Can anybody tell me what the standards are for a drill bits life, and how to know when its life is up (what to look for) as defined by some respected authority?
Although I am not ‘some respected authority’ as you requested, I could probably answer your question. First of all, you should realize that tool life is not a well-defined parameter (like say hardness) so you should define it yourself for your particular application. To do it, you should select a suitable criterion for tool life. Among those criteria commonly used in drilling, the following are common: the width of the wear land of the drill lips; wear ‘size’ of the drill corners (suitable in drilling difficult-to-machine materials); wear of drill chisel edge; drill margin wear; quality of the drilled hole (including surface integrity, drill size and burr formation); drill noise (scream or cry); excessive torque and/or axial force (sometimes, power); drill breakage (especially on small drills) etc. The criteria are used to determine tool life at different combinations of cutting speeds (rpm) and feeds.
After this info is available, tool life is selected using process economy criteria such as minimum cost per drilled hole, maximum productivity or production rate, etc. As you can see, tool life is not purely technical (or, more precisely, physical) but rather economic criterion.
Regards
Viktor
That helps, thanks. Now, would one of you guys happen to know what the wear land is for high-speeed steel and carbide DRILL BITS? I have only been able to locate the wear land of rough and finish turning thus far. Also, does anyone know what the ANSI B5.54 standard, section 7 says? I read that it has something to do with tool life. Aaron
Dear AaronA
I could probably explain the complete testing methodology for drills of any type. However, I would like you to have a look at Metal Cutting Tool Handbook, Seventh Ed., Industrial Press, 1989, p. 166 Chapter “Drill Testing.” Although this chapter does not contain direct answers to your questions, it gives general sense of drill testing.
Allow me to give you some insight:
Tool testing has been carried out for at least 150 years, in tremendously increasing volume. However, most of these tests conducted under a vast variety of cutting conditions and test methods having a little in common with each other. It is understood that test results are meaningless if the test conditions have not been specified in such a way that the different factors, which affect the test results, will all be under a reasonable and practical degree of control. Though this may sound simple, the main problem is to define these essential factors.
Unfortunately, there is a lack of information dealing with test methodology and data evaluation in tool testing. The information about setup and test conditions can be found in most reported experimental studies. On the contrary, it is rather difficult to find the corresponding information about test methodology and answers to the questions why the reported test conditions or design parameters of the setup were selected at the reported levels, what method(s) was (were) used for experimental data evaluation, etc. Although experiments in metal cutting are very costly and time consuming, there is no drive to improve or generalize the experimental results up to the level of National Standards. For example, the standard ANSI/ASME B94.55M- 1985 “Tool Life Testing With Single-Point Turning Tools” suggests conducting the one-variable-at-time test. When it comes to acquisition of the test results, the only calculations of the confidence interval limits is requested to conduct and report their results so that only influence of the cutting speed on the tool life can be distinguished for a given machine (static and dynamic stiffness, spindle runout, accuracy of motions etc.), workpiece parameters (metallurgical state, dimensions, holding method, etc), cutting tool material and cutting tool design.
A need is felt for standardization of tool testing at different levels from the research laboratory to the production shop. This need stems from the requirement of the practice and can be supported by the fact that in the USA the correct cutting tool is selected less than 50% of the time. Regarding the latter, today no one developed country may afford such huge wasting of resources. Millions of dollars spent on the re-tooling of production lines in the automotive industry due to improper cutting tool testing. There is no methodology to optimize the cutting regime, to compare different cutting tools or carbides by different manufacturers. Most of cutting tool producers cannot answer to very simple questions about their products. The carbide and HSS producers ‘feed’ (or should I say, spoon feed) the industry with the parameters – for example TRS- which have nothing to do with cutting parameters. As such (as you can guess) the most important cutting parameters are not available – they never even guess about the existence of such parameters as wear resistance, optimum cutting speed, diffusion activity depending on temperature, adhesion shear strength, etc. .
The growing acceptance of ISO 9004 as an international quality philosophy is creating significant changes for manufacturers. The most important change that ISO 9004 will create is the need for international Tool R AND R capability standards. Today, cutting tool manufactures and parts makers have many different sets of reliability and efficiency criteria for cutting tools. In establishing Tool RAND R capability standards along with ISO 9004 standards, there will be an international set of standards that applies to everyone. A set of cutting tool data from Europe will mean the same as a set from North America or a set from Asia.
However, the foregoing analysis lacks of practical significance unless a hierarchical system of cutting tool testing is specified. Unfortunately, there is no such a system available. As a result, cutting tool manufactures cannot provide to parts makers suitable data on tool reliability, tool life or tool efficiency. Parts makers have no choice but to believe that the recommended cutting regimes are optimal thus efficient. Therefore, a unified standard system of cutting tool testing is absolutely necessary to increase the efficiency of cutting tool selection and use.
I have been developing a hierarchy system of tool testing (Cutting Tool Repeatability and Reproducibility (Tool R AND R)) for years. Four levels constitute the proposed hierarchical system of tool testing. They are research, design, tool manufacturing, and tool implementation levels. Depending what level you have, the test methodology (and thus procedure, time and cost) would be different.
Well Victor, while you may not be a "respected authority" on this topic, you certainly do know your stuff, and have my respect! Basically what you are telling me then, is that there are no standard parameters for tool life, and the only way I am going to find them is by conducting the appropriate tests according to my specific conditions.
Thanks for your help, Aaron
Dear AronA
Although you’ve got the message, I would like to add that not everything is as bad as it seems. For drills, particular test methodologies are available. To select the proper one, you should use your mind, experience and common sense. First of all, you should determine what kind of test you would like to carry out. Basically, there are a number of such tests with drills:
1. Comparison of different design parameters. For example, web thickness (diameter), different shapes of the chip flutes, etc
2. Comparison of different geometries. For example, flank angles, approach cutting edge angles (different types of point grind), back tapers, width of the side cutting edges, etc
3. Comparison of different tool materials (HSS or carbide)
4. Determination of the optimum cutting regime (cutting speed and feed) or tool life for a given work material.
5. Comparison of the efficiency of different coolants (could be the coolant flow rate, pressure, methods of delivery, etc.).
Depending upon a particular test, different test parameter play different role and thus have different significance. As such, the test criterion (criteria) can be different. Moreover, an experienced engineer should not conduct a complete tool life test because it time consuming and expensive. Instead he should be able to conduct a relatively short test and get the proper result.
If you specify your particular problem, I can help.
Regards
Viktor
![[hammer]](/data/assets/smilies/hammer.gif "[hammer] [hammer]")