View Package of All Summaries

 
       An Upper-Bound Model of Edge-Radius Effects on Machining Forces
Sponsor:
National Science Foundation, Arlington, VA (CAREER Grant DMI-9734147)
Abstract:
To achieve the edge strength needed to cut harder materials, slightly negative rake angles are used with a honed radius or chamfer applied to the cutting edge. Edge effects become important when the edge feature is sizeable relative to the scale of the cut. In these cases, appropriate model-based selection of the edge feature requires a model that explicitly accounts for the edge geometry. The aim of this work is to develop a machining model that explicitly includes the effects of edge radius without resorting to the highly computational finite element method or the complexities of rigorous slip-line analysis. While it is presumed and/or known that the edge geometry affects surface finish, residual stress, cutting temperature and tool wear, the first step taken here is to model the effects of edge radius on forces. While the model achieved here is not fully predictive, it does provide a means to analyze force data to assess how well the model represents the effects of edge radius on flow stress via the edge radius’ effects on strain and strain rate.
Benefits:

• The simplicity of the model provides an analytical result that clearly shows effects of geometric parameters.
• However, inconsistencies in exercising the model justify and motivate a more sophisticated model, such as a slip-line field (SLF).

 
       The Existence of a Wear-Minimizing Corner Radius and its Relation to Edge Preparation
Sponsor:
National Center for Manufacturing Sciences, Ann Arbor, MI
Abstract:
The use of cutting tools with a honed edge radius to protect the cutting edge from chipping has become quite common. As the mechanics of straight-edged orthogonal cutting with edge-radiused tools becomes better understood, process performance for more practical tooth profiles comes to question. The objective of this project is to experimentally study how flank wear is interactively affected, if at all, by edge radius and corner radius; the corner-radiused tooth profile is commonly seen in turning, boring and face milling processes. Turning test are conducted at four corner radius levels, three edge radius levels and three feed rate levels, then replicated three times. Results indicate that flank wear is strongly influenced by corner radius, even when the depth of cut is held much larger than the corner radius per ISO standards. The corner radius dependency shifts with changes in edge radius. These behaviors are explained through known process mechanics.
Benefits:

• Flank wear can be minimized by simultaneously and properly selecting corner radius.
• Adding a corner radius to tools that traditionally have a sharp corner, such as end mills and drills, may reduce flank wear.
• When an edge radius is present, the wear-minimizing corner radius is larger, resulting in improved feed-groove finish.

 
       The Basic Effects of Flank Wear on Forces for Edge-Radiused Tools
Sponsor:
National Science Foundation, Arlington, VA (CAREER Grant DMI-9734147)
Abstract:
Some recent successes have been achieved for “fresh from the box” cutting tools that have either an edge preparation or chip control. However, these recent successes are limited in their practical utility since all cutting tools operate with some level of wear throughout their useful life. Industry practice involves the evolution of a cutting tool’s performance beyond the fresh-tool state. Predicting the change in cutting-tool performance as it wears would ultimately allow one to predict tool life — the point at which the cutting tool’s performance is no longer satisfactory and a tool change is needed. A step toward that ultimate goal is an understanding of how process mechanics are affected by the comprehensive edge condition — flank wear combined with edge preparation. The data show that for light feeds relative to the edge radius, the machining forces decrease initially as flank wear grows. A mechanics-guided function form is found to well represent the coupled effects of edge radius and flank wear land on forces.
Benefits:

• The knowledge compiled here provides substance to any further modeling of wear effects on force.
 • Edge radius may be chosen to achieve a minimal change in force up to substantial wear levels.

 
         An Experimental Study of Glass Machining
Sponsor:
National Science Foundation, Arlington, VA (Grant DMI-9734147)
Abstract:
Owing to their high stiffness, dimensional stability, heat insulation, and excellent resistance to chemical erosion, ceramic materials and glasses are attractive for applications in the computer, automotive, aerospace and optics industries. Starting with net-shape sintered parts, grinding has been the process of choice for machining structural ceramics. The use of geometrically defined cutting tools (machining) at much higher material removal rates is explored through basic orthogonal cutting tests ranging from the ductile-regime that others have studied up to much higher material removal rates. Using soda-lime glass for this initial study, due its well-defined fracture mechanics, along with simple process geometry, unclouded results are shown to highlight three material removal modes. The modes are classified based on the type (or absence) of surface damage present.
Benefits:

• If damage-free ductile-mode chip formation can remove surface cracks without further propagating them, then a rough–semi-finish–finish strategy can be adopted for high productivity machining of bulk stock.
• Rake angle can be chosen to promote rough cutting or finish cutting.

 
         Modeling Surface Damage for Glass Machining
Sponsor:
National Science Foundation, Arlington, VA (Grant DMI-9734147)
Abstract:
When machining brittle materials, to realize fully ductile material removal without surface damage productivity is still quite low by machining standards. Understanding the depth of surface damage at more aggressive conditions would allow transitions to less aggressive conditions toward the final passes without producing damage in the eventual final surface. Surface damage has been observed to occur as an array of surface cracks and, with further increases in productivity, as an array of divots produced by spalling of chips from the surface. Finite element models of the surface cracking and spalling mechanisms are discussed and used in a computer-based experiment to show how surface damage depth depends on process loading and material properties. Results are qualitatively correlated to previous experimental observations.
Benefits:

• The results support the choice of more negative rake angles for lower sur-face crack or spall depth.
• The results also provide a sense of how sensitive surface crack and spall depth are to force level and distribution (rake angle).
• The results also provide a sense of how sensitive surface crack and spall depth are to material properties of fracture toughness and elastic modulus.

