ABOUT BIW WELDING FIXTURE PROCESSES 1)Want to design your biw weld fixture? If you want to design biw welding fixture you need to know about jigs and fixtures and design them, then you can create a biw welding fixture. The jig &fixture design planning study solutions to help you quickly define and evaluate your design concepts. The site describes the process to help you do everything correctly the first. The whole process is divided into two sections: Jig and fixture design Biw welding fixture design 2)Jig and fixture design A fixture is a device for locating, holding and supporting a work piece during a manufacturing operation. Jigs are similar to fixtures, but they not only locate and hold the part but also guide the cutting tools in drilling and boring operations. In the design of a jig and fixture, a definite sequence of design stages is involved. They can be grouped into three broad: Locating methods Locating principals Clamping principals Stage One deals with information about locate the work piece surfaces for performing a machining operation. Stage Two involves the consideration of basic principal of locating is referencing and repeatability. Stage Three is the Locating and preventing movements of the work piece is the first basic function of a jig or fixture.
3)Biw welding fixture design The body of a vehicle is made up of several hundreds of stamped components which are joined together by spot welding process, accurate production of the car body (BIW) is essential if the automated assembly line is to fit parts within the required tolerance, therefore we use the welding fixture. Design a welding fixture is a complex process including: Production process of body in white Clamping plan We can use a number of fixture unit types in welding fixture design, based on clamping plan. For more detailed information on how to create a biw welding fixture and then 3d modeling of it and design detailing it, look through this site. 4)JIGS & FIXTURES We can use of jigs & fixtures for locating, holding, supporting of a workpiece during manufacturing operations. A jig is a small contrivance fastened to or inclosing a piece of work, and having hard steel surfaces to guide a tool, as a drill, or to form a shield or template to work to, as in filing. Machining jig is a device used to hold firmly and to locate firmly the work pieces and to guide machining tool accurately to the work pieces. Generally drilling, boring, loathe, milling, sawing, broaching shaping, planning, grinding are classified in this category. A fixture is a device for locating, holding and supporting a workpiece during a manufacturing operation. Fixtures must correctly locate a work piece in a given orientation with respect to a cutting tool or measuring device, or with respect to another component, as for Instance in assembly or welding. Generally jigs and fixtures are similar together, jigs not only locate and hold the part but also guide the cutting tools in drilling and boring operations, but fixtures are a device which has the function of holding and
locating of work piece. Elements of Fixtures Generally, all the jigs& fixtures consist of the following elements: Locating elements Clamping elements Supporting elements Locating Elements Locating elements are used to establish and maintain the position of a workpiece by constraining the movement of the workpiece.These position the workpiece accurately with respect to the supporting elements tool in the jigs& fixtures. A locating element is usually a fixed component and is used to establish, maintain the position of a part by constraining the movement of the part. For workpieces of greater variability in shapes and surface conditions, a locator can also be adjustable. Clamping Elements Clamping elements hold the workpiece securely in the located position during operation. A clamp is a force-actuating mechanism. The forces exerted by the clamps hold a part securely against all other external forces. Supporting Elements For prevent or constrain deformation of workpiece under the action of imposed clamping and processing forces, supporting elements are added and placed below the workpiece. A support is a fixed or adjustable element of a jigs and fixtures, but it should be compatible with the locating elements and clamping elements. 5)LOCATING METHODES One of the principal purposes of a machining jigs and fixtures is to locate the workpiece surfaces for performing a machining operation.
