In the injection molding process, the cooling step is the most inefficient and time consuming phase. Moreover, the cooling of the product often leads to defects such as unexpected warp due to unevenly distributed cooling in the mold. These conditions can be attributed to the classical manufacturing techniques for injection molds as drilling, milling and EDM. The major drawback of these techniques is their inability to produce 3D curved cooling channels, preferably parallel to the product wall. In the present study, the Selective Laser Melting (SLM) 3D printing technique is used to overcome these limitations. Moreover, SLM printed materials have superior material properties compared to Selective Laser Sintered (SLS) molds . Via numerical simulations and experimental measurements on existing molds, the original situation is characterized. Important parameters like average mold (surface) temperature, temperature gradients, cycle time, time to reach steady state condition, etc… are determined. Conformal cooling and SLM printing both have important constraints which are described in literature. In this study, different than in most other studies, constraints of both techniques as shape, max. diameter, overhangs,… are taken into account to develop mold inserts in order to obtain a conformal cooled core and cavity insert. Thermal and Moldflow simulations are combined to optimize the design of the conformal cooling channels in the core and cavity inserts. Also CFD simulations were used to optimize the flow distribution and pressure drop in the cooling channel itself. With these simulations, improvements on the process (times and temperatures) and on the product (warp) were obtained. The conformal cooled inserts were printed in maraging steel and extensively tested including in-mold temperatures measurements. Simulations and measurements showed a good agreement. Finally an economical study was made to determine the profits resulting from the conformal mold.