The workstation on which the assembly kits are made (Workstation 12) is found to include the most non-value added activities. 100% of the total work content at this workstation is not immediately adding value for the customer. Big wins can be made when the time at this workstation is reduced, especially as this workstation does not work within the cycle time.
Kitting is a bin-picking activity and the purpose of kitting is to ease the process of assembly on the production line. A big disadvantage of kitting is handling parts multiple times where a part would only have to be handled once when located in the production line. At the picking workstation, two separate kits are made in a repetitive and routine way. One contains common parts as well as specific parts for the different TrendLine types. The other contains parts for the sub assembly of the heatcell at Workstations 4 and 5. Every TrendLine boiler contains the same heatcell irrespective of the specific type.
The parts currently located in the bin picking area are picked for various reasons: - Type specific parts
- Easing picking of clips that can lock into each other
- Ensuring that employees do not forget items that cannot be detected afterwards (result of conducted FMEA analyses in the past)
- Reduce the burden of counting screws There are a couple of alternatives for the kitting area:
- Gathering the parts in a more efficient way (e.g. use vibratory fillers coupled to delivery cups) - Move parts from the kitting area to the production line
- Use the current kitting space for assembly of sub-assemblies and move the parts currently located in the kitting space to the location of use in the production line.
46 - Use a robot for kitting.
Solutions that require parts to be reallocated should simultaneously improve the current part allocation in the racks. The aim is to create a smart workspace design with use of the 5S method.
5.3.1 Gathering Parts with Vibratory Fillers
Section 5.2.2 considers a similar process. It was found that rivet dispensers and vibratory fillers are not an option.
5.3.2 (Partially) Remove Kitting Area
In a meeting with the head of the TEF department, the results of Chapter 4 were discussed. When he was presented with the kitting area (Workstation 12) being purely waste, we agreed on exploring the possibility of eliminating the kitting area. Relevant aspects are space, time and solutions that take into account why parts are picked from the kitting area at this moment. Section 5.3.2.1 discusses space, Section 5.3.2.2 discusses time and section 5.3.2.3 discusses implications of removal of the kitting area.
5.3.2.1 Space
Re-allocation of parts to the production line requires more space. This space is currently unavailable. At the moment, the entire space for racks and pallets alongside the production line is used. This is illustrated in Figure 4-4. The most important restriction is that Workstations 6, 7, 8, 9, 10, and 11 cannot be directly supplied with parts. However, Workstation 9 does not require parts. The racks for Workstations 1, 2, 3, 4, and 5 also hold parts for the other Workstations.
The first step of 5S is sort. This means that all objects that are not needed on the work floor have to be removed. The easiest way to create space is to work together with logistics. At the moment, the short side behind the packaging workstation is filled with 5 pallet locations. The first pallet location is used for trays, the second for boxes, the third for a stack of empty pallets and the fourth and fifth
for palletizing the boilers. Only one of the final two pallet locations is filled at a time. Whenever the pallet is loaded entirely, it is moved by an employee from the logistics department to the finished goods warehouse. Subsequently, the operator at Workstation 11 ensures that a new pallet is placed on the floor from the stack of pallets. If the employee from the logistics department takes care of placing a new pallet, one pallet location can be saved. Another option is to send a signal to the logistics department whenever a pallet is almost full to create JIT handling. Both options save one pallet location that can be used to supply Workstations 10 and 11.
Other options exist on the long side of the production line where racks are placed already. For example, the heat exchange is delivered on a pallet to the workstation for the sub-assembly of the heatcell. The various layers of heat exchanges are separated by a blue plastic tray. Empty plastic trays are placed next to the pallet on another pallet and await a logistics employee for removal. Creating a plate above the pallet place of the heatcell saves space for another rack.
47 Secondly, at this side, a blue container is located for empty boxes.
One could use this space for a rack and create a wooden or metal plate on top of the rack where employees can place the empty boxes to be removed by logistics.
