While many lean manufacturing techniques were pioneered in the automobile industry, it has also been successfully applied to high-mix, low-volume job shops including sheet metal forming shops.

Applying lean makes the sheet metal works and HVAC construction contractor more competitive and successful.

Lean shops need to be flexible and allow workers to change the design and workflow to fit current job requirements. Before one can apply any technique effectively and consistently, one must understand the basic principles and concepts applicable to it. Creating a lean shop starts with a foundation of lean principles.

Lean seeks to add value to the product in behalf of customers. Value is what customers pay for. Customers do not pay for sheets or coils of metal. Sheet metal is only of use to customers when it is fabricated, installed and a working system.

Value is added when sheet metal products are being physically changed into what customers need. Cutting, welding, rolling, beading, bending, etc., are value-added steps. If nothing is happening to the metal, such as waiting for the plasma cutter, or to run through the TDF machine, it is waste. Even though the material is not defective, it is still waste because value is not being added, and the customer is not using it at that time.

Value is the opposite of waste, and lean works to eliminate waste. Understanding value and waste is key to applying lean. There are seven basic types of waste:

Defects: Included are defects in fabrication, installation errors, punch lists, many kinds of change orders, and not meeting required codes. Rework is waste.

Overproduction of goods: Fabricating or ordering material too early and stockpiling material in the shop, in a warehouse or at the jobsite, is waste. This waste is the “mother” of most other wastes including: inventory, transportation and motion.

Inventory: Any material not yet installed and being used by the customer is inventory and also waste. This includes unfabricated material, work in process and finished fabrications, spare parts, unused tools and consumables. Employee stashes and personal stockpiles are very wasteful inventory. Over-production by the shop causes inventory no matter if fabricated parts are stored at the shop or job site.

Inventory is very costly though much of the costs are hidden. Inventory ties up working capital and space; it must be controlled and continually monitored; it must be audited, usually annually, and it often leads to additional handling, especially on jobsites.

Some inventory is usually needed to ensure that the work is performed in a timely manner — to avoid the waste of “waiting.” This is called strategic — or necessary — inventory. While it is still waste to attack and reduced as much as possible, it is necessary. Any additional inventory is excess and to be eliminated. The challenge is to differentiate between “excessive” and “strategic.” Get rid of the excess, and then look to reduce the strategic inventory as long as it never impacts the crews’ ability to keep installing.

Many shops have a lot of inventory in the form of just-in-case material. Shops hold on to excess partially or fully fabricated material just in case they will need it for the next job. In doing waste walks in shops, you often find piles of fabricated duct that have been around for years. Clean out the excess inventory.

Motion: “Treasure hunts” happen when workers go looking for tools, cut sheets, material or information. This is waste big time in the shop and field.

Transportation: This waste happens when material is moved around the shop, loaded on the truck or trailer, hauled to the jobsite and unloaded. 

Waiting: This includes when a shop worker waits for instructions, inspections, change orders, or material to be loaded. It also includes material waiting to be fabricated or installed.

Overprocessing: This includes over-engineering, requiring additional signatures on a requisition, multiple handling of timesheets and duplicate entry on forms. Any step in a process that is not value added is overprocessing.

When considering lean possibilities one should always start with a goal. Doing lean just for the sake of “being lean” should never be the end goal. The goal is to capture and grow market share, either through direct product sales or more often, by supporting the field installation crews. Lean is an effective pathway to this goal. For sheet metal works shops, the focus of lean should be on reducing lead times, improving on-time delivery and reducing the seven basic wastes.

Reducing lead times, meaning the time it takes for a piece of material to be fabricated, will allow contractors to respond to customers’ last-minute needs. When in-house crews or external customers know they can depend on the shop to always meet the promised delivery date, contractors may gain market share, especially in this very competitive market.

Time is money to customers and companies. We want to keep the metal — aka value — flowing through the shop and delivered to the installers. A key lean concept is to make value flow. When organizing the shop, plan so work flows.

When contractors study their shop flow, we discover that sheet metal products are waiting more often than they’re being fabricated. In one company, only 10 percent of the steps involved in the whole fabrication process were value-added. There is much waste in waiting.

