The purpose of capacity analysis is identification of the job capacities (see more in Hales and Andersen 2002). The priority is to produce the required accurate information for determining the process capacity. A time study should be conducted wherever it is necessary. As a result, the production capacity for each process will be designated.
To fulfill the processes, their necessary activities are identified and their times are measured and/or estimated. In this way, activity times per unit are obtained based on the roles in the processes. Working frequencies of the job are calculated and/or are estimated by linked them with the job results. Thus, necessary periodical workforces (for instance, monthly) are detected on the basis of the roles. Capacity requirements can be defined as the differences between the existing manpower resources and demand. Therefore, simplification, merging, and separation can be applied by comparison of capacity and work sizes.
Variables such as workforce, process error rates, activity durations, arrival and progress rates of the jobs to the system, costs and revenues, production goals, labor, and equipment utilization rates shall create a base for the improvement step. Capacity analysis investigates the following:
- • The delay at each station
- • The utilization rates of available resources
- • The scenarios that can increase production with the available resources
- • The impact of changes on all processes
As a result of the capacity analysis, the following outputs are targeted:
- • Activities with simplification requirements
- • Optimum activity finish time and capacity
- • Capacity improvement alternatives
The planner uses charts and diagrams to visualize the routings for each class or subgroup of parts, and then calculates the number of machines and/or operators and workplaces that will be required to satisfy the target production rates and quantities.
When calculating the number of machines, planners must be sure to add allowances for downtime, schedule interference, and change- overs between individual and groups of parts.
Capacity analysis shows the types and quantities of machines required. A worksheet, with an example of this capacity utilization analysis, is shown in Figure 5.22.
A good capacity plan meets the desired production rate with an appropriate number of machines and level of utilization. Usually, the analysis will reveal over- and underutilization of some equipment planned. If the analysis reveals overutilization, the planner may choose to
- • Remove parts from the cell to reduce utilization ofthe equipment.
- • Purchase more equipment.
- • Reduce process, changeover, or maintenance times.
If the analysis reveals underutilization, the planner may choose to
- • Add parts to the cell to increase the utilization of equipment.
- • Remove parts from the cell to eliminate the need for the equipment.
- • Change the manufacturing process to eliminate the need for the implications of changes to product mix and peaks in production volume.
The Capacity Utilization Worksheet summarizes the machine processing hours for a group-of-parts cell making machined metal shafts.
Figure 5.22 Capacity utilization worksheet—example.
Figure 5.22 (Continued) Capacity utilization worksheet—example. Source-. Hales, H. L., and Andersen, B., Systematic planning of manufacturing cells. Society of Manufacturing Engineers, Dearborn, Ml, 2002.
The bottom section of the worksheet summarizes the rough-cut analysis of machine requirements.
Allowances for setups, scheduled maintenance, and unplanned downtime have been calculated on worksheets such as that shown for the spline mill work center 40.
Given the use of averages and aggregate allowances, planners should examine machine utilization above 85% for possible overloading during extreme conditions. On this basis, five work centers in this example should be examined.
5W is a technique in which possible causes of the problems necessary for the evaluation are examined (see more in George and Maxey 2004). For each possible reason, ask the “Why” question five times (as far as it can go), which is illustrated in Figure 5.23.
At this point, let us take a frequently given example, shown in Figure 5.24. Let us say that the problem is that a hanged frame frequently falls on the ground.
- 1. Thesis No. 121: The selected screw is not suitable for the frame weight.
- 2. Validation: The frame’s weight is 3.5 kg. The screw can carry a 20-kg weight.
- 3. Thesis No. 2111 will be handled as one of the root causes of the problem.
Figure 5.23 Five whys.
Figure 5.24 Advanced five whys—example.