ResearchonBasedS_省略_veBodyWeldingJig_Jun.pdf

Proceedings of the 3rd ICMEM International Conference on Mechanical Engineering and Mechanics October 2123, 2009, Beijing, P. R. China Research on Based System Design for Automotive Body Welding Jig Junhua ZHANG School of Electromechanical Concurrent Engineering; NX/WAVE 1 Introduction Automotive body is the critical sub-system of vehicle, which is the supporter of the other components. It is a complicated component that is welded in rapid productive tempo by 300500 sheet metals with complex shape on 5575 workstation of welding assembly line, having 17002500 clamping and positioning datum points and 40005000 welding points. The production process of BIW is that sheet metals are grasped and transferred by robots, mechanical equipments or worker, and then welded together. So many operations and complex processing in the automotive body welding line have been a research issue in automotive industry, which presents a challenge for process planning of welding assembly and automotive body design. Automotive body welding assembly includes automatic transfer equipments among workstations, welding equipments of mainly spot weld, welding jig, testing instrument and control equipments. Welding jig is used to assembly, clamp and position sheet metals in the welding process, and ensure the assembly precision and welding quality. Welding jig directly affects the welding assembly precision of automotive body. Then it furthermore affects the precision of the whole vehicle. Therefore, a very important research topic that the automobile industry confronts is how to reduce the design cycle and improve quality of welding jig. Key issues for automotive body welding jig must be taken into account as follows. i) To meet the requirements of simultaneous engineering or concurrent engineering, welding jig design is parallel to body design. Body design can be divided into concept design and detail design in the process of development vehicle program. At the stage of concept design, the information of shape, dimension and structure of body is obtained. Tool designers and engineers make the process planning and design structure for welding jig and mould. And the information of tool is fed back to body design. The task is to determine the geometric dimension and tolerance of automotive body parts of sheet metals in the stage of detail design. Correspondingly, the geometric dimension and tolerance of welding jig is determined. For instance, RPS (Reference Point System) is adopted to ensure the consistence datum between body and welding jig. ii) The standardization of automotive welding assembly, how to standardize welding jig, welding equipments, manufacturing and production, testing and management, is another research issue. The part and component of automotive 1067 body welding jig is standardized into standard part, re-use part and similar part to some degree. Standardization of automobile body welding jig makes it feasible that they are utilized in different vehicle development program to reduce the design cycle and improve quality. Unfortunately, the standardization of welding jig is no more than 20% in quality in practical engineering. iii) CAD Technology of Automotive Body Welding Jig With the growing use of 3D CAD (such as NX, CATIA, Pro/Engineer, MDT) in design departments, 3D CAD-based design and manufacturing is becoming more and more common substituting for 2D CAD. Its necessary to customize and establish the design process, standard part library, program library on 3D CAD software, so that it fits for automotive welding jig design. Fig. 1 Structure of Welding Jig iv) Evaluation of Automotive Body Welding Jig During the design and manufacturing of automotive welding jig, it needs to evaluate their welding tool setup scheme, process and structure. Evaluation indexes usually include reliability and precision of positioning and assembly, strength and stiffness in function, standardization, machinability, cost, work time and assemblability in manufacturing. The characteristics of short time, high quality, much workload and concurrent engineering requires that automotive body welding jigs design must meet the requirements of concurrent engineering and should be based system. It also requires that the modification of process planning, global parameters and the change of automotive body model can trigger the modification of design automatically using top-down method. Design rules can be captured and enforced, the design is reused. The aim of this paper is to develop the based system method for automotive body welding jig design. So a 4-level control structure model is presented. By applying NX/WAVE, the design procedure of automotive body welding jig on single work station using NX software is described. 