A workpiece, just like any free solid body, have twelve degrees of freedom, the six axial degrees of freedom and six radial degrees of freedom. To accurately locate a workpiece in a jigs and fixtures, movements must be restricted. This is done with locators so they must be strong enough to maintain the position of the workpiece and to resist the cutting forces. During a setup it is necessary for the motion of workpiece to restrict in all these motions positively. You must be able to accurately locate each workpiece regardless of how it is made. To do this, you must know the locating method and the type of locators. There are three methods for locating of workpiece: Locating from external surface Locating from internal surface Locating from an external profile Locating from external surface Locating from a flat surface of workpiece is common locating from external surface and it is a form of plane location. You can use supports for this purpose. Before choosing a support, you must consider the shape and surface of the workpiece and the type of clamping device for selecting the type of support, because its must be strong enough to resist both the clamping pressure and the cutting forces. There is three type of support: Solid Adjustable Equalizing The other way to locate a workpiece from external surface is the 3-2-1, or six-point, location method. This way is most commonly employed. With this method, six individual locators reference and restrict the workpiece. For achieving greatest stability (based on the geometry principle that three points are needed to fully define a plane) the primary, locating surface is positioned on three points should be as far apart as possible or as large as
possible. For larger cast workpieces, the 4-2-1 locating principle is frequently used. Locating from internal surface One of the most-efficient ways to accurately position is locating a workpiece from an internal diameter, individual holes or whole patterns are used for this form of location. When you use of this an internal diameter, you should consider the logical to use holes. It is nine of the twelve directions of movement are restricted by using a single pin, and eleven directions of movement are restricted with two pins. Each pin prevents any movement along X and Y directions (4 DOF restricted) for prevent of rotation around the X and Y axes, you use of round pin with the diamond pin. In use, the round pin prevents any movement of workpiece along X and Y directions and the diamond pin prevent the workpiece to rotate around the X and Y axes. Locating from an external profile Locating a workpiece from an external profile, or outside edge, is the most common method of locating. Profile locators position the workpiece in relation to an outside edge or the outside of a detail, such as a hub or a boss. Nesting is the most accurate locating device for profile location and it is very expensive, because nest must conform to the shape of the workpiece. When you need to locate round shafts or other workpieces with cylindrical sections, you can use the vee-block locator and it should be adjusted along the axis of V for more accurate location by a screw or cam. 6)FORM OF LOCATORS AND SUPPORTS Referencing is done by using locators and supports. Referencing means to ensure precision the workpiece properly positioned with respect to the cutting tool.
The locators provide restrict a workpiece's movement and must hold the workpiece against the primary cutting forces. Locators are used to properly position the work piece and supports for locating workpiece external surface. There are three general forms of locators: Plane Concentric Radial Plane Plane locators locate a workpiece from external surfaces. The surface may be flat, curved, or have an irregular contour. Locating from a flat surface is a form of plane location. Concentric Concentric locators locate a workpiece from a central axis. This axis may or may not be in the center of the workpiece such as a locating pin placed in a hole. Radial Radial locators restrict the movement of a workpiece around a concentric locator. Before choosing a support, you must consider the shape and surface of the workpiece and the type of clamping device to be used. The support selected must be strong enough to resist both the clamping pressure and the cutting forces. Supports are the principal devices used for this location. The three major forms of supports are: Solid
Adjustable Equalizing Solid This type of support is fixed-height locators and you can use such as rest buttons. Solid support precisely locates a surface in one axis and is normally used when a machined surface acts as a locating point. Adjustable This type of support is variable-height locators and they will also precisely locate a surface in one axis. Adjustable locators are normally used with one or more solid locators to allow any adjustment needed to level the workpiece. When the surface is rough or uneven, such as cast or forged workpieces, these supports are used. Equalizing This type of support is a form of adjustable support. When a compensating support is required, you can use adjustable support. This support is float to accommodate workpiece variations and used along with solid supports. 7)LOCATING PRINCIPALES Basic principal of locating is referencing and repeatability. To ensure precision in any machining operation, the workpiece must be properly positioned with respect to the cutting tool or other tools. This is called referencing. Repeatability is the characteristic of the jigs and fixtures that allows different workpiece to be machined consistently within their required tolerances. Repeatability is directly related to accurate location, so to achieve this purpose, the locators must be contact the workpiece on a machined
