Papers by Keyword: Ductile Machining

Abstract: Brittle materials like soda lime glass can be machined in ductile mode under controlled machining conditions (feed rate, depth of cut, small tool edge radius) using high speed to generate a desired surface finish. The heat generated in high speed machining tends to promote ductile machining. In this paper, heat assisted high speed end milling is investigated to explore machinability of the soda lime glass. The heat assisted machining thus generates low surface finish on the machined workpiece. The heat assisted high speed end milling of soda lime was carried out using uncoated 2 flute carbide end mill at a constant depth of cut 25 μm, while the spindle speed and feed rate were varied from 30,000 to 50,000 rpm and 45 to 75 mm/min, respectively. The applied temperature was varied from 200 °C to 300 °C. The observations of machined surface were done on Surf-test (SV-514) and Scanning Electron microscope (SEM). A quadratic model for roughness (Ra) was developed using Central Composite Design of experiment. The optimum Ra, 0.10 μm was achieved at 49,570 rpm, 58 mm/min feed rate and heating temperature at 238°C. It is found that cutting speed has the greatest influence on the surface roughness value, followed by feed rate and heating temperature.

Abstract: For the production of mould inserts for precision glass moulding, the ultra precision grinding technique with a subsequent manual polishing operation is typically applied. These processes are time consuming and have a relatively low reproducibility. An alternative manufacturing technology, with a high predictability and efficiency, which additionally allows a higher geometrical flexibility, is the diamond turning technique. In addition the ultrasonic assisted ultra precision cutting process has already proven its potential for machining difficult-to-cut materials, such as steel and glass. By applying the ultrasonic assistance, the classic constraints of the process can be widened significantly. In this publication the process is applied on binderless, nanocrystalline tungsten carbide.

Abstract: Tungsten carbide is a crucial material for glass molding in optical industry. The present study investigated a feasibility of ductile machining of sintered tungsten carbide for glass molding by applying ultrasonic elliptical vibration cutting technology with single crystal diamond tool. Grain size and binder material of sintered tungsten carbide have an influence on hardness and/or toughness of the material. Binder material also has a chemical affinity to diamond. In order to examine the influence of material composition on ductile machining of tungsten carbide, a series of grooving and planing experiments were conducted to several different tungsten carbide workpieces with the different binder phase and the different grain size. The experimental results indicated that micro grooving in a ductile mode can be attained successfully by applying ultrasonic elliptical vibration cutting, while finished surface deteriorates with brittle fractures in ordinary cutting. It was also clarified that grain size and binder material have significant influence on the deteriorations in the surface quality, the tool shape and the cutting forces.

Abstract: Semi-fixed abrasive plate (SFAP) lapping is an effective ultra-precision lapping method. It can efficiently obtain good surface quality in ductile regime machining. Probability density function of abrasive grains cutting depth is the key factor to control removing mode. This paper verified the function by analyzing and comparing simulation results and detection results. It showed the simulation results were consistent with the detection results. The more fine grits SFAP could result in the more consistent cutting depth on workpiece surface, and standard deviation of cutting depth distribution of 4000# SFAP was only 0.0754, compared with 1000# SFAP (0.1527).

Abstract: Reaction-bonded silicon carbide (RB-SiC) is a recently developed ceramic material with many merits such as low manufacturing temperature, dense structure, high purity and low cost. In the present paper, the precision machinability of RB-SiC was studied by microindentation and single-point diamond turning (SPDT) tests. The influence of depth of cut and tool feed rate on surface roughness and cutting force was investigated. Results showed that there was no clear ductile-brittle transition in machining behavior. The material removal mechanism involves falling of the SiC grains and intergranular microfractures of the bonding silicon, which prevents from large-scale cleavage fractures. The minimum surface roughness depends on the initial material microstructure in terms of sizes of the SiC grains and micro pores. This work preliminarily indicates that SPDT can be used as a high-efficiency machining process for RB-SiC.

Abstract: This paper deals with the mechanism of surface heterogeneity due to crystallographic anisotropy effects in diamond turning of single-crystalline germanium. A microplasticity-based numerical simulation model was proposed, in which the effects of tool geometry and machining conditions can be involved. Two coefficients were introduced to compensate the Schmid factors of two different types of symmetrical slip systems. Simulation of ductile machinability was conducted on two crystallographic planes (100) and (111), and the simulation results were consistent with the experimental results. It was indicated that the simulation model can be used to predict the brittle-ductile boundary change with machining conditions and crystal orientations of germanium.