Читать книгу Plastics Process Analysis, Instrumentation, and Control - Группа авторов - Страница 17

A weld line is one of the most commonly seen defects in an injection molding process. It is the line where two polymer melt fronts weld together, or a melt front splits and comes back and welds together during the filling stage (6).

A weld line greatly affects the appearance and mechanical properties of final injection molded parts (7).

The surface of the weld line may contain small V-notch cracks, and these crack-like features are often visible to the naked eye and therefore they are considered aesthetically unacceptable in many applications, especially when using high-gloss polymers. More importantly, the polymers at the weld line do not bond perfectly, and this can cause a weak area in a molded part which can cause breakage when the part is under stress (8).

So, a weld line is aesthetically unpleasant and affects the mechanical strength of injection molded parts (9). Various studies have been performed related to the optimization of weld lines.

A weld line computer determination method based on filling simulation with surface model has been proposed, from which the positions and lengths of the weld lines can be predicted.

According to the characteristics of the surface model, all weld lines can be classified into two different types. Initial welding node searching and revision algorithms for the two different types of weld lines were developed. Starting from initial welding nodes, weld lines are then extended by a pre-extension algorithm and an extension algorithm.

Table 1.2 Recent review articles and their targeted scope (3).

Year	Scope	Reference
2006	Generic hierarchical cost estimation classification	(4)
2009	Web-based system for rapid prototyping and traditional manufacturing. Briefly highlighted the cost models utilization	(10)
2014	Categorized additive manufacturing costs by their processes and materials, which were subdivided into ill-structured costs, well-structured costs and product enhancements and quality	(11)
2016	In-depth discussion of cost methodology used in product development process. No classification technique proposed.	(12)
2016	Covered industrial sector related to the materials and management. Briefly reviewed additive manufacturing costing models	(13)
2016	Provided updated estimate of the value related to the supply chain	(14)
2016	Described cost models as a subset of design for additive manufacturing	(15)
2017	Focused on defense support services and categorized the cost models into intuitive, analogical and analytical approaches	(16)
2017	Focused on operation management where the strengths and weaknesses of the models were discussed. Included a general review of additive manufacturing	(17)
2019	Provided a broader review on additive manufacturing technologies, additive manufacturing cost models, spare part digitalization and environmental effects for the aviation industry	(18)

In the weld line extension algorithm, 135° is set as a welding angle threshold for forming weld lines. Finally, the effects of cavity thickness, process parameters, and mesh densities have been investigated. Moreover, moldflow simulation results and real parts in production have been conducted to verify the proposed determination method, which demonstrate that the proposed method is correct and effective in actual production (9).