Nested-Based Vs. Traditional Work Cells

This article discusses the factors that must be considered when deciding whether to choose nested-based vs. traditional work cells utilizing machining centers.

Nested-Based Vs. Traditional Work Cells
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1) What are the factors that must be considered when deciding whether to choose nested-based vs. traditional work cells utilizing CNC machining centers?
Michael Cassell, CNC product manager, HOLZ-HER: The key factors to be considered are:
Production Requirements — Nested-based manufacturing (NBM), while fully functional, does have a production limitation. In typical cabinet applications the daily production limit is about 50 to 60 sheets per day.
Cell manufacturing can provide production capacities of three to four times that of NBM.
It is also very important to look at your long-term production requirements to ensure the chosen system will not become obsolete in the short term
Construction Method — The one significant limitation in NBM machining is in edge profiling and horizontal drilling/boring, although a cell made up of an NBM machine and a horizontal drilling machine can be highly efficient because the machine operator can do the horizontal operations while the router is machining a new sheet.
The point-to-point machine allows access to all sides, and with special aggregates, it even allows for underside machining.
Floor Space — If floor space is an issue, the NBM method may be more attractive because a saw is not required since the machine accomplishes the panel sizing operation.Investment — While both machine styles are relatively close in price, the cell concept requires an additional investment in the saw. Additionally, in most cases, companies have one saw operator and one CNC operator for the CNC method, whereas NBM requires only a single operator as, again, there is no sawing operation.
David McFarland, senior manager, CNC processing, Stiles Machinery: The decision between implementing a nested-based solution and traditional work cells depends on three main factors: construction methods, lot sizes and space considerations. To assist with your decision-making process, I highly recommend that you seek the advice of industry experts who can help you gain a competitive edge in planning, implementing and maintaining an efficient manufacturing work flow.
Ken Susnjara, chairman/ CEO, Thermwood Corp.: Traditionally (prior to CNC), cabinet shops used manual machines such as a table saw, hand router and hand drill to fabricate cabinets. This approach has worked for many years but requires a high level of skill to produce accurate cabinets. It is also slow.
The first level of automation to gain acceptance in the industry used a panel saw to cut full sheets into individual blanks and then used a point-to-point machining center to complete any other machining needed on each panel. In this approach the individual panels are held in place using vacuum and adjustable vacuum pods.
This new approach offered several advantages over the traditional hand tool methods. It was faster and more accurate. It also made European dowel construction easy. This provided improved joints and made assembly easier so this assembly method became popular.
About 15 years after the panel saw/point-to-point approach came into the industry, yet another advance was introduced called nested-based manufacturing. It used a flat table CNC router to machine all the parts directly from full sheets and no panel saw. This offered even more advantages.
Rob Howell, Morbidelli product manager, SCM Group USA, Inc.: There are multiple factors to consider when determining whether nesting or cell manufacturing is the best solution for your application. The following are some of the factors that need to be considered.
Batch/Lot Sizes & QuantitiesNesting — Are your parts custom? If every part is custom or your batch sizes are small, you will not be able to stack sheets of material on a panel saw for increased production levels. In this scenario of custom parts, nesting may be a better solution. Another factor that will need to be addressed in your evaluation is the quantities of parts. In some cases you may need multiple nesting machines to meet your production needs. Nesting will allow approximately 40 to 80 sheets per shift depending on the nest. Again, these numbers can vary due the size of parts and the complexity of the nest. These numbers also vary due to the different types of machines available such as rake off unloading systems and pendulum nesting. Both enhance the production levels depending on the application.Cell Manufacturing — On the other hand if you need large quantities of similar parts and are able to stack multiple sheets of the same material, cell manufacturing may be your solution. Cell manufacturing will provide you much more production over nesting similar components. This could also be the answer if your looking for growth without adding additional machines in the future.Types of PartsNesting — Are your parts odd shaped or square/rectangular? If your parts are odd shaped, you may get better yields with true shape nesting. This will provide you with the best yields of material by interlocking the different shapes.Cell Manufacturing — It is much easier for edge profiling and horizontal drilling of parts. Nesting does not allow for horizontal drilling and some edge profiling unless it's done as a secondary operation, which can be very time consuming. The type of construction method also needs to be taken into consideration. If you are using dowel construction, this could be important unless you have a machine designated for horizontal drill and dowel insertion.Floor Space & Number of OperatorsNesting — Uses one machine for all operations and requires less floor space. This is critical for smaller shops. Another advantage is only one operator is needed unless production requires multiple routers.Cell Manufacturing — Uses two machines with a panel saw and CNC machining center. This requires two operators and material handling between the two machines. Layout of the equipment is also important due to material handling.Capital InvestmentNesting — One machine, less capital expenditure. Unless again, multiple machines are need for production levels.Cell Manufacturing — Two machines, more capital expenditures. A panel saw and CNC machining center are required.DustNesting — Does not usually provide a clean work environment due to the type of router bits used, and most shops blow dust off the spoil board, which creates a dusty work environment. This is not as much of an issue with cell manufacturing
Q2) There are some so-called "hybrid" machining centers available that are capable of offering both nested-based and traditional work cell configurations. What are the advantages of such machines? Is there a downside?
Cassell, HOLZ-HER: None that I can see. The META System offered by HOLZ-HER is actually our most popular model over the last few years.
This system allows for the conversion from NBM to elevated pod in three to five minutes. This provides the customer the ultimate in flexibility and also allows the machine to grow with the production requirements. The machine can initially be set up as an NBM machine, and when the time comes that the daily production exceeds the output of the NBM method, a beam saw can be incorporated and the machine permanently changed over to elevated pods. They are then fully functional in a cell method.
