Holding everything together
A die block can be defined as a component unit that mates with punches and other components, in such a way, to produce an accurate piece part. There are several factors that affect die block construction.
The four main factors that affect die block design are as follows:
- Part size
- Part thickness
- Intricacy of part contour
- Type of die
Die Blocks can be constructed in several ways. A die block may be made of a single piece or it may be an assembly of several components. When a die block is built in several components this is normally achieved in the following ways:
- The die block serves as a pocket or yoke that encloses the insert and other contours.
- The more common method of building die blocks with intricate parts, is to section the die block into several components. There are advantages to sectioning a die block and using the pocketing method/yoking. Advantages are:
- The toolmaker has greater ability to machine, grind, check, and inspect parts when sectioned
- Insert and section can be easily ground accurately because of the access leading to greater accuracy.
- The part is machined close to size before hardening; this is a more efficient use of equipment and time.
- For die maintenance, because the contours are sectioned, it is much easier to replace broken components.
One-Piece Die Rings
Having a single die block, is the simplest design, especially in a ring die block.
With a simple ring construction of a die block, most ring constructs will have at least 3 dowels for small to medium ring sizes, larger sizes may require more doweling.
There are a few rules that may be helpful to follow for one piece rings.
The toolmaker should be aware to select the appropriate bolt circle pattern. In smaller ring construction, one should space the bolts so they won’t be too close to the wall of the die shoe. To create clearance for a smaller ring the bolts should be built closer to the inside of the ring.
Foolproofing needs to be considered in a round die. Ring proper foolproofing can be achieved by offsetting one of the dies. Another method to fool proofing is making one dowel smaller, just keep in mind, offsetting a dowel requires less time because all dowel holes can be drilled at the same time.
Another method for round work is that a toolmaker can set the ring in the die shoe by boring the pocket to a wring fit or a light drive fit. You don’t want a press fit. This is a strange build design and it is more expansive.
There are 3 main reasons for recessing a die ring in a pocket:
- The material cost which relates to the size of the ring to be built
- Pocketing a die ring allows for easier replacement as the ring is located in a pocket; it may still require dowels for location.
- Interchangeability; ring die blocks may be interchangeable with other components making it a desirable design.
Yoked or pocketed die rings can be made in various ways:
- Plain ring bushing and yoke: The ring fitted in the yoke with a bushing in between, depending on the fit and application both may be necessary.
- Shouldered ring bushing: In this situation, the toolmaker makes the die ring with a shoulder. The shoulder fastens and locates the die ring and, because it is fastened by the die, shoe bolts are not necessary; what is needed are thrust plates in the heavy application.
- Depending on the application, a toolmaker will create a tapered region. This assembly requires press-fit or even shrink fit. For self-holding taper normally 1 to 1 ¾. If there is more resistance to the downward thrust then an 8° to 10° angle, this is self-releasing.
Lands and Sharpening Lands
The cutting face of a die block or section, or even a punch, is called the land. With die maintenance, the land needs to be ground for sharpening. When this happens, it reduces the land of the cutting edge of the tool and, depending on the material being cut and the application, the regrinding and sharpening of the die block reduces the cutting land. A toolmaker has to be aware of the reduction of the landing and act accordingly to support the cutting edges. One may have to shim the components or weld cutting edges.
Section Die Blocks
A sectional die block consists of two or more components. A sectional die block is the most common construction for a die block. Die blocks may be sectional for several reasons. For large die blocks it can be just to ease in manufacturing because of the size. A small die opening may need to be sectioned to allow efficient machining. A complex component may require the block to be sectioned even more. The toolmaker must balance sectioning die blocks for regrinding/ sharpening lands. In some instances sections may even have inserts installed for efficient component replacement. When describing how to section a die, one major factor to consider is the stability and strength of the section.
When a toolmaker is planning the die section, he needs to build the die for the application, so the die is able to withstand the thousands of cycles from the press, with high impact cutting and forming parts, which causes a tremendous amount of force.
The two major forces revolving around punches:
- Direct thrust in the punching motion
- Lateral thrust normally applied at a right angle to the punch
The two answers to direct and lateral thrust a toolmaker has are:
- Tilting: A toolmaker needs to plan a die section so it is self-supporting or supported by a block next to it. A toolmaker must ensure there is not tilting during punching impact.
- Spreading and separating: Because of said lateral forces, the die section will have a tendency to displace.
One effective way to counter spreading and tilting from the punching forces is to cross bolt the die sections to each other. Crossbolting clamps the section securely together and is one of the most cost-effective ways to self-stabilize large die sections. Crossbolting is an effective stabilization method mostly for a die that is bending or not blanking through.
Another effective way of building die blocks to stabilize sections, would be to fit them in a pocket. Pocketing die sections is an appropriate method of confining die sections. When pocketing die sections, they should always be stepped so each section mates with the next. The section should fit with a light force-fit so sections aren’t squeezing each other, but supporting. Having the die section stepped so they mate, is also foolproof for assembly and compensates for imbalanced forces in the die.
When sections are pocketed it is good practice to line the pocket with tooling steel hardened to RC 54-58. Some of the advantages to liners are:
- Liners protect the wall of the pocket from installation of die sections.
- Hardened liners make it faster to assemble a die during the build, because the liners can be ground to fine-tune fitting of sections.
- Liners make for quicker disassembly of a die, because as they are removed first, normally pushed out, releasing the die section.
Sometimes, depending on the application, some dies will require hardened thrust plates in die pockets to support the sections.
Another method of confining a die section to concentrate punching forces in the die block construction, is to assemble the section in a slot. Die sectioning mounted in a slot is ideal when the cutting forces spread to the left and the right as they are self-cancelling in this construction. When using a slot in the die shoe, the toolmaker still uses the bolt to hold the die section, but only one-liner is necessary as there is no corner so pushing out one-liner makes for quick and easy disassembly.
Conclusion
As you can see, die block construction is integral to the die build and, again can be quite varied, but the understanding of lateral forces and hardness and supporting sections are the takeaways. Like the previous articles, this is a summary of the text I was provided in my tooling classes based on my determination of the pertinent information in preparation for my C of Q exam. If you found this useful, please share it and, as always, if you want more articles and other info, subscribe to our mailing list.