Week 2:- BiW Fixture Basics Challenge

Q1 Ans

PROCESS OF PROJECT EXECUTION ACTIVITY:

• The above figure shows the process involved in process execution activities. It is a general activity that is involved in BIW fixture & Tooling.
• It is the starting phase of every project.
• It starts with the basic requirements/RFQ we received from the customer.
• As shown in the figure there are various steps involved in project activities, They will be explained in detail below.

1. RFQ:

• RFQ – Request for Quotation.
• In this where the customer gives the requirement/specifications in detail for the given projects in the form of data or documents.
• Also, the customer specifies its technical offer, commercial offer, etc, how the project will be executed & the timeline of the project also will be mentioned.

2. FIRST SPEC: DISCUSSION MEETING:

• After RFQ received, Technical offer, commercial offer, a timeline of the project, etc, will be discussed and prepared from outside.
• In this time required for data study, 3D design concept, simulation validation, quality check, 2d drawing release, bought-outs, manufacturing, assembly, installation & commissioning will be discussed and prepared in the technical offer.
• Based on the technical offer, the commercial offer will be finalized.

3. OFFER SUBMISSION:

• After the finalization in the meeting, the offers will be submitted to the customer end. The customer will arrange to get an offer from other suppliers too.
• Based on the technical, cost, quality, standard, and name in the industries, the customer will be finalizing the offer.

4. LOI/PO RECEIPT:

• After an offer has been finalized customer will be releasing the LOI/PO (Purchase Order). Once PO is released, we have to start the work.
• After getting the PO from the customer, we have to prepare the schedule.

5. SCHEDULE PREPARATION:

• Once the PO released from the customer, we will be working on the preparation of the schedule which should be matched our planned commitment in the technical offer/customer required time.
• Schedule preparation is nothing but dividing the different activities like kick-off meeting, design data study, DAP, simulate, Quality check 2D detailing, drawing check, Release of BOM, Manufacturing, bought outs of electrical & mechanical components, Assembly of the fixture, paint, trial run out, installation and commissioning at the customer end, etc.
• These activities will be traced in the schedule preparation chart.
• The date-wise schedule should be matched the committed date. Otherwise have to revise the schedule and prepare accordingly by discussing it in the meetings.

6.BOM PREPARATION:

Bill of materials like cylinders, motors, etc, which are required for the project are prepared

7. DESIGN CONCEPT PREPARATION:

• Before design concept, we have to study the data of consumer requirements thoroughly which is carried out in design data study activities.
• During the design data study, we will proceed with rough sketches to get a flow while designing concepts.
• The concept preparation would include the process like load act on panels, clamping process, which spot should be welded first, travel of the gun.
• In this concept preparation, we should conceptualize the basic data like spot plan, cycle time, etc,
• The weld gun should not collapse while traveling, so by considering this have to make a concept preparation.
• To avoid collapses of weld guns or robots during traveling, a spot plan will be done at the initial stage.
• In design concept preparation, the design of the layout is been prepared at a very initial level which gives the information of placements of robots and fixtures.

• Spot plan should be taken into consideration during concept design preparation
• The spot plan clears us that how many robots are to be used and the sequence of the spot will be decided along with which robot will be cover certain spot places.
• Also, the cycle time should be considered while preparing the concept design. To calculate the cycle time, we should go to the cycle time study.
• Cycle time study includes min per shift, No. of shifts, No. of days per year, No. of component per year, the total number of minutes.
• Cycle time study includes min per shifts, no. of shifts, no of days per year, no of component per year, the total number of minutes, efficiency, Total no of seconds, take time seconds, average time per spot, total no of spot, no of robots placed. From the cycle time study, we can get time taken per spot, time is taken for a single component, efficiency of production. If the efficiency is not satisfied, we have to do some reconsideration in the design.

8. CUSTOMER APPROVAL:

• It is also known as the Design Approval Process (DAP).
• After design concepts, the customer will review the design concepts.
• If the design needs to be made simple or some other correction needs to be done in concept design will be discussed and after meeting the requirement of the customer, they will give approval to the design to go on with further activities.

9. DETAILING & DRAWING RELEASE:

• Once the customer approved the process, the detailing of the fixture parts which is to be manufactured has been done by giving appropriate dimensions and GD&T symbols.
• All the dimensions which are necessary for manufacturing should be included with GD&T in the drawing before releasing the drawing to the manufacturing team.

10. MANUFACTURING/BOP ORDERING:

• The mechanical & electrical parts like sensors, cylinders, etc, which needs for a fixture are ordered as per design specifications.

11. MECHANICAL / ELECTRICAL ASSEMBLY:

• After the materials ordered received to our end. The quality will check the working conditions and technical specs, which meets our requirement.
• After the quality check, the mechanical & electrical parts are assembled as per design.

12. QUALITY INSPECTION:

• After the assembly again the quality check is done.
• In all dimensions, positional accuracy, coordinates are checked using CMM.

13. INTERNAL TRIAL:

• After QC check, internal trials are made to check the operation of the fixture.
• It is the first trial taken in-house, so we will see by putting the assembly in the fixture whether the seating of assembly/panel suited correctly, whether the clamping operation is done properly, also whether the pins are getting into the holes, etc.

14. ONLINE TRIAL:

• The trail will be done automatically made through the control panel. The process sequence of operation is checked as by the designed way.

15. PACKAGING:

• To avoid damage, occur in the fixture while transportation which may also lead to affect the Aesthetic look & proper function of fixture packaging has been done.
• After the trials taken have to get the QC confirmation whether the panels met the standards/specs, given by the customer also whether the fixture meets the customer standards.
• After approval of QC, the packaging is been done as per standards. Certain companies follow certain packaging standards, So the packaging should be one as per customer standards.

16. DESPATCH:

After the fixture has been packed for delivery as per standards. It’s been despatched to the customer.