Improving lead-time requires a focus on creating continuous or almost continuous flow of the fabricated products. Continuous flow will help identify problems quicker. This can improve quality, another customer requirement. With continuous flow, quicker communication between steps is needed because we can’t hide the problems in the large batches. Continuous flow also facilitates increased productivity and conserves resources.

Most sheet metal products fabricators continue working in batch mode. Flow is a foreign concept to most shops. Creating continuous flow starts with “FIFO,” which stands for “first in, first out.” Don’t start fabricating a product until all components are in place to finish that piece. What often happens is material is sheared and then waits on a sheet metal forming table for several days. This rolling table may even be moved around several times during a day. Finally, the items are processed a few days later. Do not start a job only to have to stop and wait for some specialty item on backorder. To get the best flow possible, think through the flow of the job. Walk through the process in the shop to identify the best ways to move product from one tool or step to the next. 

Don’t burn or shear metal for as many jobs as possible and hope to push it through the rest of the process. In a lean shop, you want the work to flow and avoid having materials waiting on tables or carts. You also want to minimize the number of times workers handle, but not add value, to the metal. Burning several jobs and placing all the pieces on the tables is batch work and causes waste. These pieces are sorted many times depending on which ones go to the edger, roller, break machine, etc.  Sorting is wasted motion and should be minimized or stopped.

Instead, burn or shear one piece of ductwork at a time and move it directly through the complete fabrication process with as little waiting as possible. Programming for metal-burning machines will optimize cuts, and may cut more than one piece of duct on one sheet of metal. As the cut pieces are taken off the burn table, put all sides for one duct piece on one table and the other sides of the next piece on another table. This may seem like you are under loading the tables, but you don’t want the jobs stacked. You lose efficiency every time you touch or sort too often. You want value to flow one duct piece at a time. Keep all sides of the duct piece on one table and move them together through forming, insulating and assembly as fast as possible. As this is done, it will also allow the duct forming equipment to be moved closer together, avoiding waste in moving pieces around, and smaller tables/carts can be used, freeing space.

In many cases, the product can’t flow continuously from one step to the next, but it can be pulled to the next. “Pull” means don’t make or send it to the next step until that step is ready. Many companies often push product through by cutting all pieces for the job at one time. Workers then batch-load the pieces and move them to the next step. You are pushing it downstream. If the welding station is not finished with the previous job and more products are brought to the work area, it congests the space and creates confusion. The worker must now worry about the next job. A better way is for the upstream step to stop fabricating, and the worker helps the downstream step catch up.

Lean especially focuses on managing the handoffs between steps. Avoid letting work pile up; don’t keep cutting more pieces, move workers around to create flow in the downstream steps. Focus on quick setup at each step to reduce time getting ready to fabricate the next piece of sheet metal. 

Nobody runs totally automated fabrication plants. Workers make the product and are necessary to make lean manufacturing work. Front-line workers need to be engaged in reducing lead times and waste. Employees become really engaged as they learn lean principles and tools, and are asked for their improvement ideas. Management must listen to employee ideas and take action where possible.

Management should discuss each job’s requirements and delivery dates with workers so they buy into the requirements and schedule. This discussion can be part of a morning meeting.

Doing a “walk through, talk through” with employees before starting any major job will improve productivity. Teach employees problem-solving skills so they will address problems in a systematic and effective way.

A key lean principle is “go and see.” This means we don’t just talk about problems and solutions in the office, but actually spend most of the time observing how the work is done and what keeps it from flowing. We watch for bottlenecks. Do frequent “muda” — the word means “waste” in Japanese — walks to watch how work flows — or doesn’t. Especially look for piles of work in progress, signaling stalled flow. Watch for when the product is waiting and/or being moved to another tool. These are non-value-added steps and should be reduced, if not eliminated. (Attack the seven basic types of wastes common in all work.)

