FR2778127A1 - Computer numerically controlled milling process with inversion of plastic workpiece - Google Patents

Abstract

The method involves a theoretical volume invoked for programming purposes. It is a two-stage process in which the upper face of a workpiece is machined, whilst the workpiece is held down flat by its base onto the milling machine table, followed by inversion and packing up, to replace lost material (or height) precisely, before machining the former base. Preferred features: The packing is formed by covering the surface initially machined by fixing a protective film (9) to it, or coating with parting agent. A hardening material (10) is cast onto it (9). A soft (plastic) spacer (7) is placed on top. This exceeds the thickness of the material machined away in the initial stage. It is precision-surfaced by milling to the required height (H) above the lower surface (112). Datums (11, 12) are defined and projected to the machine table (111, 112), to locate the principal axes after inversion. Screws, or preferably pegs fix and locate these axes, passing through extensions of the spacer (13, 15), the extensions being made of plastic resin. The workpiece is adhered to the milling table for fixation. The protective film is a plasticized adhesive.

Description

The invention relates to a milling method comprising

  a turning of the milled part.

  The invention relates more particularly to the field of manufacturing and computer-aided design in which a theoretical part to be produced is defined in computer means. These computer means provide digital control of milling means, to produce the real part from a gross volume of soft material

arranged on a milling table.

  The invention can be applied in particular to the milling of soft materials such as plastic resins to produce

prototype volumes.

  To produce a complex part by milling with computer-assisted numerical control, the raw part is fixed on the milling table, the positioning references of the raw block are taken on the milling table and then the upper face of the block is machined according to the part. defined in IT resources. To mill the underside of the raw block, and in order to be able to turn this part and position it on the milling table, it is known to make, in an additional part, an impression of the already milled part of the block. This intermediate milling in an additional part requires computer preparation. The partially milled block is then placed in the additional part which is then fixed on the milling table. We then take the positioning references of the block to be milled on the milling table and then finish machining the

  lower part of the returned block.

  However, this milling process, which requires intermediate milling and its preparation in the

  computer-aided design is long and complex.

  An object of the present invention is to provide a milling method comprising turning the milled part, overcoming all or part of the drawbacks of the art

previously noted above.

  This object is achieved by the fact that the milling process, which involves turning the milled part and which consists of defining a theoretical part in computer processing means ensuring the automatic control of milling means, to produce an actual part at starting from a gross volume of soft material fixed on a milling table, comprises: - a step consisting in placing the theoretical part in a theoretical gross volume of determined dimensions and comprising two parallel faces, respectively lower and upper, - a step of fixing of an actual gross volume of soft material on the milling table, the actual gross volume having two parallel faces, respectively lower and upper distance from a dimension corresponding to the spacing of the upper and lower faces of the theoretical gross volume, the real gross volume having a volume identical to the theoretical gross volume or likely to be contained in this rnier, the gross volume resting on the table by its underside, - a first step of milling the upper part of the gross volume, - a step of reconstituting an upper surface parallel to the lower surface of the gross volume and located at a distance from the latter equal to the spacing of the lower and upper faces of the gross volume before the first milling step, - a step of turning over the gross volume on the milling table, the gross volume being fixed on the table by its upper face reconstituted, and - a second milling step of the lower part of the

gross volume.

  According to another particular feature, the milling method comprises a step of defining, in the computer processing means, a first orientation of the theoretical gross volume relative to a reference frame, and a second orientation deduced from the first orientation by a 180 degree rotation of the gross volume with respect to an axis of the repository, the orientations before turning and after turning the gross volume on the milling table corresponding respectively to the two defined orientations

io for the theoretical gross volume.

  According to another particular feature, the step of reconstituting an upper surface, on the gross volume, consists of: - covering the milled upper surface with a removable protective film or a release agent, - pouring a layer of hardenable material on the film placed on the milled surface, - have at least one block of soft material on the cast material, the blocks having a thickness greater than the layer of material milled during the first milling step, and - to surface the upper part blocks at a dimension from the lower surface corresponding to the spacing of the lower and upper faces before the first step

milling.

  According to another particularity during the step of reconstituting an upper surface on the gross volume, at least two positioning marks are defined on the gross volume and their respective projections on the milling table, to allow the gross volume to be turned over. so that the longitudinal and transverse median axes of the gross volume remain located in two respective fixed planes before and after turning. According to another particular feature, the positioning marks consist of two housings for fixing screws or pins and located respectively at two ends of the gross volume so that the housings of the pins are located on a longitudinal or transverse median axis of the gross volume , the pin housings being provided in the leveling elements and / or in

  parts made integral with the leveling elements.

