9 Considerations to handle thick materials

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by Jeff Norman

Thick materials pose challenges to metal fabricators

The stamper needing to work with thick material is faced with a few challenges: machine strength, accurate feeding, alignment of material to the tooling, straightness of material, threading, loading, safe handling, and floor space. There are several considerations to maximize handling of thick coils.

1. Size the machine properly
With proper description of the requirements, leading to proper sizing of the machine components, safe, reliable and productive processing is possible. Parameters needed: material thickness, width, yield strength, press speed, and feed progression. 

2. Unwinding and straightening involve bending the material enough to yield it
As size and strength of materials increase, the forces required to unwind, thread, straighten and feed the material quickly increase. In fact, forces increase at roughly the square of the change of thickness and equal to the change in width and the change in yield strength.

So if a material is twice as thick, the machine must be four times stronger.  Twice the strength means twice the force, and twice the width. Multiply those factors together to show how much the machine structure must change.

3. Use a cradle style uncoiler
A cradle type uncoiler is a good choice for materials thicker than 3/16 in. (4.8 mm). With a cradle, the coil rests on motorized rollers. Control is easy, as the surface speed of the coil is equal to the motor speed, regardless of coil size. Handling is safer, as the weight of the coil holding it against the cradle rolls helps prevent the coil from springing open when the shipping bands are cut. Cost is less than a mandrel style, as the structure is simpler. Deflecting the start of coil and threading to the straightener is also simpler.

4. Use coil staging techniques
If a machine does not have a coil staging system, production will be stopped until the material handling equipment is available. This results in lost production time.

Reduce loading time by staging the next coil on a coil car or coil ramp during the run. The material handler will load anytime during the run, and will be free to work elsewhere. Time saved with a pre-staged coil can be many minutes per coil.

5. Importance of coil threading systems
The equipment must employ a threading system to guide the start of the strip into the straightening system.  With thin material, the operator may be able to move and thread the strip by hand. With thick materials, hand operation is not possible. A good design will have sufficient strength and range of motion so that the threading occurs without the operator manually touching or deflecting the material.   

6. Save space with servo driven uncoiling
The use of high power servo motors allows the coil to be driven in sync with the feeding process. This method eliminates the need for an accumulation loop, and decreases the floor space required. Before loopless operation, a coil processing system for ¾ in. (19 mm) thick material could be longer than 50 ft (15 m). With a loopless operation the systems are as short as 25 ft (8 m).

7. Straightening of the material happens at the same level as the tooling height
In a compact arrangement, the material flows off the bottom of the coil, directly through the straightener and into the tooling. Machines are often constructed with passline height adjustment to accommodate changes in tooling height.

8. Install side shift to simplify alignment
The coil processing system must deliver the material to the tooling in the correct position: side to side and in the correct progression. The servomotors will control the progression.  The sideways position is handled by the machine guidance systems. In some cases, the material will have sideways curve (camber), which may cause the strip to be off centre when it arrives at the tooling. Thick, strong materials are difficult to push sideways, so rather than attempt to fight with the material and load up the guidance rolls, machines may be set on a shifting base. The operator loads the material, threads the start up to the tooling, and adjusts the machine position to set alignment. Without the shift feature, adjusting the strip position may be time consuming.

9. Set the feeder to run as smoothly as possible
Smooth operation will reduce the wear and tear on the feeding system, extend machine life and save energy. When driving, if you floor the gas to go, and stomp on the brakes to stop, you will use more gas and wear out the motor, transmission and the brakes. The feed system is similar; by properly setting up the acceleration rate and the maximum speed, the feeder will ramp up to speed and slow and stop in position smoothly. The material will flow better, feeding will be more accurate, and the machine will give more years of trouble free operation. SMT 

Jeff Norman is vice president, P.Eng, Mecon Industries Ltd., Scarborough, ON.


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