Implementing a Nested Based Fabrication System

This article offers advice to manufacturers who are considering implementing a nested based fabrication system.  “Nested Based” or “Nested Base” fabrication is a manufacturing process that leverages the power of CAD/CAM software combined with a CNC router to efficiently cut multiple parts out of sheets of raw material.  Panels of wood, plastic, non-ferrous metals, and composites can be rapidly turned into parts.  Processes such as vertical drilling, pocketing, profiling, and others are executed in one streamlined process.  The most common application for nested base fabrication is cabinet making, but it is also used in other applications with similar requirements.  The goals of the process are to produce more parts with less labor, less material waste, and with a superior degree of accuracy. In turn, the cost of the parts is reduced, which has a direct and positive impact on manufacturing profitability.

Nested Based Fabrication Process

The nested based fabrication process includes these steps:

1.      Create CAD software drawings of parts.

2.      Use CAM software to add machining instructions.

3.      Use CAM software to automatically nest the parts on sheets of material.

4.      Use a CNC router to automatically cut the parts.

Thanks to advances in technology over the last few years, these steps have become very affordable and easy to learn.  Thousands of small, medium, and large cabinet manufacturers have purchased or leased MultiCam CNC routers and CAD/CAM software.  They routinely report that the investment pays off in less than one year thanks to the efficiencies of the nested based fabrication process.  The software and machines have become so easy to use that a typical operator requires only one day of training.  Every cabinet manufacturer today should be considering nested based fabrication in order to stay competitive.

Although adopting the nested based fabrication process may be easy, it is more difficult to select the right equipment and a vendor.  Manufacturers who are considering making such an investment need to consider many issues, and the remainder of this article will provide some food for thought.

The Nested Based System Ingredients and Considerations

A nested based fabrication system includes these ingredients:

·         CNC router

·         Spindle motor with automatic tool changer

·         Drill heads

·         Aggregate heads

·         Dust collection

·         Electrical requirements

·         Material handling

·         Plumbing and pneumatic requirements

·         Safety

·         Post purchase service & technical support

·         Software

·         Construction methods

·         Tooling

·         Vacuum hold down

The following information discusses the specifics of each of the above subjects in more detail.  This list is not in order of importance.  This list in its entirety makes up a sound nested based system and all elements must be well understood in order to implement a successful system.

CNC Router

A wide variety of CNC routers are available today from numerous vendors.  Selecting the right router requires careful evaluation of two issues:  (1) the qualities of the machine itself, and (2) the qualities of the supplier.  Any good supplier ought to be able to offer a wide range of machine options, custom-tailored to fit the application.  For this reason, buyers may find it easier to select a supplier first and then sort out the machine configuration.

When considering a potential CNC router supplier, buyers should explore the following issues.  These are not in order of importance.

·         Does the supplier offer a wide range of machine options, including different table sizes, heavy-duty machine types, light-duty machine types, add-on features, and price ranges?  Can the supplier order a machine custom-tailored to the buyer’s needs?

·         Does the supplier offer local service and support?  How many service technicians are located near the buyer?  Are replacement parts stocked somewhere near the buyer?  Are the machines manufactured domestically?  If not, how hard is it for the buyer to get engineering support if necessary?  What kind of support is available by telephone?  Over the Internet?  Does the supplier provide software support?  Can the supplier provide advice on tooling or other application issues?

·         Can the supplier provide a complete, integrated solution, including all of the ingredients listed above?  How much knowledge and experience does the supplier have in providing integrated solutions?

·         Does the supplier offer tooling?  How much tooling does the supplier keep in stock?

·         Does the supplier provide training?  When, where, and how?

·         What is the supplier’s track record?  How many references do they have and what do the references say?

When considering the machine itself, buyers should explore the following issues.  These are not in order of importance.

·         Is the machine strong, heavy, and fast enough to handle the buyer’s volume of work?  Buyers should discuss with their supplier how many hours per day and how many sheets per day the machine will be expected to cut.  This information determines how heavy-duty the machine needs to be.  Machine weight is correlated with maximum speed because fast motion requires a machine that will not excessively vibrate or backlash.  For some buyers, a light-duty machine with slower cutting speed might be adequate, but those expecting more throughput need to invest in a heavier, faster machine.  Machines constructed of steel, with all-steel gantries will handle more work than machines with aluminum gantries or frames.   Buyers should ask whether steel frames have been stress-relieved after welding to ensure that the frames are stable.  The size of the gantry, the size of the bearing rails, the span between bearing rails, and the size of the ball/lead screws are important to enhance load capacity and rigidity and to minimize backlash and vibration.

