Heated die for hot forming

A heated tool for hot stretch forming of superplastic aluminum alloy sheet metal, the tool comprising:

• a metal body portion with a forming surface against which one side of each of a succession of preheated aluminum alloy sheet blanks are to be stretched and pressed by forming fluid pressure applied to the other side of the sheets during a stretch forming cycle to successively shape each blank into a formed part;
• one or more thermally insulated body side surfaces;
• a body bottom surface for attachment to a press with thermal insulation between the bottom surface and the press;
• and
• a plurality of electrical heater cartridges inserted at locations within the body, the cartridge locations being predetermined for heating the body and the forming surface of the tool to a sheet metal forming temperature within a predetermined range of temperatures over the forming surface;
• the cartridges being connectable to a source of electrical power such that when each heater cartridge is powered on for an identical period of heating time a temperature distribution is produced within the body portion that maintains the sheet metal forming temperature over the forming surface.

A method of making an internally heated forming tool for forming of sheet materials comprising:

• designing a metal tool body having a forming surface for the sheet material, side surfaces and an attachment surface, opposite the forming surface, for attachment to a forming press;
• specifying electric power ratings of heating cartridges to be located in the metal tool body of the forming tool for heating the forming surface of the tool;
• specifying operating temperatures for the forming surface, and heat transfer coefficients for the side surfaces and attachment surface of the tool;
• conducting mathematical analyses of the resultant temperatures of locations on the forming surface of the tool for postulated locations of the heating cartridges at their specified power ratings;
• and
• optimizing the location of the heating elements to produce a predetermined average temperature of the forming surface and a predetermined range of temperatures of locations on the forming surface.

A method of continually forming a succession of sheet metal articles on the forming surface of an internally heated forming tool for said articles, the method comprising:

• designing a metal tool having a forming surface for the sheet metal articles, at least one side surface and an attachment surface, opposite the forming surface, for attachment to a forming press;
• specifying electric power ratings of heating cartridges to be located in the body of the forming tool for heating the forming surface of the tool;
• specifying operating temperatures for the forming surface, side surfaces and attachment surface of the tool;
• conducting mathematical analyses of the resultant temperatures of locations on the forming surface of the tool for postulated locations of the heating cartridges at their specified power ratings;
• optimizing the location of the heating elements to produce a predetermined average temperature of the forming surface and a predetermined range of temperatures of locations on the forming surface;
• identifying a location within the tool body for temperature measurement for the uses of a single power source and electrical power delivery controller for said heater cartridges to maintain the predetermined average temperature and temperature range of the forming surface of the tool for the forming of the articles;
• and, thereafter
• controlling the temperature of the forming surface from said power source during the forming of the sheet metal articles.