STRESS RELIEF IN LARGE PART RECONDITIONING

Lufer Industria Mecanica SA, a Brazilian company located in Sao Jose dos Pinhais in the state of Parana, has more than 30 years of experience specializing in reconditioning of large parts for customers using heavy recovery and material handling equipment. The company is currently one of the largest and most respected manufacturers in the world for spare parts for heavy material handling equipment, producing a product mix of more than 8,000 items in an industrial facility of 9,500 sq m. Lufer stocks heavy duty replacement parts for Caterpillar, Komatsu, Volvo, Liebherr, FiatAllis, New Holland, Case, Le Tourneau, Atlas Copco, Timberjack, Cummins and others.

As an important aspect of their business, Lufer provides stress relief services for large size parts with their own furnace being 4500 mm x 1200 mm x 800 mm. The company has used its thermal stress relief furnace since they started in 1975.

To be cost effective and use its time more wisely, Lufer felt they needed to consider a new direction for stress relief. Their process of thermal stress relieving had a number of shortcomings: The process was very expensive and time consuming since the parts were placed in a large industrial oven, heated to 530 deg C (1000 deg F), then slowly cooled, using more than 100 kW of power per hour. These parts had to be inserted into the furnace by using a crane that required extra handling. After being removed from the furnace, the work pieces still needed a long cool-down period to reach room temperature. Furthermore, inspectors lacked a way to measure results.

Facing these and other issues associated with their traditional thermal stress relief process, the company felt it was time to find a new way to overcome these manufacturing hurdles. They received materials about the Meta-Lax system from Bonal Technologies (Royal Oak, MI) and, after reviewing the information, decided to try the Model 2720-CC computer-controlled system equipped with a 2A force inducer.

After 30 years of using the same process to provide stress relief, the company was tentative. But immediately after receiving and using the new system in June 2007, the company noticed substantial improvements in the reduction of processing time and the amount of power necessary to run the equipment. The Meta-Lax system also provided the opportunity to certify stress relief and measure results in time savings, cost savings and in quality improvement.

With the original thermal method, stress relieving took 20 hours to complete: seven hours in the furnace plus an additional 13-hour cooling period for the part to resume room temperature. The new system reduced this time significantly, to 30-60 minutes, at least a 97.5 percent reduction in time that allows for a measurable savings in costs, along with the overall benefit of being able to ship parts to customers more quickly.

For example, Lufer used the new system to stress-relieve a Hyundai model R210-LC bulldozer table made of ASTM-A36 material that weighed 13,600 kg (30,000 lb). After stress relieving ? which took less than one hour ? the table was ready to install in the bulldozer without any waiting for thermal treatment or cooling of the part after thermal processing.

?The reduction in cycle time has a direct impact in the cost, however, just as important is the reduction in the cost of power,? said Marco Sampaio, chief engineer. ?Before using the new system, we used 100 kW of power per hour for an average part. In terms of financial savings, the Meta-Lax system has reduced more than 90 percent of our costs involved in the stress relieving process, which is a very significant savings.?

Lufer is impressed with the quality of Meta-Lax processing for two reasons ? quality assurance and quality improvement. The company likes the fact that the quality of the product can be assured. With the new system the company can now certify the completion of the stress relief treatment and generate a certification report for each project. Lufer is also impressed with the quality improvement on the parts that are Meta-Lax treated.

For example, the company noticed a considerable reduction in the warpage of ASTM A36 and SAE 1524 side plates weighing 2,000 kg (4,000 lb) that they machined which meant that there was less distortion in the completed 980H Frame that the side plates went in. ?The big benefit for us is the reduction in the distortion with this particular part,? added Sampaio. ?Also important is the fact we don?t have to wait for the part to cool to go on to our next process.?

In comparison with the companies? prior thermal stress relief system, the new system allows for much more flexibility in the parts they treat and where they treat them. The equipment is much simpler to use and is portable allowing it to be taken to the job if necessary.

To date, the company has offered a Meta-Lax stress relief service to its customers wherever it is most convenient, either at Lufer, at the customer?s facility, or in the field where the job happens to be. In the near future, the company plans to acquire more equipment to use the new system during the welding process as well.

HOW IT WORKS
The Meta-Lax process vibrates a workpiece at its sub-harmonic energy level. The sub-harmonic zone is the optimum zone when using vibration for stress relief. All metal structures exhibit harmonic and non-harmonic behavior. A metal component that contains thermal stress displays its harmonic curve as being out of phase from its natural frequency location, much like a musical instrument being out of tune.

By applying sub-harmonic vibrational energy, the pockets of high stress concentrations are redistributed, thereby reducing the effects of the residual thermal stress. Graphically, the harmonic curve shifts slightly but stabilizes into its natural frequency as the workpiece becomes relieved of thermal stress. In a sense, the system massages the metal to relieve the stress.

The Meta-Lax system can be used with all types of materials such as low and medium carbon steel, tool steel, aluminum, stainless steel, cast iron (gray, nodular and meehanite) and exotic metals like titanium, inconel, magnesium and gold.

Meta-Lax Weld Conditioning applies the Meta-Lax stress relief process during welding. Weld conditioning relieves thermal stress as it is being induced during weld solidification. Metallurgically, a finer, more uniform weld grain results. Ductility and impact values are significantly higher, up to 400 percent and 75 percent, respectively.

CONCLUSION
"This new system has made a revolution in our manufacturing process and in part recovery. We can consider that a new age of gains has begun,? noted Sampaio. ?We have already used the new equipment to stress relieve more than 50 different types of parts and the results have been great. The effectiveness the new system provides and its reporting capability increases our competitiveness. It?s added a new level of technology to our facility.?

Bottom Line: Lufer had a return on the investment with the Meta-Lax system within one year.

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Bonal Technologies, Inc., 1300 North Campbell Road, Royal Oak, MI 48067-1555, 248-582-0900, www.bonal.com.