Three-Dimensional Synthesis of Manufacturing Tolerances Based on Analysis Using the Ascending Approach

The present paper develops a new approach for manufacturing tolerances synthesis to allow the distribution of these tolerances over the different phases concerned in machining processes using relationships written in the tolerance analysis phase that have been well developed in our previous works. The novelty of the proposed approach is that the treatment of non-conventional surfaces does not pose a particular problem, since the toleranced surface is discretized. Thus, it is possible to study the feasibility of a single critical requirement as an example. During the present approach, we only look for variables that influence the requirements and the others are noted F (Free). These variables can be perfectly identified on the machine, which can be applied for known and unknown machining fixtures; this can be the base for proposing a normalized ISO specification used in the different machining phases of a mechanical part. The synthesis of machining tolerances takes place in three steps: (1) Analysis of the relationship’s terms, which include the influence of three main defects; the deviation on the machined surface, defects in the machining set-up, and the influence of positioning dispersions; then (2) optimization of machining tolerance through a precise evaluation of these effects; and finally (3) the optimization of the precision of the workpiece fixture, which will give the dimensioning of the machining assembly for the tooling and will allow the machining assembly to be qualified. The approach used proved its efficiency in the end by presenting the optimal machining process drawing that explains the ordered phases needed to process the workpiece object of the case study.

Optimization of Modular Fixture Layout by Minimizing Work-piece Deformation

Machining fixtures are utilized to locate and restrain a workpiece during different manufacturing processes. The workpiece must be properly located and clamped in order to have it to be manufactured according to the prescribed dimensions and tolerance. The real motive of fixture design is to maximize locating accuracy and workpiece firmness while minimizing deformations. The purpose of this research work is to conduct a multi-objective optimization in order to minimize workpiece deflections due to clamping forces and optimized fixture layout by taking into consideration the boundary conditions and loads applied during a machining process. The locators are employed in a 3-2-1 fixture configuration. Then the empirical relations are used to calculate the machining forces and moments generated during drilling and milling processes and after that the workpiece is loaded to model those cutting forces. ANSYS parametric design language (APDL) code which made use of sub-approximation method is utilized to automatically optimize locator and clamp positions. Afterwards the clamping forces are being optimized using balancing force-moment method. Lastly, the maximum deformation of the workpiece against the optimum clamping forces is found by harmonic analysis.

Improvement of Product Quality through Optimum Fixture Design using DOE and FEM

Machining fixtures are used to improve the productivity and quality of the finished components. It is essential to produce a component in specified accuracy and quality: this can be achieved by optimizing the precise fixture design based on workpiece geometry and machining condition. In this work, optimum fixture layouts were developed for rigid body component. Design of Experiment based optimization procedure is established for identify the optimum fixture design. Finite element software ANSYS is used for predicting the workpiece elastic deformation caused by machining and clamping forces.

The Set-Up-Map for Automating the Positioning of Castings and Weldments in Fixtures to Ensure Completely Machined Surfaces

There is considerable geometric variability of raw castings and weldments before any machining of surfaces that assemble with other components. Consequently, considerable time often is spent identifying successful set-up adjustments at the machining fixtures for such parts in a way to ensure that every machined surface will be complete. The proposed Set-Up-Map© is a point-space subset of R6 where each of the six orthogonal coordinates correspond to one of the rigid-body displacements in three dimensional space: three translations and three rotations. Any point within the Set-Up-Map (S-Map) corresponds to a small body displacement (SBD) of the part that satisfies the condition that each feature will lie within its associated tolerance zone after machining. S-Maps are derived from previous work on Tolerance Maps© (T-Maps), which represent feature deviations allowed by a given tolerance zone. Each raw casting or weldment is scanned, and the point-cloud data fitted to individual features, to determine how much each to-be-machined (TBM) feature deviates from nominal specifications. Each local T-Map is formed from a library, then shifted to be centered on its corresponding scanned feature on each casting; it becomes a local S-Map primitive. Each of these local S-Maps is then transformed to a single global reference frame. The intersection of these S-Map primitives in the global frame gives the allowable small body displacements that satisfy the positioning requirements for all TBM features. Since T-Maps are convex objects, a half-space intersection method is used to generate an S-Map. Any point within the S-Map represents a viable small body displacement specific to the global coordinate system established on the part. In the case that as-cast or as-welded features deviate from what is acceptable, the S-Map will be the empty set. Consequently, in addition to reducing the time for setup in a fixture, S-Maps can serve as a valuable diagnostic to determine that a part should be either scrapped or reworked.

KBE Application for the Design and Manufacture of HSM Fixtures

The design of machining fixtures for aeronautical parts is strongly based in the knowledge of the fixture designer, and it comprises certain repetitive tasks. An analysis of the design process allows us to state its suitability for developing Knowledge Based Engineering (KBE) applications in order to capture the knowledge, and to systematize and automate the designs.This work justifies the importance of fixtures for High Speed Milling (HSM), and explains the development of a KBE application to automate the design and manufacturing of such elements. The application is the outcome of a project carried out in collaboration with the company EADS.In the development process, a specific methodology was used in order to represent the knowledge in a semi-structured way and to document the information needed to define the system. The developed KBE application is independent of the parts design system. This makes it necessary to use an interface to input the part geometry into the KBE application, where it is analyzed in order to extract the relevant information for the fixture design process. The results obtained from the application come in three different ways: raw material drawings, fixture 3D solid models, and text files (Bill Of Materials – BOM, and Numerical Control – NC programs). All the results are exported to other applications for use in other tasks. The designer interacts with the application through an ad hoc interface, where he is asked to select or input some data and where the results are also visualized. The prototype KBE application has been carried out in the ICAD development environment and the main interface is with the CAD/CAM system CATIA V4.