Programmable Automation Technologies. Daniel Kandray
Summary
Productivity calculations provide a very effective means for identifying, evaluating, and justifying the use of automation in a manufacturing facility. Productivity of a manufacturing system is determined by the ratio of the process outputs divided to the process inputs. If only one input (such as labor) is considered in the calculation, then the calculation is called a partial productivity (PP) calculation. When two or more inputs are included, the calculation is called a combined productivity (PC) calculation.
Process measures are used to quantify manufacturing processes. These measures then fill the role of outputs in productivity calculations. The most important process measure in terms of productivity calculations is production rate—the measure of how many parts are produced over a specific time frame, typically expressed in parts per hour. Production rate is calculated from the operational cycle time that includes all time element activities involved in producing one part.
Other important mathematical quantifying concepts include production capacity (the maximum rate of output of a particular product for a manufacturing system over a specified time period), utilization (the ratio of the actual number of products divided by production capacity, expressed in percent), and availability (how often a machine is actually available to perform processing). Manufacturing lead-time is the total time it takes to convert the raw material into the finished product.
Input of the productivity calculation (PI) is the amount of money into the process over the same time frame used in the output measurement. Inputs to the process are typically broken down into categories consisting of capital, energy, labor, and material. All of these inputs need to be expressed in terms of dollars per hour. For energy, labor, and material the calculations are straightforward. Capital costs of automation are determined by breaking initial cost of equipment into annual cost spread over annual hours the machine is estimated to run, the result added to factory overhead expenses.
Productivity calculations are a very effective method of comparing automation alternatives. Productivity index is then calculated, giving a clear and concise method for comparing partial and combined productivity measures of the two options being evaluated. One of the options, typically the current method, is assigned a baseline productivity index of 1. If a proposed option has a combined productivity index greater than 1, it can be said that it is more productive than the current method. A combined productivity comparison can serve as a starting point or roadmap for identifying the type and quantity of improvements necessary to justify automation.
To ascertain whether there is sufficient production volume to justify an automation investment, it is important to consider the current and proposed methods’ fixed and variable manufacturing costs. Fixed costs are independent of production quantity; variable costs, on the other hand, are dependent on the quantity. A production volume breakeven point analysis calculates the volume that justifies automation. The quantity breakeven point of two methods is found by setting the total annual cost equations equal and solving for quantity (Q), at which the manual and automated methods cost the same. In general, when product volumes are low, manual methods are more cost effective. As production volumes increase the advantage goes to automated methods.
The USA automation strategy directs us to understand an existing process, to simplify it, and if it is called for, to automate it. Using USA in conjunction with productivity analysis greatly enhances the probability of a successful automation project.
actual processing time
availability
average production time
batch processing time
bottleneck station
capital expenditure
combined productivity
fixed costs
manufacturing lead-time
operational cycle time
partial productivity
production capacity
production rate
productivity
productivity index
quantify
quantity breakeven point
tool handling time
USA principle
utilization
variable costs
workpiece handling time
1. How can productivity calculations aid in identifying, evaluating, and justifying automation?
2. Explain the difference between partial and combined productivity.
3. A manufacturing process can produce 640 parts/hr. The process requires three laborers each earning $26/hr. What is the labor partial productivity of the process?
4. The manufacturing process described in review question 3 uses a machine that has a capital cost of $95/hr. The machine operates on 150 kW of power. Cost of electricity energy is $0.057/kWh. The machine processes 215 lb material/hr. The material costs $0.85/lb. Using the labor input costs determined in Example 2.1, calculate the combined productivity of the process.
5. The following table lists the steps for a machining process. The listed times are required to load, unload, and process one part. Calculate the operational cycle time (tc) and production rate (Rp).
6) An injection molding machine processes a 24-cavity mold in 1.3 min/cycle. The parts are automatically ejected from the mold and travel by conveyor to the next process. After every 500 cycles the mold is cleaned and sprayed with mold release. This takes 8 min to complete. Calculate the operational cycle time (tc) and production rate (Rpq).
7) Calculate the cycle rate (Rc) of the flow-line manufacturing system shown in Figure 2-11, assuming the transfer rate is 5 sec/part and the processing time for each work station is as shown in table below.
Figure 2-11 Flow-line manufacturing system
8) Calculate the monthly production capacity (Pc) of a product made by the injection molding process described in review question 6. Assume the plant uses 8 injection molding machines and molds to produce the part. Also, assume the plant operates in three 8-hour shifts per day, 5 days per week. How could the plant increase production capacity in the short term? In the long term?
9) A manufacturing system has a theoretical production capacity of 500,000 parts/ month. Typical use of the system is 97% and availability is 99%. What is the anticipated actual monthly production of the system?
10) A part is routed through 6 machines in lot sizes of 300 parts/batch. Average non-operation time is 5 hr. Setup and operational cycle times are shown in the table below. Calculate the manufacturing lead-time for the part.
11) An automated work cell is being considered to replace an existing process. The cell will cost $350,000 to purchase and is anticipated to have a 7-year service life. The machine will operate for 2080 hr/yr. Also, consider that the company spent $4,600,000 on factory overhead and $8,250,000 on direct labor costs the preceding year. If the manufacturing firm desires a 10% return on its investment, estimate