CUTTING METHOD"

FIELD OF INVENTION

[001] This invention deals with design of a machine for manufacturing rotational symmetric objects, by a computer controlled rotating wire method, with intelligent clamping mechanism to minimize manufacturing defects at end of cut. This invention also proposes an intelligent method for shaping of the wire to get parts of maximum accuracy. The present application is based on, and claims priority from an Indian Application Numbers 201741016057 filed on 8 ^th May 2017 and 201841008647 filed on 9 ^th March 2018, the disclosure of which is hereby incorporated by reference herein.

BACKGROUND OF INVENTION

[002] It is often required to manufacture rotationally symmetric cylindrical objects.

[003] Existing wire cutting methods, the raw material is rotated. This necessitates clamping of raw material for every cut, thus slowing down the production speed.

[004] Manual cutting methods are used, but time consuming and also result in shape defects at start and end of cut.

[005] Also shaping the wire to required shape is challenging.

[006] Hence there is a need to develop an automatic system for manufacturing rotational symmetric objects.

OBJECT OF INVENTION

[007] The principal object of this invention is to develop a method of manufacturing rotational symmetric objects in a quick automatic way. [008] Another objective is to develop a intelligent cutting method to avoid shape defects at start and end.

[009] Another objective of the invention is to develop an easier method of wire shaping.

[0010] Another objective is to shape the wire by providing necessary compensation for melting, which varies with linear speed of the wire.

[0011] These and other objects of the embodiments herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following descriptions, while indicating preferred embodiments and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing from the spirit thereof, and the embodiments herein include all such modifications.

BRIEF DESCRIPTION OF FIGURES

[0012] This invention is illustrated in the accompanying drawings, throughout which like reference letters indicate corresponding parts in the various figures. The embodiments herein will be better understood from the following description with reference to the drawings, in which:

[0013] FIG. 1 depicts the proposed automatic cutting machine for manufacturing rotationally symmetric objects.

[0014] FIG. 2 depicts the tool path and the reason for shape defects in conventional manufacturing method.

[0015] FIG. 3 depicts the shape defects in conventional manufacturing methods. [0016] FIG. 4 illustrates the tool path.

[0017] FIG. 5 illustrates some rotationally symmetric objects of varying radius.

[0018] FIG. 6 depicts the rotationally symmetric part to be manufactured.

[0019] FIG. 7 depicts the shape of the bent wire without dimension compensationing.

[0020] FIG. 8 depicts the constant distance offset method.

[0021] FIG. 9 illustrates the proposed variable distance offset method.

[0022] FIG 10. Illustrates variation of Kerf width vs Axial distance.

[0023] FIG 1 1. Illustrates proposed composite bent wire.

DETAILED DESCRIPTION OF INVENTION

[0024] The embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. For example, it should be noted that while some embodiments are explained with respect to cutting of EPS material using Heated wire, any other application may also incorporate the subject matter of the invention with little or no modifications. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.

[0025] The embodiments herein describe an intelligent automated cutting method for cutting rotationally symmetric objects, minimizing shape defects. Referring now to the drawings, and more particularly to FIGS. 1 through 11, where similar reference characters denote corresponding features consistently throughout the figures, there are shown embodiments.

[0026] FIG 1 illustrates the raw material 101 is resting on support 110. A cutting wire 102 is bent to the required shape (Cross sectional shape of object to be manufactured)

[0027] The bent wire is mounted on rotational axis 103 and 104. The rotational axis 103 & 104 are arranged to be collinear and they can rotate the bent wire about this axis 116. The actuator is an electric motor capable of rotating the bent wire exactly by 360 degrees and stopping. Example actuators are stepper, servo motors, DC motors fixed with limit switches etc., but not limited to these examples.

[0028] In one embodiment of the invention, both 103 & 104 has electric actuators for rotating the wire. In another embodiment, one of the side say 103 can have electrical motor and other side 104 can be driven thru a transmission mechanism 114 (rod) and 115 (belt) as shown in FIG1.

[0029] The rotational axis 103 & 104 are in turn fixed on a rigid frame 105. The frame 105 is typically made of right side frame 106, Left side frame 107 and optional top frame 108 and bottom frame 109.

[0030] By passing current through 102, raw material 101 can be melted and cut. Example 1: Wire 102 is made of NiCr alloy. Wire can be heated by passing current. Heated wire can cut foam like EPS, EPE foam etc. Example2: EDM process: Raw material 101 is immersed in dielectric fluid, wire acts as electrode, raw material as anode or vice versa and EDM type machining can be achieved.

[0031] Above cases are quoted as examples, but proposed invention applies for any other wire cutting method.

[0032] When wire 102 is rotated by 360 degrees, the desired rotationally symmetric object is produced.

[0033] Referring to FIG 2, when wire reaches -340 degrees position, the center of gravity 208 of the shape being cut, tends to pivot and rotate left over material at point 207 (due to self-weight). This results in the left side gap 206 closing and the right-side gap 204 widening. More importantly, this results in material at top left moving closer to the heated cutting wire, resulting in excessive melting. Eventually the piece BREAKS and falls off. This results in a shape defect in the manufactured object as shown in FIG 3.

[0034] Referring to FIG 3, manufactured object has an undercut 301 and a overcut (excess uncut material) 302, resulting in a shape defect.

[0035] In some scenarios, this shape defect maybe acceptable, but in some scenarios, this is not acceptable.