surface. You must keep the following principal of workpiece locating in mind while designing the jig and fixture: A workpiece, just like any free solid body, have twelve degrees of freedom, the six axial degrees of freedom and six radial degrees of freedom The location system should prevent all motions of the workpiece along and around the three major axes X, Y, Z. Location should be done on the surfaces of workpiece which have the most accurate surface. A machined surface is subjected to the action of cutting tools. We must use of surfaces datum for locating the workpiece while machining operation, the location has to meet dimensional requirements of the workpiece stated on the component drawing , where the dimensions are maintained and measured. Clamping surfaces of workpiece are subjected to the clamping forces for obtaining invariant location. You can use surfaces are usually not finishmachined surfaces as clamping marks could damage the finish. Location system should facilitate easy and quick loading of the workpiece, in case of use redundant locators for fixing surface, workpiece distortion due to redundant location when work piece is unclamped. Under such circumstance, the redundant location should be replaced by an adjustable support illustrated. You can use a locating system for prevent wrong loading of the workpiece by using a foolproofing. This wrong loading can be prevented by providing a foolproofing pin which would obstruct the path of the work piece. You ensure that the workpiece will fit into the jig and fixture only in its correct position by foolproofing. You always avoided using the duplicate locators, because they not only costs more but also could cause inaccuracies. 8)CLAMPING PRINCIPLES Locating and preventing movement's of the workpiece is the first basic function of a jig or fixture. The process of holding the position of the workpiece is called clamping and it is done by clamps. The locators should resist the primary cutting forces generated by the
operation and the clamps should resist the secondary cutting forces generated by the cutter leaves the workpiece. The only purpose of clamps is: holding the workpiece against the locators preventing movement of the workpiece resisting the primary cutting forces In every machining operation, it is necessary that to provide a suitable locking for achieving the stability of location, so the system clamping is an essential requirement. The system clamping is producing a sufficient clamping force, but without causing any undesirable effects to the workpiece and the clamping elements hold the workpiece. The principal objectives of the clamping elements are the creation and retention of locking effect against external loads. The other considerations of clamping principles done with respect to a number of factors to be considered such as: Position Strength Productivity Position All the system clamping can be defined as a device for providing a stability of location which can not be changed during machining operation. Hence, the clamping force should be transmitted on a strong supported part of the workpiece and the system clamping should be positioned to direct the clamping force. The clamping force must be absorbed by the locating elements. Positioning the clamps at the most-rigid points of the workpiece, in order to hold the workpiece against the locators and to resist any secondary forces generated in the operation, so the clamps need only be large enough.
Another consideration in positioning clamps is the operation of the machine tool throughout the machining cycle. The clamping system should not be abstract the path of loading and unloading of the workpiece and the path of the cutting tool. Most clamps are positioned on or near the top surface of the workpiece. You should use minimum height of the clamp by the type of clamp with a lower profile. The size of the clamp-contact area and the overall size of the clamp are another factor in positioning a clamp. Strength The machining operation is producing loads or moments on the workpiece, the clamping system should be capable of holding the workpiece with respect to an external force such as the vibration and stress. The clamping force should not dent the workpiece such as distortion or surface damage with excessive pressure. Surface damage is often caused by clamps with hardened or non-rotating contact surfaces. Use clamps with rotating contact pads or with softer contact material to reduce this problem. Calculations of clamping force are complicated however, an approximate determination of these values is sufficient. The clamping force should be consisted to meet the workpiece conditions, so you can use manual clamp for controlling clamping force or to replace manual clamps with power clamps. The force generated by power clamps is not only constant but also adjustable to suit workpiece conditions and faster than manual clamps. Productivity
It is also essential that to reduce the overall set-up and non-machining time, so the clamping devices must be easy to aligning, manipulate manually, low coast and simultaneous loading. The speed of clamping and unclamping is usually the most-important factor in keeping loading/unloading time to a minimum. If there is variation in the workpiece, it is also essential that the system clamping to make the clamp operable. 9)TYPE OF CLAMPS It is necessary for the clamping forces to hold the workpiece in its located position without any positional displacement under these forces. So, the force should be transmitted to the rigid sections of the body frame of the jig and fixture. In addition, the force should be directed with respect to supporting and locating elements on overhanging or thin sections of the workpiece, so the clamping force must be large enough to restrain the workpiece motion completely during machining. However, excessive clamping force can effective on location and quality of workpiece. Hence, it is necessary to determine the optimum clamping forces that minimize the workpiece location error due to elastic deformation while satisfying the total restraint requirement. Clamping elements can be classified in accordance with their force characteristics. They may be either manually operated or actuated by pneumatic, hydraulic or a combination of other power facilities. Clamping elements are also classified according to the mechanism. The three basic classes include: Operating by inclined plane theory, i.e. wedges, screws, cams, etc. Operating by lever principle, i.e. levers, toggles, etc. Operating by Pneumatic / hydraulic power Manual clamping of workpieces has the following disadvantages: Fatigue of operator due to manual clamping Difficult to determine the required force Varying force for clamping of each workpiece
