Direct digital manufacturing: projection stereolithography and incremental sheet forming

Pekka Lehtinen

Research output: ThesisDoctoral ThesisCollection of Articles


The drastic development of advanced manufacturing technologies coupled with consumer demands for more customized products are causing the manufacturing industry to move from mass production to small volume and a wide range of products. These kinds of requirements are met by direct digital manufacturing (DDM) techniques that seamlessly produce three-dimensional objects directly from digital data in a single step regardless of the complexity of the products to be built. DDM techniques include additive manufacturing and forming techniques where highly specified products are fabricated in layers. Due to the high versatility of DDM systems and low tooling costs, DDM is outstanding in one-off production. However, DDM is still an immature technology that will make a real impact across a large range of industries as it is developed further. This thesis aims to develop two DDM techniques: (i) projection stereolithography and (ii) incremental sheet forming. While the first one is an additive manufacturing technique where a plastic part is fabricated by selectively curing liquid polymer in layers, the second one is a metal forming technique where the desired shape is created through a series of small incremental deformations. First, a projection microstereolithogarphy apparatus that can produce high quality miniature objects with a resolution of a few micrometers was built and some specific issues related to the printing process were solved. The research involved increasing the manufacturing speed, developing suitable polymer solutions (resolution, conductivity, biocompatibility, penetration depth control), and providing new insight and methods to control the curing mechanisms of liquid polymers. Secondly, the effect of local heating on the formability of metal sheets in incremental sheet forming was investigated. In this research, metal sheets were formed by a round tipped tool that was attached to a 3-axis positioning system and the investigated materials were aluminum, copper and steel. To increase the formability of metal sheets, a laser light source was used to irradiate the bottom side of the sheet. With this method it was possible to produce shapes that were impossible to form without heating.
Translated title of the contributionDigitaalinen valmistus: projektiostereolitografia ja numeerinen painomuovaus
Original languageEnglish
QualificationDoctor's degree
Awarding Institution
  • Aalto University
  • Kaivola, Matti, Supervising Professor
  • Partanen, Jouni, Supervising Professor
Print ISBNs978-952-60-7619-5
Electronic ISBNs978-952-60-7618-8
Publication statusPublished - 2017
MoE publication typeG5 Doctoral dissertation (article)


  • stereolithography
  • projection stereolithography
  • photopolymers
  • incremental sheet forming
  • 3D printing
  • direct digital manufacturing


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