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When handling piping or tubing material it is important to remember that there is a constant juxtaposition between the cost of time (or speed) versus the cost of material and/or equipment (or accuracy).  There is no better example to explain this simple fact than in the material handling area and the requirements necessary. 

In doing off-line cutting, there is certain criterion that must be considered in designing an efficient operation.  Following is a synopsis of these criteria and guidelines to follow to assist in the decision-making process.

1.  What constitutes an efficient off-line material handling system and sawing
     operation?

Such considerations as space for the in-feed material handling system, the out-feed material handling system, and the saw itself are important items to consider.  Most of these items are dependent on the size of the material to be cut, the size of the final product, and the availability of cranes and/or forklifts.

 2.  How much space is available for the in-feed staging area?

 To make a successful off-line material handling and sawing operation, one of the necessary components is a staging area to hold the material as it is being fed into the sawing machine.  This allows the plant operator to load enough material on the transfer trucks to free up the crane so that it can be used for other tasks.  Some systems use feed transfer trucks on both sides of the in-feed roller tables so that material is fed alternatively from either side.  In this system some type of squaring pop-up roller system is required.  Other systems load material from one side only.  We will be specifically concentrating on the type of system where material is fed from one side only, but these items can easily be duplicated for a second supply line.

3.  What size and length of material will be loaded on the in-feed transfer tables?

This will determine the quantity, length, and spacing for the in-feed transfer trucks.  The quantity of transfer trucks to adequately support the material to minimize the amount of deflection in the material when it is being transported to the powered in-feed roller tables is a critical part of the planning process.

4.  What type of loading systems is available to load the material onto the material
      transfer system? 

Cranes and forklifts are usually used to load the material onto the transfer trucks.  The size, length, and quantity of material that needs to be moved at one time will determine how to use the crane and forklifts in conjunction with each other to load the material in an efficient manner.  What type of transfer truck system is purchased will also determine the crane and forklift requirements.  A fork load system is only capable of end loading.  A crane system is capable of loading anywhere in the staging area including side loading onto transfer trucks and therefore, is preferable for many applications.

 5.  What type of transfer truck system will work most efficiently?

There are two types of transfer truck systems in common use.  The first type is a chain drag system that feeds material to the in-feed rollers.  These side rollers drag the material down the transfer trucks or they lift the parts in a uniform manner and carry them on chains, moving them to the power roller tables.  This system is capable of moving material rapidly but creates the need for back loading the storage table to hold the material until it can be fed into the saw.   Another, and possibly a preferable, type system is a lift and carry system that moves one batch of material onto the power roller tables and each batch of material is delivered to the saw at one time.  The crane would put the material onto the transfer trucks and go on to another task until that material has been delivered onto the power roller tables and then return some time later to load another batch of material onto the side load magazine system.

6.  How much space is available for the out-feed staging area?

The type of transfer system is just as critical on the out feed or discharge side of the sawing system.  As parts leave the cutting area, a determination must be made as to the size of the support system needed to handle the parts coming out of the saw.  If the parts are large, say six feet or more, than three rollers, five feet apart are adequate.  However, if the parts coming out are only two feet or less, obviously the space between the rollers on the discharge table must be narrow enough to support greater than one half the weight of the material.  The center of gravity of the material must be supported by at least two rollers.  This problem is further complicated by parts of varying sizes coming out of the sawing machine.  Discharge tabling and transfer trucks of varying sizes are then required.  The availability of cranes and forklifts will help determine which system is best suited to each application.

7.  Are there parts of varying sizes being cut?

If there are parts of varying sizes being cut, the size of these parts will determine the spacing of the side transfer trucks.  Parts need to be supported in three evenly spaced places and the side transfers will need to have the availability  to move independently to ensure that material can be off-loaded safely, continuously, and efficiently.  Parts of varying sizes will require transfer trucks on the discharge side of varying spacing. 

8.  How will the squaring of the end of the bundle be accomplished?

Another important consideration is how to square the material.  If you are cutting a bundle or a single layer of material, squaring the material is necessary if the cutting tolerances are tight.  Since all the cut pieces going into the sawing process may not be the same length, it is very important to determine the method used to ensure straight cuts.  Squaring is not necessary when cutting a single piece.