  According to another particularity, the housings for the pins are formed in two ears fixed on the leveling elements before the surfacing step, the two ears being also surfaced the dimension determined during

of the surfacing step.

  According to another particularity the ears are made up

plastic resin.

  According to another particularity, the step of fixing the gross volume on the milling table consists in gluing the gross volume

  on a rigid plate itself clamped on the milling table.

  According to another feature, the protective film is

  consisting of a plasticized adhesive film.

  According to another particularity, the curable material is

  made of quick setting polyester resin.

  Other characteristics and advantages of the invention

  will appear on reading the detailed description which will

  follow, for the understanding of which reference will be made to the appended drawings, in which: - Figures 1A and 1B schematically represent the preparation, in computer means, of the milling steps according to the invention - Figures 2A, 2B, 3A to 3C, 4A, 4B, 5A and 5B schematically represent a succession of stages of the

  milling method according to the invention.

  The invention will now be described with reference to FIGS. 1A, 2A, 2B, 3A to 3C, 4A, 4B, 5A and 5B. FIGS. 2A, 4A and 5A show in perspective the block of raw material on the milling table at different stages of the process. Figures 2B, 4B and 5B are side views respectively of the

Figures 2A, 4A and 5A.

  The method according to the invention relates to computer-aided design and manufacturing (CAD / CAM). The computer means used (not shown) for implementing the method comprise a computer which controls, by means of appropriate software, milling means to

numerical control.

  To produce a part of determined shape, the operator begins by defining in the computer-aided design (CAD) software, the theoretical part T to be produced. In the embodiment shown, the part T to be machined has the shape of a prism with a trapezoidal base. The largest parallelepipedal face of the prism has, in its middle, a longitudinal groove 16 which extends over the entire length of the part T. The operator then places the theoretical part T in a theoretical gross volume B of determined dimensions and comprising two faces 3, 4 parallel, respectively lower and upper (Figure 1A). In the example shown, the theoretical gross volume B, or theoretical gross is

a rectangular parallelepiped.

  The operator then creates, in the same computer file or in two separate files, two representations of the theoretical gross B having respectively two

  different orientations compared to an xyz repository.

  FIG. 1A represents a first orientation known as “before turning over” of the theoretical crude B with respect to the reference frame xyz. In this first orientation, the upper face 4 of the parallelepiped B is located above the lower face 3, that is to say that the groove 16 of the part

  Theoretical T is oriented upwards.

  FIG. 1B represents a second orientation known as "after reversal" of the theoretical crude T with respect to this reference frame xyz. In the second orientation, the upper face 4 of the parallelepiped is located below the lower face 3, that is to say that the groove 16 of the theoretical part T is oriented downwards. The second orientation is deduced from the first orientation by a rotation of 180 io degrees of the gross volume B around a direction parallel to an axis x of the frame of reference. The two orientations of the parallelepiped B of FIGS. 1A and 1B will correspond respectively to two

  machining phases described below.

  The theoretical rough B makes it possible to define the block 2 (FIG. 2A) of real material, or real rough 2, which will be machined to produce the desired part. The actual crude 2 comprises two parallel faces 3, 4, respectively lower and upper, spaced from each other by a dimension H corresponding to the spacing of the upper 4 and lower 3 faces of the theoretical crude B. Preferably, the shape and dimensions of the actual rough 2 correspond to the shape and dimensions of the theoretical rough B. However, the actual rough 2 may have a volume closer to the volume of the part 1 to be produced, that is to say less to the volume of theoretical crude T. Thus, the volume of real crude 2 is either identical to the volume of theoretical crude B, or susceptible

to be contained in it.

  The operator then fixes an actual gross volume 2 as defined above on the milling table 6 (FIG. 2A). The actual crude 2, which consists of a soft material such as a plastic resin or an epoxy resin, is fixed by gluing or any other equivalent means on a rigid plate (not shown) itself clamped on the milling table 6 . The gross volume 2 rests on the table 6 by its lower face 3. The operator then takes the crude positioning references 2 on the milling table, that is to say that he informs the machine about the relative position of the crude volume 2 relative to the means 5 of

milling (Figure 2B).

  The first milling phase can then be started. During this first milling step, the milling means 5 machine the upper part of the raw block 2. The milling means 5 can be constituted, for example,

  a three-axis or five-axis milling machine.

  According to the invention, when this first milling step is completed, the operator will reconstitute, on the upper surface 8 o0 (FIG. 3A) milled from the gross volume 2, a bearing surface. This reconstituted upper surface 14 (FIGS. 3C and 4A) is parallel to the lower surface 3 of the stock 2 and situated at a distance from the latter equal to the distance H from the lower 3 and upper 4 faces of the stock 2 before the first

milling step.