17. INSTALLATION AS PER LAYOUT:

• As we discussed in design concept preparation, the design of the layout are been prepared at a very initial level which gives the information of placements of robots and fixtures.
• According to the design, the installation & commissioning team will install the fixtures.

18. TRAILS & TRAINING AT CUSTOMER:

• Production trials will be taken at the customer end.
• During the technical offer, we will be confirmed that the n-number of assemblies will be produced within 8hrs/12hrs shifts. So in customer trial, we have to achieve the confirmed quantity of assemblies.
• Once it is achieved training will be given to the operator, staff, engineers who involved in this process. The sequence of the working process by the fixture will be explained in detail.
• The checkpoints which have to be done after placing the panels into the fixture will be made clear to them.

19. BUYOFF MEETING:

• After trials and training at the customers' end, the buy-off meeting will be held.
• In this meeting customer will give reviews about the fixtures, sometimes a customer may need/feels better to do some additional work also. It will be discussed and finalize in the meeting.

20. FINAL HANDOVERS:

• The fixture and the documents support the fixtures/production will be handed over.
• Documents like clamp validation documents, ergo sheets, BOMs, charts will be delivered and handed over to customers. Documents will play a vital role in the industry. We should always have proof of our work done. The sequence of quality of work will be seen through the documents.
• Every automobile industry will follow some standards to maintain documents as per ISO, IATF.
• Now every automobile industry/vendor/supplier is maintaining the documents as per IATE (International Automotive Task Force).
• IATE – The international Automotive Task Force is a group of automotive manufactures which aims at providing improved quality products to automotive customers worldwide.

Q2 Ans

Joining processes:

• JOINING COMPRISES a large number of processes used to assemble individual parts into a larger, more complex component or assembly.
• The individual parts of a component meet at the joints.
• Joints transmit or distribute forces generated during service from one part to the other parts of the assembly.

TYPES OF JOINING PROCESS:

• The durability & performance of any structure largely depends on the quality & the design of the component joints.
• The whole structure cannot be made in one piece.
• Two fundamental options for joining materials & components are,

1. Metallurgical joining
2. Mechanical joining
3. Chemical joining

1. METALLURGICAL JOINING:

• Metallurgical joining are classified into,

1. Welding.
2. Brazing.
3. soldering.

1. WELDING:

• The process of joining similar metals by the application of heat is called Welding can be obtained with or without application of pressure and with or without the addition of filler metal, which is known as an electrode. During welding, the edges of these metal pieces are either melted or brought to plastic condition. The welding process is used for making permanent joints, which is obtained by a homogeneous mixture of two materials.

Classification of Welding Process: The types of welding process classified into,

1. Fusion
2. Electric Resistance
3. Solid-state

1. Fusion Welding.

• In infusion welding, the metal at the joint is heated to a molten state, and then it is allowed to solidify.
• The pressure is not applied during the welding process and hence it is also called 'non - pressure welding'.
• Filler materials may be required during this type of welding.

• Classification of fusion welding is,

1. Thermit welding
2. Arc welding
3. Gas welding

1. Thermit Welding

• Welding the parts by using liquid thermit steel around the portions to be welded is called thermit welding. Since it is a fusion welding process, neither arc is produced to heat parts nor flames are used. For getting high temperatures, the exothermic reaction is used.
• The welding principle is the heat of the thermit reaction used for welding in a plastic state & mechanical pressure is applied for the joint.
• It is depending on the chemical reaction between iron oxide & aluminum.

1. Arc Welding:

• In the arc welding process, the heat is developed by an electric arc. The arc is produced between an electrode and the work. This is a process of joining two metal pieces by melting their edges with an electric arc. In arcwelding the electrical energy is converted into heat energy.
• The electrode & the workpiece are brought nearer with similar a small air gap of 3mm approximately. Then the current is passed through the workpiece and the electrode to produce an electric arc.
• The workpiece is melted by an arc, The electrode is also melted, and hence both the workpieces become a single piece without applying any external pressure. The temperature of the arc is about 5000°C to 6000°C. The electrode supplies additional filler metal into the joints and is deposited along the joint. A transformer or generator is used to supply current. The depth to which the metal is melted and deposited is called the depth of fusion. To obtain a better depth of fusion, the electrode is kept at 70° inclination to the vertical.
• The electrode used in arc welding is generally coated with flux. The flux is used to prevent the reaction of the molten metal with atmospheric air. Also, it removes the impurities of the molten metal and forms a slag. This slag gets deposited over the weld metal. This slag protects the weld seam from rapid cooling.
• The molten metal is forced out of the pool by the electric arc. Hence a small depression is formed in the parent metal where the molten metal is oiled up. This is known as "arc carter".The distance between the tip of the electrode and the bottom of the arc crater is called "arc length".

The types of arc welding are,

Manual Metal-Arc

• Aiming for cleaner, high-quality welds at a lower cost. Manual Metal Arc (MMA) welding is the most flexible and one of the most widely used arc welding processes. It involves striking an arc between a covered metal electrode and a workpiece.

MIG

• MIG—i.e., metal inert gas—welding is generally used for large and thick materials. It employs a consumable wire that acts as both the electrode and the filler material. Compared to TIG welding, it is much faster, resulting in shorter lead times and lower production costs

TIG

• In TIG welding, a tungsten electrode heats the metal you are welding, and gas (most commonly Argon) protects the weld puddle from airborne contaminants. TIG welding produces clean, precise welds on any metal.

Submerged Arc

• Submerged arc welding (SAW) is so named because the weld and arc zone are submerged beneath a blanket of flux. The flux material becomes conductive when it is molten, creating a path for the current to pass between the electrode and the workpiece.

Plasma Arc

Plasma arc welding is an arc welding process similar to gas tungsten arc welding. The electric arc is formed between an electrode and the workpiece. The key difference from GTAW is that in PAW, the electrode is positioned within the body of the torch, so the plasma arc is separated from the shielding gas envelope.

