehicle in which they are used. They are classified based on their dia, i.e. dia 4, dia 5 and dia 6 glow plugs which are used in different vehicles. The above given geometry is of dia 5 glow plug.
  21. 21. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 21 4.1.2 Materials Used In Round Nut Aluminium round nuts are used in Bosch.Aluminium is a relatively soft, durable, lightweight, ductile and malleable metal with appearance ranging from silvery to dull gray, depending on the surface roughness. 4.1.3 Properties of Aluminum: a) Light Weight Aluminium is a very light metal with a specific weight of 2.7 g/cm3 , about a third that of steel. For example, the use of aluminium in vehicles reduces dead-weight and energy consumption while increasing load capacity. Its strength can be adapted to the application required by modifying the composition of its alloys. b) Corrosion Resistance Aluminium naturally generates a protective oxide coating and is highly corrosion resistant. Different types of surface treatment such as anodising, painting or lacquering can further improve this property. It is particularly useful for applications where protection and conservation are required. c) Electrical and Thermal Conductivity Aluminium is an excellent heat and electricity conductor and in relation to its weight is almost twice as good a conductor as copper. This has made aluminium the most commonly used material in major power transmission lines. d) Ductility Aluminium is ductile and has a low melting point and density. In a molten condition it can be processed in a number of ways. Its ductility allows products of aluminium to be basically formed close to the end of the product’s design.
  22. 22. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 22 4.1.3 Position of the Nut: The assembly process of the glow plug involves torqueing of the round nut onto the connector bolt of the glow plug and then caulking. The round nut is thus positioned on top of the glow plug where electrical system of the vehicle connects to the glow plug. Fig 4.3 Nut on the glow plug As shown in the fig 4.3, the round nut is fastened onto the connecting bolt and it is in contact with the insulating washer. This glow plug assembly is then placed vertically inverted into the caulking fixture such that the nut will sit onto the bottom screw of the fixture. Shown in fig 4.4. Fig 4.4 glow plug inside fixture Nut
  23. 23. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 23 Chapter 5 CAULKING 5.1 Caulking process Caulking is one of several different processes to seal joints or seams in various structures and some types of piping. The oldest form of caulking is used to make the seams in wooden boats or ships watertight, by driving fibrous materials into the wedge-shaped seams between boards. A related process was formerly employed to join sections of cast iron sewage pipes. 5.1.1 Definition of caulking Caulking is also the term to describe the process used to make riveted iron or steel ships and boilers watertight or steam tight. The same term also refers to the application of flexible sealing compounds to close up gaps in buildings and other structures against water, air, dust, insects, or as a component in fire stopping. In the tunneling industry, caulking refers to the sealing of joints in segmental precast concrete tunnels, commonly by using concrete. 5.2 Caulking of Round nut As we know round is fastened to the round pin connector (connection terminal) by using twisting force. Later for further stability and to avoid loosening up of round nut during actual working round nut is subjected to caulking process. The caulking takes place inside the groove of round nut. The round nut is caulked on two sides which are opposite to each other. After caulking a small dent like structure is visible at the caulked region. Later it will be sent inspection department.
  24. 24. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 24 Fig 5.1(a) nut before caulking Fig 5.1(b) nut after caulking Fig 5.2 cross section of round nut. 5.3 Need for caulking The glow plug is used in diesel engines. The vehicles with diesel engines being heavy duty vehicles there will be very high vibrations caused during working (movement) and thus there are chances of loosening of round nut. Loosening of round nut causes several problems in vehicles like Short circuit of wires. Unable to start during cold conditions due to no proper connection. Takes more time to produce heat. To avoid above conditions caulking of round nut is very important.
  25. 25. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 25 5.3.1 Advantages of caulking of round nut It provides more stability and secures the fastening. It prevents loosening up of round nut. Thus avoid short circuiting of wires. Helps round nut to withstand high vibration force acting on it during working. 5.4 Components used in caulking process All the components used in caulking process is enclosed in a rigid fixture. It consists of following parts: i. Bottom fixture ii. Mid plate iii. Tool guide plate iv. Top fixture v. Glow plug holder vi. Connector vii. Connector rod viii. Tool holder ix. Tool x. Fixture stand 5.4.1 Fixture used in caulking process Fig 5.3 caulking fixture Fig 5.3(a) glow plug inserted in fixture
  26. 26. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 26 5.4.2 Description of fixture parts 1) Fixture stand: It is rigid structure which provides support to the fixture components. Whole fixture is mounted on to it and it is fastened to table using nut and bolt. Fig 5.4(a) Fixture stand 2) Bottom fixture: It is placed on fixture stand and supports mid plate. It is also fastened to the stand by bolt and nuts. Fig 5.4(b) bottom Fixture 3) Mid plate and Tool guide plate: These are placed above the bottom fixture and it supports and guides the tool movement during Caulking. The grooves are provided on tool guide plate which allows the movement of tool.
