تحقیق تاثیر جریان جوشکاری بر خصوصیات مکانیکی اتصالات فولادی نرم زمان استفاده از جوش قوس الکتریکی

An Investigation of the Effect of Welding Current on the Mechanical Properties of Mild Steel Joints When Using Arc Welding

چکیده
جوشکاری نوعی فرایند ساخت است که در آن دو یا چند قطعه با استفاده از گرما یا حرارت، فشار یا هر دوی آن¬ها بهم ذوب شده و پس از سرد شدن قطعات به یکدیگر متصل می شوند. این مقاله در نظر دارد تا اثرات جریان را هنگام استفاده از جوشکاری قوسی، بر خواص مکانیکی و ریز ساختارهای اتصالات فولاد نرم بررسی کند. آزمایش جوشکاری قوسی در جریان¬های مختلفی(100 A, 150 A and 200 A) انجام شد. آزمایش¬های سختی و ضربه مطابق با استانداردهای ASTM E384 و ASTM E23-12C پیش برده شدند. نتایج نشان دادند که در طول فرایند جوشکاری قوسی، جریان بالای جوشکاری سبب ایجاد دمای سطحی بالایی می شود. افزایش در دمای سطحی بر خواص مکانیکی ناحیه جوشکاری اثر منفی دارد. بیشترین سختی و سفتی در جریان کم جوشکاری حاصل شده و مقادیر آن به ترتیب 269HV و 205.71J گزارش شد.

II. مواد
در این مطالعه از نمونه صفحات فولاد نرم S355JR با ضخامتی برابر 10 میلی متر، به عنوان فلز مرجع استفاده شد. از یک سیم جوشکاری 0.9 میلی متری (ER70S-6) به همراه گاز خاکی به عنوان ماده اتصال دهنده طی فرایند جوشکاری قوسی MIG، در جریان های مختلف استفاده شد.

III. روش
A. آزمایش جوشکاری قوسی
از دستگاه برش نواری Beka Mak BMSY 320 به همراه خنک کننده امولسیفایر، برای برش شش نمونه مشخصه به صورت مستطیلی، در ابعاد 30×30×10 میلی متر استفاده شد. همانطور که در شکل 1(a) نشان داده شده است، هر نمونه آزمایش با استفاده از یک سنگ فرز با توان 900 وات، بر روی یک سطح شیبدار با زاویه 20 درجه بریده شد. صفحات بریده شده قبل از جوش دادن به یکدیگر، با استفاده از یک برس سیمی چرخان تمیز می شوند. یک دستگاه جوشکاری PRO-MIG 350 که در شکل 1 نشان داده شده است به منظور ایجاد جوش لب به لب بین نمونه¬ها در جریان های 100 ، 150 و 200 آمپر همانطور که در شکل 2 (b) نشان داده شده است، استفاده شد. به منظور ایجاد اتصال از سیم ER70S-6 (0.9 میلی متر) در سرعت 360 میلی متر در دقیقه و گاز خاکی که دارای ترکیب، 90 درصد آرگون، 5 درصد اکسیژن و 5 درصد دی اکسید کربن است، به عنوان گاز محافظ نیز استفاده شد. سرباره(slug) ایجاد شده از نمونه¬های جوش داده شده جدا شد و اجازه داده شد تا نمونه ها به طور طبیعی خنک شوند.