The second step of 5S is straighten. This step identifies a permanent location for every item. The location should be
dependent on the order in which the items are used and the frequency of use. The order of part use is derived from work sequence cards and videos of the assembly operations. The allocation step can be performed after determining which parts will be located in the racks at the production line. This is done in the following section.
However, it is now known how much extra space is required if all parts would be stored in the racks. Analysis of the space requirements and part restrictions evidences that it is impossible to store the parts of the sub-assemblies for Workstations 1 and 6 in the production line. These assemblies are done at the kitting area to ensure that the correct items are used for the specific boiler types. Moreover, as it is done here, another check is performed in the line. If these sub-assemblies were to be performed in the line, another check has to be built in which also takes time. In addition to this, the parts for Workstations 1 and 6 require a lot of space which is not available. The different boiler types all require different heat exchanges that are supplied in crates for which space is unavailable. As a consequence, it is decided to not place the parts of Workstation 1 and 6 in the production line. Workstations 2 and 9 do not require any parts from the kitting area.
The parts of the other workstations require less space and are not boiler-specific. The next section explores whether it is (time-)efficient to place the parts in the production line.
5.3.2.2 Time
This section explores the consequences of placing the parts for Workstations 3, 4, 5, 7, 8, 10, and 11 in the production line and also performs the second step of 5S: straighten.
If a part is moved from the picking area to the rack of the workstation where it belongs, the time effect consist of three parts:
- Time for picking from the kit + Time for picking from rack - Time for kitting at WS 12
If a part is moved from the picking area to the production line, but not immediately to the rack of the workstation where it belongs, there is another time effect to consider:
+ Time for replenishing the inventory at the correct workstation In case of removing a task, the entire task time is saved.
For these time calculations the MTM method already in use at Bosch is used. A norm time table is used for time calculations (Table 5-3). This method considers the difficulty of performing a task as well as the length an operator has to overcome. For example, if one small screw has to be grabbed at a distance of 65 cm, this operation would be coded AE3 as it is difficult to grab one screw, but it can be grabbed loosely.
48
Table 5-3 UAS-Norm Time Table (Source: TEF Department)
The calculations for all workstations are given in Appendix 5. This section presents the analysis for Workstation 4 as an example and presents the final calculations for the plan on the production line level. The calculations for Workstation 4 are presented in Table 5-4. The TMU values presented in Table 5-3. Table 5-3 UAS-Norm Time Table (Source: TEF Department)Table 5-3 can be converted to seconds and seconds can be converted to costs. The exact converting values are confidential, but are known to the researcher.
Table 5-4 Time and Cost calculations for Workstation 4 when Kitting is not done anymore
The second step of 5S (Straighten) considers efficient part allocation. Hard wins are time reductions due to a more logical flow, but the most important gains are the soft wins that cannot be quantified. These are discussed after discussion of the time savings. Time savings only occur when the distance between sequential picks is reduced or when the operator does not have to turn to the kit anymore. If an operator picks all parts individually before mounting, no time savings are made because all locations are reached for once from the same position. However, there are certain parts that are combined before they are mounted and this is where time savings occur. In these cases, the operator goes back to the mounting position only once for multiple parts.
49 As the placement of all parts in the rack of Workstation 4 seems to be beneficial, a decision has to be made on the allocation of all parts in the rack. First, one should determine how much space is needed and whether this space is available. This comes down to counting the number of bins and crates. Then one should allocate the parts in the rack with an improved sequence. The old and future possible sequences are presented in Figure 5-7.
Figure 5-7 Old and improved lay-out at Workstation 4 with parts from kit in racking
Differences are the removal of the kitted bin from Workstation 12, the addition of the parts from the bin to the rack and an improved flow through the rack. One can ask why the absorber anti vibration sticker is located at F17, however, this part is placed in a machine on the left side of the rack which makes it inefficient to put the part on the right side of the rack. Allocation of parts should also take
into account the weight of the parts. Heavy parts should not be lifted above one’s head or lifted from
the bottom location. Heavy parts should therefore always be located in one of the middle two racks. Table 5-5 summarizes the changes that invoke differences in time.
