Die Design Fundamentals. Vukota Boljanovic
begin to draw, they must seriously consider a number of things. It is now possible for them to list all the items that will be required so they can begin designing intelligently. These items are:
•The part print
•The tool operation sheet, or route sheet
•The design order
•A press data sheet.
In addition, designers may have either a reference drawing of a die similar to the one they are designing or a sketch of the proposed design prepared by the chief tool designer or group leader suggesting a possible approach to solving the problem. Let us consider further the information required:
Part print. The part drawing gives all necessary dimensions and notes. Any missing dimension must be obtained from the product design department before work can proceed.
Operation sheet. The operation sheet or route sheet must be studied to determine exactly what operations were previously performed upon the workpiece. This item is very important. When the views of the stamping are laid out, any cuts that were applied in a previous operation must be shown.
Design order. This item must be studied very carefully because it specifies the type of die to be designed. Consider particularly the operation to be performed, the press in which the die is to be installed, and the number of parts expected to be stamped by the die. The latter will establish the class of die to be designed.
Press (machine) data sheet. The die to be designed must fit into a particular press and it is important to know what space is available to receive it and what interferences may be present.
In time you will come to realize the importance of careful and repeated study of the part print, operation sheet, and design order because there can be no deviation from the specifications given.
a) Die Drawing
If the information on a drawing is complete, concise, and presented in the simplest possible manner, the die maker can work to best advantage. The first step in originating plans for a new die is to prepare a sketch or sketches of significant features of the proposed die. These are a guide for beginning the actual drawing of the full-size layout. However, it is a mistake to spend too much time in this phase of the work or to try to develop the entire design in sketch form because doing so can result in arbitrary and inflexible decisions.
Always keep your mind open to possible improvements as you develop the design in layout form. You will often find that the first or second idea sketched out can be considerably improved by alteration as work progresses. Often the first idea proves entirely impractical and another method of operation must be substituted.
Before beginning the sketch, gather before you the part print, operation sheet, and design order. The three must be studied together so that a complete and exact understanding of the problem will be realized. This study will form the basis for creating a mental picture of a tool suitable for performing the operations—one which will meet every requirement. The sketch you make may be a very simple one, for simple operations, or it may be more elaborate. In fact, a number of sketches may be required for more complex operations and intricate designs. In any event, the sketch will clarify your ideas before you attempt a formal layout. In addition, it will form the basis for a realistic estimate of the size of the finished die so that you may select the proper sheet size for the layout.
Layout. Laying out the die consists of drawing all views necessary for showing every component in its actual position. In the layout stage, no dimensions are applied and neither is the bill of material nor the record strip filled out. After the die has been laid out, the steps necessary for completing the set of working drawings are more or less routine.
Assembly drawing. A properly prepared assembly drawing contains six general features:
1.All views required for showing the contour of every component including the workpiece.
2.All assembly dimensions. These are dimensions that will be required for assembling the parts, as well as for machining operations to be performed after assembly.
3.All explanatory notes.
4.Finish marks and grind marks to indicate those surfaces to be machined after assembly.
5.A bill of material listing sizes, purchased components, materials, and number (quantity) required for all parts.
6.A title block and record strip with identifying information noted properly.
Detail drawing. After the assembly drawing of the die has been completed, detail drawings are prepared, unless all dimensions were previously placed on the assembly drawing (as is done for simple dies). Detail drawings are drawings of individual components. They contain all dimensions, notes, and supplementary information so that each part can be made without reference to the assembly drawing or to other detail drawings. Such information usually includes 10 distinct elements:
1.All views required for identifying every detail of the part must be drawn.
2.Every dimension needed for making the part must be given.
3.Suitable notes for furnishing the supplementary information that dimensions do not cover must be applied.
4.Finished surfaces must be identified.
5.The name of the part and its number must be given.
6.The material from which the part is to be made must be specified.
7.The number of each material required per assembly must be stated.
8.The scale to which the drawing has been laid out must be listed.
9.The draftsman’s name or initials must be signed.
10.The date must be specified.
Dimension and notes. With the die design completed, all dimensions and notes are applied to the drawing. Figure 1.24 shows the die set note, which tells the die maker exactly what die set to order and gives required information about punch shank diameter, type of guide bushings, and diameter and length of guide posts.
Figure 1.24 A typical die set note.
b) Checking the Die Drawings
After a set of drawings has been completed and the designer has reviewed them for possible omissions or errors, the set is turned over to the group leader, who will bring it to the checkers for further review. The design order, part print, and any notes or sketches that may have accompanied the drawings when the designer first received the job will now travel with the drawings. Checkers require all of these in order to do their work properly.
Checkers first study the operation of the die to make sure that it will function properly and that its cost will not be excessive for the work it is to perform. After they are satisfied that it has been designed properly, they will check every dimension, note, and specification for accuracy. They usually work from a check print. This is a blue and white print having blue lines and a white background. With a yellow crayon, they will cover every dimension they find to be accurate, and with a red crayon they will cover every dimension they find to be wrong. Above or to the side they will write the correct dimension in red.
The tracings, along with the check prints, are then returned to the designer for correction. Incorrect dimensions are carefully erased to remove all graphite from the paper. An erasing shield is ordinarily used to prevent smudging of other dimensions or lines. Correct dimensions are then lettered in place.
After the tracings have been corrected, they are returned to the checkers, who review the job again to make sure that no correction was overlooked. They then sign the drawing in the space provided and enter the date the drawing was checked.
After drawings have been completed and checked, they must be approved by the chief designer, chief tool engineer, and possibly the plant superintendent and others who are held responsible