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Tuesday, 13 June 2017

Outstanding milling



[article by Edoardo Oldrati, original source: "Tecnologie Meccaniche" Magazine, June 2017]

The German mould maker, WFT Werkzeug- und Frästechnik, has invested in Breton milling solutions. Specifically, in the recent Flymill HD for machining superalloy, steel and aluminium parts with complex three-dimensional shapes.

Founded in 1997, but the heir of an entrepreneurial history that started in 1919, WFT Werkzeug- und Frästechnik is a German company that manufactures matrices and moulds for punching, foaming and compression moulding of all kinds for the automotive, aerospace, medical and renewable energy industries. 

State-of-the-art technology and many years of know-how”, explain Frank Elzener and Stefan Lühr, managing director and owner of the company respectively, “allow us to provide our customers with everything they need for each process phase, from design and manufacture to assembly and testing, giving them a single source procurement service”.

In the Coppengrave plant in Lower Saxony, more than 50 employees use modern production systems to machine blanks. The CNC machines have up to a maximum of 5 programmable axes and can machine workpieces up to 8 metres long and weighing up to 46 tonnes.
One of the strengths of WFT is precisely this advanced fleet of machines, which takes up four halls with an overall surface area of 3 thousand square metres. For the past three years, WFT has relied on machines supplied by Breton. Currently the company's plant houses a Breton Matrix 1000, with axis travel of 2200 x 2500 x 1000 mm, and a new Flymill HD with head change and an axis travel of 8000 x 3500 x 1300 mm.

Flymill HD in action

HIGH MILLING PERFORMANCE

A company like WFT must be able to rely on milling machines that can combine high material removal capacity with high accuracy. Precisely for this reason, a partnership was started with the Italian manufacturer Breton, which has supplied two machines in recent years.
The most recent one is the high-speed, high-performance milling machine with 5 continuous interpolated axes, the Flymill HD. It is ideal for machining superalloy, steel and aluminium parts with complex three-dimensional shapes that must be made accurately.


A sample worked by WFT with the Breton Flymill 1300 milling machine

To ensure high performance, the Flymill is equipped with sturdy shoulders made using the exclusive Metalquartz® technology, which provides high structural rigidity and a high degree of vibration damping to guarantee improved surface finish and increased cutting tool life.

The large work table size, the strength of the structure and the large operating travels make this high-speed milling machine suitable for use in a single work area or in pendulum mode, with a milling speed of up to 40 m/min for the linear axes, reaching up to 60 m/min in rapid mode. The bi-rotary heads (with continuous C-axis rotation, A-axis rotation up to 135°, power of 85 kW and rotation speeds of up to 100 rpm) allow the machine to rapidly perform even the most complex machining, working simultaneously in all three dimensions with very simple programming. In fact, considering that the A-axis can rotate up to 135°, it is easy to perform difficult undercuts without repositioning the workpiece. 

The machine model installed at the German company has an axis travel of 8000 x 3500 x 1300 mm. There are electrospindles for the Flymill HD heads that can guarantee high performance through their bilateral fork structure made of cast iron, which gives them structural strength and vibration damping ability. The Breton Flymill is equipped with the Tornado HD head, which can take a 75 kW (S1), 14,000 rpm spindle for rough machining and finishing.
Also noteworthy is the compact structure that meets the increasingly widespread demand for small-footprint systems. 



Furthermore, the Breton machine previously installed in WFT, a Matrix 1000 with an axis travel of 2200 x 2500 x 1000 mm, features high machining speed and high material removal rate.

It is a high-speed, high-precision machining centre for milling parts with complex three-dimensional shapes, ideal for applications in the aerospace, automotive, mould making and design industries. In fact, thanks to the speed of its linear axes, which can reach 60 m/min, and its Direct Drive head with a continuous C-axis rotation speed of 100 rpm, the Matrix can perform uncommon high-precision and dynamic machining of complex profiles with 5 continuous axis.