·         Does the machine have one or two x-axis motors?  Moving gantry machines that employ only one x-axis motor are not able to cut as fast with accuracy as machine with two x-axis motors.

·         Does the machine use Servo or Stepper drives on each axis motor?  Servo motor technology can enable a machine to cut faster with greater accuracy.

·         Is the machine easy to operate?  Is the user interface intuitive and easy to learn?  How much training would be required for the buyer’s employees?

·         Table size.  Most routers can be ordered in a wide variety of table sizes to exactly meet the needs of the buyer.  The most popular size for nested based fabrication is a 60″x120″ process area.

·         Phenolic table top with vacuum grid and zones.  Vacuum hold-down (discussed later) is the preferred method of holding materials for nested based fabrication, and this is accomplished with the help of a phenolic table-top that is cut with a series of air openings and connecting grid to spread the vacuum underneath an MDF spoilboard.  The grid pattern can be adjusted to meet difference needs.  Although not typically needed in nested based fabrication, zone systems are also available to enable the vacuum to be directed to different parts of the table using manual or pneumatic valves.  A very popular option in nested based fabrication is a single pneumatic valve that shuts off the vacuum to the entire table.  This enables material loading/unloading without the need to repeatedly power-up-and-down the vacuum pump.

·         Pop-up pins.  Another helpful option is a system of automatic, pneumatically-controlled pop-up pins around the perimeter of the table.  These facilitate loading because they allow the operator to quickly align the material with the table.

Spindle Motor with Automatic Tool Changer

For nested based fabrication, Advanced Machine Tools recommends a spindle motor with power in the range of 10hp to 16hp, with an automatic tool changer.  This power range enables fast cutting with excellent cut quality on materials used in nested based manufacturing, such as MDF.  With an automatic tool changer, a router can automatically switch tools without any operator intervention, based on instructions in the job’s software file.  This ability can dramatically reduce cycle time and is considered a necessity by today’s nested based manufacturers.

Drill Heads

Cabinet shops usually elect to purchase a boring unit which is mounted to the router next to the router spindle and is independently controlled by the software.  For example, MultiCam offers a 5 by 5 right angle drill head configuration.  There are four drills on the x-axis and four drills on the y-axis.  There is also one shared drill in the center.  The drill head can drill up to nine holes at once or it can drill one hole at a time or any combination there of.  Buyers should find out whether the boring unit is capable of reaching the entire working area of the router table, because sometimes this requires an extended gantry option.

Aggregate Heads

Attachments such as horizontal boring and milling, saw blades, and more are available to eliminate some off-line secondary processes.

Dust Collection

With most CNC cutting processes, a large amount of particulate is created that requires efficient control.  Airborne dust and debris left on the cutting surface of the machine, on the floor, and on the moving parts of the machine itself can be hazardous for the machine and the operators of the machine.  In addition, the faster the chip load is removed from the cutting tool, the cooler the cutting tool remains during the cut cycle.  Based on these points, it is recommended that two different cleaning methods be implemented for the CNC machine at the time that it is installed:

1. Compressed air lines should be installed to accommodate a blower that can be used to spray the working surface and moving parts on the machine.  This debris must be removed and cleaned at regular intervals in order to maintain vacuum hold-down pressure and as a maintenance precaution for the machine itself.
2. A powerful dust collection system will be required to trap and contain airborne particulate as it is created during the cutting process.  The size of the dust collection system depends on the materials that are being cut.  We highly recommend a powerful dust collection system with sufficient CFM to power the particulate collection process.  A 5 to 10 hp dedicated unit is usually sufficient. If the CNC router is to be plumbed into a central dust collection, an independent super-charge blower is recommended to remove the particulate from the cutting tool.  That blower will then empty into the central dust system.  This method will provide the best of both worlds – high suction and volume to evacuate the dust and the luxury of one collection point for all shop dust.

Electrical Requirements

Most CNC routers can be ordered in a range of electrical configurations.  They include but are not limited to: 208 to 240 VAC three phase up to 440 to 480 VAC three phase.  Based on the voltage that is available in the shop, amperages can be determined with the help of your supplier.  Since three phase electricity may not be available in all shops, your electric company should be consulted to determine cost of establishing the service.  If establishing service becomes cost prohibitive, three phase converter drives are available that convert 220 single phase to three phase.  Once your electrical service is determined, your supplier should issue a complete specification on the quantity, location, and amperage of each required disconnect which a licensed electrician must install prior to the installation of the CNC router.

