The most important utility area of the invention will be in automative industy. The main challenging problem for the today's automotive industry is"How to product lightweight and strong auto chasis and body construction in mass production with high accuracy and low cost. There are many weight loss programs carried out by car companies suppliers etc all around the world in effords to make new production technologies more responsive to needs of the low fuel consuming vehicles of tomorrow.

There are many technical teams in the automotive world, in collaboration with the national labs, universities and suppliers are working to dramatically reduce vehicle weight as compared to today's midsize family sedans. Because of this reason there are a widespread tendency to use relatively higher strength steel and aluminum alloy sheets in automotive industry. Besides this issue from aspect of saiety, energy rate that can be absurbed elastically during a crash by a metal auto part until plastic deformation limit is proportional to second force of its yield strength. Although these issues a single part made of relatively higher strength metal might require more stamping stages than a comparable part or the part may have to divided into two or more pieces that are then joined together. But these solitions add time and cost to the manifacturing process. Thus engineers have been trying to find other methods to replace or complement the conventional mechanical stamping process in order to fully realize the potential weight savings of using of higher strength steel and aluminum components. On the other hand such materials cause more wrinkles and tears during manifacture and require significiant try-out modification and completion works for dies and tools requiring too much cost, time and labourship.

Althougth there are much higher strength steel and aluminum alloys, currently used stamping technology can not form such metal thin sheets due to lack of formability.

Thin sheets made of such alloys offer very higher srength up to three or four times more strength of currently used sheets in automotive production. Such metal blanks principally can only have adequate íormabilily in high temperature rates. In practice it is generally impossible forming of hot (app. 1250 C) such thin steel sheets previously heated in a furnace and carried to press table and hold by metal binders and then formed by conventional stamping tecnology and consequently production of a complex part made of such metal alloy preciously in mass prodution. Thats why is temperature of a such a hot blank decreases very rapidly due to too much heat loss proportional to 4 force of the temperature by radiation and too less heat storage capacity of the thin sheet and additional heat loss and instant shrinkage resulted by contacting with cold metal binders and other tools.

Five Figures were prepared to explain the main process and relevant production tools and details. Figure I shows application of the main prencipe in high strength sheet stamping process and consists of a plan wiev (upper side) and a cross sectional wiev (lower side) of the press table of regarding with this invention. Figure 2 is a sectional wiev of the press table and includes some additional details about stamping stages. Figure 3 is prepared with the aim of explain how the basic process can be applicated in bending of the high strength metal workpieces and includes relevant forming stages in sequence and relevant tools. Figure 4 indicates application of basic process in a press cell type using one die and compression of solid mixture. Fig. 4 is also comprises of plan (upper side) and sectional (lower side) wievs of relevant press cell. Figure 5 shows application of the invention in blow forming of high strength sheet metal under gas pressure and heat. Fig. 5 is includes sectional (upper side) and plan (lower side) wievs of the blow forming cell The main prencipe of the invention (Fig. I) is to applicate high electric current density passing entirely blank (4) from one side to opposite side by using elecrodes (3) contacting with two opposite sides of the blank (4). Actual temperature of the hot blank can be controlled preciously by measuring electrical resistance change of the workpiece from begining of heating by using linear correlation between temperature

and electrical resistance. The heating system is controled by a controll device measuring electical resistance and calculating actual temperature, therefor control device determines acting moment of the of the forming tools In mass production if proper charecteristics of above process are determined by adequate researchs and experiences, whole process can be carried out with previously determined parameters without using a feedback control system.

As seen in Fig. 1 Electrodes (3) are placed two opposite side of the press table. At first, blank (4) is placed on the press table. Electrodes (3) are contacted with the blank (4) and applicates high density current along the blank. Preferably low voltage AC current can be used to simplify obtaining high current rate with transforming.

During heating stage, the binders (6) do not hold the blank and allows its regular thermal expansion laterally in order to avoid wrinkles. The contact pressure of the electrodes (3) is properly determined to allow expansion of the blank (4) during heating by means of controlled sliding movement between workpiece and electrodes.

