A three-axis Anilam CNC control system more usually found controlling milling machines has transformed the capability of a rebuilt Jones and Shipman 540 toolroom surface grinder at tooling manufacturer, Electro-spark. The grinder, which before being rebuilt was a manual machine, has enabled the Cwmbran (South Wales) company to reduce cycle times and improve quality levels in the production of components which are now machined under full three-axis (x, y and z) control with the Anilam system. The machine has been completely rebuilt and fitted with DC drives on all three axes, with the drives being controlled by the Anilam MK 3300 CNC.
Also, the original 1.1 kW grinding wheel spindle drive motor has been replaced by a 3.7 kW motor which drives the spindle through a poly-vee belt.
As a result of the new drives and larger motor - and in combination with the fine degree of positional and rotational control provided by the Anilam CNC - the machine is now being used also for creep feed grinding.
The benefit of this is illustrated by Electro-spark managing director, Dave Calder, who quotes one of the first jobs carried out on the refurbished machine.
"The component was previously ground by multiple passes and small downfeed movements of the wheel", he says.
"With 50 ground in one setup, the production rate was then 350 parts an hour.
On the new machine, however, a 0.020in deep cut is used to enable the work to be completed in one pass and, as a result, throughput has risen to 600 an hour.
Component quality has improved too, because there is no longer the disturbance of the work by wheel contact at the beginning of each pass as with reciprocal grinding.
Also, because of the greater degree of control on feed rate and positioning, it is possible to fast feed the wheel close to the point of cutting before reducing to the creep feed rate.
This has also contributed to the improved cycle time".
While Electro-spark provides a subcontract tool making service, its primary role is making tooling components for one of its sister companies, Iron-spray, which manufactures tools in volume for use in carpet-making and weaving machines.
It cost Dave Calder GBP 22,000 to have the machine rebuilt and the CNC integrated.
The Anilam retrofitting, which included fitting new ballscrews and drives, was carried out by Machine Tool Control of Pontypool, South Wales - Anilam's representative in Wales and a specialist in CNC retrofitting with over 20 years experience in the sales and support of the Anilam product range.
"To buy a new CNC machine with a comparable CNC would have cost three times as much, and the machine would have been too big for the light precision work we now do on it", reckons Dave Calder.
"Due to its success there are now plans to have a second grinding machine rebuilt for control by a two-axis Anilam MK 3200 unit".
As well as being good value for money, the rebuild and retrofit has provided Electro-spark with a type of machine control well suited to its toolmakers' style of working.
"It is programmed logically in the way the machine operator thinks", continues Dave Calder.
"He simply tells the CNC what he thinks the machine needs to do.
He can have a picture of the operations in his mind, as if he were turning the handles.
Nor does making a single movement change to a program affect any other movements that are part of an operating cycle".
The grinder is permanently fitted with a fixturing system to which all subfixtures accurately locate; this facilitates the transfer of workpieces to milling and EDM machines.
The axial position of the main fixture on the grinder is precisely known so that its relationship to the grinding wheel can be accurately determined by the CNC.
"The operator brings the wheel to where the cutting will start and sets the zero position.
After that, all the movements can be programmed in sequence.
The average job takes about ten minutes and it is so logical.
All the programs we have so far created are stored in the CNC's ample memory".
The versatility of the retrofit machine and its new controller is illustrated by one example which involved grinding a group of identical parts as one setup.
When completed on a manual grinder the fixture had a small error in alignment so the height of the last piece differed from the first by 0.002in.
This was compensated for by grinding the middle part to size then the first and last on top and bottom limits.
"We put it on the new machine and programmed the Anilam to give a 0.002in fall along the length of the batch", says Dave Calder.
"When we checked them they were all parallel and in tolerance.
From then on the operator felt fully at home with the control; it is so user friendly.
I know we should have corrected the fixture in the first place, but now there is no need to".
In addition to tool steel, tungsten and exotic metals, the machine also grinds ceramics.
For holding these non-magnetic materials, Electro-spark has recently started using the Cryotech ice-chuck.
This system was developed in Switzerland and last year the product and name was purchased by Dave Calder to enable him to manufacture and market the novel workholding device.
The Cryotech ice chuck creates a holding force of 15kg/cm2, sufficient for machining by grinding and other methods.
With the workpiece placed on the wetted chuck surface, the water is frozen using microprocessor control and as it turns to ice it securely holds the workpiece.
The complexity of work now possible on the Jones and Shipman machine, and in this particular instance with the aid of the Cryotech ice chuck, is shown in its ability to grind a very thin plate that has a three-dimensional crowned surface.
This called for the 100mm square plate to be held firmly and to have its top surface crowned in both directions, using both longitudinal and transverse table movements to form part of the spherical surface.
All the wheel and table movements needed to achieve the shape were programmed sequentially into the Anilam CNC by the operator to create the precise form.
http://www.engineeringtalk.com/news/ani/ani110.html
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