A major Tier One automotive supplier meets stringent requirements for the class A blanks it produces. The European-headquartered multi-conglomerate has steel production and fabricating operations located throughout the world. At its Detroit plant, it performs blanking and slitting operations for automotive plants, as well as its own production stamping facilities.

Recently, Coe Press Equipment Corp.'s SESCO Products Group (SPG) (Sterling Heights, MI) installed an in-press oscillating shear and die package in the plant (lead photo). The package includes the oscillating shear, a die that rotates a maximum of ±30°; blank eject conveyor, dampening control adapter, shear "bump" die design, and self-centering adjustable stock guides.

SPG's oscillating shear die uses a rack-and-pinion with servo motor for movement. It incorporates a "bump die" design for operation in a conventional straightside press and includes a dampening feature to allow higher strokes per minute. Cycle times are determined by the press, feed, and shear oscillation speeds. All adjustments to the die's angular movement can be controlled and programmed at the operator console.

In this example, the shear is located within the press, but there are many other shear styles and sizes available. The following looks at shearing principles and the shears themselves.

The Process

In shearing, material from coil or large sheets is cut into pieces of smaller length and width. These pieces are often used in subsequent operations such as punching and forming. Because shearing is often the initial step in a series of processes, its performance often determines the finished workpiece's accuracy.

Flying-die shears move to match coil speed. They make accurate cuts without requiring the coil to stop and restart each time, thereby increasing line speed.

At its most basic, a shear's blades come together and contact the material. The blades then penetrate the material until its tensile strength is overcome and a crack or tear develops from both sides. As explained in SME's Tool and Manufacturing Engineers Handbook, Vol. 2, Forming, blade clearance has a considerable effect on the sheared edge's quality. If the planes match, a clean cut is produced. If they do not match, a tear occurs if the gap is too great; if the gap is too small, a tongue develops and is recut as the blade passes. Insufficient blade clearance results in poor edge quality. With the correct clearance, the edge is square, uniform, and burr free.

To be considered shearing, the cutting process must take place along a straight line on the workpiece, limiting the type of work performed on a shear. Nonetheless, shears are used to cut wide coils into large blanks and narrow strips, to square blank edges for accurate blanks, and to cut parts to specific size.

This heavy-gage Pivoting™ shear from GenSystems Herr-Voss Div. is for use in continuous cut-to-length lines requiring moderate production.

Shearing offers several advantages. Since it is a chipless operation, waste scrap is reduced. It is also a fast process because the blades do not have to cut through the material's full thickness. They penetrate only slightly into the material, causing a slip plane to develop that severs the material.

On properly sheared workpieces, secondary operations to remove burrs from edges are usually not necessary. Accuracy is high. Using machines that are not fully automated, accuracies of ±Z\nv" (0.4 mm) are not uncommon. Using automated equipment, accuracies of ±0.005 to 0.010" (0.13 - 0.25 mm) can be achieved. Many shear blades have cutting edges on all four sides. As a result, time between regrinding is extended. Also, expensive tooling is not required to produce accurate blanks.

Shears cut mild, high-strength alloy, and other steels, as well as nonferrous and nonmetallic materials.

Workpiece capacity generally ranges from light gage to 1.5" (1.5-38 mm) in thickness and from 12 to 240" (305 mm - 6 m) in width. Capacity in alloy and high-strength steels generally is X\c to .75 mild steel capacity of the shear. For aluminum, capacity is generally 1.25 to 1.5 times mild steel capacity.

Tensile strength is commonly used as the indicator of shearing load, but it is not the only factor. Elongation is also a factor. For example, copper with low tensile strength but high elongation requires as much pressure to shear as mild steel.

Shear styles include stationary, flying, and rotary. Each offers advantages and disadvantages, depending on the application. Whether in a cut-to-length (CTL)/blanking line or a flexible manufacturing center, the shear must be matched to the line, speed, and material. The thicker the material, the longer it takes the shear to pass through it. Therefore, shearing heavy-gage coil may require a slower line speed or a more heavy-duty shear to maintain accurate tolerances on each cut.

The Equipment

Shears can be either hydraulic or electromechanical. Hydraulic shears are slower and are best used in lines that run in a stop-start mode. The hydraulic shear's major advantage is reported to be its relatively low cost. Electromechanical shears may be more expensive, but they cut faster, allowing for increased stroke rates and higher production levels.

Rotary shears are designed for light- to medium-gage materials and are used in continuous CTL lines requiring high-production volumes.

In CTL lines, coil stock is cut by stationary, flying, or rotating shears.

With stationary shears, the coil stops while the shear makes each cut. For those on a budget, this may be a smart choice.

With flying shears, as the name implies, the shear cuts on the fly. They, too, are available in different styles, i.e. rocking, rotary drum, and oscillating. All move in at the same speed as the coil, meaning they make accurate cuts without stopping and restarting the coil after each cut.

