Bending and handling tube

It used to be simple: Purchase the tube fabrication machinery necessary for a project and hire motivated workers to get the job done.

It's not that simple anymore.

Technology advances have made automated bending and material handling processes possible for tube fabricators. Some fabricators have found the relentless pace of competition makes such equipment necessary. While simple, manually operated machines still fit the bill for some projects, more sophisticated equipment is available for advanced bending applications.

What's Available?

Bending equipment can be categorized into three groups: dedicated benders, CNC benders, and automated manufacturing cells.

Figure 1 Approximate Cycle Times and Production Rates for a Dedicated Bender

Dedicated Bending Machines. Designed and built for a specific part on a single project, these bending machines generally perform compression bending. Operators load straight tube manually into a hopper, and the machine runs unattended for a period of time. From the hopper, the tube is introduced to the bend tooling. The machine cycles, and the bent tube is discharged from the machine. The cycle time depends on the number of bends that are performed (see Figure 1).

As the name implies, dedicated bending machines are dedicated to bending one specific part. These machines are not made to be altered, so changing the machine to produce a different part—for instance, one with a different number of bends, a different angle between bends, or different bend angles—is difficult and time-consuming. Thus, accommodating design changes usually is not economically practical, and can take more time than is available to meet demanding or changing project schedules.

CNC Bending Machines. CNC bending is a versatile process for tube bending. CNC machines can be programmed to change the degree of bend and the angle between bends, which facilitates part design changes. Multiple bends are customary when using this type of equipment. Performing up to 10 bends with similar angles is common. Draw bending is the most common bending method on CNC rotary bending machines. The cycle times for CNC bending machines tend to be longer than they are for dedicated bending machines (see Figure 2).

Figure 2 Approximate Cycle Times and Production Rates for a CNC Bender

Although an operator typically loads and unloads parts, automated part loading and unloading can reduce the need for an operator and increase production rates.

Automated Manufacturing Cells. Automated manufacturing cells combine the faster production rates associated with dedicated equipment with the flexibility and programmability of CNC bending machines. Automated cells can use either compression or draw bend tooling, with or without a mandrel. The equipment usually comprises a hopper or coil feed and cutoff system combined with one or more bending modules that use transfer units or robots to move parts from one bend head to another. Automated tube transfer from one bend head to the next results in shorter cycle times, allowing the equipment to produce more parts in less time. For example, if a tube has four bends, two bends can be made on the first bend head and two bends made on the second bend head. The cycle times for automated manufacturing cells tend to be shorter than they are for dedicated and CNC machines (see Figure 3).

For long tubes, bending modules can be positioned on both sides and grip the tube in the center. They can accommodate tubes up to 16 feet long, depending on the tube diameter and material.

Like CNC benders, these modules are fully programmable. Changes in the degree of bend, the angle between bends, and the distance between bends can be programmed, which allows tube fabricators to implement part design changes and facilitates manufacturing completely different parts.

Figure 3 Approximate Cycle Times and Production Rates for an Automated Manufacturing Cell

The modular design of automated manufacturing cells allows tube fabricators to add other operations to produce semifinished or finished components, such as coating removal, end forming, piercing/ punching, assembly, welding, leak testing, and part number etching. As long as subsequent operations are performed as quickly as the bend cycle rate, they do not affect the throughput rate.

Bending One Way or the Other

The two bending methods, draw and compression, have distinctly different attributes. Draw bending:

• Provides good control of material flow for thin-wall tube bending.
• Works well with mandrels.
• Is well-suited to CNC bending.
• Can be used with automated manufacturing cells.
• Provides low production rates.

Compression bending:

• Provides good working clearance around dies.
• Is well-suited to automation.
• Has limited usefulness for thin-wall tube bending.
• Provides high production rates.

Capital Equipment Comparison

Performing a capital equipment analysis is necessary in deciding whether to use a dedicated bender, a CNC bender, or an automated manufacturing cell.

Sample Analysis. A project requires five tube configurations. The five tubes have several things in common: all are 58-in.-diameter, 0.06-in.-thick steel; require seven bends each; require a hole to be pierced; and need a part number etched into the surface. Each tube, however, has a different end form.

The manufacturer has a two-shift operation, and the job will last three years. The annual production volume is 400,000 of each tube.

Dedicated bending machine:

• Weld seams are positioned automatically.
• Part numbers are etched while the part is in the bender.
• The cycle time per part is estimated to be 16 seconds.
• The equipment is positioned close together in a cell configuration. The tubes are transferred manually from one station to another.
• The equipment must operate approximately 10 hours per day at 80 percent efficiency to manufacture the annual production volume of 400,000 of each tube.
• Because this project requires five separate machines, approximately 1,008 sq. ft. of floor space is needed.
• After the job is complete, the dedicated bender will have little or no value.

CNC bending machine:

• Weld seams are positioned automatically.
• Part numbers are etched while the part is in the hole-piercing machine.
• The cycle time per part is estimated to be 24 seconds.
• The equipment is positioned close together in a cell configuration. The tubes are transferred manually from one station to another.
• The bending machine must operate two full shifts per day at 80 percent efficiency to manufacture the annual production volume of 400,000 of each tube. Auxiliary equipment must operate approximately 10 hours per day.
• About 1,152 sq. ft. of floor space is needed for the five machines.
• After the job is complete, the CNC bender can be used for other jobs.

Automated manufacturing cell:

• Weld seams are positioned automatically.
• Part numbers are etched by the part etcher.
• The cycle time per part is estimated to be 6 seconds.
• It's a single piece of equipment. The tubes are transferred automatically from one station to another.
• The cell must operate two full shifts per day at 80 percent efficiency to manufacture the annual production volume of 400,000 of each tube.
• The tooling must be changed when switching from part to part.
• Although it has five bending heads, it takes up less space than the other options. About 624 sq. ft. of floor space is needed.
• After the job is complete, the cell can be mechanically reconfigured and electronically reprogrammed to run other parts.

Analyzing Projects for Today and Tomorrow

To make an optimal equipment investment decision, it is important that manufacturers consider any limitations, such as the available floor space, the available labor, and equipment cycle time; and requirements, which include the floor space needed and the number of operators required.

However, these factors don't provide the complete picture. It often is beneficial to look beyond the current job and consider future projects. Manufacturers that anticipate having just one bending project might find a dedicated machine to be the most suitable way to go. Those that need some versatility should consider a CNC bender or an automated manufacturing cell that can be reconfigured later to handle other projects.

Mike Bollheimer is product manager of tube bending and fabricating with Wayne Trail Technologies Inc., 203 E. Park St., Fort Loramie, OH 45845, 937-295-2120, fax 937-295-2642, Mike.Bollheimer@waynetrail.com, www.waynetrail.com.

This article is adapted from Mike Bollheimer's presentation made at FABTECH® International, Nov. 16-10, 2003, Chicago. Copyright 2003 by the Fabricators & Manufacturers Association, Intl.®, and the Society of Manufacturing Engineers.