- Email: [email protected]
Identifying automated component handling requirements in a small batch multiple variant production system
Robotics and Computer Integrated Manufacturing 17 (2001) 139}143
Identifying automated component handling requirements in a small batch multiple variant production system N.F. Edmondson *, A.H. Redford Grundfos A/S, Poul Due Jensens Vej 7, 8850 Bjerringbro, Denmark University of Salford, UK
Abstract Traditional automation solutions are invariably implemented in a piecemeal way, where feeding and handling solutions are only selected based on the requirements of a speci"c process. This results in a wide variety of di!erent technological solutions being implemented across a factory, resulting in high maintenance costs and duplication of resources. Furthermore, automation is traditional restricted to low-variety high-volume production, where the capital cost can be easily justi"ed. However, the global market is demanding greater product variety, which results in high component variety and small batch production making traditional dedicated automation solutions uneconomical. This paper presents a methodology for component classi"cation which, identi"es #exible component feeding and handling solutions for each component group within a particular factory. The methodology analyses the component #ow within a factory and identi"es six non-value adding component handling activities. An ABC analysis is used to identify the components and processes which involve the most handling operations. Based on the results of the ABC analysis, components are grouped according to the #exible feeding and handling solution which they best suit. The analysis concludes by presenting four component groups and, four #exible feeding and handling solutions. 2001 Elsevier Science Ltd. All rights reserved. Keywords: Classi"cation; Part feeding; Flexible
1. Introduction The European Economic Community are introducing strict Health and Safety regulations concerning repetitive strain injury and noise levels. Denmark also has one of the highest labour overhead rates in Europe which will increase with the implementation of the new regulations. To overcome these restrictions and to improve its manufacturing systems pro"tability Grundfos has instigated a series of automation projects. A key requirement of any automated production system is the continuous supply of components having a de"ned position and orientation. The requirement for greater product variety has resulted in greater component variety, and smaller batch production which makes the use of traditional automation methods uneconomical. The Global market place is also changing; customers require greater variety, shorter lead times, higher quality and more competitive prices. This has resulted in a need
* Corresponding author. Tel.: #45-87-50-40-70. E-mail address: [email protected] (N.F. Edmondson).
to develop a new internal logistics system to enable the #exible automation of key processes including machining, casting, forming and "nal assembly and reduce operating costs whilst increasing e$ciency. Currently, components are transported within Grundfos in Euro-pallets having no de"ned position or orientation, and this requires operators to repetitively handle components in potentially hazardous environments. This paper presents a methodology which can be applied to any factory in order to identify the activities which involve the most component handling operations and, identify #exible part handling alternatives. The methodology is based on the study of a factory owned by Grundfos A/S in Denmark, `Factory Xa. 2. Factory classi5cation systems A classi"cation system is a method of organising knowledge by sorting and analysing information and grouping similar features, facts and elements. The various classi"cation groups are then represented by symbols, digits or group of digits [1].
0736-5845/01/$ - see front matter 2001 Elsevier Science Ltd. All rights reserved. PII: S 0 7 3 6 - 5 8 4 5 ( 0 0 ) 0 0 0 4 7 - 8
140
N.F. Edmondson, A.H. Redford / Robotics and Computer Integrated Manufacturing 17 (2001) 139}143
Table 1 Summary of classi"cation systems Classi"cation system
Function
Source
Opitz system
GT coding system developed by the Institute of Machine Tools and Production Engineering at Aachen university.
[3]
E Based on a component survey in the machine tool industry. E The main advantage is that the system can be easily implemented without the need for specialists. E The main disadvantage is that it does not represent all industrial sectors. Brisch system
E E E E
Classi"cation for forging
E Aids group technology and gives an indication of the di$culty of a particular operation, hence allowing design evaluation.
[4]
Classi"cation for assembly
E Aids GT in single small batch production of machine assemblies.
[5]
Classi"cation for structural engineering
E Group technology implementation and variety reduction.
