Unlike conventional jigs, the reconfigurable jig can change its shape depending on the shape of the product. In this study, the reconfigurable jig system is designed for the process of assembling car door inner modules. In addition, the computer-aided design helps to automatically calculate the movements of the pin jigs.
In order to evaluate the quality of the product, some experiments were carried out using finite element analysis on the product and pins. The method for evaluating product quality includes the analysis of stress and deformation of the product according to the shape of the product. Based on the results of the finite element analysis, the design priority was to determine the best location for the product.
In addition, an auxiliary method was developed to locate a part with a geometric property-based stress and strain estimation model for optimal assembly part positioning.
Introduction
To reduce the formation of defects in a product, the position of the product in the presence of external forces must be considered in the assembly process. From the point of view of an interior automotive part, we have developed a transformable jig system in which the shape of the discrete pin jigs can be reconfigured according to the 3D CAD model of part. Pin-jig reduces lead time and overhead by storing and retrieving multiple fixtures.
Due to the fixed interval between each pin-jig, a deviation or shift can occur when the potential energy of the part is not in an equilibrium state (YAMADA, YAMADA, & YAMAMOTO, 2011). Therefore, the size of the pin, the gap between the pins and the size of the physical system adapt to the size of the inside of the machine.
Literature Survey
Transformable Jig
- Reconfigurable and flexible fixtures
- Pin Tooling
Common types of actuators for implementing pin-array fixtures are pneumatic, hydraulic, mechanical, and piezoelectric methods. Hydraulic method can hold high pressure, but it is difficult to maintain and build a system. Hydraulically actuated pin (HA) activates the pin by connecting the pipe that injects hydraulic fluid to provide pressure.
Another example of a clamp using a hydraulic method is the clamp developed by Junbai and Kai (2010). The movement of the pendulum is driven by a hydraulic method and a pneumatic method, which makes the part fixed to the pins.
Part stability
They decide on the location of the part through iterative Finite Element Analysis (FEA) until some threshold is reached. One example is the listing of cutting operations, such as making holes, and setting tools according to these features in a 3D CAD workpiece (Attila, Stampfer, & Imre, 2013). And also by integrating the cad model and the real machine, the control predicts the process with parameters (Olaiz et al., 2014).
2 The basic elements of the fixture design process and typical FEM-based fixture design solution analysis framework adopted from Wang et al. Many researchers have presented various finite element and analytical solutions in the point of view of curved beam. One of the analytical solutions for mixed curved-beam finite elements was developed based on the form of the non-linear deep arch theory.
According to the fundamental equations of nonlinear deep arch theory, the local curvature of the arch is related to bending moment and normal force (NOOR, GREENE, & HARTLEY, 1977). Another researcher analyzed curvature and displacement-based finite element solution with flexible four-bar mechanisms. Their formulation is based on the two-element discretization that has a linear function of the curvature for each link (Kuo & Cleghorn, 2010).
3 Schematic diagram of the pure bending test with elasto-plastic deformation derived by Bin and Wanji compared the Young-Laplace law and the finite element method, applying both to the ventricular wall stress problem. The above methods have attempted to draw an accurate stress, comparing the finite element solution method. Siebenaler and Melkote (2006) tried to find more accurate workpiece deformation using friction parameter and mesh density of finite element analysis.
A Transformable Jig System
System configuration
- Transformable Pin-Jig
In addition, each car driver communicates with a computer that has 3D Pin-Jig Shape Transformer connected with an Ethernet cable. The gear on the motor rotates a gear, which has a hexagonal hole in the center and engages with a hexagonal rod of pin jig. As gear with hexagonal hole rotates, pin-jig rotates and screw of pin-jig moves forward and backward according to direction of rotation.
A 3D Pin-Jig Shape transformer reads the 3D CAD model of a part and calculates the heights of each pin-jig. In the 3D pin-jig transformer, there are several functions to calculate the strokes of the pin-jigs. For a calculation of pin-jig heights or interference control with the function in VTK, the STL files of a part and pin-jig must be converted to VTP.
