ME352 - Exam Questions Flashcards
Types of system models
Physical
Analytical
Simulation
Adv and disadvantages of simulation
Good for complicated systems
But only statistical estimates with uncertainty and noise
Static vs dynamic simulation
Passage of time plays no active or meaningful role in model execution; can often be done in
spreadsheets
Passage of time is essential and explicit in model execution; can almost never be done in
spreadsheets except for very simple models
Continuous-change vs discrete-change for dynamic models
Continuous-change: State variables can change continuously over time, at any point in
continuous time
Discrete-change: State variables can change only at instantaneous, separated, discrete
points in time
Deterministic vs. stochastic
Deterministic: All input values are fixed, non-random constants
Stochastic: Some inputs are random draws (or samples or realizations) from probability
distributions
Simulation methods
- Monte Carlo Method – use paper, calculator, dice, etc.
- Computer generated graphics using a simulation engine, Creo, etc.
- Computer generated tables of random numbers – spreadsheets
- Java applets, Visual Basic routines, etc.
- Computer methods using a simulation language, e.g. SIMAN in
Arena, Simio ,…
Explain how variant machining process planning works; what are the drawbacks of this approach
There are four steps in variant machning process planning:
* define the coding scheme;
* group the parts into part families;
* develop a standard process plan; and
* given a part to be made, retrieve and modify the standard plan to arrive at the final process
plan.
drawbacks of this approach:
* The components to be planned are limited to the similar components previously planned;
* Experienced process planners are still required to modify the standard plan for a specific
component;
* The approach cannot be used in an entirely automated manufacturing system, without
additional process planning and human intervention.
Root causes of the bullwhipe effect
Order Batching
Price fluctuations
Lack of communication
Free return policies
Demand information
Order of importance of taylor equation
v»_space; v_f»_space; a_p
Scope of planning
Long-term
Capacity Planning
1. Facility Size
2. Equipment Procurement
Intermediate-term
Aggregate Planning
1. Facility Utilisation
2. Personnel needs
3. Subcontracting
Medium-term
Master Schedule
1. MRP
2. Dis-aggregation of master plan
Short-term
Short-term Scheduling
1. Work centre loading
2. Job sequencing
Input and Outputs of aggregate plan
Input: Demand forecast
Output:
production rate (units completed per unit of time)
workforce level (number of workers)
inventory level (from previous period)
The projected costs if the production plan was implemented
Aggregate planning approaches
Reactive approach
Allow volume forecasts based on Marketing plan to drive production planning
Proactive approach
Production Planning strategies
Chase strategy
Match the production rate to meet the demand rate by adjusting the
workforce level (hiring/firing) as the demand rate changes. Minimize finished
good inventories by matching demand fluctuations.
Level strategy
Use a stable workforce working at a constant production rate. Use
inventories and backorders to absorb demand peaks and valleys.
Hybrid strategy
Combine elements of the chase/level strategies with other
options:
Stable workforce but variable work rate (overtime/undertime).
Subcontract production or hire part-time or temporary workers
to cover short-term peaks.
Varying work force size by hiring or layoffs
Influencing demand
Complementary product lines
Aggregate plan must balance
Costs are important but so are:
Customer service
Operational effectiveness
Workforce morale
Master Production Schedule (MPS)
A time-phased plan specifying how many and when the firm plans to
build each end item
To avoid overloading or underloading the production facility so that
production capacity is efficiently utilised and low production costs
result.
Inputs and outputs of master scheduling process
Inputs:
Beginning inventory
Forecast
Customer orders
Outputs:
Projected inventory
Master production schedule
Uncommitted inventory
Material Requirements Planning
Material requirements planning (MRP) is a means for determining the
number of parts, components, and materials needed to produce a
product (end item)
MRP provides time scheduling information specifying when each of
the materials, parts, ordered or produced and components should be
What, when, how many?
MRP is an information system
An MRP system is intended to simultaneously meet three objectives:
Ensure materials and products are available for production and delivery to
customers.
Maintain the lowest possible level of inventory.
Plan manufacturing activities, delivery schedules and purchasing activities.
What, when, how many?
Material Requirements Planning input and data requirements and outputs:
Critical input and data requirements:
Master Production Schedule (MPS)
Bill of Materials (BOM)
Inventory database
Many outputs – but primary ones are:
Planned orders to be released at a future time.
Order release notices to execute the planned orders.
Changes in due dates of open orders due to rescheduling.
Cancellations or suspensions of open orders due to cancellation or
suspension of orders on the master production schedule.
Inventory status data. Planned order releases
Mass Production Systems
Low product variety
High production volumes
Specialized labor
Dedicated equipment
High reconfiguration costs
Make-to-stock production
Batch Production Systems
Medium product variety
Products are made in larger lots
products are made to stock
Significant setup costs
Programmable/reconfigurable
equipment
Job Shops
High product variety
Products are made in small
lots
Products are made to order
Flexible equipment and
labor
Small setups
Breakdown Maintenance vs Preventive maintenance
Breakdown Maintenance: Waiting until equipment fails before
repairing or servicing it
Preventive Maintenance (PM): cleaning, or replacing parts to prevent sudden failure
Types of inspection for determining maintenance times
Infrared cameras
Detecting overheating cabling
Borescopes
Vibration monitoring
Availability vs reliability
Availability is a measure of the % of time our equipment is in an
operable state. Availability = System up-time / (System up-time + System
down-time)
Whereas reliability is a measure of how long our equipment performs its intended function.
2 types of availability
Inherent
Inherent availability is the steady state availability when considering
only the corrective maintenance (CM) downtime of the system.
Operational
Operational availability is a measure of the “real” average
availability over a period of time and includes all experienced
sources of downtime, such as administrative downtime, logistic
downtime, etc.
6 M’s of Production
Manpower
Method
Machine
Material
Milieu
Measurement
Principal queue parameters
Calling population (infinite vs finite, homogeneous (one type of customer/job, heterogeneous (several different kinds of customers/jobs))
Arrival process (pattern of arrival) - assume poisson arrival process (with interarrival times that follow exponential distribution)
Queue discipline (multiple vs single, differentiate who can join what, how jobs are selected - FCFS)
Number of servers
Service process (how do they get fulfilled, fixed time to complete or not) - exponential service times often assumed
M/M/1 - M meaning
Markovian
Characteristics of good facility layout
■Minimisedmaterials-handling costs.
■Maximised and efficientuse of space.
■Ease of accessibilityby support services
e.g. maintenance.
■Few, or no, bottlenecksin moving material or people.
■Flexibility.
■Facilitated communicationbetween all those involved.
■Reduced manufacturing cycle time or
customer servicetime.
■Eliminated or reduced waste.
■Compliance with health and safety standards.
Supply chain order
Customer
Retailer
Wholesaler
Distributor
Factory