  27. 27. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 27 Fig 5.4.(c) tool guide plate Fig 5.4.(d) Mid plate 4) Top fixture: It encloses the tool and other plates from the top and avoids obstructions to the tool movement. It also has provision to house glow plug holder which holds glow plug. Fig 5.4(e) Top fixture 5) Glow plug holder: It is used to hold the glow plug during caulking process. It has groove on both sides through which tool enters and caulks the round nut. Fig 5.4 (f) Glow plug holder
  28. 28. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 28 6) Connector and Connector rod: It is used to transmit the force from pneumatic system to tool and tool holder. Connector rod is extension of piston of pneumatic system. Connector will connect rod and tool holder. Fig 5.4(g) Connector rod Fig 5.4 (h) Connector 7) Tool holder: It is the part which holds the caulking tool firmly. It is fixed to connector and moves in groove in tool guiding plate. It usually encloses almost the half part of caulking tool Fig 5.4 (i) Tool holder 8) Tool or Caulking Tool: Tool is held in tool holder groove. It has semi circular tool profile and creates semi- circular dent on the round nut. Usually it will be made of steel or alloys of steel. Fig 5.4(j) Tool
  29. 29. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 29 5.4.3 Miscellaneous part 1. Stopper: It is important part of fixtures which checks the extra movement of the connector rod and thus helps in correct caulking or accurate caulking. Fig 5.4(k) stopper
  30. 30. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 30 5.5 Considerations There are certain considerations made while taking readings of depth of caulked round nut. Usually they are classified into 4 main categories: i. Right side right corner. ii. Right side left corner. iii. Left side right corner. iv. Left side left corner. Fig 5.5 Consideration while taking caulked depth.
  31. 31. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 31 5.6 Design of tool Fig 5.6 (b) Design of Caulking tool
  32. 32. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 32 Chapter 6 STATISTICAL PROCESS CONTROL 6.1 Introduction Statistical process control is a procedure for open or closed loop control of manufacturing process. Based on statistical methods, Random samples of parts are taken from the manufacturing process according to specific sampling rules. Their characteristics are measured and entered in the control charts. This can be done with computer support. Statistical indicators are calculated from the measurement and uses to access the current principle must be observed when taking random samples. SPC is an application of inductive statistics. Not all parts have been measured, as would be the case for 100% testing. A small set of the data, random sample measurements, is used to eliminate parameters of the entire population. In order to correctly interpret results, we have to know which mathematical model to use, where its limits are and to what extent it can be used for practical reasons, even if it differs from real situations. Despite careful process control, uncontrolled, random effects of several inputs cause deviation of actual characteristic values from their targets (usually the middle of tolerance range). The main goals of SPC is 1. Improve quality and reliability of products and services without increased cost. 2. Provide practical tools for controlling quality. 3. Establish an ongoing measurement and verification system. 4. Increase productivity and reduce cost. 5. Prioritize problem solving activities to direct effort in systematic way. 6. Improve customer satisfaction.
  33. 33. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 33 6.2 Quality Tools Seven simple tools for analysis data. The structured use of the quality tools will provide data based evidence of the relevance and trend of defects and provide quantitative effect of countermeasure activity. The quality tools should be in use bu all groups the organization involved in problem solving, also providing a common understanding on investigation directly and effect analysis. The seven quality tools are: Histogram Scatter diagram Check sheet Cause and Effect diagram 5W(why) Control Chart Pareto Diagrams 1. Histogram A histogram is a graph which shows the frequency distribution of the data of a group about the central values. The histogram is an important diagnostic tool because it gives a “bird-eye-view” of the variation in the data 2. 5-WHY What it is: Questioning technique to determine causes existing problems by several asking and answering. When to use it: To identify the real cause of a problem.
