Selecting equipment to produce flat, straight strip
May 13, 2008
Fineblanking operations require a heavy-duty press and special tooling. To produce straight, flat strip for the press and feed, stampers need a coil cradle, coil end peeler, debender, and hold-down arm, straightener, loop control.
Fineblanking requires a heavy-duty press and special tooling. The goal is to produce a part that requires minimal work after the press operation. The proper coil handling equipment will help your fineblanking operation by producing a straight, flat strip from coiled material.
The equipment required to produce straight, flat strip for a fineblanking press and feed includes the following basic machines:
A coil cradle with two powered rolls is used to support the coil. This type of uncoiler can be used when the material is thick enough to support the weight of the coil without deformation. If additional coil storage is desired, a tilting ramp can be added to the coil cradle.
If the material is thin and could deform under the coil weight, which would prevent proper straightening, then a pull-off reel with an expanding mandrel is used. If more coil storage is desired, a traveling car with a lift cylinder can be added.
Heavy-gauge and high-strength materials are dangerous to handle manually - even impossible to remove safely from the coil manually to insert into the straightener. For safety and efficiency, a hold-down arm with a powered cradle roll rotates the coil to position the coil end for peeling. Then the coil bands can be cut safely.
Fineblanked parts can be produced from thick and high-strength materials. Not only is this material dangerous to handle manually, but it might be impossible to remove it from the coil manually and safely insert it into the straightener.
For safety and efficiency, a hold-down arm with a powered roll is lowered on top of the coil. The powered cradle rolls and hold-down roll rotate the coil to position the coil end for peeling. With the hold-down arm down and the roll in contact with the coil, the coil bands can be cut safely.
The pivoting peeler table is raised and the peeler point is extended under the coil end. The coil is rotated so that the coil end is moved over the peeler point and table toward the straightener.
When the coil end is near the straightener, a debender travels downward and flattens the strip so that it can enter the straightener.
All movements of the peeler, debender, and hold-down are controlled hydraulically by operator push buttons.
The equipment required to produce straight, flat strip for a fineblanking press and feed includes a coil-end peeler, debender, hold-down arm, loop control, coil cradle, and straightener - or, as shown, a combination coil cradle and straightener with a control panel.
The straightener consists of a set of powered ingoing and outgoing pinch rolls. The upper and lower pinch rolls are hardened for surface durability and wear resistance. To create traction and minimize slippage, the pinch rolls may be grit-blasted and chromed.
Between the ingoing and outgoing pinch rolls is a set of straightener rolls. The roll diameters and roll centers are sized according to material thickness and yield strength. Fineblanking usually requires a minimum of seven straightener rolls (four lower and three upper). Many stampers specify nine, 11, or more straightener rolls to produce a flat strip from the entire coil. The higher number of rolls "works" the material effectively to reduce stress so that the strip remains straight.
The roll diameters and roll centers can be determined by mathematical calculations. However, it is difficult to calculate the number of straightener rolls required. Usually the number of rolls is determined by experience.
The lower straightener rolls and pinch rolls are driven by a common gear train. The upper straightener rolls are individually adjustable to work the material sufficiently and to ensure that it will be straight.
In addition to being straight, the strip must be flat across its width. Because the straightener rolls are smaller than the pinch rolls, they must be supported by backup rollers to prevent roll deflection. Without backup rollers, the straightener rolls can deflect and cause edge working and edge waves in the material.
Along with the backup rollers, outboard bearings and supports for the gear train can be used to prevent roll deflection caused by gear separation loads.
When the leading end of the strip reaches the straightener, it is centered by a set of adjustable side guides. The side guides typically consist of two hardened rollers on each side.
A cabinet-mounted main drive motor and reducer with a chain and sprocket arrangement power the coil cradle rolls and straightener rolls. (Note: Guards and covers are removed for clarity.)
The ingoing pinch rolls are opened by hydraulic cylinders so that the leading end is inserted by the powered rotation of the coil. The ingoing pinch roll is closed, and the strip is powered through the straightener. After the strip passes through the exit pinch rolls, they are closed.
The straightener rolls and coil cradle rolls are driven by one electric motor through chains and gears.
Parts produced by fineblanking are not large, and usually a pit in the floor is not required for the loop. The distance between the press feed and straightener must be long enough to maintain a strip radius without introducing a bend. Also, the loop must contain sufficient storage for the required feed lengths.
Usually a loop arm with limit switches or a probe-type control is used to signal the straightener to replenish the loop during the feed and press operation.