On the other hand both two electrode groups (3) are sligthly pulled back (with an hydraulic system etc) during heating in the longitudional direction in according to thermal expansion with the aim of keep flat blank surface.

Thus the workpiece instantly (within a few seconds) reaches high temperature degrees (app. 1200-1250 C for steel and 450-550 C for aluminum alloys). Then the binders hold the hot blank and upper die (5) is moved down and hot workpiece is formed.

Above system ensures workpiece temperature until contact moment of the die and workpiece. Due to forming speed of the punch (from first contact moment to the blank to contact moment to other die) of the (esp. Mechanical) presses is sufficiently high and most of workpiece area (As Shown in Fig. 2, as indicated by dashed lines 9) (esp. areas involving high local elongation rates) do not in contact directly with the cold die surface until end of the forming process, the workpiece sufficiently keeps its high temperature within little forming time. Blank holder surfaces (6) can be made of ceramic insert parts in order to isolate heat and current to avoid heat loss from workpiece to press table. Because of the rapid heating, heat loss from the blank will be fairly low thereby electric energy will be consume efficiently to heat workpiece directly.

If relatively slow hydraulic presses arc used in such a process some adjustments in dic form can bc made (Fig. 2) to reduce contact area between hot blank and cold die surface during forming (especially in chasis and frame production including ilat sufaces and rounded edges) in order to reduce heat loss until end of the process. As shown in Fig. 2 downward facing surfaces (7) of the upper die and and upward facing surfaces of the lower die are designed as concave (7) forms surrounded by rounded extensions (8). As indicated in Fig. 2 by dashed lines (9) most of the workpiece area is not in contact with the die surface (5,7) until end of the process. Since press force acting die surfaces will be signiticiantly lower in such a prosess than of conventional stamping due to forming in high temperature rates of the blank,"Fragile"ceramic dies can be used conveniently. In such a case high density current can also be applicated during forming stage due to electrical nonconductivity of the material of the dies and the binders. Additionally ceramic is fairly resistant against heat. Fleat storage capasity of a thin metal blank is fairly low even though it is heated to the high temperatures. lt enables to control temperature of the workpiece until end of the process. On the other hand the workpiece cools more slowly (than of hot stamping with metal tools) after forming resulted by low thermal conductivity of the ceramic materials. This process can be applicated in one stamping stage or can be divided into multi hot stamping stages and additional heating-annealing processes can be achieved depending of part geometry complexity and metal features between forming stages.

By contrast of Fig. I in Fig. 2 electrodes are used as binders and during heating process the blank is hold by binders. These are alternative arragements that can be preferred depending on charecteristics of the process.

This process causes serious increase in yield strength of the finished part because of two reasons. First reason is rapid cooling between two dies. Second one is regular alongation effect (app. % I-1.5) involved through whole workpiece area. These will be explained below. If the blank is formed by this process in a hydraulic press, at the end of the forming stage hot workpiece cools instantly between two dies. In high strength alloy sheets instant cooling leads to significiant increase in yield strength. On the other hand during cooling stage, formed workpiece is regularly strained to be shrinked due to rapid temperature decrease. While hot workpiece is cooling between upper and lower dies under pressure, any considerable change in dimensions can not

occurs in spite of rapid cooling. It means that a regular alongation effect occurs in whole area. Total alongation rate in unit area is sum of plastic and elastic alongation rates. After workpiece is ejected from dies the formed part shrinks elastically by ratio of actual yield strength/Elasticity modulus. At the die designing stage this shrinkage ratio should be considered. Deviations in dimensions of the finished parts essentially depend on deviations of yield strength rates of the finished parts. Because of stamped sheet cools between dies without any practical changes in dimensions and elastical shinkage factor can be calculated and considered previously, this process is precious, dependable and reproductible.

