R&D Update: Evaluating dry film lubricants for automotive applications, Part II

Stamping lubricant tend to fail if contact pressure and temperature at the interface are high. For example, depending on the stroke rate during progressive-die forming, dies may reach temperatures of 200 degrees F to 250 degrees F.

The ironing test, developed at the ERC/NSM, reproduces production conditions of contract pressure up to 94 kilo pounds per square inch (KSI) and temperatures up to 300 degrees F to evaluate lubricant performance quantitatively. During the ironing test, lubricant performance on different sheet materials. In this test, the temperature and pressure at the tool-workpiece interface can be emulated by heating the ironing die and selecting a desired ironing ratio:

(R= (t0- tf / t0 ) x 100 )

Where: t0, tf = Initial and final thickness

On the left side of Figure 1 , a tool setup is shown in a hydraulic press with a CNC hydraulic cushion. The punch is stationary, and the ironing moves downward with the upper ram. The ironing ring’s derails are shown on the right side. The right is heated with a band heater that is insulated from a drawing die.

Testing lubricants is real-world production conditions is difficult and expensive. Lubricants should be tested in production conditions is difficult and expensive. Lubricants should be tested in production only after they have been proven effective in laboratory tests that emulate production conditions.

Recently the ERC/NSM conducted ironing tests to evaluate dry film lubricants with AISI 1018 sheet materials (initial sheet thickness, t0 =0.083 inch) at room temperature and tool temperature (68 degrees F and 168 degrees F, respectively). Detailed specifications of tested lubricants are given in Figure 2. A phosphate coating was used for comparison and benchmarking purposes.

Evaluation Criteria

Qualitative and quantitive analyses to determine lubricant effectiveness were tested on the following evaluation criteria:

• Maximum ironing load (the lower the load, the better the lubricant)

• Ironed cup surface topography after testing (the lower the surface roughness, the better the lubricant)

• Cup wall thinning (the lower the wall thinning, the better the lubricant)

• Lubricant buildup on die (good lubricants have minimum coating loss though die contact)

Test Results, Conclusions

Maximum ironing loads were compared for different lubricant and testing temperatures ( see Figure 3a and Figure 3b ). Lubricant C performed best regardless of temperature. However, as the testing temperature increased, lubricant B reacted similarly to lubricant C. Lubricant A displayed high friction at both testing temperatures.

Die lubricant buildup was indirectly quantified by measuring the specimen’s initial and final weights. In Figure 4 lubricant performance ranks are summarized in terms of evaluation criteria.

It should be note that specimens coated with lubricant C were not ranked in surface analyses, because phosphate coating is difficult to remove with chemical agents to measure surface roughness. In comparison to the phosphate coating (lubricant C), lubricant B displayed superior performance to lubricant A with the exception of buildup. This study illustrates that lubricant weigh directly affects die buildup characteristics.

By comparing laboratory test results with industrial results, the ERC ironing test was validated as a reliable method for evaluating lubricant performance under production-like conditions.