The parting of die plates or punches into sections is one of themost challenging problems in the design of sectional pressworking dies.Success calls for using all your design experience and ingenuity, but ithelps to keep in mind these commonsense rules, tested and proven overmany years of actual practice: * Regular shapes. Each component part, section, segment, or insertshould have a basci cross-sectional shape that is square or at leastrectangular. * Minimal machining. It is best to make the division so that onlyone section needs to be machined while the others are straight or needvery little machining, Figure 1.
* Few divisions. Keep divisions to a reasonable minimum. However,it may be better to make one more division if it makes machining or heattreating easier, Figure 2. * Alignment.
Try for the best alignment, centering, and matchingof die shapes, Figure 3. * Divisions at corners. Locate divisions where there are suddenchanges in cutting contour–the shapr corners of die openings, Figure 4. * Symmetry. Sections should be symmetrical wherever possible.
Thecenter line or axis of symmetry should also be the parting line so thatboth halves of the die plate will be exact, mirror images, Figure 5.With multiple dies and identical openings, simultaneous machiningoperations can produce considerable savings, increase uniformity, andsimplify broken-section replacement. * Simple sections. In dies with irregular cutting contours, tomake each die section as simple as possible to simplify machining andheat treatment. This simplification can make the die sectioncutting-contour lines straighter or arcs with larger radii, Figure 6. * Die angles. Make breaks so that the included angle of thecutting edge is never acute.
Right angles are okay (certainly popular),but obtuse angles are optimum, Figure 7. Locating parting lines eitheralong or at right angles to cutting-contour lines easily avoids acuteangles. * Corner radii. Breaks should never be made through a cornerradius, even for the slightest radii, Figure 8. Separate at a pointoutside the arc to eliminate machining two curved corners instead of oneand the difficulty of making them match. If a break or curve cannot beavoided, make the parting line at a right angle to the tangent line,Figure 5.
* Limit size. With large tools, try to keep single sections nolonger than 10″ to 12″ to avoid heavy distortions in heattreatment. * Machining access. With complicated contours, always take intoaccount machining difficulties such as cutting-tool accessibility.
Thismay mean making sections shorter (more breaks). * Punch holding. Composite punch sections must be held together bya punch-holder plate, which will be thicker than for solid punches (byup to 1-1/2″ or 2/3 of punch length). The receiving hole for thepunch assembly must be carefully machined so the sections lock togethersafely, tightly, and accurately. This can be a press fit or even ashrink fit. * Avoid coincidence.
When both punch and die plate are sectional,it is important to keep the joints of the punch sections from coincidingwith the joints in the die plate, Figure 9. an offset of as little as3/16″ is usually sufficient.