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05/08/2012 11:11 AM
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Hi,
Is there a formula for calculating total number of trolleys needed for material handling in the following situation ?
Make inhouse parts => send for supplier sub processing => supplier processing and finally => receive parts inhouse
Factory = Hourly demand = 20 per hour
Transport lead time for batch of 200 parts from factory to supplier = 4 hours
Supplier processing = 100 parts per hour
Parts per trolley = 20
Regards,
gdatar
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05/15/2012 02:47 PM
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Hi Girish,
Based off how I interpret your explanation of the process, I'll try to give you a rough answer.
A. 10 would be necessary to cover the factory processing 10 trolleys for the next shipment. This would allow them to have 9 full while filling the last one.
B. Does the 4 hour trip include loading at factory and unloading at supplier? Do you use one dedicated truck, or are multiple trucks available? If everything was executed properly, you could get away with the Supplier processing the parts in 2 hours and returning the same 10 trolleys between the 2 4 hour shipments.
This would allow you to get away with 20 trolleys at a minimum.
I prefer to sleep well at night, and somehow I don't believe that you would pull this off day after day. Maximum extra trolleys in case of disruption in processing or transportation would appear to be an extra 20 (40 total) . 10 to have a full shipment ready at both the factory and supplier.
Since the supplier can produce in 2 hours what the factory can produce in 10 hours, it's possible you could get away with only having 10 extra trolleys in the system.
Other items you would probably want to consider:
How often and for how long are the flows disrupted from 100% efficiency, uptime and yield at both the factory and supplier? How expensive are the trolleys? Can trolleys be unloaded upon arrival and sit empty while the next parts are processed? How stable is the flow of 20 trolleys per hour demand? What is the "cost" of being late on an order due to trolley availability? Are the trolleys ever out of service?
Hopefully some other Forum members can jump in and help.
Brian
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05/21/2012 10:57 AM
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Thanks Brian for detailed explanation. 4 hours includes loading and unloading, trucking is flexible
Here is what I had in mind.
Assuming daily production of 22 hours = 440 parts = 22 trolleys if I just make 1 trip
then for total lead time (4 hrs one way, 4.4 hrs supplier and 4 hrs return) another 13 trolleys in the plant
so total = 35 trolleys
If trips per day = 2, then 22 trolleys for system
=============================
I was wondering if there is simpler math / formula that can be devised with
below variables
1. Parts/trolley
2. Factory thruput
3. Supplier rate
4. Lead time for transport incld load/unload
5. Frequency of trucking on daily basis etc.
and assuming no waiting or other wastes (no safety for now)
Total system trolleys
= # of trolleys based on daily trip freq and daily factory demand + (2x transport time + time for processing at supplier given lot) * hourly factory rate
Not sure if this is making sense
Edited: 05/21/2012 at 10:57 AM by Lean Moderator
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05/25/2012 11:58 AM
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Girish,
I'm still not sure I fully understand the process but here's a couple comments.
A. What are the costs associated with not having enough trolleys in the system or having too many trolleys in the system (example 5 extra?) I'm somehow envisioning a trolley to be about 4 ft x 4 ft with wheels and costing upwards of $1,000 - $5,000 each.
B. One key constraint is the 22 trolleys per truckload target quantity. Applying the rules of SMED, reducing the quantity per truckload (i.e. frequency) would seem to allow you to get away with less trolleys in the system. Unfortunately this might not be cost effective. Possibly find someone else nearby you can share transportation with so you don't need to ship full loads?
C. Stability of flow within the system and availability of trolleys are also key variables that would affect the calculation. The ability to store parts without a trolley until they are available would also impact the necessity to have extra trolleys.
D. Due to the truckload constraint, it's possible the number of trolleys is not linear with the throughput rate, but may involve incremental steps at certain rates.
It would seem that you might want to spend some time determining what are the causes of the need for extra trolleys in the system (i.e. waste) and what could you do to reduce the need?
Brian
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07/05/2012 11:07 AM
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Thanks Brian for your inputs.
I was still looking to verify from basic logical formula perspective if what I have shown as formula (sent as my comment on 5/21/12 at 9:57 am) and calculations makes sense.
There is certainly so many other subjective and real issues to be considered such as increasing freqency etc.
Anyway, thanks once again for taking time out to reply.
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