Material handling Loading/Unloading

Since loading and unloading the CNC router is labor intensive and time consuming, it can become a bottleneck in the cutting process.  Depending on the volume of sheets to be cut per shift governed by the cut speeds of the routing process, different material handling methods are available.  At smaller volumes, hand loading and unloading may be completely acceptable.  For moderate production quantities, a scissor lift or suction cup lift will speed up loading.  For higher production levels, roller tables and automatic loading systems are available.  Some keys to efficient material handling are:

·         Position raw stock for easy loading access next to the router

·         Place a cart to one side of the router for off-loading the cut parts

·         Make sure waste disposal carts are near by for scrap removal

Plumbing and Pneumatic Requirements

There are three types of plumbing that will be required in the CNC installation:  (1) vacuum hold down, (2) pneumatic, and (3) dust collection.  The vacuum hold down should be plumbed with schedule 40 PVC or PVC flex-line.  It is necessary to minimize the length of the tubing or pipes that run from the vacuum pump to the CNC router.  It is also important to eliminate the necessity to implement 90-degree bends in the line.  Each bend is the equivalent of adding 20 feet of tubing or pipe in its negative effect on vacuum force.  Whenever possible, utilize two 45-degree bends to make the 90-degree bend.

Pneumatic lines must supply and maintain 100 PSI at 3.5 CFM.  The airlines may be used for several purposes including but not limited to:

·         Blower for cleaning the table (see “Dust Collection”)

·         Cooing air-cooled spindle bearings

·         Powering automatic tool changing spindle chucks

·         Lifting dust collection hoods

·         Activating a boring unit

The air used for powering automatic tool changing spindles must be extremely clean and dry.  Most router manufacturers will require a dedicated, refrigerated air dryer in order to honor the warranty.  Your CNC router supplier ought to be able to supply you with an air dryer.

Safety

A yellow safety barrier line should be placed on the floor approximately 24 to 48 inches from all exposed sides of the CNC Router.  Only the operator should be allowed inside the yellow line.  Lift truck traffic should be minimized around the machine.  Eye and ear protection is required.  Other common safety rules must be implemented for moving component machinery.

Post Purchase Service & Technical Support

CNC routers have a variety of mechanical and electronic components that can wear and fail.  Buyers should receive training in regular preventive maintenance procedures, which mostly involve cleaning and lubricating the CNC router.  It is also a good idea to have the supplier’s technician visit periodically for more thorough preventive maintenance.

No matter the brand or strength of the machine, at some point it will break down.  Buyers should be very concerned about their supplier’s ability to provide service and support.  A good supplier will have a full-time staff of factory-trained, experienced service technicians located near the installation.  Buyers should also make sure their supplier has an adequate stock of replacement parts nearby.  Choosing a CNC router brand that is manufactured domestically is an advantage, because some problems require direct assistance from the manufacturer’s engineering department and this process is easier and faster without distance and language barriers.

Software is part of the nested based system, and software support is just as important as hardware support.  A good supplier should be able to provide software support over the telephone and via the Internet.  For example, Advanced Machine Tools utilizes an online collaboration tool that allows its service technicians to view and take control of a customer’s computer (with their permission), and vice-versa, for training or trouble-shooting purposes.  This can save the customer thousands of dollars and days of downtime when it solves problems that would otherwise require an onsite service call.

A final support consideration is whether the supplier can provide advice on tooling or other application issues.  Most manufacturers that are new to nested based fabrication will go through an extended learning period as they experiment with different cutting techniques and tooling.  A good supplier should be able to provide advice during this time, based on their experience working with many other customers who have had similar applications.

Software

Depending on the application, several different CAD/CAM software solutions are available.  Buyers will want to make sure that the software they select will work with the CNC router they select.  G&M Code, also known as “G Code”, is the open standard programming language that is output by the vast majority of CAM software and understood by the vast majority of CNC routers.  It is not necessary for buyers to understand or to program G Code, but they should make sure that their software and hardware is using this standard.  Also, there are some variations in the way G Code works with different brands of machine, so buyers should make sure that the particular combination of software and brand of machine they have selected has been thoroughly tested and proven compatible.

For design, buyers have many excellent options available.  With the right software, a cabinet maker can quickly design entire room full of cabinets using easy drag-and-drop graphical tools on a laptop or PC.   Cabinet software comes with hundreds of pre-defined cabinets and can be customized as needed.  Some software can render a 3-D photo-realistic image of the room with realistic finishes and lighting effects.  The software can automatically translate the design into shapes for cutting and drilling.  Good software packages offer automatic nesting, where the shapes are fit onto multiple sheets of raw material in the most efficient way to minimize material waste.  Some software also offers the ability to produce detailed estimates based on the user’s own cost information.  Examples of cabinet software include KCDw, CabinetWare, and CabinetVision.

