of Precision Abrasive Slicing and Dicing Blades
Abrasive Blade only differentiates from a Grinding Wheel in the process or application to which it is used. Within the scope of this paper, Abrasive Blades will be considered delicate and precise tools whereas Grinding Wheels will be generally less precise and more robust in size and in application.
Typically a very hard substance bonded to or retained within various Carrier/Bonding systems, so that in a Grinding or Slicing/Dicing process the individual abrasive particles chip away (micro fracture) the material being Ground (Cut). Listed below, are a few of the abrasive types that can be used in the manufacturing of abrasive blades, either singular or in multiples, and in various forms:
Diamond, cBN, Silicon Carbide, Boron Carbide and Aluminum Oxide.
This occurs when the interaction between the abrasive particle and the bonding system fails, this will cause the abrasive particle to pullout (dislodge). Causing rapid blade wear, loading and ultimately blade failure.
This is the amount that the abrasive is exposed from the bonding system. Typically this is from 0 to 35% of the size of the abrasive particle, depending on the state of dress and the strength of the bonding system used (Nickel bond being the strongest and Resin bond the weakest). The greater the effective distance between the abrasive particle’s leading edge and the bonding system the more efficiently the blade will cut.
Within the context of this paper it will be defined as a blade mounting and locating system that is supported on both ends by the machine system that is driving it.
This is the blade thickness to blade exposure ratio (exposure ÷ thickness = aspect ratio) for highest cut location accuracy, the following guidelines can be used:
Resin Bond = 10-1
Metal Bond = 15-1
Nickel Bond = 20-1
This is a process of preparing the blade for cutting, typically done with a vitreous or resin bonded silicon carbide or aluminum oxide abrasive dressing sticks, plates or boards. This process erodes back some of the bonding material, thus exposing the abrasive particles. Dressing is also used to remove imbedded grinding residue (swarf) as part of the cutting process (in process dressing).
When the abrasive particle is no longer exposed (abrasive protrusion), enough to cut efficiently, from either abrasive wear or swarf build up. Blade loading is minimized if the blade type and process are properly matched. There are numerous parameters that can cause blade loading, but proper Spindle speed, feed-rates, adequate coolant and blade dressing frequencies are paramount in most processes.
Machining the periphery of the blade to run concentric to the axis of rotation of the spindle and/or to adjust/ maintain the geometry of the blade.
This is the intentional incorporation of voids into the bonding structure to allow for coolant to enter the cutting area, and for the swarf to build up without interfering with the abrasives, before it (the swarf) is flushed out by the coolant at the exit of the cut. There are tremendous variations in the amount of porosity from bond type to bond type and even within each bonding system, but generally the Vitreous bonds are the most porous and the Nickel bonds are the least porous.
This is the flex or give (or lack of) that a particular bonding system has in relationship to the abrasive particle. As a general rule the more resilient the bond, the more friable (weak) the abrasive should be.
Least resilient to most resilient bonding systems:
Vitrified Bond, Nickel Bond, Metal Bond, Phenol Resin, Polyimide Resin
This is also sometimes referred to as a comet tail, this “tail” is a build up of the bond behind the abrasive particle, which helps support the abrasive particle in the bond matrix. As the abrasive wears, so does this tail, until the particle is no longer adequately supported and thus dislodges, revealing a new abrasive particle to replace it. Bond tails are readily apparent in a well-conceived cutting/grinding process.
CBN (Cubicle Boron Nitride)
The manufacturing of CBN is very similar to synthetic diamond, except the crystals are created from Boron oxide feed stock and do not react to ferrous materials and thus no graphitazation can take place. CBN is the second hardest material to Diamond.
This is the “intrinsic” radius that an abrasive blade will form through normal usage, generally speaking, the larger the abrasive particle the larger the radius will be (a strong bonding system minimizes this effect). To estimate what the corner radius on a particular blade will be; multiply the particles size by 3. Example: 35 micron abrasive = .0012 particle size multiplied by 3 = .0036, so the expected corner radius for this size abrasive is .0036”(on each edge). If the blade thickness is less than the total blade radius, the total blade life will be considerably compromised (fig.#2).
Is a multiple set of Blades and Spacers, assembled on an Arbor or a Hub.
The tendency of Diamond to revert to Graphite, in high temperature and in the presence of ferrous materials. Predominately and issue in fabrication, when using a Metal Bond sintering process, and during the cutting/ grinding of a ferrous (Iron containing) material using a diamond abrasive, regardless of what bonding system used.
This is the residue or dust generated in a grinding operation. This Swarf can imbed into the abrasive blade and cause “loading”, heat and failure if not flushed or dressed out.
