Many die & mould makers are looking for specific ways to increase machining speed, which is not as simple as it may sound. They are looking for ways to reduce the overall time to produce a finished mould by having the mould come off the machine tool with little or no post-machining finishing work.
That means dramatically larger NC program files with very small step-over to produce extremely smooth-finish machined surfaces. With a modern 5-axis machine, a mould surface that would typically be machined with a 3-axis machine tool can be cut with the milling tool at specific orientations to the cutting direction. The tool can be oriented so cutting is done with the side of the ball end mill, rather than the tip. This produces much better cutting conditions where the tool contacts material.
Many die & mould makers are also seeking to reduce the number of set-ups involved with machining a part. This in turn also reduces the amount of operator involvement and means that one operator can oversee many machines. Reducing set-ups generally requires sophisticated multi-axis CNC machinery and automation tools such as robots and pallet shuttle systems. All this automation adds complication to the prove-out process.
As machine tools and mould designs become more complex, part program verification using CNC machine simulation becomes an essential tool for ensuring that the mouldmaker’s NC programs machine the mould correctly the first time. Skipping the verification step creates costly production delays, which cause the machine tool to wait idle while the NC program errors are corrected.
To be truly effective, CNC machine simulation software must interactively simulate and display the material removal process of a NC program. NC programmers use software to verify the quality and accuracy of their NC programs while 3D simulation of the CNC machine checks for collisions. However, the goal of simulation is not simply a collision-free and efficient NC program. The first and most important goal is a NC program that produces the correct workpiece.
The right solution
Reducing the time required for mouldmakers to easily develop, analyse, inspect and document the CNC programming process is an additional simulation software objective. Mouldmakers should look for software that creates an in-process model that can help them determine whether or not the NC program will make a correct mould. For example, many NC programs use circular interpolation. In order to measure the cylinder as an as-machined feature, the software must emulate the circle motion. Most internal simulations — the simulation included with most CAM packages — do not emulate circle motion, but instead divide the circle motion into a series of linear motions approximating the cylinder. These segments are not measurable as a cylinder.
Simulation software development is often driven by the evolutionary changes in manufacturing technology: new CAD/CAM software features; new machines and tooling; new machining techniques and processes; and a mouldmaker's need to implement and improve on these changes.
Trends and challenges
More and more mouldmakers need to simulate specialised processes and complex machines. When a specialised process reduces production time or increases reliability, it becomes adopted by more companies. If a software developer supports simulating these special processes early, it instantly supports the next customers who adopt them. For example, years ago it was rare to see an NC program utilising local part coordinate transformations and tool axis vector programming. Now it is fairly common. By supporting these features when they were initially adopted, others have benefited.
Adoption of complex machines is similar. A few years ago, 5-axis machines were rarely used by mouldmakers. Today, more multi-axis milling machining centres are being used for mouldmaking that was previously done using simple 3-axis milling machines. This trend has been fueled by a significant decrease in the price of multi-axis machining centres over the past several years. Even small and mid-sized mold shops that previously would not have considered buying a 5-axis milling machine, now have to learn how to set-up and program these machines; accurate 5-axis NC program verification and machine simulation becomes a mandatory tool.
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