STATEMENT OF LOSSES CAUSED BY THE PRESETTING OF TOOLS BY THE MANUAL METHOD

Transcription

1 STATEMENT OF LOSSES CAUSED BY THE PRESETTING OF TOOLS BY THE MANUAL METHOD Ivan Correr a ; Milton Vieira Junior b ; José Martinele Alves Silva b ; Diego dos Santos Silva b ; Alan Santos Costa b a GeoTecno Soluções em Automação Rua Tupis, Santa Bárbara d`oeste SP Brazil. ZIP Code: Phone: ivancorrer@yahoo.com.br b Universidade Nove de Julho UNINOVE Avenida Francisco Matarazzo, 612. São Paulo SP Brazil. ZIP Code: Phone: mvieirajr@uninove.br POMS 22nd Annual Conference Reno, Nevada, U.S.A. April 29 to May 2, 2011 In the search for competitiveness, machining companies seek to qualify as being able to run processes of World Class Manufacturing, with the application of concepts of lean manufacturing. Among such concepts is the fast setup, essential for the elimination of losses in the process. However, most business users of CNC machines still face a significant barrier in this field: the presetting of tools is usually performed manually, and requires high times for the preparation of the machines. In this paper these times are associated with losses in production, showing not only the result in terms of delays generated in the setup operations of machines, but also reductions in the utilization rates of CNC machines. In addition, the paper also presents a method for calculating those

2 losses that can be easily accessed via the Internet by users of CNC machines in order to calculate the losses in their existing production systems. 1. Introduction The emergence of new technologies in recent times has increased the competitiveness of companies in the metal-mechanic sector. Among these technologies, which often target the reduction of time and cost reduction, is the tool presetting technology, which focuses on reducing setup times of CNC machines and increasing the availability and productivity. Although not always the costs of this technology are so attractive, it is important to analyze the cost vs. benefit and check the return in the short and medium term (VIEIRA JUNIOR et al., 2006). Presetting systems reduce the time spent on setup (machine setup times), a necessary condition which aims to reduce the costs of machining on CNC machines (FOGLIATTO; FAGUNDES, 2003). The reduction or elimination of unproductive times in an operation or a process is an important factor for those companies who want to survive and grow in a competitive environment. This factor leads the companies to invest in various systems to reach the reduction of losses in productivity. According to Harmon and Peterson, apud Fogliatto and Fagundes (2003), the reduction of times spent on setup of the machines is important for three reasons: 1) When the setup cost is high, companies tend to enlarge the size of batches, increasing investment in inventory; 2) The recent techniques for faster and simpler tool exchange diminish the possibility of errors in the adjustment of equipment;

3 3) Reduction of the setup times will result in increasing of operating times of equipments. Note then that a simple tool change can generate various costs involved in this operation, confirming that the importance of presetting systems is greater than might appear at first. In this paper presetting times are associated with the known losses in production, showing not only the result in terms of delays generated in the setup operations of machines, but also reductions in the utilization rates of CNC machines. In addition, the paper also presents a method for calculating those losses that can be easily accessed via the Internet by users of CNC machines in order to calculate the losses in their existing production systems. 2. Presetting systems Presetting systems are growing in use among the industries of the metal-mechanic sector, but it does not mean that all of them have enough knowledge on the subject and realize what presetting systems are capable of doing (Santos et al, 2006). Presetting equipment are important for a proper assembly of tools in CNC machines, quickly, accurately and safely. For these reasons, good presetting equipment can guarantee the return of the investment in CNC machine in less time than expected. Globalized markets and strong competition in the current economic scenario has virtually forced the companies, especially those that intend to survive and grow in this competitive environment, to invest in processes that reduce the unproductive cycle of production of the company, and in that regard, presetting systems have been adopted also for presetting and tool breakage detection in CNC machines. To ensure an accurate machining of a part on a CNC machine, Weatherall (1992) apud Simon et al. (2002) explains that the control system of the machine has to "know"

4 certain dimensions of the tools, and these dimensions refer to a fixed adjusting point on the tool holder. The presetting of tools can be done also manually (internally or externally of the CNC machine) or automatically (also internally or externally of the CNC machine). The manual internal presetting can only run when the machine is idle, while the manual external presetting can be performed with the machine in operation, measuring tools in metrology instruments (such as calipers or micrometers) and inserting in the CNC the measurements obtained (Shingo, 2000). The manual external method is very inaccurate and underutilized. In manual internal presetting the identification of tools dimensions can be done in two ways: 1) With the tool completely static, is done the manual approach of tool till workpiece, at slow speed, until contact occurs between the tool and the workpiece surface, and from this the coordinate values X, Y and Z are recorded and loaded into the CNC machine by hand. 2) The other way of obtaining the dimensions of tools manually is the method of experimental machining. In this case firstly the approximate dimensions of the tools are inserted on the CNC, and after an experimental machining the workpiece dimensions are measured and the deviations of the workpiece dimensions are inserted on the CNC as correction data for the respective tool used. (DE GARMO et al., 1997). These manual ways of adjusting the tools generates several unproductive times, adding costs to the process and, according to Simon (2002), depending on the type of CNC machine used in the process can consume from 50 to 75% of the total time spent on the replacement of a tool. Adjust each tool by the manual method can waste a lot of time

5 and compromise productivity, because the machines are not removing material during the adjustment (WICK, 1995). Already the way to make presetting automatically uses automatic apparatus called presetters, which may be external or internal, the latter also known as toolsetters. (VIEIRA JUNIOR et al., 2006). Toolsetter system is typically mounted on the table of the CNC machining center, and can also be used to detect tool breakage. Usually the equipment consists in a simple system that emits a laser beam to a receiver. This beam is interrupted when the tool is in its normal state, and when there is tool breakage the beam reaches the receiver, which immediately indicates the failure of this tool to the CNC machine (RENISHAW, 2003). Figure 1 shows automatic presetting equipment, the toolsetter, and its laser beam to identify the tool. Figure 1: Example of a presetting system Toolsetter laser ( ). To detect tools dimensions, the toolsetter identifies whem the laser beam is interrupted by the tools and record automatically the respective coordinates X, Y and Z on the CNC command.

6 The automated external presetter contains a transducer mounted in fixed point outside the machine tool that allows measurement of the tools off the machine, accurately and quickly. The correction data generated by the presetter can be transferred in real time and with complete confidence to the CNC control (Simon et al, 2002). For this type of process, the dimensions of the cutting edge of the tool relative to the reference point, are properly determined, ie, the tool is mounted in its holder and is placed in a presetting equipment that has the same characteristics of the housing of tools support in the CNC machine (RUN et al., 2005). Figure 2 shows one type of system presetter (VIEIRA JUNIOR ET AL, 2006). Figure 2 Optical presetter (VIEIRA JUNIOR et al, 2006). The presetting of tools made with presetters or toolsetters produces substantial savings for companies, since the settings during the machining of the first part can be reduced or even eliminated, depending only on tolerance adopted in the process. It is a fast and reliable method for the measurement of diameters and lengths of tools. (Norton, 1990; WICK, 1995). Usually presetters are suitable for cases where lots of products are high, eliminating unproductive times if the process and consequently, reducing costs; however, Aronson (2000) says that not only with lots of large volumes of parts that are

7 interesting devices of these type, but also in lots of small volumes, this due to greater accuracy and the elimination of losses of parts in the process Types of presetting system Automatic presetting systems, as described by Aronson (2000), are designed for use on CNC machines, and can range from a simple system with only a mechanical touch to measure the length and diameter of the tool, to more complex systems that can analyze up to flaws in the surfaces of the tools. The information collected is sent to the CNC machine and then it makes the necessary correction to the tool does not come out of its originally programmed trajectory. Currently, in the Brazilian market are found internal presetting systems (called toolsetters) and external (so-called presetters) with many different operating and measuring principles. Table 1 shows the types that are found in the Brazilian market, identifying the principle of operation of each, as well as their respective manufacturer. The use of presetting equipments to obtain measurements of the tools is a faster, more reliably and accurately way, since the presetters and toolsetters perform this task inside and offside the CNC machine and data correction of the tool can be transferred to the CNC with confidence and without delay. This is a feature that allows companies to be somewhat at an advantage relative to its competitors who do not use this technology. Simon (2002) noted that the largest amounts of unproductive time among the specific activities of the operation of CNC machine tools are related to activities of preparation of the CNC program, transfer the program to the machine and adjusting tools. Based on these statements, reducing the setup time of machines is essential for companies to decrease their unit cost of parts, and just thinking about those times and reduce

8 operation cost, companies are looking for intelligent solutions such as systems for presetting. Table 1 Presetting equipments available in Brazilian market. Source: prepared by the authors. Manufacturer Type Model Accure Blum Easson Flexbar Fowler Trimos Marposs M&H Metrol Omron Renishaw Speroni Touch Master Urma Zoller Toolsetter Contact X X X X X X X X Laser X X X X X Optical X Presetter Contact X X Optical X X X X X 3. Losses due to the non-use of presetting According to Antunes ET AL (2008), the existing losses in the production systems are characterized by having its origins in process (overproduction, transportation, processing of materials, inventory and defects) or operation (unnecessary movement of the operator and wait queue of lots). Losses caused by setup operations can influence both in the process (losses in the processing of materials), and in the operation (losses for queue or waiting line). As mentioned earlier, the presetting of tools causes a significant increase in setup times and reduces the availability of machine usage. Often users of CNC machines do not have that notion, either for lack of knowledge of the technologies of automatic