Within the context of this paper it will be defined as a blade mounting and locating system that is supported on one end by the machine system that is driving it.
This is a Hub/Arbor hybrid. The Arbor is used to support and locate the Hub assembly onto the drive system. This combination has some of the adaptability of the Hub, with the robustness of an Arbor.
This is the actual width of the slot, generated by the abrasive blade. It is generally, fractionally wider than the statically measured blade thickness. The actual kerf width is dependant on many factors, some of which are: Blade exposure, Blade thickness, Blade axial run-out and material the being cut (fig. #3).
Land / Part Width
This is the area within the inside edges of successive Kerfs (fig. #3). In a Gang stack, this is the spacer thickness plus the Blade thickness less the Blade run-out.
As a bonding system for abrasives, there are many different types and combinations of metals used in this system, but they can be narrowed down to two main types;
Bronze based, this group of bonds is by far the most common in the precision manufacturing industry. These are in general, soft, ductile, easy to machine and dress, with good accuracy and overall quality in a large array of applications and processes.
Cobalt based, this group of bonds is primarily used in the construction industry, although with advances in powder metallurgy they have made strong inroads to the precision manufacturing industry due to the high stiffness and thus accuracy these bonds can achieve.
Both of these bonds are fabricated in a “Sintering” process and thus there can and will be a multitude of variations within each of these to groups, by both the process and the metallurgy employed.
Shard like shape, this shape allows it to be very free cutting but also wear faster than most synthetic diamonds. These are crushed from larger particles, then sorted for size, and thus can have an inconsistent, but very sharp angular shape, and generally cause a larger chip size and rougher surface finish on the part being cut, compared to synthetic diamond of the same relative size.
Though this could be classified as a metal bond it is usually not, because the manufacturing process is vastly different it is considered by most to be in its own category. In this bonding system the abrasive is held in place with electroplated or electroformed Nickel matrix, this system is very strong, stiff and resistant to wear.
This is the Kerf width, plus the Land width (fig.#3).
An individual Pitch is one Kerf plus one land.
A Cumulative Pitch is a summation of a series of individual Pitches. A Gang of abrasive blades and Spacers are typically stacked to maintain a non-cumulative pitch specification.
As a bonding system for abrasives, this system encompasses two main groups; these are Thermosetting and Thermoplastic.
- Thermosetting Resin
Thermosetting resins used for bonding are generally stiff, brittle and “self Dressing” (free-cutting) this group of resins are widely used, for numerous applications.
- Thermoplastic Resin
Thermoplastic resins used for bonding are typically tough and but rather elastic.
A manufacturing process that uses pressure and heat to fuse the metals. There are two main process types used.
#1 Hot Press, this system applies the heat and the pressure required, simultaneously.
#2 Press/ Oven, this system uses high pressure and a sintering wax to produce a “Blank” which is then loaded into a Sintering oven or Furnace to fuse the metallurgy.
Slots, Slits or Serration’s
These are modifications done to the periphery of the blade to asset in delivery of coolant, and/or the removal of grinding swarf.
For best results, the number of and the shape of the slots should be designed specifically for the expected application.
These are used to not only retain and support the blades, but also to establish the pitch and/or land of a gang arbor or hub module assembly. Spacers should be stable, stiff and lightweight for most precision applications. Some materials used for spacers and the benefits of each are:
Sintered Alumina – stable, stiff and lightweight (but brittle).
Sintered Tungsten Carbide – stable, stiff and tough (but heavy)
Anodized aluminum – very lightweight (but not as stable or as stiff)
Steering (inconstant kerf location)
Steering can be caused by blade loading, exceedingly high aspect ratio, or otherwise poorly suited to the application can lead to the blade steering or “waviness” of cut.
Many different types, from sharp/angular to very “blocky”. These crystals are created under conditions of extreme pressures and temperatures from a Graphite/catalyst feed stock, and then (most types) are milled and/or sorted to very specific groups of shapes, thus the shape within each group is very consistent.There are two main types of Synthetic diamond crystals produced; the first group is a mono-crystalline, this type is grown from a single “seed”, thus it has very few major internal boundaries (weak areas) because of this it is very strong with very few flaws. The second group is the poly-crystalline, this type is grown from multiple seeds, thus having many cleavage points, and this makes for a crystal with many internal boundaries or flaws, the more flaws the greater the friability. Friability in abrasives is defined as a particle’s ability to self sharpen through the expulsion of dull or worn cutting faces, without causing the entire abrasive particle to dislodge or pull-out.
This is a Glass (Ceramic) bonding system that is extremely hard, but also very brittle, this limits its applications, but in suitable applications they are long lasting (similar to metal bond) and free cutting (similar to resin bond)