A rocking shear is mounted on a pivot shaft so it can rock back and forth. The shear rocks forward and fires as it matches the speed of the coil. Then it quickly rocks backward and prepares to repeat the sequence. Rocking shears are best suited to cutting lighter gage material at low speeds.

With the rotary drum, the coil passes between two round drums with knives mounted on them. As the knives meet, they pinch the coil in two. This shear is also used for light-gage materials in narrow-line applications. It is also highly accurate at fast line speeds.

The oscillating shear works much like a conventional stationary shear, except the entire device moves back and forth horizontally to meet with the coil and make a clean vertical cut. It is particularly suitable for producing high-quality finished parts on CTL lines. It costs more than rocking and rotary drum shears, but achieves higher speeds than a rocking shear, but less than a rotary drum shear.

The shear integrated into Iowa Precision's Slear™ line is dual action, meaning it can operate in feed-to-stop mode as well as on the fly.

The benefits, according to Schuler Inc. (Canton, MI), are continuous feed with a constant straightening machine speed and elimination of the pit to accommodate the coil loop. In addition, because the sheared blank moves at the same speed as the coil, there is no need to accelerate the blank, as is the case when using stationary shears. However, when compared to the stop-and-go method used with stationary shears, the return movement on flying shears results in a slightly lower output when working with short cut lengths.

Rotating shears achieve the highest number of cutting operations. According to Schuler, output is about 150 ppm, making them twice as productive as a blanking press. With rotating shears, the coil runs at a constant speed between two cutting tools moving in opposite directions.

Odds are, unless you work for a steel service center or a mill, you are not in the market for a full CTL or blanking line. However, according to Lloyd Zahn, product manager for the Herr-Voss Div. of GenSystems Inc. (Callery, PA) even the end user and supplier are interested in processing coil strip. "It's true that most OEMs and Tier Ones have steel service centers do the blanking, but there are still a host of ferrous people that do their own blanking." It is also true that most people ordering this equipment already have a line. What they are doing, says Zahn, is either adding a line to increase capacity or updating an existing line to improve the process. "People are constantly trying to address the end users requirements, whether it be for accuracy or flatness," he states.

Today, Cincinnati Incorporated (Cincinnati) makes both hydraulic and mechanical shears, which may be incorporated into CTL lines or used as stand-alone blanking machines. When integrated, these stationary shears work in stop-start lines, i.e. the material is positioned and stopped before the shear makes a cut. When the stroke is complete, a signal is generated by the shear to advance the material.

Nick Fill, product specialist with Cincinnati Incorporated, reports that both hydraulic and mechanical shears cut a range of materials, in general from as thin as 26 gage (0.45 mm) to the machine's capacity. "Hydraulic shears accomplish this range by adjusting knife clearance as well as the ram's rake angle. Mechanical shears need no adjustment. However," he continues, "if extremely thin materials need to be sheared, a mechanical shear with special knives and seats can be adjusted to cut down to 0.012" (0.3 mm) steel.

"Blank width can vary. Minimum coil width is dictated by the hold-down arrangement. Special custom hold-down arrangements allow minimum coil widths of 12" (305 mm), or even smaller if necessary."

Fill points out options and features are added when a shear is integrated into a CTL line. For example, since the feed system will feed out the correct length, the backgage and squaring arm are not needed and, therefore, are eliminated.

Also, in a CTL line, a lot of material will be moving over the shear. "To eliminate wear," Fill reports, "a wear-resistant plate is added to the table's top. This eliminates the hand slots, which are unnecessary because no operator is positioning material. If material marking is a concern, a Phenolic material can be substituted for the wear-resistant plate. A machined-steel material guide replaces hold-down guarding."

Strippit/LVD (Akron, NY) offers an hydraulic guillotine shear, the HST-C, which also can be part of a coil and/or blanking line. However, Larry Peake, a manager with the LVD Group, points out that when a standard guillotine shear is incorporated in a coil or blanking line it is usually done for economic reasons, largely due to the shear's cost. "This is a compromise," he states, "because standard shears usually do not have the speed or strokes-per-minute typically associated with a high-speed blanking line. Production blanking/coil lines typically incorporate a shear that is specifically designed for high-speed shearing."

Amada's ATF high-speed automated shear handles a range of ferrous material with speeds to 220 spm. Material from 0.015 to 0.125" can be sheared in 4, 6, or 8' widths.

Nonetheless, the guillotine shear is used in a variety of applications, ranging from production shearing to custom, low-volume requirements, and can be a suitable adjunct to the job shop. The HST-C series covers nine models with working lengths from 2.5 to 4 m, and capacities from 6 to 16 mm. "Design of the guillotine shears," says Peake, "can be characterized by having a different rake angle to the blade, commonly know as a 'bowtie' blade."

