Production Management
103 flashcards · Other · by Katie Gotlieb
What is a production system?
A production system is people and equipment and procedures organized to accomplish the manufacturing operations of a company.
Relationship between production quantity (Q) & production variety (P)
Inverse correlation between P & Q: high quantity = low variety high variety = low quantity
When is a 'job shop' layout applicable?
low quantity range: 1 - 100 units/year specialized and customized products products are typically complex (e.g. prototype aircraft, special machinery) Labour force is highly skilled
Fixed-position layout
low quantity range The product stays in one place and workers and machinery move around it used for craft-based industry and very large products, e.g. aircraft assembly, heavy machinery, specialist car manufacture. difficult to automate
Process layout (function layout)
used for jobbing manufacture and batch manufacture Q = 1 - 1000's most versatile type of layout, suits frequently changing product typical of factories manufacturing machined metal products
Batch production
hard product variety medium Q = 100 - 10,000 units/year process layout factory has fixed position manufacturing equipment that is used to make different products per batch. batch makes its way through the process layout, then next batch of different product runs through the layout
Cellular manufacturing
soft product variety medium Q = 100 - 10,000 units/year changeover time is minimal The goal is to move as quickly as possible, make a wide variety of similar products while making as little waste as possible. multiple 'cells' in an assembly line fashion
Flowline production
high Q = 10,000 - millions/year parts or assemblies make their way through multiple workstations single parts on single pieces of equipment product layout used for very high volume e.g. cars, consumer products
Cycle of information-processing activities
business functions product design manufacturing planning manufacturing control
Manufacturing support systems
manage production via. people and procedures
Automation applications relative to P & Q
Programmable automation: P is high, Q = 1 - 100 Flexible automation: medium P, Q = 100 - 10,000 Fixed automation: low P, Q = 10,000 millions
Reasons for automating
increase labor productivity reduce labor cost mitigate effects of labor shortages reduce/eliminate routine manual & clerical tasks improve worker safety improve product quality reduce manufacturing lead time accomplish processes that cannot be done manually avoid the high cost of not automating
Reasons for manual labor
very low labor rates in some nations tasks too difficult to automate short product life cycle customized products cope with ups and downs of demand reduce risk of new product failure in the market
Processes that are commonly automated
processing assembly inspection material handling
Shaping operations
solidification processes: casting (metals), molding (plastics) particulate processes: sintering (metals and ceramics) deformation processes: forging, extrusion, rolling, drawing, forming, bending Material removing processes: turning, drilling, milling, grinding
Processing operations
Basic Process: shaping operations, establishes initial geometry e.g. metal casting, forging, sheet metal rolling Secondary Processes: initial geometry is modified into final geometry e.g. machining, stamping, bending Property enhancement: treatments to strengthen e.g. heat treatment. parts don't always require this step. Finishing operations: final operation in the sequence, e.g. coating on work surface, painting
Assembly operations
permanent join processes: welding, brazing & soldering, adhesive bonding mechanical fastening: threaded fasteners (screws, bolts, nuts) & permanent fastening (rivets, interference fits)
Tc
Operation cycle time Tc = To + Th + Tth
Rp
Production rate, usually pc/hour Rp = 60/Tp
Availability
Availability is a reliability metric that indicates the proportion of time that a piece of equipment is up and working properly. A=MTBF−MTTRMTBFA = \frac{MTBF-MTTR}{MTBF}A=MTBFMTBF−MTTR MTBF = mean time between failures MTTR = mean time to repair
PC
Production capacity, maximum rate of output per period (usually per week)
U
Utilization, amount of productivity output (Q) relative to production capacity
MLT
Manufacturing lead time, time from order to delivery
WIP
Work in progress, quantity of parts still being worked on currently in the factory
To
Processing time for the operation
Th
Handling time e.g. loading/unloading the machine
Tth
tool handling time
Tb
cycle time for batch production Tb = Tsu + QTc where: Q = quantity of products Tsu = set up time
Production capacity
Max rate of output that a facility is able to produce under a given set of conditions: PC = nSHRp where: n = no. of work centres S = shifts / week H = hours / shift Rp = production rate
Plant capacity
PC = nHpcRp n = no. of work centres Hpc = no. of hours in defined period
How to adjust plant capacity
Short term: increase/decrease no of workers increase/decrease no of shift per/week increase/decrease hour per/week Intermediate - long term increase no of machines increase production rate by method improvements and/or processing tech
Lead times
Fixed costs of manufacturing operations
building equipment insurance rates
Variable costs of maufacturing operations
direct labour raw materials power
direct labour
sum of all wages connected to production
overhead costs
factoy corperate labour materials machine rates
Design for maufacture and assembly (DFM/A)
Approach to product design which systematically includes considerations of maufactuability and assembility in the design
Examples of DFM/A
organizational changes closer interaction between design & manufacturing for project teams of product designers, manufacturing, engineers, and other specalties to design a product
Benefits of DFM/A
shorter time to bring product to market smoother transition into production fewer components in the final product easier assembly lower cost of production higher product quality greater customer satisfaction
Concurrent engineering
approach to product design in which companies attempt to bring a product to market quicker by integrating design, manufacture, and others.
