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Parting tips for dies.

The parting of die plates or punches into sections is one of the most challenging problems in the design of sectional pressworking dies. Success calls for using all your design experience and ingenuity, but it helps to keep in mind these commonsense rules, tested and proven over many years of actual practice:

* Regular shapes. Each component part, section, segment, or insert should have a basci cross-sectional shape that is square or at least rectangular.

* Minimal machining. It is best to make the division so that only one section needs to be machined while the others are straight or need very 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 heat treating easier, Figure 2.

* Alignment. Try for the best alignment, centering, and matching of die shapes, Figure 3.

* Divisions at corners. Locate divisions where there are sudden changes in cutting contour--the shapr corners of die openings, Figure 4.

* Symmetry. Sections should be symmetrical wherever possible. The center line or axis of symmetry should also be the parting line so that both halves of the die plate will be exact, mirror images, Figure 5. With multiple dies and identical openings, simultaneous machining operations can produce considerable savings, increase uniformity, and simplify broken-section replacement.

* Simple sections. In dies with irregular cutting contours, to make each die section as simple as possible to simplify machining and heat treatment. This simplification can make the die section cutting-contour lines straighter or arcs with larger radii, Figure 6.

* Die angles. Make breaks so that the included angle of the cutting edge is never acute. Right angles are okay (certainly popular), but obtuse angles are optimum, Figure 7. Locating parting lines either along or at right angles to cutting-contour lines easily avoids acute angles.

* Corner radii. Breaks should never be made through a corner radius, even for the slightest radii, Figure 8. Separate at a point outside the arc to eliminate machining two curved corners instead of one and the difficulty of making them match. If a break or curve cannot be avoided, make the parting line at a right angle to the tangent line, Figure 5.

* Limit size. With large tools, try to keep single sections no longer than 10" to 12" to avoid heavy distortions in heat treatment.

* Machining access. With complicated contours, always take into account machining difficulties such as cutting-tool accessibility. This may mean making sections shorter (more breaks).

* Punch holding. Composite punch sections must be held together by a punch-holder plate, which will be thicker than for solid punches (by up to 1-1/2" or 2/3 of punch length). The receiving hole for the punch assembly must be carefully machined so the sections lock together safely, tightly, and accurately. This can be a press fit or even a shrink fit.

* Avoid coincidence. When both punch and die plate are sectional, it is important to keep the joints of the punch sections from coinciding with the joints in the die plate, Figure 9. an offset of as little as 3/16" is usually sufficient.
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Author:Strasser, Federico
Publication:Tooling & Production
Date:Jan 1, 1985
Words:520
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