Factories become increasingly dependent on network connectivity. The next generation of mobile communications, 5G, will enable better flexibility and service quality through network slicing. Network slicing is a means of creating logically separated use case specific virtual networks over the same physical network. However, there is a lack of techno-economic research related to the management of network slices. Network slice management needs to take into account the multiple network domains, business actors and value networks involved in a vertical such as smart factories. The key for network slices to succeed where other resource reservation and quality of service technologies have previously failed is with well-defined feasible management models and strategies. In this paper, we focus on network slice management, possible strategies and implications for a smart factory. We study a state-of-the-art electronics assembly factory in Finland to find existing need for network slicing and missing capabilities to support smart factory use cases. Next, we define use case specific network slices and develop a network slice management model based on 5G specifications. The model allows for distribution of network functions between business actors over multiple network domains. The value network analysis method is utilized to develop alternative configurations that constitute the network slicing strategies facilitated by the model. Factory managers can decide on the most feasible strategy based on traditional factors such as make or buy, security, and level of automation. The strategies also differ in their technical applicability to different use cases. A feasibility study reveals the strategic differences from factory, local network operator and large mobile network operator perspectives.