Matrix 1000 Dynamic




The bi-rotary continuous head with direct drive can be positioned at any angle within its operating range, thanks to powerful hydraulic brakes. This makes it possible to use spindles with continuous powers of up to 40 kW and 28,000 rpm, giving the machine a considerable material removal capacity.
It is also worth noting that it can easily handle high-speed machining and milling of both light alloys and other special alloys that are often used in the aerospace industry.

The completely enclosed structure with mechanisms at the top of the machine offer maximum operator safety with maximum machining reliability and precision. Its machining quality and precision are also achieved through the thermo-symmetry of the structure and the a thermal stabilisation system in the Z-axis lead screws and bearings and the axis drives, which keeps the temperature of these parts aligned with that of the machine structure during operation. 

This stabilisation system makes the machine practically immune to deformation caused by the thermal dilatation of the structure that is induced by continuous daily use for high-speed machining. Sophisticated finite element method (FEM) dimensioning integrated with global dynamic simulation has made it possible to obtain strong structural elements that combine stable geometric precision with dynamic high acceleration of the operating units.

THE KEY TO SUCCESS


WFT manufactures prototype moulds, pilot moulds and production moulds for a wide range of plastic machining technologies. Depending on the geometry of the workpiece, the number of components and the customer's needs, WFT can offer the optimal mould concept from both the technical and economic points of view, providing its customers with recognised know-how as well as intelligent and highly technological solutions. 




In addition to its versatility, another element behind the success of WFT is its ability to follow the whole implementation cycle of moulds and customised machines, from design to production. “Our personnel create the three-dimensional model of the component to be made on CAD/CAM workstations. The design department is connected with customers around the world, allowing them to see the data on line and to perfect the design through direct consultation”.

The target industries for the moulds made by the German company impose high quality standards.

“Quality is our watchword”, confirms the technical department, “and many years of experience and the constant training given to our engineers and experts guarantee the highest quality combined with reduced production times. To ensure excellent quality, every aspect of all moulds and machines is tested before being delivered to the customer. Moreover, visual inspection is an effective method, but it is not enough to meet the current requirements imposed by the manufacturers of components for the automotive and aerospace industry. 

For this reason, we reply on complete control systems and we manufacture measurement devices and test equipment from aluminium, steel or light material, to guarantee accurate measurement of every product. Here, the distinctive feature lies in making the measurement: in fact, the test and measuring devices provide assessment, documentation and display. We can also build custom test devices to meet customer requirements”.

The ability to innovate is also essential, not only by investing in a fleet of state-of-the-art machines, as we have seen, but also by developing new technologies. An example of this approach is the innovative joint technology for plastic products that WFT uses in its plant. 

To make products such as trims for doors or bumpers, dashboards or fuel tanks, packaging components or medical items, plastic components are applied to various objects. In these cases, WFT uses latest generation joining technology to integrate metal elements into the plastic, fold laminated materials or securely fasten thermoplastics by welding or riveting.

For more information please write to mail@breton.it.

Thank you for the attention and best regards.
Bye-bye

Sergio Prior

Thursday, 6 April 2017

Renishaw technology helps Breton calibrate its in-house machinery


Switching from processing stone materials to metals demands a significant increase in precision. Now Breton uses laser interferometers, rotary axis calibrators, ballbar systems and touch-trigger probes thanks to Renishaw technology. As a result, today, Breton’s range of high-speed, five-axis CNC machining centres are among the world’s most advanced.
 

Calibrate accuracy
Based in Castello di Godego, Italy, Breton has come a long way since its foundation in 1963. Focussing initially on designing and building machinery to process natural stone, the company soon transitioned into also producing complete systems for the manufacture of composite stone (7% polyester content). This innovative material had, in fact, been invented by Breton and proved the backbone of its growing business for many years.

A moment in the rotary axis calibration process
The 1980s saw Breton begin building CNC machinery for processing marble, granite and composite stone slabs aimed at the kitchen worktop and bathroom sector; this particular era also included the arrival of the company’s first five-axis systems. A decade down the line and Breton began to diversify its expertise into the production of high-speed CNC machining centres for the metal-cutting industry. Renishaw technology helped Breton ensure the quality and precision of its in-house production machinery, and its fully assembled machine tools.