  34. 34. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 34 Limits: Knowledge of the interviewed person. 3.control charts A control chart is a chart to examine whether a process is in stable condition or to ensure that process is maintained in stable condition. Control limits are increased by two lines viz upper and lower limits. If the points are within the control limits the process is stable, the fluctuation of point within control limits line results from common causes built into the process. Fig 6.1: Typical control chart A control chart is fairly simple and graphical way of disturbing what a process is doing, its benefits are: 1. Gives “live” information about the process. 2. Is easy to draw; only samples are required. 3. Can be drawn and used by the operator at the site of the jobs. 4. Identifies “special” cause and “random” causes. 5. Tells the operator when to adjust the process. 6. Reduce scrap and rework. 7. Increased productivity by improving quality. 8. Increases profit.
  35. 35. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 35 4. Check sheet A check sheet is a data gathering format prepared in such a way that data collection is simplified. Check sheet preparation considered the representative of the information to be recorded and simplifies the data that is to be actually recorded to mere check word. 5. Pareto diagram It is the tool used to focus improvement efforts on most important causes by identifying the vital few and trivial many causes. The Pareto chart indicates What are the problems? Which problem needs to be tackled on priority? What percentage of total does each problem present? 6. Cause and Effect diagram The causes and effect diagram is a pictorial representation of all possible causes which suppose to influence an effect. Interpretation of causes and effect diagram: The several cause’s branches are branched to main branch look exactly the structure of fish, hence called also as fish bone diagram. In order to find most basic cause of the problem look for causes that appears repeatedly. Gather data to determine relative frequencies of different causes. Finding of the sub causes from the main causes.
  36. 36. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 36 Fig 6.2: typical cause and effect diagram 7. PROCESS CAPABILITY Process capability represents the performance of a process in a state of statistical control. It is determined by the total variability that exists because of all common cause present in the system. Process capability is a measure of uniformity of quality characteristic of interest. *Capable process The process is said to be capable if distribution curve lies between the control limits and also if 3sigma<USL-LSL. For a capable process Cp must be>=1.33, if the process mean is that the target value. (Assume to be mild way between specifications limits, all items produced are well within specification limit).
  37. 37. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 37 Fig 6.2: typical capable process graph *Not capable process Process is not capable if distribution curved likes out of control limits and also if 3 sigma >USL>LSL. In this process some proportion of items produced will not meet the specifications. If there is a shift in mean or increase in standard deviation, an increasing proportion of a products will not meet the specification. There are several corrective approaches 1. Possibilities of increasing the specification limits can be exploded. 2. Measure to reduce process spread can investigate. 3. All alternative may be to shift the process average to achieve a desirable balance in the proportion of scrap and work. 4. Leave the process unchanged and perform 100% inspection to eliminate non confirming parts.
  38. 38. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 38 Fig 6.3: non capable process 6.3 Process capability index It is an aggregate measure of goodness of process performance. It relates process spread (difference between natural tolerance limit) to specification spread, assumomg two sided specification limits. Comments concerning Cp and Cpk are as follows: 1. The Cp value does not change as the process centre changes. 2. Cp=Cpk when the process is centered. 3. Cpk is always equal to or less than Cp. 4. A Cpk value greater than 1.33 indicates the process conforms to specification. 5. A Cpk value less than 1.33 indicates the process does not conform to specification. 6. A Cp value less than 1.33 indicates the process is not capable. 7. A negative Cpk value indicates the average is outside the specification limit. 8. A Cp value of zero indicates the average is equal to one of the specification. From the above statistical quality tools, root causes are determined without having any expert opinion considering all possible causes just by observation. Thus choosing cause and effect diagram.
  39. 39. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 39 6.4 Fish Bone Ishikawa diagrams (also called fishbone diagrams, herringbone diagrams, cause-and- effect diagrams, or Fishikawa) are causal diagrams created by Kaoru Ishikawa (1968) that show the causes of a specific event. Common uses of the Ishikawa diagram are product design and quality defect prevention, to identify potential factors causing an overall effect. Each cause or reason for imperfection is a source of variation. Causes are usually grouped into major categories to identify these sources of variation. Fig 6.4 fishbone diagram The categories typically include: • People: Anyone involved with the process • Methods: How the process is performed and the specific requirements for doing it, such as policies, procedures, rules, regulations and laws • Machines: Any equipment, computers, tools, etc. required to accomplish the job • Materials: Raw materials, parts, pens, paper, etc. used to produce the final product • Measurements: Data generated from the process that are used to evaluate its quality • Environment: The conditions, such as location, time, temperature, and culture in which the process operates From observations we had found few reasons for crack from that we had evaluated and found the root causes for the crack those are denoted by three stars( ***) in fishbone diagram.
