The use of simulation software to verify CNC machining programs is a cost effective method to reduce costs and improve quality. This is especially true when machining large fabrications or machining large castings. In many cases weld repair is not allowed on the work piece and any mistake in machining will result in a high cost of quality and delivery delays.
There are several CNC machining simulation packages available. This is a proven technology. There are steps the user of a CNC machining simulation package must take to tailor the software package to the specific machines, programming practices and tooling of the user.
Large CNC machines frequently have multiple axes that operate following specific rules that are specified by the machine builder or the control manufacturer. The CNC programmers also have company standard practices that are used when programming their machines. All of these rules and common practices are incorporated into a post processor that is specific to the machine, control and company that is using the machine. This post processor is used by the simulation software to insure that the simulation results accurately reflect the actual machining operations. The tooling that will be used for the machining operation must be accurately represented in the CNC machining simulation. This is accomplished by importing solid models of the tooling. Many tooling manufacturers have solid models of their tooling that can be downloaded. In other cases the user must create the solid models. Two other aspects of the machining operation can be modeled by the simulation software. These are the fixture and the physical restrictions of the machine itself. Adding solid models of these aspects will enhance the value of the simulation model.
One benefit of the simulation of CNC machining is preventing programming errors from reaching the shop floor. Errors in CNC machining that reach the shop floor can result in crashes between the work piece, tooling, fixture, and/or machine. Errors can also result in excess machining, insufficient machining, wasted machine moves, and downtime to debug programs. All of these errors can be seen and corrected during the CNC machining simulation.
The CNC simulation software begins with two solid models of the work piece. One model represents the work piece prior to machining (raw) and one model represents the desired finished work piece. The simulation drives the cutting tools around the solid model of the raw work piece. The result is a model of the raw work piece after the CNC program has been run. This model is compared to the model of the desired finished work piece. The areas where the machining does not meet the model of the desired finished work piece are visually identified. This includes areas where too much material has been removed and areas where there has not been enough material removed. The CNC programmer then modifies the CNC program and repeats the simulation until the CNC program produces a part that meets the desired finished product in the simulation.
Simulation is beneficial for all sizes of CNC machining but especially for machining large fabrications or machining large castings. In the case of machining large fabrications or castings the cycle time can be measured in hours rather than seconds as is common with small work pieces. Frequently the cycle time to machine one part can take multiple shifts. If the CNC program is proven out during the first piece run without the benefit of simulation the cost to run a first piece will be double or triple what the cost will be for a first piece run that has gone through the simulation process. Machining large work pieces requires large machines. Complex large fabrications and large castings typically require large machines with five axis capability and head changers. These large multi-axis machines have a high cost per hour to operate. The savings achieved by proving out a CNC program with a simulation package versus proving out the program on the machine is substantial. The typical lot size when machining large fabrications and machining large castings is small. Frequently, the lot size is only one or two pieces. The large savings in prove out cost spread over a small lot size results in a significant savings per piece.
The setup time for machining a large fabrication or a large casting is also a substantial part of the time required to machine the part. It is critical that the machining is correct the first time. Any errors must be corrected on the machine. If the error is found in inspection after the work piece has been removed from the machine, then the work piece will have to be set up on the machine a second time for the repair operation. Given the high cost per hour of large machines, this added setup time and repair time are very costly. Simulation of CNC machining operations and comparison of the raw model as machined to the desired finished model greatly reduces the chance of a machining error that will require repairs.
There are cases where any repair operation requires customer approval of a specific repair procedure. In these cases the work piece sits on the machine while the customer is consulted and a repair procedure is approved. The cost for this repair will include the cost to engage the customer as well as the cost to complete the repair operation. The use of the simulation of CNC machining greatly reduces the probability that this type of error will be made.
Companies that machine large fabrications and large castings are judged by their customers on quality, delivery and cost performance. They must use the technology that is available to provide the highest quality, delivery and cost performance. The use of simulation software to verify CNC machining programs is a cost effective way to prevent errors. It is one of the many tools that K&M Machine-Fabricating Inc. uses to meet and exceed customer expectations.
K&M’s video showing Large Machining Simulation
October 6, 2014
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