THE NINE PRINCIPLES OF LEAN MANUFACTURING - PARTE 2

A properly designed lean workcell must be easy to reconfigure. In fact, the ability to change the process and go from good part to good part as quickly as possible is a must. The faster the changeover, the less production time is lost.

Quick-change fixtures are one way this can be accomplished. With a good quick-change fixture, changeover can be accomplished in a matter of seconds. A number of different fixtures may be stored at the workstation and swapped as the situation requires.

An assembly fixture is locked to the T-slot at the front of a workbench with a star knob and quarter turn connector. Once the assembly of a specific product is complete, a new fixture can be easily positioned.

At times, due to process changes or other factors, a lean cell must be quickly reconfigured or even moved to accommodate assembly of a new product. In the event that a machine or workstation must be changed, the ability to move each component of the workcell quickly becomes extremely important. Lockable casters on machines or workstations provide the mobility necessary for rapid and efficient changeover.

6. Quality

One of the results of one-at-a-time manufacturing is a decrease in quality problems. As each part is produced, visual inspection by the worker can verify that it is correctly assembled. If verification is required through gages, they should be mounted to the machine or workstation and be easily replaced. Quick release of fixtures using star knobs or locking levers is a necessity.

There may be time when a quality problem cannot be easily fixed. A flawed process or malfunctioning machine may be the source of the quality problems.

In the case of a flawed process, the structural framing system allows changes, no matter how great, in a minimum amount of time. Once again, bolt-together construction solves a major problem in minimum time.

A malfunctioning machine may also be easily replaced, particularly if quick disconnects for all pneumatic or electric lines are provided for when the lean cell is designed. In addition, no pneumatic or electrical connections should be present between machines in the lean cell. These would slow the changing of the machines within the cell.

Once the machine has been disconnected from all power sources, it can be easily transported if mounted on lockable casters. Ease of reconfiguration and changeover eliminate any reluctance on the part of the worker or management to try to "make do" with machines or processes that are "almost" right. This change in attitude can contribute greatly to true quality production.

Ease of service is another requirement of a lean cell. Long down times cannot be tolerated in a pull-through system. When customer demand exists, the product must be produced. A modular structural framing system provides the ultimate in maintainability. Components can be replaced or reconfigured in a matter of minutes. Bolt-together construction ensures machine stands, guards, workstations, or parts presentation equipment can be serviced in a matter of minutes. Even entire machine bases can be rebuilt in a minimum amount of time.

The structural framing system also provides a source for common components for all machine bases, guards, and workstations. With standardized components, a minimum number of tools is required to maintain a structure. With a structural framing system, three or four simple hand tools are sufficient to build or repair any structure.

Another benefit is that common components eliminate the need for a large inventory of spare parts. It is possible to standardize on one size of aluminum profile, one or two connectors, and a few accessories to create virtually any structure.

Finally, no finish work is required with an aluminum structure. No welding or painting is required. Repairs can be accomplished in the minimum amount of time.

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8. Ease of Access

Using an aluminum framing system as the foundation of a lean cell, all necessary work components can be mounted in easily accessible locations because each surface is a potential mounting surface. Parts bins, tools, shelves, and fixtures can all be positioned in the optimum location for efficient work. The T-slot on the framing system's surface also allows quick repositioning of pneumatic or hydraulic components if clearance space is critical.

Components may be added quickly to any workstation and easily repositioned to insure accessibility for each worker. In addition, entire guards or individual panels can be removed quickly with simple hand tools, enabling service technicians to perform maintenance in a matter of minutes.

9. Ergonomics

Finally, the worker must be protected from ergonomic problems. Any properly designed lean workcell must, by definition, be ergonomically designed. Maintaining the work at the ergonomically correct height throughout the workcell is always important.

Although it is frequently not taken into consideration, designing for the average worker height is also a necessity. Since average heights vary from country to country, the height of a machine or workstation must be easily changed if there is any chance that a workstation may be shipped from country to country.

10. Lifting

Lift assist devices must be considered where the weight of parts or boxes of parts exceeds lifting standards. In this case, pneumatic, hydraulic, or electric devices may be used, but it is important to keep in mind that simpler is better in lean manufacturing cells.

In order to prevent delays in manufacturing caused by faulty design, a software package that allows you to test the ergonomics of a workcell before the workcell is constructed can be a powerful tool. Use of such a software package lets you settle ergonomic issues in the design stage rather than on the factory floor, providing significant potential savings in both time and money.

With all of its promise, the lean cell may not be the answer to all assembly needs. At times the U-shaped configuration simply does not fit the existing facility or process, and a change from automation or semi-automation to lean cell manufacturing could be counterproductive.
In keeping with the flexibility requirement for lean manufacturing, there may be times when a hybrid system rather than a pure lean system is best for the manufacturing process.

Hybrid manufacturing systems combine the economies of the lean system with the safety and efficiency of an automated system. The result is a system in which some assembly is done manually while more dangerous or ergonomically difficult tasks are accomplished by machine.

In a hybrid system, workstations or cells may be combined with non-synchronous assembly conveyor systems to achieve desired production goals. The synergy between these two technologies can produce results far beyond the capabilities of either technology alone.

It is also possible to accomplish assembly in a lean cell and to have operations which are purely automated take place off line. In this case, the automated portions of the process supply sub-assemblies or parts to the lean cell. Here, although the technologies are separated, both are still required to accomplish the task at hand.

The key to hybrid implementation is construction with components which are easily reconfigured. Bolt together technology fits the description perfectly.

Flexible assembly systems using aluminum framing as the main structural element allow companies to mix and match manual and automatic operations at will, and to change them at any time in the future. The result is a worker-friendly, economically-sound system designed for optimum production.

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