9 presetting available, either for lack of information about the gain that the use of these systems can bring. In order to assist the user in these situations, it is proposed to provide an Internet page on which the calculation of the losses resulting from the completion of manual presetting can be seen. It uses the set of equations listed by Vieira Junior ET AL (2006), which consider as a starting point the difference between the times of manual presetting and automatic presetting per tool. The user then has the home page (Figure 3) the fields to be filled, in which states: - Number of CNC machines available in the company (including turning centers, machining centers, boring and milling machines); - Number of preparations (number of lots) that each machine processes on average per shift; - Average number of tools that each machine uses for each lot; - Number of days worked per month; - Number of shifts worked per day; - Number of hours of each shift; - Average cost of hour of machining.

10 Figure 3 - Home page of the calculation of time-consuming with manual presetting. After entering the initial data, the user sends it to calculate the following information (Figure 4): - Total time of CNC machines available for work, in hours; - Productive time, also in hours; - Unproductive time, also in hours; - Rate of utilization of CNC machines (in %); - Waste of time available (in %); - Equivalent number of machine stops indirectly by the time period considered.

11 Figure 4 Screen with the results referent to losses arising from the use of manual presetting. As an example, consider a company that has the following conditions to be filled in the screen shown in Figure 3): - 6 turning centers, that process daily, on average, six different lots, with an average of 8 per batch tools; - 5 machining centers that process daily four different lots, with an average of 18 per batch tools; - 3 boring machines, that render daily three different lots, averaging 3 per batch tools; - 2 milling machines, that render daily five different lots, with two different tools; - The company works 22 days a month in 3 shifts of 8 hours each, with an average of machining cost of $ per hour of work of the CNC machine.

12 This company presents the following scenario of losses caused only by performing the manual presetting (already presented in Figure 4): - From the total of 8,448 hours per month available from the CNC machine, a little bit more than 6,194 hours are used for production and about 2,253 hours are lost with the manual presetting; - This results in a machine rate of utilization of almost 73%. That means more than 25% of the total available time the machines are stopped to perform the manual presetting. That is equivalent to four CNC machines completely stopped almost every month due to this activity (manual presetting). If we consider the loss of time in which these machines can produce, you get to a waste of almost R $ 124, per month. These values, though fictitious, are not very different from those typically found on business users of CNC machines and are alarming, because it is a loss that is rarely seen. 4. Conclusions The times of presetting of tools on CNC machines have significant contribution to the composition of the setup times of the machines. The greater the number of tools used and the number of exchanges and lots of tools over the shifts, the greater the proportion of time that the machine is unavailable, especially against a backdrop of increasingly smaller lots. The completion of presetting the by manual method contributes in large part to the increase in setup time, and has several drawbacks such as dependence on operator experience and sensitivity that is dealing with the machine. Moreover, the fact that the

13 tool is measured statically, in a different condition from that which is used (with rotation), contributes to the occurrence of errors in assessment presetting. The proposal to provide an easily accessible page on the Internet for the calculation of such waste is interesting in that it reveals values of lost times, machine downtime and loss equivalent in any production that undermine a company's financial results. Even considering that the investment in a system of automatic presetting is high, the payoff for the gains of using these devices, whether presetters or toolsetters, is significant when compared to the losses that can be observed. 5. Acknowledgements The authors acknowledge FAPESP (Fundação de Amparo à Pesquisa do Estado de São Paulo São Paulo State Foundation for Research Improvement) for the financial support of the Project PIPE 06/ and UNINOVE (Universidade Nove de Julho) for the support for the development of this work. 6. References ANTUNES, J. et al Sistemas de Produção: conceitos e práticas para projeto e gestão da produção enxuta. Ed. Bookman, Porto Alegre, 2008, 328p. ARONSON, R.B. Presetting: Prelude to Perfection. Manufacturing Engineering. Dearborn, v. 124, n. 2, p , BEARD, T. Setting tools makes small shop sense. Modern Machine Shop. Cincinnati, v. 70, n. 8, p , CORRER, I.; MARTINS, R.O.; VIEIRA JUNIOR., M. Avaliação do índice de utilização de máquinas ferramentas CNC em uma empresa de usinagem, por meio da

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