Machining Process Simulation - Industrial Engineering and Productivity Analysis

Industrial Engineering is Continuous Improvement of Processes Having Engineering Operations/Processes

Industrial engineers have to use every pathway available for productivity improvement. Industrial engineering is engineering based in operations or shop floor and it is also continuous  engineering improvement of the product and process first and then improvement of related process elements like planning, communication (information), inventory etc.

In machine shop industrial engineering or industrial engineering of machining processes and machining operations, simulation of machining process is also an important path to understand the process to increase productivity by reducing the cycle time by modifying the machining parameters or variables. Industrial engineers need to have knowledge of machine simulation and use appropriately in productivity improvement. 

Machining Process Analysis Using Simulation and Finite Element Models

"Machining Process Analysis" is the chapter name used by the authors Stephenson and Agapiou to discuss this topic. According to them, three types of analyses process are performed.  One is force, power, and cycle time analyses using kinematic simulations (or mechanistic models). Second is, structural analysis for clamping and fixturing using finite element methods. The third is the detailed chip formation analyses done using finite element models.  

Kinematic simulations of machining processes are used to calculate cycle times and time histories of cutting forces and power. The inputs required include the part and tool geometries, tool paths, and cutting pressures for the combination of "tool–workpiece material" of interest, which may be measured in tests or estimated from finite element calculations. The tool geometries and tool paths are preferably read directly from CAD and CAM systems. Based on this information, the kinematic motions of the tool with respect to the workpiece as a function of time can be simulated, and the instantaneous area of material being cut (the interference between the tool and workpiece) at any time can be computed from the tool path and part geometry.

Commercial programs for kinematic simulation include Third Wave Systems’ Production Module programs  and MillSim from Manufacturing Laboratories, Inc..

Structural finite element analysis clamping and fixturing is used to estimate workpiece distortions due to clamping and machining. The objective of the analysis is to minimize such distortions for critical features, which may be accomplished by stiffening the part or fixture in directions of heavy loading, modifying the tool path or cutter geometry to direct forces in stiff or noncritical directions, choosing clamping and locating schemes, which minimize clamping distortion and support compliant portions of the part, and minimizing clamping forces. Finite element analysis permits a wider variety of options to be investigated more quickly and cheaply than through prototype part and fixture tests.

Kinematic Simulations of Machining Processes - Applications

TURNING

Turning  is easy to simulate because the geometry and kinematic motions of the tool and workpiece are easily described. When turning large volumes of parts on CNC lathes, simulation helps to reduce cycles times and thus the number of machines and capital investment required.

Cutting forces are calculated by multiplying measured cutting pressures by the calculated uncut chip area. Various formulas are available to calculate many variables required or simulation.

FINITE ELEMENT ANALYSIS FOR CLAMPING, FIXTURING, AND WORKPIECE DISTORTION APPLICATIONS

Structural finite element analysis can be  used to estimate workpiece distortions due to both clamping 

and machining forces.

For analyzing clamping distortions, the inputs required are the clamping and locating points and the clamping forces. Finite element models of both the part and fixture structure are  required; attempts to replace the fixture with equivalent boundary conditions, such as springs or displacement constraints, save computing time but generally yield less accurate results. The part finite element model used for structural design is usually adequate, although some mesh refinement near the clamping points may be needed. If a fixture model is not available, one must be created for the support and clamping elements in contact with the part. The interfaces between the part and fixture should be modeled using contact elements with friction for optimum accuracy. A static analysis in which the clamping loads are applied at the clamping points yields a distortion prediction. The major unknowns are usually the friction coefficients at the contact points; these can be determined experimentally if the solution is sensitive to these variables. In overconstrained clamping schemes (i.e., for four-point locating schemes on planes), locator dimensional variations are also significant. This type of analysis is most often used for thin-walled, compliant parts; in this case it is rarely necessary to model additional elements of the machine tool structure.

When modeling distortions induced by machining forces, more elements of the system must generally be considered. The machining forces act between the tool and part, and may cause deflections of two broad structural assemblies: the tool, toolholder, and machine  tool structure on one side, and the part and fixture on the other. To compute deflections, cutting force histories must be estimated, often using the kinematic simulations, and applied to structural finite element models of both assemblies. In some operations, however, the compliance of one element of the system (tool/toolholder/machine structure or part/fixture) may be much larger than the other, so that the other element can be treated as rigid. Sequential or iterative analyses may be required in applications in which machining significantly changes the structural compliance of the part or in which cutting force and deflections are coupled.

Simulation - Bibliography

Seminar on DES using Python

https://iiseblogs.org/2020/10/07/resources-from-python-des-webinar/

Files in https://drive.google.com/drive/folders/1C7ZTnJePit13iwVg-Ur1trSiaASnXUWN

https://www.yumpu.com/en/document/read/28626617/status-of-fem-modeling-in-high-speed-cutting-a-progress-report

https://asmedigitalcollection.asme.org/manufacturingscience/article-abstract/144/11/110801/1131320/100th-Anniversary-Issue-of-the-Manufacturing?redirectedFrom=fulltext

Ud 24.7.2022

Pub 21.12.2020