cutoff
A pair of blades positioned in dies or equipment (or a section of the die milled to produce the same effect as inserted blades) used to separate the forging from the bar after forging operations are completed. Used only when forgings are produced from relatively long bars instead of from individual, precut multiples or blanks. See also blank.
cut and carry method
A method in which the part under fabrication is not entirely detached from the strip or is pushed back into the strip for transporting to a succeeding station in a progressive die.
curling
The act of forming an edge of circular cross section along a sheet, workpiece, or at the end of a shell or tube.
cupping test
A mechanical test used to determine the ductility and stretching properties of sheet metal. It consists of measuring the maximum part depth that can be formed before fracture. The test is typically carried out by stretching the test piece clamped at its edges into a circular die using a punch with a hemispherical end. See also cup fracture, Erichsen test, and Olsen ductility test.
cup fracture
A mixed-mode fracture, often seen in tensile test specimens of a ductile material, in which the central portion undergoes plane-strain fracture and the surrounding region undergoes plane-stress fracture. One of the mating fracture surfaces looks like a miniature cup; it has a central depressed flat-face region surrounded by a shear lip. The other fracture surface looks like a miniature truncated cone.
cup
(1) A sheet metal part; the product of the first drawing operation. (2) Any cylindrical part or shell closed at one end.
crown
(1) The upper part (head) of a press frame. On hydraulic presses, the crown usually contains the cylinder; on mechanical presses, the crown contains the drive mechanism. See also hydraulic press and mechanical press. (2) A shape (crown) ground into a flat roll to ensure flatness of cold (and hot) rolled sheet and strip.
cross over
The physical area of a trim steel that overlaps the top of another trim steel, such as the area of an upper trim steel that is notched to go over the top of a lower scrap cutter. The distance between the two steels in this area, when die is closed, should be at least twice stock thickness.
critical temperatures
Established temperatures to which metals must be heated to produce metallurgical changes, such as hardening. Also known as transformation temperatures.
crimping
The forming of relatively small corrugations in order to set down and lock a seam, to create an arc in a strip of metal, or to reduce an existing arc or diameter. See also corrugating.
creep
A term used in a hemming operation for the amount the part reduces in size along the flange radius when forming from a 900 flange to a full fold or hem.
crank press
A mechanical press whose slides are actuated by a crankshaft.
countersink
(1) A funnel shaped enlargement at the outer end of a drilled hole having an 820 included angle to allow the head of a screw to be flush with or below the surface. (2) A bit or drill for making a countersunk hole.
counterboring
Enlarging a hole to a limited depth producing a flat bottom in the enlargement.
counterbore
A rotary, pilot guided, end cutting tool, having one or more cutting lips and usually having straight or helical flutes.
corrugations
Transverse ripples caused by a variation in strip shape during hot or cold reduction.
corrugating
The forming of sheet metal into a series of straight, parallel alternate ridges and grooves with a rolling mill equipped with matched roller dies or a press brake equipped with specially shaped punch and die.
co-ordinate measuring machining
A machine for measuring three dimensional (X, Y, Z) coordinates on a component for inspection or geometry description purposes
contouring
Machining surface shape on die members. Also called kellering.
construction hole
A hole in which the center line is used to dimension other holes or surfaces. Sometimes referred to as a point of origin or coordinating hole.
compressive stress
A stress that causes an elastic body to deform (shorten) in the direction of the applied load. Contrast with tensile stress
compressive strength
The maximum compressive stress a material is capable of developing. With a brittle material that fails in compression by fracturing, the compressive strength has a definite value. In the case of ductile, malleable, or semi-viscous materials (which do not fail in compression by a shattering fracture), the value obtained for compressive strength is an arbitrary value dependent on the degree of distortion that is regarded as effective failure of the material.
compound die
Any die designed to perform more than one operation on a part with one stroke of the press, such as blanking and piercing, in which all functions are performed simultaneously within the confines of the blank size being worked.
cold-rolled sheet
A mill product produced from a hot-rolled pickled coil that has been given substantial cold reduction at room temperature. The usual end product is characterized by improved surface, greater uniformity in thickness, and improved mechanical properties as compared with hot-rolled sheet.
cold working
The plastic deformation of metal under conditions of temperature and strain rate that induce strain hardening. Usually, but not necessarily, conducted at room temperature. Also referred to as cold forming or cold forging. Contrast with hot working.
cold heading
The process of upsetting the ends of a bar, wire or tube stock while cold.
