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Additive manufacturing is becoming more and more important today by offering very advantageous opportunities. It gives the ability to manufacture parts with complex geometry, without the need of specific tools. This work focuses on fused filament fabrication process. It consists in melting the polymer, and extruding it through a nozzle to create a structure defined by a toolpath. The extruded filament solidifies while cooling. One of the major drawbacks of this process is the poor mechanical properties of the parts compared to thermoplastic injection. This is related to (i) the porosities between deposited filaments and (ii) the limited adhesion between deposited layers. This adhesion phenomenon is thermally driven by the molecular mobility of the polymer chains. The objective of this work is to understand, model and quantify heat exchanges in the process, in order to define the process window leading to optimal mechanical resistance of the parts. With this aim, a laboratory-scale instrumented 3D printing machine has been designed and manufactured. This bench is thermally controlled. Polymer and environment temperatures can be measured with an infrared camera, pyrometer and thermocouples instrumentation. In parallel, a numerical model has been developed to predict the influence of the process parameters on the cooling and adhesion. For this purpose, thermal properties have been characterized. A sensitivity analysis quantifies the most relevant properties to measure and control accurately and a comparison between numerical and experimental results validates the approach.