Require time to actuate manual clamping is more than power clamping Pneumatic and hydraulic clamping of workpieces has the following advantages: Variable-force clamping Controlling the intensity of the clamping force during a machining operation Reduce workpiece deformation A balance between cost, efficiency, accuracy, operator safety and comfort 10)BIW WELDING FIXTURE DESIGN No matter what your knowledge about fixture design, you use the following stages in design of your BIW weld fixture: Study and understanding of process Concept design Create 3D-Modeling You study your process You start design by study production process of body-in-white (BIW) this process provides valuable information for the design phase. The purpose of study BIW process includes the following: The special focus on the structure of a body (BIW) enables you to find the logic and flow of body panels, and the relationships between them. The select of master control point, which are holes or surfaces related to your body part & assembly to arrive at the dimensional integrity of the BIW by giving the steel parts in the correct position during joining. The analyzing of body is made up of several hundreds of stamped components which are joined together by spot welding with welding gun for understanding of welding points and allocate them to welding operations. Study of cycle time diagrams, for check reach ability and optimizing it. Cycle time is estimating the required working time for each station. You create your concept design based on process study
Now you can use of process study for defining the design criteria and finding or verifying the concepts. The welding fixture design is created with the following steps: The clamping plans for accurate positioning of components, while the components are aligned to a suitable plane for welding they are designed in the carline plane (as in BIW). Design of the weld fixture is unit based on clamping plan, therefore there are a number of fixture unit types used in the welding fixtures for the purpose of each unit and due to the complexity and shape of the component geometry, the choice of elements as well as configuration of each unit tends to change from case to case. The check of weld accessibility and spot weld for unrestricted access to each weld point, before and after the fixture design, the accessibility of the weld guns to all the spot points can be simulated and studied thoroughly to avoid guns colliding with other fixture elements. You create 3D Modeling fixture You need knowledge and experience in 3D Modeling software for creating 3D-Model and 2D drafting, detailing & 3D concept design. The 3D Modeling becomes the basic for following item: Create 3D Modeling of the weld fixture for visualizing the entire fixture in a three-dimensional environment. 3D Modeling of weld fixture generated by cad software, which lets you detect collisions, check reach ability spot weld and carry out weld accessibility study for ensuring your fixture efficiency. The 3D CAD Model of weld fixture unit enables you to make CAD Model of clamp location plan for ensuring that plan problems and waste are discovered before your fixture drawing to send for manufacturing. By 3D Modeling of weld fixture, you can quickly prepare manufacturing drawings. 11)PRODUCTION PROCESS OF BODY-IN-WITHE (BIW) In the study phase of planning process you find or verify the concepts of the body-in-white manufacturing process. For design welding fixture, trying to understand processes is essential. It is starting with process logic and
flow, and defines the relationships between operations. The process study is a solution that to help you quickly define and evaluate process to arrive at the best plan for designing your fixture. The result is process study containing a full description of how a product is assembled, manufactured and increases your profitability by improving critical success factors in your fixture design. The process study allows designer to leverage and optimize existing resources and to better integrate the designing process from beginning to end can not only help designer create fixture faster, but you can also begin design earlier in the overall cycle or even start later, in order to accommodate unanticipated changes. The Assembly Process studying allows evaluating alternatives, coordinating resources, optimizing throughput, plan for multiple variants, implement changes and estimate costs and cycle times, from the very early stages of concept planning through process. Studying, Analyzing and Managing Manufacturing Processes enables you to collaboratively plan and analyzing manufacturing processes for your fixture. You can create optimal design and accommodate multiple plan variations, quicker and faster than ever before. Process study provides a collaborative environment for planning designing processes. A broad range of applications enable you to define and verify body assembly sequences, create clamping plan layout, define the required time for each operation, verify plan performance, perform plan balancing and analyze of spot welding and guns. The body-in-white Manufacturing Process includes: Automotive body assembly Electric resistance welding Cycle time diagrams Automotive body assembly The major process of an automotive body is electric resistance welding.
