The production process of machinery manufacturing involves a large number of machining, especially metal cutting processing of processed products, size, shape, positional accuracy, surface morphology, etc. are related to the tool, tool performance, quality and its management directly affects the ability to successfully process the required qualified products, affecting the machining beat and production efficiency, affecting the control and reduction of manufacturing costs, and the relationship between the manufacturing The core competitiveness of enterprises, which is more prominent in automated machining.
(1) CNC machine tools in the tool development and application of new features
Modern machining and its use of cutting tool technology in recent years, the development of particularly fast, high-tech was adopted in large quantities, in the machining process, cutting methods, tool structure, tool materials, surface engineering, etc. have been with the past traditional machining is very different from the past, the first of which is the use of a large number of flexible machining production lines. The use of efficient, high-speed cutting, various types of CNC machining centers are used in large quantities, with the corresponding super-hard cutting tools such as CBN (cubic boron nitride), PCD (polycrystalline diamond) cutting tools and new cemented carbide cutting tools are used in large quantities, by the latest developments in surface engineering and tribology technology obtained by a variety of new coatings applied to the tool surface, the new cutting tool structure and a new type of cutting edge and geometry of the blade Being continuously researched and developed, adapted to the needs of CNC machine tools and high-speed machining of the tool holder and its connection with the machine tool such as HSK shanks, hot sleeve shanks, hydraulic shanks, etc., as well as other new shanks to obtain a wide range of applications. In order to improve productivity and reduce the time of tool change in the processing of automotive parts more and more use of a variety of composite tools, such as drilling and boring composite, drilling and reaming composite, drilling and threading composite and other types of composite tools, the structure of the complexity of the unfolding tool to meet the requirements of a lot of special machining requirements, and some of the tool has even been developed into a mechanical, electrical and hydraulic integration of the device has gone far beyond the traditional concept of the tool. Tools need to be maintained and maintenance, the need for pre-adjustment and testing, tool life needs to be controlled, the need for a comprehensive system and a series of management to ensure that the production line in a timely manner to meet the requirements of the number of adequate tools, and in the event of processing problems or tooling problems to get a quick response and support, rapid analysis and resolution of the problems that arise in order to enable production to normalize, and including tooling costs, including the cost of manufacturing The cost of manufacturing, including tooling costs, should be sufficiently competitive in the marketplace, all of which puts forward completely new requirements for tool management that are different from those of the past.
In the face of the rapid development of machining and tooling technology, in the face of CNC equipment to be flexible but also the challenge of efficient production, in the face of increasingly fierce competition in the market and continue to reduce the pressure of manufacturing costs, tool management has become a hotspot of growing concern in various industries.
(2) tool and its management on the impact of production efficiency
Tool performance and quality directly affects the smooth processing of qualified products required, whether the tool can meet the requirements of high-speed cutting, tool life and tool change frequency are directly affecting the production line start rate, affecting the processing beat and production efficiency, and whether the quality of the adjusted or sharpened tools will be adjusted and guaranteed quality will provide direct access to the production line. The ability to adjust or resharpen the tool on time and quality assurance will be provided to the production line will be directly related to the production can be normal and sustainable. Machinery industry is a large number of flow production, the production of the previous process directly affects the production of the next process, and in order to improve production efficiency and reduce production costs, and the use of a large number of combined tools and the resulting non-standard tools, and therefore a key tool, especially non-standard tools, such as the supply can not be on time, as in a series circuit, a component damage caused by the paralysis of the entire circuit will cause the entire machining line shut down. The entire machining line stops production, and if there is no emergency measures or can not respond quickly, may also cause assembly line or even automatic assembly line stops production, which shows that the tool and its management of the significant impact on production.
(3) the definition of tool life
Sharpened tool since the beginning of cutting until the wear amount to reach the blunt standard until the cutting time, known as tool life, expressed in T. It is the net cutting time. It is the net cutting time, excluding non-cutting time used for tool setting, measurement, fast forward, return and so on.
