Material Handling Systems Design Applied Basics of Queuing

MATERIAL HANDLING Twenty principles of material handling Selecting material handling methods Simplifying/eliminating material handling Simple analysis techniques

Material Handling Material handling adds COST, but not VALUE. as much as 60% of total production cost 20%-30% of direct labor costs 50%-70% of indirect labor costs What’s the best way to handle materials? DON’T!! Goal: MINIMIZE COSTS OF MATERIAL HANDLING

Muther’s Material Handling Equation Yes WHY ? WHAT WHERE + WHEN HOW + WHO MAT’L MOVE METHOD No B A Q D etc. E P C Type, Qty, Characteristics Sink, Source Flow; Direction Flow, Volume Type of Move, etc. Unit Manpower Equipment

Muther’s Material Handling Equation Use to analyze flow within and between: Receiving Storage Production Warehousing Shipping

The Twenty Principles of Material Handling 1. Orientation Principle: Study the system relationships thoroughly prior to preliminary planning in order to identify existing methods and problems, physical and economic constraints, and to establish future requirements and goals. 2. Planning Principle: Establish a plan to include basic requirements, desirable options, and the consideration of contingencies for all material handling and storage activities. 3. Systems Principle: Integrate those handling and storage activities which are economically viable into a coordinated system of operation including receiving, inspection, storage, production, assembly, packaging, warehousing, shipping and transportation.

The Twenty Principles of Material Handling 4. Unit Load Principle: Handle product in as large a unit load as practical. 5. Space Utilization Principle: Make effective utilization of all cubic space. 6. Standardization Principle: Standardize handling methods and equipment wherever possible. 7. Ergonomic Principle: Recognize human capabilities and limitations by designing MH equipment and procedures for effective interaction with the people using the system. 8. Energy Principle: Include energy consumption of the MH systems and material handling procedures when making comparisons or preparing economic justification.

The Twenty Principles of Material Handling 9. Ecology Principle: Minimize adverse affects on the environment when selecting MH equipment and procedures. 10. Mechanization Principle: Mechanize the handling process where feasible to increase efficiency and economy in the handling of materials. 11. Flexibility Principle: Use methods and equipment which can perform a variety of tasks under a variety of operating conditions. 12. Simplification Principle: Simplify handling by eliminating, reducing, or combining unnecessary movements and/or equipment.

The Twenty Principles of Material Handling 13. Gravity Principle: Utilize gravity to move material wherever possible, while respecting limitations concerning safety, product damage and loss. 14. Safety Principle: Provide safe MH equipment and methods which follow existing safety codes and regulations in addition to accrued experience. 15. Computerization Principle: Consider computerization in MH&S systems, when circumstances warrant, for improved material and information control. 16. System Flow Principle: Integrate data flow with the physical material flow in handling and storage.

The Twenty Principles of Material Handling 17. Layout Principle: Prepare an operational sequence and equipment layout for all viable system solutions, then select the alternative system which best integrates efficiency and effectiveness. 18. Cost Principle: Compare the economic justification of alternate solutions in equipment and methods on the basis of economic effectiveness as measured by expense per unit handled.

The Twenty Principles of Material Handling 19. Maintenance Principle: Prepare a plan for PM and scheduled repairs on all material handling equipment. 20. Obsolescence Principle: Prepare a long range and economically sound policy for replacement of obsolete equipment and methods with special consideration to after-tax life cycle costs.

Unit Load Principle Follows traditional thinking $/unit Quantity The greater the amount moved per trip, the less the cost per unit moved Maximize Unit Load

Unit Load Principle But: Creates more inventory Requires expensive, heavy-duty material handling equipment Increases lag time between operations poor process communication, slower reaction to quality problems Requires more floor space WASTE!

Selecting Material Handling Methods Systematic Approach 1. Define the problem Preliminary Survey Check sheet (see Appendix at end of section)

Selecting Material Handling Methods 2. Analyze the problem Observe activities Obtain layouts, flow patters, schedules, etc. Obtain information on existing material handling equipment Analyze situation by material handling equation, Twenty Principles of Material Handling, and/or forms such as Basic Data Form (see insert) Can activities be combined, simplified, eliminated???

Selecting Material Handling Methods 3. Identify possible solutions Organize meeting with: material handlers machine operators supervisors support engineers 4. Evaluate alternatives Meet again to rate alternatives using Factor Analysis

Improvement of MH Systems Cellular Manufacturing Eliminate Handling Eliminate Storage Eliminate Inventory Eliminate waste due to poor quality KEYS: Efficient layout, scheduling, problem prevention

Conveyor Systems Reduce handling costs Better coordination of product thru processes Design WIP level into material handling system

Simple Analysis Techniques Queuing Analysis Mathematical analysis of queues (waiting lines which occur whenever the current demand for service exceeds the current capacity to provide that service).