[6]
Classi"cation for automatic handling of parts
E Based on the suitability of parts for vibration feeding. E Aids group technology and design for feeding and orienting. E Originally designed to facilitate the selection of automatic handling techniques and tooling for parts.
[7]
Taylor made to suit a companies product range. Covers all product features within a company. Eight digit hierarchical code. Complex and di$cult to implement.
Classi"cation system for manual E Analytical method for analysing the ease of which products can be assembled and automatic assembly using manual, dedicated automation and robotic assembly systems.
[1] (original source unknown)
[8]
Fig. 1. The seven process activities.
One of the earliest industrial classi"cation systems was Group Technology (GT) [2]. GT groups components which require the same or similar machining operations and, similar machine tool set-ups and adjustments, placing them on the same machine tool. The bene"t being that savings in set-up time can be made as there is little di!erence from one component to the next, allowing small and medium batch production systems to operate in a similar fashion as continuous production systems. A standard work plan and machine set-up is created for each component group based on the characteristics of a composite component, which contains all the features of the components within the group. Swift [1] presented a detailed review of classi"cation systems, of which is shown in Table 1. However, no system exists which attempts to standardise the material handling and feeding systems across a complete factory by identifying classes of feeding systems to cover the majority of products.
3. Production facility analyses The "rst level of analysis focused on the internal logistics of the factory to gain an insight into the type of problems within the production system, the #ow within a single department was analysed. The key components within the department were identi"ed and tracked through the production system. From the component #ows it was observed that for every process there are seven activities as shown in Fig. 1. The only value adding activity is the process; the storage, transportation, loading and unloading activities (manual handling) increase the cost and time of production. The impact of this on the production system can be understood by considering that in the factory analysed, some components require 16 di!erent operations each involving the six non-value adding activities and, batch sizes ranged from 450 to 4000 units i.e. 16 operations ;6 non-value adding activities"96 non-value adding
N.F. Edmondson, A.H. Redford / Robotics and Computer Integrated Manufacturing 17 (2001) 139}143
activities for a single component. Multiplying this by a batch size of 4000 results in 384 000 non-value adding activities. It should also be noted that regardless of the process, the non-value adding activities remain the same and a methodology which can be developed reduces them or conducts them in a more e$cient manner and can be applied to every process. The six non-value-adding activities will always exist in any production system. However, the frequency which they occur and the manner in which they are conducted have a considerable e!ect on the productivity of the production system. The study of the factory highlighted that there was a high degree of manual handling and large bu!er stocks within the production system which resulted in sluggish and ine$cient production and an average component production lead time in excess of "ve weeks. From the initial study, it is also evident that many of the operations such as pressing, stamping, and welding are highly repetitive, and suitable for automation. However, if an automated system was used it would have to be capable of handling many variants in small batches (target: one days production requirements) which would require a low cost, #exible material handling system.
4. Flexible automation and feeding Traditionally automation has been applied to highly repetitive tasks, as a method of increasing the e$ciency of the non-value adding activities. However, component variety and, small batch production makes the use of traditional automation methods uneconomic for many areas in the factory. A number of studies have been conducted into #exible automation and particularly its use in assembly [9,10]. The studies identi"ed that the main obstacle in the economic application of #exible automation systems e.g. robot cells, is the lack of #exible component feeding devices, which are economically priced and meet the short cycle time requirements. For this reason the components handled within the factory were analysed based on their geometry and size, so that appropriate #exible feeding systems could be identi"ed or developed.
141
Fig. 2. Graph showing key process in Factory X.
X uses a computerised stock and materials #ow system which records the quantities of individual components ordered each year, their batch sizes, and their process route. Using this computer system, it was possible to determine the components which required the most handling by identifying the components with the largest batch size being ordered the most and having most of the operations. Analysing the process routes of the `Aa group revealed that punching processes had the greatest load followed by pressing and welding, this is shown in Fig. 2. Most of the stamping, pressing and welding processes follow the model outlined in Fig. 1, and require an operator to feed, orientate, process and unload each part, with the exception of the dedicated automation systems. The stamping and welding operations have the same characteristics and in some cases can be performed on the same machines.