Resistance welding is a group of fusion welding processes that use a combination of heat and pressure to accomplish coalescence and where electric resistance welding is not applicable ,CO2,ARC WELDING and MIG-BRAZING are performed. The body of automotive is made up of several hundreds of stamped components which are joined together by spot welding process. Overall quality of the car body (BIW) and quality of the sub assemblies, apart from quality of each stamped part, depends remarkably on quality of the welded joint. You should study of part joining, welding operations such as spot-welding and define welding points and allocate them to welding operations. The study of welding process can be classified as follow: The number of welding spot The position and volume number of welding spot The type of welding gun The material and sheet metal thickness for setting of welding condition Cycle time diagrams The cycle time is estimating the required working time of each station. Cycle time study is based on the information such as: Part loading Clamping Gun forward Welding Gun retract Unclamping Part unloading 12)RESISTANCE SPOT WELDING Resistance welding process is one of the most productive and reliable assembly processes. It is a method in which faying surfaces are joined by melting the two parts.
Resistance Welding process that use a combination of heat by electrical resistance and pressure by electrode force to accomplish coalescence the two parts to be joined. Components in Resistance Spot Welding are: Parts to be welded (usually sheet metal) Two opposing electrodes Means of applying pressure to squeeze parts between electrodes Power supply from which a controlled current can be applied for a specified time duration (a)Spot welding cycle and (b) plot of squeezing force & current in cycle: (1) parts inserted between electrodes (2) electrodes close, force applied (3) current on (4) current off (5) electrodes opened Advantages and disadvantages of resistance welding include: Advantages:
No filler metal required High production rates possible Lends itself to mechanization and automation Lower operator skill level than for arc welding Good repeatability and reliability
Disadvantages: High initial equipment cost Limited to lap joints for most resistance welding processes Spot welding method Resistance Spot Welding is one of the type resistance welding processes that used to join sheet metal parts using a series spot welds and widely used in mass production of automobiles, the spot welding include:
Principal of spot welding Structure & function of spot welding machine Conditions of spot welding Inspection method of weld
Principal of spot welding Spot welding is to join lapped metals by holding them together by electrodes, applying an appropriate pressure, Feeding enormous current, heating and melting. The generation of heat at welded spot is based on joules law. The rate at which heat is produced by a steady current in any part of an electric circuit is jointly to the resistance and the square of the current. The degree of current flow depends on current density. The contact resistance is the resistance of contact part of two steel plates is magnified, a lot of projection can be seen contacting one another. The larger amount of heat generation due to low weld pressure can not lead to a good weld. The expulsion of molten metal by higher current density is a result of insufficient weld pressure and eventually it produces spattering, so proper weld pressure is needed. Structure & function of spot welding machine Types of a spot welding machines are divided to two categories: - Classification by their form such as: Pedestal Portable spot welder - Classification by circuit in which the welding current flows such as: direct and indirect type, series type, push pull type The functions of the spot welder include: Transformer
Air cylinder Timer conductor Olier. Air filte Pressure gauge
Conditions of spot welding The most common factors of spot welding are related to the joules law, they are: Weld pressure Weld current Weld time Inspection method of weld There are some kinds of methods helps inspection of weld: -Nondestructive methods are to find the pass or reject of the welding by examining the surface of the weld zone - Destructive methods are : Tension-shear strength test Tension strength test Twist test Driver check 13)PORTABLE WELDING GUN Almost all of the automotive body parts are assembled by resistance spot welding. A spot welder consists of a transformer to obtain a large welding current, timer to control the time in which to feed the current, electrodes to hold welded articles, pressurizing cylinder to apply the necessary for the material being welded. Secondary cable lets necessary current through transformer flow to gun, spring balancer to lighten the welding gun and the cable. Resistance spot welding is passed between two copper electrodes, the
process can be performed by the operator holding a portable welding machine and moving it around the parts being welded. These portable machines called portable welding guns. The manual weld guns can have easy access to weld the components together. The resistance spot welding machines are classified according to combinations of individual sections as follows:
Fixed type Stud type Portable type: Conventional weld gun Integral weld gun
