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Improving Efficiency In CNC Routing
 
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Improving Efficiency In CNC Routing

If you are considering adding another panel saw or CNC router to your operation, or if you are a first time CNC buyer, you should consider the benefits of using Nested Based Manufacturing (NBM). Nested Based Manufacturing or “nesting” is a manufacturing method that many plastic distributors and fabricators can adopt in order to improve the efficiency of their new or existing CNC routing operation.

Simply put, Nested Based Manufacturing is a process that utilizes a CNC Router to produce finished parts ready for gluing, assembly or shipment to the customer without presawing or secondary finishing operation. It begins with part drawings (existing or newly drawn) being optimized by software within the dimensions of a defined sheet size. The parts are then machined on the CNC router in the exact pattern defined by the software or by the designer out of a single sheet. The completed run will look something like a puzzle. Parts can be arranged to provide the highest possible material yield and minimize waste. In addition to these benefits, NBM can provide faster processing and fewer mistakes due to reduced set up time and no required precutting.

While some jobs are better produced by cutting blanks to size on a saw and then machining, many distributors and fabricators are currently producing parts that could be “nested” more efficiently. Because of recent advances in CNC router technology, some parts traditionally “CNC milled” or “machined from blanks” can be processed more efficiently using NBM. Nested Based Manufacturing is an alternative way of approaching fabrication and can be used in conjunction with traditional CNC methods to maximize efficiency and productivity.

Some examples of how NBM can improve efficiencies of existing jobs are single part runs and multiple part runs to include product components. In single part runs, some parts are traditionally produced by first cutting blanks to size on a saw and then machining those blanks on a CNC Router or Mill. Utilizing NBM, the part would be optimized over a full 4’ x 8’ (or your standard size) sheet and machined in one operation. This saves dual set up time, reduces material handling, maximizes yield from the material and ensures repeatable tolerances. With multiple part runs, several different part shapes or multiple components of products such as displays can be optimized using NBM. Different parts can be combined to take advantage of the optimized material yield and streamline several operations into one.

Another example of a good NBM application would be the routing of 5 fi” diameter disks.

Conventional cutting and machining from blanks would yield 128 parts from a 48” x 96” sheet as compared to 135 pieces from the same sheet size when NBM is utilized. In this case, the yield is 5.5% greater with less material handling and labor content.

Machine Requirements

The necessary requirements for Nested Based Manufacturing are a CNC router and software with nesting capability. Depending on your needs, single or multiple head machines can be used for the nesting process. Important router features for nesting include table size and design, vacuum capability, chip evacuation, tool changing and positioning speeds. For best results, the table size should be large enough to accommodate your standard size sheet material. A minimum table bed of 4’ x 8’ or 5’ x 10’ is common.

The table design should provide for enhanced vacuum hold down with the flexibility to use many different types of fixtures. State-of-the-art table systems combine a high tech aluminum grid table with large vacuum tubes evenly distributed below the table to achieve strong, even hold down. Larger parts can be held down during machining using a blank, bleed-through spoil board; however the nesting of smaller parts may require a specialized spoil board or fixture to successfully hold down the pieces. Because parts are machined in close proximity, chip evacuation is crucial to obtain best results. An excess of chips around the router bit can result in re-melting and attaching to the tool, leading to a poor finish. The best chip evacuation can be obtained by combining an ample dust/chip collector with a CNC router that has an effective chip collection design. CNC controlled dust hoods around the router bit with 360º pickup capability are found on well designed chip collection systems. The ability to change tools rapidly provides some of the efficiency benefit when using NBM. A quick or rapid style changer with a minimum of eight positions should be considered. A CNC router equipped with this type of rapid tool-changer can move quickly from one operation to the next with a minimum of lost time. Positioning speeds are an important consideration for quick cycle times. Combined with a tool change, high speed movement from the end of one operation to the beginning of the next can save as much as 10- 15% off normal cycle times.

Software

While many current software packages available with CNC routers have a “nesting function” included in the package, not all software is equal. In addition to important features used for typical routing applications, key aspects of software used for NBM include full 3-D simulation and tool path editing capability. 3-D simulation allows a user to review the machining of the part as programmed allowing an opportunity to correct errors or make changes before any plastic is cut. This feature reduces programming time and prevents unneeded waste of material. When nesting small, hard to hold parts, it is important to have advanced tool path editing capability for full manipulation of lead in/lead out and tool insertion point. These tools allow the programmer to quickly adjust router bit point of entry and angle of attack in order to reduce pressure on parts when routing. Using these advanced tools can make the difference of being able to effectively hold small parts down when machining.

Nest Based Manufacturing can provide efficiencies over traditional routing methods when material handling costs, material yield and part repeatability are important considerations. If you are considering the nested based approach, have your staff conduct an internal study to determine the benefit of such a process. Some CNC Router manufacturers can also provide you with “time studies” that can measure the savings of moving jobs to NBM.


Written by Phil Bryant, Business Manager, Plastics for SCM Group USA, manufacturers of CNC Routers and Computerized Panel Saws.

For more information, contact SCM Group USA, 2475 Satellite Blvd., Duluth, GA 30096, 800-292- 1850, 770-813-8818, Fax: 770-813-8819, E-Mail: info@ scmplastics.com, Web: www.scmplastics.com.

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