Optimizing your Diamond Drilling Operation

There are many variables that affect diamond drill performance. Understanding these variables will help the end user select the right diamond drill specification for their application and optimize their drilling operation to ultimate level of efficiency. The objective of this article is to show the end user that each variable of the diamond drilling process is only one of the many components of a larger diamond drilling system (equation).  Changing one component or variable of diamond drilling process cannot create efficiency alone. Only when all components of the system added together can desired outcome be achieved.  Just like a mathematic equation,  it takes only one incorrectly select variable/component to affect all other properly selected variables. Making the entire diamond drilling equation/system incorrect or inefficient. Many end users approach their diamond drilling application uninformed or misled. Errors are made in the set up phase and critical steps are skipped. When problems do surface, most rush to treat a symptom rather than the cause.

UKAM Industrial Superhard Tools has over 50 years of experience in Manufacturing, Research & Development of Diamond Drills for many Industries/Applications. This article was written to help you: SAVE MATERIAL ELIMINATE / MINIMIZE CHIPPING IMPROVE SURFACE FINISH QUALITY INCREASE DIAMOND DRILL LIFE PRESERVE TRUE MATERIAL MICROSTRUCTURE REDUCE & ELIMINATE MATERIAL DEFORMATION INCREASE PRODUCTION RATE IMPROVE PART GEOMETRY, STRAIGHTNESS & TOLERANCES  IMPROVE PROCESS CONSISTENCY  IMPROVE PRODUCTIVITY  REDUCE TOTAL COST  & MUCH MORE

 Frustration leads them attribute their problems to diamond drill drill being used. What some customers refer to as serious problem for example, may be resolved by something as simple as adjusting RPM’s or feed rate. The solution can be as easy as changing mounting method, properly mounting drill in machine chuck, or educating customer about need to dress diamond drill. Selecting the right combination of these variables for a specific material / application is both an art and science that often takes years to master. Information presented in this article is not based on R & D, but primarily on many years of process optimization experience. Please, note most of the principals discussed in this article relate to sintered (metal bond) diamond drills.

DIAMOND DRILL SELECTION – (Selecting the Right Diamond drill for your Application)

Each diamond drill application exhibits similar characteristics, whether its in specification or performance. Below is a list of the most important characteristics/parameters obtained from years of experience.

Table 1

BASIC APPLICATION PARAMETERS

These parameters will play a major role in diamond drill performance. For the diamond drill manufacturer to recommend the right diamond drill for your application. It is critical that the customer provide as much application information as possible. The first step in this process is to consider the properties of the material to be drilled and to match diamond drill properties to this material. Table 2 shows a general matching of three basic diamond drill properties to three basic material properties.

Common non metallic materials drilled with diamond drills vary from hard, dense products like high alumina to loosely bonded, highly abrasive products like concrete block. No attempt is made to list specific diamond mesh sizes, concentrations or bond hardness to drill these materials. This information is to be used just as a guide in selecting diamond drill specifications.

Table 2 indicates that hard metal bonds are selected for highly abrasive material. Although physical prosperities are of primary importance in selecting drill properties, chemical properties can also play an important part. With refractory materials, for instance a high alumina content usually indicates that the material will be dense and hard requiring softer bond types and finder diamond mesh sizes.

Table 2

Matching Basic Diamond Drill Properties to Material Properties

The second step in the drill selection process is to consider the effects of operating conditions on the diamond drill. Table 3 shows these anticipated effects.

 An operating condition which causes a diamond drill to have shorter life and a faster drilling rate is said to make the drill act softer.

A drill with longer life and slower drilling rate is harder acting drill (harder drilling action). Having tentatively selected a combination of diamond drill materials from the material properties guidelines in Table 2 a change in diamond drill materials is made if there is a specific operation condition which will affect diamond drill hardness as shown on Table 3.

Table 3

Effect of Operating Conditions on Drill Actions

The third and final step in the diamond drill selection process is the consideration of the customers stated drill preference, if any. Drilling rate (speed) and drill life are the primary measurements most customers are concerned with. Usually high drilling speeds reduce labor costs and high drill life reduces diamond drill costs. There is an inverse relationship between diamond drill life and drilling speed. as diamond rill life increases, drilling rate deceases. The most common customer preference is for a diamond drill which will provide both longer life and a faster drilling speed. It is the job of the diamond drill manufacturer to evaluate which is more important to the customer, drill life or drilling speed and then to adjust drill specification selection accordingly

If diamond drill cost is the most important customer consideration

Initial cost of a diamond drill is primarily dependent on diamond content (concentration). A popular misconception among end users is that diamond content (concentration) and performance are directly proportional. However this is not the cause. In practice, there is an optimum number of diamond particles of a specific diamond mesh size in a specific bond which will produce optimum performance for a specific application. On many applications lower drilling costs are obtained user lower rather than higher diamond concentrations which, in some cases will not drilled at all. For this purpose the customer should be concerned with performance, not diamonds.

