Source: Hari Sridharan
NC software is a critical component in the arsenal of every toolmaker. Advances in NC technology continue to be made. For example, it is a given that NC software today must support programming in both surface and solid. However the role of NC software continues to expand as toolmakers look for help addressing common industry challenges such as competitive pressures, customer demands for higher quality, tighter tolerances, speed to market, and lower cost.
Here are some of the trends and requirements that toolmakers can expect to see in NC software these days.
Complex Core and Cavity Machining
As parts increase in complexity, strong algorithms are required to support complex core and cavity machining strategies. While no single strategy is appropriate for all situations, 3D step can be very helpful for machining of parts with many surfaces that require high surface quality.
3D step helps keep the cutter in constant contact with the material, minimizing entry and exit points which could lead to finishing distortions. The result is better surface quality and higher toolpath efficiency.
In addition, certain areas of the core and cavity require different offsets, touching each other in some areas while leaving other areas relieved. A typical situation would require maintaining different offsets on the parting surfaces and part surfaces (molding areas) in a single machining process, as well as allowing different offsets on walls and floors.
When coupled with 2D orbital gap capability, the NC software can help attain orbital offsets in electrodes and eliminate the need for extensive geometry manipulations that would be required in order to add these offsets to the model.
Toolmakers look for NC software to help them do things better and faster. As the use of High Speed Machining with high spindle speeds is becoming more common, so does the use of smaller tools. Smaller cutters help minimize the use of electrodes; at the same time, these tools are relatively expensive and require greater care in maintaining the load conditions to avoid tool breakage. Smaller diameter tools are mostly used as re-machining (rest machining) operation. The software can identify the areas with extra stock and automatically generate a roughing toolpath in these areas as part of the re-machining (rest machining) operation. Re-rouging before finishing saves valuable time and optimizes the use of smaller cutters while avoiding tool breakage.
In addition, using multiple cutters in a single procedure can optimize the process by maximizing the use of smaller tools with higher speeds and feeds. The software should automatically identify the areas that can be machined with each tool – the shorter tools first, the medium tools, and then the longer tools – and have the ability to define different parameters for each tool (e.g. spindle speed, feed rate, down steps, sidesteps) all in a single process.
Demands for greater accuracy and speed require NC software to continue pushing the envelope towards a flawless machining process. If knowing the stock one or two steps back used to be good enough in the past, the requirement today is for continuous in-process stock management and gouge checking not only against the part but also against the current stock. Automatic approach and retract motion calibrated based on gouge checking against the existing stock at any given time is the only way to assure both the mold and the tool are safe throughout the process.
Feature Based Machining While Leveraging User Knowledge
The trend in NC software is towards automatic feature recognition, where the software can examine the model, identify the feature (e.g. a hole, pocket, or profile) and its associated attributes and provide automated routines. Some molds can have hundreds or even thousands of holes, and programming each one of these can be time consuming and tedious.
While most users will rely on the NC software to automate the majority of day-to-day operations, no software can supplant the unique knowledge that an experienced NC programmer brings to the table. As much as we see the trend moving towards greater automation, power users are still looking for options to modify the software’s output with features such as a powerful motion editor that allows them to adjust the toolpath as they see fit.
The result is greater synergy between the NC Programmer and the software. The software leverages the user’s knowledge by capturing the operational sequences used for a specific feature and automatically invoking these sequences when the feature is recognized.
Decision Support and Simulation
With rising pressure to reduce delivery time and cost, toolmakers can ill afford running into problems during machining and fixing them later. Toolmakers are looking for their NC software to provide decision support and simulation capabilities that will help them verify the toolpath in advance, including remaining stock or extra material at any point on a part as well as any potential collision points.
Steve Hamrick, Tooling Manager at Regal Prototypes explains the benefits of the decision support capabilities offered by the software they use: “We run the program through the Cimatron Verifier and we can see if the holder or the spindle will get hit. Working with tight tolerances, there are times when the holder looks like it is going to hit, but using the Verifier confirms it is not going to. The Verifier double checks everything before I send a program out.”
The trend in NC software is towards even earlier detection capabilities which allow the programmer to preview the stock remaining prior to engaging in detailed toolpath calculations. NC preview capabilities can drastically reduce programming time by providing toolmakers with the information they need to make more educated decisions earlier in the process.
As the price gap between 3X and 5X machines gets narrower, the use of 5X machining in the tooling industry is increasing. 5-axis technology is used in a variety of applications, including the production of impellers and turbine blades, cutting tools, ports and inlets, as well as the machining of aerospace structural parts, rubber molds, patterns and models, medical implants, and deep cavity molds.
5-axis machining helps deliver high quality products by providing better positional accuracies, especially for multi-sided operations. It also enables the use of smarter and shorter tools that improve accuracy and surface quality, therefore eliminating the need for polishing and minimizing the need for electrode burning while increasing tool lifetime.
5-axis enables the production of complex parts as a single process, reducing the time and cost of production by minimizing tool changes and setup requirements. With a single machine setup, manufacturers are able to increase the use of automated and unattended production runs, increasing machine utilization and reducing labor cost.
To support 5-axis machining in a cost-effective manner, the NC software should enable multi-axis machining with no limit to geometry and part type. Vendors of 5-axis solutions are required to ensure they can support a wide range of applications and provide a selection of post processors, which are paramount to the success of the machining process.
The demand for micro-system technology presents manufacturers and toolmakers with unique challenges. Parts are shrinking in size while increasing in complexity. Miniature features must be machined with extreme accuracy and require special tools – as small as 0.1mm in diameter – to achieve the required accuracy and surface quality.
NC software that supports micro-milling requires special algorithms and is capable of addressing the following requirements:
- Read the highly mathematical machined part data while maintaining its level of accuracy.
- Include high-accuracy built-in CAD capabilities that can provide assisting geometry (e.g., capping, extending surfaces, etc.) with the appropriate accuracy and tangency within the CAM system.
- Support toolpath calculation with tolerances down to 0.1micron (0.0001mm). This is especially challenging when machining miniature details in large size parts.
- Support calculation with micro-milling level parameters considering the constraints of the physical machines. For instance, the CAM system may be required to provide super-finish results with a tool diameter of 0.1mm, a side step of 0.005mm, and a 10 times large round corner radius of 0.05mm.
- Support machining strategies optimized for micro-milling, such as the machining of rough, re-rough, and finish in the same procedure.
- Use the knowledge of actual remaining stock throughout the entire process to adjust feed to actual tool load, in order to lower machining time while protecting the delicate tools from breaking.
Modeling for Manufacturability
Toolmakers nowadays are expected to take a holistic view of the overall manufacturing process and play a pivotal role in ensuring part manufacturability. NC software, therefore, must provide the ability to perform geometry manipulation (e.g. extend a surface, cover a hole) in both surface and solid, allowing toolmakers to build a tool that best supports the manufacturing process. It is important that these design capabilities are available as an integral part of the NC software so there is no translation required. The result is greater synergy between the design and manufacturing groups, leading to better tools and more efficient performance of the tool shop from the initial engagement with the customer to the point of product delivery.