Product category:
Abrasive machining - manual and CNC machines
News Release from: Emag UK | Subject: Pin chasing and Main bearing grinding
Edited by the Manufacturingtalk Editorial
Team on 24 May 2007
Modular grinders chase crankshaft pins
Modular cylindrical grinding machines, which can be built for crankshafts up to 6m long, use pin-chasing process to machine to high accuracy and best surface finish.
The crankshaft grinding specialists, Naxos-Union, have regained lost ground and are - with their PM 3xx - once more the market leader in truck engine crankshafts With their newly developed PM 4xx series - the abbreviation stands for 'Pin chasing and Main bearing grinding' - they have penetrated the market for large diesel engines as used, for example, in engine-based cogeneration systems and in ships
This article was originally published on Manufacturingtalk on 12 Nov 2001 at 8.00am (UK)
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Naxos-Union are doing justice again to their old established image of the 'round maker': with their pin chasing process - developed by them for worldwide use in this particular field - they are achieving the highest degree of dimensional accuracy and the best surface finish.
* Demand for large diesel engines rises - assessing the market situation, Dr-Ing Jens Muckli, managing director of Naxos-Union, observed: "Market demand for large diesel engines is rising, and we have already sold four of our new PM 460s." And that happened without any of the four customers - one from the US and three from China - having seen the machine, except on the drawing board - sorry, on the CAD screen.
"It gives you a fair idea of the image value that Naxos-Union has generated over the 135 years of its existence".
Further reading
EMAG UK - a company profile
Since its foundation in 1984, EMAG UK has established a strong position in the UK automotive market supplying CNC multi-functional production centres.
Turrets feed vertical shaft turning centre
Following on from its earlier horizontal shaft turning machine, Emag has developed a vertical shaft turning machine using two turrets to exchange workpieces as well as perform machining.
Grinding and automation expertise extended
With the integration of Ingersoll Naxos crankshaft grinding machine company into the Emag Group, systems can be developed in conjunction with Karstens, Reinecker, Kopp and Heilig Automation.
Dr Muckli delights in the positive inheritance: "We are still considered the 'round makers' who are able to grind crankshafts with the greatest dimensional accuracy and the best surface finish." After all, the roundness of the bearing surfaces determines running smoothness and crankshaft wear.
Crankshafts up to 6 tonnes - what might be even more important for the larger, heavier crankshafts than for the smaller ones.
"Our new machine, the PM 460, is designed for the manufacture of crankshafts that weigh up to 6 metric tons and have a maximum length of 6m," defined Hans-Peter Wolf, marketing engineer at Naxos-Union, the application range of the new machine.
These large crankshafts demand a roundness of 10 micron or better, a tolerance the PM 460 can hold thanks to its design, and with much less effort than the previous setup required.
"Before, we used a complex, mechanical clamping system to eccentrically align and support the workpiece during the grinding operation", Wolf described the process on the older machines: "And that cost a lot of money, time and effort." The crankshafts had to be lifted from their rotational to their stroke axis and into its various angular positions.
This was difficult and time-consuming setup work.
Not only did it require sure instinct but also a great deal of experience to achieve the required component quality.
* CNC simplifies and speeds up the process - "Today, with CNC technology and special software, everything is much simpler and quicker", said Dr Muckli when he compared the difference in technologies, "And it also offers the kind of flexibility hitherto unknown." Nowadays, the crankshaft is centrically clamped once, to remain in this position until it is finish-machined.
The eccentric grinding of the pin bearing is achieved with the pin chasing movement of the grinding wheel that, in a way, 'tracks' the crankshaft, as the pin bearing - owing to the rotation on the centric plane - tries to move away from the grinding wheel.
This is made possible by the linear drive of the grinding head, which keeps the grinding wheel engaged, with required precision and speed perfectly synchronized.
And all that at micron tolerances.
This is only possible with 'cutting edge' CNC technology that has an exceptional arithmetic capability and offers high-resolution rotary encoders and scales with resolutions in the tenth of micron range, to allow the grinding wheel to reach micron standard.
The machine uses three measuring systems with high-sensitivity sensors.
One sensor measures the workpiece deflection, a second one works radially and axially, to determine the position of the bearing surfaces.
Both are available for set-up work.
The third sensor permanently follows the bearing surface as it is being ground, and in-process measures the diameter.
The CNC control uses these values to direct the grinding wheel.
