General INDUSTRY AND MANUFACTURING

Lean Workstation: Organized for Productivity.

Takt time, flexibility, standardized work and a layout focused on the operator rather than material handling are some of the differences between lean and traditional workstations that you will learn about in this article.

LIB Lean Institute Brasil Editorial team

Published on 1/31/2006

Portuguese translation by Odier Tadashi.

Pull production is the basic principle of lean production. In a pull system, downstream activities (such as assembly) signal or withdraw from the previous process what the upstream activities need, such as the distribution of materials. The same principle applies to a lean workstation; operators pick up parts and access work tools when and where they need them, in a process based on just-in-time.

Seen for the first time, a lean workstation may look very similar to traditional workstations, but they are conceptually different. For example, lean workstations must be designed so that there is minimal waste in operator motion, meaning any unnecessary time and effort required to assemble the product with quality and ergonomics. Excessive twisting or turning, hard-to-reach locations and unnecessary travel all contribute to wasted motion.

“With a lean workstation, everything must be choreographed and tuned like an orchestra, so that every movement has a purpose”, says Rick Harris, president of Harris Lean Systems Inc. (Murrels Inlet, SC). “It takes a new way of thinking. Traditionally, many workstations were laid out to make material handling easier, not for the value added by the operator”.

A lean workstation must focus on critical operator issues, such as safety, ergonomics, ease of picking up parts and speed of finding tools. A lean workstation puts all the material needed for production within the operator’s reach. Items are strategically positioned so that workers can reach tools and/or parts without even needing to look, using both hands most of the time.

In addition, a lean workstation is necessarily centered on takt time. Takt time is a common lean production term that refers to the pace of work (production cadence), normally used to relate demand to actual production. Takt time is determined by dividing the total production time available in each shift by the demand per production shift.

“A lean workstation is an area set up to perform a task that has been deemed an essential step in the manufacturing process”, says John O’Kelly, vice president of sales and marketing at Production Basics (Watertown, MA). “The station must be comfortable for the operator, as well as provide tools and supplies to complete the current task safely, while integrating into the manufacturing process. The workstation can function independently and be lean, but part of the effort is lost if the other workstations, processes and facilities are not in sync”.

In a traditional workstation, parts and tools are laid out horizontally across the entire work surface. “Not much thought went into doing that”, explains Eric Dotson, general manager of GWS Inc. (Kennesaw, GA). “A lean workstation, however, has a more vertical presentation, so that tools and parts are closer to the operator. This reduces space and the time spent searching for material”.

“Workstations reach various stages of lean manufacturing depending on how we support the principles of lean production through their inherent concepts”, adds Ray Gottsleben, sales and marketing manager at Arlink Workstation Systems (Burlington, ON). “Typically, lean workstations are broadly adaptable to accept changes in types of tasks or products, and can be reconfigured quickly. In this way they can help achieve maximum agility through unlimited layout possibilities, making them high-level lean workstations”.

Many experts consider Toyota Motor Corp. (Aichi, Japan) to be the benchmark for all lean production efforts. According to Art Smalley, president of Art of Lean Inc. (Huntington Beach,CA), Toyota engineers work hard to create workstations capable of following standardized work while also being flexible.

Four preconditions and three elements of pure work are necessary to achieve standardized work, says Smalley, a former Toyota engineer. The four preconditions are:

The workstation must comply with all safety regulations;
The station’s “in-work” time must be close to the planned ergonomics;
The input and output of quality products must be reliable so that quality is built into the process;
The work (especially manual work) must be cyclical and repeatable.

The three work elements are:

The operator’s workload must be close to takt time;
Keep only the correct (standard) amount of inventory for the intended work;
Create workstations where the operator works following the ideal sequence;

“A flexible workstation means, ‘Can the operator’s volume of work be changed as customer demand and product types change?’” says Smalley. “As volume varies, you should be able to change the number of operators in a location in proportion to the change. In a lean environment, you must always keep flexibility in mind, and be prepared for variations A, B or C of the workstation, in order to produce different (items) with quick changeover”.