Conventional weld gun Conventional weld guns have a large transformer located remotely from the weld gun. The welding current is delivered to the weld gun arms through a large, water-cooled secondary cable. J type or C type S type or X type The conventional weld guns were used in various applications because the weld controllers did not have the ability to detect and react to any hazard associated with using primary power connected directly to the weld gun. Integral weld gun Integral weld gun or tarn's guns have a smaller transformer located right on the weld gun, from which the current is delivered through short jumpers or shunts that are air cooled. Tran's guns are also called weld guns, because the transformer is part of the unit. The two configurations of portable tarn's guns are: C gun
Scissors gun For example C gun for welding around a door opening on a small flange and Scissors gun for welding large, deep boxes requiring a long reach. There are following characterizes for tarn's guns: Design Flexibility Ergonomics Cost efficiency 14)BODY IN WHITE OR BIW In process of an automotive body manufacturing, what is called the Body In White refers to the stage in automotive design or automobile manufacturing in which the car body sheet metal components has been assembled by welding before the moving parts such as, Door, Hood (Bonnet) and Trunk Lid, Front Fender and the components (chassis, motor) and trim (windshields, seats, upholstery, electronics, etc.) have been added. The body coordinate system has been widely used in the automotive industry for drawing of body parts, product and process design. A coordinate system is a reference system consisting of a set of points, lines and surfaces, used to define the positions of points in space in either two or three dimensions. The origin of the body coordinate system (OY) is defined at the front center of a vehicle, its indicates a length of car and the coordinate system (OZ) is below its underbody indicates height of car and the coordinate system (OX), its starting point is the center of car body indicates width of car. The method of entering dimensions using coordinate lines used for the drawing of the car bodies. The individual coordinate line is referred to as the numbered line the spacing between numbered lines shall be, as a rule, 100 mm. BIW is included in the following parts: Under body Upper body
Under body Under body forms the basis of Body In White, it is involving sub-assembly of engine room, front room and rear floor which put together and assembled through each small parts. Upper body The Upper Body is composed of Sub-complete assemblies such as Side Frame (body) L/R, Roof Panel, Cowl & Dash and Package Tray. Main body Main body is the core production of automotive body manufacture to assembly (weld) and set Under Body and Upper Body is included Side Body, Cowl & Dash, Package Tray and Roof Panel. MASTER CONTROL POINT In generally master control point is determined to confirm the productivity and quality of the Body- In-White. System reliability of the BIW assembly process, parts precision and constancy of qualities and to carry out problem solving are the key factors affecting the system of mass production early and economically of the BIW. In BIW assembly processes, body quality is generally defined by the dimensional accuracy of the stable points on the body parts, these points include the locating holes used for part locating and the points whose dimensional accuracy is specified in the body design. The measurements of these points are treated as the body characteristics in a BIW assembly process. A body planning designer decides master control point with a die engineer and a body designer when a body designer draws body master drawing.
The below conditions are decided to be master control point: The most important function area of the assembly part or the single part The area which requires the accuracy of the location and the shape The area which is hard to deform and easy to fix Kind of master control point & function Surface Hole Edge Surface Following the parts surface can be reference: Plane surface Shape surface Flange surface Seat surface There are two kind of reference surface: Main reference for stability in parts Auxiliary reference for improve in parts in order to control deformation by welding or equipment Hole Following the parts hole can be reference: Circle hole Longitudinal hole Angled hole Burring hole There are two kind of reference hole: Main reference for stability in parts Auxiliary reference for protection of pin in parts Edge Following the parts edge can be reference:
Straight edge Curved edge There are two kind of reference edge: Main reference for stability in parts Auxiliary reference for improve in parts in order to control deformation by welding or equipment 15)BIW WELDING FIXTURE UNIT BIW welding fixtures are used for holding the sheet metal or part assembly together in space while the components are sometimes aligned to a convenient the car-line plane of BIW for robotic or manual weld guns can have easy access to weld the components together. So, designing a fixture in this plane is often a complex process, considering the variations in coordinate systems and basic rules such as maintaining few elements in specific orientations. There is deformation of body assembly due to the welding process effect and resulting variation due to part dimensional variation, when you are designing a fixture you should eliminate them and another objective is achieving body quality within the required tolerances, so you can achieve this purpose by planning location layout. Location layout is the selection of the positions and numbers of locators and clamps for assembly of fixture components into a final configuration on a fixture base. Designing a welding fixture is based on the location layout. It involves numbers of fixture units and due to the complexity and shape of the component geometry, the choice of elements as well as configuration of each unit tends to change from case to case. Fixture unit to hold the body parts securely and composed of following item: Locating pin Locating surface Clamping device Base
