Ribs and Gussets

When designing ribs and gussets, it is important to follow the proportional thickness guidelines shown in Figures 29 and 30. If the rib or gusset is too thick in relationship to the part wall, sinks, voids, warpage, weld lines (all resulting in high amounts of molded-in stress), longer cycle times can be expected. The location of ribs and gussets also can affect mold design for the part. Keep gate location in mind when designing ribs or gussets. For more information on gate location, see page 66. Ribs well-positioned in the line of flow, as well as gussets, can improve part filling by acting as internal runners. Poorly placed or ill-designed ribs and gussets can cause poor filling of the mold and can result in burn marks on the finished part. These problems generally occur in isolated ribs or gussets where entrapment of air becomes a venting problem. Note: It is further recommended that the rib thickness at the intersection of the nominal wall not exceed one-half of the nominal wall in HIGHLY COSMETIC areas. For example, in Figure 29, the dimension of the rib at the intersection of the nominal wall should not exceed one-half of the nominal wall. Experience shows that violation of this rule significantly increases the risk of rib read-through (localized gloss gradient difference). 

Product and Mold Design

SMAW Welding

Welding is the process of switching between two or more metals by using heat energy. Metal around the welds / connections, will experience a rapid thermal cycling which leads to complex changes, metallurgy, deformation and thermal stresses. It is very closely related to the strength, weld defects, and so forth which in general will have a fatal effect on the safety of welded construction. Welding process involves heating and cooling, in general, the microstructure of the metal depends on the speed of the cooling of the initial phase formation temperature up to room temperature. Because of this structural change on its own mechanical properties owned are also changing. Basically the weld area consists of three parts, namely the weld metal (weld metal), heat affected area is often referred to as the Heat Affected Zone (HAZ), and a metal stem that is not affected by heat. Weld metal region is part of the metal during welding melts and then freezes. Regional influence of heat or base metal HAZ is adjacent to the weld metal during welding thermal cycles of heating and rapid cooling. Unaffected parent metal heat is part of the basic metal welding where the heat and the temperature did not cause changes in the structure and properties. In addition there are three parts of other parts of the area which limits the area between the weld metal and HAZ are called the limit of welding. All events during cooling of the welding process is similar to cooling in the foundry difference is: 1. Cooling in the welding speed is higher 2. In the weld heat source moves straight 3. Thawing and freezing in the welding occurs continuously 4. freezing of weld metal from the metal wall of the parent which can be equated with the walls of the casting mold, only in the welding, the weld metal should be the one with the parent metal, while the foundry should be otherwise.

Threads - Product Design Mold Design

Molded-in threads can be designed into parts made of engineering thermoplastic resins. Threads always should have radiused roots and should not have feather edges – to avoid stress concentrations. Figure 35 shows examples of good design for molded-in external and internal threads. For additional information on molded-in threads, see page 105. Threads also form undercuts and should be treated as such when the part is being removed from the mold i.e., by provision of unscrewing mechanisms, collapsible cores, etc. Every effort should be made to locate external threads on the parting line of the mold where economics and mold reliability are most favorable. 

Product Design Mold Design

Gears

Gear teeth are a repetitive feature similar to screw threads or splines. It is not necessary to show their full form. In non-sectional views, gears are represented by a solid outline without teeth and with the addition of the pitch diameter surface of a type G line. In a transverse section, the gear teeth are unsectioned whereas the body of the gear is. The limit of the section hatching is the base line of the teeth as shown in the drawing in Figure 3.17. In an axial section, it is normal to show two individual gear teeth unsectioned but at diametrically opposed positions in the plane of the section. All details of the gear type shape and form need to be given via a note. In a gear assembly drawing which shows at least two gears, the same principle as for individual teeth (above) is used but at the point of mesh, neither of the two gears is assumed to be hidden by the other in a side view. Both of the gears' outer diameters are shown as solid lines. The standard ISO 2203:1973 gives details of the conventions for gears. 

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