热加工作业考研题目答案分享——Joining processes 2

Assignment 2

版权声明

本内容由狂小虎原创整合，请不要售卖，为了防止爬虫以及保持免费性，设置为仅粉丝可见。另外，题目以及解释可能不完全正确，仅供参考，同时也欢迎各位在讨论区指点出内容的错误之处。

文章目录

9. What is meant by weld quality? Discuss the factors that influence it.

  1. Weld quality is used to describe the quality of weld joint. It means the properties and characteristics of the weld joint can satisfactorily meet service requirements or not. Because of the thermal cycling during welding, there must be some metallurgical and physical changes in the materials, and sometimes discontinuities will present in the joint. Weld quality means the quality of welding process, including the microstructure and grain size of the welded joint, the geometry of the weld bead, defects in joint, temperature and its distribution, heating, duration at high temperature, cooling and so on.
  2. There are many factors can influence weld quality:
    • Porosity
    • Slag inclusions
    • Incomplete fusion and penetration
    • Weld profile
    • Cracks
    • Lamellar tears
    • Surface damage
    • Residual stresses
    • Stress relieving of welds
    Inadequate or careless application of established welding technologies or substandard operator training may cause welding quality problems.

14. Explain the reasons that so many different welding processes have been developed over the years.

Because the science and technology are developing, which inspire engineers to invent new processes to meet every increasing requirement for better quality, high efficiency, low cost, special operation environment, or new materials and structure etc.
It is clear that proper and practical methods are supposed to applied in specific situation. For example, shielded metal arc and oxyfuel arc are utilized because of economic concern.
Also, there are quantities of factors that influence how we design the welding processes, for example, the application, the joint design, the materials involved, the shapes of the components to be joined, workpiece’s thicknesses, and their sizes, the location of the joint within the product, component numbers, the operator skill required, costs and so on.
As a result of it, a considerable amount of welding processes has been developed over the years.

20. What are the advantages of electron-beam and laser-beam welding compared with arc welding?

The beams can be focused onto a very small area which has higher energy density and more penetration ability than the arcs. Both of the high energy beams can make high qualified weld joint with deep narrow weld bead, small heat affected zone, minimum distortion and shrinkage. Another advantage is that EBW or LBW can be operated at higher welding speed, hence they have higher welding efficiency.
• The welding speed and efficiency is higher.
• These beam welding processes are even considered more suitable for alloys that are difficult to arc weld and can provide better overall weld properties compared to arc welding. The low welding heat input results in a shorter time spent in the solidification temperature range and relatively fast cooling rates, which suppresses precipitation of secondary phases during weld solidification.
• Lasers can interact with any material. It doesn’t require a vacuum and it does not produce x-rays.
• No Contamination of the tungsten electrode by the molten metal, particularly in critical applications, because it can cause discontinuities in the weld compared with GTAW.

23. Comment on the factors that influence the size of the two weld beads shown in Fig. 10.14.

For LBW and EBW:
(i) The power of beam
(ii) The square area of beam focused on the area
(iii) The density of energy
(iv) The deep-penetrating capability
(v) The shape of beam
(vi) Depth-to-width ratios of welding deep and narrow joints
For GTAW:
(i) Welding amperage
(ii) Welding voltage
(iii) Welding speed
(iv) Electrode size
(v) Electrode work angle
(vi) Electrode stick-out
(vii) Depth of flux
(viii) Polarity
(ix) Melting rate
(x) Flux basicity index

24. Which of the processes described in this chapter are not portable? Can they be made so? Explain.

Portable: OFW, SMAW. Maybe portable: GMAW, FCAW, GTAW and PAW. When carry the equipment by a cart.
Not portable: SAW, EGW, ESW, EBW and LBW are not portable. The equipment of these processes is big and heavy. The operation is complex.
OFW(oxyfuel-gas welding 氧乙炔焊), SMAW(shield metal-arc welding 熔化极电弧焊), GMAW(gas metal-arc welding 气体保护焊), FCAW(flux-cored arc welding 药芯焊丝弧焊), GTAW(gas tungsten-arc welding 钨极保护焊), PAW(plasma-arc 离子焊), SAW(submerged-arc welding 埋弧焊), EGW(electrogas welding 气电焊), ESW(electroslag welding 电渣焊), EBW(electron-beam welding 电子束焊), LBW(laser-beam welding 激光焊)
Actually, partly of them can be produced much smaller, but that is not cost-effective and time for welding would be limited because of insufficient flux, electrode, filler metal or power. Moreover, welding processes like electron beam or laser beam can not be made portable, because the equipment is complex and they have to work in stable environment.

25. Describe your observations concerning the contents of Table 10.1.

Table 10.1 lists the general characteristics of main fusion welding processes. We can simply see the operation, advantage, skill level required, welding position, current type, distortion, cost of equipment of each process from the table. Comparisons between fusion welding processes can also be drawn from the list. For example, SMAW and OFW are manual, portable and flexible, but the others can be automatic. The SAW can only be used in flat and horizontal position. The welding joint made by EBW or LBW has the lowest distortion, but needs expensive equipment.

Firstly, I will see what kinds of materials will be used to manufacture products and then search the joining process that can handle that.
Secondly, I will ask myself how absolute engineering precision of the workpiece is needed by considering the distortion of the joining process.
Thirdly, I will consider how much the welding process would cost by the skill level it required, typical cost of equipment and so on.
Fourthly, I will focus on if welding position is acceptable and the equipment is portable.
Fifthly, I will choose the welding process by whether or not they can be applied in automation.

posted @ 2020-08-21 12:47  狂小虎  阅读(103)  评论(0)  编辑  收藏  举报