Production planning
what products are to be produced, in what quantites, and when. Considers resources required to accomplish the plan
Production control
ensures that production team can achieve required production target, optimum utilization of resources, quality management and cost savings
Production control vs production planning
planning: plans the production control: ensures the plan can be achieved
Long range planning
corperate goals & strategies future product lines finanical planning obtaining the resources for the future of the company
medium range planning
aggregate prodcution plan and master schedule
short range planning
material and capacity requirements planning detailed schedule of the orders
aggregate production plan
production output levels for major product lines (rather than specific products). coordinated with sales and marketing plan considers current & future inventory levels reconcile marketing plans for current products & new product development against the capacity resources
Master production schedule (MPS)
Lists (individual) products to be manufacutred, when to be completed, and in what quantities. converts aggregate scheldule into specific schedule of individual products products in MPS divide into three categories: firm customer orders forcasted demand spares
Inventory control
Balancing objectives: minimising the cost of maintaining inventory maximising service
inventory costs
investment cost storage possible cost of obselete product or spoilage
types of inventory
raw materials purchased components in progress inventory (WIP) finished products
Independent demand
Demand or consumption of an item (finished product/end product) unrelated to the demand of other items. e.g. car computer bike The inventory control system for independent demand items is order point systems (forecasting)
Dependent demand
Demand for an item directly related to the demand for something else, usually because it's a component of a product subject to independent demand. e.g. microchips for a computer wheels for a bike The inventory control system for dependent demand items is material requirement planning (MRP)
Inventory control systems
order point system: for independent demand items (forcasting) material requirement planning (MRP) for dependent items
Issues controlling independent demand items
how much to order: often decided by means of the economic order quantity formula when to order: accomplished by using re-order points replenishment
Economic Order Quanity (EOQ)
the order quantity that minimizes the total holding costs and ordering costs. EOQ = 2DaCsuCh\sqrt{\frac{2D_aC{su}}{C_h}}Ch2DaCsu where: Ch = holding cost $/pc/year Csu = set up cost Da = annual demand for the item
Total inventory cost (TIC) in terms of EOQ
usually /year TIC = ChEOQ2\frac{C_hEOQ}{2}2ChEOQ + CsuDaEOQ\frac{C_{su}D_a}{EOQ}EOQCsuDa where: Ch = holding cost $/pc/year Csu = set up cost Da = annual demand for the item EOQ = the order quantity that minimizes the total holding costs and ordering costs
EOQ and TIC example
Annual demand for a certain part is 6000 units/year. At present the setup time on the machine tool thatm akes the part is 4hr. Cost of downtime on the machine is $200/hr. Annual holding cost per part is $2.40/pc/year. a) Determine Economic Batch Quantity Da = 6000 units/year Csu = 4 hr x $200/hr = $800 Ch = $2.40/pc/yr EOQ=2×600×8002.40=2000EOQ = \sqrt{\frac{2\times600\times800}{2.40}} = 2000EOQ=2.402×600×800 =2000 pc b) Determine total inventory cost TIC=2.40×20002+800×60002000TIC = \frac{2.…
Re-order point system
when the inventory level for a given stock item declines to some point defined as the reorder point, the signals an order to restock the item. reorder point is set at a high enough level to minimize the probability that a 'stock out' will occur
Material requirement planning (MRP)
Computational process to convert the MPS for end products into a detailed schedule for raw materials and components used in the end products. detailed schedule indicates the quantities of each item, when to order it, and when to deliver it most appropriate for job shop and batch production of products consisting of many components. determines quantity of dependent items: raw material purchased parts WIP used to manufacture independent demand products.
