Technology to Improve Competitiveness in Warm and Hot Forging: Increasing Die Life and Material Utilization
The main thrust of this research was on improvement of profitability in industrial warm and hot forging processes by increasing die life and material yield. Firstly, the root causes of die failure and material loss were identified by developing "fishbone" (Ishikawa) and interaction diagrams. Using an example hot forging process, finite element (FE) simulation techniques were developed for determination of die-workpiece interface conditions at start-up and under steady-state production. Unlike current simulation practice of analyzing only the deformation stage, these techniques used production cycle-time data to analyze an entire forging cycle (die chill, deformation, dwell and lubrication stages). Start-up conditions were analyzed by considering the first forging cycle, whereas steady-state conditions were predicted by simulating multiple cycles. This methodology was used for selection of alternative die materials through prediction of their thermal fatigue performance. Preform and finisher die designs were developed for reduction of contact time and relative sliding. Production trials showed 50% reduction in scrap rates with significantly reduced thermal fatigue on the critical regions of the die.
Analysis methods were developed for the design of shrink-fit dies, with ceramic or carbide inserts, in the context of warm forging (upsetting and forward extrusion). Current design practices neglect the loss of compressive pre-stress resulting from thermal expansion during pre-heating and forging. In this study, simulation techniques were developed for analysis of different pre-heating methods. The sensitivity of the pre-stress to dimensional variations of the die components was also analyzed. Thus, the corrections and process changes necessary to maintain the inserts under compression (at start-up and steady-state) were determined. Carbides and matrix high-speed steels were recommended, with modified pre-heating methods, for improved wear and thermal fatigue resistance.
An FEA-based design and optimization sequence was developed for improvement of material yield in multi-stage hot forging processes. Using volume distribution analysis, a 15% improvement in material yield was obtained for an example process through preform optimization alone. An additional 3-4% improvement was predicted through optimization of the blocker die design.
The desired solutions were, thus, developed through mutually-beneficial alliances with the US forging industry. The application of the developed methods in an efficiently managed production environment will enable US forging companies to achieve and maintain a competitive edge in the global marketplace.
School:The Ohio State University
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:forging shrink fit dies die wear thermal fatigue preform design finite element analysis lubrication
Date of Publication:01/01/2008