Research on Template-Based Parameterized Structure Design for Drawing Dies
The structure design of drawing dies is a very compLicated and knowledge-intensive process. This paper describes a template-based parametric design system for drawing dies which adopt template as the die design knowledge base and instantiate it to complete the design of the main components of drawing die. Some key technologies such as the template technology, the parameterization technology and the top-down assembly design technique have been studied. The template for drawing dies is defined by using the "top skeleton" assembly structure, and the associative geometry-driven design and parameter-driven design of dies structure is reaLized by adopting WAVE technique and parameterized design method. The design process of template-based drawing dies structure is estabLished and the rapid design of structure is implemented by applying UG secondary development. At last, effectiveness of our method is verified by some examples.
An Automated Progressive Process Planning and Die Design and Working System for Blanking or Piercing and Bending of a Sheet Metal Product
This paper describes the development of a computer-aided design and manufacturing system for irregular-shaped sheet metal products for blanking or piercing and bending operations. The approach is based on knowledge-based rules. Knowledge for the system is formulated from plasticity theories, experimental results and the empirical knowledge of field experts. This program for the system has been written in AutoLISP using AutoCAD and on SmartCAM using a personal computer and is composed of nine modules, which are input as shape treatment, flat pattern-layout, production feasibility check, blank-layout, strip-layout, die-layout, data-conversion, modelling, and post-processor modules. Based on knowledge-based rules, the system is designed by considering several factors, such as material and thickness of product, complexities of blank geometry and punch profile, diameter and material of a wire, and the availability of a press. This system is capable of unfolding formed sheet metal to give a flat pattern and automatically accounts for the adjustment of bending allowances to match tooling requirements by checking dimen-sions and generating NC data automatically according to the drawings of the die-layout module. Results obtained using the modules enable the designer and manufacturer of blanking or piercing and bending dies to be more efficient in this field.
Analysis of the stress wave effect during coal breakage by a high-pressure abrasive air jet
In view of the defects of borehole collapse, inhibition of gas desorption and migration of gas existing in hydraulic fracturing and other hydraulic permeability–increasing measures for soft coal seams with low-permeability technology is proposed for coal breakage by a high-pressure abrasive gas jet for relieving pressure and increasing permeability. The comparative analysis of gas jet flow field structure between convergent nozzle and Laval nozzle has been given by numerical simulation. For Laval nozzle, the expansion wave and compression wave alternate and move forward steadily in gas jet and vanish when potential core length reaches maximum. So, the Laval nozzle can form more stable flow filed structure of gas jet and avoid shock wave in gas jet. Furthermore, a high-speed camera is adopted to analyze the jet structure and verify the conclusion of numerical simulation. Based on thermodynamic theory, this article calculates and analyzes the critical local sound velocity and pressure generated from the stress wave during the process of coal breakage by the gas jet. Furthermore, experimental coal breakage by a high-pressure abrasive gas jet is carried out. The high-pressure abrasive gas jet impacts the coal body as a quasi-static load and a dynamic load and forms corrosion pits on the surface of the coal body. Penetrating cracks are formed within the coal in the pattern of the loaded stress wave which leads to coal breakage. The effects of porosity and permeability on the propagation of the stress wave in coal are analyzed by establishing the dispersion equation for the spread of the stress wave in coal. The results show that porosity has a significant effect on wave velocity and that the attenuation of the stress wave is intensified with an increase in porosity. Moreover, the stress wave attenuation is more obvious at high frequency. The effect of permeability on the wave velocity is not significant at low frequencies. In contrast, at high frequency and relatively low permeability, the wave velocity increases with the permeability, and the attenuation of the wave velocity initially increases and then decreases. When the permeability is greater than 10−11 m2, the wave velocity is not affected by the permeability. However, the stress wave is not attenuated.