Crystallinity control in parts produced from stereolithography injection mould tooling

Abstract

• This is an article from the journal, Proceedings of the Institu- This item was submitted to Loughborough's Institutional Repository (https://dspace.lboro.ac.uk/) by the author and is made available under the following Creative Commons Licence conditions.For the full text of this licence, please go to: http://creativecommons.org/licenses/by-nc-nd/2.5/ Crystallinity control in parts produced from stereolithography injection mould tooling R A Harris*, R J M Hague and P M Dickens Rapid Manufacturing Research Group, Loughborough University, Loughborough, UK Abstract: The use of moulds produced by stereolithography (SL) for injection moulding provides a quick route to manufacturing a low volume of parts without expensive hard tooling. However, these parts have been shown to exhibit different material property characteristics than those produced from metal tooling. The aim of the present work is to research methods that would allow SL moulds to produce parts of similar material property characteristics to those from conventional metal tools. This work has identi ed that the different part characteristics are due to differing levels of crystallinity developed in the parts from the comparative mould varieties (SL and metal). These crystallinity differences have been associated with the cooling rates imparted owing to the thermal properties of the mould material. The latter part of this work concerns controlling and manipulating this degree of crystallinity. After a discussion of possible methods, two approaches are taken to modifying the crystalline content of parts produced by SL moulds. One of the approaches is material based, the other concerns the injection moulding process. Differential scanning calorimetry (DSC) is used to quantify the resulting levels of crystallinity in the parts. The results show that by process modi cation it is possible to produce parts by SL moulding that possess a similar crystalline content to those moulded from metal tooling. The use of modi ed materials allows parts created in SL and metal tools to be of a consistent crystalline content. The work concludes that not only are SL moulds capable of producing parts that are more like those from metal moulds but also present some unique opportunities that have been demonstrated to be unachievable in metal moulds.

Comparative study of rapid and conventional tooling for plastics injection molding

“…In spite of using a cycle time over four times longer than the steel and DMLS inserts, the PolyJet inserts exhibited considerably higher temperatures. Similar results were found by Harris et al (2003) for polymeric SLA tools compared to metallic aluminum tools.…”

Direct polymer additive tooling – effect of additive manufactured polymer tools on part material properties for injection moulding

“…Further, a difference in shrinkage using amorphous Acrylnitril-Butadien-Styrol-Copolymere (ABS) could not be observed suggesting special caution for shrinkage compensation when crystalline polymers are used. Harris et al (2003b), therefore, proposed two approaches to control crystallinity behaviour in parts from SL tools. First melt temperature alteration was used to lower the possible melt temperature resulting in a lower crystallinity in PA66 parts from SL tools.…”

Materials analysis of stereolithography resins for use in Rapid Manufacturing

“…The heat input and temperature rise for the material under test is compared to those for the comparison pan while both are subjected to constant linear temperature increase. The results from these measurements allow the heat flow to be plotted as a function of temperature that can indicate the periods of thermal transition of the sample material [20]. The apparatus used was a modulated DSC machine by TA Instruments, model 2920 [21].…”

“…The temperature range of the DSC analysis used was 10 to 170•C with a heating rate of 10•C/min. The recommended weight for each DSC analysis sample was 5-20 mg [20].…”