* Pin chasing with CNC - pin chasing was only made possible with the development of a CNC technology that can process a large amount of data and handle a large number of NC axes.
For the benefit of its customers, Naxos-Union has fully integrated the advantages of the new technology in its crankshaft grinders, which offer great flexibility in the machining of a large range of components by drastically reducing resetting times and, at the same time, producing a much better quality of crankshaft.
And all that is accompanied by much lower cycle times than can be achieved with traditional grinding methods.
One of the reasons for this: both, main and the pin bearings, can be machined in a single setup, i e, in a combined process, for which two different machines were required in the past, with a correspondingly greater capital outlay.
The grinding wheel is another important component with considerable effect on a component's dimensional accuracy, surface finish and roundness.
In the past, these were mainly corundum wheels.
Today, they are being replaced more and more by CBN-coated wheels that offer higher cutting speeds - up to 125m/s - compared with the corundum wheel's 50m/s.
However, the latter can be produced in diameters of up to 1600mm, which makes them ideal for the larger workpieces, whereas the CBN wheels reach only maximal 900mm diameter but offer a correspondingly higher performance level.
The coolants used are emulsion (for corundum) and grinding oil (for CBN).
Naxos-Union's experts favour oil for the smaller machines, as it permits the use of higher feedrates that offer CBN grinding wheels a better life expectancy.
* Corundum or CBN wheels - all grinding spindles on Naxos-Union machines are designed to use CBN as well as corundum wheels.
The quality of the grinding results is enhanced by the use of a structure-born noise measuring system that registers when contact is made with workpiece or dressing attachment, and also by the employment of an integrated, automated grinding wheel balancing fixture.
The wheel dressing system is a particularly outstanding machine component, as it makes it possible to dress the grinding wheel in its working position.
It saves time and has no negative effect on the very important relative axial position of headstock and grinding wheel.
"Every smallest detail helps that has a positive effect on the result as a whole," evaluated Wolf the innovation his company has presented.
Another important part in component quality is played by the two-jaw back rests.
They grip the centrally located bearings from below and in front, prevent weight and grinding pressure from bending the long crankshafts and ensure a vibration-free, concentric run.
Their positions can be freely adjusted to suit the various crankshaft sizes, providing maximum flexibility.
Movement of the back rests is controlled by an NC axis.
This makes it possible to adjust the support as grinding progresses and workpiece dimensions change.
It also eases setup work.
A Naxos-Union machine can easily feature 16 axes, or more, that require optimal control.
"We use a high-precision control system for this purpose," explained Wolf the electronic brain behind the PM 460, "That we purchase from Siemens or Indramat, according to customer preferences".
* Linear motor drives - Naxos-Union uses linear drives for the slide movements on all their machines.
"We have been doing that quite consistently since 1995", said Wolf, describing the entry into linear technology, "And we where the world's first grinding machine manufacturer to use linear drives." This decision was not made to satisfy a love for technology but exclusively for reasons of improved component quality.
Linear drives offer higher workpiece speeds, by moving the grinding head very quickly and very accurately to and fro, a decisive factor in the quality of continuous path control systems.
Ball screws do not achieve the same result, as the play they develop on the return movement is simply too great, however small it may be.
And that has quite an effect on the ground surface considering the mass that has to be moved.
The grinding head of the PM 460 alone weighs 7 tonnes.
And still, the development engineers have been quite smart: the heavy protective cover for the grinding wheel is designed in such a way that it does not have to follow the wheel's oscillating movement.
Grinding spindles and work spindles also feature direct drive motors.
The grinding wheel is driven by a motor spindle - the larger diameter wheels by a block spindle with step-up drive - while the rotary movement of the crankshaft is governed by a torque motor or, to be exact, two motors, as the workpiece is driven on both sides, electronically synchronised.
High-resolution rotary encoders and linear measuring systems make sure the CNC control always knows every axis position.
"Axis referencing is a thing of the past," claimed a pleased looking Wolf.
The modular machine concept is flexible enough to be easily adjusted to suit different customer components and requirements.
All larger modules on Naxos-Union grinders are of fabricated construction that can be redesigned without having to make changes to the basic model and without loosing precision and stability.
The sturdy machine base of the PM 460 weighs nearly 40 tonnes and represents an extremely solid foundation for the tooling and workholding equipment that is adequately dimensioned for the high-precision machining of large, heavy workpieces. Request a free brochure from Emag UK ...
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