January 16, 2003
An ironworker can be an important and versatile machine in a metal fabricating shop. Quite often ironworking is the first step in the manufacturing process, and one ironworker typically can provide enough fabricated material to keep up to seven welders or assemblers busy.
Since its invention in the late 1800s, the ironworker's main strength has been its ability to perform a variety of operations. It can punch a range of materials with punches of various sizes and shapes. It also can shear rod, flat bar, angle, and channel. In addition, it can notch angle iron, pipe, channel, and flat bar. Many ironworkers are available with special tooling to bend, stamp, and form too.
As versatile as the ironworker is, however, it is possible to purchase the wrong machine—or at least not the best machine—for your application. Important considerations for selecting a machine include its capacity, versatility, safety features, and quality.
The material thickness you process will indicate whether to use an ironworker or a turret punch press. An ironworker punches plate up to 1 inch, and sometimes even thicker. Typically, turret punch presses are used on sheet material 1/4 in. and thinner. Ironworkers usually are used for shorter production runs and applications for which tolerances are not as critical.
Ironworkers typically are rated by tonnage at the punch station. A 40-ton ironworker should punch a 1-in. hole in 1/2-in. material; a 60-ton machine should punch a 1-in. hole in 3/4-in. material; and an 80-ton machine should punch a 1-in. hole in 1-in. material (see Figure 1).
The first step, therefore, is to determine the maximum material thickness so you can establish the tonnage range needed for your punching application. Examine the steel rack and the product that you are fabricating. Determine the maximum hole diameter to be punched; the maximum thickness of the material to be punched; and the maximum thickness and width of the channel, angle, and rod to be sheared or bent.
The material or part width plays a part in your ironworker selection. The throat depth of an ironworker punch station should be greater than half of the part or material width. Material length, however, really is not an issue. An ironworker can process almost any material or part length.
Because many different types of steel and ranges of hardness in mild steel exist, it is advisable to get a machine that is at least 20 percent larger than you think your everyday use requires to avoid getting a machine that is too small. Most machines are rated for material with tensile strengths between 60,000 and 65,000 pounds.
Many mild steels have tensile strengths between 50,000 and 70,000 lbs. or higher, and your machine may not have the power to punch the material at the higher end of the hardness values. When punching hard steel, such as stainless steel, it is better to increase the estimated tonnage by 50 to 100 percent, depending on the grade of steel.
Beware! Not all tons are created equal. A metric ton actually is heavier than a U.S. ton (2,200 lbs. versus 2,000 lbs.). A machine rated for metric tons should be able to punch a larger hole than a machine rated on the same number of U.S. tons. For example, 80 tons of pressure by U.S. standards can punch a 1-in. hole through 1-in. material; 80 metric tons should be able to punch a 13/32-in. hole through the same material thickness.
Be sure to compare the rating of the machine not only in tons, but also the diameter of the hole and thickness of material it can punch. Ironworker tonnage ratings can vary from ironworker to ironworker.
All ironworkers are equipped with flat bar shears. The main differences between flat bar shear stations are the length and the approach of the blade to the metal. Some ironworkers use a guillotine, or fixed-rake-angle shear, and others use a scissors-type shear (see Figure 2).
The advantage of the fixed-rake-angle shear is that the blade angle remains constant throughout the cut, sometimes offering larger capacity without increasing machine tonnage. The advantage of the scissors-type shear is that it can vary the rake angle of the blade, thereby minimizing distortion.
The advantage of the fixed-rake-angle shear is that the angle of the blade as it approaches the work remains constant throughout the cut, sometimes offering larger capacity without increasing machine tonnage. The disadvantage is that without the ability to vary the rake angle, the distortion of the drop piece will remain the same throughout the cut.
The advantage of a scissors-type shear is that it can vary the rake angle of the blade. Thicker material is cut closer to the pivot point, and thinner material is cut farther from the pivot point, where the rake angle of the blade is flatter, thereby minimizing distortion. Scissors machines typically have a longer flat bar shear, some up to 24 in. long.
On some ironworkers, the rake angle of the bar shear blade is adjusted by inserting and removing wedge-shaped shims above the shear blade. This may require substantial mechanical ability and substantial time. Also, if the shims are not adjusted each time material thickness changes, the machine could be damaged.
Ironworkers are available with different designs to enhance versatility. For example, the stations on some machines are permanently built in. These machines offer punching stations, angle shears, rod shears, notchers, and short flat bar shears.
