Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21D26/00—Shaping without cutting otherwise than using rigid devices or tools or yieldable or resilient pads, i.e. applying fluid pressure or magnetic forces
  • B21D26/02—Shaping without cutting otherwise than using rigid devices or tools or yieldable or resilient pads, i.e. applying fluid pressure or magnetic forces by applying fluid pressure
  • B21D26/053—Shaping without cutting otherwise than using rigid devices or tools or yieldable or resilient pads, i.e. applying fluid pressure or magnetic forces by applying fluid pressure characterised by the material of the blanks
  • B21D26/055—Blanks having super-plastic properties
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/16—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of other metals or alloys based thereon
  • C22F1/165—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of other metals or alloys based thereon of zinc or cadmium or alloys based thereon

Definitions

• composition and properties of some superplastic alloys are described in detail in the article Superplasticity in an Al-Zn Alloy by BackofemTurner and Avery, Transactions of the A.S.M., Volume 57 (1964), pages 980-990.
• superplastic alloys An important property of superplastic alloys is that their strength under certain conditions is extremely low; thus when fabricating superplastic alloys deformation forces will be small. It has been demonstrated that superplastic alloy sheets may be thermoformed in a manner similar to conventional plastics materials; a typical group of superplastic alloys which may be thermoformed are those based upon the Zinc-Aluminium eutectoid composition, viz 78 percent Zn 22 percent Al.
• the formed component may be heated for several minutes in the die from the forming temperature of 250 to 270C to a temperature in excess of 275C, for example 300C, and the component then removed.
• This method relies upon the fact that the superplastic structure of a Zn-Al eutectoid alloy is only stable up to 275C, above which temperature the metallurgical structure is irreversibly transformed into a non-superplastic structure. This means that the structure of the alloy sheet is stronger above 275C than below.
• the die is maintained at 300C while the sheet to be thermoformed is preheated to 250C.
• a variation of the method described above would be to employ a cold die so that on striking the die the sheet cools and is thus strengthened.
• This method suffers from the disadvantages that only components which require short forming times are amenable to this technique and thus the amount of detail and sharpness of angles which may be moulded are restricted. Also local thinning may be accentuated due to temperature variatrons.
• the invention provides a method of moulding superplastic alloy sheet material comprising holding a moulded sheet, after the latter has been removed from a mould, at a temperature of to 220C to remove undesired distortions or warping from the moulded sheet.
• the invention consists in a method of moulding superplastic alloy sheet material comprising heating a blank of the sheet material to a temperature at which the material exhibits superplasticity, moulding the heated blank to conform to a mould surface of desired shape. removing the moulded sheet from the mould, and holding the moulded sheet at a temperature of from 180 to 220C to remove undesired warping or distortions from the moulded sheet.
• the heat treatment of the moulded sheet is preferably carried out for at least 10 minutes, and may be done in a suitable oven. Alternatively, the heat remaining in the moulded sheet after the moulding operation may be utilised for removing the distortions. In such a case the hot moulding is supported in a mould of complementary shape and allowed to cool ensuring that it is held for at least 10 minutes at from 180 to 220C.
• Either surface of the moulded sheet may be cooled after moulding, i.e., either the surface adjacent the mould or the surface remote from the mould may be cooled to facilitate removal of the moulded sheet from the mould surface.
• the cooling of the surface of the sheet may be effected by air blowing or water spraying.
• the sheet should preferably be supported on a surface which is generally complementary to the overall shape of the sheet, that is a flat surface is employed for a flat sheet and a surface of suitable curvature for a curved sheet.
• the heated blank may be subjected to a moulding operation in which it is caused to conform to a mould surface of desired shape by means of an applied fluid pressure or vacuum.
