The industry 4.0 defines a new era of much efficient and intelligent manufacturing processes that works in integration with other advanced technologies like AI, Big data, Block chain, etc. The smart manufacturing industry has remarkably evolved due to integration of advanced technologies like cyber-physical systems (CPS), Internet of Things (IoT), digital twins that makes up a highly connected infrastructure where data flows in real time. However, the involvement of these technologies has also significantly increased the exposure of manufacturing industry to the cyber threats. This article investigates several security challenges and major threats that are associated with the manufacturing industry. It evaluates various security implementations including digital twins, machine learning, and block chain based on their effectiveness, scalability, and feasibility in terms of security. Through a comprehensive literature review, case study analysis of notable cyberattacks and qualitative exploratory methods, this study explores the best line of defence against the cyber threats. Our findings highlight the critical role of robust and adaptive multiple line of defense mechanisms in mitigating cyber risks. The research concludes by emphasizing the need for an effective security strategy that combines advanced technological solutions with continuous employee education and proactive threat management to safeguard smart manufacturing processes against evolving cyber threats.