[Tom Vaught]

A question was raised about how to grind a camshaft quickly.

By using abrasive belts!!!!!
This was developed in Italy in 1977; it was successfully implemented by GM engineers only in the early 1990s. Production Camshaft machining cannot have a camshaft grinder spending 1/4th of an hour grinding one camshaft.

Obviously the technology has been out there in production: (GM) camshafts for the last 30 years.

https://www.pfonline.com/articles/th...t-cam-grinding

The changing shape and composition of camshafts are challenging those responsible for surface finishing. As a result, an increasing number of cam-grinding operations are being performed with cubic boron nitride (CBN) superabrasives and technologically advanced conventional abrasives.

Camshaft grinding requires instantaneous changes in wheel-work contact length and material removal rates. In camshaft grinding, the arc of the contact between the wheel and the camlobe changes continuously as the base circle, flanks and nose are ground (seeillustration). The arc of contact can be represented by means of the equivalent diameter (De) and can be calculated:

De = Ds x Dw
Dw ± Ds

with:

Ds is the wheel diameter
Dw is the work diameter
+ is to be used when Ds > Dw
- is to be used when Ds < Dw

A large equivalent diameter represents a longer arc of contact between the wheel and work material. So the arc of contact is large as the wheel passes over the flanks and becomes smaller as the nose and base circle are ground.

As the De increases, more abrasive particles come in contact with the work material. This reduces the force acting on each grain, and makes the ploughing and sliding interactions more dominant. This is usually observed as increased grinding power or force for the same grinding condition.

In camshaft grinding, as the De is larger while grinding the flanks, higher power will result if the radial infeed and work speeds are maintained the same as when grinding the nose or base circle. This can result in unacceptable thermal damage on the lobes. In order to avoid this problem, the work speed is generally reduced as the wheel grinds the flank portions. This reduces the rate of material removal and helps lower the grinding power.

Camlobe grinding is a complex variant of cylindrical grinding. When raw camshafts are manufactured—by casting in sand or shell molds (cast iron), forged or machined from barstock (steel)—roughly 0.02 to 0.12 in. of stock is generally available for grinding. After the lobes and journals are induction hardened, the journal bearings are ground, usually on a centerless or cylindrical grinder. Since the camshaft is supported on workrests, with the journals as a reference during camlobe grinding, it is important that the journals be ground properly because any imperfections will be translated to the camlobes during lobe grinding.

Although the necessary surface finish on the lobes and journals is usually provided by the grinding, they are often lapped with fine-grit abrasive belts. Lapping after grinding has been found to be effective in reducing initial friction during the engine break-in period.

New Profiles

During the past decade, camlobes with a re-entrant profile have been gaining popularity because this design helps increase engine torque and horsepower and reduces emissions. In re-entrant camlobes, the ramps are concave instead of a straight line; this helps in opening and closing the valves much faster.

Also, the use of roller bearings at the interface with the camshaft in place of flat tappets has reduced friction, permitting higher engine speeds. However, the sharp line contact results in significant increases in contact stresses, which can exceed 250,000 psi. These high stresses can result in spalling and accelerated camlobe wear. So depending on the magnitude of the contact stresses, camshafts of different construction are used.

For lower contact stress applications, induction hardened or chilled nodular cast iron may be acceptable.

For contact stresses of 250,000 psi and above, steel cams can provide the most-reliable solution.

Composite Approaches

Composite camshafts of medium- and high-alloyed powered metal lobes mounted on a hollow tube are popular as they have the capacity of withstanding high contact stresses and offer improved tribological properties. Composite camshafts can be 50% lighter than cast iron or steel shafts; can have lobe material tailored to the application; and they can have lobes molded to near-net shape, which means that the amount of grinding stock, and consequently grinding time, are both reduced.

The requirements to have high-strength, low friction and minimal wear have prompted Japanese researchers to consider ceramic camlobes.

