Induction-heating technology is widely used in the automotive sector, and the benefits to manufacturers are well known. Hardening specifications (depth, profile, cycle times, etc.) are mandatory requirements that any induction-system provider must meet. Especially in the current economic climate, all companies involved in the supply chain should be looking for unique solutions that directly impact the customer’s business strategy.

Fig. 1. Rotating inductor system for hardening large parts. Shown is the functioning scheme, parts and their positioning.

Solutions could be oriented to increase the production with the same investment, to save operating and maintenance expenses or to improve the quality. GH Induction Group has been working in partnership with automotive and other sectors for many years to arrive at the best solution for their needs. Its offerings include standard, customized and, in some cases, new and unique systems. Some of the developed solutions are highlighted here.

Rotating inductorsare used for hardening bores of large parts that cannot be easily rotated (Fig. 1). This patented system avoids the need for parts to be mechanically handled and turned. Parts are fixed while the inductor rotates along the Z axis, and the hardening quality and process speed increase dramatically. Other benefits are that the machine design becomes lighter, less floor space is consumed and the operation is safer.

A multi-axis CNC machine combined with specialtwin-centered inductors(Fig. 2) is designed to efficiently harden small and large diameters on the same part. Using a single inductor with different diameters (twin-centered inductor) is a convenient solution when the part has different cross sections (e.g., camshafts). The design permits improved relationship between part and inductor with just one heat station/inductor for the heat treatment of the whole part. The direct benefit is to produce a complete part (no batches), simplifying the process. In addition, because the inductor fits the part, the consumed energy is much lower and the quality is improved.

Fig. 2. GH twin-centered inductor system showing functioning scheme, inductor and hardening profile.

Edge tracking inductors –EdgeTrack system– are used for precise pattern hardening of camshaft lobes (Fig. 3). In vertical-hardening machines the inductor follows the surface of each cam during the heating cycle. This technique allows even heating around the cam, improving the hardening profile, and it reduces the energy consumption.

Parts such as CV-joint components areinduction tempered in a tunnel installation. This represents an advantageous alternative to conventional furnaces mainly because of the reduction of the intermediate stock of parts, integration in the automatic production line and the reduced footprint.

The automatic, high-productionstarter rings installation(Fig. 4 – lead photo) shows the capacity to develop challenging solutions. Hardening, tempering, marking and drying are carried out in a 7-second cycle time. The short cycle time, the different type of parts, the quick changeover time and the input ring stack buffer maximize the production.

In Europe, GH Group is offering acuring systemthat provides complete and spot heating on structural-adhesive material on automotive panels – door, hood, lift gate, trunk lid, fender and roof. The main customer benefit is to obtain a high-quality finish via fixation of inner and outer panels in the hem flange borderline, corrosion protection (sealing) and polymerization of the adhesive. All German car manufacturers like Audi, VW, Mercedes, BMW and Porsche are employing this application.

Fig. 3. GH edge-tracking system for camshaft lobes showing functioning scheme and inductor positioning.

The power systems portfolio covers wide frequency-range power solutions,Transithermic® Generators. With a large frequency and power range, 6 kW–2,400 kW and 500 Hz–400 kHz, these generators offer different combinations of parallel or series circuits. With the same power supply, different power outputs provide for treating a variety of parts, or multifrequency capability gives process flexibility for hardening and tempering. The configuration flexibility, high power factor, energy efficiency and modularity contribute to a reduction in operating expenses.

Solutions exist using multi-axis CNC machines forhardening large gears and raceways – GTH and GTV. In addition to the automotive sector, GH Group has been working with other industrial sectors with contributions in wind energy, cranes or handling vehicles using large slewing bearings (Fig. 5).

Other versatile installations have been developed to harden any combination of raceways and gears – inner or outer – adjusted to the customer volumes and type of production (Fig. 6).