After conversion, load pin-jig and a part file, calculate center of mass and store coordinates in the local memory with center of mass. For calculating distance from each pin-jig and iso-surface of a part, draw a line from the center of pin-jig along with y-coordinates through a part. The distance is calculated by finding the distance between an interference point that is on the top of the pin-jig surface and a lowest interference point of the part.
14 The distance between an interference point that is at the top of the stud surface and the lowest interference point of a part. However, transforming a pin-jig by distance may cause interference between the pin-jig and a part as shown in Figure 3.5, regardless of the shape of the part and a pin-jig. These interferences can be easily resolved by transferring each pin-jig down repeatedly until the number of points and lines meet a suitable threshold according to the volume of the part and a pin-jig.
Finite Element Analysis for Part Positioning on Pin-Jigs
Plate bending element model
I will compare the result of finite element analysis with a triangular element with the result of a rectangular shell element. 2 is a comparison of the results between the tetrahedral element finite element analysis and the commercial analysis. I implement finite element methods with a plate element and a 3d solid element and compare the result of compressing the split part with the result of commercial software.
There are some errors in the amount of deformation, but the trend of its result shows similarity.
Finite element analysis for extract estimation factors
In addition, I conduct an experiment to examine the investigation of the effects of plate shape on the results of the finite element analysis. The amount of external load and deformation assume that the experiment is under linear elastic deformation. Each result shows the deformation within the zone affected by the external load, because the area of interest for assembly quality is within the assembly zone which is the zone affected by the external load.
For the experiment, I simplified these shapes and performed finite element analysis with the simplified shapes. An interesting area of deformation is the location of the external force because it is at the point of assembly joint. Each step has an external load with a different distance from the origin and support points with a different distance from the origin.
Total number of external load is nine and total number of support points is five. 3 shows the deformation data organized with making the origin the point of support point so that the deformation is not affected by the distance between support points and external load. On the third table, bold deformations have the same gap between supporting points and external load.
The deformation when supports support the L-shape is 25% smaller than that when the supports do not support the L-shape. Deformations in bold have the same gap between supports and external loads, but have different locations of supports. The result shows that the distortion when supports support a pillar is smaller than that of not supporting a pillar by 6%.
Force and Deformation Estimation for Optimal Part Positioning
Geometric feature-based Von mises stress and deformation estimation
In a 3D solid model, we can extract various geometric features such as element type, resolution, contact point, curvature, tangent angles, etc. For points only, the important features we can use are the curvature and the tangent angle at the point. Using these variables, I perform FEA experiments to find the relationships that are Von Mises stress-curvature, strain-curvature, Von Mises stress-tangent angle, and strain-tangent angle.
As the radius of curvature increases, the maximum Von Mises stress increases as shown in the figure. When the x-axis is concerned with curvature, the trend of maximum y-displacement shows a quadratic form. However, when the x axis is concerned with the radius of curvature, the trend of the maximum y displacement takes the form of a linear expression.
Therefore, it is more useful to use the radius of curvature as a parameter when creating an estimation equation. The experiment shows that the model is closer to a quadratic equation than to a linear equation, as shown in figure. The FEA experiments were performed 45 times depending on the radius of curvature and tilted angle of the plate.
The experiment observes the deformation when an external force presses on a certain point, which is the joint point. To observe the component, the two panels were partially overlapped as shown in the figure. In each experiment, the location of the external force changes according to the distance between the pin and the external force.
Optimal part positioning experiment
The estimation model result is the smallest deformation result when the part moved +60 mm along the x and y axes from the initial position. The average von Mises stress and strain at an optimized position is less than that of the initial position. Moreover, the maximum vonmises stress at an optimized position is smaller than that of the initial position.
These estimated values from the estimation model have an error rate of 14% on average when compared to the result of commercial FEA software.
Conclusion and Future Research
However, the actual boundary condition includes the contact surface between the pin jigs and a part. Modern fastening systems for the manufacture and assembly of rigid components: An overview. Rapid manufacturing and rapid tooling with Layer Manufacturing (LM) technologies, state of the art and future perspectives.
Paper presented at the 2015 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), Hamburg, Germany.