Talking about accuracy
Samuele Salvalaggio, Sales Engineering Office, explains how Breton’s own production machines, as well as those the company builds, follow practically the same control and calibration procedures.
You cannot produce precision machinery if the components are not produced using precision machinery,” he stated. “Our quality control methodology essentially encompasses three phases: linearity control, the checking of axes, and overall control of kinematics, which are all carried out using Renishaw products.”

Ballbar system calibration technology
Once a machine is assembled, a XL-80 laser calibration system is used to test the positioning, linearity and the angular errors of the machine tool. These controls are carried out on all the machine tools produced by Breton. This process is also performed annually on all in-house production machinery and repeated on the rare occasion that deviations are recorded. The company opted for the XL-80 after experiencing difficulties using other systems on axes over 4 metres, a problem which is non-existent with the XL-80.

XL-80 laser calibration system

Machine axes are also the subject of strict quality control routines facilitated by using a Renishaw QC20-W ballbar system. The QC20-W is used to quantify the squareness between each linear axis and to check a machine tool’s fundamental performance via a quick check.
Once staff in the maintenance division, who already used a ballbar system for their periodic checks, showed others how easy to use and accurate the system was, it became a standard tool in every part of the company needing calibration controls.

Among other things, this check is also the first one conducted when customers request technical support for machines installed in the field. At Breton’s 40,000 m2 premises, checking the three linear axes of in-house production machining centres is also a straightforward operational routine. In just 20 minutes the operator can check the condition of the machine and prevent possible manufacturing errors. The ballbar system is now used internally to calibrate the production machines and externally for technical support, particularly when a customer suffers a machine collision.

At Breton, which today employs around 700 people, core business remains the stone processing sector, and here too, despite the fact that precision levels are lower, the benefits of calibration are now fully appreciated. All of Breton’s machines for natural/compound stone processing undergo calibration routines which guarantee their optimum operation.


For more information about Breton's 5-axis machining centers, please write to mail@breton.it.

Many thanks to Renishaw for the provided case study document. 

Wednesday, 29 March 2017

Breton automatic countersink solution for aerospace and automotive industry

Countersink? No problem!


The use of rivets is 
one of the most common standards for the permanent assembly of structural parts in aerospace and automotive sectors.
For reference only, the image on the right shows a typical distribution of different rivet types in a famous aircraft with a very recent design.
 
                                                             
Tratto da: http://www.france-metallurgie.com/2011/04/

Despite some minor limitations, this system offers useful advantages in the assembly process:
  • Rivets are cheap
  • The procedure is easy and fast
  • They are available in many different types covering any need
  • There is a long history and experience in their use leading to a good reliability guarantee 
  • Compared to other permanent fixations, they can be disassembled quite easily with specific tools 
  • They allow a calculated residual flexibility of the assembly 
  • They allow easy and fast repair even on the field                   




When rivets are used to assemble the external layers on the supporting structures, they need to fulfill another very important role because the resulting assembly is directly exposed to the airflow: the final surface must be as smooth as possible in order not to affect the aerodynamic performances.
This specific need is very common in the aeronautic and aerospace field and all designers solve it by selecting rivets with countersunk head.

It becomes therefore evident the need of an accurate hole on the surface prepared with a countersink: the rivet head needs to be hidden below or in line with the external surface profile.

Tratto da: https://www.aircraftcompare.com/helicopter-airplane/piaggio-p180-avanti-ii/356


Just to reinforce the importance of the final surface quality the rivet head flush requirement is directly expressed on the assembly  drawing  through specific symbols (like a welded joint) and described in detail through dedicated quality procedures involving, very often, also a source qualification need.

