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Procedia CIRP 29 ( 2015 ) 293 – 298

The 22nd CIRP conference on Life Cycle Engineering Life cycle oriented tool management in small scale production

Dominik Heeschena* Fritz Klockeb Kristian Arntza

aFraunhofer-Institute for Production Technology (IPT), Steinbachstraße 17, 52074 Aachen, Germany bLaboratory for Machine Tools and Production Engineering (WZL), RWTH Aachen University, Steinbachstrasse 19, 52074 Aachen, Germany * Corresponding author. Tel.: +49-241-8904-324; fax: +49-241-8904-6324. E-mail address: [email protected]

Abstract

The milling technology is characterized as the most important technology in a variety of industries. Moreover, recent developments in hardware and software issues have increased technology’s complexity which is, beyond others, caused by different milling variants and a high number of different milling tools. Milling tools are responsible for a significant cost position in manufacturing driven companies which is shown in the paper by an industry wide survey. Due to the costly and wasteful production it can be shown that this is a significant cost driver. This paper introduces an integrated life cycle oriented approach for the standardization and optimization (including the reuse of tools by standardized repair processes) of milling tools in order to enhance the life cycle of milling tools, reduce overall costs and therefore raise the company’s sustainability. © 20152015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (Peerhttp://creativecommons.org/licenses/by-nc-nd/4.0/-review under responsibility of the International). Scientific Committee of the Conference “22nd CIRP conference on Life Cycle PeerEngineering.-review under responsibility of the scientifi c committee of The 22nd CIRP conference on Life Cycle Engineering

Keywords: Life Cycle Management; Life Cycle Optimization; Life Cycle Costing; LCC; Manufacturing; Milling Tools

1. Introduction equipment and projects [5]. A more detailed definition is proposed by Landers [6]: “Life cycle costs are summations of Manufacturing is a significant important industry for many cost estimates from inception to disposal for both equipment economies. About 16 % of global GDP in 2012 is contributed and projects as determined by an analytical study and estimate by the manufacturing industry [1]. In the context of of total costs experienced in annual time increments during manufacturing, especially European companies have to cope the project life with consideration for the time value of with global cost competition. Their financial and technical money”. Main purpose of LCC is determining cost- performance must remain at the desired and competitive level. effectiveness of alternative investments and business Many improvement projects are targeted to enhancement of decisions, from the perspective of an economic decision performance levels which can be seen in current literature [2]. maker such as a manufacturing firm or a consumer [7]. Life Cycle Engineering is a key to enhance financial and LCA is characterized as “a technique to assess technical performance by concurrent considering their environmental impacts associated with all the stages of a environmental impact. The question of how to minimize product’s life from cradle-to-grave” [8]. According to environmental loads and resource consumption throughout a Klöpffer the basic principles of LCA are the following [9]: product life cycle (LC) is a major issue in the manufacturing industry [3]. Analyzing the literature, two methodologies were x The analysis from cradle-to-grave developed during the past years to analyze life cycles as well x All mass and energy flows, resource and land-use, etc., and as to evaluate costs and environmental impacts generated the potential impacts connected with these ‘interventions’, along the whole life cycle: Life Cycle Costing (LCC) and Life are set in relation to a ‘functional unit’ as a quantitative Cycle Assessment (LCA) [4]. measure of the benefit of the system(s) LCC is characterized as “cradle-to-grave costs summarized as an economic model of evaluating alternatives for

2212-8271 © 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the scientifi c committee of The 22nd CIRP conference on Life Cycle Engineering doi: 10.1016/j.procir.2015.02.048 294 Dominik Heeschen et al. / Procedia CIRP 29 ( 2015 ) 293 – 298

