Geometric dimensioning, tolerancing and inspection

As known, incremental forming is a flexible and innovative sheet metal forming process which allows complex shape shells forming without the need for any die. For these reasons, incremental forming is nowadays suggested for rapid prototyping and customised products. The present paper is focused on material formability in incremental forming and, in particular, on the evaluation and compensation of elastic springback. The latter significantly modifies the imposed shape. For this purpose, a deeper assessment of the process was developed following three different approaches. First of all, a wide experimental investigation on the influence of some relevant process parameters was developed. At the same time, an explicit FEM analysis of incremental forming process was carried out in order to verify its effectiveness and, as a consequence, its ability to be used as a design tool. Furthermore, the obtained parts were analysed by a reverse engineering technique and the measured geometry was numerically compared with the desired one, with the aim to quantify the geometrical discrepancies. In this way, an integrated numerical/experimental procedure is proposed in order to limit the shape defects between the obtained geometry and the desired one. © 2004 Elsevier B.V. All rights reserved.

Keywords: FEM , Geometrical accuracy , Incremental forming

Incremental forming is nowadays increasing its presence in industry as a new but interesting process, especially for production of small batches or unique components. Anyway, relevant efforts have to be spent in order to reduce the typical incremental forming processes drawbacks that risk to belittle the high advantages in terms of costs and simplicity. In fact, the process duration, usually equal to several minutes even if the operations are carried out on high speed numerical controlled units, and a certain tendency to produce no precise parts, can reduce industrial interest about incremental forming. A possible strategy to reduce the latter item is the design of modified trajectories able to take into account both the springback effects and the stiffness reduction due to the particular clamping equipment. In this paper the above introduced strategy is pursued integrating an on-line measuring system, based on a digital inspector, and a CNC open program. The actual geometry is acquired in some remarkable points and a compensation routine modifies the coordinates of the future punch path. The modification policy has been developed by using an effective FE code. An experimental verification shows the good potentiality of the suggested methodology.

Tolerance design plays an important role in the modern design process by introducing quality improvements and limiting manufacturing costs. In this paper a method for statistical tolerance analysis and synthesis is presented. This method is implemented using the mean shift model of Chase and Greenwood, providing a systematic approach to evaluate the mean shift model method considers all the principal factors that affect the statistical sum of a certain number of assembly dimensions. In particular, the considered factors include the mean shift ratio, the confidence level, the number of dimension of the assembly and the tolerance assortment between the component dimensions. An implementation of the mean shift model for tolerance synthesis is described. The tolerances synthesis is performed in an unusual way, taking into account in the optimization process the typical parameters that affect the product variability. For this purpose the method uses four types of condition for the dimensional tolerances: fixed tolerance value, fixed mean shift ratio, fixed mean shift and fixed natural variability. Furthermore, in the optimization process, the service variability is considered under two conditions: fixed and valuable service variability. A case study is presented and the results of some simulations are discussed.

Keywords: Mean shift model , Tolerance analysis and synthesis

This article presents a review of a commercial computer-aided tolerance analysis tool, eM-TolMate, which is embedded in four major CAD systems (Catia [1], UG [2], Pro/E [3], SDRC [4]). eM-TolMate combines the Monte Carlo statistical simulation techniques with an internal tolerance management system and identifies the key characteristics (i.e. dimensions/clearances of interest) of nominal component models that are critical to proper assembly. Features and tolerances are directly created in CAD models and both single component or multi component analyses are available. For assemblies, eM-TolMate offers the capability to apply user-defined assembling rules or to automatically detect mating conditions. Actual features are varied within the specified tolerance range, and standard or user-defined statistical distributions are used in simulation runs to determine variations of key characteristics. It also offers the capability to rank tolerances based on contribution to the variation, so the user can identify where tolerances need to be tightened or can be loosened. eM-TolMate [5] represents a useful tool in tolerance analysis of mechanical assemblies.

In this paper is analysed the problem, using soft models, of soft dependence of parameters in design systems. A new form of computing, called Soft Computing, is recently used in many emerging disciplines because it is tolerant to imprecision, uncertainty and partial truth. The Soft Computing uses many disciplines as Bayesian inference and maximum entropy method. The logic relationship that ties the different elements can be defined more easily using the axioms of soft design emanating from MinEnt principle. The fundamental axiom of design is: valid design has minimum values of information and depends on a finite and limited number of independent, or soft dependent, parameters. © 2002 Published by Elsevier Science B.V.

Keywords: Axiomatic design , Entropy , MaxEnt , Soft Computing , Soft design , Uncertainty

The results of an experimental study conducted to detect subsurface defects in a thick Gr/PPS composite test sample using a non-contact ultrasonic system are presented. Surface waves are generated by a pulsed laser and detected by a air-coupled capacitance transducer. By controlling the surface wave wavelength through a shadow mask, it is possible to control surface wave penetration depth in the sample. Surface wave peak-to-peak amplitude is related to the near-surface material condition. Results indicate that signal amplitude decreases as the width of the defect increases and an approximately linear relation can be deduced.

Screw Theory is well known to do kinematic computations. Recently it has been used to create kinematic models of assembly features so allowing to do assembly analysis. Motion Limit Analysis uses the mathematics of screw theory to model the ability of mechanical assembly features to allow or constrain rigid body motions in six degrees of freedom. A user of this theory is able to determine the directions and quantitative amounts of possible finite rigid body motions of a part that is being added to an assembly via calculation applied to a defined set of assembly features. The ability to calculate rigid body motions of a part is important for enabling in-process adjustment during assembly to precisely establish key assembly dimensions. MLA software is a part of a suite of software programs used to do assembly analysis.