6. Component groups The top 60% of the components handled were collected and grouped based on their size, geometry and which automated feeding method they best suited. The following component groups and feeding solutions were identi"ed: 6.1. Group 1: discs
5. Where is the handling problem the greatest? It was important to identify where the handling problem was the greatest within Factory X as "nding a solution for this point would provide the greatest savings and demonstrate the solutions robustness. An ABC analysis using a 60}30}10 ratio was conducted to identify the components which involve the most handling. Factory
A large majority of components within Grundfos begin their lives as circular metal discs (height/diameter (0.8) see Fig. 3, which are pressed into three-dimensional shapes or have holes punched in them. All the discs are transported from the punching factory in Euro-pallets following which they are manually separated and fed to a press or stamping machine. Alternatively, they are
142
N.F. Edmondson, A.H. Redford / Robotics and Computer Integrated Manufacturing 17 (2001) 139}143
Fig. 3. Disc geometry.
Fig. 5. Small complex components.
size and cycle time. The manual loading task takes an average of 5 min and minimises manual handling. The payback of a robot process cell incorporating such a devise is generally less than 1 year. 6.3. Group 3: small complex
Fig. 4. Cylindrical components.
manually loaded into a magazine feeder which separates and feeds the discs to a press or stamping machine. The major disadvantage of these handling techniques is that they involve repetitive manual handling of components having sharp edges and which are covered in oil. This is not only hazardous to operators but also a nonvalue adding activity. Based on this, a feeding system has been developed which can automatically separate and feed directly from the Euro-pallet, at a rate of 2 blanks every second, which gives a wide variety of blank sizes, and a pay back time between 0.5 and 1 year depending on the cycle time. 6.2. Group 2: cylinders This group of components is approximately symmetrical with a height/diameter ratio *0.8 and )1.5, with a main dimension greater than 80 mm e.g. cups, short tubes and impellers. This component group is often the product of pressing operations where discs are transformed into cylindrical components. Non-symmetrical features may be present in the form of o! centre holes or projections see Fig. 4. A simple belt feeder has been developed and implemented which can be quickly adjusted to handle di!erent cylinder diameters. The feeder is manually loaded and has a capacity of 30}60 min work depending on component
This group contains those components traditionally handled using vibratory bowl feeders having their smallest dimension less than (80 mm (see Fig. 5). A more detailed description of components, having suitable features for vibratory bowl feeding is described by Swift [1]. A new high speed #exible feeding device has been developed which is capable of feed rates in excess of 60 parts/min. The system can be automatically set-up to feed di!erent component types simply by selecting a new control program. The feeding system cost is equivalent to that of a standard vibratory feeder and allows a payback of less than 1 year. 6.4. Group 4: large components This group contains components which are not symmetrical, have their smallest dimension greater than 80 mm or are fragile; examples are motor assemblies an long tubes. It is not practical or cost e!ective to feed this group of components using active feeding systems or the belt feeder. The most practical solution for this group of components is the use of modular pallet magazines, where component pallets are assembled from standard modules. The cost of such a system is high and depends on the quantity of pallets required.
7. Flexible process cell The four standard handling systems can be used to construct #exible automation systems focused around key processes as identi"ed in Fig. 2. Such cells would achieve the payback targets by automating the production of many di!erent components using a single automated cell, allowing the capital investment to be distributed over a number of di!erent components not just one as with dedicated automation systems. The control of the #exible process cell is via the Kanban system,
N.F. Edmondson, A.H. Redford / Robotics and Computer Integrated Manufacturing 17 (2001) 139}143
143
10. Further work E The basic methodology needs to be applied to more facilities to demonstrate its robustness. E The classi"cation system needs further development to increase the number of feeding and handling solutions, and to enable easier identi"cation of component groups. E The concept of the #exible process cell could be extended to include automated assembly.
