Hot stamp­ing

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Hot stamp­ing is a process by which ad­vanced high strength steel is formed into com­plex shapes more ef­fi­ciently than cold stamp­ing. The process in­volves heat­ing of the steel blanks un­til they are mal­leable, fol­lowed by for­ma­tion and then rapid cool­ing in spe­cially de­signed dies, cre­at­ing in the process a trans­formed and hard­ened ma­te­rial.

Be­cause of this abil­ity to com­bine strength and com­plex­ity, press hard­ened parts ac­com­plish in one rel­a­tively light­weight piece what would typ­i­cally re­quire thicker, heav­ier parts welded to­gether in more than 1 process un­der cold stamp­ing. The process is such that blanks are cut from a foil of steel. The patch-welded blanks are made to pass through the in­put feeder rollers with the help of pick and place robots into the fur­nace.

In the fur­nace, the blanks are heated up to a tem­per­a­ture of 940 de­gree Cel­sius. On pass­ing through the fur­nace, the blanks come out red hot in a mal­leable state. This fa­cil­i­tates the shap­ing of blanks when made to pass through a die, be­yond the realm of cold stamp­ing. A blank with a hard­ness of 500 MPa, af­ter hot stamp­ing, re­turns with 1500 MPa hard­ness. The im­ported raw ma­te­rial (coated steel) used here in­cludes boron, which gives it the hard­ness over ma­te­ri­als used in con­ven­tional cold stamp­ing pro­cesses.

In the die, cold wa­ter through a chan­nel in the punch en­sures punch­ing in a con­trolled man­ner which in turn con­trib­utes to the hard­ness. At the out­put, the BIW parts man­u­fac­tured in­clude door im­pact beams, A-pil­lars, bot­tom and front rails and B-pil­lars among other parts that con­sti­tute the un­der-body and side-body parts. Loire Ges­tamp, a com­pany from the Group spe­cial­is­ing in the de­sign and man­u­fac­ture of press lines, has in­stalled in the new plant a hot stamp­ing line with a 1,200 tonne press, in­cor­po­rat­ing au­to­matic con­nec­tions for chang­ing tools, ther­mal im­agers and a mon­i­tor­ing sys­tem. At the last stage, un­like cold stamp parts, fur­ther pro­cesses like trim­ming, cold­pierc­ing is pos­si­ble only through lasers mak­ing it a cru­cial ad­di­tion to the hot stamp­ing lines. A ro­tat­ing type fi­bre laser, 6-axis laser cut­ting ma­chine is used for th­ese.

In the qual­ity check­ing process each fix­ture is checked for zero dis­par­ity be­fore declar­ing the part as ap­proved. It fol­lows the first of ac­cep­tance, mid­dle of ac­cep­tance and last of ac­cep­tance from an en­tire batch of prod­uct like in any stan­dard man­u­fac­tur­ing process. The hot stamped parts are later merged with cold stamped parts to make an assem­bly for sup­ply to the cus­tomer.

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