Product category:
Abrasive machining - manual and CNC machines
News Release from: Schmitt Europe | Subject: Rotary table grinding machine refurbishment
Edited by the Manufacturingtalk Editorial
Team on 26 October 2004
Refurbishment pays off for rotary table
grinder
When it comes to getting the best return on your production equipment, specialist machine tool builder says it's often better to refurbish existing plant than to buy complex new machines.
When it comes to getting the best return on your production equipment, specialist machine tool builder Ostcliffe Electronics knows it's often better to refurbish existing plant than to buy complex, high capability machines from new For one thing, the equipment is already installed on site
This article was originally published on Manufacturingtalk on 16 Jul 2008 at 8.00am (UK)
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Its operation will be familiar to existing production staff; and refurbishment enables its capabilities to be tailored precisely to user requirements.
That was certainly the verdict when Ostcliffe came to evaluate one of its Sheffield-based customer's well-used Reform rotary table surface grinders.
The machine was employed to produce precision machine knives used in the packaging, paper, graphics and food processing industries.
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However, the nature of the work - coupled with dimensional tolerances specified to 10 microns - meant that grinding wheel wear had become a significant factor affecting product quality.
When the father and son team of Paul and Adrian Ostcliffe inspected the machine, they found that it was already equipped with a Schmitt SBS automatic grinding wheel balancer.
"The system consists of a vibration sensor, spindle mounting adapter, balance head and electronic control unit, which effectively minimises vibration and provides important surface finish and throughput benefits," says Adrian Ostcliffe.
The balance head is mounted on the grinding wheel and incorporates two eccentric balance weights; each of which is driven independently by electric motors through a precision gear train.
In operation, vibration or unbalance detected by the sensor is relayed to the system's electronic control unit.
The signal is processed by the controller, which sends commands to the balance head to advance the weights in the correct direction to reduce the amplitude of the input.
When the minimum vibration level is achieved, the balance cycle is complete.
SBS equipment typically achieves balance accuracy of 0.1 micron peak-to-peak vibration displacement, which compares to 5 microns for normal unbalanced grinding operations and a figure of around 3 microns using statically balanced wheels.
The system is suitable for grinders operating at up to 30,000 rev/min and, by continuously monitoring machine performance, provides a fully automatic system that maintains adjustment even if the wheel is stopped and re-started.
Probe System During the initial assessment, one of the Reform machine's weaknesses was found to be a 2D probe system, which had been supplied as original equipment.
This was designed to detect the edge of the grinding wheel at the start of each cycle in order that its diameter could be calculated accurately.
Even so, reliability issues meant that its operation was far from successful in practice.
Furthermore, the 13-year-old machine was showing its age in terms of general wear to its spindles and bearings.
Ostcliffe Electonics' task was to find a cost-effective method of enhancing the equipment's capabilities to meet the customer's demanding quality and productivity targets.
"The key to the problem was to find an accurate and reliable method of monitoring the grinding wheel's size," continues Adrian Ostcliffe.
Through a series of discussions with Schmitt Europe, the Ostcliffes devised a solution based on the company's Acoustic Emission Monitoring System (AEMS), which they believed could be easily integrated into the machine's rebuild.
Comprising an acoustic sensor and add-in card for the same SB-4500 controller used to operate the automatic balancing system, Schmitt's AEMS system is an advanced process control tool capable of eliminating gap time in CNC machining cycles, as well as monitoring the condition of cutting tools or optimising grinding wheel dressing operations.
However, it also provides an exceptionally fast response over a wide frequency band and will report contact between components and rapidly in-fed tools in less than a millisecond - signalling the machine controller to immediately halt movement before significant damage can been caused.
In this application, the system's acoustic sensor was fixed to a probe just ahead of the machine's rotary table.
At the start of each cycle, the wheel is brought to this point, where the acoustic system's capabilities enable its diameter to be determined precisely.
The process can be repeated automatically between each machining pass if necessary, with the updated wheel size immediately recalculated by the machine's controller.
As a result, the optimum balance between material removal and accuracy can easily be achieved in production; with coarse initial cuts complemented by a relatively light finishing pass ensuring that workpiece dimensions are maintained to the required micron tolerances.
Furthermore, the Schmitt system even allows for re-dressing operations mid-cycle, as it will automatically compensate for the removed wheel material.
Alternative The use of in-process gauging was investigated as an alternative approach, but was ultimately discarded in favour of the Schmitt solution.
"We particularly liked the way that the wheel balancing and acoustic monitoring systems could be operated by a single SB-4500 unit, as this could be integrated more easily into the machine control panel than two separate units," adds Paul Ostcliffe.
"This was our first experience of Schmitt equipment," notes Adrian Ostcliffe.
"We not only found it to be accurate and durable, but also backed by excellent applications engineering and support, which enabled us to harness the full potential of the machine.
I was also impressed by the company's 'try before you buy' free trial offer, which allows potential users to see for themselves the benefits that can be achieved on their own machines - in their own manufacturing facilities." Since installing the Schmitt equipment, the refurbished grinder has performed well above the end user's expectations.
So much so, that Ostcliffe has already received a further order to refit another similar rotary table machine.
"The Schmitt equipment is at the heart of the solution.
Without it, the grinders simply would not be able to maintain the demands placed on them," concludes Adrian Ostcliffe. Request a free brochure from Schmitt Europe ...
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