  In the nonlimiting exemplary embodiment shown, the reconstitution of this support surface 14 begins with the

  laying, on the milled upper face 8, a protective film 9.

  This protective film 9, which is preferably a plasticized adhesive film 9, is such that it can be easily removed from the milled surface 8 on which it is bonded. As described below, the adhesive film 9 will constitute the surface on which a curable material 10 will be poured. Thus, the film 9 can be bonded to the machined surface 8 of the stock 2 with folds, to improve the setting of the hardenable material which has been cast. The adhesive film 9 can be replaced by a release agent of known type which will be chosen according to the material machined, or any other

equivalent means.

  As mentioned above, the operator pours a pasty material 10 onto the film 9 which solidifies after a determined period of time (FIG. 3B). This curable material can consist, for example, of a setting pasty polyester resin.

  fast or any other equivalent material.

  The operator then places one or more blocks 7 of soft material on the layer 10 of resin before it sets (FIG. 3C). The blocks 7, which can be made of the same material as the stock 2, have a thickness greater than the layer of material milled during the first milling step. These blocks 7 of material are intended to fill the

  theoretical gross volume defined above in computer-aided design software. The blocks 7 are solidly bonded to the crude 2 after the pasty resin 10 has set.

  The operator also defines at least two marks 11, 12 for positioning on the stock 2 as well as the projections 111, 112 of these marks 11, 12 on the plate on which the stock 2 is glued (FIGS. 4A and 4B). These pins 11, 12 and their projection 111, 112 are provided to allow the turning over of the rough 2 so that the longitudinal and transverse median axes of the rough volume 2 remain located in two respective fixed planes before and after turning. That is to say that in its position after turning the stock 2 is located in the same place and with the same orientation on the table 6 of

  milling only in its position before turning.

  In the example shown, the positioning marks consist of two housings 11, 12 for fixing screws or pins and are located respectively at two ends of the blank 2. The two housings 11, 12 are located at equal distance L / 2 of the two longitudinal edges of the gross parallelepiped 2. The two housings 11, 12 of the pins are located on the gross longitudinal median axis 2 and are formed respectively in two ears 13, 15 fixed on the leveling elements 7. The two ears 13, 15 can be made of plastic resin or of the whole

  equivalent material made integral with the blocks 7.

  The method according to the invention continues with a step of surfacing the upper part of the blocks 7 fixed to the stock 2 (FIG. 3C). The blocks 7 are surfaced at a dimension H relative to the lower surface 3 of the stock 2 which corresponds to the spacing of the lower 3 and upper 4 faces before the first milling step. For the sake of simplification, the ears 13, 15 are not shown in FIG. 3C, however, the latter are also surfaced at dimension H

of the reconstructed surface 14.

  The operator then takes off the half-machined part from the table top of the milling table 6 and cleans it of the adhesive residues. It then makes two holes in the tray for the installation of the pins at the locations 111, 112 identified during the production of the housings 11, 12 for the pins of the

lo ears 13, 15.

  The stock 2 is then turned over so that the upper face 14 reconstituted by the blocks 7 rests on the flange plate on the milling table 6. The operator positions and fixes the reconstituted stock 2 with the help of pinning. The stock 2 can again be fixed by gluing or any other means on the flange plate on the milling table 6. During this step, the operator ensures that the turning of the crude material 2 is carried out by a rotation around the same direction as during the theoretical turning in the computer-aided design software. That is to say that the positions before turning and after turning the rough 2 on the milling table 6 correspond respectively to the two orientations

  defined for the theoretical gross volume B in FIGS. 1A and 1B.

  Thus, the "front-rear" orientation of the crude 2 relative to the milling means 5 is retained in the phases of

  milling before turning and after turning.

  Once the stock 2 is turned over and fixed on the milling table 6, the operator starts the second machining phase of the

  rough, i.e. the machining of the lower part of the rough 2.

  When the milling of the part is finished, the operator only has to disassemble the finished part from its gangue of resin isolated by

the film 9.

  Of course, the invention is not limited to the embodiment described above, thus, in an alternative embodiment, the two housings 11, 12 for the means for fixing and positioning the crude can be provided in the ends of the resin block (s) 7 rather than

  in ears reported on these.