Inputs to MRP
master production schedule (MPS) production design data, as a bill of materials file inventory records capacity requirements planning
How MRP works
MRP computes how many of each component or raw material will need in future time periods. 'Explodes' the end product schedule into successively lower levels in the product structure.
Complications of MRP
Adjustments for inventory on hand or on order common use items lead times
MRP output reports
order releases: authorize placement of orders planned. purchase orders: authority to purchase raw materials/parts from outside vendors work orders: authority to produce parts or assemble sub-assemblies in own factory planned order releases in future periods rescheduling notices: indicating changes in due dates or open orders Canceling notices: indicating certain orders are canceled due to changes in the MPS Inventory status reports Exception reports: showing deviations from schedule (overdue or…
Benefits of MRP
inventory reductions faster response to changes in MPS reduced setup and changeover costs better machine utilization improved ability to respond to changes in the MPS helpful in developing the MPS
Why MRP may not succeed
applications not appropriate product structure didn't fit data requirements (e.g. end product doesn't have many components) MRP computations based on inaccurate data MPS not coupled with capacity planning MRP generated an unrealistic schedule of work orders that overloaded the factory
Process planning limitations
available processing equipment technical capabilities of the factory/staff parts or sub-assemblies that cannot be made internally
Process planning steps
Analysis of part requirements Selection of raw workpiece Determining manufacturing operations and their sequences Selection of machine tools Selection of tools, work holding devices, and inspection equipment Determining machine conditions (cutting speed, feed, and depth of cut) Manufacturing times (setup time, lead time, and processing time)
Process planning for parts
The process to manufacture a given part are determined largely by starting raw material. Selected raw material limits the choice of possible processes.
Route sheet
'route sheet is to the process planner what the engineering drawing is to the product designer' specifies details of the process plan has all the manufacturing operations listed in order
Make or buy decision example
Quoted price from a vendor: $8.00/unit for 1000 units Same part made in home factory: $9.00/unit cost breakdown of make: unit material cost = $2.25 direct labour = $2.00 Labour overhead at 150% = $3.00 equipment fixed cost = $1.75 analysis vendors quote seems to favour buy, but consider the possible effects on the factory if it is accepted: equipment fixed cost is an allocated cost based on an investment already made. If said equipment is rendered idle by a decision to buy, the fixed cost of $1…
Retrieval computer-aided process planning (CAPP) systems, a.k.a. variant CAPP systems
based on GT, parts classification, and parts coding standard process plan is stored in computer files for each part code number standard plans are based on current part routings in use in factory or ideal plans prepared for each family for each new part, the standard plan is edited as necessary.
retrieval/variant CAPP process
group technology (GT) and part families
GT is a manufacturing philosophy in which similar parts are grouped together to take advantage of their similarities in design and production similar parts are arranged into part families (similar design and/or manufacturing characteristics) e.g. 10 parts all different in size, shape, and material, but quite similar in terms of manufacturing as all parts are machined from cylindrical extrusions by turning, then drilling and/or milling.
Generative CAPP systems
A process planner automatically creates a process plan using rules that might be applied using a human planner. In fully generative CAPP systems, the process sequence is planned without human assistance or pre-defined process plans.
Components of an expert system for a generative CAPP system
knowledge base: technical knowledge of manufacturing and logic used by process planner captured and coded in a program computer compatible part description: the description must contain all pertinent data needed to plan the process sequence interference engine: algorithm that applies the planning logic and process knowledge contained in the knowledge base to a given part descripton
dynamic generative CAPP systems
AI used to produce plan considers plant and machine capabilities, tooling availability, work centre, and equipment loads, and equipment status (e.g. maintenance downtime). process plan likely to vary over time depending on factory resources online display of process plan at workstations blending of process planning and production planning
benefits of CAPP
Overall: CAPP works well for discrete parts manufacturers with significant numbers of products and process steps. process rationalization and standardization: leads to more logical and consistent process plans than traditional process planning increased productivity of process planners reduced lead time to produce process plans improved legibility over handwritten route sheets can be interfaced with other application programs such as cost estimating and work standards.
main aspects of quality in design and manufacture
product features characteristics that result from design functional and aesthetic features that appeal to the customer, e.g. design configuration, size, weight distinguishing features of the model aesthetic appeal ease of use availability of options reliability/dependability durability and long service life serviceability freedom from deficiencies product does what it is supposed to do product is absent of defects and out of tolerance conditions conforms to specs components within tolerance no…
Traditional quality control
widespread use of statistical quality control (SQC) in which inferences are made about the quality of the population of manufactured parts based on a sample.
