Research On Availability-Based Product Warranty And Its Maintenance Optimization

With the fierce market competition,manufacturing enterprises are facing various challenges,including more complicated structure and function of the product,shorter product research and development cycle,higher frequency of products' updating and replacement.Under this background,the customer also puts forward higher requirements on products' quality and reliability,and the attractive warranty clause has become an important tool for product marketing.Existing researches on warranty management predominately focus on warranty policies for standard products,such as free repair/ replacement warranty,pro-rata warranty or combination warranties policies.For such kinds of engineering equipment,including CNC machine tools,wind turbines,engineering machinery,etc.,they are expensive and usually key equipment for their users,and their failure or shutdown may result in substantial production loss.Thus,availability is important performance for these kinds of equipment.In order to satisfy users' high availability requirements for such products,the research on availability-based warranty has received attention in recent years.Based on theories of one-dimensional warranty,twodimensional warranty and maintenance service contract,etc.,this thesis focuses on the actual availability requirement of engineering equipment,and carries out the research of availability-based warranty and its maintenance optimization.The main achievements are as the follows:(1)An availability-based warranty policy is investigated from the manufacturer's perspective.Imperfect preventive maintenance(PM)activities are implemented to reduce the number of equipment failures,so as to meet product's availability requirement and minimize warranty servicing cost during the warranty period.A hybrid hazard rate model is used to describe imperfect PM actions;maintenance plan and warranty servicing cost are optimized by considering learning effects.PM schedule within a warranty period is optimized cycle by cycle,and the warranty cost rate is minimized under the requirement of availability within each cycle.The results show that by considering learning effects on maintenance,the equipment can maintain a higher availability level with a lower warranty cost than the case without consideration of learning effects.(2)A two-dimensional(2D)availability-based warranty policy is investigated from the view of the manufacturer.Under the policy,the manufacturer guarantees a negotiated availability level of products during the warranty period,with the exception of providing repairs or replacements upon failures.This study aims to meet products' availability requirement with the lowest cost by optimizing 2D PM strategy.Moreover,customized PM programs are designed for different customer categories.The results show that compared with age-based or usage-based PM strategy,2D PM strategy is superior in terms of warranty cost and operational availability.(3)An availability-based maintenance service contract is investigated.A two-stage warranty model is established that includes basic availability-based warranty and maintenance service contracts,and three different maintenance service options are provided to meet customers' different needs after the warranty expired.In the first stage,manufacturers optimize PM schedules to ensure products' availability level with the lowest service cost.In the second stage,with the objective to maximize the benefit of the manufacturers,manufacturer's revenue and customer's cost under different service options are compared.The results show that the service contract combined with overhaul and PM can not only significantly increase the availability level of the warrantied equipment,but also benefit to both the transaction sides.The contributions of this thesis lie primarily in the systematical investigation of availability-based product warranty and its maintenance optimization,and also in the new ideas on availability-based warranty policy,learning effects,2D PM,customized PM and availability-based maintenance service contract.This research promotes the development of availability-based warranty theory,and it also provides theoretical guidance for manufacturers to meet customers' availability requirements.