Locating pin Typically, the locating pins are used to lock a body part in a position sufficiently accurate to execute a welding process. The body part is constrained by a set of appropriately locating pin so total constraint by locating pin should be fully constrained at all times to prevent any movement. Usually two locating pins are enough to properly locate the body part on one plane. One of the pins is round, and another one is diamond shaped. This configuration will allow easier loading of body part. The end of each pin has a round or conical shape or is chamfered for the purpose of maintaining workability such as ease of loading and quality such as prevention of damage. The taper lead angle is large, 60 degrees or less, for small-size body parts and manual operation, but it is frequently between10 and 30 degrees for large-size body parts that are difficult to handle. The difference between the locate hole in the panel or body part and the locating pin diameter should be 0.2 mm and a tolerance for locating pin should be 0,+0.05. The dimension from the panel to the locating pin leading end (straight area) should be 5 mm. Locating pins are available in numerous shapes and sizes in a design. There are two configurations for position of locating pin: Keep two dowel pins for positioning as far apart from each other as possible Set the dowel pins in symmetrical positions Locating surface
One of the principal purposes of a locating surface is to locate and support the panel surfaces for performing a welding process. This is usually done with the datum surfaces that are reference for locating surface. The dimensions of datum surface are decided by selecting a necessary cross-section from the part drawing. The shape of locating surface is a form of cross-section of panel. Locating surface is configured to receive panel for setting in a correct position and locating a body part from any surface such as flat, curved, or have an irregular contour. In most applications, locating surface devices locate a panel by its external flat surfaces and flat area, such as: edges, flanges, steps, faces, shoulders, and slots. Clamping device In every welding operation for body assembly, clamping of panel is an essential requirement. A clamp can be defined as a device for providing an invariant location with respect to an external loading system. In other words a clamp is a force-actuating mechanism of a fixture unit. The forces exerted by the clamps hold a panel securely in the fixture against all other external forces. When a welding process is producing a load or moment on the body part, it is necessary that a sufficient clamping force must be exerted to withstand such actions. The generalized requirements of clamping device can be summarized as: To provide a suitable fixing for achieving the stability of location To produce sufficient frictional effects but without causing any undesirable effects to the body parts such as distortion or surface damage The clamping forces hold the body part in its located position and should not cause any positional displacement or excessive distortion under the action of the clamping forces Clamping forces should be directed towards supporting and locating elements on thin sections of the panel
Clamping force should be transmitted to the rigid sections of the body frame of the base unit There are two configurations of clamping device: Manual clamp Air clamp cylinder Base The base for BIW welding fixture should be attached with fixture unit such as locating pin, locating surface and clamping device to maintain the accuracy of body parts. The surface of base should be flat smooth and the base should be rigid enough for easy welding and machining. The framework of the base is usually made of shape steel. Load condition and configuration are not uniform, so it is impossible to set a base shape in general. CLAMPING PLAN The structural frame of the automobile, the Body-In-White (BIW), it's made of sheet metal parts are joined together, clamping of parts is one of the most critical issues in quality of an automotive body assembly Such parameters of location such as contact area, state of contact, clamping force, wear and damage in the contact area and deformation of the component are of special interest. The precision of the BIW assembly is one of the key factors affecting the productivity and product quality. In general, quality variation in the body parts is caused by: Effective of part-to-part Lack of part location stability The stamping process variation The sheet metal components are often flexible and compliant, and welding
process routinely bend and deform components through clamping forces and heat distortion. One objective of this study of the dimensional variation characteristics of body is achieving body quality within the required tolerances. In order to control quality variations within a certain range, it is critical to understand the types and positions of locators in a BIW assembly. One of the important items is sufficient datum to restrict six degrees of freedom of parts. In general, the goal is to constrain the part to the point where repeatable measurements can be taken. In other words, assembly quality is maximized if individual part means are produced to target specification with minimum variation. The method of part locating for automotive body assembly includes locator map or clamping plan. Positioning and fixation of the body parts is carried out using clamping plan, which are inserted into holes, surfaces and edges in the body parts. Clamping plan in process of designing fixture is activity to perform this function during the assembly process on the welding fixtures. Clamping plan is determination of clamps types, their position and the force is assigned to each clamp. Clamps play an important role in restraining the parts. The clamping plan is widely used to determine the part location and orientation by locating the parts with respect to a suitable datum, and clamping the parts against it. You can precisely locate a part in the x, y and z directions and eliminate all six degrees-of-freedom of a body part by clamping plan. The process of clamping plan involves: The locating point Clamp surface
