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| UNIT F. PROCESS ORGANIZATION AND PRODUCTION PLANNING |
| COMPETENCY: 011.00: Assess and apply problem solving methods to the solution of technological problems. |
| OBJECTIVE: 011.01 : Design and Evaluate Workstation Setup |
Now that the tools and processes have been identified, it is time to study each workstation and design ways to reduce time and increase accuracy and safety of each operation. Time and motion studies are used to analyze workstation design. The purpose of conducting studies is to eliminate wasted motion. The process involves observing motion, collecting time data, identifying wasted motion, implementing solutions and testing. To achieve the most efficient work cell design, motion to perform the operation can be divided into the slightest movement and studied. Environmental factors such as lighting, temperature, color and sound are often studied to improve the work place.
To introduce this aspect of manufacturing system design, three areas of the material processing sequence will be presented. Areas of study in the sequence of material processing include:
Performance: Cutting, forming, conditioning or assembling the material. Involves either feeding the material into the machine or guiding the machine across material.
Completion: Inspect the completed process, transport part to the next station, and clear for receiving the next part. If the part is custom produced, procedures to safely shutdown the machine must be included.
Each step of this sequence can be analyzed to improve workstation or cell design. Can time be reduced by reducing motion? Can accuracy and quality be increased with tooling. Can safety be improved by reducing potential hazards. As you study each step, ask yourself these questions. Think of ways to refine workstation design with improved tooling or equipment layout.
Proper tooling increases speed, accuracy and safety. But first, be sure the proper tool or machine is used for the job. The most inefficient operations usually start by poor selection of processing equipment. Carefully think about your choice of tool or machine, cutter or blade and any accessories that will increase the quality and efficiency of the operation. These items are the base of workstation design. Equipment can be an asset or limitation depending on what is chosen.
Design of tooling for a specific process is the most effective way to increase efficiency. Common tools used to increase speed, accuracy and safety include:
Patterns and Gauges: Patterns and gauges are specialized measurement tools. It takes time to measure with a ruler and there is a chance to misread a dimension. Gauges and patterns are faster, easier and there is less chance for error. Patterns are forms or models used to replicate a design. Typically, patterns are used for layout and inspection. Gauges are used to measure a specified size. Material cut to length can be compared to a gauge to insure accuracy. Go-no go gauges are a special type used for quality control. Upper and lower tolerances can be checked to identify rejects.
Jigs and Fixtures: Jigs and fixtures are used for clamping and positioning material for processing. Jigs are stationary devices that are mounted on a machine. Material placed in a jig is positioned and clamped in place readied for processing. Fixtures serve the same function. The difference is that fixtures are designed to move the material to the process area. A fixture would be used to position and feed material through a cutter. Both jigs and fixtures reduce or eliminate layout time and provide accurate and consistent positioning. Quick clamping devices, such as toggle and cam clamps, are often used to secure the material quickly.
Feed and Transport Devices: Feed devices are used to move material into the processing area. Feed devices have several advantages. They move material at a constant rate so it is easier to control the process. For example, power feed on cutting machines allows precise control of feed rate so cutter speed and depth can be optimized. Mechanical feed systems are usually safe because workers do not have to be in hazardous areas. Transport devices are also used to move material to and from workstations. Conveyors, hand trucks, forklifts, robots, and automatic guidance vehicles help move material to work cells.
Safety is an important part of workstation and cell design. Safety device should be included in all machine setups. Machines have built in safety devices that must be used. In addition, devices often used to increase safety include:
1. Fixed Enclosures: Non-movable devices that are commonly used to prevent access to pulleys, gears, belts and other movable parts. Fixed enclosures can be used at the point of processing if they are designed to allow stock to be fed while preventing access of fingers or hands.
2. Adjustable Enclosures: Adjustable enclosures are designed to limit access to the point of processing. These enclosures can be adjusted to accommodate different sizes of material. They do not, however, prevent hands or fingers from entering the point of process. Proper adjustment and compliance with safety rules provided by the manufacture are essential.
3. Mechanical or Electrical Interlock: Enclosures that shutoff or disengage the power when opened. Interlock enclosures are commonly used on computer controlled machines and machines with automatic feed systems.
4. Two-Hand Trip: Mechanical or electrical control that requires simultaneous use of both hands to activate. This device prevents hands from being free to enter the danger zone.
5. Automatic or Semiautomatic Feed: Feed systems eliminate the need for the operator to be near the danger zone.
Safety is the most important aspect of work space design. When designing setups, jigs and fixtures, analyze safety requirements and incorporate safeguards in the design.
Time data should be collected during workstation and cell design and continue during the production run. Time data is required for line balancing in Step 5 and is essential for decision making during this step. Experimenting with different setups, jigs and fixtures require a measure of time as well as quality to compare methods and select the best. There are several methods for collecting time data. The common element of most is to calculate the average of multiple measurements. By calculating average, unusually long or short durations have less effect on the result. Since unexpected things happen, math and statistics reduce the chance that decisions are made on abnormal events.
The table below shows three data sets, Trial 1, 2 and 3. Time data are collected for each category of motion and the total is calculated.
| Preparation | Performance | Completion | Total | |
|---|---|---|---|---|
| Trial 1 | 15.2 | 12.5 | 3.8 | 31.5 |
| Trial 2 | 5.0 | 11.9 | 4.1 | 21.0 |
| Trial 3 | 5.5 | 8.2 | 4.0 | 17.7 |
If the three trials were used to test different setups, a comparison can be made to choose the best. Also data collected during these trials will be used to balance the production line.
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Print a |
To improve workstation design through time and motion studies, you need to:
With time and motion studies, you will learn:
