The sawing of bar stock into billets is one of the first steps in many forging processes, yet for some reason the bandsaw operation and equipment often do not get the attention they deserve. This article discusses how to improve your bandsaw’s operational and performance efficiency.
If there is one machine on your manufacturing floor that isn’t getting the attention it deserves, it’s most likely your bandsaw. For many forging houses, it is a bottleneck at worst and ignored at best. But by measuring and improving bandsaw blade life and efficiency, it is possible to reduce costs and increase productivity across the entire operation.
Bandsaw efficiency and performance depend greatly on these four things:
- The type of blade you are using
- Whether that blade has been properly honed or broken in
- How well the bandsaw operator has been trained
- How well the machine is maintained
In most forgers’ saw rooms, blade life and speed of cut take priority over other performance criteria such as surface finish. But it is important to remember that just as your car’s gas mileage goes down the faster you drive, blade life and speed of cut also have an inverse relationship.
One of the more recent improvements in blade design is the wavy bandsaw blade (WBB). By milling a series of gradual slopes, or waves, into the blade’s back edge, blade manufacturers have been able to increase performance by up to 20%. WBBs increase tooth penetration by exerting more force into a cut with the same amount of feed pressure. The largest benefits from WBBs can be seen when cutting larger-diameter materials. Because the design also reduces the amount of friction generated, they are ideal for aerospace alloys and other alloys that harden with rubbing.
A wavy-back edge can be applied to both bimetal and carbide-tipped blades. What’s the difference? Bimetal blades have a tooth tip hardness of 67-69 RC, and carbide blades are 90 RC or more.
If carbide blades cut faster and last longer, shouldn’t everyone use them? Not necessarily. Determining which type is right for your operation depends on a variety of factors such as the rigidity of your saw and the type and condition of the material being cut. Plus, the cost of a carbide-tipped blade can be up to three times that of a bimetal blade. To further explore these options, consult your local bandsaw specialist.
This cost difference only partly explains why bimetal bandsaw blades have remained standard in the forging industry, while most other machining operations have switched to superior carbide-tipped tools. While carbide blades cost significantly more than bimetal, their benefits can easily be negated by incomplete operator training or a poorly maintained machine.
Target chip load depends on the material being cut. Too high a chip load per tooth stresses the machine drive, increases blade wear and results in a rough surface finish. With too low a chip load, the blade will rub instead of cut, which increases the risk of shattering.
Chips themselves can also indicate a machine running too high or too low of a chip load. Thin, pulverized chips often mean that the feed should be increased or band speed decreased. Thick, heavy chips indicate the opposite – feed should be decreased or band speed increased. A bandsaw running at the correct chip load will result in medium, loosely rolled chips.
Equation for Determining Bandsaw Chip Load/Tooth
Training bandsaw operators on chip load per tooth and proper break-in procedures is often a low priority on a busy floor and prevents the investment in carbide-tipped blades. Knowing chip load per tooth is critical in order to apply the correct amount of force needed and control the amount of heat generated. Chip load can be calculated by dividing the height of a cut (in inches) by the product of the average TPI (teeth per inch) multiplied by the blade speed (surface feet per minute) and cut time (in minutes).
Breaking in a New Blade
The other critical piece of knowledge for bandsaw operators is how to properly break in a new blade and why it’s important. Slowing down a bandsaw to improve cut speed seems counterintuitive, but it can increase blade life by as much as 20%.
Although some manufacturers offer pre-honed (broken-in) carbide-tipped blades for specific materials like stainless steel, most blades need to be broken in before they can operate at peak efficiency. Breaking in a blade also decreases vibration and noise.
A new blade is similar to a pencil sharpened to a fine point. Too much pressure will snap the tip of the pencil, creating a jagged, blunted tip. When a bandsaw blade’s teeth are first milled, there is a microscopic burr at the tip of each tooth. Immediately exposing those teeth to production feed rates will rip the burr off and take part of the tooth with it, leaving a blade with blunted, jagged teeth from the beginning.
What break-in procedure is used in your facility? That information was likely communicated by word of mouth, handed down from one employee to the next, with most of the details getting mottled in the translation.
First, a target blade speed and feed rate should be established based on the material grade and size being cut. For bimetal blades, the blade speed can remain constant, but the feed rate should be lowered by 1/3 or 1/2 for the first 10 minutes or 100 square inches of cutting, whichever comes first (with some exceptions). Using your senses to ensure the blade isn’t vibrating, the feed rate can then be increased incrementally until the target rate is reached. For carbide blades, begin with a blade speed that is 3/4 of the target and a feed rate that is 1/2 of the target. After 10 minutes, raise both incrementally until reaching the target speed and feed.
Maintenance and Measurement
A bandsaw is more than just its blade and only as good as the technicians operating and maintaining it. The hydraulic fluid and coolant levels should be checked with every shift. Changing the blade should also include cleaning the machine out, checking guide wear and alignment, and replacing the chip brush if needed.
This last item cannot be emphasized enough: chip brushes are not optional. They are meant to remove chips from the teeth of the blade and prevent those chips from re-entering the cut. Common chip brushes consist of bristles made of steel or reinforced nylon. Missing or worn-out chip brushes will result in chips welding to tooth tips, poor surface finish, blade dulling and reduced blade life.
Forges demand a lot from their bandsaws – fast cutting, often of hard and exotic alloys, under punishing conditions. Is your sawing operation running more efficiently today than it was yesterday? How are you measuring efficiency?
Establish your benchmark, then try implementing some of the recommendations listed in this article. What gets measured gets improved, and that’s as true for bandsaw performance as it is for any other part of your operation.