Optimizing your Diamond Drilling Operation

 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  

Operator

• Skill

• Temperament

• Objectivity

Purchaser

• Flexibility

• Communicativeness  

2. Material Being Drilled (Raw Materials)

• Particle Sizes

• Particle Size Distribution

• Grog Size & Type

• Chemical Composition

Processing

• Weighing

• Pressing

• Firing

• Kiln Location

Final Product

• Tensile Strength

• Chemical Composition

• Refractoriness

• Abrasiveness

• Hardness

• Density

• Permeability

Many factors can affect each of the variables listed above and methods used to control and minimize these variations. Manufacturer of diamond drills goes to great length to control the quality of the diamonds and powders used and to control the processing conditions which affect the performance of the finished product.

By the same taken raw material manufacturers that supply material that is drilled by diamond drills also have formable quality control standards to minimize process and manufacturing variation. Unfortunately the drilled ability of these materials is seldom taken into consideration in initial raw material design and process control when designing original product. Refractory products for example are closely controlled for properties such as thermal conductivity, spalling and refractoriness, but drilled ability (hardness and abrasiveness) is not specifically controlled. Operating conditions are typically under poorer control than either material properties or diamond drill properties. For instance, the objectivity of the saw operator and the communicativeness of the purchaser are major sources of variations that have important effect on drill performance.

Typically the diamond drill manufacturing processes are in far better control than other factors of the application environment in which those diamond drills perform.

AFFECTS OF PRODUCT, PROCESS AND APPLICATION VARIABLES ON DIAMOND DRILL PERFORMANCE

This normal variation curve represents a hypothetical population of diamond drill performance results on the a specific application. The curve represented by range Rb depicts the relative amount of variation caused by diamond product variables. Curve represented by range RM accounts for the amount of variation cause by variables in the material being drilled.

The range Ro represents the variation in performance results due to variations in operation conditions. The goal in this case is not to relieve the diamond drill manufacturer of the all responsibility of application variations, but it does express the experience of diamond drill manufacturers.

One of the most difficult tasks an application engineer faces is solving application problems that are cause by variation. For example, in drilling one material typical drill life is average of 500 holes per drill is considered normal.

Figure 1 presents another frequency distribution curve showing the average and range of performance on this specific hypothetical application

DISTRIBUTION OF POSSIBLE DIAMOND DRILL  PERFORMANCE RESULTS

NUMBER OF HOLES PER DIAMOND DRILL

Figure 2

Diamond Drill represented by point A made 350 holes. The user of this drill is not happy and may request a credit. However what the end user should realize is that diamond drill life they have experienced is not out of the ordinary and still falls within the normal distribution curve. When using this particular diamond drill the user was affected by all variables discussed above. Therefore, credit is not really warranted (despite what the customer may feel).

This problem occurs frequently and it is the diamond drill manufacturers application engineers task to explain to the disappointed end user that the 350 drilled holes performance level, although low is normal. In these situations, note that diamond drill performance represented by point B is rarely mentioned.

On other hand if a diamond drill provided only 200 holes as shown  in point C, this would be outside the normal distribution curve. There could be more than one explanation to attribute to this poor drill performance. In statistics this performance would be attributed to assignable cause. Finding and assigning cause and correcting the problem behind this poor performance is a challenging task. Most customers logically conclude that there is something wrong with this diamond drill. However, this is not always the case. In this situation it is very important of the customer (end user) and drill manufacturer (supplier) to face these circumstances with an open mind in order to resolve the problem. Both diamond drill manufacturer and user can dramatically benefit by working together to resolve problem, instead of approaching it as advisories.

The end users lack of cooperation with diamond drill manufacturer or supplier will be costly to the end user. Important information will be lost unless the end user communicates complete drill application information to manufacturer.

The manufacturer can assist the end user by providing important recommendations in changing operation conditions or usage parameters. And in some cases provide different drill specification that will more closely and better match customers application parameters.

It’s important for the customer to understand that manufacturers do not rule out diamond drill variability as cause of poor diamond drill performance. Its just very rare. Most diamond drill manufacturers maintain elaborate records documenting diamond drill manufacturing and quality control process at every stage.

Each batch and drill produced is frequently assigned as serial number. Every processes underwent in diamond drill manufacturing process can be reexamined and traced to each individual diamond drill.

This information is frequently inspected when looking into validity of customer poor drill performance claims.

Most customers when experiencing poor diamond drill performance or variation frequently assume the tool used (diamond drill) is at fault. Rarely do these users consider material variations or changes in operating conditions as a factor behind these problems.

DESIGNING DIAMOND DRILL TESTS

Rarely does the first drill specification recommended by diamond drill manufacturer provide optimized level of performance desired by customer. Even if by chance the first diamond drill specification tested hits the target, subsequent drills would not perform to most optimized level of performance. This is why results of one diamond drill test is not particularly valid. It is recommended that several drills of same specification by used to establish a average and a range of performance results before adjusting a specification of optimum results.

It is therefore in customers best interest to sample as many drill specifications and their variations as possible to establish a precedent (performance benchmark) from which they can measure all other diamond drills.

In constructing field tests, the end user should attempt to control operating conditions and material specifications as much as possible to minimize diamond drill performance variation. For this reason laboratory tests utilize statistical methods such as random or multiple drill deigns to minimize the affects all variables that may cause variation, except for those being specifically evaluated.

Here are some of the methods used to control and minimize variation in laboratory testing environment

1. when possible, use automatic drilling equipment which operates at a constant surface speed, infeed pressure and power consumption. A cnc operated machine can be used to same RPM and feed rate peck cycle. If using a manual process with human operator becomes necessary, specific amperage levels should be selected and operators drilling technique closely monitored to make sure physical movements are as consistent as possible.

2. material being drilled is consistent and carefully controlled. We recommend purchasing large lot of material to represent a total range of variation in drilling properties of that specific material. Doing so will minimize effect of piece to piece variation, when selecting individual pieces at random. In order to minimize material hardness variation, we recommend selecting different places of material and drilling at each different location.

3. when evaluation one or several variables such as diamond mesh size, bond hardness, concentration, and etc in same test, select specific diamond drill specification combination at random. By selecting random sequent in which only a few holes are made with each combination of variables and then another random sequence selected. This is important to minimize variation cause by factors such as operator fatigue, weather conditions, power sources variations and machine condition changes.

The customer stands much to gain by following proper diamond drill testing procedures.

PREDICTING DIAMOND DRILL PERFORMANCE RESULTS

Frequently customers ask the manufacturer to make certain predictions about diamond drill performance.

Questions such as “How many holes will this drill make?” are frequently asked. Unfortunately, there is not real answer to this question. Because it takes a considerable amount of time and patience to explain all of possible variations behind diamond drill performance.

Why can performance results be more accurately predicted?

One customer may achieve certain drill life or chipping level on specific application. While another customer may experience longer or shorter life on exact same material and application. Even though operating condition and materials appear to be relative same. Any estimate from drill manufacturer may be interpreted by customer as a commitment or statement of performance guarantee. This is unrealistic and discourages for objective testing, the results of which will benefit both customer and manufacturer.

UKAM Industrial Superhard Tools   Division of LEL Diamond Tools International, Inc.

28231 Avenue Crocker, Unit 80  Valencia, CA 91355  Phone: (661) 257-2288  Fax: (661) 257-3833

e-mail: lel@ukam.com