Camlobes are usually machined to final shape by grinding with bonded abrasive wheels containing aluminum oxide or CBN. Usually, one lobe is ground at a time, although in order to improve productivity, machines using multiple abrasive wheels are available. With this equipment, two wheels are mounted on a one-piece precision-balanced hub to grind two lobes at a time. But this approach can be used only if the lobes being ground simultaneously have similar lift profiles.

Abrasive Belts

Another approach to improve cycle time is using machines with abrasive belts. This was developed in Italy in 1977; it was successfully implemented by GM engineers only in the early 1990s. In these machines, the abrasive belt is pressed against the workpiece by a cylindrical contact shoe that, together with the belt, replaces the curved surface of the grinding wheel. These multiple-belt cam grinding machines can grind all lobes simultaneously for cycle time reduction.

Another advantage offered by these machines is in the grinding of re-entrant camlobes. Grinding of re-entry type cam profiles with grinding wheel requires that smaller diameter wheels be used. This restricts the life of the wheel, making its use less cost-effective. With abrasive belts, the curvature of the belt can be controlled by changing the contact shoe diameter, so re-entry lobes of high negative curvature can be easily ground.

Higher Speeds

The current trend to reduce cycle time involves grinding at high wheels speeds. Machine builders in Europe and Japan are marketing high-speed cam-grinding machines with wheel speed capability of up to 200 m/sec. High grinding wheel speeds offer the advantage of longer wheel life, lower forces, and high removal rates. Higher metal removal rates at higher wheel speeds reduce cycle time.

A variation of the high-speed approach involves high wheel speeds, large depth of cuts, and low work speeds. This approach is similar to High Efficiency Deep Grinding (HEDG) and is essentially high-speed, cylindrical, creep-feed grinding.

Another approach uses a high-speed grinder with a pair of wheel heads. One wheel head uses a brazed, single-layer CBN wheel and is used to rough grind the lobes very aggressively. The other wheel head uses a small-diameter vitrified CBN wheel for finishing the lobes. This approach has been successfully used to grind re-entry type camlobes.

Vitrified bonded aluminum oxide wheels are still popular for grinding camshafts, but most CNC machines are now shipped with superabrasive wheels.

CBN & Beyond

The hardness, thermal conductivity and chemical inertness of CBN
have made it an abrasive of choice for production grinding of ferrous and aerospace alloys. Several bond systems—resin, metal, glass, and brazed—are available with CBN. Among these, the glass, or vitrified, bond system has proven to be the most popular. These bonds are rigid, free-cutting and have good form-retention. In addition, the porosity in these bonds can be controlled for more chip clearance and better coolant application at the grinding zone. Vitrified bonded wheels are easy to true and do not require additional dressing procedures.

The inherent brittleness of the vitrified bond system contributes to the self-sharpening action during grinding, but the brittleness also makes the wheels susceptible to chipping and breaking if used improperly.

One answer to this problem is a segmented wheel design, where individual segments are cemented to a steel or aluminum oxide core. Benefits include:

•Easy replacement of damaged sections
•Safety at high wheels speeds—up to 150 to 200 m/sec.
•Properties of individual segments can be measured and monitored so there is consistency along the wheel periphery and from wheel to wheel.
•Special wheel adapters can be resegmented and reused after the CBN layer has worn out.

There is also a ceramic aluminum oxide abrasive that's making an impact in cylindrical grinding operations. This elongated, high-aspect ratio abrasive can make a difference in high speed grinding of cast-iron camlobes. They provide high removal rates compared to a vitrified CBN wheel. The lower cost and single-point truing capability compared to CBN could make them excellent alternatives.

By the way, Harvey Crane and Don Hubbard (Camshaft Machine Company)
were the very first to offer Roller Follower Camshafts (Ford production vehicles). Mustangs I believe.

GM had been doing Typical Flat Tappet Hydraulic camshafts with their high speed grinding knowledge for several years prior to that.

Tom V.