After the CAD software there is a CAM process, where the software translates the CAD-designed shapes into machine instructions (usually in G Code).  Sometimes this CAM functionality is packaged with the CAD functionality in a full CAD/CAM software package.  Other times the CAM process is achieved with a separate software program.  In either case, buyers should look for CAM software that is very easy to use and does not require extensive training or computer programming.

Manufacturers who are interested in adding graphical elements to their products will want to be sure to purchase software that is capable of free-form drawing and/or importing graphics files.  SAi’s EnRoute, for example, is a complete CAD/CAM package for adding ornamentation such as carvings, logos, and other graphic images to traditional wood working tasks.  Its famous scan-to-cut technology enables the user to scan graphic images from paper, and then machine them in minutes.  With EnRoute’s optional 3-D package, a user can use 2D and 3D geometry as well as bitmap images to add texture to a 3D relief.

Construction Methods

Each cabinet shop has specific construction methods that they apply to their products.  Face-frame and frameless cabinets are very common.  While some use screw or dowel construction, others use blind dado or strong box construction.  Most CAD/CAM software systems will accommodate these and other methods.  While your goal may be to keep your current construction method, minor changes may enhance your product or further eliminate manufacturing costs.  It is wise to investigate and plan for a variation of methodologies in order to streamline the production and assembly processes.

Tooling Requirements

Nested based manufacturers employ several types of consumable tooling, including tool holders, collets, and especially router bits.  Router bits come in thousands of varieties and it can be a daunting task to select the correct bit.  The incredible number of options to choose from when buying a router bit include manufacturer, material of construction, number of flutes (edges), shape of spiral, and dimensions.  Once a bit is selected, users must decide what feed rate and RPM at which to operate the tool, and this depends on the material being cut.

For these reasons it is important to find a tooling vendor that is very knowledgeable and is willing to give advice over the telephone.  Tooling vendors should also offer a variety of tooling brands and styles, and maintain on hand a large inventory of router bits.

Vacuum Hold-Down

In nested based fabrication, vacuum hold-down is the preferred method of holding raw materials down on the router table.  The vacuum hold-down system includes three components: (1) the vacuum pump (or “blower”), (2) the phenolic table top on the router, and (3) the plumbing from #1 to #2.  With vacuum, more is (almost) always better!  Opting for a lower-horsepower pump/blower to save some money now can result in years of frustration later.  When in doubt, choose the higher horsepower pump.  Several different vacuum pump/blower technologies are available.  There are two main performance dimensions to consider:  (1) how much pressure/suction can be generated (measured in degrees of mercury or hg) and (2) how much air flow can be generated (measured in CFM).  Although more of both is always better, inevitably there will be a trade-off between performance in these two areas.  Some pump technologies are best for creating high pressure, but only if there is minimal flow.  These are great for holding down small shapes but bad for nested based manufacturing applications where many shapes are being cut out of a sheet and thus creating lots of flow along each cut-through line.  Some high pressure pumps can be damaged if subjected to a high flow situation for an extended period of time.  Other technologies can generate lots of CFM but with less pressure.  And some technologies are a good compromise between pressure and flow.  Nested based manufacturers will want a pump that can handle medium to high flow.  Advanced Machine Tools recommends a 33hp regenerative blower for nested based manufacturers who have a 60″ x 120″ table.

Vacuum plumbing is extremely important.  The distance between the pump/blower and the router should be minimized, and right-angle turns in the plumbing should be avoided, because one right-angle turn is equivalent to 20 feet of extra distance.  The phenolic table should have a grid cut into it that spreads out the vacuum efficiently.  It should also enable the use to isolate that vacuum using gasket tape and/or rubber plugs.  For manufacturers that frequently need to isolate the vacuum in different parts of the table, a pneumatic or manual valve system should be considered. A very popular option in nested based fabrication is a single pneumatic valve that shuts off the vacuum to the entire table.  This enables material loading/unloading without the need to repeatedly power-up-and-down the vacuum pump.

Noise is also an important consideration because most vacuum pumps are very loud.  Isolating the pump in a sound-proof area is desirable for this reason, but only if it can be done without adding too much plumbing and reducing the pump’s effectiveness.

Vacuum hold-down is a complex topic that will be addressed in more detail in another article.

 

Copyright © 2008 AMT Op Co, LLC d/b/a Advanced Machine Tools

Date Last Updated: February 29, 2008.