  40. 40. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 40 Chapter 7 STATISTICAL DATA BEFORE THE PROJECT Measurement sheet: The measurements given below are the caulking depths of each glow plug that were measured individually using dial gauge. BOSCH MEASUREMENT SHEET DEPT : MSD MODEL NAME : DESCRIPTION : To measure caulking depth. SHEET DATE : Glow plug 1 of 2 SPECIFICATION : 0.5+/-0.2PURPOSE OF MEASUREMENT :To identify the cause for the crack . GAUGE NAME : BAKER METHOD OF MEASUREMENT: Dial gauge. GAUGE NUMBER :3181 Sl No. CHARECTERISTICS :Caulking depth in mm Right side Right side Left side Left side Right corner Left corner Right corner Left corner 1 0.57 0.52 0.45 0.7 2 0.56 0.57 0.5 0.7 3 0.46 0.6 0.5 0.6 4 0.45 0.54 0.6 0.63 5 0.5 0.54 0.46 0.68 6 0.52 0.6 0.48 0.55 7 0.32 0.68 0.58 0.42 *8 0.75 0.6 0.15 0.3 9 0.52 0.64 0.53 0.58 10 0.52 0.58 0.6 0.65 11 0.47 0.66 0.6 0.5 12 0.5 0.64 0.54 0.63 13 0.52 0.68 0.54 0.55 14 0.43 0.7 0.57 0.52 15 0.52 0.64 0.51 0.66 16 0.46 0.61 0.47 0.59 17 0.42 0.58 0.56 0.63 18 0.41 0.62 0.52 0.52 *19 0.75 0.85 0.26 0.41 20 0.5 0.61 0.52 0.58 21 0.51 0.61 0.51 0.59 22 0.43 0.69 0.58 0.54 23 0.52 0.61 0.55 0.65 24 0.49 0.61 0.51 0.58 25 0.52 0.54 0.49 0.69
  41. 41. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 41 In the above table, the rows marked with(*) indicates the values of caulking depth at which the round nut cracked. BOSCH MEASUREMENT SHEET DEPT : MSD MODEL NAME : DESCRIPTION : To measure caulking depth. SHEET DATE : Glow plug 2 of 2 SPECIFICATION : 0.5+/-0.2PURPOSE OF MEASUREMENT : To identify the cause for the crack GAUGE NAME : BAKER METHOD OF MEASUREMENT: Dial gauge. GAUGE NUMBER :3181 Sl No. CHARECTERISTICS :Caulking depth in mm Right side Right side Left side Left side Right corner Left corner Right corner Left corner 26 0.5 0.58 0.45 0.62 27 0.57 0.52 0.41 0.67 28 0.5 0.61 0.54 0.45 29 0.45 0.63 0.52 0.62 30 0.57 0.63 0.52 0.65 *31 0.66 0.66 0.48 0.41 32 0.4 0.61 0.5 0.64 33 0.44 0.65 0.54 0.63 34 0.5 0.65 0.54 0.55 35 0.45 0.66 0.57 0.6 36 0.45 0.66 0.44 0.56 37 0.51 0.61 0.49 0.61 38 0.52 0.6 0.52 0.65 39 0.43 0.7 0.6 0.52 40 0.46 0.6 0.5 0.6 41 0.47 0.71 0.55 0.54 42 0.5 0.49 0.48 0.68 43 0.48 0.66 0.55 0.58 *44 0.6 0.65 0.34 0.37 45 0.54 0.5 0.42 0.66 46 0.52 0.66 0.52 0.56 47 0.48 0.61 0.52 0.61 48 0.54 0.55 0.49 0.66 49 0.36 0.66 0.59 0.51 50 0.42 0.65 0.53 0.56
  42. 42. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 42 Capability of the round nut caulking machine: Fig 7.1 process capability chart Calculation of Cpk : Mean = Xbar = ∑ = 0.55 Standard deviation, S= ∑( ) ( ) = 0.09 Process capability indices, Cp= ( ) = 0.67 Cpk=Minimum = min (0.5 | 0.84) = 0.5 From the above results, it can be concluded that both Cp, Cpk of the machine is not meeting the global specification of 1.33 so the caulking process is very unstable. 0 20 40 60 80 100 120 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Numberofparts caulking depth Process Capability Chart LSL 0.30 USL0.70 Mean 0.55 Median 0.55 Mode 0.52 n 200 Cp 0.67 Cpk 0.50 CpU 0.50 CpL 0.84 Cpm 0.63 Cr 1.50 ZTarget/∆Z0.54 Pp 0.72 Ppk 0.53 PpU 0.53 PpL 0.90 Skewness-0.49 Stdev 0.09 Min 0.15 Max 0.85 Range 0.70 Z Bench 1.45 % Defects3.0% PPM 30000.00 Exp PPM ST73577.28 Exp PPM LT58037.96 Sigma 3.38
  43. 43. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 43 Control chart: Control charts for analyzing the stability of a process. As shown in the graph , the points marked in blue are controlled , which are within the range. The points marked red are uncontrolled and are exceeding the range Fig 7.2(a) control chart Fig 7.2 (b) control chart CL 0.212 UCL 0.485 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 1 2 3 4 5 6 7 8 9 10111213141516171819202122232425 Range Period control chart CL 0.552 UCL 0.707 LCL 0.397 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.65 0.70 0.75 1 2 3 4 5 6 7 8 9 10111213141516171819202122232425 Average Period control chart
  44. 44. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 44 Chapter 8 PROBLEM DEFINITION 8.1 Observations 8.1.1 Caulking depth of cracked nut After the caulking process of round nut .we had measured the caulking depth in the cracked round nut of the glow plug. Caulking depth at the cracked side of the round nut was 0.75mm and at the other side that is at no crack side was 0.15mm. This is due to uneven tool movement. Fig 8.1 round nut showing crack
