tailieunhanh - 21st Century Manufacturing Episode 2 Part 7

Tham khảo tài liệu '21st century manufacturing episode 2 part 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 314 Metal-Products Manufacturing Chap. 7 where d grid circle diameter before pressing dị major diameter of ellipse after pressing dị minor diameter of ellipse after pressing It is frequently more convenient to express the resulting principal strains in terms of engineering rather than true or natural strain definition that is d di - d e and e2 -i d d If the analysis is made for the circles immediately adjacent to necked or fractured regions a plot of major strain ej against minor strain e2 will yield a curve that separates the strain conditions for successful pressings from those that result in weakness or fracture . forming limits will be established . Thus as indicated in the experimental press shop data of Figure safe regions and fail regions for different materials and thicknesses can be established. It is informative to consider some day-to-day uses of the forming limit diagram. The die setter can quickly determine from a single pressing on a gridded sheet whether a new component with its given set of tools is going to be easy bard or Minor surface strain Figure 731 Forming limit diagram. Different sheet thicknesses shown on right data from Rose 1974 . Management of Technology 315 impossible. Then it might be possible to argue quantitatively for a design modification or a change of material. Or as discussed previously it might be possible to move from failure to success by increasing one of the strain components through a slight change in die geometry. In many cases special lubricants containing molybdenum disulfide can be locally applied to critical areas of the pressing just to change the strain distribution near potential thinning and fracture points. In a different scenario it might be found that the material being used is too good and that a cheaper grade of sheet could be introduced. By keeping a satisfactory reference pressing the die setter can also locate a source of trouble if later on in the production run the press gets out of .