Sebelum suatu fabrikasi di mulai, tahap mendesign weldment merupakan tahapan yang penting. Dari design weldment diharapkan akan dapat menghasilkan design joint yang optimal baik dari segi kekuatan, produksi, cost , dan safety.
Tulisan di bawah ini merupakan bagian dari prinsip utama dalam mendesign suatu weldment
Welding Design –
Before an arc can be struck on metal, the product must be designed to serve its purpose, the material chosen and the method of welding determined in more or less detail. The weldment design engineer must
(i) Know the limitations and specific requirements of the processes as well as the equipment available on the shop floor.
(ii) Have a good working knowledge of the shop problems of shrinkage and distortion.
(iii) Have accurate knowledge not only of suitability but also of availability of materials or the costs of extras.
(iv) Be able to calculate stresses, strengths and determine weld sizes and put these together to work out a design that meets all service requirements.
(v) Be able to make his design
Principle of Welding Design –
1. Approach the redesign of previously cast, forged or riveted products as a new design, on the basis of the functions to be performed.
2. Use materials, where possible, which require the least in welding precautions and least skill.
3. Welding is a means to an end, but to the designer not an end in itself. Avoid extra and unnecessary joints by flanging, bending or rolling, and use of standard sections, stampings, small castings or forgings, wher ever necessary or advisable.
4. At least mentally review all the welding processes available and applicable to various parts of the design on the basis of material, thickness, form and quantity.
5. Estimate the stress pattern under load with respect to stress concentration and examine the design for the possibility of notches. Notches give rise to stress concentration.
6. Welds should always be placed in regions of lower stress.
7. Secondary members should not be loaded up as main members.
8. Welding more than necessary should not be specified.
9. Welding should not be done where it offers no benefits.
10. Design should not demand a consistency in welder’s performance as it is difficult to maintain.
11. Design should specify critical weld location.
12. Design should not generate unnecessary problems in the production department.
The weld designers must consider the practicalities production.
Welding Joint Design – Since, welding joins metals, design for welding is chiefly concerned with joints when to use a joint, how to weld it, where to place it, what to do and what not to do. Selection and preparation of weld joints is an important step in the fabrication of a weldment.
Selection of correct joint design is very essential if welded members are to perform within the load service, corrosive * atmosphere and safety requirements.
Not only must the product have sufficient strength to perform well under the load conditions expected but it must be pleasing in appearance also. Proper joint design is a vital part of a welding procedure because it helps to
(i) Control distortion.
(ii) Minimize residual stresses,
(iii) Facilitate good workmanship,
(iv)Achieve proper weld strength,
(v) Reduce welding costs, and
(vi) Result in greater reliability.
The weld joint design should be such that the welds can be tested nondestructively for necessary quality control, especially if the welds are in pressurized or contaminated and inaccessible areas.
The considerations in joint design include
(iii) quality, and
(iv)cost or economy.