Managing priorities

An important principle of lean is to focus on the three priorities for managing work. They are:

  1. Keep the crews doing value-added work. The customer is paying you for a completed job that meets their requirements and expectations. For the fabrication shop, the install crew is usually the next-in-line customer. The crew is the contractor’s most expensive per-hour work unit and should always be installing value-added work. All support functions and efforts should be focused on this priority — keep the crews doing value-added work. This means you don’t want to gain efficiency in the shop that creates greater work in the field.
  2. Reduce inventory. Because of the hidden costs of inventory, you want to reduce work in progress, and inventory, as much as possible without impacting priority No. 1.
  3. Reduce other costs. Any way to save money in how you purchase, store and ship sheet metal works parts and material and in how you cover administrative costs, helps you be more profitable as long as it does not interfere with the No. 1 priority.

Lean thinking starts with understanding value and waste, and the priorities of managing work.

Tools for the shop

In construction, there is much “treasure hunting” going on. Workers looking for material, tools, equipment, etc., do not add value. The same goes for sheet metal products shops — there is too much time wasted looking for materials and tools. Five S (usually shown as “5S”) is a lean tool for creating a more effective shop. It is used to organize the shop’s tools, material and equipment so workers have what they need, when they need it and where they need it. This eliminates hunting that happens every day, all day.

You want to locate the tools used at each machine right next to it or even on it.

Organizing where things go is actually the second “S” — “simplify.” The first “S” should be done first for a good reason. It is “sorting” and means to sort out all that is necessary for ductwork fabrication from that which is not. Many shops have materials and tools lying around, cluttering the work area. Much of this clutter is not needed or used very often. If you haven’t used something in the last year and don’t have a specific use upcoming — get rid of it. Or, at least, move it out of the main shop work area.

Clutter is waste. Get it out of the way.

To simplify the shop, put tools and consumable material used in fabrication such as corners, screws, etc., based on where each is used.  You want it at the point of use. A shadow board or other visual can show the location and make it easier to find.

Locate tools and parts by frequency of and in the order used. Workers should carry some basic tools on them while working. It is inexcusable when workers hunt for tape measures that they should have had on them.

The third “S” is “sweeping.” It means to physically clean up the work area. Less clutter makes it easier to spot problems and creates a safer work area. Sweeping is more than cleaning. It means to deliberately pick up the work areas for tools and material that are out of place and return each to its assigned place as defined in the previous step (simplifying). By returning tools to the place they are to be kept, the next user can find them quicker (less treasure hunting). Sweeping is also a form of respect for one’s fellow workers.

The fourth “S” is “standardizing,” meaning to create standard ways to keep the work areas organized, clean and orderly, and standard ways to do 5S. You want to have a standard color code, standard gauges, welding machines, etc., to reduce learning curves.

Self-discipline (also translated “sustain”) is the last “S” and means to follow through with the 5S’ agreements. You want to “maintain the gain.” One way to do this is to design a 5S checklist and have different workers score the shop monthly, using the list. This helps maintain focus and indirectly educates those doing the assessment. A simple test to see how far efforts have come is to use the 30-second test. Can a worker go to a toolbox or material storage area and, excluding travel time, find what he needs in 30 seconds or less and move on? If not, then more 5S work is needed.

For 5S to be successful in a shop, the workers need to understand why they are important and they need to be involved in applying them, otherwise the shop will soon default back to its disorganized past.


“Kanban” is a Japanese word meaning a signal to replace. It is a method for keeping strategic inventories, especially consumables, in place and excess to a minimum. There are many variations of how this works, but all are similar: 

  • The min-max approach uses a mark or painted level to show the maximum level to fill parts. A second level or mark is shown to know when to reorder parts. Reorder information including part name, number, and quantity to order, vendor names and contact information is contained on a card pulled when the minimum level is reached.
  • The dual-bin system is similar to the min-max. In this case two bins of parts are located together. When the first bin is empty it is removed and contains the reorder card. The work draws from the second bin and does lose time doing value added work while the first bin is refilled.
  • A red-green color code system is often used to signal time to reorder. Workers draw product from the green marked shelf or bin, then when it is empty they draw from the red shelf and a kanban card is pulled to reorder stock.

Quick and easy

“Kaizen” is the Japanese word for continuously improving. One way to improve is to get all workers to identify and implement improvement opportunities they see. Consultant Norman Bodek coined the term “quick-and-easy kaizen” as a way to involve workers. This is not your traditional suggestion system with cobwebs in the suggestion box. This is a simple form asking workers for their ideas and how they have implemented them. Many sheet metal fabrication shops do daily huddles to identify the work priorities and allow workers to voice their ideas. When workers are encouraged and supported in their improvement ideas, great things happen. When management tries to control, limit or manipulate the workers’ ideas, this tool fails, and you will not have engaged employees.