Fig. 6. The automated #exible process cell.
enabling the factory stock levels to be minimised. The concept is illustrated in Fig. 6. 8. Limitations The basic methodology to date has only been applied to one factory and it cannot be claimed that this technique is truly universal. However, the ABC analysis can be applied to a wide variety of di!erent production facilities to identify feeding and handling systems, although they will not always be the same as those identi"ed in this study. 9. Conclusions E Every process requires six non-value adding activities. E Regardless of the process the non-value adding activities remain the same. E The processes which require the most manual handling can be identi"ed by performing an ABC analysis. E Components can be divided into four groups which can be handled and fed using four #exible automation methods. E The #exible automation methods can be combined with the process involving the most handling operations to form #exible process cells.
Acknowledgements This work was supported through funding from Grundfos A/S Denmark.
References [1] Swift KG. A system of classi"cation for automatic assembly. M.Sc thesis, University of Salford, 1980. [2] Mitrofanov SP. National Lending Library for Science and Technology, 1959. [3] Opitz H, Eversheim W, Wiendal HP. Workpiece classi"cation and its industrial classi"cation and its industrial application. Int J Mach Tool Des & Res 9:39. [4] Spies K. Eine Foremenardung fur Gensenk chienderstucke, Werkstattstechnik, 2, 1957. [5] Eversheim W, Miese M. Group technology developments and modes of application. Proceedings of the 15th Machine Tool Design and Research Conference. Oxford: Pergamon Press, 1975. [6] Chow CC, Gallagher CC. Classi"cation of structural engineering components and assemblies for group technology, J Mechan Working Technol 1977;1:67}84. [7] Boothroyd G. Automatic handling of small parts. CIRP Ann 1975;24(1):393. [8] Boothroyd G, Dewhurst P. Product design for assembly Boothroyd Dewhurst, Inc., 212 Main street, Wake"eld, RI 02879, USA, 1986. [9] Zenger D, Dewhurst P. Automatic handling of parts for robot assembly. CIRP Ann 1984;33:279. [10] Redford AH, Lo EK, Killeen PJ. Parts presentation to multi-arm assembly robots. CIRP Ann 1983;32:399.
Identifying automated component handling requirements in a small batch multiple variant production system N.F. Edmondson *, A.H. Redford Grundfos A/S, Poul Due Jensens Vej 7, 8850 Bjerringbro, Denmark University of Salford, UK
Abstract Traditional automation solutions are invariably implemented in a piecemeal way, where feeding and handling solutions are only selected based on the requirements of a speci"c process. This results in a wide variety of di!erent technological solutions being implemented across a factory, resulting in high maintenance costs and duplication of resources. Furthermore, automation is traditional restricted to low-variety high-volume production, where the capital cost can be easily justi"ed. However, the global market is demanding greater product variety, which results in high component variety and small batch production making traditional dedicated automation solutions uneconomical. This paper presents a methodology for component classi"cation which, identi"es #exible component feeding and handling solutions for each component group within a particular factory. The methodology analyses the component #ow within a factory and identi"es six non-value adding component handling activities. An ABC analysis is used to identify the components and processes which involve the most handling operations. Based on the results of the ABC analysis, components are grouped according to the #exible feeding and handling solution which they best suit. The analysis concludes by presenting four component groups and, four #exible feeding and handling solutions. 2001 Elsevier Science Ltd. All rights reserved. Keywords: Classi"cation; Part feeding; Flexible
1. Introduction The European Economic Community are introducing strict Health and Safety regulations concerning repetitive strain injury and noise levels. Denmark also has one of the highest labour overhead rates in Europe which will increase with the implementation of the new regulations. To overcome these restrictions and to improve its manufacturing systems pro"tability Grundfos has instigated a series of automation projects. A key requirement of any automated production system is the continuous supply of components having a de"ned position and orientation. The requirement for greater product variety has resulted in greater component variety, and smaller batch production which makes the use of traditional automation methods uneconomical. The Global market place is also changing; customers require greater variety, shorter lead times, higher quality and more competitive prices. This has resulted in a need
* Corresponding author. Tel.: #45-87-50-40-70. E-mail address: [email protected] (N.F. Edmondson).
