LA CHAÎNE NUMÉRIQUE : De l'idée à la réalisation

The part has been designed and now it must be manufactured; first, by the one-part production method.

The part is going to be machined from a parallelepiped piece of metal cut from a metal chip^[1].

We can see the first shape appears with machining^[2], then the outline, or profile, and the drilling of holes.

Then it is necessary to hollow out the central bore and thus we obtain our part.

We are now going to see 2D ½ Computer-Aided Manufacturing^[3] (2D ½ CAM) which allows us to use the programmes to machine parts, as we have just seen.

The first stage in 2D ½ CAM consists of assembling the rough part, in green, with the reference part, in orange.

We use the reference model without the rounded edges or cut-outs as the part is made entirely by machining and is not cast.

The second stage is not an obligation, but it is very useful to validate the manufacturing method chosen. It consists in setting up the positioning^[4] and clamping elements. In this way, during a simulation, we can detect possible interference. The set up in this case consists of:

• a vice,^[5]

• a fixing plate^[6],

• the protection plate^[7], whose utility will be explained during the simulation,

• a locking screw^[8].

It can be noted that the positioning here is incomplete, however, in the case of one-part machining, this is not a problem, as long as the part is not removed^[9].

It is now important to input the machining functions to allow the software to calculate the paths its tools must take in order to develop a programme to machine the part.

To define a machining function you must:

• Select a surface to machine,

• Select a tool^[10],

• Define the cutting conditions in relation to the part/tool couple,

• Decide on the machining method.

Once the functions have been created, the rough part (in green) disappears from the image. The machining functions appear in the tree diagram on the left of your screen^[11].

Once all the elements have been set up, a digital simulation of machining can be carried out. We begin with phase 10. We see the rough part in yellow and the rest of the clamping^[12] set-up in grey.

Machining starts with the facing^[13] of the part.

It continues with the profiling, to form the five branches of the star. The profiling operation consists of a series of passes carried out at different heights. The tool follows the paths defined, on an XY plane in this case, and which are repeated at different heights, which explains why it is called 2D1/2 CAM. 2D refers to the plane for the trajectory, and ½ for the successive passes on the Z axis.

It is to be noted that the simulation can also be compared to a subtraction of volumes. The software knows the volume of the part and that of the tool, and because it is informed of the tools' paths it can remove from the part, the intersections differentiating the two volumes which appear during the trajectories. This means that the simulations can be close to reality in terms of trajectory. Only the cutting conditions cannot be verified during the simulation.

Here, in red, is the machining operation. This corresponds to the machining of the clamping elements, in grey, and in particular to the protection plate. This means that the tool can go lower than the lower plane of the rough part in order to allow maximum machining without machining the clamping plate.

The programme then carries out the machining of the notches, punches the hole positions, does the boring and the countersinking.

We are going to simulate step 20, which is the second step in machining. It can be seen that

the clamping position has changed. The part is now held by two clamps^[14] which were put into place before removing the central screw which held the system in position in step 10.

Step 20 consists simply in machining the central bore. As was the case in the previous step, the mill machines the protection plate just a little, indicated in red in the diagram.

You are now going to see a summary of the machining operations of the crown adaptor on a 3-axis milling machine.^[15] In reality, this action, corresponding to steps 10 and 20, lasts 20 minutes.

This machining operation produces the part presented on this slide.