Projection lines

In third angle projection, the various views are projected from each other. Each view is of the same size and scale as the neighbouring views from which it is projected. Projection lines are shown in Figure 2.14. Here only three of the Figure 2.12 views are shown. Horizontal projection lines align the front view and the left-side view of the block. Vertical projection lines align the front view and the plan view. The plan view and the left-side view must also be in orthographic third-angle projection alignment but they are not projected directly from one another. A deflector line is placed at 45 ~ This line allows the horizontal projection lines from the plan view to be rotated through 90 ~ to produce vertical projection lines that align with the left-side view. These horizontal and vertical projection lines are very convenient for aligning the various views and making sure that they are in correct alignment. However, once the views are completed in their correct alignment, the projection lines are not needed because they tend to complicate the drawing with respect to the main purpose, which is to manufacture the artefact. It is normal industrial practice to erase any projection lines such that the views stand out on their own. Often in engineering drawing lessons in a school, the teacher may insist projection lines be left on an orthographic drawing. This is done because the teacher is concerned about making sure the academic niceties of view alignment are completed correctly. Such projection lines are an unnecessary complication for a manufacturer and therefore, since the emphasis here is on drawing for manufacture, projection lines will not be included from here on in this book. 

Engineering Drawing for Manufacture
by Brian Griffiths
Publisher: Elsevier Science & Technology Books

Thermoforming

Thermoforming is a set of processes for forming a thermoplastic sheet or film around the mold by applying heat and pressure. In this process, the sheet is heated in the oven until softened but not to the melting point. Sheet is then removed from the oven, spread out around the mold and then the sheet is sucked by the vacuum process. Because the mold at room temperature, then the formation of the plastic mold will be in accordance with smoked During sheet in contact with mould. That the types of products generated with this process are Billboards, packaging, household applications. Product-open or hollow products can not be formed Because the pressure can not be maintained During the formation. Since thermoforming is the process of withdrawal and toning, as well as sheet metal forming, the material must have a high uniformity of strain, if not Will there be a failure. -Mould for thermoforming molds are usually made ​​from aluminum Because of the high fracture strength is not required. Tooling is not too expensive and quality considerations, including wear, unequal thickness is not too significant. (bid / multiple sources)

First angle projection

The other standard orthographic projection method is first angle projection. The only difference between first angle and third angle projection is the position of the views. First angle projection is the opposite to third angle projection. The view, which is seen from the side of an object, is placed on the opposite side of that object as if one is looking through it. Figure 2.13 shows the first angle projection layout of the bracket shown in Figure 2.12. The labelling of the views (e.g. front view, plan, etc.) is identical in Figures 2.12 and 2.13. Note that in first angle projection, the right-side view is not placed on the right-hand side of the front view as in third angle projection but rather on the left-hand side of the front view as shown in Figure 2.13. Similarly, the left-side view appears on the right-hand side of the front view. The other views are similarly placed. A comparison between Figures 2.12 and 2.13 shows that the views are identical but the positions and hence relationships are different. Another first angle projection drawing is seen in the title box in Figure 2.13. This is the truncated cone. It is the standard ISO symbol for first angle projection (ISO 128:1982). It is this symbol which is placed on drawings in preference to the phrase 'first angle projection'. First angle projection is becoming the least preferred of the two types of projection. Therefore, during the remainder of this book, third angle projection conventions will be followed. 

Engineering Drawing for Manufacture
by Brian Griffiths
Publisher: Elsevier Science & Technology Books

Rotational molding

Most thermoplastics and thermosets can be formed into products with a large cavity with Rotational molding process. Mould with thin metal walls are made in two pieces and is designed to rotate in two mutually perpendicular axes. Plastic powder that has been measured previously placed in a warm mold. Mould then heated in an oven usually large, while the mold is rotated in two axes. This process makes the powder pressed into a mold where the mold surface will heat the powder without melt. The types of products made with this process are tanks with a variety of sizes, trash, baket, housing, ball. The liquid polymer called plastisol (usually used vinyl plastisol) can also be used in slush molding process. Mold simultaneously heated and rotated. After contact with the wall of the mold material to melt and mold wall wrap. Products to be cold when it was still spinning and removed by opening the mold.