Primary sampling methods of statistical quality control (SQC)
control charts: graphical technique used to track measured variable over time acceptance sampling: if the sample passes, the population passes
Modern view of QC
high quality is achieved by a combination of: Three objectives of total quality management: Achieving customer satisfaction continuous improvement encouraging involvement of whole workforce good tech: traditional SQC tools combined with modern measurement and inspection tech
Total quality management (TQC) management principles and practices
quality is focused on customer satisfaction (both internal and external customers) quality goals are driven by top management quality control is pervasive in the organisation quality is built into the product, not just inspected afterwards production workers must inspect their own work continuous improvement
Process variability
Manufacturing process variations are of two types: random variations: result from intrinsic variability in the process assignable variations: indicate an exception from normal operating conditions
random process variations
a result of intrinsic variability in the process when process is operating normally human variations from cycle to cycle minor variations in starting material machine vibration
assignable process variations
indicate an exception from normal operating conditions operation errors defective raw materials tool failures equipment malfunctions
Process capability (PC) formula
the inherent process variability of a given characteristic, the ability of a process to produce output within spec limits. Mathematical definition: Process capability equals ±3 standard deviations about the mean output value (a total range of 6 standard deviations) PC=μ±3σPC = \mu\pm3\sigmaPC=μ±3σ where: μ\muμ = process mean set at nominal value of the parameter of interest (bilateral tolerances assumed) σ\sigmaσ = standard deviation of the process variability assumptions: output is normally di…
Process capacility index (PCI) formula
PCI=UTL−LTL6σPCI = \frac{UTL-LTL}{6\sigma}PCI=6σUTL−LTL where: UTL = upper design tolerance limit LTL = lower design tolerance limit 6σ6\sigma6σ = process capability (PC) if PCI ⪖\eqslantgtr⪖ 1.33, the process is capable and meets spec limits.
tools of statistical quality control (SQC)
control charts histograms pareto charts check sheets defect concentration diagrams scatter diagrams cause and effect diagrams
Control charts
Measured values of a process characteristic are plotted over time to determine if the process remains in statistical control. two basic types of control charts: control charts for variables requires a measurement of the quality characteristic of interest two principle types: X-bar chart, and range chart 2.control charts for attributes requires a determination of either fraction of defects in the sample or number of defects in the sample two principle types: proportion chart, and count chart
Interpreting control charts
the most obvious sign is when the sample mean or range are outside UCL or LCL. Less obvious signs: trends or cyclical patterns in the data sudden changes in average values points consistently near UCL or LCL eight consecutive points that lie on one side of CL six consecutive points in which each point is high (or lower) than its predecessor
Histogram (bar graph)
statistical graph consisting of bars representing different members of the population, in which the length of each bar indicates the frequency or relative frequency of each member. a useful tool as it is easy to visualize features such as: shape of distribution any central tendency in the distribution approximation of the mean and mode amount of scatter in the data
Pareto chart
a special form of histogram in which attribute data arranged according to some criterion such as cost or value. based on Pareto's Law: 'the vital few and the trivial many' often identified as the 80% - 20% rule, e.g. 80% of a nations wealth is held by 20% of the population 80% of sales are accounted for by 20% of the SKU's 80% of defects are of type A and B
Check sheet
data collection tool often used in the preliminary stages of a study of quality program.
Defect concentration diagram
A drawing of the product (all relevant views) onto which the locations and frequencies of various defect types are added. useful for analysing the cause of product or part defects so the underlying cause of the defects can be identified.
Scatter diagrams
an x-y plot of data collected on two variables where a correlation between the variables is suspected. The data are plotted as pairs; for each xi value, there is a corresponding yi value • The shape of the collection of data points often reveals a pattern or relationship between the two variables
Implementation of SPQ
five main elements are usually present in a successful SPC program: management commitment and leadership (management sets the example for others to follow) team approach to problem-solving (team members contribute a wide pool of knowledge) SPC training for all employees Emphasis on continuous improvement throughout organisation recognition and communication system to recognise successful SPC efforts
Examples of net shape processes
sand casting die casting injection moulding
Utilization
utilization tells us how well a resource is being used. Amount of productivity output relative to production capacity, %
internal vs external customers
external customers are people who buy the final product. Internal customers are people within the organisation (owner, board members, staff) who consume internal processes e.g. the assembly department is the customer of the parts production department within the same company