9.  What are the cutting tolerances required?

There are two methods that can be used.  First, the material can be moved against a hard stop before banding.  The second option is to make trim cuts on the saw to square the material.  It depends how much drop is available and how tight cutting accuracies are required for the finished product.  If the hard stop method has been chosen, cutting accuracies can be sacrificed.  As the material hits the hard stop, the stop can actually bend, shift, or warp, especially over time and when moving heavier material.  Additionally, the material may rebound against the stop.  Trim cutting the material may be preferable to the hard stop method of squaring the material because it can be more accurate and cost efficient.  If the material is greater than 12’ and the tolerances do not need to be held closely, then a fixed stop is adequate.

The material is fed into the saw and a trim cut is used to achieve a straight end.  A shuttle vise system is used to index the material into the saw.  If cutting tolerances are within plus or minus one inch, trim cutting may be inefficient.

10.  How will trim cut pieces be removed from the saw?

If the decision is made to use the trim cut method of squaring the material, how to handle the trim cut pieces must also be determined.  Again, there are basically two methods that can be used.  The first is probably the most inefficient.  A saw operator can stand at the output side of the saw and manually remove the trim cut pieces.  This would mean that the saw and feed systems would have to be turned off to prevent injury to the operator thus creating an additional, time consuming step in the work flow.  The second method is to add an automated gate section that lifts, creating a larger opening for trim pieces to fall into the automated removal system.  The trim parts would be automatically dumped into a parts container or chip conveyor to remove them from the sawing area.  Obviously, this method increases the speed of flow through the sawing process.

11.  What coolant system will be used?

Once the area for the cutting process has been designed and planned, the available coolant systems to use during the sawing process have to be analyzed as well.  Mist systems can be very effective when cutting tubing or pipe.  They are cleaner with less dripping than conventional flood systems but are still effective because the sawing operation is cutting air much of the time thereby creating less heat and friction.  Flood coolant systems can also be used and do provide better heat transfer, provide better lubricity, and provide better blade life than a mist system.  However, coolant tends to flow through the tubing and spill on the floor creating OSHA concerns, EPA concerns, and a general housekeeping nightmare.  These issues can be resolved by using lift and tilt system on the discharge side of the saw to drain the coolant before using the crane to lift the material.  This system can be used in conjunction with pans on the in-feed, bar feed, discharge tables, and transfer trucks to return the coolant to the saw, thus saving the mess and providing the ability to reuse the coolant.

II.  Sawing Application and How it Applies to Various Types of Saws

12.  Will the saw be expected to perform miter cuts?

The plant manager must determine according to the customer’s needs whether miter cutting is required.  Will the material be moved in a bundle or a single layer?  If you are going to cut in a single layer, you have the availability of miter cutting on a vertical saw since you can cut all the way across the single layer.  If you are going to bundle cut, than you can only cut 90 degrees and miter cutting is impossible because the part lengths would vary.

13.  If bundle cutting is required, what are the shapes of the bundles to be cut? 
       Are they square, hexagonal or some other shape? 

Square material is easily stacked for bundle cutting since you would create a square or rectangle bundle for greater stability during clamping.  If you are using round bundles they are typically stacked in a hex bundle that requires special vise jaws for even clamping.  These vise jaws have to be interchangeable or have the ability to be adjustable.

14.  Will the material be banded before moving through the saw and what type of
        banding is being used? 

If you are using banded bundles and cutting tolerances are less than 1/16^th of an inch a shuttle system should be used and a bi-directional vise will be necessary to allow the banding to pass through the vises of the saw without getting caught.  This banding could affect the trueness of the cut.  Banded material travels easily across roller tables but where the band is crimped to hold it together is important. 