If this process is made in a mechanical press formed workpiece can be ejected from lower die by an automatic mechanism while upper die is moving up after stamping. By contrast of cooling between dies, in this case formed workpiece cools and shrinks in air freely. Shrinkage ratio will be higher than above process but it is possible to control cooling and shrinkage chracteristics by means of changing press speed, workpiece temperature and ejecting mechanism speed. In this process heating and forming systems should be controlled and operated in accordance by the same control device. Because of the rapid heating, heat loss from the blank will be fairly low thereby electric energy will be consumed efficiently to heat workpiece directly.

The invention can also be used in bending (Fig. 3) of high stength alloy sheets featuring very low formability. In such an application only a long and narrow bending stripe (18) is heated by a set (10,12) of electrodes placed two sides of the bending line. A set of apparatus as seen in Fig. 3 are used for instant heating with current and bending of the workpiece. These tools 15) are moved in sequence by pneumatic or hydraulic etc. system in accordance with instant heating process. At first electrodes (I and 3) are pushed onto the workpieces (2,8) and applicate high density current to be conducted by bending area (9). It leads instant heating along this stripe. Without loosing time and heat as soon as sufficient heating obtained, electrode (12) is moved back and first bending tool (13) is moved up and down thus workpiece is bended by 90 degrees. A portion (16) of the electrode (13) can be made as a ceramic insert with the aim of reduce heat transfer between hot area (18) and tool (13). At this moment Part (15) is moved ahead thereby the blank

is bended by 180 degrees. Part (15) is also used as electrode (made of copper alloy) and remain a little time contact position on the bended sheet, therefor current is applicated between electrode (14) and electrode (15) with the aim of welding bended workpiece. If bending of the workpiece will be realized along a curved (eg. body or door panel for automotive ind.) line (18) tools of this process should be designed in accordance with curved bending line. Similar well known technologies about bending and resistance welding simplify to achieve above process.

This invention can be applicated in (Fig. 4)"Hot stretch sheet forming with pressure of sand/lubricant mixture". To product low volume and high strength panels and frames this technology will be an attractive alternative with low tooling cost due to requiring only one die (made of ceramic or concrete) and not requiring long design time and cost. The die (21) is placed inside the cover of the press cell.

Hydraulic pistons (22) are used for opening or closing upper side of the press cell.

Part (20) is used for locking of upper side of the press cell. As seen at Fig. 4 in this process the hot blank (19) flows smoothly into the die (21) under pressure of the sand & lubricant mixture (23). Sand & lubricant mixture (23) is pushed up by hydraulic cylinders (24) placed bottom of the mixture bowl. In this process solid mixture (23) is in contact directly (without any flexible membrane) with the hot blank. The main prencipe of the invention"Instant Heat generation in the workpiece by applying high current rate"is achieved in a similar way like above processes. Two opposite sides of the blankholder are made as electrodes (18) and other parts are made of ceramic inserts. Due to thermal conductivity of the sand mixture (23) is very lower than that of metals, heat can be generated by current along the forming process while the hot blank (19) is bulguing into the die (21). Sand mixture (23) (or any other proper solid material Aluminum Oxid etc.) is very durable against heat and features very low thermal conductivity. Because of this reason heat generated in the workpiece will not be absorbed instantly by the sand. If the die is made of ceramic or concrete, the workpiece cools slowly.

Another application area of the invention is"Superplastic forming"process as shown schematically in Fig. 5. This invention solves main problem of Superplastic Forming "precious temperature control along the process". This process can manifacture high

strength aluminum alloy parts especial ! y fur aerospace industry and enables diffusion bonding between metal layers. To enhance this process's reproductibility and reliability this invertion offerus a very beneficial instrument. As seen in Fig. 5 there are two electrode series (25) placed into two opposite sides of the blanl ; holder around the blank (26,27). Current (31) applicated to the workpiece (26,27) via these electrodes in order generate heat inside the sheet in accordance with main prencipe of the invention. Gas pressure (30) blocs the hot blank (27). Hot workpiece is bulgued and is placed inside the die surface and gain its shape.

Temperature is measured with change of electric resistance as explained above.

Temperature is controlled preciously by adjusting current rate along the process in spite of considerable heat loss from the workpiece during the process.