Shape Of Workpiece Surface Research Articles

Effect of pad surface morphology on the surface shape of the lapped workpiece

Double-sided lapping is currently the mainstream manufacturing method for obtaining plane-parallel optical workpieces with high surface shape accuracy, and the fixed abrasive lapping pad is the main machining tool. However, the effect of pad surface morphology on the workpiece surface shape has rarely been studied, and its formation mechanism has not yet been revealed. In this paper, based on probabilistic statistics and contact mechanics, an analytical model that takes into account the pad surface morphology for predicting the workpiece surface shape evolution is developed. Notably, this model considers the cross-scale relationship between the formation of lapped surface shape and the scratching process of a single abrasive grain in material removal for the first time. Furthermore, the real-time dynamical contact relationship between the workpieces and the measured actual pad surface morphology is also considered. The surface shape and peak-to-valley value of the workpiece under different parameters were simulated and analyzed, and the influence mechanism of the local profile and macro shape of the lapping pad on the lapped workpiece surface shape are clarified. Moreover, the double-sided lapping trial experiments were performed to validate the theoretical model, and the experimental results demonstrated good agreement with the simulation results. The maximum error of the surface shape evolution prediction model is less than 14.6 %. This result verifies the correctness and validity of the established model. This work not only provides new ideas for controlling the workpiece surface but also forms the theoretical basis for understanding the double-sided lapping process.

Investigation on Tool Wear Mechanism during dry cutting 304 Stainless Steel

With the determined parameters of cutting speed, feed rate and back cutting depth, cemented carbide tool was adopted to dry cut 304 stainless steel, exploring the tool wear failure mechanism and its effect on the surface quality of the workpiece under different cutting times. The morphology of the tool surface is observed by scanning electron microscopy, and the component of the tool is analyzed by energy dispersive spectroscopy. The three-dimensional microscopic shape of workpiece surface is observed by a three-dimensional shape analyzer and the surface rough-ness Ra was measured. The results indicate that during the process of 6-minute cutting, the abrasive wear and adhe-sion wear are occurred on the tool, the surface quality of the machined workpiece is good; during the process of 12-minute cutting, oxidation wear is appeared while the tool subjects abrasive wear and adhesion wear, and the surface quality of the machined workpiece become pool; during the process of 18-minute cutting, the tool is under the com-bined action of various wear mechanism. Because of the passivation of tool nose, the surface quality of the work-piece is deteriorated, and it can’t meet the requirements of finish machining. In the process of dry cutting workpiec-es by cemented carbide tool, the tool suffers abrasive wear, adhesion wear and oxidation wear. The surface quality of the workpiece is declined due to the passivation of the tool nose.

Study on etching process of fused silica with concentrated HF

Optical elements will go through grinding, lapping and polishing to reach the final accuracy, and large amount of time is consumed between grinding and polishing in order to remove cracks and defects left by grinding. This manuscript tries to employ HF etching process into the manufacturing of fused silica optical elements to improve the efficiency and quality, so the concentrated HF etching process of fused silica was studied systematically. Firstly, the principle of HF etching fused silica is introduced. Then, the process of concentrated HF is studied, which shows that the etching rate of concentrated HF is as high as 1.14 μm/min and the surface shape of workpiece can be basically kept unchanged after etching. Finally, the observation results of fused silica samples processed by concentrated HF show that the concentrated HF processing can eliminate the cracks on the surface left by grinding and improve the roughness of the surface. So the concentrated HF etching can be used to process the fused silica sample after grinding, it will eliminate cracks and defects quickly, improve the surface quality of the component, and promote the subsequent polishing process.

In-process monitoring of shape accuracy of flat surfaces of optical and microelectronic components in polishing

The in-process monitoring of surface shape of optical surfaces directly in the course of polishing is demonstrated to be accomplished through the confocal chromatic imaging technology. A linear relationship has been found between the deviation from square waveform and the variation of the workpiece surface shape.

Influence of the Cutting Tool Compliance on the Workpiece Surface Shape in Face Milling of Workpiece Compounds

A currently common method to design high-performance workpieces is to combine two or more materials to one compound. In this way, workpieces can be composed of the most qualified materials according to local loads. When machining high-performance workpiece compounds high quality requirements concerning the accuracy of dimension and shape as well as surface roughness must be fulfilled. However, in case of parallel machining, where the cutting edge moves from one material into the other within one cutting tool revolution, unequal cutting properties have a significant negative influence on tool wear and surface quality. Shape deviations of the surface occur, which are not detected when machining the single materials. The four most significant shape deviations that affect the workpiece quality are the material height deviation, transition deviation at the material joint as well as surface roughness deviation. This paper contains new approaches on the prediction of the surface shape that is generated by a face milling process. The focus is on the transition deviation at the material joint. It arises from a force impulse that is applied on the cutting tool and creates a wavy surface on the workpiece. This shape is predicted via cutting force prediction as well as frequency response analysis of the cutting tool and workpiece in relation to different tool holders. Furthermore, deviations between calculated surface shapes and measured surface shapes subsequent to machining tests are evaluated.

Convergent Pad Polishing of Amorphous Silica

A new method of optical polishing termed “Convergent Polishing” is demonstrated where a workpiece, regardless of its initial surface figure, will converge to the lap shape in a single iteration. This method of polishing is accomplished by identifying the phenomena that contribute to non‐uniform spatial material removal, and mitigating the non‐uniformity for each phenomenon (except for the workpiece‐lap mismatch due to the workpiece surface shape). The surface mismatch at the interface between the workpiece and lap causes a spatial and time varying pressure differential which decreases with removal, thus allowing the workpiece to converge to the shape of the lap. In this study, fused (amorphous) silica workpieces are polished using ceria slurry on various polyurethane pads. Polishing parameters were systematically controlled to prevent various sources of non‐uniform material removal which include: (i) moment force, (ii) viscoelastic lap relaxation, (iii) kinematics, (iv) pad wear, and (v) workpiece bending. The last two are described herein. With these mitigations, removal uniformity has been demonstrated to within 1.0 μm over the surface after 83 μm of material removal corresponding to a within workpiece non‐uniformity (WIWNU) of <1.2%. Also, convergence has been demonstrated down to 0.18 ± 0.04 μm peak‐to‐valley flatness on 100 mm‐sized workpieces.