Twin machining centre system performs end-working

Machining the ends of various types of components simultaneously is carrried out essentially by a twin machining centre system without having to move or reposition the component.

The CNC Machining centre is for the machining of the ends of various types of components simultaneously and is the most recent evolution of the classical end-working machine for the machining of the extremities of bars, forgings, tubes, etc.

Thanks to this evolution, this machine-tool is making a "technological impact" placing itself at the level of the most advanced machine-tool products and, being able to solve the most different applications of more demanding companies.

The machine concept is a reply to those companies who require the availability of the modern engineering manufacturing processes.

Machining both ends without moving the component - the MC 650 machining centre, produced by CAORLE, is a CNC machine with 6 controlled axis (3 + 3): the longitudinal "Z" (Z1-Z2), the transversal "X" (X1-X2) and the vertical "Y" (Y1-Y2).

It works by means of two operating units and two tool-changer facilities and it was conceived and designed for the machining of the extremities.

The MC 650 - said Alberto Caorle, managing director of the Company, "Has to be considered the evolution of the concept of the simple end-working machine, a type of machine which was always considered as a secondary machine but now, thanks to this new advanced project, it has become a true machining centre qualified for any kind of machining on the extremities of the most varied types of components and for the most different types of industrial sectors.

Using MC 650 it is possible to complete finished-machining and complex machining by interpolation (threading, facing, drilling, routing, execution of keys, etc.) without having to move the work piece.

Different examples of applications, from the machining of finished extremities (threads, chamfers, "little channels") on the bodies of sunken pumps, which are polished pipes of stainless steel, to the machining of finished extremities (facing, drilling, tapping of the various holes on the end, execution of "channels" and keys) of camshafts: for both there is not a need of a further machining on a lathe.

In particular, for one of our important customers involved in the "automotive field", we have supplied machines equipped with customized facilities able to execute facing and centering with reference to the cams, in order to share the stock metal in a balanced way for a better off execution of the following machining.

Tooling breakage control devices (for drills and taps) are also present.

A double machining centre - the bed is an electro-welded and normalized structure made of a thick section heavy duty steel plate, strategically reinforced for obtaining a maximum stiffness and rigidity; the longitudinal guideways (flat guideways with a "T" shape of 100mm surface) mounted on the bed are made of a hardened steel.

The two cast iron saddles units slide above these guideways and on the same guideways are located the self-centering jaws.

The saddles are driven and positioned by precision ball-screws and AC brushless servo motors Siemens.

The two longitudinal box-type guideways and the spindle unit are made of cast iron, the vertical upright is an electro-welded structure.

"We have developed a machine-tool," continued Caorle "that has to be extremely rigid in order to assure the maximum machining quality, so that we have used cast iron for the production of all those components with a need of high rigidity and also for the absorption of the vibrations".

Each one of the two machining units (MC 650 is equipped with two independent powered and horizontally opposed machining units) consists of: a longitudinal saddle unit made of cast iron with the surface in contact covered with a special antifriction material; a transversal saddle unit mounted above strong and dimensioned rollers re-circulation slide-shoes (on this saddle is also mounted the tooling stock group); a vertical saddle unit is mounted above strong and dimensioned rollers re-circulation slide-shoes and there is also installed the support for the ISO50 spindle (the spindle is equipped with a fast hydraulic unclamping device) together with its motor; an oil-dynamic balancing device for the vertical saddle.

The two spindle units are designed for the axial flow of the coolant through the spindle, in addition to the external one on the machining area.

"The two operating units," said Caorle, "Are located exact opposite each other so that the spindles are horizontally positioned, facing one to the other one; these two groups are positioned on the same guideways of the steel-bed, which means that the two operating units are displaced on the same longitudinal axis.

On these guideways is mounted a pair of self centering jaws for blocking the workpieces: bars, pipes, forges, crankshafts, camshafts, ranks, axle shafts and so on.