Table 5-5 Time and Cost calculations for New Lay-out
A total of € 0.14 cents per boiler can be saved on Workstation 4 if the proposed changes are made. However, this saving is only realised when the saved time is filled with other operations, when less employees can do the same amount of work or when the cycle time can be reduced.
Soft wins related to improved part allocation are: - An improved flow
- Eased training of new employees
- Less time needed for finding the correct bin - Less wrongly chosen screws/bolts and nuts
- Less forgotten parts as employees know where to grab next approximately
The boiler loss information registration contains cases where wrong nuts were mounted and other parts were forgotten. This does not happen often (<2 per month on the TrendLine Production Line),
Bin WS12 F11
Electrode
F9 Seal condensate collector F18 Rivet single earth tab F17 Seal ignition assy F16 Nut F15 Screw shoulder F14 Seal fan F13 Cap F23 Absorber anti vibration
sticker
F21 Pipe
F19 Label data plate DNA TLA-F Gepickte kitjes WS 12 F5 Bracket transformer F4 O-ring F2 Seal F1 Screw
50 but these are quick wins resulting from an improved layout. No investment is needed, apart from the time needed for reallocation of the bins.
The entire analysis of placing all parts of Workstations 3, 4, 5, 7, 8, 10, and 11 from the kitting area in the racks is presented in Table 5-6. All these changes would save a total of 101 seconds of which 27.5 in the production line. The line balancing application presented in Section 5.1 has to reveal if these time savings can also be achieved by rebalancing the production line.
Table 5-6 Total time and cost savings of placing certain parts in rack
5.3.2.3 Implications
If parts from Workstations 3, 4, 5, 7, 8, 10 and 11 are removed from the kitting area and placed in the racks of the production line, it causes the work content on Workstation 12 to be reduced with 47.2%. The manager of the TEF department assumes that the remaining 2.8% can be done somewhere else in the factory to half the work content entirely. As there are two employees at work at Workstation 12 to supply both Trendline Production Lines, it is assumed that halving the work content means that one FTE is saved. The other employee can serve both Trendline Production Lines. If only one Trendline Production Line is operational, the employee can prepare kits in advance and work either half days or every other day.
The parts cannot be placed in the racks without taking any further precautions. Therefore, it is recommended to use PTL systems or Active Assists. The parts from Workstation 3 and 10 can be checked by adding a visual check at Workstation 4 and 11. This concerns only two parts and it is not efficient to place a PTL system for one part. The input data for the Line Balancing Application is adjusted to take into account the time needed for these visual checks. The other workstations (4, 5, 7, 8, and 11) have to be equipped with a system to ensure that all parts are assembled. Moreover, a rack must be moved from Workstation 12 to the production line.
Result of Line Balancing Application
Now we can determine the consequence of the changes for the cycle time and see whether we can achieve the prospected time savings in the line. The discussed changes have consequences for the operation times. The input for the line balancing application is updated with these time changes. The result of the application for this scenario is presented in Table 5-7.
51
Partial removal of kitting area Baseline
Near-optimal SALBP solution for the current situation, 5S improvement and placement of
certain parts in line
Cycle Time (sec) 226 226
Number of Workstations 11 11
Line Balancing Efficiency (%) 94.5 95.2
Smoothness Index 53.1 52.6
Table 5-7 SALBP solution (partial) removal of kitting area
Unfortunately, this change only affects the non-bottleneck workstations. This means that the cycle time is not positively affected by the change. Consequently, the line balance and smoothness index are worse, because the total work content is less. However, next year the final test on the bottleneck station (Workstation 9) will be adjusted. An entirely different test will be used that takes less time. The Industrial Engineers estimate the process cycle time of the future final test at 188 seconds including coupling and uncoupling of test heads. The scenario where the current test is replaced with the future test is also run through the application. The results are presented in Table 5-8.
