Shaving. Shaving is a secondary operation after blanking or piercing. It produces a smooth edge on the workpiece instead of the breakaway edge. This is accomplished by removing only a small amount of stock from the edge of the part. The deformed, fractured portion of the edge is removed, leaving chiplike scrap material and a relatively square and unfractured edge on the part.

Trimming. This method is similar to blanking except that it occurs after forming, drawing, or other operations when extra metal is left in the part for holding or locating purpose or as a stock allowance. The removal of this extra stock is called trimming.

Embossing. Embossing produces shallow surface designs from alternately raised and depressed areas with little or no change in material thickness. Raised areas in the punch correspond to depressed areas in the die. Nameplates and stiffening ribs are two applications. “Designing for Making,” for illustrations of embossed parts and simple embossing dies.

Coining. In this process, the blank is entirely captive within the stamping die. The die squeezes the workpiece under very high pressure, causing the workpiece material to flow into every stamping die depression. Dies of quite substantial proportions and special presses are often required because of the high tonnage involved.

Unlike embossing, coining permits different designs to be imparted on either side of a blank, as is the case with all coins.

Swaging. This process involves an “open” die, also of substantial construction. The part is also squeezed into a cavity, but in contrast to coining, the excess material is not contained but allowed to flow at will.

Knuckle-joint presses are customarily used for both coining and swaging because they combine high tonnage and a slow squeezing action to the workpiece rather than the sharp impact of a conventional press.

Short-Run Methods

General - purpose - equipment methods involve a variety of means for working sheet metal. They differ from conventional metal-stamping processes in utilizing tooling of universal or wide-range applicability rather than dies made for only one operation. They rely on the skill of the operator rather than on tooling for their accuracy. Their production rates are far lower than those of conventional stamping. Common general-purpose sheet-metal processes are the following:

Straight-Line Shearing. This process utilizes two blades. The lower blade is stationary; the upper is movable. Sheet material is placed between the blades. The movable blade is forced down into the stock, cutting and fracturing it with an action similar to that which occurs when sheet metal is blanked.

Notching. Similar to straight shearing except that it produces angle cut in the workpiece, notching is used to remove excess stock prior to a forming, bending, or drawing operation.

Nobbling. This process involves cutting out a contoured or other shape by punching a series of overlapping round or square holes along the edge of the part.

Folding-Machine Bending. This process produces straight-line bends. The sheet is clamped between two beams, while a movable beam pivots upward, folding the sheet against the edge of the clamping beam. Sharp or rounded folds can be made. Hand-lever force is adequate for most metal thicknesses.

Rotary Shearing. This process is a means for cutting sheet in a contoured shape or a straight line by passing it between two tapered wheel cutters.

Press-Brake Bending. This process is performed in a long, narrow gap-frame press. Bends are normally made on the center line of the ram in V-shaped dies. Universal tooling of a wide variety, however, can produce many different bend shapes. With successive operations, complex forms are possible.

Turret Punching. This process involves the use of a machine that has punches and stamping dies mounted on synchronized indexing tables. As the tables are indexed, different sets of punches and dies come into operating position. Thus, as a sheet is moved on the machine’s work table and different dies are used, holes and notches of various sizes and shapes can be punched and various-shaped blanks can be produced by nibbling. Some turret punching machines reply on manual manipulation of the workpiece and manual indexing of the turret. Others provide for numerical or computer control of these elements. Although primarily used for blanking, with appropriate dies, these machines can produce embossed shapes, countersunk holes, welding projections, electrical breakaway holes, and louvers. Tapping heads can be added as accessories.

Steel-Rule Die Blanking. This process utilizes a die that employs a thin strip of hardened steel bent to the outline of the blank and held on its edge by a wooden base. The exposed edge of the steel band (or steel rule) is sharpened to a cutting edge. The workpiece is placed between this edge and a flat opposing surface. The cutting edge penetrates the workpiece and cuts it to the outline of the part. Normally, soft material such as leather, paper, and rubber are blanked with this method. However, it is surprisingly effective for short runs of nonferrous metals and even unhardened steel. Steel-rule dies are quite inexpensive.