This paper is adapted from an article published by BMR Group in Industrial Laser Review, August 1996, p. 13

Laser material processing is a great technology, but the cost of ownership is so high that many manufacturers are turning to job shops to enjoy the benefits.  Here’s why.

The CO2 laser has proved superior for case hardening steel components in a wide range of applications.  This type of laser is well-suited to transformation harden (heat treat) short runs of virtually any type of part and longer runs of heavily machined parts or critical high-value components.

Most manufacturers of steel components recognize the value of laser heat treating for these applications. But laser heat treating has been slowly accepted in the US because it is difficult to cost-justify a high-power CO2 laser and the technical expertise required to operate and maintain the equipment required for laser materials processing applications. Adding to the problem is the low utilization of most in-house laser systems used to process materials.

This cost problem is often at the root of some difficult engineering challenges as well. The optimum design for a part frequently will not tolerate the more widely-available heat treatment methods. That means that parts must be designed differently or additional post-treatment machining will be indicated, both of which require excess material and labor. In these instances, design and performance will be degraded unless laser heat treating is available.

While it is easy to understand these issues, the fact remains that lasers suitable for materials processing are expensive for most manufacturers to purchase and operate, and they require high-level skills to operate and maintain.  However, two Midwest companies have discovered there are ways to get parts laser heat treated reliably without absorbing the costs of owning and operating a laser.

A CASE IN POINT

A manufacturer of manual automobile transmissions in Indiana experienced a high scrap rate from cracking of a machined synchro hub for a new transmission design. The hub was machined from 1142 steel with gear teeth around the hub that had to be hardened to withstand heavy wear.

The company was using induction hardening, but experienced problems with cracking at the root where the shoulder had a cross section of less than 0.060 inches. The problem was so severe that 15% of the induction-hardened parts were rejected after a die-penetrant inspection. Metallurgical analysis of 100 sample items revealed another 8% that were likely to fail in operation because of cracking. Further, there were a small number of samples that were warped by the heat treatment and, consequently, would not run true on the shaft.

Because the part had so many variations in its cross-sectional dimensions, flame hardening was not an option. When the company learned about laser heat treating, they decided to treat a number of samples to determine if laser technology could provide the needed hardness. They turned to Light Beam Technology (LBT) one of the companies in the BMR Group family in Wolf Lake, Indiana, for help. LBT is a small laser job shop that operates a 5kW transverse flow CO2 laser with dual CNC workstations.

LBT used its laser to harden the surface profile of the gear tooth to a case depth of from 0.015 – 0.020 inch. Of the sample lot, no parts were warped, and metallurgical analysis of 100 sample parts revealed no cracks. In performance testing of the hubs, the company discovered that wear rates were improved by from 15 to 20% with laser heat treating because of the finer microstructure that resulted from laser heat treating.

LBT used induction heat treating equipment on other components, none of which experienced the same kinds of problems as the synchro hub. That meant that the entire capital cost of a laser and the associated maintenance and operator costs had to be charged against the synchro hub. The resulting financial analysis revealed that, for the volume of parts anticipated, the laser was not economically viable.

There still remained the problem of potential failures from cracking after the pans were in service, so the company remained exposed to a significant performance problem. The clear solution was to contract out the laser heat treating of the part to LBT. The financial analysis of this option revealed that the per unit cost to treat each part with the laser was somewhat higher than induction heating, done either internally or externally. However, scrap was eliminated by the laser heat treating process and failures from cracking after treatment were reduced to zero. As a result, the actual unit cost of the finished part from LBT was less than in-house treatment.

ANOTHER CASE STUDY

The same discovery was made by a Midwest steel processing company, who has multiple sites with huge capital investments in equipment and an extensive fabrication shop that makes all of its own equipment. The shop is outfitted to design and build virtually all of the company’s processing and handling hardware.

They use a large number of expensive take-up and pay-out mandrels. The take-up mandrels receive significant abuse from the mill edges of the steel being rolled. When the mandrel faces are cut or gouged, they damage the steel strips being coiled, turning the first few turns into scrap. In addition, the mandrels are expensive to tear down and repair, and lost production time is an enormous burden. The company designed a take-up mandrel for a pickling line and wanted to harden the entire surface area of the four segments. Although they have flame hardening capabilities, they knew this process could warp the mandrel segments and possibly even destroy the part. They could not afford lost production time, and they were not willing to accept rebuilding costs should the pans be scraped during heat treatment.

They asked LBT to laser harden the entire surface area of each mandrel segment. The segments were machined from 4150 material, hardened to from 60 to 62 HRC. They also hardened the grip area where the coil ends strike, an area never hardened because it could not be reached by flame or induction methods. When the company analyzed the results, they discovered the surface face hardness exceeded that obtained from all other processes they were using, in addition to greatly extending life on the grip areas. The risk of scrapping expensive parts was eliminated, and build schedules were shorter and simpler because there was no need to factor re-machining or re-manufacturing of the segments.

As the company evaluated the results of the laser heat treating process for their mandrels, they discovered numerous other components in their plants that could benefit from laser heat treating. However, the costs of owning and operating a CO2 laser for materials processing were prohibitive. As a result, they elected to contract their laser heat treating requirements to LBT.

A valuable technology asset to defeat wear problems

As these two examples illustrate, laser heat treating may be the only answer to many case hardening requirements. Shafts, sleeves, bearing seats, tools, and guide rails are potential laser heat treating applications. There are also many production components that can derive significant financial and engineering benefits from laser heat treatment. Currently, many of these parts simply enter service without being properly hardened, or their costs are excessive because of extra material and/or machining costs associated with preventing or repairing distortion from other conventional heat treating methods. Finally, there are untold thousands of component designs that cannot be manufactured because they cannot be hardened adequately without the use of a laser.

Materials processing lasers are expensive, and only a few manufacturers can justify installing these systems in their production lines. So the typical approach is to over-design the part and prescribe post-treatment machining, or to change the entire design or the material specification. This approach, however, flies in the face of wise financial or engineering management, especially when there are ways to incorporate laser heat treating into the manufacturing process by using laser job shops.

Laser job shops capable of processing various steel components are normally small companies that specialize in certain markets or applications. If they have the appropriate material handling and workstation equipment, they can service a wide range of products and applications efficiently and economically. Like LBT, these companies usually offer other materials processing services like cladding, welding, and coating as well as machining and fabricating.

The optic systems on CO2 lasers used for these applications are complex and frequently beyond the abilities of many shops, large or small. There may be no more than 12 to 15 laser materials processing job shops in the United States, so the problem for most manufacturers is usually locating a qualified laser job shop to perform the desired services.  However, when they can be located and qualified, the benefits in improved performance and reduced costs associated with scrap and rework for many components make laser job shops an attractive addition to the manufacturing process.

If you have components that require case hardening and you’re tired of problems of distortion and failure, call BMR Group at 260-635-2195 and discover how easy it can be to gain the advantages of laser heat treating.