Near-optimal SALBP Solution for the future situation with test of
188 seconds
Cycle Time (sec) 219
Number of Workstations 11
Line Balancing Efficiency (%) 97.8
Smoothness Index 19.4
Table 5-8 SALBP solution with future test of 188 seconds
In the future situation the baseline measure is no longer 226 seconds, but 219 seconds. The effect of removing certain parts from the kitting area on this baseline is also calculated by running the scenario through the application. The results are presented in Table 5-9.
Future test and partial removal of kitting area Baseline
Near-optimal SALBP Solution for the future situation with test of 188 seconds, 5S improvement and
placement of parts in line
Cycle Time (sec) 216 219
Number of Workstations 11 11
Line Balancing Efficiency (%) 98.0 97.8
Smoothness Index 17.0 19.4
Table 5-9 SALBP solution with future test and (partial) removal of kitting area
The progress and task division of these solutions are added in Appendix 4. One can see that the removal of the kitting area does have a positive impact on the cycle time in the future situation. As Workstation 9 is no longer the bottleneck, the time savings do impact the cycle time. The baseline cycle time of 219 seconds is reduced to 216 seconds because of the changes at Workstation 12.
Economics
In terms of economic benefits, the changes to the kitting area eliminate 50% of the work content at Workstation 12. If both Trendline production lines operate 1 FTE is saved. Unfortunately, the change does not result in additional time savings for the current improved situation. The cycle time will remain 226 seconds. Then this change requires two investments. The line has to be reconfigured and equipped with Pick-to-Light and or Active Assist systems. As the reconfiguration requires quite some changes in the line, it is assumed that more time is needed compared to solely rebalancing the line. Parts have to be reallocated and racks have to be replaced. The economic analysis for this change with implementation of 5 Pick-To-Light systems (€ 9,500 Euros per system) for the racks at Workstations 4, 5, 7, 8 and 11 is presented in Table 5-10. All tables take into account a 2% inflation rate.
52 Year Initial Investmen t (€) Maintenance cost (€) Reconfiguratio n cost (€) Labour Saving s (€) Yearly Cash Flow (€) Cumulative Cash Flow (€) NPV (€) 1 47500 4750 4000 45624 -10626 -10626 -10626 2 4845 46536 41691 31065 27623 3 4942 47467 42525 73591 63416 4 5041 48417 43376 116967 96910
Table 5-10 Economic Evaluation of Partial Removal of Kitting Area with 5 PTL Systems
The pay-back period of the investment is 1 year and 94 days. Considering the time value of money this changes to 1 year and 124 days.
Even more interesting is the implementation of Active Assists in the production line. The cost of an Active Assist system for one Workstation is estimated at € 20,000 Euros (external correspondence with supplying company). The Active Assists are especially interesting for Workstations 4 and 5 where a subassembly is made. Inclusion of 2 Active Assists instead of 2 Pick-to-Light systems changes the economic evaluation as presented in Table 5-11.
Year Initial Investmen t (€) Maintenanc e cost (€) Reconfiguration cost (€) Labour Savings (€) Yearly Cash Flow (€) Cumulative Cash Flow (€) NPV (€) 1 68500 6850 4000 45624 -33726 -33726 -33726 2 6987 0 46536 39549 5823 2558 3 7127 0 47467 40340 46164 36512 4 7269 0 48417 41147 87311 68285
Table 5-11 Economic Evaluation with 3 PTL systems and 2 Active Assists
The pay-back period without considering the time-value of money is 1 year and 312 days. When considering the time-value of money the pay-back period increases to 1 year and 341 days.
However, in the upcoming year, the final test on workstation 9 will be replaced with a new test that has a shorter process cycle, the partial removal of the kitting area will then save another 3 seconds on the cycle time. Inclusion of these extra time savings, changes the economic evaluations to the numbers presented in Table 5-12 and Table 5-13. The baseline of the economic evaluations in these tables is the