A CNC 5-axis micro-machining centre carries out super precision and delicate machining to 1 micron accuracy using a 40,000 rev/min spindle and highly accurate feed motors.
UK government agency, the Rutherford Appleton Laboratory (RAL), supports the work of over 10,000 scientists and engineers from the university and research community.
When it needed to meet component accuracies of one micron, for micro-machining, RAL consulted Kern about its micro-machining centre .
With 1200 employees and eighteen in its Millimeter Wave Technology group, RAL is at the forefront of research into new materials and structures for space-based astronomy, particle physics and the manufacture of temperature sensors and detectors plus many more far reaching research projects.
However, it was the demand for components with small dimensions and tight tolerances that led to the introduction of a Kern micro-machining centre supplied by Deckel Grinders of St Helens, UK.
One example is a backlight component for the Laser Department.
It originally consisted of three parts that complete an assembly with an overall dimension of 4.5mm by 2.5mm.
The intricacy and size meant that prior to the Kern acquisition; the backlight parts were painstakingly machined and assembled manually under a microscope.
* 5-axis micro-machining - the Laser Department initially wanted four backlighters but this soon increased to 40.
Such quantities would be a long process, so the Millimeter Wave group redesigned the assembly to incorporate 5-axis machining without compromising the physics of the part.
The target was to design a part that could come off the machine with no secondary operations.
Handling problems and picking up dimensions are major issues with second operation machining and this was something that had to be eliminated.
Originally, the three backlighter parts took a working day to produce with an additional 2-3h spent assembling the parts under microscope.
The Kern and its 5-axis capability enabled a re-design.
The combination of the machine and the re-design now sees one complete backlighter finished in little over 30 min in one hit as opposed to three parts.
A remarkable reduction considering the backlighter is now manufactured in batches of 120-140 on a regular basis.
The intricate nature of the backlighters, the batch quantity and the productivity gains have warranted the purchase of the high accuracy 3-axis Kern micro machine with its fifth axis bolt-on attachment.
In most cases RAL manufactures a small quantity of parts and optimise the design to improve the part or the processing times.
If it gets to batch production quantities, the company looks to work with commercial entities to manufacture the parts externally.
In some instances it is very difficult to transfer the technology to industry because of the sheer scale of the parts.
* Machining at fine tolerances - the then existing CNC machines at RAL have spindle speeds up to 15,000 rev/min and hold a tolerance of 10 to 15 micron on the workpiece, but the Kern is a super precision machine with an accuracy of a few micron.
The Kern conducts super precision machining that cannot be done on the company’s alternative CNC machines, said Deckel Grinders to manufacturingtalk.com.
The 40,000 rev/min spindle and precision of the feed motors allow for delicate machining, which is a necessity for components of this scale.
It allows RAL to expand the scope of its work and move on to the next project.
Following market evaluation RAL bought the Kern in summer 2006.
The company wanted a machine for a long time and after reviewing the market it felt the Kern machine was a clear market leader, said Deckel Grinders.
The decision was initially founded on the temperature controlled spindle and positional accuracy of a machine based on a rigid and substantial polymer concrete base.
However, an in depth review of the machine and an opportunity to see examples of components manufactured on the machine supported the decision.
* Sensors and probes - the Kern has a Blum laser detection system on the bed that allows the operator to measure the cutter diameter and position in Z-axis.
It also has an infra red probe to measure the position of the X- and Y-axis of the workpiece.
Data from this delivers a macro program into the main program to provide exceptionally accurate positioning.
Previously RAL was doing this manually under a microscope.
* Mini-cutters - high accuracy is a necessity for RAL, as the largest cutter used on the backlighter is 2mm diameter slot drill used to mill the external form.
From this point a 0.8mm diameter ball nose cutter is used to machine an optical form then a 0.1mm wide slitting saw is used to cut 1.3mm deep at a 70 deg angle.
This is followed by further milling operations of similar scale to micron tolerances.
Adding to the difficulty of machining this part is its material - pure silver.
An aspect that demands exceptionally sharp cutters at all times to prevent swarf build up.
To quantify these miniscule dimensions, a component recently manufactured for a space launch project that measures ozone depletion at a frequency of 2.5 tHz has overall dimensions of 0.023 by 0.090mm.
With the average human hair measuring 0.080mm, this particular job can be compared with machining a rectangle on the end of a human hair.
* Extreme accuracy - another example of the extreme accuracy achieved at RAL has been noted on a plate component that filters light for the satellite and space sectors.
The 0.2mm thick plate was manufactured from a number of materials but RAL eventually used brass for its properties and ability to remain intact under the extensive drilling involved.
The 0.2mm thick plate that measures approximately 20mm square required a series of holes drilled to a set pattern for not only filtering light but also for maintaining its strength.
At the centre of the plate, RAL drilled over 8,000 holes of 120 micron diameter in an overall diameter range of 10mm.
Drilling over 8,000 holes in a 10mm diameter area was completed by slotting each hole at 100 micron and finish drilling at 120 micron to prevent component breakage.
The holes drilled in a diamond formation only had a web thickness of 10 micron between each hole.
This close proximity gives the plate the filter specifications required and to the naked eye is transparent.
In conclusion, RAL was confident the machine could meet all its micro machining needs.
However, the combination of the MMT group’s highly skilled technicians and the KERN Micro machine has meant that the expectations have been exceeded and the Facility is extremely pleased with the acquisition.
Posted by admin under Micro- and nano-machining | No Comments »