The impact of liquid drops onto a solid surface, both dry and wet, has been quite well characterized in the literature. However accurate information is still missing about the physics of the relevant phenomena when multiple drops impinge successively onto a solid which is a quite ubiquitous phenomenon in ink-jet printing. In a previous work, the authors have studied the fate of an incoming drop impinging in an axisymmetric manner onto another droplet resting under steady state conditions on the substrate. This situation which is much easier to perform experimentally was also chosen as a test case for studying the coalescence of two drops and some preliminary results have been given.In this paper, the previous work is extended to rather quite frequent cases in digital printing, such as miss hit and/or the mixture of colors when printing on impervious substrates. For this purpose, a new set-up was built consisting of at least two multi-nozzle printheads mounted on translation and rotation tables which can be used to simulate different printing situations. The experimental methods are based on visualization techniques such as high speed cinematography for large drops and phase controlled ultra short snap shots of the impact process when micro-sized drops are used. The experiments are performed at low enough velocities and the emphasis is now given to asymmetric configurations.Image processing with specific algorithms helps to delineate the contour of the merging drops and to follow accurately the drainage of the interface film and the subsequent coalescence process. The experimental results are shown to compare favourably with theory for drops colliding at low velocity. Experiments close to actual operating conditions are also performed and the merging behavior is detailed for both axisymmetric and non-axisymmetric configurations. Finally the stability of the printed pattern is analyzed and discussed with relevance to the spreading behavior of drops on differently wetting substrates.