Predictive Modeling of Scribing Brittle Material Using Diamond Tool with Improved Geometry

A comparative study on FeAl and NiAl bonded diamond tools for dry grinding based on wear characteristics at elevated temperature

Chapter 6 - Analysis of hardness testing indentations

Tearing a thin sheet by forcing a rigid object through it leads to complex crack morphologies; a single oscillatory crack arises when a tool is driven laterally through a brittle sheet, while two diverging cracks and a series of concertinalike folds forms when a tool is forced laterally through a ductile sheet. On the other hand, forcing an object perpendicularly through the sheet leads to radial petallike tears in both ductile and brittle materials. To understand these different regimes we use a combination of experiments, simulations, and simple theories. In particular, we describe the transition from brittle oscillatory tearing via a single crack to ductile concertina tearing with two tears by deriving laws that describe the crack paths and wavelength of the concertina folds and provide a simple phase diagram for the morphologies in terms of the material properties of the sheet and the relative size of the tool.

Brittle materials like semiconductor wafers and ceramic substrates are usually cut by diamond tools, where the generation of microcracks cannot be avoided. Recently, thermal stress cleaving of a thin strip using a point heat source is studied to cut brittle materials without leaving any microcracks on the cleaved surfaces. However, this method often causes thermal damages to the workpieces because of the very high temperature reached around the heating point. It is desirable to cut the electronic substrates, on which precise circuits were already formed, with minimizing the temperature rise. In the present paper, based on the plane thermoelasticity, the time dependent thermal stress intensity factor of a line crack has been obtained for two heating ways : by two point heat sources and a circular zone heat source located symmetrically with respect to the crack line. It was found that a zone heating is better than a point heating in the case of a thin strip cleaving under the restriction of the temperature rise. The most successful cleaving is generally achieved when a radius of a heating region is expanded up to the crack tip. The present calculation was compared with the experimental results and good agreement was found.

Experimental investigation on the ductile machinability of fused silica during in-situ laser assisted diamond cutting

Diamond tools have been widely used in grinding hard and brittle materials such as stone, glass, and ceramics, because of the excellent performance of diamond abrasives, including extremely high hardness, thermal conductivity, and wearing feature. Diamond abrasive layers are the most important part of diamond tools. However, the traditional methods for fabricating diamond abrasive layers are time-consuming. This study proposed a new method for fabricating diamond abrasive layers. The diamond abrasive layers were fabricated on 304 stainless steel plates by electrical discharge machining (EDM) with a diamond-cobalt powder green compact electrode. In order to improve the performance of the fabricated diamond abrasive layers, the influences of fabrication conditions such as the diamond abrasive content and compaction pressure of the electrode, discharge current, and fabrication time were experimentally investigated. Experimental results showed that 100 MPa electrode compaction pressure, 40 wt% electrode diamond abrasive content, and 20 A discharge current were the best fabrication conditions. A 400-μm diamond abrasive layer with diamond abrasive content of 13.5% was fabricated under such fabrication conditions in 5 min. Diamond abrasive layer fabricating speed of EDM was much faster than electroplating and the diamond abrasive layer fabricated by EDM demonstrated satisfactory grinding ability.

A procedure and the equipment necessary for single-point diamond flycutting (loosely referred to as diamond turning) potassium di-hydrogen phosphate (KDP) crystals are described. It is based on current KDP diamond turning activities at the Lawrence Livermore National Laboratory (LLNL), drawing upon knowledge from the Nova crystal finishing development during the 1980`s and incorporating refinements from our efforts during 1995. In addition to describing a step-by-step process for diamond turning KDP, specific discussions are included on the necessary diamond tool geometry and edge sharpness, cutting fluid, and crystal preparation, handling, cleaning, and inspection. The authors presuppose that the reader is already familiar with diamond turning practices.

Study on micro-grinding quality in micro-grinding tool for single crystal silicon

Because composite laminates are very susceptible to impact loading even at low velocity, low-velocity impact is an important subject in laminated composite analysis. The impact-induced damage is usually invisible to the naked eye and can cause serious structural degradation. Many low-velocity impact tests were performed in previous studies; however, most were phenomenological analysis. In an effort to further understand the responses of composite laminates under low-velocity impact and to develop an accurate and efficient quantitative simulation in the future, this study was aimed at performing instrumented impact tests and computer simulations. A commonly used computer code—LS-DYNA3D—was evaluated in this study, and the results are valuable for future development of a new computer code. In the study, a low-velocity impact event investigated by Sun and Chen with an indentation law and verified by experiments was used to justify the finite element model and contact parameters. Once the computational scheme was established, it was used for a broader investigation consisting of composite laminates with various thicknesses, fiber angles, and impact velocities. Computational results revealed that the peak contact force and maximum deflection were strongly affected by the thickness of composite laminates, while the fiber angles investigated seemed to play a less significant role. In addition, it was concluded that because delamination modeling was not included in the LS-DYNA3D, the computer code needed to be modified if it was to be used for accurate impact simulations.