Atomic hydrogen Arc

• Atomic hydrogen welding (AHW) is an arc welding process that uses an arc between two tungsten electrodes in a shielding atmosphere of hydrogen. The process was invented by Irving Langmuir in the course of his studies of atomic hydrogen.

Carbon Arc

• Carbon arc welding (CAW) is a process that produces coalescence of metals by heating them with an arc between a non-consumable carbon (graphite) electrode and the work-piece

Electro slag

• Electroslag welding (ESW) is a highly productive, single-pass welding process for thick (greater than 25 mm up to about 300 mm) materials in a vertical or close to a vertical position. (ESW) is similar to electro gas welding, but the main difference is the arc starts in a different location.

III. Gas welding

• Gas welding is a welding process that melts and joins metals by heating them with a flame caused by a reaction of fuel gas and oxygen.
• The most commonly used method is
• Oxyacetylene welding, due to its high f la me the temperature.
• The flux may be used to deoxidize and cleanse the weld metal.
• The flux melts solidify and forms a slag skin on the resultant weld metal.

. Electric Resistance Welding:

• Resistance welding is a welding technique widely used in the manufacturing industry for joining metal sheets & This type of welding is very much used in BIW assemblies most common.
• The weld is made by conducting a strong current through the metal combination to heat up & finally melt the metals at localized points predetermined by the design of the electrodes or the workpiece to be welded.
• A force is always applied before, during, and after the application of the current to confine the contact area at the weld interfaces and in some applications to forge the workpieces.

Types of Resistance welding are,

1. Resistance Spot welding
2. Resistance Seam welding
3. Resistance Projection welding
4. Resistance spot Welding:

• The process is used for joining sheet materials & uses shaped copper - chromium or zinc conium alloy electrodes to apply pressure and convey the electrical current through the workpiece.
• Heat is developed mainly at the interface between two sheets, eventually causing the material being welded to melt, forming a molten pool, the weld nugget.
• The molten pool is contained by the pressure applied by the electrode tip & the surrounding solid metal.

2. Resistance Seam Welding:

• Seam welding is a resistance welding process for joining metal sheets in continuous, often leak-tight, seam joints by directly applying opposing forces with electrodes consisting of rotary wheels.

The current & the heat generation are localized by the peripheral shapes of electrode wheels

3. Resistance Projection Welding:

• Projection welding is a resistance welding process for joining metal components or sheets with embossments by directly applying opposing forces with electrodes specially designed to fit the shapes of the workpieces.
• The current & the heat generation are localized by the shape of the workpiece either with their natural shapes or with specially designed projection.
• Large deformation or collapse will occur in the projection part of the workpieces implying high.

1. Solid-State Welding:

• Solid-State Welding is a welding process, in which two workpieces are joined under a pressure providing intimate contact between them and at a temperature essentially below the melting point of the parent material. The bonding of the materials is a result of the diffusion of their interface atoms.

The following processes are related to Solid State welding:

1. Forge welding
2. Cold welding
3. Friction welding
4. Explosive welding
5. Diffusion welding
6. Ultrasonic Welding

1. Forge Welding:

• Forge Welding is a Solid-state welding process, in which low carbon steel parts are heated to about 1800°F (1000°C) and then forged (hammered).
• Prior to Forge Welding, the parts are scarfed in order to prevent entrapment of oxides in the joint.
• Forge Welding is used in general blacksmith shops and for manufacturing metal art pieces and welded tubes.

2. Cold Welding (CW):

• Cold Welding is a Solid-state welding process, in which two workpieces are joined together at room temperature and under a pressure, causing a substantial deformation of the welded parts and providing intimate contact between the welded surfaces.
• As a result of the deformation, the oxide film covering the welded parts breaks up, and clean metal surfaces reveal. Intimate contact between these pure surfaces provides a strong and defectless bonding.
• Aluminum Alloys, Copper Alloys, low carbon steel, Nickel Alloys, and other ductile metals may be welded by Cold Welding. Cold Welding is widely used for manufacturing bi-metal steel - aluminum alloy strips, for cladding of aluminum alloy strips by other aluminum alloys, or pure aluminum (Corrosion protection coating).
• Bi-metal strips are produced by Rolling technology. Presses are also used for Cold Welding.
• Cold Welding may be easily automated.

3. Friction Welding (FRW):

• Friction Welding is a solid-state welding process, in which two cylindrical parts are brought in contact by a friction pressure when one of them rotates. Friction between the parts results in heating their ends. Forge pressure is then applied to the pieces providing formation of the joint.
• Carbon steels, alloy steels, tool & die steels, adequate steels, aluminum alloys, copper alloys, magnesium alloys, Nickel alloys, Titanium alloys may be joined by Friction Welding.

4. Explosive Welding (EXW):

• Explosive Welding is a Solid-state welding process, in which welded parts (plates) are metallurgically bonded as a result of oblique impact pressure exerted on them by a controlled detonation of an explosive charge.
• One of the welded parts (base plate) is rested on an anvil, the second part (flyer plate) is located above the base plate with an angled or constant interface clearance.
• An explosive charge is placed on the flyer plate. Detonation starts at an edge of the plate and propagates at high velocity along with the plate.
• The maximum detonation velocity is about 120% of the material sonic velocity.
• The slags (oxides, nitrides, and other contaminants) are expelled by the jet created just ahead of the bonding front. Most of the commercial metals and alloys may be bonded (welded) by Explosive Welding.
• Dissimilar metals may be joined by Explosive Welding: Copper to steel; Nickel to steel; Aluminium to steel; Tungsten to steel; Titanium to steel; Copper to aluminium.
• Explosive Welding is used for manufacturing clad tubes and pipes, pressure vessels, aerospace structures, heat exchangers, bi-metal sliding bearings, ship structures, weld transitions, corrosion-resistant chemical process tanks.

