Method of electrochemical manufacture of metallic plates and apparatus therefor

Abstract

 A method of electrochemical machining of metallic plates, which is characterized in that the metallic plate (1) is first covered, at least on one side, with a layer of electrically insulating material that leaves exposed the regions (2) to be removed ; the plate to be machined is then immersed in an electrolytic bath constituted by an aqueous solution of NaCi and is placed opposite a metallic plate (4) which has substantially the same dimensions; the two plates (1,4) can be connected to the positive and respectively negative poles of a direct supply voltage which is such as to allow metal removal from the exposed regions.

Description

[0001] The present invention relates to a method of electrochemical manufacturing or machining of metallic plates.

[0002] In particular, the method is suitable for machining metallic plates, for example to form holes, slots, grooves and cuts of any shape and size on metallic plates having a thickness comprised between 0.01 and 1 mm.

[0003] As is known, holes, slots, grooves and cuts, generally termed "openings" hereinafter, are formed according to various methods, each of which has specific limits and drawbacks.

[0004] For example, with mechanical machining by blanking, it is not possible to form openings that have complicated shapes within the desired tolerances, due to the unavoidable deformation of the part caused by the blanking force.

[0005] Furthermore, blanking forms burr along the edges of the openings, requiring subsequentfinishing operations.

[0006] With machining that requires the application of heat and the removal of parts by means of mechanical and/or electromagnetic forces, considerable drawbacks are encountered due to the overheating of the workpiece, which particularly produces plastic deformations and work-hardening of the metal, changing its hardness and its crystalline structure.

[0007] Thermochemical and laser machining techniques are also known. The former entail removal of metal in an airtight chamber in which a mixture of hydrogen and oxygen is introduced and then ignited electrically.

[0008] However, this intrinsically expensive machining technique forms burr and oxides on the plates, deposits scale and requires rooms protected against fire and noise.

[0009] Laser machining does not allow to machine thin plates, since it causes conspicuous burr and cambers which can be eliminated only by additional treatments. Furthermore, some metals, such as copper, aluminum and alloys thereof, can be treated only with extreme difficulty due to their high degree of reflection.

[0010] Finally, chemical machining techniques are known that are based on the corrosive power of certain acids on metals. This technique, too, is linked to severe problems, including the excessively long time required for the treatment, the need to use a type of acid for each material to be treated, the installation of units for eliminating acid fumes, which form during treatment and might be harmful to operators, and for eliminating spent acid solutions that contain all the removed products. From the point of view of machining quality, it is noted that, using acids, it is not possible to achieve a flat cut at right angles to the surface of the plate, especially in case of significant thickness thereof. The cut in fact slopes.

[0011] With reference to these machining techniques, electrochemical machining techniques are known in which direct current is fed to the plate to be treated and to the forming tool. In these techniques, the plate assumes a shape complementary to that of the tool, which must accordingly be pre-shaped. Furthermore, it is necessary to ensure that the metal removed from the plate does not deposit onto the tool, since its shape would be altered, consequently altering the shape of the plate.

[0012] The technical aim of the present invention is to provide an electrochemical method, applicable to metallic plates, which can obviate the above- described drawbacks and allows to form extremely small openings of any shape.

[0013] This aim and this object are achieved with a method for the electrochemical machining of metallic plates, which is characterized in that the metallic plate is first covered, at least on one side, with a layer of electrically insulating material that leaves exposed the regions to be removed; the plate is then immersed in an electrolytic bath constituted by an aqueous solution of NaCi and is placed opposite another metallic plate which has substantially the same dimensions as the first plate, said two plates being connectable to the positive and respectively negative poles of a direct supply voltage which is such as to allow metal removal from said exposed regions.

[0014] This method does not require preparation of a tool so as to form openings in the plate.

[0015] An object of the present invention is to provide an apparatus for performing the described method.

[0016] Further characteristics of the method according to the invention will become apparent from the following description with reference to the accompanying drawings, wherein:

figure 1 is a schematic view of an apparatus suitable to perform the method according to the invention; and

figure 2 is a diagram that plots metal removal as a function of the electric current and of the distance between the plate and the cathode.

[0017] With reference to figure 1, the reference numeral 1 designates the workpiece, which in the specific case is constituted by a metallic plate in which the openings to be formed are designated by the reference numeral 2. In figure 1, the openings 2 are constituted, by way of example, by a plurality of parallel slots, but their shapes and dimensions may be any, and so may be those of the plate 1 itself.

[0018] The openings 2 to be formed are traced by covering the remaining part 3 of the plate 1 with a layer of electrically insulating material applied in any manner, such as paints or films.

[0019] Although the plate 1 may in theory be several millimeters thick, its thickness is preferably comprised between 0.01 and 1 mm so as to keep the method within the limits of economic competitiveness with respect to currently known methods in order to obtain optimum results in qualitative terms.

[0020] The plate 1 is immersed in an electrolytic bath which is constituted by an aqueous solution of NaCI. The best results have been obtained with an aqueous solution of NaCI at a concentration comprised between 100 grams of NaCI per liter, and saturation which is equivalent to approximately 350 grams per liter at a temperature of 25°C.

[0021] A plate 4 is placed in the electrolytic bath in front of the plate 1 and is made of a metal that has high h resistance to dissolving in the aqueous NaCI solution, for example titanium.