  45. 45. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 45 8.1.2 Visual inspection 1. As seen in the figure below, the position of right tool is more compared to the left tool. This may be due to offset between the top fixture and the bottom fixture Fig 8.2 top view of tool 2. The glow plug placed in the fixture will not be tilted before caulking. Whereas during caulking, some degree of tilt is observed. Fig 8.3(a) glow plug does not tilt before caulking Fig8.3(b) Glow plug tilts during caulking
  46. 46. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 46 8.2 Software inspection The same model of the caulking machine is made and stimulated in CATIA V5R20 as shown in fig (2).Let us consider the offset distance of 1mm between the central axis of top fixture and to that of the bottom fixture as given in fig(3). Due to stimulations and constrains the whole component setup of the machine changes that is Distance from tool tip to the central axis of the top fixture changes and then viewing from the top of the machine we founded the same case of visual inspection as shown in fig (3). Usually the offset is due to fastening fit of the bolt between the top and the bottom fixture. Hence proofed the offset of the machine was the reason for the tool uneven visualization from top view of the fixture. 8.2.1 Distance from Tool tip to the central axis of top fixture After giving the offset distance of 1mm. The cross sectional view of the machine is as shown in figure (4). In the left side, the distance from the tool tip to the top fixtures central axis is found to be 7.097mm and in the right side, the distance from the tool tip to the top fixture central axis is found to be 4.965mm as shown in figure (4).This indicates that the right tool first contacts the round nut groove surface by 2.132mm (7.097mm -4.965mm) earlier then left tool during caulking as shown in figure (5). Fig 8.4(a) distances from tool tip to Fig 8.4(b) contact of tool on round nut the central axis of top fixture
  47. 47. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 47 8.2.2 Tilting of the glow plug The more allowances is given to the round nut holder (glow plug holder) with respect to the round nut. Looking from the top view as shown in fig (6) and also during caulking the right tool first contacts the round nut groove surface as shown fig (5) and (6) Fig 8.5 Top view of glow plug holder with round nut During caulking the right tool first contacts the round nut groove surface and pushes the round nut with glow plug towards left for certain distance till the round nut holder surface touch and then the glow plug slowly tilts as shown in fig(7). While glow plug tilts, the tip of the connector pin of the glow plug does not touches the bottom round nut stopper hole surface as shown in fig (7) and then the left tool comes in contact to round nut to form the caulking depth. This type of round nut caulking does not crack the round nut. Fig 8.6 Tilting of glow plug when crack does not occur
  48. 48. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 48 While caulking when the glow tilts, the tip of the connector pin of the glow plug touches the bottom round nut stopper hole surface as shown in fig (8) and then the right tool makes some extra caulking depth (0.6mm) in round nut on right side and then the left tool comes in contact to round nut. That is when the left tool makes a caulking depth of 0.15mm in round nut. Then the right tool will make caulking depth of 0.75mm (extra caulking depth (0.6)+ left caulking depth(0.15)). The right side caulking depth of round nut exceeds the specification limits of 0.5+/-0.2mm that is from lower specification limit of 0.3mm to upper specification limit of 0.7mm. Caulking depth of 0.75mm>0.7mm which leads to crack on right side of the round nut. Few cracked nut caulking depth readings and of this case is shown in table (1).The cross sectional cut of the cracked nut with caulking depth is as shown in figure (120) Fig 8.7 shows the connector touching the supporting rod
