Characterization of shape and dimensional accuracy of incrementally formed titanium sheet parts with intermediate curvatures between two feature types

Single point incremental forming (SPIF) is a relatively new manufacturing process that has been recently used to form medical grade titanium sheets for implant devices. However, one limitation of the SPIF process may be characterized by dimensional inaccuracies of the final part as compared with the original designed part model. Elimination of these inaccuracies is critical to forming medical implants to meet required tolerances. Prior work on accuracy characterization has shown that feature behavior is important in predicting accuracy. In this study, a set of basic geometric shapes consisting of ruled and freeform features were formed using SPIF to characterize the dimensional inaccuracies of grade 1 titanium sheet parts. Response surface functions using multivariate adaptive regression splines (MARS) are then generated to model the deviations at individual vertices of the STL model of the part as a function of geometric shape parameters such as curvature, depth, distance to feature borders, wall angle, etc. The generated response functions are further used to predict dimensional deviations in a specific clinical implant case where the curvatures in the part lie between that of ruled features and freeform features. It is shown that a mixed-MARS response surface model using a weighted average of the ruled and freeform surface models can be used for such a case to improve the mean prediction accuracy within ±0.5 mm. The predicted deviations show a reasonable match with the actual formed shape for the implant case and are used to generate optimized tool paths for minimized shape and dimensional inaccuracy. Further, an implant part is then made using the accuracy characterization functions for improved accuracy. The results show an improvement in shape and dimensional accuracy of incrementally formed titanium medical implants

Investigation of material deformation mechanism in double side incremental sheet forming

Double side incremental forming (DSIF) is an emerging technology in incremental sheet forming (ISF) in recent years. By employing two forming tools at each side of the sheet, the DSIF process can provide additional process flexibility, comparing to the conventional single point incremental forming (SPIF) process, therefore to produce complex geometries without the need of using a backing plate or supporting die. Although this process has been proposed for years, there is only limited research on this process and there are still many unanswered open questions about this process. Using a newly developed ISF machine, the DSIF process is investigated in this work. Focusing on the fundamental aspects of material deformation and fracture mechanism, this paper aims to improve the understanding of the DSIF process. Two key process parameters considered in this study include the supporting force and relative position between master and slave tools. The material deformation, the final thickness distribution as well as the formability under varying conditions of these two process variables are investigated. An analytical model was developed to evaluate the stress state in the deformation zone. Using the developed model, an explicit relationship between the stress state and key process parameters was established and a drop of stress triaxiality was observed in the double contact zone, which explains the enhanced formability in the DSIF process. Based on the analytical and experimental investigation, the advancements and challenges of the DSIF process are discussed with a few conclusions drawn for future research

Tool path generation for single point incremental forming using intelligent sequencing and multi-step mesh morphing techniques

A new methodology of generating optimized tool paths for incremental sheet forming is proposed in this work. The objective is to make parts with improved accuracy. To enable this, a systematic, automated technique of creating intermediate shapes using a morph mapping strategy is developed. This strategy is based on starting with a shape different from the final shape, available as a triangulated STL model, and using step-wise incremental deformation to the original mesh to arrive at the final part shape. Further, optimized tool path generation requires intelligent sequencing of partial tool paths that may be applied specifically to certain features on the part. The sequencing procedure is discussed next and case studies showing the application of the integrated technique are illustrated. The accuracy of the formed parts significantly improves using this integrated technique. The maximum deviations are brought down to less than 1 mm, while average absolute deviations of less than 0.5 mm are recorded