[0022] The dimensions of the plate 4 are substantially equal but preferably larger than those of the plate 1, and its distance from said plate 1 is chosen according to criteria for optimizing the speed and quality of metal removal. This distance (gap T) is usually confined within an interval comprised between 0.2 and 5 mm.

[0023] During operation, the plate 1 is connected to the positive pole of a direct voltage, the negative pole of which is connected to the plate 4.

[0024] The flow of current releases metal ions Me++ at the anode, i.e. from the exposed regions of the plate 1, whereas gas forms at the cathode, i.e. on the plate 4. The removed material that deposits does not affect the shape of the openings.

[0025] Erosion of the plate 1 is thus produced at the openings 2 and can lead to the partial or total perforation of the plate 1 in a time interval that depends on various factors. Particularly, the erosion process is a function of the concentration of the electrolytic bath, of the current intensity, of the temperature of the electrolytic bath and of the distance between the plates.

[0026] In the diagram of figure 2, the dashed line indicates the value of the gap T in millimeters, as a function of the intensity of the current D in A/sq dm, that allows to optimize removal of the metal from the plate 1 without damaging it. The removal rate v in mm/min that corresponds to the optimized value of the current intensity D is shown in solid lines.

[0027] Thus, for example, a gap T = 0.5 mm is matched by a current intensity D = 60 A/sq dm and by a removal rate v = 1.5 mm/min; this means that if the plate 1 is placed at 0.5 millimeters from the plate 4, a current intensity D = 60 A/sq dm causes the thickness of the plate 1 to decrease by 1.5 mm/min.

[0028] The value of the current is the one required to form the openings 2 as accurately as possible within the limits of the allowable treatment time.

[0029] As can be seen, the invention allows to achieve the following substantial advantages:

a) the possibility to machine extremely thin parts, as thin as 0.01 mm, without altering their geometry due to the absolute absence of traction, compression and shearing forces;

b) no structural alteration;

c) no phase transformation;

d) no change in chemical composition;

e) no recrystallization;

f) no grain enlargement;

g) no plastic deformation;

h) no continuous tension;

i) no work-hardening;

I) no change in hardness;

m) extreme precision and compliance with dimension tolerances;

n) lack of burr along the cutting line;

o) use of an electrolytic bath that does not pollute and is not harmful in any way to personnel;

p) the removed material deposits and can be eliminated, whereas the electrolyte can be recirculated;

q) a very cheap electrolyte (aqueous NaCi solution) is used;

r) since no gases that are toxic or explosive or otherwise harmful to human health and to the environment are produced during the method, no elimination equipment is required, thus providing a considerable saving in terms of system components;

s) the machining method allows to achieve very short machining times.

[0030] The method according to the invention is susceptible to numerous modifications and variations. Particularly, it allows to machine metallic plates of any kind, for example even those used to manufacture printed circuits. In another embodiment it is possible to remove the metal by placing multiple metallic plates 1 to be machined, connected to the positive pole, between plates 4 connected to the negative pole. In this manner, metal removal occurs on both faces of the plates being machined, and thus a faster perforating effect is provided.

[0031] In the same manner, it is possible to arrange multiple plates to be machined, connected to the positive pole, on a same plane, arranging respective plates, connected to the negative pole, opposite the various plates to be machined.

[0032] Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly such reference signs do not have any limiting effect on the scope of each element identified by way of example by such reference signs.

Claims

1. Method forthe electrochemical machining of metallic plates, characterized in that the metallic plate to be machined (1) is first covered, at least on one side, with a layer of electrically insulating material that leaves exposed the regions (2) to be removed; the plate is then immersed in an electrolytic bath constituted by an aqueous solution of NaCI and is placed opposite a metallic plate (4) which has substantially the same dimensions as said plate to be machined (1), said plate to be machined (1) and said plate (4) being connectable to the positive and respectively negative poles of a direct supply voltage which is such as to allow metal removal from said exposed regions.

2. Method according to claim 1, characterized in that said aqueous NaCi solution has a concentration comprised between 100 grams/liter of NaCi and the saturation value at room temperature.

3. Method according to claim 1 or 2, characterized in that the intensity of the current during the removal method is comprised between 10 A/sq dm and 120 A/sq dm.

4. Method according to one of claims 1 to 3, characterized in that the distance between the plate being machined (1), connected to the positive pole, and the plate (4), connected to the negative pole, is comprised between 0.5 mm and 5 mm.

5. Method according to one of claims 1 to 4, characterized in that the plate (4) connected to the negative pole is constituted by a metal that has high resistance to dissolving in the electrolyte, preferably titanium.

6. Method according to one of the preceding claims, characterized in that multiple plates to be machined (1) are connected to the positive pole and in that plates connected to the negative pole are placed between said plates to be machined.

7. Method according to one of claims 1 to 6, characterized in that multiple plates to be machined (1) are placed on a plane and connected to the positive pole, respective plates (4) connected to the negative pole being arranged opposite said plates to be machined.

8. Apparatus for performing the method according to one of the preceding claims, characterized in that it comprises a bath containing an aqueous NaCi solution and at least one plate (4), made of a material highly resistant to dissolving, which is immersed in said bath and connected to the negative pole of a supply voltage, the positive pole of said voltage being connected to at least one plate to be machined (1) which is immersed in said bath and arranged opposite said plate (4).

Drawing