Tratto da: http://www.aslgroup.eu/en/fleet/12/piaggio-p180-avanti-ii
In order to better understand how important is to respect 
the perfect surface continuity we can consider that, on 
some aerodynamic very demanding design, the aircraft  performances are so sensitive that just the surface cleaning has a perceivable impact on the overall performances.


The standard way of performing the rivet assembly is manual with specific tools that allow improving the reliability of the process.
Tratto  da: http://www.northerntool.com/shop/tools/product_200451725_200451725



Generally, the structural parts and the sheet metal pieces are NC machined and prepared with smaller holes in order to guide the manual tools used to create the final hole and countersink prior to assemble the rivet.


Sometimes only one of the two element to be assembled is pre-drilled in order to allow compensation of assembly misalignments; in this case, operator’s job become even more complex and sensitive, thus requiring higher manual skills.

There are a few reasons for the aircraft manufacturer to choose this way rather than finishing the hole and the countersink on the NC machine:
  • The hole and the countersink must be perfectly perpendicular to the surface
  • The countersink depth need to respect quite a tight tolerance in order to avoid rivet head to be above the surface. We must consider that the material  thickness tolerance can be easily equal or even higher than the countersink one
  • The position tolerance need to be very tight as well in order to guarantee that the two parts will match during the assembly
  • Even if in a modern design all the parts are 3D modelled (it’s not the same in an older aircraft) the production processes of a structural part and a sheet metal one do not guarantee the same level of precision 
  • The sheet metal is a flexible piece and it’s  very difficult to create a fixture that maintain the overall surface in the 3D model  theoretical position
All these reasons made the manual rivetting process the more convenient one, leaving to an expert operator the responsibility to recover all the previous processes misalignments.         
Tratto da: http://www.chinadaily.com.cn/bizchina/motoring/2014-09/17/content_18612888.htm

Everything said above is valid even if the sheet metal is classical aluminum or composite based. In this second case, some other points must be considered:
  • The dust produced is very dangerous for the operator's health
  • The material cut is very critical and need better control of the cutting  parameters
  • The material surface control is even more complex
Until the business remains focused on small quantities and the market is ready to reward the “hand-made”, and the consequent high value added, as a “plus”, it’s possible to sustain the manual production process with respect to massive  production competitors.

How does all this match with NC 5 axis machining?
Tratto da: http://www.youtube.com/watch?v=Ih89unYl0-g
When the scenario changes to big numbers (typical of the civil market) with reduced prices and margins, the only solutionthe only solution to stay competitive is the process standardization   and automation, so the aerospace industry needs to find a partner who can help it achieving critical goals.                              



Tratto da: http://www.capmac-industry.it/en/aerospace/
On the market, it is possible to find solutions that substitute the operator job with a quite complex machine that request to introduce the full assembly jig into the machine in order to drill and rivet the components replicating the operator’s gestures.

Tratto da: https://www.youtube.com/watch?v=Ih89unYl0-g

This strategy is very expensive, requesting a huge space allocation and presenting many times issues due to aircraft structures accessibility limitations.

Breton is following a different way, allowing to save the huge amount of money necessary for the previous type of investment and keeping the maximum flexibility to apply the solution to any type of component.
Breton has developed specific machines and several solutions to support this type of challenge and has also a very strong and experienced process development team available to support customers before and after the integration of a fully comprehensive solution.

The only ground condition is the availability of a 3D part model, Breton takes care of anything else.
For each of the previous points supporting the benefits of a manual riveting process, Breton has a specific automatic solution leaving the final fastening to the operator but with the hole and countersink already prepared in the correct position, shape and  depth:
  • Position precision is not an issue for any Breton equipment that is designed  to  achieve  the  best  5-axis  tolerance  on  the market.
  • A specific automatic probing head is capable to calculate the real surface position in respect to that of the 3D model and calculate the corrections in order to recover depth of cut and surface perpendicularity
  • The machine position is automatically modified without any operator assistance before drilling the hole and   countersink
  • With this solution the fixture only needs to keep the piece well fixed but it can leave to the machine probing capability the real shape calculation
  • The composite dust issue is solved avoiding the operator to be exposed to it during the material cutting
  • The composite integrity is guaranteed using a special developed solution that avoids any contamination and completely removes any dust
  • All the cutting parameters can be controlled much better than in a manual mode
  • The software is also capable to monitor the surface stability during the cutting operation and can be programmed to react in different ways according  to  the material responsiveness.
  • The structural part can be machined on the same trimming machine in order  to have the same level of precision. This way is the first step to guarantee a good assembly performance.