to develop a new internal logistics system to enable the #exible automation of key processes including machining, casting, forming and "nal assembly and reduce operating costs whilst increasing e$ciency. Currently, components are transported within Grundfos in Euro-pallets having no de"ned position or orientation, and this requires operators to repetitively handle components in potentially hazardous environments. This paper presents a methodology which can be applied to any factory in order to identify the activities which involve the most component handling operations and, identify #exible part handling alternatives. The methodology is based on the study of a factory owned by Grundfos A/S in Denmark, `Factory Xa. 2. Factory classi5cation systems A classi"cation system is a method of organising knowledge by sorting and analysing information and grouping similar features, facts and elements. The various classi"cation groups are then represented by symbols, digits or group of digits [1].
0736-5845/01/$ - see front matter 2001 Elsevier Science Ltd. All rights reserved. PII: S 0 7 3 6 - 5 8 4 5 ( 0 0 ) 0 0 0 4 7 - 8
140
N.F. Edmondson, A.H. Redford / Robotics and Computer Integrated Manufacturing 17 (2001) 139}143
Table 1 Summary of classi"cation systems Classi"cation system
Function
Source
Opitz system
GT coding system developed by the Institute of Machine Tools and Production Engineering at Aachen university.
[3]
E Based on a component survey in the machine tool industry. E The main advantage is that the system can be easily implemented without the need for specialists. E The main disadvantage is that it does not represent all industrial sectors. Brisch system
E E E E
Classi"cation for forging
E Aids group technology and gives an indication of the di$culty of a particular operation, hence allowing design evaluation.
[4]
Classi"cation for assembly
E Aids GT in single small batch production of machine assemblies.
[5]
Classi"cation for structural engineering
E Group technology implementation and variety reduction.
[6]
Classi"cation for automatic handling of parts
E Based on the suitability of parts for vibration feeding. E Aids group technology and design for feeding and orienting. E Originally designed to facilitate the selection of automatic handling techniques and tooling for parts.
[7]
Taylor made to suit a companies product range. Covers all product features within a company. Eight digit hierarchical code. Complex and di$cult to implement.
Classi"cation system for manual E Analytical method for analysing the ease of which products can be assembled and automatic assembly using manual, dedicated automation and robotic assembly systems.
[1] (original source unknown)
[8]
Fig. 1. The seven process activities.
One of the earliest industrial classi"cation systems was Group Technology (GT) [2]. GT groups components which require the same or similar machining operations and, similar machine tool set-ups and adjustments, placing them on the same machine tool. The bene"t being that savings in set-up time can be made as there is little di!erence from one component to the next, allowing small and medium batch production systems to operate in a similar fashion as continuous production systems. A standard work plan and machine set-up is created for each component group based on the characteristics of a composite component, which contains all the features of the components within the group. Swift [1] presented a detailed review of classi"cation systems, of which is shown in Table 1. However, no system exists which attempts to standardise the material handling and feeding systems across a complete factory by identifying classes of feeding systems to cover the majority of products.
3. Production facility analyses The "rst level of analysis focused on the internal logistics of the factory to gain an insight into the type of problems within the production system, the #ow within a single department was analysed. The key components within the department were identi"ed and tracked through the production system. From the component #ows it was observed that for every process there are seven activities as shown in Fig. 1. The only value adding activity is the process; the storage, transportation, loading and unloading activities (manual handling) increase the cost and time of production. The impact of this on the production system can be understood by considering that in the factory analysed, some components require 16 di!erent operations each involving the six non-value adding activities and, batch sizes ranged from 450 to 4000 units i.e. 16 operations ;6 non-value adding activities"96 non-value adding
N.F. Edmondson, A.H. Redford / Robotics and Computer Integrated Manufacturing 17 (2001) 139}143
activities for a single component. Multiplying this by a batch size of 4000 results in 384 000 non-value adding activities. It should also be noted that regardless of the process, the non-value adding activities remain the same and a methodology which can be developed reduces them or conducts them in a more e$cient manner and can be applied to every process. The six non-value-adding activities will always exist in any production system. However, the frequency which they occur and the manner in which they are conducted have a considerable e!ect on the productivity of the production system. The study of the factory highlighted that there was a high degree of manual handling and large bu!er stocks within the production system which resulted in sluggish and ine$cient production and an average component production lead time in excess of "ve weeks. From the initial study, it is also evident that many of the operations such as pressing, stamping, and welding are highly repetitive, and suitable for automation. However, if an automated system was used it would have to be capable of handling many variants in small batches (target: one days production requirements) which would require a low cost, #exible material handling system.
