Process Standards & Capacity
What would I do with the expected time each of the omelette tasks would require?
- To obtain reliable/robust data to allow us to drive proceed design and then operations decisions, e/g/ scheduling, Capacity, control/monitoring, inventory related decisions.
Intro to Standards
Strandard time
- A ‘standard time’ is the expected time to do a task.
- it assumes that the task is carried out correctly and consistently in a pre-determined way, and includes allowances for natural breaks, complexity, environmental factors, etc.
- it does not account for unexpected/unplanned events, that is for things that may go wrong - problems with the process, materials, data, interruptions or human errors.
- it is the average (expected) time that a trained operator could achieve when working on the task all day, and involves working at a rate of ‘100%’ – as determined by the International Labour Office, Geneva
- Accurate standard times are essential:
- in operations if capacity and costing calculations are to be meaningful, and if scheduling is to be effective
- used most often for activities that are regularly repeated
- Setting standard times is straightforward (but is hard work!)
- Determine the job activities
- Time the activities
- Develop the standard time for the job
Determine the job activities
- Direct work measurements: Time studies
- Stopwatch studies: obtain activity timings by direct observation under specified conditions
- Record a (large) number of instantaneous observations of a group of resources
- Indirect work measurements: Synthetic Data
- Production data applicable to a given context not obtained by some direct measurement technique Add up elemental times
- from previous time studies of other jobs (a.k.a. past experience)
- account for results of ergonomic laboratory studies of work and tasks
Process Plans
Process Analysis
- Process flowcharts
- Symbolic representation of processes
- Incorporate
- nonproductive activities (inspection, transportation, delay, storage)
- productive activities (operations)
Line balancing
- Objective
- Balance the assembly line
- Line balancing
- tries to equalize the amount of work at each workstation
- Precedence requirements
- physical restrictions on the order in which operations are performed
- Cycle time
- maximum amount of time a product is allowed to spend at each workstation
Process Design
Cycle Time Example
$$C_d=\frac{production\ time\ available}{desired\ units\ of\ output}$$
$$C_d=\frac{(8 hours \times 60 minutes / hour)}{(120 units)}$$
$$C_d=\frac{480}{120}=4minutes$$
- Flow Time vs Cycle Time
- Cycle time = max time spent at any station
- Flow time = time to complete all stations
Efficiency of Line
Line Balancing Procedure
- Draw and label a precedence diagram
- Calculate desired cycle time required for the line
- Calculate theoretical minimum number of workstations
- Group elements into workstations, recognizing cycle time and precedence constraints
- Calculate efficiency of the line
- Determine if the theoretical minimum number of workstations or an acceptable efficiency level has been reached. If not, go back to step 4.
Basic Line Balancing Example
| work station | Next station | Demand |
|---|---|---|
| A | - | 0.1 |
| B | A | 0.2 |
| C | A | 0.3 |
| D | B/C | 0.4 |
Demand for product
d=6000 unit per week
Production time available
p=40 working hours per week
PS: per week here is the time period
$$C_d=\frac{40hours\times60mins/hour}{6000 unit}=0.4 mins$$
$$E=\frac{0.1+0.2+0.3+0.4}{4\times0.4}=1/1.6=0.625=62.5percent$$
Balance Line
How many workstation i need to obtain a balanced line
$$N=\frac{0.1+0.2+0.3+0.4}{0.4}=1/0.4=2.5$$ round up tp 3 workstation
| work station | Work Element | Loading(in time) |
|---|---|---|
| A | 0.1 | 0.4-0.1=0.3 |
| B | 0.2 | 0.3-0.2=0.1 |
| C | 0.3 | 0.4-0.3=0.1 |
| D | 0.4 | 0.4-0.4=0 |
my target: workstation->3, $C_d=0.4$
we got:
$$E=\frac{0.1+0.2+0.3+0.4}{3\times0.4}=0.833=83.3percent$$
Process Seletion
Process Selection with Break-Even Analysis
- Cost
- Fixed costs
- constant regardless of the number of units produced
- Variable costs
- vary with the volume of units produced
- Revenue
- price at which an item is sold
- Total revenue
- is price times volume sold
- Profit
- difference between total revenue and total cost
Process Selection with Break-Even Analysis
Total cost = fixed cost + total variable cost
$$TC=c_f +vc_v$$
Total revenue = volume x price
$$TR = vp$$
Profit = total revenue - total cost
$$Z=TR–TC=vp-(c_f +vc_v)$$
- Solving for Break-Evan Volume
$$TR=TC$$
$$vp=c_f+vc_v$$
$$vp-vc_v=c_f$$
$$v(p-c_v)=c_f$$
$$v=\frac{c_f}{p-c_v}$$
Example
Fixed cost = cf = £2,000
Variable cost = cv = £5 per part
Price = p = £10 per part
Break-even point is:
$$v=\frac{c_f}{p-c_v}=\frac{2000}{10-5}=400parts$$
Quiz
ans:$\frac{8000}{3}$
Process A:
Fixed cost = cf = £2,000
Variable cost = cv = £5 per part
Price = p = £10 per part
Process B:
Fixed cost = cf = £10,000
Variable cost = cv = £2 per part
Price = p = £10 per part
Capacity Management
##What is Capacity?
It is a limitation that determines the ability to yield some output (products or service) per unit time
Formally it is defined as:
The maximum rate of output per period that a resource can achieve under assumed operating
conditions
Resource can be:
human, individuals or groups of individuals
machine, e.g. work centre or groups of work centres
facility, e.g. storage space
It can be measured in:
terms of output, e.g. number, weight, volume etc.
hours of labour
hours of machinery/equipment
Types of Capacity
- OPERATING CAPACITY
- IMMEDIATE
- that, which can be made available within the current budget period
- EFFECTIVE
- that, which is used within the current budget period
- POTENTIAL
- That, which is subject to long term strategic planning
What limits immediate Capacity?
The plant/equipment size
Availability of equipment
Availability of manpower
Availability of cash - financial policies
Availability of Material
The number of different tasks being undertaken – e.g. product mix
The technical demands of the tasks – production strategy and manufacturing system
configuration
What influences effective Capacity
Product design – design for manufacture
Planning policies
Purchasing policies
Sub-contracting policies
Maintenance policies and practices
Flexibility of workforce
Efficiency of workforce