Fig. 4. Overall view of automatic high production for starter rings

Detailed Description of Unique Solutions

GH Tempering Tunnel
Tempering by induction represents an advantageous alternative to conventional furnaces:
  • Small dimension (surface less than 6 m2) instead of big furnaces
  • Reduction of the intermediate stock of parts, with a maximum of 15 parts in process at the same time
  • Ease of incorporation in an automatic production line
  • Immediate availability of parts
  • Part-by-part control
Induction treatment allows perfect control of the process – better than conventional furnaces – achieving a homogeneity of heating, with differences in temperature of less than 10°C. Tempering-tunnel installation is divided into two parts: the heating tunnel and cooling tunnel.

The parts pass on a chain conveyor through the tunnel. At the exit, a pyrometer controls the output temperature and selects acceptable parts to pass through the cooling tunnel. A configuration based on a 50-KW generator can achieve a production greater than 300 parts per hour. Tempering-tunnel installation main process characteristics:
  • Power – 50 KW
  • Frequency – 2-5 kHz
  • Production – 300 parts/hour (12 seconds/part)
  • Maximum part length – 275 mm
  • Maximum part diameter – 150 mm

Fig. 5. GTV-type (vertical) machine for gear and raceway hardening slewing bearings up to 4,500 mm in diameter. Note the part standing on machine.

Edge-Tracking Inductors - EdgeTrack System

The machine equipped with this system is composed of four servo-controlled axes – X, Y and Z for the inductor table and the rotation of the vertically positioned camshaft. The inductor is designed to ensure a close distance between the part surface and inductor and at the same time allow both cams and bearings/supports to be treated in one station.

By synchronizing movement of the inductor with the rotation of the camshaft, hardening profiles are achieved that are not possible with traditional machines. This method also avoids the problem of overheating the cam top while trying to harden the whole perimeter of the cam.

Combining the two systems (EdgeTrack System and twin-centered inductor) incorporates the benefits of both.

Fig. 6. GTH-type (horizontal) machine with dual head and six-arm table for large gears and raceways up to 4,500 mm in diameter.

Large Gear/Raceway Machines

GTH (horizontal) and GTV (vertical) machines are commonly used in industries with low production and short series but with a wide range of part sizes.

Parts are slewing bearings and large rings composed of a combination of inner or outer gears (teeth) and inner or outer raceways (single or double). Teeth hardening is by scanning, tooth-by-tooth (some machines are able to treat two teeth at same time), and raceway hardening is performed by scanning or single shot in some cases (Fig. 6). The two basic formulas used in these treatments are:
  • GTH-type, manual-loading machine where the part is treated in horizontal position. Depending on the diameter and the section of the part, the table is composed of three arms or six arms.
  • GTV-type, manual-loading machine where the part is treated in vertical position.
The same installation is able to harden different-size pieces, and coils are designed for the desired hardening profile of each customer.

These systems include mostly two inverters to perform multiple heating (preheating and heating) of large raceways and sometimes the treatment of teeth two by two. The GTH and GTV machines use one or two inverters at 150-200 KW and single or multiple frequencies depending on the treatment specifications.IH

For more information:Contact Frank Wilson, GH Induction Group, 1840 Roslyn Road, Grosse Pointe Woods, MI 48236; tel: 313-432-1602; e-mail:; web:

Additional related information may be found by searching for these (and other) key words/terms via BNP Media SEARCH at induction, tempering, inductor, frequency, tunnel furnace

SIDEBAR: GH History and Experience

GH Induction Group is young in North America. However, the GH tradition of service to different industries using low-, medium- and high-frequency induction goes back for decades. Over 4,000 systems supplied since 1961 to over 50 countries form a well-established experience base.

Automotive manufacturers and suppliers are among GH’s customer base: Audi, GKN, Mercedes, Chrysler, BMW, Citroen, Nissan, DANA, Delphi, Peugeot, Eaton, Ford, TRW, Honda, John Deere, Kia, VW, etc.

GH’s philosophy involves working closely with customers to find customized solutions for their needs. Special focus is given to complete solutions and turnkey projects.

Constantly increasing the local presence, it has sales representation and technical service in almost every country in Europe, U.S., South America and Asia. Its production facilities are located in Germany, Spain, China, India, Korea and Brazil.