x LCA is essentially a comparative method (also Tool Work Tool storage M ac hining Tool storage Tool disposal improvements of one system are compared to the status procurement preparation quo). Tool Tool measuring checking Literature review shows that the main objective of LCC Regrinding and LCA lies in development or selection of LC optimized Core processes products within the B2B or B2C business. Up to now, there is no discussion for the case that the user is not able to influence Figure 2: Rough analysis of milling tool's life cycle the product design or the product design is not sufficient for adaption on life cycle oriented design. In spite of this lack of companies. exertion of influence, life cycle engineering can be used to optimize the cost and environmental effectiveness of 2. Investigation of life cycle analysis of milling tools industrial goods. This paper introduces an innovative approach for enhancement of cost effectiveness by using life As a first step for life cycle oriented management of cycle engineering tools for products which cannot be milling tools their detailed life cycle within a manufacturing influenced by the decision-making company. That means that company was analyzed. This analysis was conducted top- out of the three fundamental phases in life cycle management down, which means that the first step was a rough analysis of we focus on the life time management. involved departments, their interactions, in process loops and For this purpose the authors selected the application of necessary data flows. This rough analysis is based on a flow milling tools as prime example for an industrial good which chart development, which is shown in Figure 2. cannot be influenced by a company. Milling is next to turning The flow chart shows the life cycle of a single milling tool the most applied cutting technology in manufacturing which begins with the procurement and subsequent storage of companies. Furthermore, cutting tools are a relevant cost the tool. After measuring and determination of needed driver in modern manufacturing companies. A study was technological process parameters the tool is applied within the conducted in Germany with 292 participants. Beyond others it . If the predicted milling tool’s life time is was identified that cutting tools have a share of about 12% of reached during processing, the tool will be transferred to tool overall manufacturing costs (see Figure 1). checking. The tool checking will investigate if the milling tool The technology is characterized by multiple process is still operational, a regrinding is required (and possible), or a variants which also include different kinds of milling tools. It disposal is necessary. In the case that the tool is still is possible to characterize milling tools beyond others in terms operational the tool is moved back to the start of the process of their shape, application fields, material, diameter, etc. flow. If a regrinding is necessary, the tool is moved to the Furthermore, the life cycle oriented management focused on regrinding and subsequently moved to the start of the process manufacturing industries is characterized by small scale flow, too. production. That means that there are small lot sizes of This rough analysis has shown that the level of detail is not workpieces and these do not have any repetition frequency. sufficient for a holistic life cycle analysis, which is caused by This results in a further complexity enhancement since two facts. First life cycle data cannot be integrated within the process flows and milling tool consumption vary. Moreover, flow chart in order to perform a quantitative analysis. But a there is no consistent tool wear so that predictability of tool quantitative analysis is required in order to execute an lifetime and process flow is limited. optimization. Second milling tool’s process flow could not be The process flow of milling tools in manufacturing analyzed with the necessary level of detail, since the companies is highly complex and experience shows that there transparency of the chart does not provide a detailed analysis. are many inefficiencies within the process flow. Due to this For this reason, it was decided to apply a special process fact, this paper shows that the process flow of milling tools modelling language which was specifically developed for non- can be optimized by using life cycle engineering tools in order standardized processes and offers a maximum of transparency. to enhance the cost effectiveness of manufacturing

20 21,6 20,4 20,2 15

13,7 10 12,1 12,0

Costs [%] 5

0 Others Services External External Cutting Tools Raw Material Standard Parts Manufacturing

Figure 1: Cost shares within manufacturing

Figure 3: Process element of aixperanto modelling language Dominik Heeschen et al. / Procedia CIRP 29 ( 2015 ) 293 – 298 295

This modelling language is called aixperanto and was tool application so that tool procurement is highly project developed by researchers at the Laboratory for machine tools related. This lack of standardization causes many (WZL) at Aachen University in Germany. Developed for the inefficiencies within the life cycle which will be described at industry practice it has been used for scientific topics, too. selected process steps. Albers et al. used aixperanto for modelling a reference process After tool procurement the milling tools have to be stored for tool-based micro technologies [10]. in a central tool storage since the machine internal storages Main components of aixperanto are horizontal swimlanes, have limited space. This is due to the fact that the variety and detailed process descriptions, and process connections. The consequently the number of milling tools is high. horizontal swimlanes illustrate different involved parties The tool application begins with fixing the tool into the tool within the process flow, e.g. manufacturing, work preparation, holder. In common this is a standardized process. This process data storages, etc. The differentiation between involved contains two central problems. First, commonly different tool parties enables the cross-functional life cycle analysis of holders are necessary because of milling tool variety. That milling tools within a company. reduces the standardization degree and lowers the possibility Aixperanto’s process descriptions contain a rash of process to track different technological impacts during . details in order to characterize the milling tool’s life cycle (see Second, tool holders in precision manufacturing are quite Figure 3). Beyond others it contains a characterization of the expensive whereas a reduction is difficult when using lots of process content, evaluation of the value adding, different milling tools. standardization degree as well as time, cost, and resource Time parallel to the tool fixing CAM (computer aided aspects. Process connections visualize the interconnections of manufacturing) programs have to be created for the single processes within the life cycle and furthermore contain workpiece. The programs contain beyond others the information about the kind of material or data flow. technological parameters for each applied milling tool as well In a first step the processes contained within the life cycle as a forecast for the lifetime of each tool in order to take into have been detected and described. After this these processes account that tool changes are necessary during machining. are characterized according to above mentioned descriptions. Today, CAM programming is focused on the quality of the After connecting these single processes by material and data result and hardly considers life cycle oriented aspects. These flows, weaknesses within the life cycle have to be identified. aspects should include the tool life time and tool life travel Weaknesses are documented by a flash (to be seen in Figure path which expresses the tool life in terms of time and path 4). length [11], respectively. The life cycle shown in Figure 4 is a tentative draft the After tool fixing the tool and its holder are transferred to authors developed with an industry consortium of 13 measuring. Here displacement data is measured in order to manufacturing companies. The whole life cycle of a milling guarantee required precision during machining. This data is tool within a manufacturing company is explained in detail in transferred to the machine tool which uses this data when the the following based on this tentative draft. specific tool is applied. The measured tool is transferred to the The first process step in milling tool’s life cycle is project machine internal storage and thus ready for machining. related tool procurement. Because of low repetition frequency Machining starts with consolidation of workpiece, CAM most companies do not have comprehensive tool program and milling tool. In many manufacturing firms, standardization. This results in the need for workpiece specific machining processes are observed by workers in order to 296 Dominik Heeschen et al. / Procedia CIRP 29 ( 2015 ) 293 – 298

