Process and Facility Selection
cycle time cont
relates to speed of assembly line -longer cycle time- slower assembly time -shorter cycle time- faster assembly -more stations- faster assembly -less stations- slower assembly which cycle time do we choose? -minimum possible- cycle time= longest individual task time, fastest production, more work stations -maximum possible- cycle time= sum of task times, slowest production, less work stations (min # of work stations = 1) -work stations help determine range of output CT= OT / D OT- operating time (available production time available per day) D- demand per day (desired output/day) CT= how long you will run the line / how much you want rot produce
product layout
(assembly line) -products or customers move from workstation to workstation in a continuous, unchanging pattern product focus, MTS advantages: -low variable cost per unit, low material handling, reduced WIP inventory, easier training and supervision, rapid throughput, high rate of output, high utilization of labor and equipment, established routing and scheduling, routine accounting and procurement, automated disadvantages: -high volume is required, fairly inflexible to volume changes, work stoppage (if one process goes down, entire line stops), shutdowns, creates dull, repetitive jobs, higher equipment costs (specialized major design issue: line balancing (diving up work)
fixed position layout
(construction site) -the product or customer doesn't move. workers, materials and machinery move instead advantages: -no other choice disadvantages: -communication and coordination, complicating factors- limited space at site and different material is required at different stages of project and culture of material is dynamic major design issue: scheduling and project management
hybrid aka cellular layout or group technology
(lean) cellular manufacturing-A complex production facility subdivided into smaller product layouts. products or customers are divided up into "families" (groups of products with similar requirements: and each "family" is produced in its own small product or process layout known as a "cell" (advantages of product and process layout) advantages: -more efficient than process layout, allows more customization than a single product layout, reduced WIP, need less floor space, reduce direct labor, higher employee participation, reduced material, raw materials and finished goods inventory disadvantages: -higher investment in equipment than process layout, less flexible than process layout major design issue: group technology or product families
closeness ratings
-highly generalized procedure, allowing for "subjective" input from planners 1. list all depts you're trying to locate 2. rate the "importance of closeness" for each pair of depts A= absolutely necessary - 100 points E= especially important- 50 points I= important- 25 points O= ordinary important - 5 points U- unimportant- 0 points (indifferent) X= undesirable- -100 points 3. no practical optimizing technique exists. use trial and error -most process layouts are trying to minimize traffic -supermarkets are trying to maximize traffic so they spread out essential items to encourage impulse buying (look on spreadsheet on UBlearns to read the chart) -what makes something important - if you have something that creates lots of sawdust so you want that to be near vacuum and away from areas you want to keep clean, or places you want to keep traffic minimized
to balance an assembly line
1. determine its cycle time (how fast will it run) 2. draw a precedence diagram (what has to be done, in what order) (each letter goes after its immediate predecessor) 3. assign tasks to workstations (who is going to do what)- heuristic decision rule- "rule of thumb"- choose task with longest processing time theoretical minimum= Nmin= ST / CT ST= sum of task times if Nmin= 3.17, round up to 4 -sometimes, due to precedence diagram or decision rules, it is not possible to attain the theoretical min # of workstations 4. compute idle time and efficiency (how good is your finished design- lots of idle time = low efficiency) if CT= 1.2 min/cycle- each work station will have 1.2 min, every 1.2 min a widget will come off assembly line -efficiency= ST / (CT * n) n= # of workstations
precedence relationship
A dependency between two tasks, usually requiring that one task be completed before the other task is started. -immediate predecessor- a task that must be completed before another task can start -balanced delay- percent of a. workstation time not in productive use during the operation of a product layout -dynamic- actively and continuously changing -process layout- a configuration in which transformation proceeds along multiple, shifting patterns through a facility -job shop- process layout -load distance- a quantity multiplied by the distance that the quantity will travel to create an overall expression of the work required by that action
line balancing
A product layout design technique which assigns the tasks to be performed at consecutive workstations, seeking to balance the workload among them.
