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Thread: Cam and Shape Grinding
05-23-2008, 10:42 AM #21
Another reason is that by making the model lobe directly, we are simply transferring the computer designed lobe shape directly 'as designed' to the model lobe. If we were to use the computer 'model' to shape the master pattern directly we would have to write some new software to 'scale' the shape to suit, as the master pattern is not simply 'the model lobe shape but bigger'. Its diameter is substantially larger, but the amount of lift from base circle to lobe peak is the same, so the larger master pattern is a much smoother, rounder looking shape. Would require some tricky software to 'translate' the model shape to the master pattern shape, much easier to let the machine do it for you, since the geometry of the machine does it automatically.
The main reason the master pattern is substantially larger than the model lobe is a function of the machine design - the master pattern keys onto a hub sleeve that rotates on the end of the headstock shaft to allow the master pattern to be re-indexed for each cylinder in turn. Also keyed to this hub is an index plate that is rotated to align the master pattern with the lobes for each cylinder in turn and held in place with a pin. The headstock shaft is hollow (a skewer passes through it to lock the removable headstock in against a tapered seat) but needs to be very rigid, so by the time it is large enough to be strong enough, then has a sleeve hub fitted over it, the master pattern by necessity has to be much bigger again to fit over the hub.
Some pictures are done and labelled, I just have to find the time to write up a clear description of the machine's operation and the grinding process.
05-25-2008, 03:32 AM #22
HOW TO GRIND AN AUTOMOTIVE CAMSHAFT
Some of the photos here are taken by myself, some are still images captured from a DVD produced by a car magazine that visited our factory to film a ‘how cams are made’ segment. I’m not the disembodied hand in the pictures, by the way - that's our Marketing Manager. I work for a living rather than blow hot air, so my hands are always much dirtier than that, even though I wear gloves all day!
This is the start of the process, the machine used to shape the model lobes, based on computer designed specifications, that is then transferred to the Berco camshaft grinder to shape the master pattern that is then used to grind camshafts. The model lobe is a rough-shaped piece of steel plate that is slid over and secured to a holder that is designed to fit in the lathe-style holding arrangement. It is rotated through small steps by a stepper motor adapted to the headstock gearbox, and at each step the grinding wheel takes a pass transversely across the model lobe, with the height of the grinding wheel varied according to the desired lobe lift at that angle of the lobe. Over a number of hours the model is slowly machined down step by step to the desired finished shape.
A finished model lobe, in this case an exhaust lobe for a Ford overhead cam 6 cylinder car engine (Australian market only).
Model lobe in 'installed' position in machine.
Stay tuned for next instalment....
05-25-2008, 04:02 AM #23
Here's our factory floor.
Four Berco camshaft grinders, a machine for stamping identifying grind numbers on the ends of the camshafts before grinding, a machine for checking the camshaft after grinding (checking straightness, base circle runout, lobe centreline angle, lobe taper and other variables).
Camshaft checker - uses a rotary encoder (to left of picture) to read cam position, while a linear guage (top of picture) reads lobe lift. The checker reads off each journal to check for journal ovality, to check for bend in the cam, and uses any journal runout to establish a 'corrected' cam centreline for accurately checking base circle runout in each lobe. For flat tappet cams that require taper across the face of each lobe to make the flat-faced lifters rotate in an engine (to minimise wear) the checker measures the left and right side of each lobe and compares the two to display the taper in the lobe.
After checking, steel roller cams have their bearing journals polished on the cam polisher, then have a lapped finish put on the lobe surfaces. This is done in the lapping machine, where the cam is rotated between centres that are mounted on bearing slides, with the cam oscillated longitudinally back and forth by an eccentric drive as it rotates, so that a slight 'crosshatch' pattern is formed on the lobe surface. This helps to give the roller followers slight traction on the lobe surface, to ensure the rollers do roll on the lobe rather than skid, which can cause rapid wear and follower failure. After checking, cast iron flat tappet cams are coated with a crystalline maganese iron phosphate coating in the granodising tanks, by immersion in a heated solution. This helps with protecting the cam lobes during initial cam 'break-in' in an engine. After granodising the cams go into the polisher the polish the granodising coating off the bearing journals and any oil seal running surfaces on the cam. Both the polisher and lapper are computer controlled so the whole process can be done automatically.
Stay tuned for more, as we get to the fun bit - the Berco camshaft grinder.......
05-25-2008, 04:39 AM #24
I was wondering whether your company set these machines up for cnc or bought them as is.
My old company had similar machines in Sydney which we set up but were either sent to Melbourne or sold.
05-25-2008, 06:54 AM #25
This thread is cool!
I always wondered what the machines looked like, and the methods that were used to grind camshafts. This thread filled a LOT of the gaps in my understanding of such things. I'd like to watch a video of a cam being ground, or just sit in front of the machine and watch. Very interesting!!!
05-25-2008, 07:12 AM #26
05-25-2008, 11:01 PM #27
MorganGT: Gosh all fishhooks, I feel like I hit the jackpot! Sure do appreciate the work you have put into the photos and explanation. Now for the new questions:
The model lobe grinding process breaks the cam contour into small flats. How many steps are used? The workhead looks like a dividing head, so its ratio times the number of steps generated by the stepper motor ... probably a big number ... and you did tell us that it took hours to generate a model lobe. Is the lobe finished by hand at all? Checked on the measuring machine before grinding the master? Would it be possible to ground a continuous contour on your surface grinder if the dividing head were turned at right angles?
