This paper develops the statistical error analysis model for assembling, to derive measures of controlling the geometric variations in assembly with multiple assembly stations, and to provide a statistical tolerance prediction/distribution toolkit integrated with CAD system for responding quickly to market opportunities with reduced manufacturing costs and improved quality. First the homogeneous transformation is used to describe the location and orientation of assembly features, parts and other related surfaces. The desired location and orientation, and the related fixturing configuration (including locator position and orientation) are automatically extracted from CAD models. The location and orientation errors are represented with differential transformations. The statistical error prediction model is formulated and the related algorithms integrated with the CAD system so that the complex geometric information can be directly accessed. In the prediction model, the manufacturing process (joining) error, induced by heat deformation in welding, is taken into account.

No abstract

Abstract-In this paper, we introduce unilateral fixtures, a new class of fixtures for sheet-metal parts with holes. These fixtures use cylindrical jaws with conical grooves that facilitate part alignment; each jaw provides the equivalent of four point contacts. The fixtures are unilateral in the sense that their actuating mechanisms are restricted to one side/surface of the part, facilitating access to the other side/surface for assembly or inspection. We present a two-phase algorithm for computing unilateral fixtures. Phase I is a geometric algorithm that assumes the part is rigid and applies two-dimensional (2-D) and three-dimensional (3-D) kinematic analysis of form closure to identify all candidate locations for pairs of primary jaws. We prove three new grasp properties for 2-D and 3-D grips at concave vertices and define a scale-invariant quality metric based on the sensitivity of part orientation to infinitesimal relaxation of jaw position. Phase II uses a finite element method to compute part deformation and to arrange secondary contacts at part edges and interior surfaces. For a given sheet-metal part, given as a 2-D surface embedded in 3-D with edges, concavities and mesh nodes, Phase I takes ( + 4 3 log 1 3 + log ) time to compute a list of pairs of primary jaws ranked by quality. Phase II computes the location of secondary contacts in ( 3 ) time.Note to Practitioners-This paper was motivated by the problem of holding sheet-metal parts for automobile bodies but it also applies to other sheet-metal components that have cut or stamped holes. Existing approaches to fixturing such parts generally have contacting mechanisms on both sides of the sheet that restrict access for welding or inspection. This paper suggests a new approach using pairs of grooved cylinders, activated from only one side of the part (hence "unilateral"). These cylinders mate with opposing corners of holes in the sheet and push apart to hold the sheet in tension, thus acting as both locators and clamps. In this paper, we mathematically characterize the mechanics and conditions for a unilateral fixture to hold a given part. We then show how such fixtures can be efficiently computed; this can allow a computer-aided design (CAD) system (with finite element capability) to automatically generate and propose unilateral fixtures for a given part. Preliminary physical experiments suggest that this approach is feasible but it has not yet been incorporated into a CAD system nor Manuscript

No abstract

The development of lightweight vehicles, in particular aluminum intensive vehicles, require significant manufacturing process development for joining and assembling aluminum structures. Currently, 5xxx and 6xxx aluminum alloys are being used in various structural applications in a number of lightweight vehicles worldwide. Various joining methods, such as MIG, Laser and adhesive bonding have been investigated as technology enables for high volume joining of 5xxx, and 6xxx series alloys. In this study, metal inert gas (MIG) welding is used to join 5754 non-heat-treatable alloy sheet products. The objective of this study is to develop optimum weld process parameters for non-heat-treatable 5754 aluminum alloys. The MIG welding equipment used in this study is an OTC/Daihen CPD-350 welding systems and DR-4000 pulse power supply. The factors selected to understand the influence of weld process parameters on the mechanical properties and metallurgy (weld penetration) include power input (torch speed, voltage, current, wire feed), pulse frequency, and gas flow rate. Test coupons used in this study were based on a single lap configuration. A full factorial design of experiment (DOE) was conducted to understand the main and interaction effects on joint failure and weld penetration. The joint strengths and weld penetrations are measured for various operating ranges of weld factors. Post weld analysis indicates, power input and gas flow rate are the two signficant factors (statistically) based on lap shear load to failure and weld penentration data. There were no 2-way or 3-way interaction effects observed in ths weld study. Based on the joint strength and weld penetration, optimum weld process factors were determined.