The effect of scanning strategy on laser fusion of functionally graded H13/Cu materials

Abstract

In recent years, research has been undertaken on manufacturing of functionally graded materials (FGM) using layered manufacturing technologies (LMT), also commonly known as rapid prototyping (RP), solid free-form fabrication (SFF) etc. The use of LMT to build complex FGM parts could meet optimum engineering design for various applications such as high performance die casting tools. In this context, H13 tool steel is considered a suitable material because of the high resistance to thermal fatigue and dimensional stability. Nevertheless, H13 with a low heat conduction coefficient is not thermally efficient for certain part geometries. With this in mind, the use of functionally graded techniques to disperse copper to specific regions/volumes of a H13 mould could lead to higher performance of the tool. The laser fusion of different proportions of Cu (0, 25 and 50% by weight) powder dispersed in H13 were analysed in this work. Additionally, different laser strategies were used to statistically analyse effects with respect to the composition of Cu. It was found that the refill strategy produces better results compared to all other scanning methods. The H13 with 25% Cu mix produced a homogeneous structure but cracks were observed along the cross section of the 25% Cu specimens. The pure H13 had a lower porosity with fine dendrite structures. The H13 with 50% Cu produced a non-homogeneous structure. This paper also discusses the microhardness tests results with respect to Cu composition and scanning strategy. Also, in order to identify the effect of powder composition layer on the subsequent layers and the cooling rate effect, samples were produced and analysed. One started with 100% H13 and ended with H13+50% Cu while the other started with H13+50% Cu and ended with 100% H13.