guarantee machining quality. This is especially due to the fact action. The model’s fields of action cover identified problems that tool life time and tool life travel path are commonly not in terms of milling tool management. known. Both figures are detected by worker’s experience e.g. Problems associated with the technological perspective of machining noise and vibration. Tool life travel path is not only milling processes occur mainly because of a lack of dependent on cutting parameters and workpiece material but standardization within the milling tool portfolio. Tools are also on engagement geometry. Since the repetition frequency procured customer project based and show a high variety. As is almost zero, it is not possible to derive tool life travel paths already stated standardized milling tools provide lots of from experience or by statistical data. Moreover, not known advantages for manufacturing companies. Due to this positive tool life time or tool life travel paths result in quality problems impact of milling tool standardization it is defined as the first which have a huge cost impact when producing lot sizes of action field of the model. one. Cost aspects are also related to the fact that machining The process presented in Figure 4 was documented within processes have to be observed by workers. In serial a basically well organized company. Nevertheless many productions the processes are more stable so that a worker discontinuities and problems were identified. Moreover, the may observe several machines or it is possible to produce non-standardized process led to inefficiencies of the overall without work force for a specific lapse of time. That results in organization since employees had to do many enquiry calls lower labor costs per machined workpiece. and milling related tasks were characterized by technical By the end of a machining process the milling tool is faults. checked in regard with tool wear and its impact on subsequent A positive correlation was identified between worker tool application. Tool checking mainly considers wear in experience and accurate product quality and its productivity. terms of crater wear, flank wear, and notch wear. These wear This correlation is historically strong but in modern mechanisms can be detected by special measurement knowledge based organizations inacceptable. For this reason, instruments. In spite of wear detection, an implication for the the suggestion is a strict standardization of the overall process tool life cycle in terms of remaining tool life time and tool life in order to reduce steering effort and the risk of cost intensive travel path is not necessarily possible. This fact needs special discontinuities. Milling process (as presented in Figure 5) attention, since there is no quantitative method for forecasting standardization is therefore defined as the second action field the remaining life cycle. of our model. At the end of checking a decision has to come how to Machining process and applied milling parameters form proceed with milling tools. In general, three alternative ways the core of any milling process. It was identified that milling are possible. First, the tool is still operational and it is given parameters are often set by experience and solely focus on back to the machining process or tool storage waiting for the quality and process stability. Especially in small scale next application. Nevertheless, it is now a used tool which will productions quality and process stability should be in the not show the manufacturing capability of a new milling tool in focus of any production planning. But in today’s global terms of surface quality and life time. Second, the milling tool competition and associated cost pressure a manufacturing is feasible for regrinding. That means the milling tool is company has to take efficiency issues into account, too. transferred to another process step which can be characterized For this purpose, we propose to set milling parameters life as a typical recycling. The worn-out milling tool gets cycle oriented under consideration of life cycle costing. devarnished, regrinded and revarnished. After this, the tool is Consequently, our model should contain life cycle oriented ready for a new milling application. The third alternative is a milling parameters. tool’s disposal since regrinding or reuse is not possible. This The presented milling process has shown that several alternative is characterized as the end of a milling tool’s life decisions have to be made. Beyond others there are two cycle. central decision processes which are more or less quantitative The whole life cycle is characterized by a number of based, which have a fundamental impact on milling tool’s life decision processes. As already stated many of these decisions cycle. are based on experience. The analysis of a milling tool’s life First, selecting the right milling strategy and associated cycle discloses many important fields of action within milling milling tools is conducted by CAM programming. Today’s tool’s management for small scale manufacturers. The life CAM programming in small scale productions decides for cycle analysis also showed that any local optimization is not every workpiece again which milling tools have to be applied. sufficient. For this reason, a model for the milling tool’s Although, this decision cannot be suppressed since management in manufacturing companies was developed. workpieces differ in those productions the foundation for This model is introduced and described in the following these decisions should be quantitatively founded. This results chapter. in comprehensible results. Second, the decision about the further application of 3. Model for holistic life cycle oriented milling tool milling tools after machining is life cycle relevant. Three management alternative procedures have been identified for this case which differs in their cost impact heavily. After machining the tool Within the milling process (see Figure 4) the main can be used again because of acceptable wear, it can be problems were described in chapter 2. In order to derive a brought to regrinding in order to refresh its technical holistic model for a life cycle oriented milling tool performance, or it can be sorted out. The decision which management it is necessary to detect the overall fields of procedure is taken within the industry practice is mostly based Dominik Heeschen et al. / Procedia CIRP 29 ( 2015 ) 293 – 298 297