5. Diffusion Welding (DFW):

• Diffusion Welding is a Solid-state welding process, in which pressure applied to two workpieces with carefully cleaned surfaces and at an elevated temperature below the melting point of the metals. The bonding of the materials is a result of the mutual diffusion of their interface atoms.
• In order to keep the bonded surfaces clean from oxides and other air contaminations, the process is often conducted in a vacuum.
• No appreciable deformation of the workpieces occurs in Diffusion Welding. Diffusion Welding is often referred to more commonly as Solid-state welding.
• Diffusion Welding is able to bond dissimilar metals, which are difficult to weld by other welding processes: Steel to tungsten; Steel to niobium; Stainless steel to titanium; Gold to copper alloys.
• Diffusion Welding is used in aerospace and rocketry industries, electronics, nuclear applications, manufacturing composite materials.

6. Ultrasonic Welding (USW):

• Ultrasonic Welding is a Solid-state welding process, in which two workpieces are bonded as a result of pressure exerted on the welded parts combined with the application of high-frequency acoustic vibration (ultrasonic).
• Ultrasonic vibration causes friction between the parts, which results in a closer contact between the two surfaces with simultaneous local heating of the contact area. Interatomic bonds, formed under these conditions, provide strong joint. The ultrasonic cycle takes about 1 sec. The frequency of acoustic vibrations is in the range of 20 to 70 kHz.
• The thickness of the welded parts is limited by the power of the ultrasonic generator.

Ultrasonic Welding is used mainly for bonding small workpieces in electronics, for manufacturing communication devices, medical tools, watches, in the automotive industry

1. Brazing:

Brazing is a metal-joining process in which two or more metal items are joined together by melting and flowing a filler metal into the joint, the filler metal having a lower melting point than the adjoining metal.

Brazing differs from welding in that it does not involve melting the work pieces and from soldering in using higher temperatures for a similar process, while also requiring much more closely fitted parts than when soldering. The filler metal flows into the gap between close-fitting parts by the capillary. The filler metal is brought slightly above its melting temperature while protected by a suitable atmosphere, usually a flux. It then flows over the base metal (known as wetting) and is then cooled to join the workpieces together. A major advantage of brazing is the ability to join the same or different metals with considerable strength.

There are different methods/techniques in brazing. They are:

1. Torch Brazing: In this method, acetylene, natural gas & butane, or propane are combined with air, or oxygen is used to supply the required heat to melt the filler rod and diffuse the base It is not used for mass production, and flues are used in the form of paste or powder.
2. Furnace Brazing: In this process, the heat is supplied by gas or electric heating The furnace can be either box type or continuous type. The preformed shape of filler metal is placed on the parts to be joined before entering the furnace. The use of flux can be avoided if an inert atmosphere is maintained in the furnace. It is used for mass production and the flux is used in the form of a paste.
3. Induction Brazing: In this process also, the filler metal is used in the form of preformed The parts are heated by placing within the field of a high-frequency induction coil. The electric and magnetic resistances of the changing induction field are used to produce the eddy current. This eddy current is used to heat the metal. It is also used for mass production and the flux is used in the form of a paste.
4. Dip Brazing: The dip brazing is of two They are: i) Chemical dip brazing: In chemical dip brazing, the parts with preformed filler metal are placed into a molten bath of flux. This method is mainly used for joining large parts. ii) Molten metal bath process: In this process, the assembled parts are first prefixed & then immersed into a molten bath or filler metal. It is used only for joining smaller parts.
5. Resistance Brazing: In this process, the filler metal is placed in the joint, Rapid heating minimizes oxidation and the heat-affected zone is
6. Laser Brazing & Electron Beam Brazing: The laser & electron beam brazing methods are costly In laser brazing, the laser beam is used to join the metal and the beam produced by the heat source is used to join the metals in electron beam brazing. It is used only in precision work of high value & relating high-temperature materials.

iii. Soldering:

Soldering is a process in which two or more items are joined together by melting and putting a filler metal (solder) into the joint, the filler metal having a lower melting point than the adjoining metal. Unlike welding, soldering does not involve melting the workpieces. In brazing, the workpiece metal also does not melt, but the filler metal is one that melts at a higher temperature than in soldering. In the past, nearly all solders contained lead, but environmental and health concerns have increasingly dictated the use of lead-free alloy for electronics and plumbing purposes

There are different types of soldering methods. They are:

1. Hard soldering: In hard soldering, the filler metal is also known as silver soldering. This method is more expensive than plain brazing because the filler metal is more expensive. This hard soldering method is used for joining electrical & refrigeration parts.
2. Soft Soldering: This is the most commonly used In this method soldering iron is a copper rod with a thin tip that is used for flattering the soldering material. The soldering iron can be heated by keeping it in a furnace or by means of electrical resistance. The filler material used in soft soldering is called soft solder.
3. Dip soldering: In this method, a large amount of solder is melted in a closed Then the parts to be soldered are cleaned & properly dipped in a flux bath as per the requirement. It is then dipped into the molten solder pool and lifted after completing soldering.
4. Wave Soldering: It is a different method in which the parts to be soldered are not dipped into the solder tank but a wave is generated into the tank. So the solder comes up & the joint is made. It is used for the mass production of electronic equipment.
5. The other methods of soldering are Oven soldering, Resistance soldering, Induction soldering & Infrared.
6. Resistance & Induction soldering: In this method, electric energy is used to join the.
7. Infrared soldering: In this method, the ultrasonic waves are used to join the.

2. MECHANICAL JOINING:

• Mechanical joining includes bolting, riveting, caulking, shrink fitting, Hemming, Seaming, and folding, all of which join workpieces by using mechanical

1. Self Piercing Riveting:

• It is a high-speed mechanical fastening process for point joining sheet material, typically steel & aluminum alloys.
• It is a single-step technique generally using a semi-tubular rivet to clinch the sheets in a mechanical joint.
• As the name suggests pre-drilled holes are not required, allowing the joint to be made rapidly in one operation.