4. Flexible automation and feeding Traditionally automation has been applied to highly repetitive tasks, as a method of increasing the e$ciency of the non-value adding activities. However, component variety and, small batch production makes the use of traditional automation methods uneconomic for many areas in the factory. A number of studies have been conducted into #exible automation and particularly its use in assembly [9,10]. The studies identi"ed that the main obstacle in the economic application of #exible automation systems e.g. robot cells, is the lack of #exible component feeding devices, which are economically priced and meet the short cycle time requirements. For this reason the components handled within the factory were analysed based on their geometry and size, so that appropriate #exible feeding systems could be identi"ed or developed.
141
Fig. 2. Graph showing key process in Factory X.
X uses a computerised stock and materials #ow system which records the quantities of individual components ordered each year, their batch sizes, and their process route. Using this computer system, it was possible to determine the components which required the most handling by identifying the components with the largest batch size being ordered the most and having most of the operations. Analysing the process routes of the `Aa group revealed that punching processes had the greatest load followed by pressing and welding, this is shown in Fig. 2. Most of the stamping, pressing and welding processes follow the model outlined in Fig. 1, and require an operator to feed, orientate, process and unload each part, with the exception of the dedicated automation systems. The stamping and welding operations have the same characteristics and in some cases can be performed on the same machines.
6. Component groups The top 60% of the components handled were collected and grouped based on their size, geometry and which automated feeding method they best suited. The following component groups and feeding solutions were identi"ed: 6.1. Group 1: discs
5. Where is the handling problem the greatest? It was important to identify where the handling problem was the greatest within Factory X as "nding a solution for this point would provide the greatest savings and demonstrate the solutions robustness. An ABC analysis using a 60}30}10 ratio was conducted to identify the components which involve the most handling. Factory
A large majority of components within Grundfos begin their lives as circular metal discs (height/diameter (0.8) see Fig. 3, which are pressed into three-dimensional shapes or have holes punched in them. All the discs are transported from the punching factory in Euro-pallets following which they are manually separated and fed to a press or stamping machine. Alternatively, they are
142
N.F. Edmondson, A.H. Redford / Robotics and Computer Integrated Manufacturing 17 (2001) 139}143
Fig. 3. Disc geometry.
Fig. 5. Small complex components.
size and cycle time. The manual loading task takes an average of 5 min and minimises manual handling. The payback of a robot process cell incorporating such a devise is generally less than 1 year. 6.3. Group 3: small complex
Fig. 4. Cylindrical components.
