tool management study

1. A Simulation Study of
FMS Tool
Allocation Procedures

2. INTRODUCTION
 A flexible manufacturing system (FMS) is a group of numerically controlled
machine tools with an automated material handling system and a central
supervisory computer system.
 The advent of FMSs has greatly increased the productive potential of
manufacturers; however managing the increased number of tools required for
these systems and their application has hindered increases in productivity.
 Proper tool allocation is important because of the large number of tools
that might have to be allocated to the tool magazine and the fact that only
a limited number of tools can fit on the tool magazines.

3. INTRODUCTION
 lack of attention to tool management has resulted in poor performance of
many FMS.
 The question to be addressed then is: Given the limited tool magazine
capacity at the machines, what is the impact of using different tool
allocation procedures on FMS performance.

4. PROBLEM IDENTIFICATION
 The problem being addressed in this paper is that, although machine capacity
might be sufficient, it might not be possible to process all orders required
for a particular planning period due to the limited number of tool slots at
the tool magazines attached to the machines.
 a subset of orders has to be selected and the required tools allocated to
the machines before the orders can be processed.
 it is important that the time required for tool changes between subsets of
orders be minimized. Tool changes affect the efficiency of the FMS.

5. PROBLEM IDENTIFICATION
 The first aspect of tool allocation is the loading and placement of a set of
tools in the magazine.
 Any tool allocation policy must also take into account the tool replacement
strategy to be used.
 Daoud and Purcheck argued that more focus should be placed on developing
tool management strategies that aim to minimize the frequency of tool
changes due to tool wear, rather than tool changes imposed by part type
variety.
 the need for tool changes due to part type mix might override the need for
tool changes due to tool wear. The focus in this study is therefore on tool
changes due to part type variety.

6. Heuristic Tool Allocation
Procedures
 The complexity of solving the part type selection and tool allocation problems
simultaneously for a reasonably realistic FMS has been recognized by several
researchers and heuristic procedures have been proposed.
 The Heuristic tool allocation procedures studied in this paper are:
1.Tool and part batching
2.Tool sharing
3.Flexible tooling

7. TOOL AND PART BATCHING
 Assuming there is enough machine capacity to process all the
parts during a planning period.
 the need to divide the parts into batches arises mainly because of limited tool
magazine capacity at the machines.
 The main criterion of interest in this case is to minimize the number of batches
required to process all the parts, thereby minimizing the idle time associated with
batch changeovers.
 procedure for assigning parts to batches:
1. selecting part types that require the largest number of too slots.
2. first selecting part types that requires the smallest number of tools.

8. TOOL AND PART BATCHING
 Tool allocation is incorporated into the batching decision as follows:
 For each part type in the batch, a copy of each tool type needed for that part
type on a particular machine is allocated to the machine's magazine.
 For example, if two part types use the same tool type, two copies of the
tool will be allocated, one for each part type.
 In addition, if a particular part type requires multiple copies of the same tool,
then depending on the tool life and processing time of the part, the
appropriate number of copies of that tool are allocated to the tool magazine.

10. TOOL AND PART BATCHING
 This approach ignores tool sharing among part types. Also, when using this
approach, no tool changing occurs until the entire batch of part types is
processed.
 this approach has the potential to reduce the frequency of tool changes
but provides no savings in tool magazine capacity.
 Tool tracking is also reduced.
 An implication of this strategy is that, because the tool magazine capacity on
each machine is fixed, a part will not be assigned to a particular machine
for the production window if there is not enough space on the tool
magazine to hold the required tools.
 This approach can also lead to excessive tool inventory and greater tool
handling time.

11. TOOL SHARING
 Failure to recognize tool commonality can lead to unnecessary tool duplication and
further underutilization of tool magazine capacity. A suggested approach for overcoming
these limitations is the tool sharing approach.
 It is assumed that only one copy of each tool type is needed for each part type
requiring that tool. Also assume each tool occupies only one slot.
 the common tool has to have sufficient tool life to meet the processing requirements of
all part orders needing that tool.
 more sophisticated tool-monitoring logic will be needed to keep track of the expended
tool lives of the various common tools and to keep track of how the remaining tool
lives will be allocated among other part orders.

13. FLEXIBLE TOOLING
 These flexible approaches are aimed at minimizing the bottleneck effects of
the tool magazine capacity at each machine.
 When part types are selected for production, their required tools are also
allocated to the machines, and the tool slot consumption at each machine
is updated just as in the tool-part batching procedure. Following the
completion of the part types requiring those tools, any tools not fully consumed
are removed from the tool magazine while another part is being machined.
This frees up space on the tool magazine to permit the selection of another
part type to be processed and the allocation of the needed tools to the
machine.

14. FLEXIBLE TOOLING
 The flexible tooling procedure thus has the potential of reducing cutting
tool inventory because it permits tool sharing during the production window. It
also leads to higher utilization of the tool magazine capacity because tool slots
are not "tied down" by idle tools.
 this approach requires frequent tool changes, and thus another constraint is
imposed on the system by the mechanism of tool changes.
 the use of this approach means that no prerouting of part orders is necessary
during prerelease planning.

15. COMPARISON

16. PERFORMANCE MEASURE
 the tardiness of orders, percentage of orders tardy, and mean flow time of
orders processed on the FMS will be determined.
 Tardiness refers to the average lateness of all orders completed after their due
dates.
 The percentage of orders tardy measure represents the percentage of total
orders completed after their due dates
 Flow time is a measure of throughput and can also provide an indication of
the level of work-in-process inventory.

18. EXPERIMENTAL ASSUMPTION
 A static daily demand for parts is assumed rather than a dynamic demand,
meaning that a fixed quantity of part orders is introduced into the system
in each production period.
 the arrival rate was generated by assuming a machine load capacity of 75%.
 due date is not a performance measure in this study; rather, due dates are
used to preferentially determine the part input sequence at the FMS.
 The total processing time per part type is assumed to be based on a 2-Erlang
distribution with a mean of 60 minutes.
 The cutting life of tools is assumed to be exponentially distributed with a
typical mean of 30 minutes.

19. RESULT

20. CONCLUSION
 Tool allocation approach for FMS production planning is particularly important when
the FMS is being used to process a few part types. Although the use of a flexible
tooling approach produces results superior to the use of either a tool batching or tool
sharing approach at both low and high part mix.
 The frequency of tool changes within a production period is still high for the flexible
tooling, as reflected in the higher utilization of the robotic material handling unit.
Any waiting times at the machines due to tool changes are overridden by the
greater opportunity provided by the savings in tool magazine capacity as a result of
the frequent removal of tools from the tool magazines. Thus, it is concluded that a
tool allocation approach focused on greater utilization of the tool magazine capacity
is better than a tool allocation approach that seeks purely to minimize the
frequency of tool changes within a given production period.

21. CONCLUSION
 Sharing approach allows the benefits of greater tool magazine utilization to
be achieved while at the same time requiring a lesser frequency of tool
changes. Thus, a tool sharing approach might be better if the FMS is
operated in an environment where the system for tool flow and tool changes
is not efficient and imposes a lot of delays on the machines, especially if the
FMS is the bottleneck unit in the shop's operations.

22. THANK YOU