By using the multiple zone feature, the machine can be set up and operate with both or either table styles at the same time as well.
Having the ability to run in either method opens up a wider range of opportunities to the customer, thereby allowing entrance into new markets or to expand their present product or capabilities.
McFarland, Stiles Machinery: "Hybrid" machining centers allow the user to flex toward the type of machine configuration that is most applicable to the needs of a particular moment in time. When volume work is required, the pod-and-rail machining center can be used in conjunction with a panel in a cell-based operation. Conversely, when just-in-time work is required, the machine can be converted to nested-based manufacturing.
Susnjara, Thermwood Corp.: First, there is only one machine needed instead of two, which means less cost and less floor space. It also eliminates a number of steps, making it even more efficient. It is no longer necessary to transport parts between the panel saw and the CNC. It uses a flat vacuum table to hold the sheet, so it also is not necessary to adjust vacuum pods for each panel. It also proves to be faster, not because the machine cuts faster, but because there are fewer tool changes.
Another advantage is nested-based tends to free up the machine operator to do other tasks, such as edgebanding. In nested-based, an entire sheet of parts is machined before the operator needs to attend the machine, giving him time to do other things. On a point-to-point the operator needs to constantly load and unload panels and adjust pods, so he or she doesn't have time for anything else.
The nested-based approach, however, doesn't support European dowel construction very easily. This construction method requires that certain parts be edgebored, and edgeboring requires the part be elevated on vacuum pods. While it is possible to operate a CNC router as a type of hybrid machine by adding vacuum pods, this eliminates many of the advantages of nested-based manufacturing.
Luckily, there is an answer that is even better. Instead of using bored holes and dowels for the joints, nested-based manufacturing uses a joint called a "blind dado," which can be machined in the flat. It is actually easier to assemble than dowel construction and is stronger.
Probably the biggest advantage of nested-based, however, is some emerging technology that allows the production of products beyond just cabinet boxes. Drawer boxes can be machined using the same system and software, and a new technique has been introduced to machine dovetail drawer boxes in the flat. Also, door and drawer fronts can be machined using the same system. The nested-based machine can process either traditional five-piece solid doors or MDF doors directly from the same nested data used for the cabinets. The latest introduction is the ability to machine face-frame parts in the nest, including an exciting new joint called the "puzzle joint," which can also be machined in the flat.
Howell, SCM: There are two different types of hybrids to consider. One is a machine that has half of the table pod and rail and the other half is a nesting table. The other type is a pod and rail machining center that can accept a nesting table on top.
The half-and-half hybrid machine allows for rigidity and flexibility. Different applications fit one (nesting) or the other (pod & rail) better. This is the reason both are still offered. Sometimes secondary operations are required after nesting such as edge profiling, and this allows for fast set-ups on the pod and rail portion. Otherwise, nesting tables require the operator to close off vacuum, remove the spoil boards or connect hoses with pods, which take time. Also some applications are better suited for a pod and rail environment such as stiles and rails for entry doors due to quick set ups. The only downside to this type of machine is the size, which requires more floor space.
The other type of hybrid that accepts the nesting table on top does not provide as much vacuum to the nesting table and could be an issue with smaller parts. These types of conversion tables also do not have the tolerances that a standard table has and take more time to set up.
Q3) Is there a steeper learning curve with nested-based technology vs. traditional work table configurations? Why or why not?
Cassell, HOLZ-HER: Again, no. The design principles and requirements are virtually the same; the software provides for immediate nesting optimization. Graining can be automatically controlled, and with the Windows-based software systems you still maintain important editing functions (copy-paste, rotate).
As software develops, I believe, it will continue to be more user-friendly and more automated.
McFarland, Stiles Machinery: For a first-time user of CNC technology, the learning curves are similar. Machine operation and maintenance are similar, and both systems require an understanding of software and cutting tool technology. However, nested-based manufacturing employs certain techniques related to vacuum fixturing, programming and material handling that must be learned and mastered for success. This learning curve can be a little bit steeper.
Susnjara, Thermwood Corp.: You might think that with all this technology the learning curve for nested-based might be much greater than the panel saw/point-to-point, but that is not true. With the industry-leading nested-based systems, the design software has been so smoothly integrated with the machine that all you do is design your job and send it to the machine without all the technical tweaking that was necessary with older systems. All this is actually pretty easy. You can even get libraries of designs from other cabinetmakers and skip the design step altogether, making it even easier.
The latest advance in nested-based is the ability to build traditional furniture using the same technology. Renowned furniture designers are supplying beautiful furniture designs that can be machined using the same nested-based system. The CNC programs for complex parts such as carvings and mouldings can be rented, making it easy for even the smallest shops to produce custom high-end furniture.
Howell, SCM: Both types of manufacturing usually require some type of design software on the front end. This requires a learning curve for both scenarios. Nesting has to train only one operator for one machine, while with cell manufacturing you have two machines with two operators. These are different interfaces on each machine, which requires additional setup time and training. Cell manufacturing also requires the operator to make more decisions on the floor such as panel orientation, correct labeling and proper placement of the part in the proper field of the machining center.
Both types of technology have a place in the market. Sometimes manufactures push one over the other because they don't offer both solutions. As previously noted, there is not one factor that determines the best solution but multiple factors that need to be taken into consideration.



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