روش های نوآورانه برای پردازش بهینه از سرباره های متالورژیکی

Innovative approaches for an optimized processing of metallurgical slags

Abstract

Metallurgical slags are produced in large quantities all around the world as a result of smelting, refining or  alloying  processes  applied  to  metals,  ores  and  recycling  material.  The  slag  phase  serves  different purposes  in  metallurgical  processes.  It  prevents  heat  losses  and  protects  the  metal  phases  from contaminations and absorbs gangue and extracted impurities. Due to achievable metallurgical efficiencies certain  amounts  of  valuable  metal  contents  always  remain  in  the  residual  slag.  Recycling  of  these metallurgical  slags has  several positive effects, such  as  optimized ecological  and economical compliance of the producing industry. If recycled metal contents can be reintroduced into existing processes, required inputs of raw material can be lowered. High metal prices enable the economic recovery of metal contents in  metallurgical  slags  by  applying  different  non­metallurgical  processing  methods.  Conventional processing  of  metallurgical  slags  utilizes  processes  such  as  hand  picking,  selective  comminution, screening and magnetic separation. Those state of the art processing techniques have limitations in terms of achievable metal recoveries and required energy demand. The approach for an optimized processing of metallurgical slags targets enhanced metal recoveries in combination with lower specific treatment costs. Processes  such  as  coarse  and  ultrafine  density  separation,  as  well  as  sensor­based  sorting  as  a  preconcentration stage are used to enable an efficient recovery of metal contents in slags. By applying these methods a completely dry working process is possible. This paper reviews the commonly used methods and  describes  approaches  for innovative  processing  of  metallurgical  slags  to  enhance metal  recoveries. Focus of this paper is laid on sensor­based sorting as well as on processes for dry density separation.

1 Introduction

In a situation of steadily increasing demand for raw materials, the issue of how to use our resources most efficiently is a contentious economic and environmental political issue today. A combination of sustainable exploitation and use of primary resources in combination with an optimized handling and processing of secondary resources, such as metallurgical slags is the key for a better handling of existing resources.

Metallurgical slags are by­products from metal extraction, refining and alloying processes and are produced in significant amounts. The slag phase is used to encapsulate impurities and additives added during casting and alloying processes for further purification of metals. Besides impurities, slags usually contain significant amounts of metal contents (Van Oss, 2002). A suitable recycling and reintroduction of such metal contents and non­metallic slag residues is highly desirable but, yet, not always applied. Besides recycling of metallurgical slags in existing processes, the recycling of old dump sites is important. If not properly recycled and reintroduced into the raw materials cycle as new products, an important resource is lost. Numerous technologies exist which differ in terms of costs and efficiency. Applied state of the art technologies for recovering metal contents from slags include, for example, selective comminution, wet and dry density separation, magnetic separation, dense media separation or combinations of the proposed techniques. However, metal recoveries, especially for fine, intergrown metal contents as well as energy and resource efficiencies are low for many applied processes. In many cases, the fine fraction is not even treated and discarded as waste material (Wotruba, Weitkaemper, 2013).

This paper reviews current application fields for metallurgical slags. Applied technologies for recycling and recovering of metal contents and non­metallic compounds, with emphasis on mechanical processing technologies are described, and new approaches for a more economical, environmentally and therefore sustainable treatment with focus on stainless steel slags on a dry basis are introduced.

مدلسازی نیروها و ارتعاشات برشی استاتیک و دینامیک برای ابزارهای سرامیکی فرزکاری کارگذاری شده

Modeling Static and Dynamic Cutting Forces and Vibrations for Inserted Ceramic Milling Tools

Abstract

Cutting tools with ceramic inserts are increasingly being used in machining of super alloys typically used in aerospace industry. The ceramic inserts make higher cutting speeds possible due to the higher temperature resistance compared to carbide inserts. However, the success of the process is very sensitive to the right selection of process parameters. In this study, analytical process models for indexable milling tools with round ceramic inserts are presented. These models can be used to determine the cutting parameters for optimum quality and maximum productivity. Firstly, geometry of the insert cutting edges under the effect of angles on the inserts was formulated. Then, an analytical cutting force model was developed. This allows analyzing the effects of the parameters on the cutting forces. A time-domain model was also developed to analyze the dynamic cutting forces and stability limits for the milling process. Afterwards, the models were implemented in a Matlab® GUI to make the applications of the models in the industry easy. Cutting force coefficients, which are needed to calculate cutting forces, were identified from cutting tests with Inconel 718 material. Then, the cutting force model was validated with cutting experiments. After obtaining modal data of the tool via tap testing, dynamic cutting forces and vibrations were simulated by means of the time domain model. A series of simulations was carried out to determine stability limits at certain operating conditions using the time domain model, and stability lobes for the tools under study were plotted.