If you are a structural steel fabricator, you may prefer these machines because the stations cover the majority of the materials you process and do not require tooling changes.
If you are a general welding, fabrication, maintenance, and structural steel fabricator who does not know what a customer will bring in the door tomorrow, you may want an ironworker that offers the capability to adapt to all customer needs. Tabletop tooling concepts, which provide a wider variety of tooling, may suit your needs.
In addition to angle shears, rod shears, notchers, and flat bar shears, tabletop ironworkers offer options such as larger press brake bending attachments, tube shears, channel shears, pipe notchers, V notchers, picket tools, square tube shears, and a variety of special tooling. Although these machines can use a larger variety of tooling than those with built-in stations, time is required to switch from one operation to the next.
Safety is an important factor when choosing an ironworker. Be sure to choose an ironworker that meets ANSI B 11-5 standards.
Examine the guarding. Be sure it can be adjusted down to within 1/4 in. from the top of the material to be punched, and to the bottom of the guard or stripper (this is an ANSI standard). This will prevent operators from placing any part of their bodies between the material being punched and the stripping mechanism. All other stations should offer complete safeguarding as well.
Beware of machines with automatic urethane hold-downs. Most operators realize the danger of the blade but do not expect to be hurt by safety guards and may not watch them. Automatic urethane hold-downs, if not adjusted properly, also come down with many tons of force and can be dangerous pinch points.
For productivity as well as safety, the machine you choose should offer an infinitely adjustable stroke control to minimize machine movement, decrease the number of pinch points, and increase strokes per minute and production. This is especially important in bending applications and for special tooling for which the upstroke must be adjusted in addition to the downstroke.
Electric stroke controls offer advantages over mechanical linkage controls. Electric stroke controls have quicker cycle times and more precise stopping because they use switches that send signals to the control valve almost instantly. Machines that use mechanical linkage stroke controls must be in motion to cause the linkage to close the control valve. As the valve closes, the machine slows down and is more difficult to regulate.
Safety instructions should include proper alignment of the punch and dies. Because punches are usually hardened to 58 Rockwell, the punch will not bend as it collides with a die. If it is out of alignment, it is more likely to flake or even explode, causing serious harm to the operator.
The preferred and most widely used method of aligning the punch and die is similar to the way punch presses have been aligned for many years. This is done by bringing the punch ram to the bottom of the stroke and installing the punch and dies with the stroke down. This way, the punch already has been entered into the die, the alignment can be checked, and guards may be replaced without machine movement.
In trying to determine quality, consider the size of the pivot points and beam strength of the steel that is under pressure. Since your ironworker produces many tons of force, the force must be generated and transferred through the pivot points as well as the beam.
Another good indicator of quality is how much shock is produced when the ironworker punches. Excess shock, which can be identified by a loud popping or banging noise as the punch goes through the material, could indicate the beam or side frame is stretching and snapping back into place. Continued shock can cause welds to break, as well as other failures. Higher-quality machines control this by increasing side frame, beam, and pin size.
The number of grease points also can be an indicator of quality. Although all machines have grease points on pivot points and guide assemblies, some machines have an excessive number of grease points—as many as 20 or more. Usually these additional grease points have been added in an effort to correct galling problems. It is unrealistic to expect operators to grease more than five or 10 grease points, and machine failure or galling most likely will occur.
The hydraulic system also should be a consideration. You are buying the machine for the tons of pressure it produces, not for the motor's horsepower rating. Some ironworkers are designed through mechanical advantages to produce more tonnage with less horsepower, thus making the machine more efficient. Machines with higher-horsepower motors usually operate at a higher hydraulic pressure, or pounds per square inch, and this increased pressure can produce more wear on hoses, pumps, and valves.
Because an ironworker is an important part of most shops, when even one ironworker breaks down, the negative impact on production is significant, even paralyzing. Before purchasing an ironworker, take the time to analyze your needs and carefully assess the quality of the ironworker. It will be time well spent.
Jim Hoag is marketing director for Scotchman® Industries, 180 E. Highway 14, Philip, SD 57567, phone 605-859-2542, fax 605-859-2499, e-mail firstname.lastname@example.org, Web site www.scotchman.com. Scotchman Industries designs and manufactures ironworkers and saws for metal fabricators, machine shops, and technical schools.
American National Standards Institute, 1819 L St. N.W., 6th Floor, Washington, DC 20036, 202-293-8020, www.ansi.org.
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