Simon C. Tung

Application of Nanofluids in Minimum Quantity Lubrication Grinding

This research investigated the wheel wear and tribological characteristics in wet, dry, and minimum quantity lubrication (MQL) grinding of cast iron. Water-based Al2O3 and diamond nanofluids were applied in the MQL grinding process and the grinding results were compared with those of pure water. During the nanofluid MQL grinding, a dense and hard slurry layer was formed on the wheel surface and could benefit the grinding performance. Experimental results showed that G-ratio, defined as the volume of material removed per unit volume of grinding wheel wear, could be improved with high-concentration nanofluids. Nanofluids showed the benefits of reducing grinding forces, improving surface roughness, and preventing workpiece burning. Compared to dry grinding, MQL grinding could significantly reduce the grinding temperature.

Tool life and wear mechanism of uncoated and coated milling inserts

Abstract A systematic study was conducted for face milling inserts cutting 4140 preheat treated steel. The flank wear of uncoated C5 carbide insert, as well as TiN, TiAlN, and ZrN coated inserts was evaluated and ranked. Tool life was expressed as the function of cutting speed and feed. This information is useful for production optimization. Wear mechanisms of attrition, abrasion, mechanical fatigue, and thermal fracture were identified and were represented by wear maps. The TiN and TiAlN coatings provided significant improvement in tool life. The ZrN coated inserts performed about as well as the uncoated C5 carbide inserts.

Scuffing and wear behavior of aluminum piston skirt coatings against aluminum cylinder bore

Abstract Various coatings, especially nickel based ceramic composite (NCC) coatings, have been considered as an alternative to the use of iron plating on aluminum pistons in aluminum cylinder bore engines. Laboratory simulation tests were conducted to determine the scuffing and wear behavior of piston coatings against 390 Al engine cylinder bore. The tested piston coatings included nickel–tungsten (Ni–W) plating, electroless Ni plating, Ni–P coatings with ceramic particles such as boron nitride (BN), SiC, or Si 3 N 4 , as well as titanium nitride physical vapor deposition (PVD) coating, diamond-like carbon (DLC) coating, and hard anodizing. The scuffing and wear resistances of these coatings were evaluated and compared with tin plating and iron plating. Wear tests were performed in lubricated sliding at 400 K, using a modified Cameron Plint High Frequency test machine with a special fixture to hold the piston samples. Scuffing tests were conducted under the conditions in which lubricant starvation occurred. Metallographical work and chemical analysis of the interactive surface layers were performed on the tested samples. The simulation test results ranked the relative performance of the coatings against 390 Al bore, and revealed their tribological characteristics. Ni–P–BN coating, iron plating and Ni–W plating showed very good scuffing resistance when sliding against 390 Al bore samples. DLC, electroless Ni plating and Ni–P–SiC coating had moderate scuffing resistance against 390 Al. Ni–P–Si 3 N 4 and TiN coatings had marginal scuffing resistance against 390 Al. TiN PVD coating had the most severe wear on 390 Al bore samples. Hard anodizing, DLC, Ni–P–SiC and Ni–Si 3 N 4 coatings had less severe wear on 390 Al than TiN coating. With very good wear resistance themselves, Ni–W plating, electroless Ni plating, iron plating and Ni–P–BN coating produced the least wear on 390 Al. Engine dynamometer tests were conducted to confirm the simulation test results. This work indicates that the scuffing and wear bench simulation tests can be used as a rapid, low-cost and repeatable means of screening and studying the tribological behavior of the potential material combinations of piston coatings and cylinder bores.

An experimental investigation of piston skirt scuffing: a piston scuffing apparatus, experiments, and scuffing mechanism analyses

Abstract Piston skirt/cylinder bore scuffing is one of the main failure mechanisms affecting the life of automotive engines. A piston scuffing apparatus that simulates the relative motion between the piston and the cylinder liner of a typical engine has been designed and constructed to investigate scuffing mechanisms and determine the conditions under which scuffing happens. With this apparatus, the scuffing performance of an aluminum–silicon piston material with a variety of skirt coatings is studied and scuffing mechanisms investigated. The research also explored the influence of the piston skirt surface texture and cylinder bore surface roughness on the cylinder bore–piston skirt contact, as well as the microstructures and morphological features of the surface and the near-surface materials in scuffing.

Modeling of Abrasive Wear in a Piston Ring and Engine Cylinder Bore System

Engine-related improvements such as more efficient engine components, improved engine oils, and high-performance coating materials, need to be verified in terms of their effects on the tribological performance of the piston ring/cylinder bore system. The main purpose of this research is to develop an abrasive wear model for the piston ring/cylinder bore system during steady-state operation by considering the effects of temperature, load, oil degradation, surface roughness, and material properties. The model can be used either in theoretical modeling or integrated with finite element analysis. Based on a laboratory simulator, a three-body abrasive wear model has been developed to model the wear progression of the piston ring/cylinder bore system during steady state operation. The proposed novel abrasive wear model addresses the effects of temperature, load, oil degradation, surface roughness, and material properties. The feasibility of the proposed model is illustrated by a numerical example.