Simple Analysis Techniques Queuing Analysis Suitable for “quick and dirty” evaluations when a high degree of detail is not necessary. System Server (s) Arrivals Departure l Arrival Rate m Service Rate

Simple Systems FIFO (FCFS) Single Server, Single Queue - M/M/1 System Poisson Arrivals Exponential Service Times

Simple Systems LIMITED: Mathematical complexity becomes insurmountable if the above is not true SIMULATION Objective Wait $ Service $

Material Handling Applications Highway Trailers: Ship/Receiving Parts on Conveyor Pallets/Mc. Waiting for Fork Trucks Orders Waiting at AS/RS Many More

QUEUING PHENOMENON Example If m > l, why Queues? LOADING DOCK arrive every 40 min on avg. l = 1.5/hr. 30 min avg. time to unload m = 2.0/hr.

QUEUEING PHENOMENON EVENT Time (min) Truck Being Serviced Truck in Queue Truck Wait Time Truck 1 Arrive Truck 2 Arrive Truck 1 Leave Truck 3 Arrive Truck 4 Arrive Truck 2 Leave Truck 3 Leave Truck 4 Leave 30 50 62 63 80 90 125 156 1 1 2 2 2 3 4 -- -- 2 -- 3 3,4 4 -- -- -- -- 32 -- -- 40 62 76 156 min 4 arrivals = 39 min. avg.

FORMULAS for M/M/1 Model = avg. arrival rate m = avg. service rate l m U = utilization = 1 l-m W = avg. wait time in system = l m(m-l) Wq = avg. wait time in queue = l2 m(m-l) Lq = avg. length of queue = l m-l L = avg. number of “customers” in system = Pn = probability that there are n customers in the system n l m l m Pn = 1 - l m P0 = 1 -

M/M/1 EXAMPLE LOADING DOCK arrive every 40 min on avg. l = 1.5/hr. 30 min avg. time to unload m = 2.0/hr.

M/M/1 EXAMPLE l2 m(m-l) Lq = = 2.25 trucks in line l m-l L = = 3 trucks in line & being served also (L = Lq + l/m) Lq = Lq/l = 2.25/1.5 = 1.5 hrs/truck Lq = L/l = 3.0/1.5 = 2.0 hrs/truck l m 1.5 2.0 Lq = 1 - = 1 - = .25  25%

Cost Function E[TC] = E[WC] + E[SC] E[SC] E[TC] Cost E[WC] No. of servers

WAITING COST TC = CW[E(n)] + S(CS) Type I. Internal Customers Example: Forklift truck drivers Cost: Lost productivity of drivers Type II. External customers Example: People waiting for cabs Cost: ?? E[WC] = CW[E(n)] SERVICE COSTS Total Cost: S(server cost) = S(CS) THUS TC = CW[E(n)] + S(CS)

Example #1 Tool Crib Storage Service Time found by sampling! Inter-arrival time 60 sec/arr. 50 sec/service

Example #1 l = 1/60 = 1 arrivals/min. m = 1/50 = 1.2 services/min. Idle Time of Server = P0 = 1 - l/m = 1-1/1.2  16.7% Assume:1. Service Attendant Paid $12.00/hour 2. Customers (machine oper) paid $16.00/hour Cost of Servers E[SC] = 8 hrs/day  $12.00/hour = $96.00/day Cost of Machine Operators Waiting for Service plus Service) L = l/(m-l) = 1/(1.2-1) = 5 E[WC] = $16.00/hr (5 people) (8 hrs/day) = $640.00/day

Example #1 1 Conclusions? _________ E[SC] 640 $ 96 E[WC] Number of Servers Conclusions? _________

MH Cost Justification of Cellular Manufacturing Compare: I. Functional Layout --Fork truck Maint. Labor: $10,000/yr Parts: $1,000/yr Driver: $30,000/yr Truck Cost: $4,000/yr ($20,000/5 yrs) $45,000/yr *1 yr = 2000 hrs

MH Cost Justification of Cellular Manufacturing Compare: II. Cellular Layout --Fork truck --Cart/Basket Cart Cost: $40/yr ($200/5 yr) 4 Baskets Cost: $24/yr ($120/5 yrs) $64/yr

Questions