make to order
a system that produces low volumes of customized product no finished stock- longer lead time -assemble to order- a system that produces standard modules to be modified/combined into a customizable product -work in process- inventory resulting from transformation of ew material but not yet ready for sale to consumers -business process reengineering- evaluation and improvement of an existing process design -delayed differentiation- an ATO strategy for stocking highly standardized components for later customization into finished goods -remanufacturing- production of finished goods from the recycled components of returned goods -product layouts- a configuration in which transformation proceeds along a single, unchanging pattern through a facility
facility layout types
product, process, fixed position, hybrid -layout- a physical arrangement of an operation
process layout
products or customers move between workstations as needed and not necessarily in the same sequence (MTO, customized) n depts -> n! layouts- 7!= 5040, 8!= 40000 advantages: -to provide highly customized products -can handle a wide variety of processing requirements -not particularly vulnerable to equip ent failure or employee absenteeism (dont have to fully shut down if missing one dept), equipment used is less costly- less capital investment disadvantages: -lower volumes- higher unit cost, in process inventories can be high, challenging routing and scheduling, equipment utilization is low, material handling is slow and inefficient, accounting and procurement are more involved (special materials) major design issue: n depts -> n! layouts
load distance
the procedure assumes that you are worried about traffic between areas in the layout suppose that there are 10 trips between area A and area B daily, 20 trips between B and C daily, and 200 trips between A and C. where should they be located in the layout load distance: (load x distance) + (" ")... LD= (10 x 1) + (20 x 1 + 200 x 2)=430 (AB, BC, AC) LD= (10 x 1) + (200 x 1) + (200 x 2) = 250 (AB, AC, BC) LD= (200 x 1) + (20 x 1) + (10 x 2)= 240 (AC, BC, AB)- this is the best option (lowest)
processes
activities that transform inputs into outputs -make to stock- a system that produces high volumes of standardized product hig volumes- lower cost. finished goods- shorter lead time -raw materials- inventory brought in from outside the system -finished goods- inventory awaiting sale to consumers -lead time- delay between requesting a product and receiving it -continuous processing- a make to stock strategy emphasizing uninterrupted production
balance delay
amount of time where work station isn't busy -Percent of a workstation time not in productive use during the operation of a product layout. BD= 1 - efficiency or BD= idle time / CT * n
efficiency
percent of a resource in productive use -mixed model assembly- product of a range of products with a single assemble Line, primary by varying features on an otherwise standardized product -line balancing- a product layout design technique which assigns the tasks to be performed at a consecutive workstations seeking to balance the workload among them -algorithm- a procedure described by a series of steps -cycle time- the pace of a product layout being the total amount of time each workstation has to complete its assigned tasks once during ongoing operation of the system -heuristic- a procedure to develop a good, through not necessarily optimal solution
closeness ratings definition
standard scoring system for the desirably of proximity with a facility -hybrid layout- any mix of elements from a product layout and a process layout to gain the advantages of both -cellular manufacturing- a complex production facility subdivided into smaller product layouts -group technology- the organization of dives products into families of similar production requirements -functional organizational structure-an organization of specialists grouped into distinct departments -matrix organizational structure an organization that groups differing functions together according to requirements of the work -fixed position layout- a configuration in which transformation cannot more, requiring all supporting resources and processes to travel to that location -project- a unique collection of activities creating a particular outcome
cycle time
the maximum time allowed at each workstation to perform its assigned tasks attach label/open envelope (10 sec) -> fold letter and study (30 sec)-> attach postage and seal (20 sec) -min cycle time- 30 sec (longest task time), output/hour- 120 envelopes -max cycle time- 60 sec, output/ hour- 60 envelopes where is he bottleneck?- station 2 (longest task time) what is a bottleneck- something that limited capacity/output - The most heavily utilized resource within a system. -cycle time- how much time each worker has to complete their set of tasks (how long the product spends at a station)- the time between finishing one product and the next