Unfortunately, Smalley says, workstations are sometimes neglected, especially when only engineers focus on lean production initiatives. “There are many variations in lean workstations”, he points out. “Lean is very subjective. I see enormous variations”.

Wasted Motion

Eliminating wasted motion is a critical component of any lean production initiative. Unfortunately, workstations are notorious sources of waste.

According to O’Kelly of Production Basics, the most common wasted motion occurs when trying to reach for something. “This has a huge impact on workstation productivity and can easily be avoided with the correct size, height and configuration of the workstation (ergonomics)”, he claims.

“The act of reaching is a “waste” of time, since no value is added when trying to reach something”, adds Gottsleben of Arlink. “Excess of this motion is probably the most common type of waste, and usually the easiest to identify. “Reaching” combined with “standing still”, bending and stretching compound the problem through excessive use of physical force and wasted time”.

When muscle strain is combined with excessive reaching, as when bending the back to lift heavy objects or look for tools, these are causes of falling productivity, increasing fatigue over the course of the shift. “Excessive walking is another indicator of a sub-optimized workstation”, says gottsleben, “except in cases of cellular production, where an operator moves between adjacent stations”.

Wasted motion on an assembly line can vary with production and the associated volume. “In low-volume, MTO manufacturing situations, the typical waste occurs in searching for tools, parts and information to finish the job”, explains Art Smalley. “In high-volume production, waste is typically related to the operator turning, twisting, trying to reach for something or walking after parts”.

Quarteman Lee, president of Strategos Inc. (Kansas City, MO), believes it is time for engineers to revive “the principles of motion economy”. Ralph Barnes, a professor of business administration at the University of California – Los Angeles (UCLA), systematized the principles in 1930 and they were applied successfully during World War II. In 1950, Toyota incorporated motion economy into its famous production system, which forms the basis for most lean production efforts today.

“Then, in its fascination with computers, American industry largely forgot about motion economy during the 1960s”, Lee points out. “When lean production was re-imported from Japan, motion economy was left behind”.

“The principles of motion economy reduce waste at the workstation on a micro scale”, explains Lee. “They make repetitive tasks easier, more efficient and more effective. They also reduce cumulative injuries, such as tendinitis and Carpal Tunnel Syndrome”.

“At first, they seem simple, obvious and merely common sense”, adds Lee. “But if motion economy is common sense, then common sense is not very common”.

However, Lee cautions that motion economy has limitations. For example, it does not take into account operators’ physical limitations or differences.

“A motion that seems inefficient from the perspective and analysis of motion economy may prevent fatigue and possible injuries from static loading postures”, Lee stresses. “However, using them together with the principles of ergonomics and streamlined procedures will ensure workstation productivity, safety and optimization”.

What to Look For

For it to be a truly efficient lean tool, manufacturing engineers must devote more time and effort before developing a workstation.

“Many workstations simply happen”, says Lee. “Nobody spends much time developing them”. When evaluating a workstation, he recommends focusing on specific areas, such as transport and handling of product or materials, of tools and parts, as well as organization and storage.

“It is especially important to analyze how often a part is reached for”, adds Lee. “The most commonly used parts should always be located as close as possible to the operator”.

Other experts believe that adaptability to process and product changes is the most important thing. “The only certainty is the inevitability of change in products, processes and the tools used to produce them”, notes Gottsleben. “The workstation must not be a barrier to change, but a complement to and an aid for change”.

“The workstation must be easily and inexpensively adaptable to changes in processes and tasks, and of course set up according to the physical attributes and work habits of those who use it”, argues Gottsleben. “As a production tool, the ultimate goal of the workstation is to increase the productivity of the people who use it, while providing constant flexibility and agility to meet the changes in assembly processes defined by engineers”.

