Computer Aided Process Planning for Rapid Prototyping With Incremental Sheet Forming Techniques (Computer ondersteunde proces planning voor rapid prototyping met incrementele plaatvormtechnieken)

De laatste jaren is er een verschuiving merkbaar naar steeds kortere ont werpcycli en doorgedreven geiındividualiseerde producten. Voor vers chillende productietechnieken zijn er varianten beschikbaar die snelle p rototyping of snelle productie mogelijk maken. Voor gesculpteerde plaats tukken echter, was er tot recent geen valabele techniek beschikbaar. Inc rementeel omvormen is er op gericht om snelle productie van dubbelgekrom de plaatstukken mogelijk te maken. Deze geautomatiseerde techniek maakt gebruik van standaard machines die beschikbaar zijn in de meeste werkpla atsen en heeft geen nood aan op maat gemaakte werktuigen. Met behulp van een generisch, sferisch werktuig wordt een vlakke plaat door een CNC ge stuurde machine bewerkt tot het finale product. Incrementeel omvormen is gekenmerkt door lage vaste kosten en lage opstarttijden langs de ene ka nt, maar een hoge variabele kost per stuk langs de andere kant, wat het proces uiterst geschikt maakt voor kleine reeksen. Om incrementeel omvor men geschikt te maken voor industriele toepassingen moet de techniek nog verder uitgewerkt worden. Het onderzoek uitgevoerd voor dit doctoraat i s gericht op het verhogen van de nauwkeurigheid en het verschuiven van d e proceslimieten door gebruik te maken van slimme programmatietechnieken en geavanceerde proceskennis. De nauwkeurigheid van het proces kan op vele manieren verbeterd worden. Door het detecteren van vormelementen in het CAD model van het werkstuk en het gedrag van elk vormelement in rekening te brengen, kan de gereeds chapsbaan aangepast worden om nauwkeurige stukken te bekomen. Compensati e van onstijve machines gebeurt door het modelleren van het gedrag van d e machine onder bepaalde krachten en de werktuigbaan aan te passen om zo de nauwkeurigheidsfouten, veroorzaakt door de machine, te compenseren. Het vergroten van de proces limieten wordt gerealiseerd aan de hand van aangepaste werktuigbaanstrategieen. Werkstukken die onmogelijk te vormen zijn met klassieke incrementele omvormtechnieken, worden mogelijk door geavanceerde strategieen die materiaal verschuiven naar de regio waar ee n grote verdunning optreedt. Procesvarianten met laserondersteuning late n toe om het proces warm uit te voeren, wat de limieten en de nauwkeurig heid nog verder ten goede komt.nrpages: 206status: publishe

Study on the achievable accuracy in single point incremental forming

Single-Point Incremental Forming (SPIF) is a sheet metal forming technique that is gradually evolving towards industrial applicability. As recent market analysis studies have shown, accuracy is one of the most important limiting factors for the deployment of SPIF in industrial applications. The case studies described in this paper aim to illustrate the state-of-the-art in achievable accuracy for a number of realistic parts having different geometric complexity and produced by different tool path strategies. A secondary goal of this study is to demonstrate the applicability of SPIF for prototyping or small batch production. The results of the different strategies were measured and compared to the geometric specifications. The achieved accuracy for the respective parts and process strategies are reported. © 2007 Springer-Verlag Berlin Heidelberg.status: publishe

Laser assisted incremental forming : formability and accuracy improvement

Single point incremental forming accuracy suffers from contradictory material requirements: while a low yield strength and low hardening coefficient are favourable in terms of limiting process forces and springback, they also result in excessive, unwanted plastic deformation in zones bordering processed areas. Dynamic, localised heat input, for example through radiation of the tool contact area by means of a laser beam, allows to differentiate material properties in time and space. Experimental results demonstrate that this process variant results in reduced process forces, improved dimensional accuracy and increased formability for a range of materials. Initial results also indicate that residual stresses can be significantly reduced by means of the dynamic heating system that was developed.status: publishe

Obtainable Accuracies and Compensation Strategies for Robot Supported SPIF

Single point incremental forming (SPIF) is a flexible forming method allowing to shape sheet metal without the need for die. This process is particularly well suited for rapid prototyping and small series production. The classical setup for incremental forming is a specialised rig mounted on a standard milling machine. While this is an economic solution for small to medium size workpieces, large parts require the availability of a big and therefore expensive machining centre. A cheap solution consists in using a robot, which typically has a much better workable range to cost ratio. Unfortunately a robot is usually not a stiff machine, with the consequence that during forming, due to the forming forces, the deformation of the robot can be orders of magnitude greater than the accuracy of the process. In consequence the accuracy of the achieved part is significantly affected. To overcome this problem, a strategy for compensating the deflection of the robot at the level of the tool has been implemented. To support this strategy, two variables have to be examined: the forming forces on one hand and the stiffness of the robot on the other. In this paper it is demonstrated how, based on robot kinematics, the tool deflection can be computed from the knowledge of compliance of each joint in terms of angle deflection versus the moment load applied to the joint. Experimental results illustrate the effectiveness of this approach.status: publishe

Medical application of single point incremental forming: cranial plate manufacturing

Single Point Incremental Forming (SPIF) is a new sheet metal forming technique that, unlike other forming processes, does not require a dedicated tool set. Because of the absence of a die, SPIF is ideally suited for small batch or tailored production of sheet metal parts. Medical applications typically fit within these categories. The case presented in this paper deals with the production of a cranial plate used in reconstructive skull surgery. The SPIF process is compared to the conventional manufacturing methods. © 2005 Taylor & Francis Group.Book subtitle: ADVANCED RESEARCH IN VIRTUAL AND RAPID PROTOTYPINGstatus: publishe

Customised medical implant production by means of single point incremental forming

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Investigation of Deformation Phenomena in SPIF Using an In- Process DIC Technique

Single point incremental forming (SPIF) is a promising new production technique in which a metal sheet is formed stepwise by a spherical tool. However, the technique still shows some particularities. It is observed that the final geometry of a SPIF part can deviate significantly from the programmed tool path. As illustrated in this paper, elastic springback is only to a minor extent responsible for this phenomenon. The goal of the presented paper is to illustrate the gradual emergence of unintended deviations as measured by means of a Digital Image Correlation (DIC) technique. Two CCD cameras were used to take the necessary in-process images. The mechanism of deformation in function of the forming depth is documented and discussed.status: publishe

Multi-step toolpath approach to overcome forming limitations in single point incremental forming

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