  49. 49. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 49 Caulking depth of cracked nut ig 8.8 Cross sectional cut of the cracked nut with caulking depth Sl No. CHARECTERISTICS :Caulking depth in mm Right side Right side Left side Left side Right corner Left corner Right corner Left corner 1 0.75 0.6 0.15 0.3 2 0.75 0.85 0.26 0.41 3 0.66 0.66 0.48 0.41 4 0.6 0.65 0.34 0.37 5 0.78 0.72 0.27 0.31
  50. 50. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 50 Chapter 9 RESEARCH AND DEVELOPMENT 9.1 Distance from Tool tip to the central axis of bottom fixture While keeping the same model of 1mm offset distance. The cross sectional view of the machine is as shown in fig (9). In the left side, the distance from the tool tip to the bottom fixtures central axis is found to be 6.097 mm and in the right side, the distance from the tool tip to the bottom fixture central axis is found to be 5.915mm as shown in fig ().This indicates that the right tool first contacts the round nut by 0.182mm (6.097 mm-5.915mm) earlier then left tool during caulking that is when the glow plug is placed from bottom as shown in fig (new). So we suggested that the glow plug should be placed from bottom. Fig 9.1 distance from tool tip to central axis of bottom fixture 9.2 Modified model The glow plug is placed manually by hand on to the glow plug holder as shown in fig (10). Switch on the bottom pneumatic piston cylinder. It lifts the glow plug up to the bottom fixture and gets stopped by the round nut stopper for a required position for caulking process. Such that the tool contact should be to the round nut groove surface as shown in fig (11), But still the bottom pneumatic piston cylinder is activated.
  51. 51. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 51 Fig 9.2 shows glow plug placement Fig 9.3 showing caulking in modified fixture
  52. 52. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 52 Switch on the top pneumatic piston cylinder that pushes the connector rod in longitudinal direction that in turn is connected to the guide plate which is converted into rotational motion. On the guide plate there is a groove as shown in fig (6.4.2 (c)), where the tool holder is placed on the groove surface and the guide plate guide the tool movement longitudinal by the help of the top fixture which also guide the tool. As the guide plate rotates the tool moves forward, such that both the tools come closer to each other, there are in opposite direction as shown in fig (12). Then the tool makes the caulking to the round nut and then the tool come back to its initial position has the top pneumatic piston cylinder switches off. And then the bottom pneumatic cylinders get switched off and the glow plug comes back to its initial position. The caulked glow plug is replaced by new glow plug in which the round nut is not caulked and the process cycle is continued. Fig 9.4 Tool movement mechanism
  53. 53. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 53 9.3 Modification in existing component 1) Bottom fixture Existing component: In the existing component of bottom fixture the holes where threaded to fasten the bolt on both top and bottom surface of the fixture as shown in fig (13) design fig (14) Fig 9.5(a) bottom fixture Modified Existing component: The threaded hole of diameter 10mm on the top surface is replaced by sliding rod of diameter 8mm and in the bottom surface the threaded hole is replaced by sliding hole of same size as shown in fig (15) design fig (16). Fig 9.5(b) modified bottom fixture
  54. 54. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 54 2) Top fixture Existing component: In the existing component of top fixture on the top surface the hole of diameter 15mm is tapped to a depth of 8mm and the hole of diameter 10.2mm is tapped to a depth of 18mm as shown in fig (17) Fig 9.6(a) existing top fixture Modified Existing component: In this component the tapped hole of diameter 15mm to a depth of 8mm and hole of diameter 10.2mm to a depth of 18mm is replaced by single sliding hole of diameter 8mm to an depth of 26mm as shown in fig (18) Fig 9.6(b) modified top fixture 9.3.1 Advantage of modifying the component 1. It reduces the offset distance and misalignment between top and bottom fixture. 2. It also reduces the uneven tool tip distance from central axis. 3. Easy to fit top fixture to the bottom fixture by means of sliding fit.
