2D beats 3D – if you focus on distortion control

Concept of 2D – heat treatment

(29.07.2019) Controlling distortion is of key importance during the case hardening process for the production of gear components. By effective control of distortion and the variation of distortion, significant costs in post heat treatment machining processes can be avoided. In some cases, it is even possible to eliminate all post-machining operations. In other cases, it may be possible to avoid the press-quenching of individual components, resulting in huge cost-benefits.

New vacuum furnace designs allow the treatment of small batches in a single layer of parts (“2D-treatment”) which allows for easy automated loading and unloading of the fixture-trays. By using the small batch concept, a continuous flow of parts can be established (“One Piece Flow”). There is no need to wait until enough parts are collected to build a large batch with multiple layers (“3D-treatment”). This compact furnace unit can be implemented into the heart of the production chain and provides heat-treatment processes which can be fully synchronized with the green and hard machining-operations.

Gear manufacturing with central hardening shop and with “One Piece Flow” integrated manufacturing lines

When performing case hardening, the components are Low Pressure Carburized (LPC) at high temperatures followed by gas quenching. The treatment in single layers offers an optimum in quality regarding

  • temperature homogeneity,
  • quench homogeneity and
  • distortion control.

Furnace system for 2D-treatment

The following figures show the SyncroTherm-system® from ALD Vacuum Technologies GmbH, which was developed specifically for the needs of 2d-treatment.

SyncroTherm® - system for 2D heat treatment

View into the SyncroTherm® - system providing 6 hot-zones for heating and carburizing

Six hot-zones are provided in one system for the process of Low Pressure Carburizing (LPC). Each hot zone is individually controlled regarding temperature and the supply of process-gas.  Once the targeted carbon-profile for the gear components is achieved in the hot-zones, the tray is transferred to the quenching chamber for the process of high pressure gas quenching (HPGQ) using nitrogen (N2) as inert quench medium.

Results

The superior distortion control of 2D treatment compared to 3D-treatment was demonstrated in several studies on transmission components. E.g. for a Final Drive Ring gear from a 6-speed automatic transmission, the average change of flatness during heat treatment was reduced by 24 percent when changing from 3D-treatment to 2D-treatment. The average change of roundness was reduced by 50 percent (see figure below). This improvement in distortion control will result in significant cost savings for subsequent hard turning and grinding process steps.

Batch of Final Drive Ring gears for 2D-treatment (a coupon-sample was placed in the center of the batch for metallurgical analysis)

Change of roundness during LPC-treatment of Final Drive Ring gears; comparison between 3D - treatment and 2D-treatment

Further practical examples for improved distortion control on Internal gears, Input shafts, Sliding sleeves and other transmission components when applying tailored LPC-processes with 2D-treatment will be published at the 3rd International Conference on Gear Production 2019 organized by VDI.

Outlook

Meanwhile more than 30 SyncroTherm® - systems are in operation providing superior quality regarding

  • distortion control
  • microstructure (no surface oxidation, homogenous carburizing) and
  • cleanliness (no need to wash parts after treatment).

In addition, this new concept in heat treatment allows full integration and full synchronization of heat treatment into the line of manufacturing.


Author

Dr. Volker Heuer; Director R&D,  ALD Vacuum Technologies GmbH, Hanau, Germany