The core of Breton automatic countersink solution is the special probing head and compensating software.
They have both been designed at Breton’s and patented due to their specific and unique capabilities on the market.





The special probing head is stored in a specific holding device on the machine, protected and located outside the working area; when necessary, the machine automatically picks it up, while keeping  the tool change capability monitored through a specific application in order to avoid any collision with the device.


The system is composed of three mechanical transducers managed by a specifically developed NC control application in order to acquire the true position and orientation of the piece surface around the hole to be done.















The drilling program is a standard one where the machining cycle is substituted with the Breton routine to activate the countersinking head.
The typical drilling process follows these  steps:
  • The machine collects the special probing device
  • The machine picks up and measures the cutting tool (using a specific   Breton routine)
  • The machine sets up the probing device on a reference gauge integrated in the machine (using a specific     Breton routine)
  • The machine probes the surface in the theoretical position and orientation
  • The real position and orientation is recalculated by Breton software
  • Depending on the surface type and scratch sensibility, the machine position and orientation are corrected by either keeping the probes in contact with the piece or retracting the machine from it (average time of the full probing and position adjustment is 6 seconds)
  • The drilling and countersinking cutter proceeds along the real hole axis until the probes detect the correct depth of cut (this time depends on the type of material, layer depth, type of cutter, etc..). The system is capable to respect a depth tolerance of +- 0.03 mm on a stable surface (or +- 0.06 mm if the surface is not perfectly supported and fixed by the fixture)



The machine head is also equipped with a special dust extraction hood in order to collect all the dust generated by the drilling process.
There is no limitation in spindle performances as all the probing systems are static and connected to the head flange without any external   wire.

Depending on the material type, the head can supply compressed air, spray oil mist or pressurized coolant up to 40 Bar as the probing devices are fully sealed.

The following pictures explain the capability of the special head comparing the results of countersinking with and without the Breton solution:




This sequence is useful to understand better how the full process is working:


The system can be installed on any Breton machine giving the customer huge advantages compared to the manual process, spending just a small portion of the investment requested by more sophisticated solutions. 


(Breton is not yet assembling the rivets…).


Summarizing the points of strength of Breton solution:
  • One machine to trim, drill and countersinking
  • Precise process control
  • Small investments in a machine accessory
Since one of Breton’s major points of strength is its capability to hear the customer’s requirements, we are working to further improve this system reviewing the design and testing a contactless   solution.

Test Case: Composite panel
Machine type: Eagle 1500 2T K80 
(5 axis overhead  gantry machine) 

Machine size:  
X=8000 mm
Y=4000 mm
Z=1500 mm


Machine accuracy:  
X=+-0.02 mm 
Y= mm
Z= mm

Number of countersinks on each side of the part: 55
Countersink depth: 0,31 ± 0,08 mm 
Process stability achieved: Cp 1,34
Cpk (lower) 1,14

The following graph shows how the system recovers the hole surface perpendicularity starting from the theoretical one, measuring the real surface orientation (red lines in the graph), correcting the head A and C axis and checking the final result (green lines in the graph).


After this first phase, the system starts monitoring the countersink depth comparing the probes data with the target   values.
The final result, achieved on a composite part not perfectly stable on the fixture, is shown in the process control chart here   below:

Consideration:

The process stability is very nice giving a big safety margin. The customer chose to further increase the safety margin moving the average countersink depth in the lower tolerance direction (as show by the Cpk value).


For more information please write to mail@breton.it.

Thank you for the attention and best regards.
Bye-bye

Sergio Prior

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