Also used to reach the grinding standard before the cutting distance lm. to define the tool life. lm is equal to the cutting speed Vc and tool life (time) T product, that is
lm = Vc-T (6-3)
This needs to be pointed out in the past to the above definition of the tool life is known as the tool durability. In the past, tool life tool endurance has had different meanings. Tool life means the total cutting time of a new tool (e.g., a welding lathe or twist drill, etc.) until it is scrapped, including multiple resharpenings. Tool life is therefore equal to tool durability multiplied by the number of resharpenings, but in the spirit of the current recommended standards, it should be referred to as total tool life.
Tool life is very important data. Cutting the same workpiece material under the same conditions, you can use the tool life to compare the cutting performance of different tool materials; the same tool material cutting a variety of workpiece materials, you can use the tool life to compare the cutting and processing of the workpiece material; you can also use the tool life to determine whether the tool geometry is reasonable. Workpiece material, tool material performance on the tool life has the greatest impact. In the cutting capacity, the most important factor affecting tool life is cutting speed, followed by feed and depth of cut. In addition, tool geometry parameters also have an important impact on tool life.
(a). Relationship between cutting speed and tool life
The relationship between cutting speed and tool life is obtained experimentally. The standard for grinding dullness of the tool's rear face is selected before the experiment. In order to save material and at the same time to reflect the wear intensity of the tool under normal working conditions, according to the provisions of IS0: when the main cutting edge to participate in the middle of the working part of the wear of the uniform wear, bluntness of the grinding standard to take the VB = 0.3mm; in the wear of uneven, take the VBmax = 0.6mm [106].
Selected wear standard, in the case of fixed other cutting conditions, only change the cutting speed (such as take V = Vc1, Vc2, Vc3, Vc4, ..., etc.) for the wear test, resulting in a variety of speeds under the tool wear curve (Figure 6-11); and then based on the strong selection of the wear standard VB to find out the corresponding tool in the various cutting speeds. Cutting speed under the corresponding tool life T1, T2, T3, T4, ... and so on. Then in the logarithmic coordinates of the paper set out (T1, Vc1); (T2, Vc2); (T3, Vc3), (T4, Vc4); ... and other points (Figure 6-12). Within a certain range of cutting speeds, these points are essentially distributed on a straight line. This line on the double logarithmic coordinate graph can be expressed by the following equation:
lgVc=-mlgT+lgA
in which m = tgφ, that is, the slope of the straight line; A is when T = 1s (or 1min) when the straight line in the longitudinal coordinates of the intercept. m and A can be measured from the graph. Therefore the Vc-T (or T-Vc) relationship can be written as:
Vc = A/Tm (6-4)①
or
(z = 1/m) (6-5)
(b). Relationship between feed, depth of cut and tool life
Following the same method of finding the Vc-T equation, the f-T and ap-T equations can be found:
f = B/Tn (6-6)
ap = C / Tp (6-7)
Equation B, C - coefficients;
n, p - indices.
Integrated formula 6-4, formula 6-6 and formula 6-7, you can get the three-factor formula for tool life:
(6-8a)
or
(6 -8b)
Equation CT, Cv - coefficients related to the workpiece material, tool material and other cutting conditions;
Exponent xv = m / p, yv = m / n.
