High-Frequency, Quick-Change Tube Welding System for the Manufacture of Contoured and Precision Tubing by Dipl.Ing. Heinz Scherble, Schopfheim, Germany
1 Welded Contoured-Tubing The manufacture of welded contoured-tubing with difficult sections is becoming more and more important to the rollforming industry, challenging knowledge, experience and innovation. Furthermore, the continuously increasing demand for contoured-tubing is most often based upon component weight reduction and requirements to provide one product with multiple functions. The characteristics of contoured-tubing with regards to material thickness, part geometry and overall quality can be varied and therefore adjusted to the component requirements. Contoured-tubing can be supplied with various hole- and punch patterns on the line or prior to or after the forming operation. It is also possible to obtain changes to the tube ends during the cutoff operation. Contoured-tubing produced with these characteristics can cover a wide range variety of shapes and applications.
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Picture 1 ; Welded Contoured-Tubing
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2 Welded Precision-Tubing The trend of material- and weight savings, orginally started in the automotive industry, is continuing and rapidly gaining importance in other fields. The use of "integrated functionelements“ as structural components for chassis is also increasing. Through the use of innovative high pressure forming, also known as hydro-forming, a new tube forming process has been successfully developed. In this process the tubing is formed in a special press system into the desired component. Through the application of mechanical loads and a very high hydraulic pressure on the inside of the tube, the forming takes place until the tube finds its final expansion on the inside surface of the form die. Therefore the prerequisites placed on the tubing, especially on the weld seam, are very high and cannot be met by conventional tube-welding systems. The manufacture of welded precisiontubing, which is suited for the hydro-forming process, requires a special tube-welding line which allows for forming of the strip into the round tubing profile with the least possible amount of stress. This in turn will fullfil the requirement of a low amount of strain-hardening, eliminate stress cracks on the tube surfaces and provide a premium weld seam.
New Possibilities in Steel
In recent years the steel industry has been able to provide a number of new developments. For example : • • • •
Tailored blanks Fine grained material Stainless steel with good weldability Aluminized and electro-galvanized steel
A modern tube-welding systems is able to provide products out of all usual material. For example: • • • • • • •
Fine grained steel Cold rolled steel Micro composition metal Aluminized steel Hot-dip galvanized steel Electro-galvanized steel Stainless steel
This represents only a limited selection and cannot cover the entire range of possible materials which could be used for special customer requirements.
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4 Rollforming of Contoured and Precision Tubing The manufacturing of welded contoured and precision tubing requires a comprehensive knowledge of rollforming and many years of experience. New sections are developed in collaboration between the machine manufacturer and the tube producer. It is importan, to understand the full range of applications and their requirements in order to ensure the proper function of the rollformed product and its economical production. The latest technology and the design software are also continously being improved through collaboration with technical institutes involved in R & D for tube manufacturing. The solutions are checked and optimized using modern CAD and expert-system, in order to guarantee the highest process capability of production as it is required today.
Picture 2 ; Rollforming of Contoured-Tubing
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Picture 3 ; Contoured-Tube, 3D-Flower, Rollforming-Flower
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5 Structure and Build of the Tube Welding System A typical modern tube-welding line can produce tubing with the following parameter: Contoured-Tubing Maximum Size Max. wall thickness Max. production speed
Width x Height 10“ x 6“ 0.160“ 200 FPM
4 - ¾“ 0.200“ 400 FPM
On average, these types of lines require a line operator ( or set-up person ) and a general operator. The line set-up is accomplished through a quick change system with an automatic coupling of the stands to the gearboxes.
In general the tube-welding systems consists of : • Material feeding
decoiler coil-end welder horizontal strip accumulator
weld unit welding table weld-bead machining calibration unit Eddy-Current weld tester
• Strip sizing stand • Tube welding machine
• Cooling Section • Automatic quick-coupling system • Post-galvanizing unit • Flying cut-off
High-performance circular saw Single and Double cut-off-tool High-speed circular cut-off saw with automatic blade changer
• Exit ramp • System controls
Picture 4 ; Tube-Welding System
Horizontal Strip Accumulator
Tube Welding Process Page 7-16
Tube Welding Machine
6 Material Feeding With strip feeding units the material is continuously fed into the tube-welding systems. During the coil change, which takes approximately 3 minutes, the strip stored in the accumulator keeps the system supplied so that no machine down time will occur.