Some observations on the wear of diamond tools in ultra-precision cutting of single-crystal silicon

This paper reviews the theory and evaluation of ultraprecision-machined surfaces. Carbide and single crystalline diamond tools were used to machine brittle, ductile and metal matrix composites in macro and micro scales. Data for ductile mode micromachining of brittle materials (silicon, Al2O3, SiC) and ductile materials (Cu-Be, Cu-Zn, Al-Si) were presented and compared. Models for surface finish were presented and evaluated with experimental data. The surface finish and surface integrity were characterized with scanning electron microscopy, scanning probe microscopy, and profilometry techniques. The models agreed with experimental data for ductile materials machined with a diamond tool in macro scale, but deviated from the data at micro scale because of the effect of the material microstructure. The drawbacks of the models were highlighted, i.e., they should include the crystalline orientation of the material and the effect of microstructure on surface finish.

The paper presents experimental results of microcutting brittle materials (granite). The analysis was conceived on the observed interaction between the workpiece and two tools of different shapes. Experiment was based on scratching the workpiece surface with diamond tools. Applied tools had tip radius R0.2 and R0.15 mm. The experiment determined the changes in the value of perpendicular and tangential components of the cutting force based on the geometric properties of tools, as well as the changes of the specific energy of microcutting granite (Jošanica and Bukovik types). The experiment has shown that reduction of tool radius causes reduction of the cutting force intensity and specific cutting energy. Because of its physical/mechanical properties, more energy is required for micromachining granite “Jošanica” than “Bukovik.” Based on the topography of the surface, the value of critical tool penetration depth was established, after which the brittle fracture is no longer present. For granite “Jošanica” values of critical penetration depth are 6 and 5 μm when micromachining with tools R0.2 and R0.15 mm, while for Bukovik those values are 6.5 and 5.5 μm. The paper should form the basis for understanding the phenomena which occur during microcutting brittle materials.

The main, and sometimes the only method of mechanical processing of sapphire is diamond-abrasive processing - grinding, finishing, polishing. Technological processes for the manufacture of parts from materials similar to sapphire are characterized by high labor intensity and cost. Based on the above, the development of effective shaping schemes, high-performance methods and corresponding technological equipment and, ultimately, improved technological processes with a high level of automation are in high demand. A progressive method of diamond-abrasive processing of super-hard brittle. difficult-to-machine materials, including single crystals, was developed at the Georgian Technical University - low-temperature precision grinding - LPPG refers to the methods of diamond-abrasive processing, which was implemented in a number of special, precision grinding machines and successfully tested on a number of super-hard, difficult-to-machine, brittle materials. This scientific article is devoted to the study of diamond-abrasive processing of a sapphire single crystal, taking into account the anisotropy of the material, the NPS method and the determination of optimal processing conditions (grinding modes and characteristics of the diamond tool).

Machining of hard and brittle materials such as ceramics and semiconductors has been a challenge for many years. They have many applications in optics, MEMS and electronic industries due to their many desirable properties, such as being light weight, strong, and hard. Achieving good surface finish, avoiding surface and subsurface damage and at the same time achieving a high material removal rate are extremely challenging for these materials. Materials such as single crystal silicon and sapphire have a crystal orientation or anisotropy effect which makes their machining even more difficult. Because of this characteristic, their behavior is directional and they have different fracture toughness for each direction. In past works in our research group, it has been demonstrated that machining of brittle materials in ductile regime is possible due to the high pressure phase transformation (HPPT) occurring in the material caused by the high compressive and shear stresses induced by a single point diamond tool tip. In the current study scratch tests were performed on the monocrystal sapphire in four different perpendicular directions and to further augment the process, traditional cutting is coupled with a laser to heat and soften the material to either enhance the ductility, resulting in a deeper cut, or reducing brittleness leading to decreased fracture damage. Results of scratch tests, with and without laser heating, for different cutting loads have been compared. The effect of laser heating was studied by analyzing the image of cuts and verifying the depth of cuts which were made using varying laser power during the process. Microscopic images and three-dimensional profiles of the cuts taken by using a white light interferometer were investigated.

A giant magnetostriction-type ultraprecision positioning device (GMUPD) was manufactured from newly developed giant magnetostriction materials with compositions of Tb1-xDyx(FeyMn1-y)n. The output power of them is several times and the displacement is several ten times that of PZT without a magnifier. An ultraprecision machine tool was developed with the present GMUPD. The workpiece can be fed at a rate of 0.1 mm/min or 600 mm/min and is cut by a turning diamond tool. The hard and brittle materials such as glass and ceramics were finished in the ductile mode, and surface roughness was obtained within several nanometers.