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Q: 1. What are the factors that must be considered when deciding whether to choose nested-based vs. traditional work cells utilizing CNC machining centers?
Alex Colic, CNC product manager, Akhurst Machinery Ltd.: The primary factor to consider when deciding between nested-based and cellular manufacturing is volume. When processing a large or small order, you would look for common parts or quantity of the same thing that would be conducive to stacking sheets of material in a beam saw. As the quantity of the "common" parts gets lower to the point that only one or two sheets would be loaded into a beam saw, the advantage of the higher processing speed of a beam saw is lost. If the quantity of sheets does in fact get to be one or two sheets in a beam saw, then it's on to the point-to-point machine. The time to process using this method will in most cases, along with handling of the parts between two machines, be considerably longer than that of a nesting machine. The cutting speeds of nesting machines in conjunction with current cutter technology have proven to be a much faster method and, more importantly, a lower cost production option.
Another factor that comes into place is the floor space requirement. When you compare the floor space required for a nested-based machine vs. a beam saw and machining center, there is a big difference. The beam saw and point-to-point take up close to twice the floor space compared to the nested-based machine.
Nested-based machines come in a wide range of price points but typically are directly comparable to their machining center counterparts. With cellular, you need to calculate in a panel saw and an additional operator. Your capital costs will be much greater with the cellular approach. Also there is a cost associated with the additional floor space required for both machines.
Chris Burns, vice president, ShopBot: The top two reasons for integrating CNC in production are increasing output capacity and adding capabilities that your workforce may not have. The main factor for choosing nested-based over traditional (automated) work cells would be the size of your business and the number of employees in your facility. Larger facilities have the advantage of utilizing custom material sizes to avoid waste and use a lean manufacturing flow that can maximize throughput from individual operations. Smaller CNC machines that incorporate only a few operations can be placed in the production flow individually or in multiple arrays. By having one skilled machine integrator, a large company can bring its newer employees up to speed more quickly than if it had to train then on the entire production process. At MasterBrand Cabinets, the operator uses only a bar code reader and must keep outside of a light curtain or the machine will not run. New machine operators can be trained for production in as little as 15 minutes.
Contrary to its name, the Bennoni Furniture Group is a one-man shop that completed 90 kitchens in the last nine months of last year. It was the ultimate apartment job; with half left-handed and half right-handed kitchens. A nested-based approach made much more sense due to the repetition of parts, efficient nesting and complete machining. Since the apartment contractor only wanted about a dozen units at a time, Bennoni (aka Curtis Gumbs) cut all the parts ahead of time and stored them as standard components, pulling them down for assembly as needed. The longer run time of five to nine minutes per panel freed up his time to continue working on other operations, and when his components came off the table, they were finished. This nested-based approach also addresses a skilled labor force shortage by creating independence from partnering with a robot.
Considerations: company size, labor force, single piece flow, lean approach, manufacturing model, design flow, design to manufacturing flow, nested array, optimizing workers' time, skilled labor shortage.
Q: 2. 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?
Colic, Akhurst: For manufacturers that continue to have vastly varying quantities of any one item whereby they will process an order of all the same thing and then the next day process a one-off product, a hybrid machine can be another solution. There are a few versions of hybrid machines: ones that actually have a permanent bed setup of pods and rails along with a flat table portion, and then there is a flat table machine that has the ability to use vacuum pods on the flat table. The first one has no "additional" setup and therefore works as two individual machines. Both can be a time-consuming process when it comes to switching from pods to flat table use. It is a compromise, and hence a potential loss of production time.
Burns, ShopBot: The two downsides to a hybrid machining center are the size of real estate that it occupies in your shop and the complexity of your machine.
As long as the size of your machine has a cutting area that handles your largest sheet size, you can handle all jobs. The addition of an automatic tool changer will also assure that you have an inventory of operations.
Considerations: machine size, flexible work area, retool manufacturing process
Q: 3. Is there a steeper learning curve with nested-based technology vs. traditional worktable configurations? Why or why not?
Colic, Akhurst: As machine technologies change so do software providers. The software that is used today in nested-based manufacturing does not require the user to "program" each individual part as on a point-to-point machine. In fact, the user does not actually program the parts but rather selects them from a library and modifies them through drop-down menus; the operator is more of a designer than a machine code programmer. The task has changed from programmer to designer and in the process, as an added bonus, has also become an accountant of sorts because not only is the software creating code for the machine, but it is also calculating the cost of the job with all the required materials, hardware and the final selling price to the customer. The time taken to learn traditional programming software can be confusing for some. Today's nesting software typically has users up and running at full production in a couple of weeks — not really programming but rather creating the assembly.
Burns, ShopBot: The small shop nested-based solution requires full ownership of both design and CAD/CAM aspects of production from one person. However, today's software solutions have simplified that process dramatically. A kitchen designer today can go into a home, measure out a floor plan in the room, draw that out on a laptop in a design program, and in less than half an hour have a design ready to discuss with the client. When everything is approved for production, they are less than 10 minutes away from having cutting files for fully nested sheets.
The traditional automated work cell requires much less of the operator and much more from a skilled machine integrator. This person now becomes the most valuable person in the production process. He or she is required to come up with solutions for hold-down, tooling, fixturing and part file sequence in a way that takes all the setup and worry from the operation. The machine operator's job is simplified to a point where they can work on fast, continuous part flow.