EMAG Salach Maschinenfabrik has brought out the VTC 315 DS for the simultaneous vertical grinding of shaft-type components.
In contrast to the conventional process, the VTC 315 DS uses two opposing grinding spindles for the four-axis simultaneous grinding of vertically chucked workpieces.
The advantage is the axial forces cancel each other out and optimal access to the workpiece is possible.
At AMB 2008 Emag will present the next stage of the machine’s development: a version for four-axis simultaneous grinding.
The idea was triggered by the VTC platform.
EMAG introduced the first four-axis vertical turning centre of the VTC series in 2003 and since then the VTC series has been developed further.
Although there are some common denominators, the VTC 315 DS is in direct competition with the classical horizontal two- and four-axis grinding machine.
Salach’s vertical machine was designed for the machining of smaller component batches, where it offers short setup times and great flexibility.
For larger quantities, the single-purpose machine still remains the first choice.
The vertical design still offers advantages in the application of grinding technology, especially when it comes to the machining of gearshafts with a number of bearing seats.
One of these advantages is the two independently travelling compound slides mounted to the inner wall, featuring X- and Z-axes with integrated grinding spindles.
In the centre is the workpiece, which is held from below by a fixed tailstock centre and from above by a moveable work head centre, allowing simultaneous grinding from left and right.
This design ensures good access and makes use of the naturally developing forces.
With the grinding process, the main force input is usually generated by the axial forces, which are often three to four times that of the tangential forces.
On the VTC 315 DS the axial forces are neutralised by the grinding wheels that face each other.
The contra-rotational movement of the grinding wheels cancels out the grip torque created by the tangential forces.
This is particularly effective with workpieces that are moved only by the traction created by the centre in the work head.
In terms of resetting, it means no clamping equipment or separate drivers are required.
Adjusting the span and restarting the program is all that needs to be done.
For grinding machines, precision is usually the top priority and this is no different when it comes to the VTC 315 DS.
Dr Guido Hegener, senior executive responsible for grinding technology at EMAG Salach Maschinenfabrik, said: ‘We have tested the machine thoroughly and made a number of comparisons with our horizontal machines.
‘The sturdy, rigid machine construction with its base in Mineralit (a polymer granite that has a much greater damping effect than cast iron) forms an excellent basis for achieving the required precision.
‘Owing to the internal dimensions, there are sections where rigidity is even greater than at the equivalent points on a classical grinder of similar size.’ Although development has, in some areas, required a rethink of the original idea of combination machining, the changes did not pose any great technological difficulties.
Dr Hegener added: ‘The changes that had to be made included the installation of vertical grinding spindles and the accommodation and handling of the grinding wheels.
‘For instance, we had to design a special fixture for the changing of grinding wheels, as the construction of the machine does not allow the use of a crane for the purpose.’ A receptor with a taper similar to the HSK is used to change the grinding wheels.
As the machine concept favours the use of CBN grinding wheels, the receptor must be of great precision.
The CBN wheels can be used for infeed grinding, multiple plunge-cuts and longitudinal grinding as well as for the machining of various shoulders and radii.
The precision of the workholding system minimises the dressing effort, which would otherwise make the use of these cost-intensive CBN wheels uneconomical.
The people in charge of developing the VTC 315 DS have studied market requirements for on-board measuring equipment, automation and programming and the machine has been equipped accordingly.
For instance, the standard equipment includes a length-measuring probe for the correction of centre offsets.
The machine also features an in-process gauging control and the post-process measuring device.
For automation, EMAG relies on a robot that loads and unloads the workpieces from the side of the machine.
The small footprint and the compact construction of the Siemens 840D control makes it an economically priced alternative to the classic grinding machine.
The VTC 315 DS with two grinding wheels covers workpieces that are produced in medium-sized batches using grinding technology only.
Simultaneous grinding shortens the machining time.
This is advantageous in the machining of thin, less stable workpieces.
Generally, CBN offers higher stock removal rates and shorter cycle times.
CBN also has a much greater life expectancy.
This reduces the unit costs when compared with machining using corundum wheels.
A more compact machine was able to be built by concentrating on the use of CBN technology.
This would have been impossible using corundum.
The classical horizontal four-axis grinding machines lack accessibility, operator-friendliness and the compact design, but the vertical concept has solved these problems.
The machines are compact considering they handle workpieces of up to 700mm in length
Posted by admin under CNC Machining | No Comments »