7 Tube Welding Machine Due to the complexity of the shapes, the manufacture of contoured-tubing requires substantially more forming passes than the manufacture of precision-tubing. The lay-out of the tube-welding systems shows that, for contoured-tubing, up to 30 forming passes with the corresponding side roll tables can be used. However in the past, tube-welding systemss with up to 50 forming passes have been built. In general, for the manufacture of precision-tubing, the average forming units required are limited to 8 forming passes with the corresponding side roll tables. Considering the potential number of forming stands, most forming units are equipped with a quick-change system. In these systems 2, 4 and 6 forming stands and the corresponding side roll tables are mounted onto quick-change cassette. These cassettes are loaded and unloaded through an overhead crane. It is possible to fully automate the connecting process of the drive to the gear box. Most impresssive is that the time required for the coupling process is entirely independent of the number of stands and is estimated to be approxinately 5 minutes.
Picture 5 ; Tube Welding Machine
8 Welding Unit After the forming of the tubing, a high-frequency unit welds the formed shape into a tube. The inductor coil of the HF-unit is mounted three-axis adjustable table and allows for an optimal positioning of the inductor to the welding table. This set-up guarantees the high weld quality. An important prerequisite for a perfect weld is a clear definition of the strip edges. This is obtained through a special edge-conditioning unit at the strip entry. A five roll weld table guarantees the exact location of the strip edges for the tube welding. The vertical bottom roll supports the profile and the two top rolls ensure the precise guidance of the strip edges in such a manner that the edges meet each other in a guaranteed parallel plain. The horizontal rolls of the welding table, equipped with hydraulic positioning features, press the heated strip edges together and create the weld seam. As soon as the tube-welding systems comes to a halt, the welding rolls will retract to a predetermind and adjustable distance and remove the load from the bearings of the weld-spindle supports. These units can be exchanged and therefore provide the selection of the best possible welding rolls for each application.
Picture 6 ; Welding Unit
9 Weld-Bead Machining (ID / OD Scarfing )
The weld bead resulting from the weld process is eliminated through an internal and external scarfing unit. The hot chips from the scarfing operation are guided through a funnel into the chips-compression press, which is located in the frame structure of the machine. In this press the chips are collected and then compressed into small packages, which allows for the easy disposal of these chips without any danger of injury. The OD-scarfing unit is equipped with two scarfing stations. This allows a switch between these units and ensures the disposal of the compressed chip packages without any line shut-down. The weld bead on the inside of the tubing is removed through an ID scarfing unit.
Picture 7 ; Weld-Bead Machining and Chip-Removal
Automatic Quick-Coupling System
The prerequisites for economical production of contoured and precision tubing are good process capability and high system availability. The process capability is ensured through the machine builders knowledge in system technology and rollforming. A high system availability results from a combination of a modern quick-change concept and automatic coupling features, which will connect the work shafts to the gear boxes. This takes a great portion of the set-up time away from the forming line. The frame structure of the machine, or base, should be built so that the quick-change cassettes can be equipped with 2, 4 or 6 stands at any location on the roll forming unit. Of course, this still requires maintainance of the center-center distances. The quick-change cassettes are fixed to the machine frame by index pins and held in place with hydraulic clamps. Forming stands, side-roll tables, entry table, straightening unit, and other components can be mounted on top of the quickchange cassettes. Change-overs and set-up of the roll form tooling and other accessories can now be completed in a separate set-up area so that only the material feeding and the fine adjustment are required. The transportation and exchange of the completely set-up quick-change cassettes is accomplished by a forklift or an overhead crane. On overage, the change-over of a quick-change cassette requires approximately 5 minutes. When all quick-change cassettes are positioned, the work shafts need are connected to the gear box by means of universal shafts. However, recent developments have shown that the connection can be established through a fully automatic system where the number of stands does not have any influence on the required time. This coupling system will always find its position to the spindle in question, thanks to a specially designed key-way system. The average time for this coupling process has been established at approximately 5 minutes.
Picture 8 ; Automatic Quick-Coupling System
Picture 9 ; Quick-Change Cassettes Picture 10 ; Quick-Coupling System
Post Galvanizing Unit
Due to the high weld temperatures, the galvanization of the base material in the area of the weld seam is burned off approximately 1/8 to 1/4 inch from the weld seam. In order to ensure the corrosion protection of the tubing, this area needs to be post-treated. This is accomplished in the same tube-welding line through a system simular to an arc-spraying process. The arc is ignited between two automatically fed zinc-aluminium wires thus melting the wires. A continuous stream of blown air will then apply the liquid to the bare material.