Furthermore, the studies are focused on serial production C ontinuous Milling Technology D evelopment which is characterized by different boundary conditions in terms of CAM programming sequence and optimization Milling Tool S tandardization M illing P roc es s S tandardization potentials.

Focus on high Technological S atis fac tory S tatus-Q uo Further research has shown that there are no relevant runner tools ideal tool portfolio S tatus-Q uo O ptimization studies on life cycle oriented milling parameters, milling

Resource-oriented P rocess-oriented process standardization, and verified, quantitative decision making in the field of milling tools. Life cycle engineering Life C ycle oriented Milling Verified, quantitative Decision P arameters Processes was mostly done in the field of adapting products in order to achieve optimized life cycles. Quality Cost guarantee Tool Life C ycle Tool selection guarantee Due to our new approach on using life cycle engineering on products the user cannot influence or reengineer, there is a C onverting E xperience to K nowledge lack of knowledge up to now. This encouraged us to set-up a research project with 13 Figure 5: Model for life cycle oriented milling tool management manufacturing companies in order to find suitable solutions for the identified action fields. The developed framework is on worker’s experience. For this reason verified and our first result. quantitative decision processes as the fourth action field of our model were defined. 4. Conclusion and outlook In our model, the four identified action fields are surrounded by two central managerial aspects. Continuous This paper introduces a model for life cycle oriented milling technology development is necessary in order to milling tool management in small scale productions. An improve status-quo over time. Innovative technology industrial project considering 13 manufacturing companies developments must be considered and evaluated for a future from Germany supports this study which guarantees the application within the company. Furthermore, a structured industrial relevance of the topic. This research introduces a process for converting experience into knowledge is new approach of life cycle management since it does not necessary. This transforms a manufacturing company to a focus on the engineering of life cycle optimized products but knowledge-driven company in order to fulfill the introduced how to handle industrial equipment which cannot requirements of today’s knowledge society. be influenced by end users. This is especially relevant for The final model for the life cycle oriented milling tool small and medium sized companies. management in small scale productions is presented in The developed model consists of four main action fields figure 5. which are surrounded by two managerial aspects. The main The developed model provides a framework for the life action fields for the life cycle oriented management of milling cycle oriented management of milling tools in small scale tools in small scale productions are: productions. Identified action fields have to be detailed in order that this framework forms an industry-relevant x Milling tool standardization with two subtasks of focusing optimization tool. Literature review of relevant scientific on high runner tools and development of a technologically work has shown that identified action fields are not ideal portfolio by considering life cycle costing aspects. sufficiently elaborated. x Development of milling parameters which have to be Currently milling tool standardization is just a side issue in designed for life cycle optimized application with a special production research. Usher and Fernandes [12] developed a focus on life cycle costing aspects. systematic method for identifying and ranking alternative tool x Standardization of the whole milling process starting with sets, machine sets, and plan sets for a given part. The system milling tool procurement and ending with the decision how has to match the geometrical and technical requirements of to proceed with applied milling tools. A standardized the job with the available set of tools within the shop floor. process is the perfect basis for further optimizations. A Fernandes and Raja introduced an integrated system to process modelling language was introduced from Germany capture the experience of a worker by heuristic methods, to this new topic which is suitable for status-quo analysis and to compute analytically the cutting parameters [13]. and subsequent optimization. This work is completed by those that based on CAD x Whole milling process has to be supported by verified standards files extraction which exemplary done by Lim et quantitative decision processes which are particularly al. [14], Zhao et al. [15], or Shakeri [16]. Furthermore, located on the process steps of milling tool selection and Balasubramaniam et al. proposed a procedure analyzing tool checking. the reachable region for complex tools (embedded in a stacked cylinder model) for three axis machining [17]. Lim This model shows a further development of existing life developed a similar approach, exploiting the effects of cycle engineering approaches. It especially enlarges the residual material [18]. applicability of life cycle related research. The detailing of The analysis of these studies has shown that a main focus introduced action fields within the model will be the next step is set to selecting the technologically optimal solutions but of our research. without considering any life cycle oriented aspects. That means that costs and complexity are not considered. 298 Dominik Heeschen et al. / Procedia CIRP 29 ( 2015 ) 293 – 298

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