1 Introduction

Round ceramic inserts represent economic advantages over other type of inserts since higher material removal rate (MRR) is possible owing their high heat resistance and gradual entry to the cut. Analytical process models, that allow reliable predictions of cutting forces and machine-tool vibrations, facilitate the optimum process parameter selection, which is a challenge before making cutting tests. Main concerns are to control the cutting forces and to avoid chatter vibrations, as high and fluctuating cutting force magnitudes generally indicate chatter. This is the major limiting factor for increasing MRR, as it may cause severe machining problems [1]. Besides, power consumption and tool life are dependent on cutting force magnitudes.

Several researchers have been working in analytical, numerical and experimental models for predicting cutting forces and vibrations. In the past, the research was focused on modeling the mechanics and dynamics of standard end and face milling cutters with different geometries, such as cylindrical, ball-end and tapered. Indexable tools appeared in the mid-20th century. Fu et al. [2] presented pioneering work in the study of inserted face milling cutters. Engin and Altintas [3] developed a generalized mathematical model for inserted cutters, but it was experimentally validated for rectangular shapes. Recently, Altintas et al. [4] presented a unified cutting force model for inserted cutters that can be applied for different types of machining operations, but it is experimentally verified for straight line cutting edges too. Kim et al. [5] and Liu et al. [6] considered round cutting edges in the cutting force calculations which were experimentally verified, but the dynamic part of the forces was not taken into account.

In the next section, geometry of the cutting edge on the insert is described. In section 3, the cutting force model is detailed. The time-domain model is explained in section 4. In section 5, the verification of the static and dynamic forces with experimental data is exposed. Finally, stability analysis and conclusion are presented in section 6 and 7 respectively.

تکنیک های کامپوزیت برای تحلیل کیفیت در جوشکاری لیزر خودرو

Composite Techniques for Quality Analysis in Automotive Laser Welding

Abstract

Real-time monitoring of the laser-based applications is becoming a main issue for quality analysis in the steel manufacturing industry. The paper suggests a solution achieving an automated real-time quality inspection in laser welding applications. A composite system composed of soft computing and traditional techniques has been considered for its positive impact on the reduced computation compared with more traditional approaches.

1 Introduction

Early detection of defects in metal manufacturing industries is becoming a main economical issue for its impact on quality analysis of the artifact and the industrial process.

Automated laser welding is having an increasing growth and diffusion due to the powerful and versatile process that allows for joining metals or non-metals at high speed with a relatively low heat input [l]. Lasers can produce welds in air, vacuum, controlled atmospheres, and pressurized chambers with a high reliable and automated process. Moreover, laser light may be focused to very small areas [2].

In general, the quality analysis of the process is assessed by offline inspection of each welded component. Such inspection phase is a time-consuming activity that rarely provides useful feedback to the expert user on how to improve the process itself (e.g., by tuning some parameters). In addition, external inspection of the welded artifact requires a costly procedure, most of times carried out with ultrasonic devices [3]. A different approach envisage an on-line quality analysis implemented directly during the process. A set of information is extracted from the sensors observing some critical parametedphenomena associated with the process [4]. Following this philosophy we address the laser welding quality analysis with a selftuning classification system that detects defects directly during the welding process. Moreover, the suggested procedure enables the process engineer to assess the quality of the process and study it aging effects for a subsequent process tuning. The quality analysis system is a composite system, namely a synergic composition of traditional algorithms for signal processing and sot?- computing techniques [5]. During development of the solution we addressed not solely the performance issue (in tenns of detected defects) but also the required computational burden in order to satisfy real-time requirements.

In particular, the industrial process under monitoring refers to the laser welding of automotive components carried out at the CW-FIAT laboratories [17]. The specific test bed is a steel gear, a critical part in the gearbox for a passenger vehicle (see Figure I).

Seven types of gear, built joining two rings (i.e., a light syncro gear and the principal gear), are actually butt welded using a CO2 laser. The test-bed is part of the Intelligent Manufactory Systems project SLAPS (Selftuning and User-independent Laser Material Processing Units) [ 161 a European Union effort to advance the applied research on the development of intelligent laser processing unit [15].

The structure of the paper is as follows. Section 2 introduces a general background on laser welding and a description of the typical defects. Section 3 presents the features extracted from our industrial set-up and in section 4 is described the overall composite algorithm describing also the classifier selection, the tuning methodology and the experimental results.