Fabricated tubes are processed and used for a wide variety of structural, plumbing, and manufacturing applications. Steel is often used for construction tubes over other metals like aluminum when extra strength is necessary. Steel tubes are also used in automotive applications and as parts of furniture or other manufactured consumer products. Aluminum, and other alloys, are widely used for a variety of tube applications because of the unique properties of each alloy that lends additional functionality to the particular piece of equipment or process that each part is intended to be used with.
Fabricators are generally somewhat familiar with the “tube cutoff machine.” Cutoff machines are in wide use around the world and achieve their purpose, a cleanly cut and accurate length tube without any unintended crimping or malformation of the tube end. In order to process a tube quickly and efficiently (profitably), the end-cut most often needs to be made very quickly. The process of getting the tube to the cutting device, accurately measuring the tube length before the cut is achieved, and cutting the tube so that the diameter or the “roundness” of the tube remains true, can be much more difficult than it seems. Moving a tube into a tube cutoff machine and, potentially, into other manufacturing processes is not as straightforward as sheet handling. Sheet metal is not likely to roll away or shift out of position.
There are five primary factors that fabricators should keep in mind when specifying and designing an optimal automatic material handling system for any tube-cutoff operation.
1. What length tube will be processed?
If the fabricator is working with a single tube length, the material handling system is usually much simpler than when working with multiple length tubes. The tube bundle, as packaged from the raw material supplier, is placed in a loading device, usually a nylon belt or sling which allows the tubes to flow freely within the cradle. The bundle is raised on one side to align the tubes with an inclined magazine table, which allows one tube at a time to gravity feed in single row orientation into the ready position and to be fed into the cut-off apparatus. The tube will be moved forward by the machine until it hits the tube stop, which has been pre-set to the desired cut length. Contact with the tube-stop triggers the cut-off machine to engage the shear or saw blade which will make the precise cut, in the precise length, required by the process. At this stage the cut tube is conveyed out of the cut position to a collection point and ready to move to the next step of the process, at which point another tube moves into the cut-off position and the process is repeated as necessary.
The procedure described in the previous paragraph is most efficient for high-volume applications in which the same length cut will be performed hundreds of times and allows for extremely high material handling speeds, increasing overall efficiency. Many modern fabricators are embracing the trend towards lower volume tube processing in which a high variability of lengths are processed. This trend, often referred to as “just-in-time” manufacturing, requires a cutoff machine with more flexible feed options and the ability to pre-program a variety of part lengths to be cut.
Servo hitch feeds offer this flexibility for modern tube-cutoff machines. Instead of relying on the tube stop to determine cut-length, the machine operator can program a variety of cut-lengths before the cradle is loaded with material. When the tubes are indexed into the machine, a servo controlled linear rail first securely clamps the tube to be cut, then moves the material forward to the precise length programed by the operator, achieving an exact, and variable according to the operator’s pre-determined program, cut length. Finished tube length should help the process designer determine what type of transfer system is used, but the process designer also needs to consider the next step, after the tube is cut to the proper length, in the tube finishing process. The secondary operation: de-burring, testing, washing, packaging, or a combination of operations- should also be a major consideration when determining a material transfer system.
The process designer should also consider the probable length range of the processed tubes. To cut short-length tubes it may be necessary to integrate a hopper feeding system that accepts randomly distributed raw lengths and re-orients the unprocessed tubes into a pre-determined pattern for feeding into the cutoff machine. Short lengths can be efficiently transferred by a “stair step” style of elevating system that indexes parts one flight at a time, up and into a magazine loading rack. Long-length tubes are easily controlled through a simple drop box system or a conveyor kick-off device that converts the tubes from an end-to-end orientation to a side-by-side orientation. The tubes can then be indexed one at a time into the next operation.
2. What is the weight of the tube to be processed?
Any material handling system needs to be designed to meet the maximum probable stress. If the system is intended to process small diameter or light material such as aluminum tubes, weight should not be of too much concern. These materials are typically light enough that off-the-shelf, aluminum frame conveyors can be easily integrated into the system design. Larger diameter and heavy-wall tube, because of its increased weight, presents much more of a challenge to the system designer. It is important that any system be built to withstand the potential day-to-day abuse that is inherent when handling larger and heavier material. These more rigorous systems require custom design and fabrication work; off-the-shelf systems won’t withstand the increased abuse that is inherent when handling larger, heavier materials.
3. How many stations in the manufacturing process?
Most simple processes, those with the least number of steps, can rely of gravity as an efficient means of moving work from one station to the next. The best option may be to simply move the tube in process to a chute and let it drop into place for the next step. For applications in which multiple stations are required and a greater degree of control is needed, gravity-fed systems may not be the best solution. For more complex processes a transfer system, such as a “walking beam” or “pick and place gripper” system is often the best solution.
A “gripper” system is often the best choice when shorter length material is to be processed. The overhead gripper is used to pick each individual piece of work-in-progress and move it to the next station. The “walking beam” system relies on an integrated cam system to lift and move the in-process tubes from one station to the next. An example of a typical process in which the “walking beam” system might be the best choice is a double –end chamfering operation with length checking. The process would start with a tube, already cut to the desired length in the cut-off station, feeding into a station in which both ends of the tube are machined. The walking beam rotates and retrieves the newly machined tube, moves it to the next station where it is fed into a measurement unit to verify the length of the tube. The tube is then moved, again by the walking beam, to a third station where a blower removes the chips and debris left in the tube interior by the machining process. The process is repeated for each tube as the tubes are deposited into a collection area to await the next step of the manufacturing process.
4. What type of finished work collection system should be used?
Gravity is the most typical and usually the most efficient conveyance method for finished tubes. This method works best in a scenario in which large numbers of the same length material are processed. The material typically rolls down a short incline into a collection rack or bin and is ready to be conveyed to the next step in the manufacturing process. If the manufacturer plans to cut multiple length tubes within the same setup, he may want to invest in equipment capable of handling the varied length parts. By relying on the data used to program the variable length tube cuts made in the first step of the process, the operator can program the collection system to trigger exit locations from the conveyor collection system into individual collection points for each length tube. When those containers are filled, they are moved to specific production lines and a new collection bin continues to collect the specified length finished tubes.
5. If the tube finish is a concern
An important consideration for any collection system is the potential for damage to processed tubes at the collection point. If the tubes are collected in a parallel manner (side-by-side) they with typically “cushion” themselves as they are dropped from the collection incline into the collection bin. The potential for damage is greatest when a tube is dropped on its end, which will often distort the end of the dropped tube and potentially mar the exterior of the struck tube.
If the tube to be processed requires a surface-sensitive finish, nylon gripping surfaces are typically used to eliminate the potential for marring the material during transfer between stations. To avoid possible damage that can occur with gravity-fed collection and transfer systems, magnets or vacuum cups can be used to transfer materials.
For more information, contact Haven at www.havencut.com