Fixtureless automated incremental sheet metal forming

Die-based forming is a technology used by many industries to form metal panels. However, this method of forming lacks flexibility and cost effectiveness. In such cases, manual panel beating is typically undertaken for incremental forming of metal panels. Manual panel forming is a highly skilled operation with very little documentation and is disappearing due to non-observance and a lack of interest. Confederation of British Metal forming (CBM) and Institution of Sheet Metal Engineering (ISME) have realised the need for capturing and understanding manual skills used by panel beaters to preserve the knowledge. At the same time, industries seek for alternative panel forming solutions to produce high quality and cost-effective parts at low volume and reduce the repetitive, yet adaptive parts of the panel forming process to free up skilled workers to concentrate on the forming activities that are more difficult to automate. Incremental forming technologies, currently in practice, lack adaptability as they require substantial fixtures and dedicated tools. In this research a new proof-of-concept fixtureless automated sheet metal forming approach was developed on the basis of human skills captured from panel beaters. The proposed novel approach, named Mechatroforming®, consists of integrated mechanisms to form simple sheet metal parts by manipulating the workpiece using a robotic arm under a repetitive hammering tool. Predictive motion planning based on FEA was analysed and the manual forming skills were captured using a motion capture system. This facilitated the coordinated hammering and motion of the part to produce the intended shape accurately. A 3D measurement system with a vertical resolution of 50μm was also deployed to monitor the formation of the parts and make corrections to the forming path if needed. Therefore, the developed mechatronic system is highly adjustable by robotic motion and was closed loop via the 3D measurement system. The developed automated system has been tested rigorously, initially for bowl shape parts to prove the principle. The developed system which is 98% repeatable for depth and diameter, is able to produce targeted bowl shape parts with ±1% dimensional accuracy, high surface quality, and uniform material thickness of 0.95mm when tested with aluminium. It is envisaged that by further research, the proposed approach can be extended to form irregular and more complicated shapes that are highly in demand in various industries

Enhancement of process capabilities in electrically-assisted double sided incremental forming

© 2015 Elsevier Ltd. Electrically-assisted incremental sheet forming (E-ISF) is an effective method to improve formability by introducing the electric current in ISF process. This method is particularly useful for production of lightweight 'hard-to-form' materials such as magnesium and titanium alloys. However, the use of electricity and heat may also lead to side effects to formed components, such as unacceptable surface finish. In this work, an improved E-DSIF process has been developed by combining the electrically-assisted forming technology, the double sided incremental forming (DSIF) and a newly designed slave tool force control device to ensure stable tool-sheet contact. Different types of forming tools and toolpath strategies are explored to improve surface finish and geometrical accuracy by using a customized DSIF machine. AZ31B magnesium alloy sheets are formed into a truncated cone shape to verify the proposed E-DSIF process. In the investigation, the causes of rough surface finish are investigated in detail, and the surface finish is refined by improving the contact condition at tool-sheet interface. In addition, a hybrid toolpath strategy is proposed to further enhance the geometrical accuracy. The results demonstrate that the two challenging issues, surface finish and geometrical accuracy, could be improved by using the enhanced technologies of E-DSIF

Single point incremental forming: An assessment of the progress and technology trends from 2005 to 2015

The last decade has seen considerable interest in flexible forming processes. Among the upcoming flexible forming techniques, one that has captured a lot of interest is single point incremental forming (SPIF), where a flat sheet is incrementally deformed into a desired shape by the action of a tool that follows a defined toolpath conforming to the final part geometry. Research on SPIF in the last ten years has focused on defining the limits of this process, understanding the deformation mechanics and material behaviour and extending the process limits using various strategies. This paper captures the developments that have taken place over the last decade in academia and industry to highlight the current state of the art in this field. The use of different hardware platforms, forming mechanics, failure mechanism, estimation of forces, use of toolpath and tooling strategies, development of process planning tools, simulation of the process, aspects of sustainable manufacture and current and future applications are individually tracked to outline the current state of this process and provide a roadmap for future work on this process