  It is therefore understandable that there is a very simple milling process which makes it possible to reduce the machining times for complex parts which require turning over on the milling table. Indeed, according to the invention it is not necessary to perform an intermediate milling of a "mold" to turn the part. Thus the computer-aided design and manufacturing work and the machining journeys corresponding to this mold are saved. Furthermore, according to the invention, only a single reference point of the crude 2 is made on the milling table 6. Indeed, thanks to the reconstitution of an upper surface 14 on the stock 2 and its precise reversal by means of positioning marks, it is not necessary to carry out a new reference point after turning the stock, no more than 'a new

  clamping of the plate on which the stock is fixed.

  Although the invention has been described in connection with particular embodiments, it includes all of the

  technical equivalents of the means described.

  Finally, the marks inserted after the characteristics

  techniques set out in the claims are for the sole purpose

  to facilitate understanding of these and cannot

limit its scope.

Claims (10)

CLAIMS R E V E N D I C A T I O N S   1. Milling method comprising turning the milled part (1) and consisting in defining a theoretical part (T) in computer processing means ensuring automatic control of milling means (5), to produce a part (1) real from a gross volume (2) of soft material fixed on a milling table (6), characterized in that it comprises: - a step consisting in placing the theoretical part (T) in io a theoretical gross volume (B) of determined dimensions and comprising two parallel faces (3, 4), respectively lower and upper, - a step of fixing an actual gross volume (2) of soft material on the milling table (6), the volume real gross (2) having two parallel faces (3, 4), respectively lower and upper distance from a dimension (H) corresponding to the spacing of the upper and lower faces of the theoretical gross volume (B), the real gross volume ( 2) having a volume identical to the volume theoretical gross me (B) or likely to be contained in the latter, the gross volume (2) resting on the table (6) by its lower face (3), - a first step of milling the upper part of the gross volume (2), - a step of reconstituting an upper surface (14) parallel to the lower surface (3) of the gross volume (2) and situated at a distance from the latter equal to the spacing (H) of the lower faces (3) and higher (4) of the gross volume (2) before the first milling step, - a step of turning over the gross volume (2) on the milling table (6), the gross volume (2) being fixed on the table (6) by its reconstituted upper face (14), and - a second step of milling the lower part of the gross volume (2).   2. Milling method according to claim 1 characterized in that it comprises a step of defining, in the computer processing means, a first orientation of the theoretical gross volume (B) relative to a reference frame, and a second orientation deduced from the first orientation by a 180 degree rotation of the gross volume (B) relative to an axis of the reference frame, the orientations before turning and after turning the gross volume (2) on the corresponding milling table (6) respectively to the two orientations   defined for the theoretical gross volume (B).   3. Milling method according to claim 1 or 2 characterized in that the step of reconstituting an upper surface (14), on the gross volume (2), consists in: - covering the upper surface (8) milled d '' a removable protective film (9) or release agent, - pour a layer (10) of hardenable material on the film (9) placed on the milled surface (8), - have at least one block (7) of soft material on the cast material, the blocks (7) having a thickness greater than the layer of material milled during the first milling step, and - to surface the upper part of the blocks at a dimension (H) relative to the lower surface (3) corresponding to the spacing of the lower (3) and upper (4) front faces the first milling step.   4. Milling process according to any one of   claims 1 to 3 characterized in that during the step of   reconstruction of an upper surface (14) on the gross volume (2), at least two positioning marks (11, 12) are defined on the gross volume (2) and their respective projections (111, 112) on the table ( 6) milling, to allow the gross volume (2) to be turned over so that the longitudinal and transverse median axes of the gross volume (2) remain in two respective fixed planes before and after reversal.   5. Milling method according to claim 4 characterized in that the positioning marks consist of two housings (11, 12) for fixing screws or pins and located respectively at two ends of the volume (2) gross so that the housings (11, 12) of the pins are located on a longitudinal or transverse median axis of the gross volume (2), the housings (11, 12) of the pins being formed in the leveling elements (7) and / or in parts (13, 15) made integral with the elements (7) for setting level.   6. Milling process according to claims 3 to 5 taken   in combination characterized in that the housings (11, 12) for the pins are formed in two ears (13, 15) fixed on the leveling elements (7) before the surfacing step, the two ears (13, 15) being also surfaced   the dimension (H) determined during the surfacing step.   7. Milling method according to claim 6 characterized in that the ears (13, 15) are made of a plastic resin. 8. Milling process according to any one of   claims 1 to 6 characterized in that the fixing step   of the gross volume (2) on the milling table (6) consists of gluing the gross volume on a rigid plate itself clamped on the table (6) milling.   9. Milling method according to claim 3 characterized in that the protective film (9) consists of a plasticized adhesive film. 10. Milling method according to claim 3 or 8 characterized in that the hardenable material (10) is   made of quick setting polyester resin.