15.  Will miter cutting be done, what percentage of the time, and what tolerances
        will be required?

This will determine whether a vertical band saw or a horizontal band saw should be used.  When miter cutting more than 5% or 10% of the time and you need to cut miters on both ends of the piece (box frame or opposite miters), a vertical band saw is the logical choice because the vertical saw pivots around the horizontal axis of the center of the machine, allowing you to keep the vises closer to the work.  The closer the vises are to the piece being cut the greater stability and accuracy of the cut.  Keeping the vising closer to the cutting zone also dampens out the vibrations that naturally occur during the cutting process.  When using horizontal mitering band saws, the saw head moves away from the vises as the head is rotated.  Depending on the style and type of machine the vises can be a considerable distance from where the blade is cutting, allowing greater vibrations to occur on the material.  Vibration destroys blade life and the straightness of the cut.  A vertical saw will enable you to miter in one direction, index the material, and miter in the opposite direction by doing nothing more than indexing the material and rotating the head.  This is extremely important if you are cutting round, tubular products, since on an automatic index your material is always in contact with a vise, preventing the material from rolling or shifting.   

16.  What shapes are going to be cut, square or round?

If round material is to be cut than the saw used can be a standard non-canted vertical or standard non-canted horizontal.  If you are cutting square or rectangular material than a forward canted blade is very advantageous.  A canted blade cuts a more consistent cutting area achieving approximately a 30% faster cut rate and better blade life.  If you are going to cut both materials, a forward-canted blade is the proper choice since you gain all the benefits when cutting square or rectangular material and will experience none of the drawbacks when cutting round stock. 

Mitering in both directions with a single miter horizontal machine is also time consuming and is, therefore, an inefficient method to use.  In order to double miter a piece of material, you would need to cut the material, remove the material from the machine, rotate it 180 degrees, put the material back in the machine, adjust the angle, measure the length between the two angles, and re-cut the material.  A vertical machine allows you to do the same operation in 1/5 the time or less because it has the capability of double mitering without readjusting the vises.  The only thing you need to do is move the material forward and tilt the head. 

Some horizontal machines are made to double miter.  This means swinging the head in both directions.  However, with this type of design the vises have to be moved out of the way because the head will be moving into the vise to miter the second cut.  All of this takes time and, once again your vises are clamping the material at a further distance from the cut, creating instability. 

A vertical band saw also uses less floor space, since the head retracts out of the cutting area and the material can be top loaded.  So, if you were splitting a 20’ bundle, the amount of space required would only be slightly larger than the 20’ material and the material can be loaded with an over head crane, a forklift, or even manually.  Conversely, if a mitering horizontal machine were used, the material would have to be loaded behind the machine then fed through the machine, requiring a lot more space. 

Now, if an automatic bar feeder is added to a mitering machine, there are several different scenarios that could occur.  First, if it is a horizontal mitering machine mitering in both directions, the automatic shuttle index cannot move close to the blade since, as the saw is rotating, the shuttle vise must be further away since the saw is rotating towards the bar feeder.  This creates a very large remnant length in the material.  Once again, as the saw rotates into the vise it needs to be moved out of the way either manually or hydraulically.  If the horizontal saw only pivots in one direction, then the saw head pivots away from the fixed vise and once again the vise is further away from the cutting zone.  In addition, you do not have the ability to cut box frames since the saw is only capable of cutting 90 degrees and up to 45 or 60 degrees depending on the manufacturer.  This means only one part can be cut at a time unless the material is stacked up vertically on top of each other in a single row.  Otherwise, the part lengths would vary depending on their position laying in a flat row. 

Using a horizontal saw also precludes the use of an outboard top clamp.  An outboard top clamp is very difficult to use on a mitering horizontal since the clamp would have to be so far away from the work piece in order to allow room for the head to swing.  In this situation, full utilization from the structure of the saw cannot be achieved to provide the stability needed for accurate cuts.   

On a vertical machine, box frames can be cut automatically since the head is rotating around the horizontal axis of the machine, which allows the clamping to be closer to the cut zone.  Mitering in both directions without the vise interfering with the mitering of the head is achieved.  This also allows you to cut a layer of parts across the table to the same length substantially increasing the productivity of the saw.  Using a vertical saw to miter cut has the added benefit of leaving a shorter remnant end compared to that left by a horizontal double mitering machine, giving you greater material utilization. This is not true with a single mitering horizontal machine since the arm is mitering away from the cutting area and the shuttle vise system always comes to the same forward stop.  Thus, you lose the ability to double miter.