Clamping point The locating point In locating plan you should identify the locating points, they are on the position of body parts that has high degree of precision. The locating point includes the locating holes used for part locating and the points whose dimensional accuracy is specified in the product design. Clamp surface The clamp surface represents the shape of cross section of the main datum plane of a body parts. It is based on locating plan and used for the planning of fixture unit to fix every part is performing in clamping plan. Since the shape of cross section of body parts and number of fixture units are drawn in the clamping drawing, it is basic for making clamping plan for designing spot welding fixtures. Clamping point One of the key factors to determine clamping points is to minimize the deformation of a clamped body parts. Such optimization of clamping points becomes possible by estimating the deformation of clamped body part The feasible clamping plan was constructed by selecting one clamping point from each district of clamping point of the body parts. The clamping plan was evaluated according to the height and location of each clamping point and the relationship between the clamping points and the actual support region of the main datum plane of a body parts. 17)3D MODELING SOFT WARE You need to clearly see new ways to higher productivity, speed and quality of BIW welding fixture design. To arrive at the best plan for designing your fixture, 3d modeling software, a suite of digital designing solutions that helps you the modeling and simulation of welding fixture.
Software solutions that allow designer to leverage and optimize existing resources and to better integrate the designing process from beginning to end can not only help designer create fixture faster, but they can also begin production earlier in the overall cycle or even start later, in order to accommodate unanticipated changes. 3D simulations of the fixture units let you detect collisions, check reach ability and optimize cycle time, so you ensure that your design problems and waste are discovered before manufacturing of your fixture. Allows you to manage data from multiple CAD sources, integrate legacy systems and adapt to new technological developments. The solid model solution supports the designing process life-cycle from process planning and detailed engineering to full production. For you, trying to balance between cost and quality, and time is critical. Through the use of 3d solid model software can rapidly analyze new concern and structural requirements for design ability. 3D model helps you quickly analyze new designs for productivity and ensure that they conform to planning processes. CAD software, enables you to create 3D design of accurate 3D model of the fixture and manage all the information generated during the process planning. You can manage designing of fixture in a proven architecture providing access to critical information such as geometry, tolerances, features and datum. 3D modeling is flexible designing solutions that dramatically increases your design profitability by evaluating dimensional requirements and improve decision-making in design between quality demands and purposes. CAD models are generated from the existing 2D drawings. 3D modeling assignments for various components of welding fixture are done, as the starting point. You can design your fixture faster than you could with 2D CAD drawings. And since these 3D models have embedded object intelligence, they?re easier to visualize and more informative than 2D drawings. It takes the
input geometry data in standard data exchange file formats (IGES/BREP/STEP) and provides output in the same formats. The CAD solution includes a broad range of applications to optimize design sequences: -Product design 3D modeling 2D drafting & detailing Geometrical dimensioning & tolerance Sheet metal design -Migration from 2D to 3D Conversion 2D drawing in to parametric 3D model -Legacy data conversion Digitization of legacy drawings -Reverse engineering 2D drafting and 3D model from real components -Manufacturing engineering Process/setup sheets, tool design, NC programming After creation of the part models, the different parts can be assembled for interference checks, tolerance analysis and mass property calculations. Digital Mockup (DMU) can be simulated to visualize the kinematical functioning of the Assembly. Additionally, 3D solid model of fixture provides tools to analyze design flow and detail design in your fixture, there by optimizing from conceptual design to detail design. Utilized all of the CAD software fundamental knowledge to: Sketch, design and assemble engineering parts and product Use the sheet metal module to produce simple sheet metal parts/products Generate drawings for production purposes
Major CAD Systems are used: Catia V5 Uni Graphics Pro- E
