Nesting is the process of positioning the components on the screen within the material to be cut. The human eye is extremely good at judging the optimal layout of complex shapes and a good operator can achieve very high yield and minimal waste. This process is made easier by on-screen tools that limit parts from overlapping etc. Unfortunately, manual placement of parts can be extremely time-consuming. Valuable personnel can be tied up doing mundane job layouts when they could be used in other areas.
Automatic Nesting
Automatic nesting software is now available that optimises the cut parts into the raw material for minimal waste. For cutting rectangular parts such as cabinet panels, a process known as rectangular nesting is sufficient. This is the simplest form of automatic nesting and does not allow for irregular shapes. This type of nesting aligns parts of similar dimensions in rows efficiently but is not satisfactory for more complex shapes.
‘True Shape’ Nesting
‘True Shape’ nesting is a much more sophisticated algorithm that is able to fit complex shapes around each other much like a human operator would. When cutting obscure shapes, then True-Shape nesting is required to maximize yield. The operator usually must specify which material is to be processed, and then import drawings into the software for nesting onto that sheet. The automatic nesting function can then be used to fit the parts into the sheet. If the sheet is filled then another sheet will be added to the job and the parts will continue to be nested until the nesting is complete.
Start Points, Tabs and Cut Order
To achieve trouble free processing of an entire nest the operator must usually perform further steps to re-position start positions and specify the order the parts will be cut etc. These processes are vital to eliminate movement and damage to parts due to thermal expansion or vibration. Tabs or bridges can be added in order to leave small connecting pieces between each part and the surrounding material. This can also aid in reducing movement. Failure to do these extra steps may damage tooling in the case of mechanical machining processes. The cut order is also important because a lot of valuable machine time can be wasted by needless traversing if the cut order is not optimal.
The process of nesting can be time consuming, even with the aid of automatic nesting. What happens when you need to produce hundreds of nests? How can you reduce the setup time without reducing the performance and quality of the job? These will be answered next in this article.
ATP
ATP or Automatic Tool Pathing is the next step in efficient processing of sheet material on a CNC cutting machine. Modern ATP nesting software has the ability to process whole jobs automatically. ATP brings together many of the disciplines required into a fully automated environment. A good ATP software package will be able to make many decisions on behalf of the operator by following predefined strategies.
List File Processing
The first step in a comprehensive ATP based software package starts with a list file. It is basically a list of parts that is generated from a Material Requirements Planning (MRP) program, a parametric design package, stock control software or even a manually entered list. This is usually in the form of a spreadsheet or text file that specifies some or all of the following details:
| File | Qty | Name | Rotation | Material Type | Thickness |
|---|---|---|---|---|---|
| C:\CNC\frntpanel.dxf | 2 | FRONT PANEL | 90 | MILD STEEL | 5 |
| C:\CNC\LHpanel.dxf | 2 | LEFT PANEL | 90 | MILD STEEL | 5 |
| C:\CNC\cover.dxf | 6 | ACCESS COVER | 5 | ALUMINIUM | 10 |
The source CAD files must also exist at the specified path for access by the software and be drawn with the process in mind.
Material Management
A good software package should also be able to manage stock levels of materials. The list file will be analysed and the required materials will be drawn from the available material stocks and automatically added to the current job as required.
