Machine Tools And Devices For Special Technologies Chemical machining Slovak University of Technology Faculty of Material Science and Technology in Trnava

Chemical machining Local melting of material by suitable diluent. Machining of metal materials, Removing speed of material independence on hardness and on toughness, Surfaces with complicated shape with high accuracy and quality, Here is no originated heat and mechanical influence area, Large areas – more economical than milling

Chemical machining 1 – base material, 2 – mask, 3 – holes carved out of mask, In the place of holes the material is melted by influence of diluents.

Material machinability Four groups of materials by chemical machinability: Copper, bronze – easy they are melted, good machinability by chemical machining, nickel, zinc, aluminium manganese, molybdenum, chrome, gold, wolfram – they are hard melted, bad machinability by chemical machining

Diluents for chemical machining Ferrous metals – different acids, copper, alloys of copper, heavy metals – chloride of ferrum FeCl 3, Aluminium, alloys of aluminium, light metals – caustic soda NaOH

Workpiece preparation for chemical machining Grease removal and surface cleaning – removing the allochemicals from surface and oxidic coats too (Al alloys – AL 2 O 3 coat), dipping into 5% medium NaOH and next into 30% medium of acid of nitride, steeping – increasing of mask adhesion, dipping into medium H 2 SO 4 and next duochrom of patassic, masking – coating resisted on influence of diluent (resin, enamel) thickness till 2 mm.

Workpiece preparation for chemical machining Mask drying – mask coating is drying 6 till 8 hours, it can be accelerated in the furnace (small workpieces), Engraving of mask – into drying mask are created holes (hand engraving, engraving by laser...),

Time needed for machining It is independence on the size of the machined surface, It is depend on depth of machining only, Speed of outline 0,01 till 0,5 mm/min., mask resisted to outlining approximately 8 hours.

Mask undercutting Speed of outline in homogenne material is the same in all directions. Rate of undercutting is approximately the same as depth of outlining.

Mask undercutting Is not possible to make shape rims, In immersion into etching pool is needed to assure that origin gas is not to mass in the place of undercut (scaling of mask, non-constant speed of undercutting....), side long immersion, mixturing, Mixturing of etching pool:  Washing off etching impurities,  Asked concentration of etchant in the place of etching,  Outflow of gas bubbles.

Spraying of etching solution

Kinds of chemical machining Chemical clipping, chemical milling (deeping), Chemical engraving chemical sharping, Chemical polishing, Machining by active substance, Photochemical machining, termic removing of burrs.

Chemical clipping Thin plates, Completely component is sinking, Small, shape difficult components Example: Plotters of shavers

Chemical milling Accuracy shaping of difficult big shape surfaces. Speed of removing is moving round 0,025 mm/min. Originated undercutting, is necessary to speculate with undercutting in the mask production. Dimensions accuracy is given by thickness of removing layer. Roughness is between R a =0,75 to R a =3,8.

Chemical milling Using of chemical milling: aerial and cosmic industry – local releasing of casts and forgings of light and high strength alloys, Small metal components of high strength material when is not economical to produce dies.

Chemical engraving, grinding, polishing engraving – dimension of picturing is small for using of mechanical engraving – matrixs of post marks, grinding – very accurated shapes (accuracy under 1mm), low roughness (Ra 0,01), polishing – still softer than grinding, using in small and shape difficult components that by mechanical kind is not possible to polish.

Machining by active substance Machining shape difficult surfaces. Semi-solid substance of cellulose (electro gel) impregnated by acid is attach to the workpiece surface. In the place of contact the workpiece is melted. Is possible to achieve step by step removing until depth 10 mm. Dimension accuracy is from 0,02 to 0,07 mm. For acceleration of process is possible to connected electric voltage until 10V.

Machining by active substance

Photochemical machining Mask is created by photographic kind. Using in production: Masks of TV set and screening, Code disks, Optical divider, gasket, Ornamental object, Semiconductor components.

Photochemical machining Patern of production – laser beam creating the sign in the photographical film. This picture (master) is frequently applied to photo tool. (patern). Preparation of surface – surface must be cleaned, grease removing, eventually to pickle, Coating of photoresist – it is polymer sensitive to ultraviolet emission is necessary to dry him. Processing of photoresist – through the pattern is photoresist emissed by light of suitable wave length (UV) and is created mask (positive, negative).

Photochemical machining Advantage of photochemical machining: Low costs of tools, Low costs of modification, Simply transmission to series production, Properties of the base material are not damages, No originated burrs.

Thermic removing of burrs Burrs are removed by influence of thermic wave (by explosion). Thermic wave has temperature more than 3000°C and lasted particular  s. Burrs are melted or evaporated but workpiece is not in time to absorbing a lot of heat. Burrs are verily removed from inaccessible places.

Thermic burrs removing