1. Hemming & seaming process:

• Hemming & seaming are two similar metalworking processes in which a sheet metal edge is rolled over onto itself.
• Hemming is a process in which the edge is rolled flush to itself, while a seam joins the edges of two materials.

iii. Bolting:

• Bolted joints are one of the most common elements in construction and machine design. They consist of fasteners that capture and join other parts and are secured with the mating of screw threads.
• There are two main types of bolted joint designs: tension joints and shear joints.
• In the tension joint, the bolt and clamped components of the joint are designed to transfer an applied tension load through the joint by way of the clamped components by the design of a proper balance of joint and bolt stiffness. The joint should be designed such that the clamp load is never overcome by the external tension forces acting to separate the joint. If the external tension forces overcome the clamp load (bolt preload) the clamped joint components will separate, allowing relative motion of the components.
• The second type of bolted joint transfers the applied load in shear of the bolt shank and relies on the shear strength of the bolt. Tension loads on such a joint are only incidental. A preload is still applied but consideration of joint flexibility is not as critical as in the case where loads are transmitted through the joint in tension. Other such shear joints do not employ a preload on the bolt as they are designed to allow rotation of the joint about the bolt but use other methods of maintaining bolt/joint integrity. Joints that allow rotation include clevis linkages, and rely on a locking mechanism (like lock washer, thread adhesives, and locknuts).

Proper joint design and bolt preload provide useful properties:

• For cyclic tension loads, the fastener is not subjected to the full amplitude of the load; as a result, the fastener's fatigue life is increased or—if the material exhibits an endurance limit its life extends indefinitely.
• As long as the external tension loads on a joint do not exceed the clamp load, the fastener is not subjected to motion that would loosen it, obviating the need for locking mechanisms. (Questionable under Vibration Inputs.)
• For the shear joint, a proper clamping force on the joint components prevents relative motion of those components and the fretting wear of those that could result in the development of fatigue cracks.

In both the tension and shear joint design cases, some level of tension preload in the bolt and resulting compression preload in the clamped components is essential to the joint integrity. The preload target can be achieved by a variety of methods: applying a measured torque to the bolt, measuring bolt extension, heating to expand the bolt then turning the nut down, torquing the bolt to the yield point, testing ultrasonically, or by applying a certain number of degrees of relative rotation of the threaded components. Each method has a range of uncertainties associated with it, some of which are very substantial.

1. shrink fitting:

• Shrink-fitting is a technique in which an interference fit is achieved by a relative size change after assembly. This is usually achieved by heating or cooling one component before assembly and allowing it to return to the ambient temperature after assembly, employing the phenomenon of thermal expansion to make a joint. For example, the thermal expansion of a piece of a metallic drainpipe allows a builder to fit the cooler piece to it. As the adjoined pieces reach the same temperature, the joint becomes strained and stronger.
• Other examples are the fitting of a wrought iron tire around the rim of a wooden cartwheel by a wheelwright, or of a steel tire to the wheel of a railway engine or rolling stock. In both cases, the tire will be heated and expands to slightly greater than the wheel's diameter, and is fitted around it. After cooling, the tire contracts, binding tightly in place. A common method used in industry is the use of induction shrink fitting which refers to the use of induction heating technology to pre-heat metal components between 150˚C and 300˚C thereby causing them to expand and allow for the insertion or removal of another component. Other methods of shrink-fitting include compression shrink fitting, which uses a cryogen such as liquid nitrogen to cool the insert and shape memory coupling, which is achieved using a phase transition.

3. CHEMICAL JOINING:

Chemical joining includes Adhesive bondings.

Adhesive Bonding:

• Adhesive bonding is used to fasten two surfaces together usually producing a smooth bond.
• This joining technique involves glues, epoxies, or various plastic agents that bond by evaporation of a solvent or by curing a bonding agent with heat, pressure, or time.
• Adhesive bonding (also referred to as gluing or glue bonding) describes a wafer bonding technique by applying an intermediate layer to connect substrates of different types of materials. Those connections produced can be soluble or insoluble. The commercially available adhesive can be organic or inorganic and is deposited on one or both substrate surfaces. Adhesives, especially the well-established SU-8, and benzocyclobutene (BCB), are specialized for MEMS or electronic component production.
• The procedure enables bonding temperatures from 1000 °C down to room temperature. The most important process parameters for achieving a high bonding strength are:

1. adhesive material
2. coating thickness
3. bonding temperature
4. processing time
5. chamber pressure
6. tool pressure

• Adhesive bonding has the advantage of relatively low bonding temperature as well as the absence of electric voltage and current. Based on the fact that the wafers are not in direct contact, this procedure enables the use of different substrates,
• e.g. silicon, glass, metals, and other semiconductor materials. A drawback is that small structures become wider during patterning which hampers the production of an accurate intermediate layer with tight dimension control.
• Further, the possibility of corrosion due to out-gassed products, thermal instability, and penetration of moisture limits the reliability of the bonding process.
• Another disadvantage is the missing possibility of hermetically sealed encapsulation due to the higher permeability of gas and water molecules while using organic adhesives.

Q3 Ans

Resistance Welding:

• Resistance welding is the joining of metals by applying pressure and passing current for a length of time through the metal area which is to be joined. The key advantage of resistance welding is that no other materials are needed to create the bond, which makes this process extremely cost effective.
• There are several different forms of resistance welding (e.g. spot and seam, projection, flash, and upset welding) which differ primarily by the types and shapes of weld electrodes that are used to apply the pressure and conduct the current. The electrodes, typically manufactured from copper based alloys due to superior conductive properties, are cooled by water flowing through cavities inside the electrode and the other conductive tooling of the resistance welding machine.
• Resistance welding machines are designed and built for a wide range of automotive, aerospace and industrial applications. Through automation, the action of these machines is highly controlled and repeatable allowing manufacturers to staff production readily.

