Case Studies in Practical Application of the TD Process

By H. Glaser, TD Center, USA
(reprinted with permission from Tube & Pipe Technology, September/October 1991 issue)

The world headquarters of Arvin Industries are located in Columbus, Indiana. The TD Center is also located in Columbus.

Arvin brought the TD process to the US industrial market. For the first six months, Arvin treated only parts for its own plants. Later, Arvin received its commercial license from Toyota and actively marketed TD services to other companies throughout 1989. The TD Center has 450 customers including 29 Japanese companies that have operations in the United States.

The range in size for parts treated has been from 1.2mm diameter punches to 160kg rolls for forming. Tool life improvements on the various tools that have been TD treated are, in many cases, 30 to 50 times greater. TD treated surfaces are extremely hard with excellent metallurgical bond to the substrate materials.

The TD Center has treated such tool steels as S5, S7, A2, A7, D2, D5, HIS, M2, M42 to CPM-1OV, CPM-9V, CPM-M4, CPM-M42, QR-90, ASP-23 and ASP-30. Post-heat treatment of high speed steel is not always necessary. Under-hardened high speed (RC57 to 59) steel that is TD treated sometimes outperforms fully hardened steels. However, substrates must be selected to withstand operating surface pressures or shock inherent in the conditions under which the specific tool operates.

Where higher substrate hardness is required, a cemented tungsten carbide substrate is recommended. For best dimensional stability, cemented tungsten carbide or properly heat treated D2 are the best selections.

Savings were realized not only in the reduction of downtime for maintenance, but also in the reduction of rejected parts and the cost of tooling replacement.

The die in Figure 2 is used to make a stainless steel bracket (1.35mm thick, 3000 series stainless steel) and is produced on a progressive die. The tool steel treated was D2. Prior to TD treatment this tool had been treated with TIN by the PVD process. Even with the TIN treated die, galling and scoring would occur after 4,000 pieces, causing substantial equipment downtime. After the initial treatment and diamond polishing, quality of the part was improved and the die produced 110,000 pieces without servicing. To date, this die has been re-TD treated three times with the same positive results.

The tool in Figure 3 is used to expand tubing for fuel systems used in the automotive industry. The tool is 19.05mm in diameter.

Initially the tool was made from cemented tungsten carbide. Due to galling, breakage would occur about every 400 pieces. TD Center engineers selected A2 as a replacement tool steel. After TD treating the A2 material and diamond polishing, tool life was improved to 22,000 pieces on average. Savings realized were significant, especially in tool replacement.

The product shown in Figure 4 is the inside liner of a microwave oven. Two deep draws are required which are very difficult due to small radius requirements. The part material is draw quality, aluminium killed. The tool steel used in this application was D2.

Prior to TD treatment, galling would occur every 650 pieces. This resulted in costly equipment downtime and polishing costs, along with rejected parts for scratches and cracks.

The two draw caps, weighing a total of 115kg, were TD treated and diamond polished. Some 58,000 parts were produced with no polishing to date, and the part rejects due to galling and fractures have been reduced to almost zero.

Figure 5 is a valve cover used on a diesel engine. The part is produced in a very large 9-station transfer die (approximately 1.8 meters x 3.7 meters). All wear-related sections of the die, which were made ofA2 and D2, were TD treated. The goal was not only to extend tool life but to eliminate all die lubricants. Substantial savings are realized by the elimination of lubricants, reduction in maintenance, and cost for part cleaning prior to welding.

Another savings not shown above was in material used to produce the part. Initially, interstitial free (IF) or vacuum degassed steel was required to produce the part within tolerance. After TD treating, common draw quality aluminium killed steel could be used. The tool is operable after 272,000 parts without maintenance, compared to 4.200 prior to TD treatment.

The tool shown in Figure 6 is used for bending 400 Series stainless steel tubing used for automotive exhaust systems.

To produce parts prior to TD treatment, the tool was inserted with wear-resistant bronze to prevent galling and maintain the dmnensions on the bend radius. The tool was capable of running an average of only 13,750 pieces prior to servicing. The TD treated D2 replacement tool has processed 256,000 pieces and is still operating.

In addition to the savings realized from tool maintenance, improved quality was realized through dimensional stability.

In Figure 7 the extrude punch tool is shown in front of the part produced. This punch extrudes a bearing seal mounting area and the metal is extruded to control very tight dimensional tolerances. The major problem with conventional tooling approaches was galling of the sealing surface.

When the die was initially made, D2 was used for the punch and only about 300 pieces between polishing were possible. Also, large amounts of die lubricant were required. To improve this condition, cemented tungsten carbide was tried next. With the tungsten carbide punch, 4000 pieces could be produced between die servicing, with lubricant still required.

Next a new punch was made from D2 and TD treated. All die lubricant was removed from the operation and the process is still functioning after production of 202,000 units.

Proper surface preparation prior to TD treatment is the key to enhancing the movement or sliding action of metal. Surfaces should have a finish of 5 to 7 RMS (Root Mean Square). Post-treatment finishing, such as diamond polishing, will further improve the quality of the surface treated adding to surface lubricity.

A trend we are experiencing in the U.S. TD market is the increased use of TD treated cemented tungsten carbide in tooling. Although the harder carbide substrate (1200 to 1700 Vickers) alone solves many problems compared to a typical A2 or D2 tool steel (700 Vickers) application, galling still occurs in many applications. A TD treated carbide tool (3200 Vickers) yields superior performance in many applications. It has a very high substrate hardness which resists surface pressure and an extremely hard surface which yields superior galling performance. Several producers of cemented tungsten carbide are now recommendinq TD treatment to US toolmakers for major wear improvement to their product.