[0036] This invention proposes an intelligent clamping mechanism to avoid/minimize this shape defect.

[0037] Referring to FIG 1, some sharp pin like objects 113 are mounted on a movable frame 111. The frame can be lifted up/down (112) along axis y (117) as shown in the XYZ co-ordinate system in FIG 1.

[0038] The number of pins 113 and distance between pins is adjustable depending on shape being cut or it can be constant. .

[0039] In one embodiment of the design, the up down lifting of the pins can be achieved by simple 2-position RC servo motors. This can be activated by a simple On/Off digital signal resulting in low cost system. In another embodiment, this can be a programmable linear axis, so that depth of penetration of the pins into the workpiece can be controlled.

[0040] The automatic programmable controller 120 is programmed such that the pins are lifted up after the wire crosses the 180 degrees or the bottom most point. The pins will first pierce the support 110 and then the material being cut. This pin forms a bridge support between the cut and uncut material. This bridge support will maintain the position of the material being cut, thus avoiding any shape defects. [0041] It should be that the support material 110 is also pierceable soft foam or can have pre-drilled holes at desired location. The speed of piercing is controlled, to avoid any shaking of the raw material.

[0042] The pins are moved back down, once the wire reaches the 360-degree top position.

[0043] By this intelligent and automatic workpiece clamping, shape defects in the output is avoided/minimized.

[0044] In another embodiment of the invention, the whole frame 105 along with cutting wire is mounted on a programmable linear motion axis 121, that can move along the length of the block (axis Z in FIG 1).

[0045] This indexing motion can take the cutting wire to the next position on the raw material, where one more set of parts can be manufactured by rotating the wire by another 360 degrees.

[0046] The indexing distance is typically the shape diameter plus melting allowance, as shown in FIG 4. The tool path is shown in FIG4 as "abcdefghij".

[0047] Thus, multiple objects can be manufactured without re-clamping the workpiece.

[0048] This moving wire method results in a compact machine, compared to a machine in which the block is moved.

[0049] The frame 111 holding the pins 113 is also mounted on bottom frame 109 and moves along Z axis 121. This way the pin mechanism is available and ready for supporting next cut. [0050] In another embodiment of the invention, the rotary axis 103 and 104 are in turn mounted on another programmable linear motion axis 118, as shown in FIG1.

[0051] This axis motion can be programmed simultaneously with wire rotation to produce rotationally symmetric objects of varying radius as shown in FIG 5.

[0052] In system with this extra linear axis 118, the supporting pins can be at bottom or optionally in the top zone also and engages with the object after wire has rotated ~ 90 deg. At end of cut, 118 axis lifts up first along with the pins. Then the pins are dis-engaged. Then the system moves forward for next cut.

[0053] FIG 6 shows a rotationally symmetric object to be manufactured.

[0054] Typically, this is achieved by bending a heating element (Nichrome wire etc.) to the desired shape and rotating about an axis, as shown in FIG 7. (or block is rotated at times)

[0055] Because the heated wire melts the foam material, a geometric compensation is typically added to the wire shape as shown in FIG 8. The amount of melting is estimated experimentally and wire is bent with allowance, so that dimensions of part is exact, after cutting. Constant distance offset method is typically used as shown in FIG 8, where D1==D2==D3==D4 etc.

[0056] However, the effective linear federate of the wire is lesser for the wire closer to the axis compared to the wire away from the axis. This results in uneven melting, i.e. more melting near the axis and less melting away from the axis.

[0057] To compensate for this variable material melting, an intelligent method is proposed in this invention. Here "Variable Distance Offset method" (VDO) is proposed. To arrive at the exact shape of the wire, the original desired cross-section geometry is offset. But the offset distance is inversely proportional to the distance from the axis as shown in FIG 10. A sample wire shape obtained by applying this VDO method is shown in FIG 9. The relation between offset(d) & R can be linear or non-linear, based on the material being cut and temperature of wire etc. This relationship can be obtained experimentally or analytically.

[0058] A method of bending wire to reqd. shape is proposed, as shown in FIG 11.

[0059] 501 is a core stiffer wire/strip. This can be cut to reqd. shape in CNC router. Or it can be formed using a fixture/template. Before forming, the wire can be softened by annealing. After forming, the wire is hardened by heating & quenching (rapid cooling by dipping in water). Then wire is tempered by heating & slow cooling.

[0060] Insulation sleeve 502 is then inserted around the wire 501. The sleeve can be a single long sleeve or multiple short sleeves for easier insertion, covering the bare wire 501 fully.

[0061] Above 502, heating element 503 is applied. Either wound in a spiral coil fashion OR one or more straight wire can be used, instead of spiral winding. Alternately, a pre-insulated heating element can be wound on 501, thus eliminating need for separate insulation 502.

[0062] This composite wire can be used as it is or an optional fiber sleeve is installed on top of this 503, thus giving a smoother finish on the foam being cut with this shaped wire.

[0063] This method allows for a reliable shaped wire to be produced to accurate dimensions instead of using thick bare NiCr wire. [0064] In another embodiment, the shapeable non-heating metal core can be a hollow metal tube, with the heating coil 503 passing inside or outside the tube with insulation sleeve 502 between 501 and 503.

[0065] Such hollow tube can be shaped in a cnc bending machine or by slitting to appropriate angle and depth at reqd. precomputed locations and then bent.

[0066] The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.