In the cooling box the contoured tubing is cooled down to room temperature. Stable, adjustable guide elements ensure that the contoured tubing remains straight during the cooling process and that the cooling process takes place in a controlled manner.
In the calbration station, the tubing receives its surface finsh and its finalized shape dimensions. The calibration unit for the contoured tubing, as well as for the precision tubing, is equipped with calibration stations and side-calibration rolls. For the straightening of the contoured tubing this unit is equipped with two motorized "TurkHeads“, which contain motorized side-, vertical, and torsion-positioning. The adjustment of these positions is remot controlled by the measuring unit located at the exit end.
Picture 11 ; Calibration Unit
Flying Cut-Off Machinery
The flying cut-off machine is equipped with a synchronizing position control, through which the cut-off tooling, mounted on the tool-carriage, moves synchronously to the contoured-tubing and enables the cut-off at the predetermined length. The length measurement is done through a measuring wheel, which is mounted after the calibration unit, directly on the contoured tubing. When the defined part length is reached, the tool carriage accelerates exactly to the current production speed. As soon as the movement of the carriage and the tube are synchronised, and the required product length is reached, the cut-off cycle takes place. After the cut has been completed, the carriage returns to maximum speed. Due to the high system accuracy of +/- 0.004 inch, which is based on "0" slippage of the measuring wheel to the tubing, very low length tolerances can be realized. In the case of prepunched contoured-tubing, the cut-off is defined in relation to the hole pattern through the use of an optical indexing system, which ensures a constant distance from the cut edge to the hole pattern. The product cut-off program is easily fed into the machine controls through the key pad in the operator console and is clearly displayed on a color monitor. Since a wide variety of tubing can be produced on these tube-welding systems, it is possible to use different cut-off units. These units are : • Circular cut-off saw for cut speeds of up to 5,500 linear inches per second, used for cut-off of contoured tubing. • Metal circular cut-off saw for cut speeds of up to 12,600 linear inches per minute, for cut-off of contoured and precision tubing, with automatic saw blade change. • Single and double-cut punch tooling, for the cut-off of precision tubing. These cut-off units are mounted on the above-mentioned tooling carriage. Even in this area, the quick-change concept has become a reality. The change of a cut-off unit takes approximately 15 minutes. The units are pre-positioned through index pins and the couplings establish a hydraulic and an electronic connection. The system control of the tube-welding line recognizes which type of cut-off unit is being used and automatically refers to the corresponding cut-off program.
Picture 12 ; Flying Cut-Off Machinery Picture 13 ; Automatic Saw Blade Change
The exit ramp transports the cut-to-length contoured and precision tubes out of the line and sorts them into four deposit areas, to each to the left and right hand side of the unit. Two areas for the finished product, one area deposit for quality control and the other area for non-welded tubes, which are produced during the start-up period.
In general today`s system controls are of the highest level of technology and ensure, through proven control technology, easy and safe operation of the entire tube-welding systems. In the previous examples, the operation of the tube-welding line was carried out through the main control console which is ergonomically located in the area of the welding unit. For ease of set-up of the tube-welding line and feeding of the strip material into the line. Two additional operator consoles have been installd. One console is located at the material feeding area, while the other one has been placed at the flying cut-off carriage. All consoles are equipped with foil-key pads and a large color monitor. The operator is prompted by display text and is continuously updated on the status of the tube welding line. In case of an error occurring, the failure is diagnosed and recommendations for the failure correction are displayed as well. Should the operator not be able to elimate the cause of the failure, a direct communication service to the machine builder via modem can be utilized. With this integrated modem, it is possible to diagnose the entire condition of the tube-welding system and to eliminate potential failures and to modify the system-control programs. This ensures a very high degree of machine availability for the end-user and -provides direct full time support of the machine builder at all times, regardless of the machine builder`s location.
Reflecting on the progress the entire industry has made from the early beginnings of the tubewelding systems to today`s high-tech systems should give one a feeling of satisfaction. However, it also shows that with today`s global competition and with the new technologies, the posibilities for the usages of tubing are endless. Tube manufacturers and machine builders have been able to benefit from their knowledge and experience and are still forming a unique partnership. These examples are only a small portion of what this innovative industry is capable of. For us, the next century starts now and the goal is :
to recognize and develop new avenues and to use the potential to its fullest !