Wear and scuffing characteristics of composite polymer and nickel/ceramic composite coated piston skirts against aluminum and cast iron cylinder bores

The purpose of this research was to evaluate the tribological behavior and compatibility between coated piston skirts and aluminum or cast iron bore counterfaces. Aluminum piston skirts with either composite polymer coatings (CPCs) or nickel/ceramic composite coatings (NCCs) were evaluated. Among the NCC coated piston skirts, Ni–P–BN showed consistent low wear on either cast iron or the aluminum bores. The tin plated piston skirt generated low wear depths on cast iron or 390 Al bore surfaces, but higher wear depths on 413 Al or 356 Al bore. All the CPCs generated much less wear on cast iron or aluminum cylinder bores compared with the Ni–P–SiC or Ni–P–Si3N4 skirt coatings. Even the wear tests using 413 Al and 356 Al bores showed very low wear depths. Among the CPCs, two coatings with different percentages of molybdenum disulfide and graphite particles dispersed in the resin generated the lowest wear on 390 Al bore. Using a CPC over a hard-anodized surface, the bore wear depth was further reduced and became much more consistent compared with using a CPC alone. The response of the coatings to a simulation of the oil starvation associated with scuffing conditions revealed that the CPCs had intrinsic resistance to scuffing. However, the durability was not very good. The Ni–P–BN coating had intrinsic resistance to scuffing and good durability when sliding against 390 Al bore in the unlubricated conditions. The hard anodized surfaces with the CPCs showed much improved coating durability with good scuffing resistance.

A diamond-like carbon film for wear protection of steel

Abstract We have deposited diamond-like carbon (DLC) and amorphous SiN films on a tool steel coupon. In order to make the DLC adhere to the metal, we used an interlayer of amorphous SiN, taking advantage of the fact that the SiN coating adheres to the metal and the DLC adheres to the SiN. The DLC/SiN-coated substrate showed a significant reduction in friction compared with either uncoated or SiN-coated substrates in our laboratory bench tester after lubricated sliding for 30 h. In addition, on the basis of surface profilometry analysis, the DLC/SiN-coated plate showed less wear and a much smoother surface. The films were analyzed using X-ray photoelectron spectroscopy and sputter depth profiling. Our results suggest that DLC is a promising coating for wear protection.

In-situ electro-charging for friction reduction and wear resistant film formation©

A technique has been developed to form friction-reducing and antiwear films in-situ by means of an electric field applied between rubbing metal surfaces. Using this in-situ charging technique, the effectiveness of zinc organodithiophosphate (ZDP) additives as antiwear and friction reducing agents can be enhanced by electrochemical reactions which form surface coatings. The coatings formed on sliding surfaces compared with uncharged surfaces reduce friction by up to 35 percent. In addition, during the sliding process, the films formed on the surfaces are replenished and protect the rubbing surfaces from wear. A steel plate subjected to rubbing and in-situ charging for four hours had a smooth surface and a yellowish reaction film; the one without charging was rougher and no yellowish reaction film was formed. The improved tribological characteristics are attributed to an increase in the electrochemical reactivity of the ZDP-mineral oil blends and the formation of phosphate or sulfate films on the metal surf...

Wear Testing of Seals in Magneto-Rheological Fluids©

Magneto-rheological (MR) fluid-based dampers can be used in suspensions to modify ride, handling, and suspension frequencies in autos. We have developed a unique seal wear test method to simulate the wear of rod seals in Magneto-rheological fluid-based dampers. In this test, seal material samples in the form of rectangular coupons are immersed in a bath of MR fluid, and a section of the rod is brought into contact with the seal coupon. The rod is loaded against the coupon with a known normal force, and a variable-frequency reciprocating machine is used to stroke the rod back and forth across the material coupon surface. Test conditions such as normal load, frequency and amplitude of oscillation, and temperature are adjusted to simulate desired conditions. This bench test method ranks various seal materials qualitatively in the correct order (as determined in field tests with these seal materials) in terms of wear and abrasion resistance and constitutes a valid test procedure for the screening of seal materials, MR fluids, and rod surface coatings.

Tribological Investigation of Piston Ring Coatings Operating in an Alternative Fuel and Engine Oil Blend

The tribological performance of piston ring coatings, including Mo, CrN and physical vapor deposited Diamond-Like-Carbon, sliding against cast iron cylinder segments was studied using a reciprocating bench friction and wear machine. The surface interaction of ring coatings with the blend of 85% ethanol I 15% unleaded gasoline (ethanol 85) fuel and energy-conserving engine oil containing molybdenum dialkyldithiocarbamate (MoDTC) was compared and analyzed. The results show that the DLC coating has the lowest coefficient of friction among all the coatings when running in a blend of engine oil and E85 fuel. The CrN coating has the lowest ring wear but produces the highest wear on the mating cylinder segment. With MoDTC in the engine oil, the wear volumes for all ring coatings are higher while the wear volumes of the cylinder segment are lower than those operating without MoDTC. Based on the surface profile and roughness measurements, the surface roughness becomes smoother and the skewness becomes more negative after the running-in process. Presented at the 57th Annual Meeting in Houston, Texas May 19–23, 2002