posted on June 01, 2009 16:30
By Mike Kojima
|The WPC treatment process works by bombarding the metal surface with a special media at high velocities leaving a hard micro dimpled surface.
No, in this case special treatment isn’t the parting of the velvet rope in the VIP line at an exclusive club, in our case, it's something better. In this present struggling economy, anything that adds cost to an engine build is a hard sell when engine builders are struggling to stay in business and racers search far and wide for sponsors to fund their programs. Street performance fans move car mods way down on their list of money spending priorities as well. However, now more than ever, it is time to use value added processes that offer significant gains in both performance and longevity to engine builds. Many times it pays to spend more on your engine build to save money in the long run. In this series, we will be investigating special treatments such as exotic metal treatments, coatings and other state of the art processes. WPC is such a process. WPC is such a unique process in our industry with an amazing range of positive attributes that it deserves a stand alone article of its own.
Contrary to popular belief, WPC is not a coating; WPC is a metal improvement process, developed in Japan. WPC is a well kept motorsports secret that is used extensively at high levels of the sport, such as JGTC, MotoGP and WRC. Recently WPC has been gaining popularity in North America in venues such as Pro Stock drag racing, IRL, ALMS and NASCAR. WPC is also gaining acceptance from the OEM auto and motorcycle manufacturers such as Honda and Yamaha as a better performing alternative to coatings to enhance wear resistance, extend service life and to reduce friction.
WPC is very secretive about their exact process but we have been able to glean a few important details from indirect observation and our own personal experience with the process. WPC is closely related to shotpeening except it is done in a very different manor. Like shotpeening, WPC involves impacting a part with spherical projectiles to produce surface compressive stress, plastic deformation and grain refinement. Like shotpeening this action greatly improves fatigue strength and stress corrosion fracture resistance. However WPC differs from shotpeening in that the peening media is several orders of magnitude smaller, much harder and the impact velocities are much higher.
|The above chart compares stress load Twp the amount of cycles to failure. Notice the WPC treated part greatly outperforms untreated and shotpeened parts even with a much higher load
Although WPC will not divulge exactly what their media is made from, it resembles baby powder to the casual observer. We conjecture that the material is some sort of ultra hard ceramic whose dimensions and roundness can be precisely controlled like silicon nitride. These spheres are in the low micron range size wise and the impact velocities are near sonic in speed. We also believe that metallic additives such a zinc, tin and molybdenum disulfide are added to the mix to add some anti-galling lubricity or extreme pressure characteristics to the surface. At high velocities, the additives are probably inter-granularly incorporated into the surface of the metal at a molecular level, making their effects permanent and long lasting. We asked the folks at WPC to confirm this but they sort of just smiled and said nothing.
We can say that WPC, however secretive they were about the exact process was generous in showing us reams of empirical test data to back up their claims; much of it was from some of their OEM and high end racing customers that we had to swear not to reveal. Coming from an OEM and Motorsports engineering background, we can assure you that these tests are very thorough and repeatable.
WPC offers some advantages over shotpeening. Due to the small low mass projectiles and high impact velocities, WPC produces a higher amount of compressive stress and an increase in the degree of grain refinement to the base metal over shotpeening. The velocities are so high that in addition to shotpeening-like grain refinement via cold working, there is also a melting and quenching phenomena going on at a very micro level as well. The result is an extremely fine grained, slip plane less nano crystalline structure with a high degree of surface hardness formed over the surface of the part, unlike shotpeening which has only a slight effect on surface hardness and strength. Because of this ultra fine grained surface, WPC has superior fatigue strength gains and stress corrosion fracture resistance when compared to shotpeening. Due to the small mass of the media, the affected zone of WPC treatment is less than 0.001", much shallower than shotpeening.
| This is a metallograph of a WPC part. A metallograph is a thinly sliced cross section of a piece of metal that is polished and acid etched so the crystal grain of the metal can be observed. WPC refine the grain, make it finer and thus reduce the chances of stress cracks forming on the surface. WPC also removes the fine scratching left by machining and converts it to homogeneous dimpling, eliminating these small potential stress risers in the surface
Mostly because of the smallness of the media, WPC does not affect the dimensions of a part. WPC does not damage delicate machined surfaces. WPC can be applied straight to areas where dimensional control and surface finish is critical, such as bearing bores, pistons, cylinder bores, camshafts, crank fillets, valve bodies, cam followers, valve stems, valve springs, seal surfaces, axle splines, CV joints etc. In our opinion, this is a huge advantage over shotpeening whose severe stress and abrasive action can literally damage surface finishes and blast-distort parts. Due to the light mass of the media, WPC can be used for fragile dimensionally critical parts such as piston rings and even plain bearings. Amazingly, every metal engine part can benefit from WPC treatment without fear of damage.
Another big advantage that WPC has is a big reduction in friction. The WPC process leaves an extremely fine dimpled surface on the treated surface. The WPC media is so fine that the surface dimpling cannot be seen with the naked eye and can only be observed with a microscope. The micro dimpled surface is one of the secrets to why WPC works so well. WPC’s micro dimpled surface helps reduce friction in three ways. First the dimpling helps maintain an oil film which reduces metal to metal contact. Second the dimpled surface helps reduce contact area in general to reduce friction. Third WPC creates a slippery hard surface with anti friction and extreme pressure materials embedded into it.
|More metallographs showing grain refinement of WPC. Another special polarized light photo shows the reduction of point contact stress of WPC treated gear teeth
These properties make WPC an excellent process for treating cylinder bores, pistons, rings, wristpins, gears and anywhere reduced friction can help. Test data by a major OEM manufacture has shown that WPC treatment of pistons can reduce friction and wear of pistons by two fold over the best skirt coatings. Recent testing by a major forged performance piston manufacture has also shown WPC to be more effective to the reduction of skirt wear and scuffing over any coating presently on the market.