manually loaded into a magazine feeder which separates and feeds the discs to a press or stamping machine. The major disadvantage of these handling techniques is that they involve repetitive manual handling of components having sharp edges and which are covered in oil. This is not only hazardous to operators but also a nonvalue adding activity. Based on this, a feeding system has been developed which can automatically separate and feed directly from the Euro-pallet, at a rate of 2 blanks every second, which gives a wide variety of blank sizes, and a pay back time between 0.5 and 1 year depending on the cycle time. 6.2. Group 2: cylinders This group of components is approximately symmetrical with a height/diameter ratio *0.8 and )1.5, with a main dimension greater than 80 mm e.g. cups, short tubes and impellers. This component group is often the product of pressing operations where discs are transformed into cylindrical components. Non-symmetrical features may be present in the form of o! centre holes or projections see Fig. 4. A simple belt feeder has been developed and implemented which can be quickly adjusted to handle di!erent cylinder diameters. The feeder is manually loaded and has a capacity of 30}60 min work depending on component
This group contains those components traditionally handled using vibratory bowl feeders having their smallest dimension less than (80 mm (see Fig. 5). A more detailed description of components, having suitable features for vibratory bowl feeding is described by Swift [1]. A new high speed #exible feeding device has been developed which is capable of feed rates in excess of 60 parts/min. The system can be automatically set-up to feed di!erent component types simply by selecting a new control program. The feeding system cost is equivalent to that of a standard vibratory feeder and allows a payback of less than 1 year. 6.4. Group 4: large components This group contains components which are not symmetrical, have their smallest dimension greater than 80 mm or are fragile; examples are motor assemblies an long tubes. It is not practical or cost e!ective to feed this group of components using active feeding systems or the belt feeder. The most practical solution for this group of components is the use of modular pallet magazines, where component pallets are assembled from standard modules. The cost of such a system is high and depends on the quantity of pallets required.
7. Flexible process cell The four standard handling systems can be used to construct #exible automation systems focused around key processes as identi"ed in Fig. 2. Such cells would achieve the payback targets by automating the production of many di!erent components using a single automated cell, allowing the capital investment to be distributed over a number of di!erent components not just one as with dedicated automation systems. The control of the #exible process cell is via the Kanban system,
N.F. Edmondson, A.H. Redford / Robotics and Computer Integrated Manufacturing 17 (2001) 139}143
143
10. Further work E The basic methodology needs to be applied to more facilities to demonstrate its robustness. E The classi"cation system needs further development to increase the number of feeding and handling solutions, and to enable easier identi"cation of component groups. E The concept of the #exible process cell could be extended to include automated assembly.
Fig. 6. The automated #exible process cell.
enabling the factory stock levels to be minimised. The concept is illustrated in Fig. 6. 8. Limitations The basic methodology to date has only been applied to one factory and it cannot be claimed that this technique is truly universal. However, the ABC analysis can be applied to a wide variety of di!erent production facilities to identify feeding and handling systems, although they will not always be the same as those identi"ed in this study. 9. Conclusions E Every process requires six non-value adding activities. E Regardless of the process the non-value adding activities remain the same. E The processes which require the most manual handling can be identi"ed by performing an ABC analysis. E Components can be divided into four groups which can be handled and fed using four #exible automation methods. E The #exible automation methods can be combined with the process involving the most handling operations to form #exible process cells.
Acknowledgements This work was supported through funding from Grundfos A/S Denmark.
References [1] Swift KG. A system of classi"cation for automatic assembly. M.Sc thesis, University of Salford, 1980. [2] Mitrofanov SP. National Lending Library for Science and Technology, 1959. [3] Opitz H, Eversheim W, Wiendal HP. Workpiece classi"cation and its industrial classi"cation and its industrial application. Int J Mach Tool Des & Res 9:39. [4] Spies K. Eine Foremenardung fur Gensenk chienderstucke, Werkstattstechnik, 2, 1957. [5] Eversheim W, Miese M. Group technology developments and modes of application. Proceedings of the 15th Machine Tool Design and Research Conference. Oxford: Pergamon Press, 1975. [6] Chow CC, Gallagher CC. Classi"cation of structural engineering components and assemblies for group technology, J Mechan Working Technol 1977;1:67}84. [7] Boothroyd G. Automatic handling of small parts. CIRP Ann 1975;24(1):393. [8] Boothroyd G, Dewhurst P. Product design for assembly Boothroyd Dewhurst, Inc., 212 Main street, Wake"eld, RI 02879, USA, 1986. [9] Zenger D, Dewhurst P. Automatic handling of parts for robot assembly. CIRP Ann 1984;33:279. [10] Redford AH, Lo EK, Killeen PJ. Parts presentation to multi-arm assembly robots. CIRP Ann 1983;32:399.