Mechanised of titanium in the medical sector

The pieces are complex, with big quantity of operations realised on the piece splitting of bar. The precisions comprised between 0,01 and 0,02 millimetres. The oils of cut are special for this type of materials, with drop viscosidad and highly aditivados. The correct election of the oil of cut incide directly in the length of the tools, the superficial state of the piece (rugosidad and characterisation).

The tools of cut to use are usually those that possess edges of cutting very acute and are realised in hard metal micrograno. They exist specific coatings to increase the resistance to the wear of the edges, avoid the adhesion of the material to the same and increase the length of the life of the tools. By his part, the refrigeration of the point of cut is vital for the obtaining of good surfaces. Likewise, pressesures in the order of 20-60 bars are ideal to achieve two basic aims: avoid adhesion of the material in the edge of cutting and elimination of the shavings in the same moment in that they are generated.

On the other hand, the titanium is a material with a big tendency to inflame , that burns very quickly and generates a big quantity of heat. Thus it is very important the contribution of a refrigerante suitable in the point of contact of the tool with the material and, of preventive way, is necessary to foresee a system anti-fires. This, very placed and with the suitable probes, will reduce to a large extent the propagation of the fire in the machine.

The threaded of the pieces is one of the operations that is used to to be of more difficulty if it does not tackle with the suitable tools. In the outside of the piece can use technicians like the threaded conventional to tip of blade, threaded by laminación (in cases very specific), threaded by milling, threaded by eddy. This last system is the one who offers better guarantees of quality, greater control of the final profile regarding form and dimensions, greater length of the tool and lower time of mechanised.

Implemented by Lathes at the beginning of 1990, has gone showing that impossible pieces to realise without this system, are nowadays perfectly feasible and offer a degree of normal difficulty. Resolved technically without problems by the companies of the sector, the eddy bases in a cabezal where go mounted a series of blades or insertos that turns to big speed.

This cabezal mounts in the device of torbellinar and to the group gives him the inclination of the thread to generate. The eddy situates in the diameter of core of thread and out of the piece. From this moment, to generate the thread, to each turn of the piece the cabezal (or the piece) displaces the step of thread to generate.

The rotation of the piece realises by means of the rotary presses axis C. A turn of the piece requires 360º.

Like this, for example, if it requires do a thread in passing of 2 millimetres and the distance between the point of entrance of the eddy and the full stop of thread is of 20 millimetres, will be necessary:

• Number gone back=Length thread/happen= 20/2= 10 turns.
• Number degrees = Number gone back x 360° = 3.600°

The time of mechanised of this thread will depend directly of the speed of rotation (vel. Of cutting) of the cabezal of torbellinado and of the advance in degrees/minute of the rotary presses axis C. Besides, the increase of the number of blades favours the advance of the axis C because keeping the same advance by tooth, increase the number of teeth and therefore the advance of the rotary presses axis C.

Regarding the threaded interior, the problematic is different. The possibilities of threaded are lower and besides have to take into account that the big problems, although with solution, are the small threads of big depth.

The threaded with male, although it follows evolving and companies like DC Swiss contribute interesting solutions, is only applicable to metric upper to 2-2,5 millimetres and in upper titaniums to degree 2.

For the inferior threads and materials less aleados the valid alternative is also the eddy.

The tools for the inner eddy are very small. If we think, for example, in as a thread of M1.8x0.35 with a diameter of core of 1,45 millimetres. In this hole has to go in a tool, of one or several tips, that turning on himself same have to generate the profile of thread during all the distance of the same. Really they are micro incredible tools.

In this type of inner threads the challenge is to delete the shaving, micro shaving, in the same moment in that it generates .

The threaded is used to to be from the interior of the thread to the outside of the piece, with what the entrance of oil of cut is very difficult but indispensable. If the lubricante does not achieve to go in in sufficient quantities will produce a thread of appearance very rough and a small length of the tools. Small improvements in the system of lubricación contribute big results in the final appearance of the piece and in the length of the tools.

The speeds of rotation of the tool are in the order of 20.000 until 60.000 rpm and, in this appearance, as in other a lot of, is indispensable to have the ‘know how' of technicians of mechanised skilled and the punctilious annotation of the results obtained so much in the proofs of mechanised as in the production of the series.

In case it was not sufficient challenge the threaded longitudinal interior, from does some time proliferate in implantología threads of metric even inferior, ej. M1.5, bent. This type of threads realise also by eddy, being necessary in these cases that the machines, the lathes, since we are speaking that a lot of pieces produce from bar, have the suitable devices to bear these eddies bent and that besides facilitate to the operator the programming of this type of helicoidal interpolations, is for example the case of the macro G960 of Lathes. With 5-7 parameters is able to realise this type of threaded bent without any difficulty added for the technician preparador.

In Lathes receive each day pieces with profiles more complex, many carry milling impossible does very little, the tolerances are really strict, besides our specialists are very consent that the superficial states and the absence of rebabas mark the difference between a good product and an excellent product. It is not sufficient with 4, 5 or 6 axles. The pieces require desbastes, finishings, crowd of tools, rotary presses axles, etc. For this reason, Lathes in addition to this type of machines, puts to the disposal of the market machines with 10 and 12 axles.

The batches of production are inferior and this forces to the reduction of time of manufacturing and tuned of the machines to keep on being competitive.

Add an axis more than facilitate the milling of a pillar angulado without having to change the support or can program the angle of this pillar without having to disassemble the manufacturing is something very valuable. Also the new axis B in the machines that facilitate us this work.

Likewise, the reduction of time of manufacturing involves reduction of time of unemployment of machine. The machines have to be stopped the minimum possible time. The programming, tuned of the program, chequeos of collisions, control of the final profile have to realise while the machine is in production with the previous piece.

The tuned final already can do with the same philosophy and directly in machine, without going through intermediate computers.

As we have seen in brief with some examples (could treat other a lot of processes and difficulties of the own pieces of the medical sector), the mechanised of pieces of this sector involves always different and new challenges that are not frequent in another type of pieces. Thus, the one who wishes to initiate in the sector or be to the avant-garde of the same requires machines of big precision, with tool holders and new toolings and at all conventional, functions macros adapted with helps to the programming and a manufacturer with the knowledge and the will of sufficient service to assist him in all and each one of the difficulties that the sector involves.