The vice-jaws customize the machine - the self centering blocking jaws are mounted on the longitudinal guide ways and they work by means of an hydraulic device; the related positioning is made by an hydraulic hooking up (hydraulic blocking/de-blocking system on the guide ways); a system of automatic hooking up of the jaws to the working unit allows to move them to the desired position and, by means of an automatic de-blocking procedure, the unit leaves the jaws which block itself to the guideways of the steel bed.

The structure of the jaws is made of a cast iron body, on which are mounted the hardened steel sliding guide ways and where the blocking vices move themselves.

All the movements are automatically lubricated by means of a centralized systems; the positioning of the jaws is carried out by means of the operating units; hydraulic is the blocking systems device.

The precision heavy duty hardened and ground vice jaws allow to block large components thanks also to the possibility of specific set of jaws.

"An interesting application which has required a customisation of the jaws," said Caorle, "It was when we had to machine the extremities (drilling and tapping) of different types of racks (from a size of 25/30mm of side up to a maximum of 250mm) and we had to consider that, each machined piece, was going to be connected to the following one in order to obtain very long racks.

In fact, whereas the classical concept of end-machining consider the use of jaws for clamping round pieces, having to machine racks (of squared or rectangular shape) is necessary to use flat jaws, with reference to the tooth angular shape.

Thanks to the achievement of a clamping system for the workpieces with reference to their teeth, the required machining have been carried out by means of only one positioning of the piece into the machine- tool and obtaining in this way a really short cycle time, but above all with the great advantage of the results obtained in terms of quality.

Before this technological possibility, the various racks had to be machined with a lathe and with a milling machine, and the process was done in various steps because of the difficulties to get the desired tolerances, so that the cost of production was really high.

Another interesting issue regards the end-machining of underwater pump bodies.

In order to reply to this specific need, it was necessary to design a specific and customized version of encircling vices having the function of blocking the pipe, without making any deformation on it, and avoiding to get an oval shape.

The machining, obtained by interpolation of the three NC axis, is carried out with a modular milling cutter which obtain the required thread in only one pass by an encircling movement.

This solution allowed to reduce by ten times the cycle time with regards to the previous machining, which was carried out with a lathe; another advantage was the achievement of a really higher quality of the thread, in fact the roughness on the surface of a "milling-cut thread" is really better than the one we can get from a lathe.

This type of machining made on a low thickness stainless steel pipe may "pull" the thread.

Our solution allowed to achieve a finished pipe with a constant thickness.

Elimination of the traditional "bottlenecks - the basement has been designed considering specific inclined internal surfaces for evacuation of the chips and it incorporates in its structure the chip evacuator chutes and the coolant tank with the related pump.

The coolant plant is equipped with one pump for the continuous washing of the bed and another one for the coolant liquid which is piped to each spindle: the flow is controlled by an electronic flowmeter which control the coolant circulation and also by electric control valves.

It also has a spray facility for removing chips and for cleaning the working area.

"We have improved the chutes evacuator facility," added Caorle - "In fact, it has always been the "bottleneck" of the classical end-working machine because of its longitudinal mechanical structure and of the reduced room available for the chutes.

The bed of MC 650 is strongly reinforced, but at the same time it is also openly made.

The longitudinal guide ways are supported each 500mm and in between these supports there is an open area which is useful for the falling of chips through the longitudinal collection slit.

Designed for an high productivity - MC 650 is provided with a full sheet metal enclosure guarding and front sliding doors with emergency micro-contact and observation windows for the operator needs.

This structure incorporates easily removable panels which allow an easy access to the inner zone in order to execute maintenance, cleaning and service operations.

Halogen lamps light the inner working area.

The twin doors works pneumatically: they open themselves in automatic mode at the end of the working cycle, but they are closed by command of the operator.

The decision to work in this way was taken with regards to the working time, which is on average approximately a couple of minutes and with this solution the change of the piece is helped.