 
       Parallel-Process Machining — Its Mathematical Definition and Stability
Sponsor:
National Science Foundation, Arlington, VA (ERC for Reconfigurable Machining Systems)
Abstract:
Parallel-process machining (PPM) applications date back to the early twentieth century. Applications include simultaneous boring of multiple engine cylinders, using multi-drill heads to generate hole patterns, simultaneous turning of journals on engine camshafts, and multi-spindle screw-cutting operations. Numerous improvements in terms of cycle time, idle time, tool-change time and accuracy may be realized through PPM if the process conditions are chosen carefully. Presented here is an analytical solution for a specific case of PPM in which the multiple processes exhibit the same process conditions (e.g., simultaneous engine-cylinder boring). En route to the solution, a mathematical definition of PPM is formulated — it differs dramatically from the intuitive perspective of having multiple slides and/or spindles. Experimental validation shows good agreement with the analysis.
Benefits:

• Perplexing effects of flexible cutters and spatially varying workpiece dynamics are explained through the mathematical definition of PPM.
• Limits on process-to-process dynamic coupling may be specified so that a PPM application does in fact result in productivity and cost benefits relative to using multiple single-process machine tools.

 
         Stability of Ultrahigh-Speed Intermittent Machining
Sponsor:
None
Abstract:
It is well known that when increasing spindle speed to increase productivity the stability limit — the limiting depth of cut — undergoes repeated increases and decreases forming stability peaks. Beyond the final highest-speed peak, the limiting depth of cut is understood to increase continuously with a further increase in speed. Operating at theses speeds is referred to here as ultrahigh-speed machining. Intermittency, or more generally periodic time variation, is present in milling processes as well as continuous boring and turning processes where the dominant structural mode is associated with the workpiece. The objective is to understand and model the behavior of the added stability lobe that this effort has identified for intermittent machining at ultrahigh speeds. Numerical simulation, basic experimental study and an analytical solution show the existence of the added lobe(s), good quantitative validation of the models and an insightful study of the effects of parameters, such as the degree of intermittency and regenerative overlap factor.
Benefits:

• Structural damping becomes unimportant if the process can be operated at ultrahigh speeds, keeping in mind that higher-frequency/stiffness dy-namic modes of the structure could eventually enter the picture.
• The unbounded increase in limiting depth of cut as spindle speed increases comes only at even higher speeds than originally thought.

 
       The Effects of Corner-Radiused Tooth Geometry on Machining Stability
Sponsor:
National Science Foundation, Arlington, VA (ERC for Reconfigurable Machining Systems)
Abstract:
Coming Soon
Benefits:

Coming Soon

 
         An Experimental Study of Fixed-Interface Dynamics under Harmonic Multi-Dimensional Loading
Sponsor:
National Science Foundation, Arlington, VA (ERC for Reconfigurable Machining Systems)
Abstract:
Research on the dynamic characteristics of fixed joints has to date focused on time-varying loads in either the normal or tangential direction. The objective here is to experimentally investigate the dynamic response of a simple, uniformly loaded, annular interface under simultaneously time-varying (harmonic) normal and tangential loads. The experimental apparatus is designed to allow generation of this loading scenario with control of their relative load magnitudes and phase. The setup allows controlled and measurable application of normal preload and real-time measurement of the normal and tangential loads and displacements at the interface. Results show that the hysteretic loops of tangential force versus displacement as well as interfacial damping (energy dissipation) are highly dependent on normal preload, normal-to-tangential load amplitude and, in particular, loading phase. Equivalent tangential stiffness is shown to depend on preload as expected but to be relatively constant with phase.
Benefits:

• It is conceivable that joints can be oriented to achieve a loading amplitude ratio and/or phase that optimize damping and/or stiffness.
• The apparatus conceived and implemented here allows for future experimental studying of specific joint types (e.g., bolted, spot welded) and interfaces (e.g., adhesive) to support design and modeling efforts.

 
       Modeling of Fixed-Interface Dynamics under Generically Time-Varying Multi-Dimensional Loading
Sponsor:
National Science Foundation, Arlington, VA (ERC for Reconfigurable Machining Systems) , MTU Graduate School
Abstract:
Interfaces in structures are known to be the primary source of damping. Experiments and models formulated over the years have focused on both the asperity- level interaction and surface-level interaction. These studies have mainly constrained themselves to time-varying loading in ether the normal direction or tangential direction. However, joints in many real structures are subjected to time-varying loads that vary simultaneously in both directions. A new asperity-based model is presented here to describe the dynamic response of fixed joints to these more general loading conditions, which also includes generic time variation (i.e., not necessarily periodic). The model is exercised for the special case of harmonic loading, showing in terms of joint stiffness and energy dissipation the relative importance of preload and normal-to-tangential load amplitude and phase.
Benefits:

• Model-based orientation of joints to optimize damping and/or stiffness based on the load amplitude ratio and/or phasing seen by the joint.
• Model-based preload specification to balance stiffness and damping.