Inside Machines: Practical Feedrate Limits for 5-Axis Machining of Thin Parts

When looking at cutting feedrate, a typical specification for 5-axis machines, consider “worst-case” part geometry.

10/21/2011


Part geometry matters when calculating maximum machine feed rate. If the radius is decreased, then X needs to move even faster to maintain the 50 inches per minute at the tool center point. Courtesy: Matt Goska, SiemensWhen purchasing a 5-axis machine, one of the typical specifications is the maximum feedrate for cutting. The machine’s ability to meet this specification is commonly verified during buy-off with the Circle-Diamond-Square and Cone-Frustum tests as defined in National Aerospace Standards 979 (NAS 979).

For traditional aerospace parts, where a large percentage of aluminum is removed from a billet, this is a very reasonable test when run at the planned production feedrates. As more aircraft parts are being made from composites and titanium stampings, where a part is trimmed out of a contoured sheet, NAS 979 may need to be run at much higher speeds to represent the real machine usage. These concepts frequently apply to milling machines, waterjets, lasers, and fiber placement machines.

A simple example of this is a 0.1-in.-thick carbon fiber sheet with a “C” cross-section, intended for use as a beam, where edges need to be trimmed to the final size with an end mill. For this example, the intended path feedrate is 50-in. per minute (IPM) at the tooltip, the tooltip is 0.05-in. through the skin, and a 5-axis milling machine with a “C carries A” forked head is being used. Also assume a pivot length (tool tip to A axis) of 18 in. and that the machine performed perfectly on the NAS 979 tests at 300 IPM. During the flat sections of this contour, the machine should have no problem; the radius is the concern. If the radius (R) is 2 in. (2.15 in. at the outside of the skin), then the length (L) along the path is 3.1 in. (pi*R/2). At 50 IPM, this means the machine should take about 3.8 sec to make this radius. During this move, “A” moves 90 degrees to stay perpendicular to the surface. When the pivot length is considered, and excluding the distance for the programmed radius, X and Z each need to move 18 in. just to keep the tool center point (TCP) stationary. At a 2-in. radius, X would need to average 285 IPM to make this move. This is still well within the 300 IPM from the NAS 979 test. If the radius is decreased, then X needs to move even faster to maintain the 50 IPM at the TCP as the diagram and table show.

As the radius is decreased, axis speeds start exceeding what was tested with the NAS 979 for this machine, even though the path feedrate is not increasing. For this reason, when considering a machine for purchase, the geometry of the production parts needs to be considered. When considering a new machine for purchase, the worst-case part geometry should be determined early in the bidding process, as a machine that performs well at 285 IPM is in a very different price class from one at 1,140 IPM.

- Matt Goska, mechatronics engineer, Siemens, Elk Grove Village, Ill., is among Control Engineering Leaders Under 40, Class of 2011. Posted by Chris Vavra, Control Engineering, www.controleng.com 

www.usa.siemens.com/drives

CNCs provide faster processing, easier integration, customization | Control Engineering 

Machine Control Channel 

Motors and Drives Channel



No comments
The Top Plant program honors outstanding manufacturing facilities in North America. View the 2015 Top Plant.
The Product of the Year program recognizes products newly released in the manufacturing industries.
The Engineering Leaders Under 40 program identifies and gives recognition to young engineers who...
IIoT grows up; Six ways to lower IIoT costs; Six mobile safety strategies; 2017 Salary Survey
2016 Top Plant; 2016 Best Practices on manufacturing progress, efficiency, safety
2016 Product of the Year; Diagnose bearing failures; Asset performance management; Testing dust collector performance measures
Future of oil and gas projects; Reservoir models; The importance of SCADA to oil and gas
Big Data and bigger solutions; Tablet technologies; SCADA developments
SCADA at the junction, Managing risk through maintenance, Moving at the speed of data
What controller fits your application; Permanent magnet motors; Chemical manufacturer tames alarm management; Taking steps in a new direction
Tying a microgrid to the smart grid; Paralleling generator systems; Previewing NEC 2017 changes
Package boilers; Natural gas infrared heating; Thermal treasure; Standby generation; Natural gas supports green efforts

Annual Salary Survey

Before the calendar turned, 2016 already had the makings of a pivotal year for manufacturing, and for the world.

There were the big events for the year, including the United States as Partner Country at Hannover Messe in April and the 2016 International Manufacturing Technology Show in Chicago in September. There's also the matter of the U.S. presidential elections in November, which promise to shape policy in manufacturing for years to come.

But the year started with global economic turmoil, as a slowdown in Chinese manufacturing triggered a worldwide stock hiccup that sent values plummeting. The continued plunge in world oil prices has resulted in a slowdown in exploration and, by extension, the manufacture of exploration equipment.

Read more: 2015 Salary Survey

Maintenance and reliability tips and best practices from the maintenance and reliability coaches at Allied Reliability Group.
The One Voice for Manufacturing blog reports on federal public policy issues impacting the manufacturing sector. One Voice is a joint effort by the National Tooling and Machining...
The Society for Maintenance and Reliability Professionals an organization devoted...
Join this ongoing discussion of machine guarding topics, including solutions assessments, regulatory compliance, gap analysis...
IMS Research, recently acquired by IHS Inc., is a leading independent supplier of market research and consultancy to the global electronics industry.
Maintenance is not optional in manufacturing. It’s a profit center, driving productivity and uptime while reducing overall repair costs.
The Lachance on CMMS blog is about current maintenance topics. Blogger Paul Lachance is president and chief technology officer for Smartware Group.
Motion control advances and solutions can help with machine control, automated control on assembly lines, integration of robotics and automation, and machine safety.
This article collection contains several articles on the vital role of plant safety and offers advice on best practices.
This article collection contains several articles on preventing compressed air leaks and centrifugal air compressor basics and best practices for the "fifth utility" in manufacturing plants.
Maintenance Manager; California Oils Corp.
Associate, Electrical Engineering; Wood Harbinger
Control Systems Engineer; Robert Bosch Corp.
click me