Amada America Inc. (Buena Park, CA) offers the ESH hydraulic shear series, available in seven models with a range of capacities dependent on model and tensile strength of material. This series has a new frame design in which the ram and table are slanted to concentrate force in the direction of cut. Also, cylinders are placed to balance the pressure exerted laterally, thus maintaining suitable clearance and allowing higher-precision cutting.

These machines allow automatic switching between a direct power circuit for thick-sheet cutting and a speed-increasing circuit for thin-sheet cutting, resulting in a 40% increase in ram speed from 19 spm to 25.

Shearing Systems

Amada also manufactures the ATF-1332 mechanical shearing cell. In one application, using only one machine with one operator, the fully automated system equaled the output of three manual shears and six operators. It handles 29.7 X 92.9" (754 X 2360 mm) sheets and turns them into 10.2 X 20.7" (259 X 526 mm) blanks at the rate of 3.4 tons (3 t) per hour.

The system includes motor-driven unloading rollers and a table system that floats on a cushion of air, allowing an operator to square a full cart of material at once. The ATF is configured with an automated two-cart loading system that maintains a continuous flow of metal to the shear. The system for feeding parts into the cutter is also totally automatic, as is a stacking system for offloading sheared parts.

Shears for Coil Blanking Lines

Should you be in the market for a full CTL or multi-blank line, the shear is an important factor, but not the only one. As GenSystems Lloyd Zahn points out, leveling has vastly improved over the years, providing the end user with flat product. "Our feeding apparatus has also improved so we can maintain more accurate blanks," he states.

In many cases, lines are dedicated to specific materials, but that doesn't mean the user can't switch from one material to another. "People run hot rolled and cold rolled, nonferrous material on the same line, as well as galvanized," Zahn reports. "You have to design for the worst-case scenario, which is bright material. You could still run hot rolled on the line, but then you would have a problem with build-up or pick-up in the leveler rolls. You have to clean them before you can run bright material again. Therefore, for most people, it's best to have a dedicated line, but it is not necessarily a requirement."

As far as material properties are concerned in the multi-use lines, shearing is not a problem. It is material thickness that is important. "We can control the gap," says Zahn, "and we can preset the knife clearance to compensate for thickness. True, you're going to get more penetration in aluminum than you will in stainless, but you compensate for that by adjusting the gap."

In any line, the production requirements and materials being run through it will determine the type of equipment in that line. Zahn explains, "It is not just the shear. It's everything from the leveler to the feeder to whether the user wants to run a continuous line. If it's heavy strip and you can't live with roll marks developed from stopping in the leveler, then you have to run the material in a continuous line. If it's heavy strip, you can't loop it. What you need is a shear that actually traverses with the materials, that cuts and returns."

For this purpose, GenSystems offers Pivoting™ and traversing shears that handle materials up to 0.780" (20 mm) thick. In this configuration, a high-speed shear is mounted to a traversing accelerator drive, and is used in a continuous CTL line in those instances where heavy-gage surface condition is critical or on lighter gages when short line length is desired and production requirement is low.

Like GenSystems, Iowa Precision (Cedar Rapids, IA) manufactures complete coil processing lines. Slear™ systems produce blanks from mild steel, aluminum, prepainted, and polished metals from 28 gage (0.4 mm) to .125" (5 mm) thick coil stock up to 72" (1.8 m) wide. The integrated dual-action hydraulic shear can operate in feed-to-stop or flying modes, depending on the application.

Flexible Manufacturing Systems

The versatile shear operates not only as a stand-alone machine and in cut-to-length blanking lines, but also as part of flexible manufacturing systems. For example, Strippit/LVD produces a right-angle shear, which can be integrated into its Omega 1500 turret punch press and/or laser cutter. According to Larry Peake, the Omega shear can be used as a stand-alone shear, but it is better suited for automation. Its greatest value, he believes, is when it is used in conjunction with a punch and/or laser in shearing nested parts.

One of the shear's benefits is its progressive shear feature that allows a sheet to be automatically fed through the shear. This function is programmed through the machine's control. Peake explains, "Using a shear that is 40" long (1016 mm), a sheet 10' (3 m) long would progressively move through the shear blade three times in order to cut the full length of the sheet."

Each 60 X 40" (1524 X 1016 mm) shear blade has four cutting edges, allowing more production between sharpenings and extending blade life. For this to happen, the blades must be rotated between sharpenings. "This process," Peak reports, "requires approximately 1.5 to 2 hours, and is accomplished manually. If the blades are not rotated, a radius forms on the blade's edge, causing the blade to dull. This requires the shear to produce more pressure to shear the part and also creates burrs on the material. Neglecting to sharpen the shear's blades impacts part quality as well as blade life," he states.