Value-stream mapping

A value-stream map is a flow chart identifying all the activities, operations, steps and work times for a process. Once the process is mapped it is analyzed to identify waste. Each step is categorized into one of these three categories: value-added, non-value-added but necessary, or non-value-added and not necessary. Times to perform each operation, or step in the process are noted along with the distance traveled from operation to operation. Wait and delay steps are recorded. Improvements come by reducing the travel time or distance and by reducing or combining steps of operations. Any non-value-added and not-necessary steps should be stopped immediately. 

Sheet metal works shops can apply value stream analysis to the entire process from shop work order to delivering fabricated product.

Value-stream mapping is often used in kaizen events and with process-improvement teams. One of the core benefits of mapping the actual process is to get everyone to agree on what the process is and is not, and what the desired future state is.

How to do mapping

  • Identify the process to be mapped.
  • Create a current-state value-stream map. See how the process is done and draw it as is, not what you think it is or should be.
  • Create a future state value-stream map.
  • Create an action plan.
  • “Spaghetti” charts.

A spaghetti chart is a useful and simple tool to see how a product flows or work is performed. A physical map of the work area is used and one draws the actual path taken by a specific product, form or person being observed. A line is drawn from start to end, indicating the path moved by the product, form or person. A completed chart usually looks like a plate of spaghetti because the product, form or person typically moves all over the area being studied.

In one sheet metal shop, the spaghetti chart helped surface questions about how the various machines were located in relation to each other. This led to a closer and more logical relocation of several machines and substantially reduced the distance fittings traveled through the shop. Once the “as-is” chart is made, one can determine what to change to improve flow and reduce movement.

Make it visual

Post the jobs to be done each week on a board so workers can see the priorities. Update progress daily so everyone is aware of the status.  Mark on the floor where the material is to be placed for the next job.

Color-code the pieces for each job. Most fabricators use a simple printed color-coded label that cannot be seen or read clearly at any distance away from the label. Design a more visible system so that, at a glance, one can see if everything is correct or parts are mixed.  Kanban cards are one form of visual control.

Post and review, at least monthly, key measures such as: quality, safety and actual on-time delivery.

Lean thinking in shop

While there are obviously differences in how a sheet metal facility is set up, depending on the shop volume’s or size, there are many lean similarities that apply regardless of size. Flexibility is key. Avoid locking in the location of equipment and machines. This is always easier in designing a new shop than dealing with an existing layout. Design the shop so product flows and has little clutter or stacks of inventory, or free space for it.

Lean is often counterintuitive to traditional shop process thinking. Lean shops organize the work not by function (welding, insulation, etc.), but by product type. Each shop workload is unique but some common principles apply. Look at the majority of the work: straight rectangle duct, fittings, specialty orders, spiral ductwork and special metal orders. Layout and organize the shop around these three types of work:

  • Core: what you do every day.
  • Repeaters: work fabricated less often but several times a month or year.
  • Strangers: one-of-a-kind work.

Put the tools in groups by these types of jobs. For example, one might assign a less efficient or older brake machine for less frequent work orders.

Flexibility is key, design — or redesign — the shop so tools and machinery can be moved around to match workload and work types. Many vendors are now selling their equipment with mounted wheels or pallet skids for easy movement.

Other lean approaches include:

Instead of running expensive machines such as a plasma cutter at near capacity, it may be better operated at it at 70 percent to 80 percent capacity or less. Build one fitting at a time rather than many fittings in a batch mode. Not building products until the field needs it, instead of fabricating duct weeks ahead — aka just in case — and stockpiling it at the shop or sending it to the jobsite early.

Match the material fabrication to the capacity of the slowest station rather than running each area independently and stockpiling work-in-progress inventory at the next station. One shop burned so many jobs, putting each on rolling carts that they ran out of the carts. This limited downstream operations that needed the carts too.

Focus on having tools and needed parts at the point of use to reduce hunting.