Types of Resistance Welding Application:

• Resistance Spot Welding, like all Resistance Welding Processes, creates welds using heat generated by resistance to the flow of welding current between the faying surfaces, as well as force to push the workpieces together, applied over a defined period of time. Resistance Spot Welding uses the face geometries of the welding electrodes themselves to focus the welding current at the desired weld location, as well as to apply force to the workpieces.
• Once sufficient resistance is generated, the materials set down and combine, and a weld nugget is formed. Resistance Seam Welding is a subset of Resistance Spot Welding using wheel-shaped electrodes to deliver force and welding current to the parts. The difference is that the workpiece rolls between the wheel-shaped electrodes while weld current is applied. Depending on the particular weld current and weld time settings, the welds created may be overlapping, forming a complete welded seam, or may simply be individual spot welds at defined intervals.

Projection Welding:

• Like other Resistance Welding Processes, Projection Welding uses heat generated by resistance to the flow of welding current, as well as force to push the workpieces together, applied over a defined period of time. Projection Welding localizes the welds at predetermined points by using projections, embossments or intersections, all of which focus heat generation at the point of contact. Once the weld current generates sufficient resistance at the point of contact, the projections collapse, forming the weld nugget.
• Solid Projections are often used when welding fasteners to parts. Embossments are often used when joining sheet or plate material. An example of Projection Welding using material Intersections is cross-wire welding. In this case the intersection of the wires themselves localizes heat generation, and therefore resistance. The wires set-down into one another, forming a weld nugget in the process.

Flash Welding:

• Like other Resistance Welding Processes, Flash Welding uses heat generated by resistance to the flow of welding current, as well as force to push the workpieces together, applied over a defined period of time. Flash Welding is a Resistance Welding Process which generates resistance using flashing action. This action is created using very high current density at very small contact points between the workpieces. At a predetermined point after the flashing process has begun, force is applied to the workpiece, and they are moved together at a controlled rate. Rapid upset created by this force expels oxides and impurities from the weld.

Upset Welding:

• Like other Resistance Welding Processes, Upset Welding uses heat generated by resistance to the flow of welding current, as well as force to push the workpieces together, applied over a defined period of time. While similar to Flash Welding, in Upset Welding the workpieces are already in firm contact with one another, so no flashing occurs. Pressure is applied before the current is started, and is maintained until the process is complete.

Q4 Ans

Fusion Welding

• Fusion welding processes are all those welding processes where faying surfaces of parent part as well as filler material meltdown during welding for weld bead formation. So heat is always associated with these processes. External application of pressure is not required for these processes, except for the resistance welding group where substantial contact pressure needs to be maintained during welding for sound joining. The filler material may or may not be applied.
• A typical fusion weld has got few zones like (i) fusion zone, (ii) weld interface,

1. Fusion zone: It consists of a mixture of filler metal and base metal that have completely melted. A high degree of homogeneity is present among the component metals that have been melted during welding. Infusion zone, the solidification occurs by epitaxial grain growth, in which the atoms in the molten metal solidify at the preexisting lattice sites in the unaffected base material. Moreover, the grain structure in the fusion zone has got preferred orientation and they are oriented roughly perpendicular to the weld interface. This results in a coarse columnar grains infusion zone. R. Ganesh Narayanan, IITG The grain structure depends on various factors namely welding technique, metals being welded like similar metals and dissimilar metals welded, usage of filler metal, and the traverse speed at which welding is done.
2. Weld interface: It is a narrow boundary that separates the fusion zone from the heat-affected zone. This zone consists of a thin band of base metal that was partially melted during the welding process but immediately solidified without mixing with the metal in the fusion zone. Its chemical composition is generally the same as that of the base metal. Heat affected zone: This zone is between the weld interface and base material. This experience temperatures below the melting point, but sufficient enough to change the microstructure and hence the mechanical properties. The mechanical properties are such that most of the failures occur in this region.

Advantages of Fusion Welding

1. The filler material can be applied easily. So a large lacuna can be filled.
2. No need to apply external pressure, so primary shape of the components does not matter (a suitable shape is required to uniformly apply pressure).
3. Joint design and edge preparation are not crucial as these parameters affect only achievable penetration.
4. More than two components can easily be welded at a step.

Disadvantages of Fusion Welding

1. The process is associated with distortion and residual stress generation as it involves melting and solidification.
2. A palpable heat-affected zone (HAZ) exists in the welded components. HAZ is always considered as the weak portion of is welded assembly.
3. Mechanical properties of parent materials are also severely affected by intense heating.
4. Joining dissimilar metals by fusion welding is a challenging task, especially if the metals have a substantially different melting point and coefficient of thermal expansion.

There are so many types of Fusion welding. Let us discuss some of the fusion welding processes below:

1. Shielded Metal Arc Welding (SMAW):

• Shielded metal arc welding (SMAW), also known as manual metal arc welding (MMA or MMAW), flux shielded arc welding, or informally as stick welding, is a manual arc welding process that uses a consumable electrode covered with a flux to lay the weld.
• An electric current, in the form of either AC or DC from a welding power supply, is used to form an electric arc between the electrode and the metals to be joined The workpiece and the electrode melts forming a pool of molten metal (the weld pool) that cools to form a joint. As the weld is laid, the flux coating of the electrode disintegrates, giving off vapors that serve as a shielding gas and providing a layer of slag, both of which protect the weld area from atmospheric contamination.
• Because of the versatility of the process and the simplicity of its equipment and operation, shielded metal arc welding is one of the world's first and most popular welding processes. It dominates other welding processes in the maintenance and repair industry, and though flux coat arc welding is growing in popularity, SMAW continues to be used extensively in the construction of heavy steel structures and in industrial fabrication. The process is used primarily to weld iron and steel but aluminum nickel and copper alloys can also be welded with this method.

