For CNC operators, the concept of nesting should be very familiar since it has been around for over 20 years. To summarize, nesting uses computer software to efficiently manufacture parts from sheets of material with the goal of minimizing material waste and increasing material yield. The following outlines four methods of nesting that are currently in use:
1. Traditional nesting: is the simplest and most inexpensive method to incorporate into your CNC software making it the most widely used. Treating each part to be cut as its own piece, the CNC tool will plunge into the material and cut around the contour of the first part. The tool then retracts from the material, plunges in again, and repeats the process with the subsequent part. This entire process is completed for each part that is nested on the sheet until all of the parts have been machined. Traditional nesting is very simple, but also very time consuming. The CNC moves several times to plunge, go around the part, retract, and then go over to the next part. All of these movements reduce the efficiency of the machining process because the overall throughput time is increased. Additionally, the greatest amount of heat is generated the moment the tool plunges into the material right before it begins cutting. Since traditional nesting has more frequent plunges, the tool is also being heated more often, and with heat comes tool wear.
2. Common line cutting: uses the software system to nest the parts so that each one is separated by a space the same width as the cutting tool. The tool will only have to use one pass to cut between two parts simultaneously which saves time because the machine does not have to go around each part one by one. This method may also reduce the number of plunges the tool makes into the entire sheet, but one downfall is that the tool’s width will determine how accurate the cuts between the parts are. For a better understanding, since the parts are spaced by exactly the tool’s width, using a sharpened tool with a reduced width can cause a part’s cut to be off by over 0.005”. Another downfall of common line nesting is that the software may favour the placement of parts in order to create simpler cut patterns, but in the end this decreases the material yield.
Essentially, common line nesting should be used with inexpensive materials and parts such as those need for upholstery since they do not require exact sizes and superior edge quality.
3. Bridge nesting: is a very popular method used widely in shops that have experience with CNC nesting. It is a one-of-a-kind process that increases cutting efficiency, reduces tool wear, maintains part precision, and helps to reduce the risk of small parts moving.
With bridge nesting, the CNC machine plunges the tool only once to cut out all of the parts on the sheet, while maintaining the direction of the cut. Imagine two parts, side by side, with the tool plunging into the material, cutting the bottom half of both parts, and then swinging around to the top to cut two top halves before retracting. Now imagine cutting 10-20 parts on the sheet and only retracting the tool after all of the cuts have been completed.
Only a few software applications currently offer the bridge method of nesting which has proven to have had a major impact on the efficiency of nesting.
4. Face 6 nesting: is the most current advancement in nesting methods. Since parts often need to be machined on both sides, a common practice is machining the parts, clearing the table, flipping each part, and finally performing the remaining machining on the reverse side. This solution proves to be very time consuming and the likelihood of an error increases. Face 6 was created to ease the double-sided machining process by programming the CNC to first perform all of the operations on one side of sheet, and then cut one long edge and one short edge on the sheet to square it off. Instead of each piece being flipped over, the entire sheet is flipped and repositioned using the two edges that were cut square; the CNC then runs a second program to perform all of the reverse side operations. Finally, the machine finishes cutting out all the parts using the nesting method of choice.
Remember to program your CNC machine using a nesting method that results in optimal tool life and cycle time so that your quality is not being compromised. The nesting method you choose should be efficient and profitable for your shop so it is important to explore all of the options that are at your disposal.