Die Design Fundamentals. Vukota Boljanovic
for the cost and quality of dies used in the plant. Usually, these approvals are routine after drawings have been approved by the checker. However, it may sometimes happen that these personnel will refuse to sign because they believe that the die will not work as well as expected, will not deliver the number of parts required per day, will be too expensive to build, or for some other reason. If they convince others that their objections are valid, the drawings will have to be altered or a new design begun, depending upon the extent of the changes to be made.
c) Prints and Distribution
After drawings have been approved, blueprints are made from the tracings, or originals. A small print is taken of the bill of material only. This is sent to the stock cutting department where steel is stored and cut as required. The stock cutter goes over the list, selects bars of proper thickness and width, or diameter, and saws the bars to the lengths specified for each item listed. These cut blocks and plates are placed in a pan, along with screws, dowels, and other parts, which are kept in stock. When purchased components are delivered to the plant, they are also placed in the pan. Finally, the pan contains a set of die prints and a part print and it is delivered to the tool room, where the tool room foreman turns it over to the die maker, who will build the die.
One of the prints is sent to the purchasing department. There, orders are written to authorize purchase of all components needed to build the die. If the entire die is to be built by an outside tool shop, a purchase order is sent to it. If it is to be built within the plant, an order authorizing construction is sent to the tool room. In addition, requisitions are made out for the following:
•Standard parts or assemblies that are not kept in stock and which must be purchased.
•Castings, forgings, or weldments required for construction of the die.
•Steels of special analysis not carried in stock.
•Special sizes of steels or other materials not stocked.
The purchasing agent must plan for delivery of all these components before the date set for beginning construction of the die.
The files for the die drawings—whether electronic or card—are then made out by the die design department. The file contains the number of the drawings and the job by name and number. Each die has only one file.
1.3.4 Tool and Die Inspection Department
After a die has been designed, a set of prints is sent to the tool inspection department. Then after the die has been built, the department will inspect it to make certain that it was constructed to specifications given in the tool print.
When the die is built by an outside tool shop, it is inspected by the tool inspection department upon delivery. The same inspection procedures are followed to determine if the stampings it produces hold to tolerances specified on the part print.
1.3.5 Production
After the tool inspection department has approved its construction and accuracy, the die is delivered to the production department where it will be used. The set-up person for that department installs it in the press where it will be operated. A few sample parts are then produced under the same conditions in which the die will run in actual production. These parts are taken to the production inspection department. There, they are inspected to determine whether or not sizes hold to tolerances specified on the part print.
Once the production inspection department has determined that the samples are satisfactory, a form is issued and signed by the chief inspector authorizing production with the die. After receiving production orders from the production department, the production foreman will proceed to go into production of the stampings. Production orders specify how many parts are to be run, when they will be required, and where they are to be delivered.
After a new die has been in production for a few hours or so, and it is found to perform satisfactorily, the order that was issued to the tool room to build the die is closed. No more time may be charged against it. In this regard, it is worth noting that records are kept of all time devoted to designing, building, inspecting, and trying out the die in order to determine the actual tool cost, illustrating perfectly that “time is money.”
Just exactly what operations are performed in dies? This question is asked often and we have prepared the following illustrated list of the 20 types of operations.
1.4.1 Blanking
Stampings that have an irregular contour must be blanked from the coil or from the strip (Figure 1.25). Piercing, embossing, and various other operations may be performed on the strip prior to the blanking station.
Figure 1.25 A blank and the strip from which it is been cut.
1.4.2 Cut-off
Cut-off operations (Figure 1.26) are those in which strip of suitable width is cut to length. Preliminary operations before cutting off include piercing, notching, and embossing. Although they are relatively simple, many parts can be produced by cut-off dies.
1.4.3 Piercing
Piercing dies pierce holes in previously blanked formed, or drawn, parts (Figure 1.27). It is often impractical to pierce holes while forming or before forming because the holes would become distorted in the forming operation. In such cases they are pierced in a piercing die after forming.
1.4.4 Piercing and Blanking
Compound dies pierce and blank simultaneously at the same station (Figure 1.28). They are more expensive to build and they are used where considerable accuracy is required in the part.
Figure 1.26 Part separated from strip in cut-off operation.
Figure 1.27 Holes pierced in a previously drawn part
Figure 1.28 Part is blanked and pierced simultaneously in a compound die.
Figure 1.29 The result of trimming in a trimming die.
1.4.5 Trimming
When cups and shells are drawn from flat sheet metal the edge is left wavy and irregular due to uneven flow of metal. This irregular edge is trimmed in a trimming die. Figure 1.29 shows a flanged shell, as well as the trimmed ring removed from around the edge.
1.4.6 Shaving
Shaving consists of removing a chip from around the edges of a previously blanked stamping (Figure 1.30). A straight, smooth edge is provided. Therefore, shaving is frequently performed on instrument parts, watch and clock parts, and the like. Shaving is accomplished in shaving dies especially designed for the purpose.
Figure 1.30 The result of shaving in a shaving die.
Figure