2 Structure of Automotive Welding Jig Shown in Fig.1, a typical structure of automotive body welding jig is composed of support bracket, locator, positioning pin, clamper, clamping arm, connected plate, connected bracket and pneumatic clamping cylinder. Support bracket is the basic part, which connects base and connected plate. Locator as only located part is used to support automobile body panel. The feature of positioning pin as positioning part is to locate the hole in body pane. Locator and positioning pin are the critical part of jig, whose precision and quality directly affect the quality of automotive body. Clamper and clamping arm are the kinetic component, which is used to clamp and unclamp body panel. Connected plate is the jointed part, which is used to fasten support bracket, locator, connected bracket and pneumatic clamping cylinder. Pneumatic clamping cylinder is the driven power source. There are four types of structure in view of driven mode, that is, non-driven, pneumatic (hydraulic) driven, manual and motor driven jig, whose structure is dealt with in reference 1. 1068 3 Control Structure of Automotive Welding Jig 3.1 Systems Based Modeling Approach using NX/WAVE2 WAVE (What-if Alternative Value Engineering) is a technology that enables associative interpart modeling so that designer can base a design of one part on the geometry and/or position of another part. Parametric modeling allows you to build associative relationships between features within a single piece part. WAVE allows designer to extend this concept to build associative relationships between geometry in different parts. Because of the interpart relationships, it becomes easier to modify a product design. The WAVE tools are able to support the WAVE process, which is described in detail as follows. 3.1.1 Design in Context NX/WAVE can process whereby geometry in a part that needs reference geometry in some other part in its definition. Localized interpart modeling is the ability to relate the geometry of interacting parts residing within the same assembly. Cost is reduced because changes made to a single part can be automatically propagated to other related component parts in the assembly. Design integrity is maintained because the parts will always have correct geometric and positional relationships. Tool to establish interpart relationships by selectively copying geometry between parts, resulting geometry is associatively linked to parent geometry. 3.1.2 Top-down design NX/WAVE has ability to represent the various states of a part as it is modified during the steps of a manufacturing process. The states are linked associatively so that changes to the part at an earlier stage in the process are seen by the later stages. An important application of WAVE is for top down design processes. Overall parameters, envelopes, and component locations can be defined in the upper levels of the assembly and associatively passed down to the detailed component parts in the lower levels of the assembly. The data defined at the top of the assembly may consist of datums, sketches, or common sheet bodies used for trimming. The lower level components would contain links to this parent geometry. WAVE allows designers to automate the update of component designs when high-level product design changes are required. A key parameter can be changed at the top level of the assembly and propagate down to the detailed piece parts. Concurrent engineering can take place because the conceptual design data and the detail design data are defined in different parts. Work on the detailed parts can begin before the constraints in the top level assembly parts are finalized. 3.1.3 System Engineering Method In a system engineering environment, modular design is utilized to split a product design into logical subsystems. Each subsystem then has its own design criteria and constraints. This allows each subsystem to be designed somewhat in isolation, while meeting the requirements of the overall product. For example, the subsystem constraints would define its position, envelope, and geometric interfaces with the controls and the product. These constraints would be managed in the product layout, where product wide design decisions can be made. Layout changes are passed on to the subsystem designers by updating the subsystem constraints. WAVE provides tools and technology that support the systems engineering approach to design. WAVE is able to process whereby a (typically small) assembly, termed a Control Structure that is used to define the key dimensions, datums, and interfaces of a product. Designer can isolate the product layout and subsystem design criteria in a control structure, which is an assembly where the master layout geometry is defined and managed. This makes it possible that control structure is driven by key product parameters, incorporates design rules and publishes constraints for product design. 1069 Fig. 2 Control Structure links to product Assembly Shown in Fig.2, the top level of the WAVE control structure assembly can contain key product parameters, such as the wheel base of a car. These parameters can then drive geometry (datums, sketches, trim sheets, etc.) that defines subsystem constraints and incorporate design rules. The control structure publishes the subsystem constraints for downstream design activities. A Linked Part can be created from an appropriate Start Part in the control structure and used as the starting point for the component design in a product assembly. 