Tekes projekti SuperMachines loppuraportti

Tutkimuksessa kerättiin best practice aineistoa ja kehitettiin internet alusta kerätyn aineiston tutkimiseen ja hakujen suorittamiseen. Aineisto löytyy internet osoitteesta: http://www.amcase.info/. Rekisteröitymällä kuka vain voi syöttää alustalle lisää aineistoa. Kappaleiden suunnitteluohjeet on julkaistu Suomen pikavalmistusyhdistyksen sivuilla: http://firpa.fi/html/am-tietoa.html. Ohjeesta löytyy mm. suositeltu minimi seinämänvahvuus, suositellun pienimmän yksityiskohdan koko, tyypillinen markkinoilta löytyvä rakennuskammin koko, sekä tyypilliset materiaalit. Valmiiden kokoonpanojen ja mekanismien suunnitteluun muodostettiin Objet 30 ja UPrint SE+ laitteelle ohjeistus josta löytyy pienin radiaalinen välys, aksiaalinen välys, sekä pienin rako riippuen rakennussuunnasta. Tutkimusprojektin aikana seurattiin alan teknologian kehitystä. Kahden vuoden aikana markkinoille ilmaantui noin. 50 uutta laitevalmistajaa, sekä noin 300 erilaista laitetta, sekä lukuisia materiaaleja. Merkittävimmät uudistukset listattiin ja pohdittiin mahdollisia kehityssuuntia. Kaikki uudet toimijat ja laitteet päivitettiin Firpan ylläpitämään tietokantaan: http://firpa.fi/html/am-tietoa.html. Markkinoilla on selvä suuntaus tuotantokomponenttien valmistamiseen, kotitulostimien hintojen laskemiseen, sekä isompien kappaleiden valmistamiseen. Muovilevy komponenttien muovaamista tutkittiin laserin ja alipaineen avulla DDShape laitteella. Laitteella onnistuttiin tekemään testikappaleita ja laitetta saatiin kehitettyä eteenpäin. Laitteiston kehittämiseksi ja kaupallistamisen tueksi Tekes on myöntänyt "Tutkimusideoista uutta tietoa ja liiketoimintaa" (TUTLI) rahoituksen. ISF mini projektissa onnistuttiin kehittämään edullinen pienten kappaleiden painomuovauskone. Samalla kartoitettiin laitteelle soveltuvat parametrit ja rajoitukset. Laseravusteisella muovaamisella päästään kuparilla isompaan seinämän kaltevuuteen ja pinnalaatu pysyy hyvänä. Teräksellä laserista ei ollut juuri hyötyä ja alumiinilla muovattavuus kyllä parani, mutta pinnalaatu huononi. AM kappaleiden viimeistelykoneistuksessa tutkittiin muovisten kappaleiden viimeistely jyrsimällä, sekä metallikappaleiden automaattista hiontaa. Jyrsinnässä vertailtiin eri menetelmillä tehtyjä kappaleita, sekä mitattiin kappaleiden mittatarkkuutta ja geometrisia toleransseja. Huonosta kotitulostimella tehdystä kappaleesta on vaikea saada hyvää kappaletta vaikka se viimeisteltäisiin koneistamalla. Suurimmat ongelmat liittyvät kappaleiden vääntymiseen johtuen lämpöjännityksistä valmistusprosessin aikana. Kappaleiden automaattisessa hionnassa parhaat tulokset saatiin DMLS kappaleille käyttämällä hionta-aineena teräshauleja ja pyörittämällä niitä hiottavat kappaleen kanssa rummussa. Ra arvo parani tällöin noin seitsemästä mikrometristä kolmeen mikrometriin

On the manufacturing of highly-customized near net-shape medical implants using magnesium alloy sheet

Incluída en Procedia Manufacturing 50The purpose of this work is defining a global methodology framework for the manufacturing of medical implants using Mg alloys by Incremental Forming process from the results attained by the authors in this field. The methodology proposed considers two main steps, an indispensable related to material characterization that includes from the classical and mechanical to spifability testing and it includes numerical simulations. And another one related mainly to implant forming taking into account the best process parameters from the analysis carried out in the previous step. As newness, two variants of the incremental forming process, Single (SPIF) and Two-Point (TPIF) Incremental Forming, are used for the same magnesium implant geometry. Different outputs variables, mainly: Ra, Shape accuracy and Thicknesses, besides Force and Temperature were analysed for comparison purposes.Universidad de Girona MPCUdG2016 / 036Ministerio de Educación, Universidad e Investigación (Italia) CUP - D94I18000260001Ministerio de Educación (España) DPI2016-77156-

NUMERICAL SIMULATION OF SINGLE POINT INCREMENTAL FORMING FOR ASYMMETRIC PARTS

Single point incremental forming (SPIF) that will produce non-symmetric sheet metal parts has been rarely dealt with so far. SPIF of a Francis hydro-turbine vane made of aluminum alloy is studied as a typical example in this work. At first, a concave geometry, encompassing the desired vane shape is designed, from which the formed part will be ultimately cut out. The necessary SPIF toolpaths are created by using the CAM software normally used for milling processes. Based on these toolpaths, a finite element simulation is setup using shell elements with a particular emphasis on substantial time scaling and due care on tool-sheet contact parameters. For validation purposes the part was manufactured and digitized by a white light scanner. It exhibited tolerable deviation from the targeted nominal geometry. Simulation predicted a significant part of this deviation, proving its indispensability in checking out toolpaths and process parameters for non-symmetric parts, yet at non-negligible computational time