Although slide forming machinery has existed for over eight decades as a metal stamping technology, it persists as a competitive method for manufacturing specific parts, including those going into medical devices that connect internal workings. As compared to standard stamping presses, slide forming machinery is usually inexpensive due to the simplicity of the tools. Parts can also be produced relatively quickly, resulting in a lower cost per part. In addition, slide forming machines do not need a carrying web, like those of progressive tools, resulting in reduced scrap loss.

Slide forming machinery is a metal stamping technology in use since the 1930s, where it was first used to produce brackets, clamps, and electrical connectors. The technology uses four or more different slides to carry tooling horizontally to a central position on the part. The accurate, repeatable, and powerful slide forming machines can be used to produce parts economically, at much lower cost than those manufactured with power press tools. Tooling is also substantially less expensive, since complex forming operations that add cost to progressive tooling can be formed easily on slide forming machinery.

While an older technology, slide forming machines can be an extremely competitive method for manufacturing specific parts, particularly intricate springs, stampings, and wire forms used for welded medical bands, surgical staples, wire formed clamps, retention spring clips, blade locks, clutch springs, and float wires. In addition to comparing favorably with progressive tooling, slide forming machinery can outperform other more expensive radial wire/strip bending machines.

In addition, the slide forming machines produce a significantly reduced amount of material scrap because they do not require a carrying web like that needed by progressive tools. When the cost of materials is high, minimizing waste is essential to running the part cost-effectively. The advantage of a slide forming machine is particularly pronounced in parts made of higher cost stock.

Slide forming basics

A slide forming machine

A slide forming machine is essentially a horizontal stamping press that uses a system of cam-controlled tools for producing small parts from sheet metal or wire. The machine is used for progressive or transfer stamping operations. Unlike other presses, the slide forming machine has moving slides with tools attached. These slides, driven by the shafts that outline the machine, strike the workpiece to form it.

The driving mechanism is an electric motor linked by gears or belts to shafts, which operate the tools. The four shafts completely surround the machine to form a rectangle. The shafts are connected at all four corners of the rectangle by gears. The slides of the press are connected to cams mounted on the shafts, and the slides can be moved to the die area from all four sides of the press. In addition, several slides can be attached to each shaft, which increases the machine’s flexibility and the number of operations that can be performed.

The shafts are connected by bevel gears, meaning that one shaft is driven by an electric motor, while that shaft’s motion drives the other shafts. Then, each shaft has cams that drive the slides, which are usually of a split-type. The driving action allows the workpiece to be worked on four sides, making the machine quite versatile. A hole near the center of the machine is provided to expel the completed workpiece.

Frequently referred to as fourslide, slide forming machinery actually comes in several varieties, fourslide, multislide and vertislide tools. Fourslide, as its name suggests, is the basic slide forming machinery, in which one slide is attached to each of four shafts. Multislide machines have eight slides, permitting extra forming motions. A multislide tool is typically somewhat stronger than a fourslide, to accommodate thicker parts. Vertislide is a fourslide or multislide machine, with the sides and tooling in a vertical position. The newest of the slide forming machines adds a fifth slide that comes in from the top of the machine to add expanded forming capabilities.

The biggest advantage of the slide forming machine is its ability to complete all of the operations required to form the workpiece from start to finish. Moreover, the machine can handle certain parts that transfer dies and progressive dies cannot manage because it can manipulate from four axes. The machine’s flexibility reduces the cost of the finished part since it requires fewer machines and less setup and handling. Also, given that only one machine is required for a number of operations, less space on the manufacturing floor is required for any given workpiece. As compared to standard stamping presses, the tooling is usually inexpensive, due to the simplicity of the tools. Parts can be produced relatively quickly, depending on the number of operations per part. Such speed usually results in a lower cost per part. Lastly, slide forming machines do not need a carrying web, like those of progressive tools, resulting in reduced scrap loss. Most tooling is designed so that no material is removed from the width of the part, which greatly reduces the amount of scrap loss.

Fourslide machines do have disadvantages, the most significant of which is size constraints. The largest machines can handle stock up to 2.5 inches (76 mm) wide, 16 inches (320 mm) long, and 3⁄32 inches (2.4 mm) thick. Wire size is also limited, as is travel on the slides, and the throw of the forming cams. Shearing and bending operations can be done, but extrusion and upsetting operations are impractical as they hinder the movement of the workpiece to the next station. Drawing and stretching require too much tonnage and the mechanisms required for the operations are space prohibitive. Finally, fourslide tooling set up requires a long lead time, making it most feasible for relatively high volume parts. 

Adapting older technology to today’s market needs
Given the characteristics of slide forming, it is especially well suited to smaller parts that require precise shape and size, several bends, and tabs that go in different directions. It is also useful when the part requires a bend that is greater than 90°, for precise control of burr location and direction, and for control of bend orientation as it relates to the grain of a particular material. Grain direction is very important to the part’s lifecycle when used in a spring application. Part use can range from medical, firearms, electronics, and commercial applications.

A variety of parts made using slide forming machinery

 The manufacture of tooling at lower costs than a progressive tool is a great advantage in today’s market. While certain parts can only be made with a progressive tool, there is a huge area where parts could be produced with either machine. In those instances that lend themselves to production with slide forming machinery, it is important for OEMs to investigate the feasibility of using the lower cost process, especially where material costs are high. For parts made with stainless steel, Inconel, copper, brasses, and beryllium copper, which can range as high as $60-70 per pound, using slide forming machinery may cost far less in tooling costs, while reducing scrap losses. Such scrap reduction can save costs, since scrap losses usually range from 20 percent to 50-60 percent. Setup times are higher with slide forming, implying that the greatest cost advantages are found when running a fairly high volume of parts.

One strategy for OEMs is to seek out a vendor capable of manufacturing a part with either progressive stamping or slide forming machinery, and to obtain quotations for both options. In regards to a recent blade lock for the aircraft industry in which Connecticut Spring and Stamping (CSS) was involved, tooling costs for slide forming machinery were estimated at $7,100, while those of progressive stamping for the same part were $16,500. CSS also reduced the scrap loss by 27 percent since carrying tabs were no longer needed.

Compare slide forming with other options to get the best solution
Although it is a technology that has existed for nearly a century, the slide forming machine is still a particularly cost effective option for the right combination of material, part configuration, and number of parts needed. Fourslide, multislide and vertislide machines often prove economical for the production of intricate springs, stampings, and wire forms. The equipment can be used effectively to produce parts going into medical devices that connect internal workings, as well as blade locks found in jet engines, and even float wires in gas tanks that connect back to a sensor. Where material can be as high as $60-70 per pound, reducing waste is important. By eliminating the carrying strip and using material efficiently, tooling costs can be reduced, and that’s a welcome result in any era.

Pete Marut and Dale Pereira are Sales Engineers at Connecticut Spring & Stamping(CSS). They can be reached at 860-677-1341.