The primary information usually received when receiving an RFQ for a stamped part is a part drawing that specifies the complexity of the part, material, precision requirements and monthly/yearly volumes needed. The part size, complexity and material specs of course determine the size and complexity of the die required, so a strip layout is the first best step in determining tooling costs.

All of the engineering problems involved in stamping a part to print from a strip of coil stock need to be considered and solved at this stage. The required precision of the finished stamping must be considered, starting with the control dimensions and tight tolerance dimensions on the part that will dictate the operations and their sequence. The strip layout can be done in a 2D drawing but a 3D model is always more revealing. It helps to visualize exactly what the strip layout will look like rather than having to assemble such an image in your mind from 3 or more projected 2D views. It is in the strip layout where the part is broken down into a sequence of operations ordered in such a way that all features and tolerances can be controlled. Once the sequence of operations is established, idle stations can be inserted where necessary. Once completed, the die set size, and tonnage requirements can be calculated that dictates some of the Press requirements.

The questions of dimensional control, the demands of volume and precision, and strip control should all be addressed by the strip layout. Part dimensions that are unrealistic should be addressed with the aim of a part print revision.

Once having settled upon a stamping process that you are satisfied with, it is a good idea to give your client the opportunity to review the strip layout, suggest improvements and/or sign off on it. And by the way, this is another good reason to present a 3D model of the strip layout. After all, your client hasn't been staring at these lines for hours like you have, and a 3D model will give your client an immediate apprehension of your concept and how you intend to insure parts to print.

The concept design stage for me, is a complete 3D die assembly design, including all screw and dowel holes because even the quantity and placement of screws and dowels are an integral part of the design concept. The Die is designed around the strip layout, from the inside out and often times it is something as simple as needing room for screws and dowels that will force the need for an idle station.

Since all of the manufacturing process questions have been already addressed in the strip layout, now is the time to consider the effects of required production. Does the volume requirement dictate that the Die must be designed to be serviceable in the Press? If so, then every working section must be designed for easy removal and service. Every punch must be easily removed for service. If there are heavy stripper plates they will need removable windows for access to punches, etc.

At this stage in the design process, all the pertinent force calculations need to be done to determine blanking, stripping and forming pressures. Unequal side thrust forces will have to be counter-balanced because this is not the job of the guide pins in the die set.

Also, at this stage there is the matter of considering the Press that this die will run in. The main considerations are tonnage, die space, feed height, shut height and target strokes per minute. The main issues affecting die costs are part size, material, precision and volume. Part size just dictates how big a die will be, but material, precision and volume affect the complexity of the die and whether or not premium steels and/or treatments will be needed.

For high precision dies it may be necessary to guide punches, which means you may need to guide the strippers as well. For dimensions that can change as the stock in the coil changes, it may be necessary to make location adjustments on the fly. If you have holes with tight tolerance hole positions affected by bends, it may be necessary to use cam-punches to pierce after forming to guarantee dimensional control.

High volume means high maintenance and/or premiums materials and surface treatments that will stand up to high volume production. Higher volume also suggests higher press speed, higher feed rates and the need for electronic die protection. Stock lift and feed through the die needs special attention and this is probably one of the most overlooked features of die designs. Every movement of the stock strip needs to be controlled and accurately registered in location while at the same time offering as little resistance to feed movement at possible. It is popular these days to use gas springs for everything in a die including stock lift, but gas springs do not have as fast a return rate as coil springs do and therefore there coil springs are sometimes superior to gas springs in a high speed press. Also to be considered in a high speed stamping operation is punch shoe and stripper plate weight. Light materials present less mass to accelerate and for this reason, aluminum die sets and stripper plates are sometimes preferable. All wear surfaces in the die should be inserted as well, both for ease of mainenance and economy. In a high volume press tool, in-press replaceable items insure less down time.

Pitch sensors, part out sensors, slug pulling sensors, even dimension check sensors can be built into a die, but this expense is not usually considered except when production volume prohibits down time. Once upon a time, all that was available was a misfeed detection pilot. It was not very effective since it could not sense a misfeed and stop the press before damage was done. Now with the use of proximity sensors, a misfeed can be detected and the press stopped while in the up-stroke thereby preventing any damage that might occur in the next stroke.

I use Solidworks personally for die design. This means that by the time I have completed and revised my concept design, I have a complete solid model die design. Hence, all that is needed is to generate the 2D drawings, add dimensions, notes, and a bill of materials. Furthermore, since the design was completed as a 3D assembly model, I have every detail in the die available as it's own 3D model that can be imported directly into CNC programming software for machining.

No die design can be adequately documented with paper drawings anymore. These are essential for documentation, but for producing the die components that do the work, 3D models have become essential. Often I am asked just to send the paper drawings in pdf format and the solid models in some other usable format, usually parasolid, step or iges. I am sometimes asked for dxf formatted drawings but this is rare anymore.

There are always updates and/or revisions. Any pre or post-construction changes should be made on the original 3D assembly model. If this is done correctly, all of these changes will automatically update the 2D drawing files and the 3D component models. This is so important that I offer FREE updates on all my designs. It is just always true that when the die construction and development is in process that changes are made, either to facilitate manufacture or to improve the tool. There will be updates, and these should be incorporated into the original die design. The die design you have in your file should be true to the die you have in your press. Sadly, and to the chagrin of your toolroom, this is too often neglected.

Machine tool design should always be a team effort. People from the engineering dept., toolroom, and pressroom should be involved in every design project. A company should know that it will cost less in the end if they do not rely on the expertise of just one person to design a machine tool that they are going to have to live with for a long time.

There should be a team review of the strip layout before the die concept design is started. There should be a thorough team review of the die concept design where every party has the opportunity to review the design individually to make notes, before the team review meeting. This review can be done online. Webex or Netmeeting have made it possible to have an effective design review meeting online. Finally, there should be one more review after the final design is delivered because this is the first time they will have seen the bill of materials. There are often issues with purchase item selections or sources that should be addressed at this time.

Finally, every company should have their own set of design standards. Every company has their preferences and toolroom standards and these should be written, kept up to date, and in the hands of your design team. The bottom line is always the issue, and the more problems resolved at the design stage of any project is going to result in less cost and more profit.