Laser welding improves catalytic converter production

Novi, MI -- Eberspaecher N.A. manufactures stainless steel catalytic converters and exhaust products required by automotive customers including Chrysler, Dodge, Jeep, Pontiac, Buick, Chevrolet, and Mercedes-Benz. The company, in the automotive exhaust business since 1931, currently manufactures in Brighton, MI, as well as Tuscaloosa, AL, and Brampton, Ontario, Canada.

FIGURE 1. The Twinmaster machine from Weil Engineering combines a de-stacker, roll former, and laser welder to produce various lengths and shapes.

For its new catalytic converter production line, the company installed a laser-welding short-tube production cell based on a Twinmaster roll-forming and laser-welding production system supplied by Weil Engineering North America, Troy, MI (www.weil-engineering.com). This unit combines two major functions: roll-forming and welding. Blank feeding and post-welding expansion of tubes for perfect roundness are directly linked to the Twinmaster, creating one complete production center. The control functions for the entire system are supplied by Siemens, using a SINUMERIK 840D for CNC controls and a SIMATIC OP170 operator panel for dialog functions.

The production capabilities of this short-tube manufacturing system are:

Min. and max. tube diameter:       3 to 8 inches
Min. and max. tube length:            8 to 50 inches
Tube shapes:                                    Round or oval
Wall thickness range:                    0.02 to 0.08 inch
Materials:                                          Mild and stainless steels
Output:                                               Up to 500 parts/hour
Welding speed (3.2-kW laser)     4–5 meters/min.

In operation, two sheet-metal de-stackers, each with approximately one hour's production material, feed the blanks into the roll-former. The blanks are inspected for double-sheet condition during the transfer movement.

FIGURE 2. Some of the shapes produced on the Twinmaster machines.

Next, depending on tube length, multiple blanks can be rolled into tubes during the same machine cycle. These blanks are automatically transferred from the roller to the seam welder, where they are clamped and butt-welded using a laser beam generated by a Trumpf TLF 3200 laser.

Once welding is done, the cans are extracted from the tooling and transferred onto an inline weld annealing system, to relieve the stress in the welded seam. After a cooling, the cans are loaded into a hydraulically operated tube expander, where they receive a pre-selected inside dimension. This final dimension is calculated from the diameter of the converter substrates, the thickness of the insulation mats, and the spring-back of the stainless steel material used for the converter cans.

The sequences of these operations, the exact timing for each process, and the control of all movements are monitored and operated by the Siemens controller that also monitors the position, the power, and the on/off condition of the laser beam, as well as all the transfer mechanisms and the tooling.

Onboard the Twinmaster, Siemens CNC technology controls eight rotary axes on the de-stacker and chamfering device and operates four axes on the expander and handling system. All drive systems can communicate in a reliable fashion with the Siemens Profibus field bus system that permits one CNC program to be written, and then adapted by Weil Engineering, to modify the controls based on the particular functionalities of the equipment. The Trumpf laser on the Twinmaster machine has a 200-mm optics bifocal mirror with a constant focal length. When the material thickness changes, the CNC tooling varies the position of the workpiece.

For details, e-mail: SiemensMTBUMarCom.sea@siemens.com.

A comparison of fiber and CO2 laser cutting

Nottingham, U -- Since the advent of commercial fiber and disk laser cutting machines, there has been a lot of controversy about the performance of these devices, particularly in comparison to their more established CO2 counterparts. In the early days, the sales staff promoting fiber technology would often declare that the new lasers would very quickly replace CO2 lasers, but this has not happened. Even taking into account the entrenched position of the older technology, fiber and disk lasers have not been as widely accepted as was predicted, although they have been proven to out-perform CO2 lasers in certain important areas.

Here we present a direct comparison of fiber laser and CO2 laser-cutting machines from "what laser should you buy next?" point of view. Both types of machine have their drawbacks and advantages, and a direct comparison needs to compare costs, cutting speeds, cut quality, and several other factors including maintenance and safety considerations. A quantitative comparison of the two machines is surprisingly difficult -- having given several talks on the subject, the best analogy we can give is that it's like comparing a sports car with a family car.

The benefits of fiber laser cutting over CO2 are: higher cut speeds at thin section and reduced maintenance and energy costs. The disadvantages are reduced cut-edge quality on stainless steels and non-ferrous alloys at thicknesses above ~4 mm and the fact that fiber lasers cannot cut most plastics, which creates difficulties when cutting plastic-coated stainless (although special plastic coatings, which can be cut, are now becoming available).

If you are a jobshop boss with the usual widespread cutting requirements, then you should buy CO2 machines until you have enough suitable work to fill the capacity of a fiber laser. This will usually mean that you will have approximately three CO2 machines for every fiber machine. If you are the boss of a manufacturing firm making items from thin-section metals, copper, or aluminum alloys, then your first choice should probably be a fiber laser.

However, in either case, it's a good idea to get the potential suppliers of the equipment to carry out actual cutting trials on typical jobs, and d'n’t forget to include the sheet changeover times in your assessment.

John Powell is with Laser Expertise Ltd., Nottingham, and Alexander Kaplan is with the Department of Applied Physics and Mechanical Engineering, Luleå, Sweden. Reprinted with permission from the Spring issue of the AILU Magazine.

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