Gottsleben wants manufacturing engineers to become familiar with the basic principles of ergonomics. For example, he says it is important to know the three primary ergonomic operating zones: the optimal work zone, the optimal handling zone and the maximum handling zone.

“Assembly sequence, parts movement and the organization of tools and equipment should all be considered in light of these three zones”, claims Gottsleben. “And (engineers should make) an effort to encompass all the work within these zones, with emphasis on the two optimal zones”.

“When developing a workstation, it is important to remember that people move in arcs, not in straight lines”, says Chris McIntyre, president of Ergonomics at Work Inc. (Waterloo, ON). “Many workstations tend to be designed in a rectangular shape. As you move parts and tools away from the body, they end up becoming difficult to reach”.

Ergonomic reach zones extend vertically and horizontally. Reach locations lower than shoulder height are less tiring. Routinely used tools and parts should be placed within the horizontal reach areas whenever possible.

Engineers should also choose workstations that are in line with the principles of lean production. For example, engineers should incorporate the 5Ss into every workstation they design.

The Lean Enterprise Institute (Brookline, MA) defines 5S as five related terms, each beginning with an S, that describe workplace practices conducive to Visual Control and lean production. For example, a 5S approach should be used to label and mark tools. A simple tool outline would serve as a visual reference and help ensure easy identification and quick access.

5S is based on Japanese words translated into Portuguese as Sense of Utilization, Sense of Organization, Sense of Cleanliness, Sense of Standardization and Sense of Discipline. However, Toyota traditionally refers to only 4 Ss:

Sort – analyze what is in the work area, separating and eliminating what is not needed;
Set in order – organize the items that are needed in a clear and easy-to-use way;
Shine – clean the work area, equipment and tools;
Spick and span – general organization and cleanliness resulting from the disciplined practice of the first three Ss.

The fifth S, sustain, is not used by Toyota because it is redundant within the company’s system of daily, weekly and monthly audits that check work standardization.

Smalley says that Toyota emphasizes Safety first, Quality Assurance second and then Standardized Work. When planning a production operation, Toyota engineers fill out detailed forms to think through the motions the operator will have to perform. “It is a fact-based verification system that is very rigorous, but that leads to safe and repeatable manufacturing processes”, notes Smalley.

“When I ask an operator ‘What makes a good day?’, the typical answer I get is: ‘My machine is running well today; I have the parts I need at the right time and I have no quality problems”, adds Smalley. “Toyota (ensures this happens through) standardized work and by creating a safe and repeatable work pattern, set close to takt time. When people can find an uninterrupted rhythm, the day goes by faster, and quality and productivity tend to increase”.

Operator Concerns

Watching the operator at work is an important part of the workstation improvement process. “They know better than anyone how products are manufactured and processed”, says O’Kelly of Production Basics. He suggests asking operators a series of questions, such as: What bothers or annoys you? How does the workstation fit into the simplification of the environment? What happens before and after the product reaches the workstation? What would you like to change in the work area? What do you like here?

“These factors affect the size, shape, choice of accessories and placement of the workstation, and whether it should be mobile or stationary”, says O’Kelly. “Document the different tasks that need to be performed at the workstation and the accessories that might be able to help. Use the operator’s input to define modular workstations that provide variations in work area, configurations or size, such as height, depth and width”.

For example, O’Kelly says engineers can add adjustable components, such as articulated arms that allow tools to be moved within the operator’s optimal work zone. “Height-adjustable worktables are the best options for work areas used by several people”, he points out. “Using a crank or an electric button, operators can easily adjust the height of the work surface. These factors contribute to a lean workstation, eliminating unnecessary motion and increasing operator productivity”.

According to Gottsleben, raising ergonomic discussions as part of the workstation development process will avoid many costs in the long run. “Operators need to feel that they have some control over their work environment and can adapt the workstation as best they can without compromising the manufacturing process”, he points out.