An advantage to using a double column designed machine is the center of gravity on the head remains constant.  The cutting force, therefore, remains uniform all the way through the cut giving better controllability.  Since the head travels straight up and down on columns, the sawing head is guided on both sides of the cut providing greater rigidity and stability in the arm.  This allows the guide arms to be closer to the work since the saw head is not traveling through an arc. 

One disadvantage of the double column design is when cutting rectangular or square material with a non-canted double column, the blade wants to enter the material all at one time making it more difficult to control the squareness of the cut during the entry.  Putting a cant on the blade reduces the square inches on the entry and the exit allowing the set of the tooth to help guide the head through the material.  The cant also becomes important in cutting square tubing and bundling applications since it is very important to have as uniform a cross sectional area as possible in cutting the material.  Since the center of gravity does not shift and the head weight remains constant, the head descent can be controlled very precisely through hydraulic cylinders using computerized traversing systems.  As the material size becomes greater, over 16”, the saw head becomes more massive and controlling the head becomes more difficult.  The double column design provides the ability for greater controllability and stability of the saw head

17.  What blade size machine is needed? 

The first thing to take into consideration is the type of materials to be cut.  If you are cutting harder materials, beam strength is critical.  The harder the material, the more critical the beam strength becomes.  The size and hardness of the material together create the requirement for a specific blade size.  An example is a 1 x 1 piece of stainless tubing could be cut very successfully with a 1” blade but a 5” piece of stainless tubing would struggle to make the cut.  The beam strength of the blade decreases by the cube.  If the guide spacing between the fixed guide and the moveable guide moves from 2“ to 4”, you have 8 times less beam strength available from the blade to cut the material.  This is important since the beam strength and the set of the blade controls the squareness of the cut and the amount of deflection as you transition through the material.  As a blade wears it has a greater propensity to cut out.  This occurs because every time the saw head is raised, the blade drags against the material being held by the fixed vise.  The blade dulls to the backside first so when you try to cut the material the blade wants to cut out to the front side.  The beam strength of the blade restrains the blade from trying to cut out.  Also, as you get into the tougher materials, the amount of feed force required to cut the material can increase drastically.  It is once again the beam strength of the blade that is restraining the blade from wandering.  The larger and the harder the material, the more beam strength is required to provide a straight cut.  For example, a 1” blade is .035” thick by 1” high.  A 1-1/4” blade is .042” x 1-1/4 thick.  A 1-1/2” blade is .050” thick x 1-1/2”.  As you can see, the larger blades have a much larger cross sectional area, providing greater beam strength. 

18.  What tooth selection will be used?

Tooth selection also becomes critical because the blade is cutting a smaller cross section as it cuts through a square or rectangular piece of material.  As the cut progresses, the blade addresses a larger cross section of material, requiring more force.  The general rule of thumb is to keep three teeth engaged in the work at all times. This can be difficult to achieve when cutting thin walled material.  It is critical to have a very independent feed rate and feed force to ensure that three teeth are engaged in the work at all times. 

In summary, for straight cutting a horizontal machine is more cost effective and efficient than a vertical machine.  For occasional mitering, a horizontal mitering saw is appropriate for the application until such time as the mitering requirements exceed 20% of the time.  At that point a vertical band saw is the best choice to achieve high production rates and versatility at a reasonable cost.  Remember that the harder and larger the material being cut, the greater the beam strength required to perform a fast and accurate cut.  Greater beam strength is achieved by using a larger band.  Always consider the proper machine requirements for the application being considered prior to any purchase of a band saw so that cost effectiveness and cutting efficiency is achieved.  We need to consider the proper material handling systems as well as the saw.  This is critical because if we cut twice as fast and the material handling system cannot keep pace, the increase in time-savings is actually minimal.