Each one of the working units is provided with a 20 pockets disc tool changer made by the Italian company Colombo Filippetti (considering the speedy machining it is necessary to use a fast tool changer device): the hydraulic unclamping device of the spindle cone is activated by the operator acting on the pedal facility in order to dispose of both his hands for placing or removing the tooling during the equipping phase of the machine.

The CNC control Siemens 840 D allows the execution of various and complex machining, two push-button panels are used as a command for the two tool-changers in order to make easier the set up of the machine.

Siemens also supplied the motors and digital drives.

The hydraulic plant for the oil-dynamic commands of the machine counts one oil-dynamic centralized unit complete with tank, pump, filters and electric valves.

The spindles are of the pressurized type with carriage using permanent grease and they are made by CAORLE.

Customized solutions for any requirement - the machine is designed to be connected with a robot for the automatic loading of the workpieces; the related automatic doors, covering the frontal and adjacent sides of it, allow for easier loading of the pieces.

MC650 is able to do the machining of pieces having a diameter range of from 20 - 250mm and a length range of 120 - 3000mm considering a maximum total weight of the workpiece of 1200kg.

"This niche of machine-tools," said Caorle, "Often needs different types of customisation in order to reply to the customer's requirements.

The most significant aspect of Caorle's strength is related to the capacity of studying and developing a variety of different technical solutions, clamping systems and tooling with the target of obtaining a high level of working precision and a reduction of the cycle time rates.

A particular issue, where Caorle can show his "engineering know how", regards the study of the automation; in fact, all types of loading/unloading solutions are designed by our technical department.

The development of a customized automation is always an important issue as the cycle times of our machines are really short: i.e., for the machining of a medium dimension shaft the cycle time for carrying out a simple facing (on both ends) is of 20-25 seconds; if the shaft is drilled and tapped it will be up to 1-1,5 minutes for a type of M16 or M20 tapping (and it includes the time needed for changing the tools).

It is for sure that any effort has to be addressed for obtaining the maximum reduction of the cycle time rate, and also considering this aspect we have carefully studied the time for the set up of the machine: i.e., thanks of the self-centering jaws it is possible to block pieces having a diameter range of 15-130 mm by means of only one change of vices, which have been studied for a rapid positioning.

With regards to the tool changer facility, you can further reduce the time if you keep mounted on the tool magazine disc the main used tools (milling-cutters, drills, taps, etc.) and you prepare on a bench a series of pre-set tools.

Talking now about the automation, we have recently developed an interesting solution for the hydraulic actuated loading/unloading device, equipped with a stock area constituted of a V chain, which allows the loading of bars or forgings even the ones with a unusual and irregular shape.

The loading system consists of two mechanical arms with a vertical transversal movement and a double "V" shape, which allow to load and unload at the same time two pieces.

Its functioning can be described as follow: simultaneous loading from the stock of one piece to be machined and from the jaws of the already machined one; by means of a pilgrim step these two pieces are lifted and moved towards the front doors of the machine; meanwhile it loads the new piece on the jaws it unloads the finished one above the unloading trolley which transports it by a longitudinal movement out of the machine.

The automation is completely controlled by the NC unit of the machine and the loading/unloading operations are executed with the doors closed, another way to save time.

In case of external loading devices (i.e.: robot), the machine is provided with connection to the new device and automatic door for the loading/unloading of the pieces on the jaws.

This solution allows a machining process in more than one shift without the presence of the operator.

The machine is normally purchased "stand alone", but it is possible to install it as a part of an automatic island.

Primary target: customer's satisfaction - "The philosophy of our company," concluded Caorle "Is orientated to the complete satisfaction of the customer's needs.

In fact, we are able to do this only because of the choice we have made of totally develop (design, mechanical machining, assembling) the MC 650 inside our Company: this is a solution which allows us to forward to the customer a technological customized product, but without having to make each time a special machine because we work on the customisation of a standard machine.

Finally, it is for us extremely important also the quality of the service: we are able to assure a fast technical service and also a supplying of the mechanical spare parts for all life of the machine.

We are talking about a type of machine with a really long life, whose second hand models maintain a high level in terms of prices.

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