3.2 Control Structure of Assembly Welding Jig on Single Workstation Applying WAVE to a design process of automotive body welding jig requires careful planning. Designers need first to think about the design intent and how the parts are really related. To optimize the use and develop best practices and standards, designer should consider creating interpart relationships using NX/WAVE. A 4-level control structure model for automotive body welding jig design is presented shown in Fig.3. Control Structure is the “nerve center” for welding jig design. It can manage master layout geometry and maintains subsystem design constraints (locations, envelopes, interface geometry). 3.2.1 Body Model The top level of the control structure is body model, which includes the basic information of panels: panel list, panel exploded view, welding assembly sequence. 3.2.2 Processes The second level of the control structure is processes, which includes the information of scheme design: basic information of welding jig process, welding information and MCP (Master Control Point) and MCS (Master Control Section). Basic information of welding jig process include productive tempo, work cycle, type of jig, height of work, setting and transfer method. Welding information describes the distribution of welding points, posture models of welding Processes Assembly of Jig Unit Body Model Start Part Control Structure Assembly of Jig Fig. 3 Application of 4 Level Control Structure of Automotive Body Welding Jig 1070 gun and operators. MCP describes the information and pattern of positioning datums for each jig unit. The quantity, location, main control width and type of jig can be obtained from MCP. MCS (Master Control Section) corresponding to MCP describes the pattern of positioning and clamping and the location surface in panel in each jig unit. 3.2.3 Assembly of Jig Unit The third level of the control structure is assembly of jig unit, which is usually the smallest design work. According to MCP and MCS, the control geometries are linked or created in the level. The concept design of jig is accomplished meanwhile. The levels depicted above are also called What-if levels. The “What-if” level contains the jig definition information and critical requirements. 3.2.4 Start part The bottom level of the control structure is start part. Start parts have two basic functions: They function as seed parts from which other parts may evolve. They also provide the buffer between the what-if studies of the control structure and the actual model geometry in the review assembly. The level is also called “Isolation” level, that is, where start parts reside. 4 Based System Design Procedure of Welding Jig on Single Workstation By applying NX/WAVE, the design process of automotive body welding jig on single work station using NX is explored as follows: Step 1 Create Assembly of Workstation Assembly of workstation is the root node in assembly tree. Step 2 Create Control Structure Sub-Assembly i) Control Structure Sub-Assembly is created under the node of assembly of workstation. ii) The assembly of automotive body panels is created under the node of control structure sub-assembly. The components of automotive body model are added to the assembly of automotive body panels in the way of absolute positioning with reference to VCS (vehicle coordinate system). Thus car lines are created with reference to VCS, which are linked and used as the positioning datum of part and assembly in jig design. iii) The assembly of welding points is created under the node of control structure sub-assembly. The model of welding points is created in the component. iv) The assembly of posture models of welding gun is created under the node of control structure sub-assembly. The components of welding gun are added to the assembly in order to simulate welding process. v) The assembly of base datum relied on the height of work is created under the node of control structure sub-assembly. vi) The assemblies of unit jig are created under the node of control structure sub-assembly in terms of MCP. In each assembly of unit jig, the concept design is completed according to MCS. The sketch for MCS is constructed. And datums for positioning hole on body hole are created. vii) The start pars are created under the node of control structure sub-assembly, which are linked the geometries in the assembly of unit jig. Step 3 Create Jig Sub-Assembly i) Jig sub-assembly is created under the node of assembly of workstation. ii) The assemblies of jig unit is created under the node of jig sub-assembly. iii) In each jig sub-assembly, master control parts for positioning and clamping that include locator, clamper, clamping arm, connected plate and pin is created. And the control object is linked from the start parts. iv) In accordance with the way of clamping (manual, pneumatic etc.), the suitable pneumatic cylinder or toggle is 1071 selected. And appropriate bracket is selected according to the location of the base information in the process sheet. Finally the assembly model of single jig unit is completed. Step 4 Design Component ofof Base After finished the design of all single jig units in the work station, base component is designed according to height of work.