1. Gas metal arc welding (GMAW):

• Gas metal arc welding (GMAW), sometimes referred to by its subtypes metal inert gas (MIG) welding or metal active gas (MAG) welding, is a welding process in which an electric arc forms between a consumable MIG wire electrode and the workpiece metal(s), which heats the workpiece metal(s), causing them to melt and join.
• Along with the wire electrode, a shielding gas feeds through the welding gun, which shields the process from atmospheric contamination. The process can be semi-automatic or automatic. A constant voltage direct current power source is most commonly used with GMAW, but constant current systems, as well as AC, can be used. There are four
• primary methods of metal transfer in GMAW, called globular, short-circuiting, spray, and pulsed-spray, each of which has distinct properties and corresponding advantages and limitations.

iii. Electro-Gas Welding (EGW):

Electrogas welding (EGW) is a continuous vertical position arc welding process developed in 1961, in which an arc is struck between a consumable electrode and the workpiece. Shielding gas is sometimes used, but the pressure is not applied. A major difference between EGW and its cousin electro slag welding is that the arc in EGW is not extinguished, instead remains struck throughout the welding process. It is used to make square-groove welds for butt and t-joints, especially in the shipbuilding industry and in the construction of storage tanks. EGW uses a constant voltage, direct current welding power supply, and the electrode has positive polarity. The welding current can range from 100 to 800 A, and the voltage can range between 30 and 50 V. A wire feeder is used to supply the electrode, which is selected based on the material being welded. The electrode can be flux-cored to provide the weld with protection from atmospheric contamination, or a shielding gas—generally Carbon dioxide —can be used with a solid wire electrode. The welding head is attached to an apparatus that elevates during the welding process. Also attached to the apparatus are backing shoes which restrain the weld to the width of the workpieces. To prevent them from melting, they are made of copper and are water-cooled. They must be fit tightly against the joint to prevent leaks

1. Oxyacetylene welding (OAW):

• In this case, welding is performed by a flame formed by the combustion of oxygen and acetylene. The flame comes from a torch. A filler rod coated with flux is used sometimes which prevents oxidation, creating a better joint. Acetylene is a famous fuel because it is capable of generating a temperature of 3500°C.
• The chemical reaction between oxygen and acetylene happens at two stages as given as C2H2 + O2 = 2CO + H2+ HEAT (First stage; inner core)
• The products of the first reaction are combustible and the second reaction occurs as, 2CO + H2 + 1.5O2 = 2CO2 + H2O + Heat (second stage; outer envelope)
• When both oxygen and acetylene are mixed in a ratio of 1:1, then a neutral flame is seen as shown in the figure. The outer envelope delivers a temperature of 1260°C and the inner core has an app. 3500°C. The first stage reaction is seen in the inner core of the flame (bright white color), while the second stage reaction is seen in the outer envelope (colorless but with tinges ranging from blue to orange). The temperature is very high at the inner core which is app. 3500°C. Total heat liberated during the two stages of combustion is 55×106 J/m3 of acetylene. But the heat transfer factor in OAW is 0.1 to 0.3 as the flame spreads over a large region. neutral flame in oxyacetylene welding

Problems and advantages of OAW:

1. The combination of acetylene and oxygen is highly flammable and hence hazardous to the environment.
2. It is unstable at pressures much above 1 atm
3. It is mandatory for the welder to wear gloves, goggles, etc. as preventive measures.
4. The equipment is relatively cheap and portable. So it is used as an economical, versatile process that is well suited for low quantity production and repair jobs.
5. It is rarely used to weld plates thicker than 6.5 mm.

v. Electron beam welding:

In this process, welding is carried out by highly focused, high-intensity electron beam bombarding against the workpiece. Generally carried out in a vacuum, otherwise, there will be disruption of the electron beam by air molecules. Metals that are arc welded can be EB welded. Some of the refractory objects and difficult to arc weld materials can also be EB welded. EB welding is noted for high-quality welds with deep, narrow profiles, limited heat-affected zone, and low thermal distortion. No filler metal is used. No flux, shielding gases are needed. Also, in non-vacuum EBW, the work must be located close to the orifice of the electron beam gun, approximately 13 mm or less. Finally, the lower vacuum processes cannot achieve the high weld qualities and depth-to-width ratios accomplished by EBW-HV.

vi. Thermit welding:

A mixture of aluminum powder and iron oxide that produces an exothermic reaction when ignited. In thermit welding, the heat for coalescence/joining is produced by superheated molten metal formed from the chemical reaction of thermit.The following chemical reaction is seen when a thermit mixture is ignited at 1300°C. The temperature of the reaction is 2500°C.8Al + 3Fe3O4 = 9Fe + 4Al2O3 + heat .At this temperature, superheated molten iron plus aluminum oxide is made that floats on the top as a slag and protects the iron from the atmosphere.

Applications of TW:

Joining of railway lines, repair of cracks in large steel castings and forgings like ingot molds, large diameter shafts, frames for machinery etc.

Q5 Ans

3-2-1 principle is used for the design of the fixtures

• For a fixture designer, the major portion of design time is spent deciding how to locate the workpiece in the fixture.
• You know that any free body has a total of twelve degrees of freedom as below:

6 translational degrees of freedom: +X, -X, +Y, -Y, +Z, -Z And

6 rotational degrees of freedom:

• Clockwise around X-axis (CROT-X)
• Anticlockwise around X-axis (ACROT-X)
• Clockwise around Y-axis (CROT-Y)
• Anticlockwise around Y-axis (ACROT-Y)
• Clockwise around Z-axis (CROT-Z)
• Anticlockwise around Z-axis (ACROT-Z)

• To make sure the proper fixing of the part we need to restrict all 12 degrees of freedom of the workpiece. The major portion of the time of BIW fixture designer is spent deciding how to fix these all DOF.