For different workpiece materials and tool materials, under different cutting conditions, the equation 6 -8 in the coefficients and indices, can be found in the information [73]. In fact, Eq. 6-8 is the tool life or a certain tool life under the cutting speed prediction equation. For example, with carbide cylindrical turning tool cutting σb = 0.75GPa (75kgf/mm2) of carbon steel, when f> 0.75mm / r, empirical formula
By the above formula can be seen, the cutting speed on the tool life of the greatest impact, followed by the feed, depth of cut has the least impact. So in the preferred cutting to improve productivity, the selection of the sequence should be: first try to choose a large depth of cut ap, and then according to the processing conditions and machining requirements to select the maximum permissible feed f, and finally in the tool life or machine tool power allowed to select the maximum speed of cutting Vc
From the above formula, it can be seen that the cutting speed of the tool life of the greatest impact, followed by the feed, the depth of cut, the most important thing is that the cutting speed of the tool life, and the depth of cut. Next is the feed, depth of cut has the least impact. So in the preferred cutting to improve productivity, the selection of the sequence should be: first try to choose a large depth of cut ap, and then according to the processing conditions and machining requirements to select the maximum permissible feed f, and finally in the tool life or machine tool power allows the selection of the maximum speed of cutting Vc
(c), T - Vc relationship between the Humping
Equation 6-5 shows the empirical formula for the T-Vc relationship is only applicable within a certain range of cutting speeds. If the tool life experiment in a wide range of cutting speeds, the resulting T-Vc curve is often not a monotonous function, but the formation of a hump-shaped curve (Figure 6-13). In the lower speed range, when Vc increases, T not only does not decrease, but increases; to a certain speed, T has a maximum value. The velocity continues to increase before T decreases monotonically. The falling portion of the corresponding curve is the range of velocities for which Taylor's formula is valid. Similarly, the lm-Vc relationship has a hump.
Does the fact that the hump has the highest tool life or the longest cutting distance mean that this is the "optimum cutting speed"? No, it doesn't. Here the cutting speed is low, the gold chip removal rate is also lower, often in the production of no practical value. General production is often chosen to be located in the hump of the right cutting speed.
(d), the distribution of tool life
The following is the distribution of tool life under normal wear conditions. When the workpiece, tool and cutting conditions are fixed, tool life is not constant. If the cutting experiment or processing is repeated, the tool life varies within a certain range and according to a certain pattern. Because the workpiece, tool material manufacturing quality, microstructure, mechanical (mechanical) properties, geometric parameters, sharpening quality, as well as machine movement and other process conditions, are randomly changing. Changes in each factor can not not affect the tool life, so the tool life is also a random variable. Mathematical and statistical studies have shown that under certain cutting conditions, the pattern of change of tool life obeys normal distribution or lognormal distribution [146].
The probability density function of the normal distribution is
In the formula μ--mean value;
σ--standard deviation.
The probability density function of the lognormal distribution is
(when T>0)
Equation μ - location parameter,
σ - scale parameter.
The authors turned 38CrNi3MoVA tempered steel with P10 carbide inserts, taking ap = 1mm, f = 0.2mm/r, Vc = 150m/min, and sharpening standard VB = 0.2mm. 60 cutting edges were used, and the cutting was repeated 60 times. Statistics in different intervals of tool life frequency of occurrence, plotted the tool life distribution curve (Figure 6-14). After testing, it is considered to obey the normal distribution. μ = 15.284, σ = 1.34.
Mastering the distribution of tool service life is of guiding significance to production. In modern processing, the tool life needs to be scientifically managed, timed tool change, must understand the distribution of tool life. For example, in Figure 6-14 used cutting conditions, the requirements of P10 tool to meet the probability of tool life T ≥ 12mm
Such a probability that the P10 tool to meet the requirements of the process processing.
In the process of CNC machining, the quality of the tool and the effective management of the tool use process has a vital role in machining quality. In the field of automobile manufacturing quality process control system (TS16949 quality certification system) also has a very specific and clear requirements for tool management. HARDINGE VT2 CNC vertical lathe is produced by the U.S. HADRGINE company, the CNC system for the FANUC18T system. This article describes how to use the FANUC18T system tool life management function to manage the use of tools to ensure the quality of processed products.1 add tool life management function in order to carry out the life management of tools, to realize the number of times the CNC equipment on the tool use of automatic counting
The above text is extracted from the "tool management"
Hahan International Clothing