• the method according to the invention is most suitably applied to large flat components with small depths of draw when the component only requires to be supported in a horizontal position on a flat surface. With deep draws and for more complex shapes the components will require to be supported by an accurately contoured jig of a material sufficiently rigid to withstand the annealing temperature.
• the sheet material may suitably be a Zinc- Aluminium alloy containing from 15 to 40 percent, preferably 18 to 30 percent, by weight of aluminium,
• a third component particularly copper or magnesium.
• Various methods may be used for rendering such materials superplastic but in general include the steps of a. Heating the body of alloy to homogenize it.
• EXAMPLE 1 A rectangular wall panel of dimensions 1m X /zm and a depth of draw less than 3cm was pressure moulded in superplastic zinc/aluminium alloy sheet containing 78 percent by weight of zinc and 22 percent by weight of aluminium of thickness 0.035 inches for 12 minutes and at 250C, using an air pressure of 60 lbs per square inch.
• the distorted moulding was stored and at a convenient time was placed on a flat hot plate at a temperature of 200C.
• the panel was freed from distortions within about 15 to minutes.
• EXAMPLE 2 A moulding of overall dimensions 30 inches X 13 inches X 8 inches deep having a central dome and a peripheral flange was pressure formed in superplastic zinc/aluminium alloy sheet containing 78 percent by weight of zinc and 22 percent by weight of aluminium of thickness 0.060 inches for 6 minutes at 250C, using an air pressure of 150 pounds per square inch.
• the moulding was removed from the mould by cooling it around the peripheral flange and allowing it to fall under gravity onto the lower platen of the mould press. This caused some distortion of the domed portion of the moulding due to impact of the moulding on the lower platen.
• a method of moulding superplastic zinc- /aluminium alloy sheet material containing from 15 to 40 percent by weight of aluminium comprising heating a blank of the sheet material to a temperature at which the material exhibits superplasticity, moulding the heated blank to conform to a mould surface of desired shape, and removing the moulded sheet from the mould, the improvement comprising holding the moulded sheet at a temperature of from 180 to 220C to remove undesired warping or distortions from the moulded sheet.
• a method as claimed in claim 1 comprising carrying out the heat treatment of the moulded sheet for at least 10 minutes.
• a method as claimed in claim 1 comprising cooling at least one of the surface of the moulded sheet adjacent the mould and the surface of the moulded sheet remote from the mould to facilitate removal of the moulded sheet from the mould.
• a method as claimed in claim 3 comprising cooling the said at least one surface of the moulded sheet by air blowing.
• a method as claimed in claim 3 comprising cooling said at least one surface of the moulded sheet by water spraying.
• a method as claimed in claim 1 comprising supporting the moulded sheet during the heat treatment on a surface complementary to the surface of the sheet.
• a method as claimed in claim 1 comprising moulding the heated blank of sheet material to conform to a moulded surface of desired shape by an applied fluid pressure.
• a method as claimed in claim 1 comprising moulding the heated blank of sheet material to conform to a moulded surface of desired shape by an applied vacuum.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Physics & Mathematics (AREA)
• Crystallography & Structural Chemistry (AREA)
• Materials Engineering (AREA)
• Thermal Sciences (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Fluid Mechanics (AREA)
• Shaping Metal By Deep-Drawing, Or The Like (AREA)
• Straightening Metal Sheet-Like Bodies (AREA)
• Heat Treatment Of Nonferrous Metals Or Alloys (AREA)

Applications Claiming Priority (1)

Publications (1)

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Cited By (4)

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Citations (3)

• 1972
  • 1972-06-14 GB GB2789172A patent/GB1388159A/en not_active Expired
• 1973
  • 1973-06-12 AU AU56848/73A patent/AU5684873A/en not_active Expired
  • 1973-06-13 FR FR7321549A patent/FR2187450B1/fr not_active Expired
  • 1973-06-14 JP JP48067311A patent/JPS4952123A/ja active Pending
  • 1973-06-14 US US370035A patent/US3864176A/en not_active Expired - Lifetime

Patent Citations (3)

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