[Half-Inch Stud]

Okay. Got a Research paper (by Ford?) on cam lobe wear being related to cam lobe grinding speed. Sub-surface defects were increased with grinding speed increase. Realted to local thermal rise. Verified the correlation with Lobe failure in application.

Roller cams sound great until the equivalent duration for lift profile to flat tappet shows a radical lobe, thus the line contact pressure of the roller-on-lobe gets exciting.

We all know RollerCam with roller follwers are darn good in new cars, with small valves, or Cam-overhead, But the big old Musclecar profiles need so much Spring Pressure for them Big Valves and rocker pushrod and lifter deals at High RPMs.

[Tom Vaught]

Can't disagree with that HIS. The post was made to refute the comment that you could NOT grind a PRODUCTION camshaft very quickly. The knowledge on HOW to do that WAS available since 1977 with GM doing it in volume since the early 90s. (about 30 years ago).

Harvey Crane made use of that technology in the early days of owning Camshaft Machine Company to get the Work on the first Ford Roller Camshafts, which as YOU POSTED were NOT RADICAL GRINDS with massive acceleration rates.

But again the post was made to refute the comment THAT you could not grind a camshaft quickly.

Tom V.

[Half-Inch Stud]

I think there is a market for reliable HYD Flat Tappet cams. There's even a selection of profiles Avail for The ancient Pontiac. I suspect few suppliers grind em and many rebox as their own.

Fun Fact: I never used ZDP or any light metal additives in my cheap oil.

Since we know this, what is the market-ability of slow-ground Flat Tap Lifter Cams?

I think, theoretically, if we showed a video of all 16 valve lifters spinning right upon start-up thru warm up and a few revs, the enthusiasts would kick the door down for these cam and lifter combos.

PS: Fast ramp cams are just no good. All 16 lifter gotta be spinning throughout the rpm range.

[steve25]

Ask me how I like my GM V6 in my Olds I had ?
It failed two cams, but not in the normal west!

These Cam are hollow core with the lobes pressed on.
It’s so great that they can make Lobes fast for these types of Cams until the hollow core gets stressed too much from the load of driving the oil pump , or the block even changes shapes / warps by .00005” , or a combination of both and snap’s the cam core!

What a great idea GM!

[Tom Vaught]

Lots of oldsmobile vehicles made, lots of GM V-6 engines.
How about some SPECIFICS, Steve25.

Your post tells me nothing.

Tom V.

[Tom Vaught]

Originally Posted by Half-Inch Stud

Okay. Got a Research paper (by Ford?) on cam lobe wear being related to cam lobe grinding speed. Sub-surface defects were increased with grinding speed increase. Realted to local thermal rise. Verified the correlation with Lobe failure in application.

Roller cams sound great until the equivalent duration for lift profile to flat tappet shows a radical lobe, thus the line contact pressure of the roller-on-lobe gets exciting.

We all know RollerCam with roller follwers are darn good in new cars, with small valves, or Cam-overhead, But the big old Musclecar profiles need so much Spring Pressure for them Big Valves and rocker pushrod and lifter deals at High RPMs.

HIS lost his paper he was going to quote from, but the paper was done by an engineering student going for his master's degree and interning at Ford Research. The study was on a 2.3L 4 cylinder mule engine, and was some really nice work for a student. Several Research Engineering people signed off on his paper. Basically the paper did not address the subject we are discussing here. Can you grind a camshaft with accuracy using a very high speed grinding technology. The answer to that has been yes for many years.

Tom V.

[Half-Inch Stud]

Uhm, per PM, tossed hard copies, and have the VPT (Virginia PT) digital version in my Tech Library.

The paper on Cam lobe Reliability vs original grinding speed was my aim.

[jerry455]

He must not have had a 3800 v6, my buddy just turned 320,000 miles on his 2001 Lesabre. I see lots of high mileage 3800's quite regularly.

[Tom Vaught]

3800 V6 engines, especially the Turbo versions, were known for their outstanding durability, both on the street and drag strip.
Ken Duttweiler being one of the most famous of the V-6 Buick guys.

Tom V.