What application parameters are the most significant in making application decisions? In general, the most important factor is the type of material being drilled. Manufacturers recommended stock specifications have been developed to drilled specific materials under average operating conditions where no specific customer preference has been expressed.

For example soft diamond bond, with coarse diamond size and high diamond grade has been found to provide optimum performance on most alumina (Al203) drilling applications. This specification was developed as a result of many laboratory and field tests of various diamond drill specifications drilling same material. However when this specification does not provide optimum performance, specifications changes are made following the general guidelines presented in Table 2 and Table 3.

OPTIMIZING DIAMOND DRILL PERFORMANCE

For a any set of application conditions there is a combination of diamonds and bond which will produce optimum diamond drill performance. Finding that combinations depends on

1. the customers knowledge and ability to communicate initial application conditions, drill performance results and operating conditions changes
2. application engineers knowledge and ability to interpret those results and take appropriate action.

Except on most common applications, a successful initial diamond drill tests is rare. In many cases it may take several attempts and adjustments on both part of customer and diamond drill manufacturer to come to optimum solution.

APPLICATION RULES

Diamond Drill performance is adjusted by changing drill materials, but it can also be adjusted by changing operating conditions. Information presented in Table 2 and Table 3 implies certain application rules. Table 4 summarizes these rules showing the effect of changing either drill materials or operating conditions, holding all other variable constant.

1. Increasing diamond concentration causes a diamond drill to act harder because there are more diamond particles in contact with the material which reduces the unit pressure per diamond particle and the grain penetration depth.

2.  Increase diamond mesh size cause softer drill action because the fewer diamond particles are subjected to higher unit pressures.

3. Increased bond hardness’s make a drill act harder because of increased diamond holding capacity and abrasion resistance.

4. Increase machine operating speeds (RPM’S) make a diamond drill act harder because each diamond particle is in contact with the material being drilled for a shorter time period reducing grain penetration and removing less material per diamond particle per drill revolution.

5. Increased infeed rates cause a drill to act softer because the increased unit pressure causes each diamond particle to do more work per drill revolution. Some diamond particles may be prematurely pulled out of the drill because of increased pressure.

6. Increased horsepower causes a drill to break down faster because of premature pull out of diamond particles caused by higher drilling pressures. Stated another way, higher horsepower applications allow the use of harder bonds with hold the diamond particles longer because dull diamond particles drilled better at high rather than at low horsepower ratings.

7. An increased coolant volume aids drilling swarf removal which reduces the amount of wear on the bond making the drill act harder

8. Increased drill drilling depths cause a drill to act harder because the increased contact area reduces the pressure per unit particle and the grain penetration depth

These are the few important rules which guide the diamond drill manufacturer and customer in changing drill elements or operating conditions to optimize drill performance

Table 4

APPLICATION RULES

Nevertheless there are frequently exceptions. For example beyond optimum point O, diamond drill life decreases with increased concentration. This may occur because the harder acting drills require dressing to maintain a satisfactory drilling action, or increased infeed pressures may have to be used to maintain satisfactory drilling rates.

Increased diamond size beyond optimum point O cause a drill to act harder because the coarser particles do not penetrate a very hard material. There is a complex relationship between the number of diamond particles in a drill and the contact area of a single diamond particle. For example a change from 20/30 mesh diamond to 30/40 mesh diamond at the same concentration level provides approximately three times as many diamond particles but reduces the individual particle contact area by approximately  one third. It is common to expect harder bonds to produce longer drill life.

One theory that supports the contradiction beyond optimum point O is that harder bonds are more brittle and start to break away rather than wear away, This causes shorter drill life

Other changes in diamond drill materials or operating conditions which make a drill act harder will produce similar effects. Contradictions beyond optimum hardness’s can be explained with similar theories. The accuracy of these theories is not important when considering the drill selection process. 

VARIATION

Variation is a critical factor which further complicates the drill selection process. Some degree of variation is fairly common and is to be expected involving most aspects of diamond drill usage, raw material composition, operating conditions and etc.

Some sources of variation diamond drill applications:

Table 5

1. Diamond Drill

Diamonds

• Origin

• Friability

• Hardness

• Internal Structure

• Processing

• Sizing

• Ovalizing

• Tabling

• Sorting

• Grinding

Powdered Metal

• Particle Sizes

• Particle Size Distribution

• Physical Properties

• Chemical Properties

• Flow Rate

Processing

• Weighing

• Mixing

• Pressing Pressure

• Processing Temperatures

• Finished Dimensions

• Tensioning

• Core Quality

• Hardness

1. Machine Operating Condition

Machine

• Speed

• Feed

• Horsepower

• Type

• Power Source

• Condition

• Coolant Volume