Make sure equipment is properly maintained and correctly operated so it functions when needed.

Minimize the time it takes to change over a tool to a new size or metal thickness (such as a plasma cutter or a large brake machine).

Separate the operation of a machine from the operators. Watching a machine work is waste. Lean seeks to use machines that can operate autonomously and will signal operators when the job is done, when a defect is produced or when any abnormal situation happens.

A mistake often made by sheet metal works shops as they expand to a larger shop is to spread out and move tools and equipment further apart. Two basic wastes are movement of material and of people. Movement is not value-added work. When a shop spreads out; the extra space is soon filled with stuff. Don’t spread out in new facilities; keep the distances safe and to a minimum.

Use gravity to help where possible. Go from a higher level to a lower level to feed the machine and taking product off when done.

Selecting new equipment

Most contractors hope the new equipment will increase capacity and improve productivity to make them more profitable. New equipment poorly placed or used can actually cost more than it returns.

Lean manufacturing offers great possibilities to improve productivity if implemented correctly. Running a shop using lean techniques is a different way of thinking about how work is fabricated. When lean is taken seriously in a shop, productivity will improve by 30 percent or more. When new or even used equipment is being considered for a lean-operating shop, here are some key considerations.

Acquiring new equipment for the shop is always exciting, just like buying a new car, but is there a better way to achieve fabrication goals? A basic lean approach is to use creative thinking rather than money. By looking in detail at the way material is fabricated, one may discover that more productivity can be gained by applying such lean tools as the 5S and kanban without buying new equipment.

Consider used equipment as a better alternative than purchasing new. Used equipment may be especially useful where the need is low, such as in a line of products fabricated less often. Adding used equipment for a product line like this could free up a better machine for the fabrication of the main product lines.


Involve those workers who use and/or maintain the equipment every day in any decisions to acquire new equipment. This gives trust and ownership to the operators and they in turn can look for ways to implement lean.

Some ductwork fabrication contractors pay big bucks for a machine with great capabilities, which is used only a small percent of the time. You don’t need one super machine to run large volumes of spiral duct very fast, unless you only produce one type and size of duct. Smaller equipment offers more flexibility to meet the variable flow demands and smaller batches. It wastes resources to have a fast machine when the operator has to stand at the machine instead of doing a different task. A “fast” machine will often sit idle while the rest of the process gets caught up. Look for equipment that fits a specific task, has limited set-up requirements and fits well within the rest of the value stream.

Seek to minimize the time it takes to change over a machine to a new size or metal thickness. One HVAC construction contractor had a burn table that could not burn metal fast enough to keep up with demand. By analyzing the setup, the company was able to increase throughput and avoid the need to run an extra shift.

Match the material fabrication rate to the capacity of the slowest station rather than running each area independently and stockpiling work-in-progress inventory between stations. 

Look at install requirements including time to install. No matter who does the installation and startup, the process should be user friendly.

Equipment should be easy to maintain, with clear, easy-to-follow maintenance instructions. Read it, or better yet, test it before purchasing.


The ease of moving equipment should be considered. Lean work requires flexibility to move equipment around to meet the ever-changing product requirements. We may not be able to move the plasma cutter, but may be able to move other machines.

A machine should be easy to run with a quick learning curve for the operators. The less steps the better. You want one that, if possible, does not need watching while it runs so the operator is free to set up the next job, or do another task. The equipment should include signals and mechanisms that will notify the operator of abnormal operations. Operating instructions should include checklists, visual diagrams and pictures to easily show how to operate it.

Research to determine if the equipment you want is built by a company that applies lean manufacturing techniques. If so, that company is more likely to meet its commitments for on-time delivery, quality and performance. Many salespeople will claim they deliver quality products on time, but not all suppliers do. Look at the install requirements. Contact actual customers who have purchased this product recently to learn their experiences with the vendor. No matter who does the installation and startup, the process should be user friendly.

Use the lean concept of go and see. Before buying more equipment to replace the current machinery, or to add capacity, go watch how work is done in the shop. Take time to really observe how the work is performed. See how, or if, it flows. Look for bottlenecks and batch piles on the floor or carts. Watch for workers treasure hunting. Observe how well the equipment is maintained and used, and how material and tools are stored and moved. Don’t just watch one time, but do it over several days and weeks. Use a spaghetti chart to map the flow of various products. Ask “why” questions, never placing blame.