However, manufacturing engineers must do more than just watch workers at work. “Engineers need to get in and perform the task to get a better perspective of reality”, says McIntyre. “Try it yourself. Try working at the workstations you have designed. Ask questions such as: How much force do I have to use? What position should I use?”

“Most engineers talk to the operators, but they don’t really sit down and do the work”, adds Ken McCormick, flow cell production manager at Unex Manufacturing Inc. (Jackson, NJ).

“Many engineers also fail to build a prototype of the workstation, using cardboard, polyethylene and PVC pipes”, says Harris of Harris Lean Systems. “We always invite the operator during the simulation. He becomes the king at that moment. We put him in his workplace and let him evaluate the station”.

Parts vs. Tools

When designing a lean workstation, engineers must determine whether it is more important for operators to be able to pick up parts efficiently or to find tools quickly. The answer depends on several factors, such as the type of product being manufactured.

“Engineers must consider the trade-off between efficiency and speed”, says Dotson of GWS Inc. For some applications, a successful workstation starts with the tools in a central place where they will be used. The rest of the workstation can be designed around that place, placing parts where they are needed. In other cases, parts receive greater consideration than tools.

“Both are needed to do the work”, explains O’Kelly. “The ideal workstation allows parts and tools to coexist peacefully”. He says stations can be designed to accommodate all the parts and tools needed for a day’s work by incorporating drawers, shelves, racks and modular carts.

While parts and tools are equally important, Harris believes there must be some trade-off. “The tools the operator will use in every cycle should be placed as close as possible”, he points out. “Many engineers focus heavily on tool position without enough interaction with the operator. They fail to get input from the operator”.

The parts vs. tools dilemma should be resolved by the nature of the work being done. “If it is a parts-intensive task, requiring many parts to be incorporated within a short production cycle time, then it is probably more important to have efficient access to parts”, comments Gottsleben. “If it is a tool-intensive task, where only a few parts are needed but many different tools are required to produce, adjust or calibrate the assembly, then it may be better to focus on tool retrieval”.

“Either way, the engineer developing the process should categorize the assembly operation by its dominant activity, whether ‘parts’ or ‘tools’, and then optimize the process by placing the most frequently used items within the optimal work and handling zones”, adds Gottsleben.

Volume also affects which of the two, parts or tools, is more important for the workstation. Typically, with lower volumes, the location of tools becomes more important, especially if special use of tools is required to assemble the product. In high-volume production environments that use standardized parts, efficient parts picking for the operator becomes a more important consideration.

“It depends on the type of product going through”, concludes Smalley. “With low volume, there is typically more operator movement, such as having to walk more. Flexibility may be more important to accommodate a greater variety of products. In a high-volume production environment, the operator can rarely move around during the shift”.

Principles of Motion Economy:

The two hands should begin and complete their motions at the same time;
The two hands should not be idle at the same time except during rest periods;
Arm motions should be made in opposite and symmetrical directions and should be made simultaneously;
Hand motions should be the simplest with which the work can be done satisfactorily;
If motion through muscular effort is required, it should be minimized;
Smooth, continuous hand motions are preferable to zigzag motions or straight-line motions with sudden, sharp changes of direction;
Ballistic motions are faster, easier and more accurate than restricted or controlled motions;
Rhythm aids smooth and automatic performance. Arrange the work so that it has a natural, easy rhythm;
There should be a definite and fixed place for all tools and materials;
Tools, materials and controls should be located close to and directly in front of the operator;
Gravity-feed bins and containers should be used whenever possible;
Materials and tools should be located so as to permit the best sequence of motions;
Relieve the hands of work that can be done more advantageously by a jig, a powered device or a foot-operated device;
Combine tools whenever possible;
Pre-position tools and materials;
Where each finger performs some specific motion, the load should be distributed according to the capacity of each finger;
Levers, crossbars and handwheels should be placed in positions where the operator can manipulate them with the least change in body position and with the greatest mechanical advantage.