Does your grinder use ball or Acme leadscrews? The wheelhead leadscrew is a major factor in the accuracy of the model lobe. The weight of the wheelhead is down so backlash is probably not so important, but wear on an Acme leadscrew would be.
Cam checker: does it measure in steps generated by a stepper motor or continuously. I have heard that a unit available in the US can co-ordinate the angular position and lift as the cam is rotated continuously. Rather more difficult I would guess.
I liked the over-view of the shop and description of the manufacturing process. What material is used for the camshaft stock?
Stay tuned?? MGT, you have my full and undivided attention. Can't thank you enough.
05-26-2008, 06:32 AM #28
05-26-2008, 06:20 PM #29
You guys carry on without me: I'm out of town for several days. Be back Friday.
06-01-2008, 12:36 AM #30
OK, I'm back from far places and am awaiting MGT's pictures of the Berco cam grinder.
06-01-2008, 06:10 AM #31
Here's an overall pic of the Berco machine. The section of the machine above the lower red line is the main bedway, which moves laterally (driven by the lefthand wheel on the front of the machine) and carries the tilting bed that in turn carries the headstock, tailstock, camshaft steadies and the cam itself. The bedway also carries the motor and gearbox that rotates the camshaft during the grinding process.
Above that, the next bit outlined in red is the tilting bedway and headstock that tilts in and out on 3 sets of bearings. This allows the master pattern to bear against the following wheel so that the camshaft follows the desired lobe profile as it rotates against the grinding wheel. The belt drive for the headstock is designed so the drive pulley centreline on the gearbox is in line with the tilt bearings, so the drive belts remain at a constant tension as the bed tilts in and out. In the original 'manual' version of the machine the tilting bedway is tilted in and held against the following wheel by hydraulic pressure, but the CNC conversion has seen these machines converted to use a pneumatic cylinder to tilt the bed inwards and to act as an 'air spring' to hold the master pattern against the following wheel. An air pressure regulator and needle air valves are used to ensure the movement is carefully damped and slowed so the master does not 'crash' onto the following wheel, which if allowed to happen creates flat spots that eventually require remaking the master patterns and refacing the following wheel.
The top outlined section is the grinding head. It does not move laterally, hence the need for the main bedway to move laterally to position each lobe in turn in line with the grinding wheel. It sits on its own fore/aft sliding bedway and has a hydraulic ram that moves it from a rearwards 'Park' position (keeping it clear of the cam when loading/unloading the machine or measuring the camshaft) in to a 'Start' position closer to the camshaft. From this Start position the wheel is then moved in and out using the right hand wheel on the front of the machine. The bedway base for the grinding head also has a hydraulically operated taper mechanism, that moves the upper part of the grinding head (including the grinding wheel) through a small angle, rotating around a vertical axis. This puts the face of the grinding wheel at an angle to the centreline of the camshaft, which causes the lobes to be ground with a taper across their faces (one side of the lobe a smaller base circle than the other side) which causes the lifters in the engine to rotate as the engine is running, which prevents premature lifter and lobe wear. It needs to be adjustable as, some cams need no taper (roller cams), some use positive taper, some negative, and some both positive and negative on different lobes on the one cam.
These are some of the front controls on the machine. Fairly self-explanatory, but it shows the addition of the stepper motors which are part of the CNC conversion. Also shows the pneumatic cylinder that tilts the bedway in, and the pneumatic cylinder added to the machine to switch automatically from high to low gear on the headstock drive motor. The cam grinding process involves one pass across each of the lobes in high gear, with the wheel winding in at a preset speed to the desired base circle size, then a preset time delay with the wheel remaining in its final position against the lobe to allow the wheel to 'spark out'. After all lobes are rough ground the machine switches to low gear, does a slow dress of the grinding wheel and does a finish grind of each lobe in turn, taking off a preset amount (usually 0.001") to give the desired smooth lobe surface finish.
Next installment and more pictures to come, plus I have some short video snippets I am trying to reformat so I can post them up......
05-01-2009, 10:56 AM #32
Cam grinding machines and techniques
We still have several manual machines including Berco cam grinders which we use for regrinding cams. For regrinding, a manual machine can be more efficient because you only grind a lobe until it cleans up, instead of wasting material by taking the lobe down to a particular size and risking that you've ground through the hard layer (we check all of our cams for hardness after grinding).
As some cam cores became difficult to locate, we began manufacturing cams from bar stock in the 1990's. We have become the nation's leading supplier of new replacement OEM and aftermarket cam shafts, cam lobes, cam muffs, and cam sections for industrial engines.
For our new production, many operations are required before and after heat treat. These are mostly done on CNC lathes, mills, and grinders. The material used is SAE 8620 low-carbon steel. It is carburized and case hardened to Rockwell C 60-62. Any non-wear surfaces are masked during heat treat.
Our cam profiles are checked on an Adcole precision cam measurement machine, which has a lot more accuracy than most applications require.
Sometimes we need to grind a new cam which is too large for the capacity of our CNC grinder, and the cam profile we are grinding onto it is one that we have designed to solve particular problems the engine operator is seeing. We can digitize the original profile, make the necessary design changes, grind a "master model" on the CNC grinder, and then make a master on the Berco and grind the cam lobes on the Berco.
Please visit our website to see pictures of our machines and shop.
Kams, Inc. - indsutrial engine camshaft regrinding design and manufacturing