Every ductwork fabrication shop measures efficiency (aka productivity) in terms of pounds — or tons — of metal per hour or day. While this measure may be useful in bidding jobs and for quick estimates, it has little real value in driving improvement. This measure means nothing to the customer — the one who is paying for the duct. The measure is also distasteful to workers who see its pitfalls. Managers who use this measure to judge shop performance are fooling themselves about its usefulness. Don’t focus on this measure.

Measure cycle time, percent of material fabricated right the first time, and the percent of times the shop delivered as promised. These are better measures for evaluating shop performance. These measures are also meaningful to customers.

Cycle time is the time between when a job is released for fabrication until it is ready to leave the shop. This is the total time spent at each ductwork fabrication step, plus moving from one step to another and the time waiting in between steps. Ductwork fabrication steps are for the most part, value-added work in customers’ eyes. All waiting, sorting pieces, moving from process step to step are waste. By measuring the total cycle time it helps surface questions about how much waste is in the process and where opportunities are for improving. Customers, internal or external, care about how long it takes to get product out of the shop, because giving the shop sufficient lead time is not always possible.

Measure the percent of material fabricated right the first time. This is a quality measure and should be used to eliminate defects and rework. Some metal scrap is a natural consequence of fabricating sheet metal but often it is also caused by work done over.

To get a true measure of how much work is not right first time, you must get honest and accurate information from the field. In many cases, field crews make necessary repairs not because it is less costly than returning damaged duct, but because they fear reporting quality problems will cause contention with the shop. Lean is about getting honest information so improvement can be made, not about punishing mistakes.


Measure on-time delivery. Customers also care about having ductwork when needed. Many shops say they mostly deliver on time so they may feel using this measure would have little value. The truth is that they usually deliver per the negotiated need date of the customer, not the real need date. Many installation crews usually ask for duct long before it is actually needed. The lean way is to have the customer or supervisor be honest in identifying the duct’s real need date and the shop should deliver it on that date. If the shop cannot make the original need date, then a negotiated date should be set.

Field crews will become more truthful about their actual need dates when they see the shop is serious in meeting their needs.

Consider how duct is loaded for delivery to the job. The tendency is to stack as much duct as possible — any way possible — into the truck or trailer. This may save some fuel by resulting in fewer trips, but it often increases the cost of unloading, installing and may result in damaged ductwork.

Instead, load the truck or trailer so that it can be unloaded quickly and if possible, in the order it will be installed. Load all pieces together that are to be installed on the same area/floor. Coordinate with the field installation crews to deliver when and where the duct is needed and not too much time before it is needed. Some general contractors believe that if something sits on the jobsite in the same place for more than a few days, it should be moved, as if moving is real work. Each move is waste and runs the risk of damaging the product, causing more waste. Less material inventory is better.


There must be a sense of urgency for the lean journey to move forward. Employees need to know that implementing lean is not something to do when there is time, but something that is needed to survive today’s challenging market.

Every day, employees need to see they make a difference in what really matters. They need to feel both, a sense of accomplishment and sense of urgency, to stay focused. This doesn’t happen in one speech from the owners. Workers must be reminded frequently of the need to stay focused on using lean tools to be more competitive. Employees also need to see the value their efforts are adding. 

Leaders must demonstrate the urgency. They must start living lean principles and using lean tools. When a waste problem is identified, the leaders must show they are focused on attacking it.

Lean manufacturing did not come out of scientific research think tanks, but out of workers trying to find better ways to deliver value and reduce waste. It is all about experimentation and any real experimentation includes failures as well as successes. In lean terminology, the testing process is called “PDCA.” It stands for “plan, do, check, act.” Plan what you think will be a better way, and then try it. Check by asking two questions: Did we follow our plan? And is it a better way? If it is a better way then make it the standard. If it isn’t better, keep trying. Keep pursuing perfection even though you will never reach it.

For reprints of this article, contact Renee Schuett at (248) 786-1661 or email schuettr@bnpmedia.com