Friday, June 12, 2009 12:31 AM
Now I know why I've missed you, Mike. Just the right amount of information, no cheesy come ons. In an alternative life, I could see me doing this to my daily SE-R. And, anything that keeps road racers out on the road longer(wish Speed would show more) is a good thing.
Friday, June 12, 2009 1:50 PM
I wonder if WPC can be used in an additive way with cryo or if one supplants the other. Or, is one less expensive than the other? What are the trades? Very glad to see you doing this Mike, thank you.
Friday, June 12, 2009 1:57 PM
Yes it does, in the article I explained this and I explained the order things should be done, cryo first, then hard peening and finaly WPC.
Cryo and shotpeening are pretty cheap but ultimatly WPC probably does more, if you were to do only one thing, WPC would be it. It is slightly more expensive that cryo and shotpeening though.
I am happy you like this place!
Wednesday, June 17, 2009 12:40 AM
Is it possible to have the piston skirt wpc treated and have the dome ceramic coated?
Wednesday, June 17, 2009 7:14 AM
Yes, thats what we are doing on some of our builds right now. We WPC treat the cylinder walls and piston skirts and coat the domes.
Friday, June 19, 2009 3:48 PM
Mike, thanks for your reply. For a budget rebuild, what parts should take priority for WPC treatment?
Friday, June 19, 2009 4:52 PM
Since most of an engines wear and friction occurs in the cylinders, I would do the cylinder walls, pistons and rings. The next area of friction is the valvetrain, so the cams and cam followers, Finlay I would do the crank and bearings.
However if your engine has problem areas where failure occurs frequently, I would give those areas priority
Sunday, June 21, 2009 5:30 AM
It seems to me kind of counterintuitive to treat LSD clutch plates with this. This is the one place you desire heat/friction, so while it may last longer because its wearing less, how would it not make the LSD lock up less?
Sunday, June 21, 2009 9:39 AM
Most JDM Salisbury diffs have way to much lock and are way to aggressive for grip driving. We usually deactivate 3-4 clutches per side. Otherwise you can't get the power down on the exit of turns, the car just wants to drift. If the WPC is smoother and reduces this excessive lock, its a good thing. On a Kaaz diff which is the most chatterly and aggressive diff on the market, It locks so hard, a car wanders from side to side with it in on/off throttle and it just doesn't chatter, it bangs, WPC eliminates the chatter and makes it way more drivable. In fact WPC treatment is now a factory option with KAAZ.
Tuesday, July 21, 2009 11:39 AM
Just curious as I'd like to use WPC on my next engine. With cylinder wall finish so critical in many engines how does WPC affect that with regard to ring seal?
Thanks, great place you've got here guys.
Tuesday, July 21, 2009 11:42 AM
WPC helps ring seal and life. It improves both greatly.
Thursday, September 17, 2009 11:46 PM
Does this influence in any way the break-in procedure of a completely rebuilt engine? With reduced friction and increased surface hardness of the ring, it would take much more revolutions (miles) for the ring to wear down, and take up the the shape of the cyl. bore, and seal correctly, or am I seeing it wrong? Or is a different, more aggressive hone pattern necessary? Or the treatment should be applied to the piston and ring after broken in? (sorry if this sounds silly, I'm new to the scene)
Do you know if WPC treatment is available anywhere in Europe?
Thursday, September 17, 2009 11:50 PM
With some types of rings WPC does take longer to break in but once broken in, it lasts longer and has lower friction. I think WPC is only available in the USA and Japan.
Friday, January 08, 2010 6:58 AM
Will this increase the strength while decreasing the elasticity of the material?
What are some of the disadvantages other than the ones listed in that article?
Friday, January 08, 2010 11:16 AM
It mostly increases the fatigue strength, it doesnt change the modulus of elasticity. We havent found any disadvantages other than perhaps that some motors have taken longer to break in. THey wear a lot better though.
Saturday, May 15, 2010 7:08 PM
Mike, do you know if there would be enough benefit to the WPC process if used with a cerametallic coated rotor housing such as that sold by JHB Performance as used on a ~300hp street/mild time attack engine?
Sunday, May 16, 2010 2:33 PM
You mean WPC a turbine housing? I don't think thats worth it.
Saturday, July 24, 2010 4:31 PM
I briefly studied the wpc process on the mechanical properties of steel. From what i remember the projectiles are a steel shot whose speed can be adjusted by the size of the shot. I do remember the speeds were between 100-200 m/s!
The wpc process greatly improves ferrous metals such as steel. The projectiles rapidly heat the surface and then the metal cools rapidly when not bombarded. The result is full martensite. So, you are correct Mike when you say it isn't BCC crystal structure, because it's BCT.
Thursday, July 29, 2010 10:03 AM
Has anyone used the WPC process on a Journal Bearing turbo (All the internal friction surfaces)? How much (if any) improvement would there be in spoolup or transient response?
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