Optimizing NC programs for machine tools

Today’s Medical Developments (TMD): How can medical manufacturers successfully manage the tools in their manufacturing workflow?

Alan Levine (AL): hyperMILL’s extensive database enables users to manage tools of all types – from drills and milling cutters to complex turning tools – which can all be mapped virtually and linked with technology data. Depending on the machining application, speed and feed values can be controlled with maximum precision. Individual process data for materials and applications can be stored while manufacturing standards are stored in a central database for easy access by a programmer. The hyperMILL tool database helps ensure only proven, efficient tools and machining values are used. A well-organized tool database is also required for automation procedures.

TMD: What is high performance cutting and what does it bring to medical device manufacturing?

AL: Open Mind offers a high performance cutting (HPC) module, hyperMILL Maxx Machining roughing for 2.5-axis, 3-axis, and 5-axis machining. Based on Celeritive’s VoluMILL kernel and extended by Open Mind to have application for 5-axis roughing, it combines many advantages, including optimum milling paths, maximum material removal, and the shortest possible production times. An alternative Perfect Pocketing technique finds optimal inscribed rectangles or circles to use simple paths over those regions, and then automatically identifies remaining rest material.

A comprehensive 5-axis HPC package allows trochoidal-like paths to be mapped to curved component surfaces. Trochoidal toolpaths are ideally suited for efficiently roughing medical components in a tool-friendly way, even when handling materials that are difficult to machine, such as titanium and stainless-steel alloys.

hyperMILL Maxx Machining roughing offers high material removal rates which facilitate extremely fast machining. The Maxx Machining roughing module controls tool engagement to improve material removal in corners, avoiding the need to reduce feed rate in certain areas and running the entire job at lower feed rates. Further, with well managed cutting, the depth of cut can be greatly increased, further reducing machining times. Avoiding large cutter engagement in corners also reduces stress on tools and can significantly extend tool life.

TMD: Medical devices are not simple parts – many have unique shapes, complex geometries, and stringent surface requirements that require many steps to complete. How does Open Mind technology minimize finishing processes?

AL: Various milling strategies make a better part that requires less post-machining finishing, saving time and process steps. For example, hyperMILL Maxx Machining finishing uses a conical barrel cutter (also known as circle segment or arc segment end mills) with contact radius of up to 1,000mm or more, producing a step-down of 10x to 15x greater than using a ball-nose end mill. This can improve surface finish and reduce cutting time by 90%. The conical barrel cutter has the large barrel radius ground on a tapered feature, compared to a traditional barrel cutter where the large radius blends to be tangent to the cutter shank. Smaller radii such as 250mm are common in medical applications when matching shaped surfaces in bone plates and knee joints. The smaller radii decrease cutting forces on hard materials and when matching the shaped surfaces.

Open Mind has added technology to focus on producing a good part, more than just developing a good tool path – smooth overlap blending and high- precision finishing.

Smooth overlap blending techniques address the complex physical problems encountered in manufacturing such as deflection between adjacent program areas that use different cutters or cutter orientation, cutter wear, and spindle growth. The smooth overlap process adds some passes to overlap adjacent paths, while simultaneously avoiding double-cut surfaces. The result is imperceptible mismatches and near-perfect blends.

High-precision finishing shifts the final tool path locations from an approximated mesh surface to the actual design surface. Though the tool path adjustments may be only a few microns, there’s marked improvement in the resulting surfaces, with no remaining witness from the approximated mesh surface, saving time on post-machining finishing. The smoothing algorithms within the CNC controls also work better when fed smoother data from the CAM system.

TMD: What does Open Mind bring to users for tool path prove-out prior to putting the job on the machine?

AL: hyperMILL Virtual Machining Center simulates and analyzes the manufacturing process while modeling the real machining environment. This streamlines throughput by avoiding surprises and costly errors at the machine from inefficient operations. It enables constant real time bi-directional communication between machine and control, improving safety, reliability, speed, and process control optimization from CAD/CAM to machine. Actual machining situations are mapped virtually and simulated based on the NC code in the hyperMILL Virtual Machining Center. The simulation solution consists of three modules: Center, Optimizer, and Connected Machining, enhancing communication between the hyperMILL CAM suite and the machine tool.

One example, in addition to checking toolpaths against the part and the machine model, Optimizer looks at toolpaths in respect to machine tool kinematics and specific geometry elements, such as an asymmetric or offset head, calculating the best toolpath while considering the entire machining environment.

TMD: How does Open Mind software support automation, especially when handling families of parts in medical manufacturing?

AL: Automation is a broad topic and is essential for manufacturers to maintain an edge against local and offshore manufacturing competition. Automation is extremely important in medical fields where many implant components are individually sized to the patient. The machined components are therefore all unique but can be machined with common workflow.

hyperMILL’s Automation Center brings together structured programming processes that model best practices, including tooling and cutting procedures. The automation scripts don’t require any special programming languages and easily map to the general cutting process more than specific geometry elements. It’s broad-based and not limited to typical holes and pockets, and can provide complete programming, or only segments of repetitive steps.

TMD: Open Mind Technologies USA is celebrating 25 years in North America. What do you consider some of your key accomplishments?

AL: As we reflect on the development of Open Mind Technologies USA throughout the years, the key accomplishments are the development of our strong team of colleagues and the service provided to our customers. Together with our hyperMILL CAM system that has many novel techniques, we’ve been able to assist many companies large and small make meaningful impact to their productivity and business results.

Open Mind Technologies USA Inc.
https://www.openmind-tech.com

About the author: Elizabeth Engler Modic is editor of TMD. She can be reached at 216.393.0264 or emodic@gie.net.