  55. 55. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 55 9.4 Components used in the new caulking machine The new components used in new caulking machine are has given below: 1) Stand: The stand has two supporting plates, top plate and bottom plate supported by three rods which are bolted on to the top plate. The bottom plate has two pipes which support the sliding rods. The fixture is place upon the top plate as shown in fig. Fig 9.7 stand 2) Sliding rods: These rods help for vertical movement of sliding plate. Fig 9.8 sliding rods 3) Sliding plate: This serves for two purposes, one it holds the glow plug holder in place, and also is connected to the pneumatic system which gives it the movement. Fig 9.9 sliding plate
  56. 56. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 56 4) Glow plug holder: The glow plug to be caulked is placed onto the holder which ensures that the glow plug is held rigidly without tilting. Fig 9.10(a) glow plug holder Fig 9.10(b) position of glow plug holder 5) Round nut stopper: It is fixed on top of the fixture; it facilitates the adjustment of the screws on top to stop the nut from moving more than required. Fig 9.11 stopper stopping glow plug movement
  57. 57. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 57 Chapter 10 APPROACH TO WALL THICKNESS Fig 10.1 design of round nut 10.1 Old and new design The above figure shows the old design of the round nut of 6mm diameter. Calculation of wall thickness: Groove surface dia =6mm Inner dia of round nut = 4mm Therefore wall thickness, T = = 1mm, for specification limit 0.3mm to 0.7mm Table showing specification and deviation
  58. 58. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 58 Applying the critical tolerance- Dia of groove surface = 6 - 0.15 = 5.85 mm Wall thickness, T = . = 0.925mm Specification is given as 0.3mm to 0.7mm; the upper limit is 0.7mm for 1mm wall thickness. If caulking depth is 0.7mm or more, crack might occur. When wall thickness is 0.925mm crack will occur at around the depth of 0.625mm. i.e. (0.925mm – 0.3mm). In this type of cases crack occurs for values shows in table. Fig 10.2 table showing caulking depth value exceeding 0.625 10.2 Modified design From above calculation it is confirmed that due to small wall thickness the possibility of occurrence is more. Thus the increase in thickness on 1mm was suggested as shown below. Fig 10.3 Modified nut design
  59. 59. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 59 Calculation of wall thickness: Groove surface dia = 6.4mm Inner dia of round nut = 4mm Therefore wall thickness, T = . = 1.2 mm, for specification limit 0.3mm to 0.7mm. Applying the critical tolerance- Dia of groove surface = 6.4 - 0.15 = 6.25 mm Wall thickness, T = . = 1.125mm When wall thickness is 1.125mm, crack will occur at around the depth of 0.825mm. The caulking depth never exceeds 1mm; therefore the crack doesn’t occur in this case.
  60. 60. ROUND NUT CAULKING PROCESS OPTIMIZATION AND CRACK ELIMINATION DEPARTMENT OF MECHANICAL ENGINEERING, RGIT, BANGALORE. Page | 60 Chapter 11 CONCLUSION The crack in round nut was countered by increasing the wall thickness from 1mm to 1.5mm, and it was successful in reducing the crack. This resulted in reducing the scrap rate and inspection time Process optimization was done correcting the tool positioning ,eliminating of tilting and reducing offset of top and bottom fixture Suggestion of automated caulking fixture, where manual loading replaced by automated uphill loading of glow plug in the fixture. Improved process capability and reduced lead time. 11.1 Scope for improvement Eccentricity of round nut was countered by suggesting concentricity factor. So we concentrated on the hardness material , and suggested them for changing grade of material being used Automated caulking fixture has in built safety sensors which facilitate actuation of hydraulic caulking system only after placing the work part and workers hand is removed from proximity of fixture.

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