PRIMARY LOCATOR:

First, the three locators or supports are placed under the workpiece. It will be positioned on the primary locating surface also known as a datum. It will restrict 5 degrees of freedom.

• Axial Movement downward along Z-axis ( No.6 in Fig 1 )
• Rotation about the X & Y axis ( No. 7, 8, 9 & 10 in Fig 1)

SECONDARY LOCATOR:

The next two locators are normally placed on the secondary surface, restricting an additional 3 degrees of freedom.

• Axial movement along the Y+ axis ( No.3 in Fig 1 )
• Rotation about the Z-axis ( No. 11 & 12 in Fig 1 )

TERTIARY LOCATOR:

This locator is positioned at the end of the part. It restricts 1 degree of freedom

• Axial movement along the X-axis ( No.2 in Fig 1)

• All these 6 locators will restrict a total of 9 degrees of freedom. The remaining 3 degrees of freedom ( 1, 4 & 5 ) will be restricted by the clamps.
• To minimize the time consumption in assembly and disassembly, Have to use minimum numbers of pins to arrest a maximum number of degrees of freedom.
• The jig and fixture are tools used for holding the workpiece in a correct location for mass production. Various types of fixtures (like drilling fixtures, milling fixtures, and welding fixtures) are used in industry. The 3-2-1 method is the fundamental principle for all types of fixture design.

Q6 Ans

Body Co-ordinate System:

• The body coordinate system has been widely used in the automotive industry for drawing of body parts, product & process design. A coordinate system is a reference system consisting of a set of points, lines & surfaces, used to define the positions of points in space in either two or three dimensions. In general, BCS is also called as car line & body line.
• Car lines are the (grid lines) shown on the fixture, which virtually represent the same location in BIW. All the car line on fixture displays the coordinate at corner for reference. With these lines one can easily relate the location in BIW.
• Sometimes single coordinate hole is given in fixture that also represents the car line coordinates, from that reference point fixture is made & can be inspected. Body coordinate are mentioned near hole. Below figure show car line on fixture.

• Automotive sheet metal components are designed in CAD (Computer aided Design) software e.g. CATIAv4-v5, UG, ProE, Ideas, In any cad tool, there is a default axis system X, Y, Z.
• Lets us consider if every designer starts the design of the BIW Door Assembly part a default axis system, then it will be difficult to assembly or position the part with respect to each other.
• Due to avoid this issue, BIW car panels are designed with reference to car axis means at their Original position of the final car built.
• Reference axis system of the software is used for the design of the various features of the parts (e.g. hole, fillet, threads,) To correlate the position of all the automotive components during the final assembly the axis system of the vehicle is used. Most of the time vehicle axis system and software axis system is the same. e.g. In most of European OEM, The X-axis represents the length of the vehicle Y-axis represents the width of the vehicle Z-axis presents the height of the vehicle. Y-axis is considered to be located at the front axle. All BIW welding fixtures are designed with reference to the car line
• These datum schemes provide a reference system for all part surfaces and features using body coordinates. Figure below illustrates a typical body coordinate system. This system replaces the traditional X, Y, and Z directional designations with fore/aft (X), in/out (Y), and up/down or high/low (Z). The 0,0,0 point of the car is the front, lower, and center position.

VEHICLE ORIENTATION:

• All vehicle product drawings are identified numerically relative to three vehicle planes described and shown below.
• X= longitudinal direction (fore & after-F/A) or (Front O line-FOL). Y= transverse direction (Cross car-C/C) or (Centre O line-COL).
• Z= Vertical direction (Up & down- U/D) or (Bottom O Line-BOL).
• The origin of the body coordinate system (OX) is defined at the front centre of a vehicle. It indicates a length of car & the coordinate system (OZ) is below its underbody indicates height of car & the coordinate system (OY) its starting point is the centre of car body indicates width of car.
• Maintaining X,Y & Z coordinates in fixture is very important factor.
• We should try that the coordinates of locating & clamping points should not be in three decimal (e.g. X=100.124, Y=245.127, Z=450.458)
• They should be in the whole nos or max upto 1 decimal. Once these coordinate are maintained automatically the BIW base structure is mainteined.

Q7 Ans

BODY PLANE SYSTEM:

• Body planes are the reference plane in an automotive car. These planes are used to define the GD & T of all car parts in a automotive domain.
• Body planes are three mutually perpendicular imaginary planes. These are generally considered to be present at the driver position or sometimes at the engine location or at the front end of the car depending on the customer.
• The measurements from the body planes to the parts are called as body line dimension.

These body planes are called as

• FOL Front “O” line.
• COL Centre “O” line
• BOL Body “O’ line
• The measurement along FOL or X-axis is called as F/A Frontaft.
• The measurement along COL or Y-axis is called as C/C Cross car.
• The measurement along BOL or Z-axis is called as U/DUP down.

In below figure origin is somewhere below driving sheet as it depends or changes from customer to customer. But axis system is commonly same.

Bodyline dimensions are essential for the reasons stated below,

• It defines the exact position of each product in the vehicle w.r.t. a fixed origin.
• It ensures flawless design for assembly.
• While designing lines, all the designs are carried out relative to the bodyline, viz, fixture, turn table etc.
• It assists in easy location of different parts in a vehicle.
• It aims in creating a standardized system.
• It assists in quality checks.

These are basic essential thing that body line dimension would help in BIW. It could help in designing lines like welding lines, assembly lines or car body through fixture & turntable etc. This help in designing every tools. Particular assembly or parts are designed w.r.t body lines or an axis system or car line also helps in quality while doing CMM of that system. CMM is basically done with the help of coordinate. It has relate particular fixture with that car part, because that dimension, coordinates of hole & pin should match so it will help in quality check also. We just give co-ordinates that belong to that hole both coordinate should match. With this matching means quality is approved. Below figure shows some example.

Below figure shows use of Z plane to define height of car.