Molds costs

In this process, resin is injected into a closed mold containing the reinforcement preform. The resin can be injected either under pressure [22] or under vacuum [23]. The potential advantages of this process are (I) low mold cost, (2) inserts can be incorporated, (3) low pressure requirements, (4) accurate fiber orientation, (5) automation possibilities, and (6) versatility. The resin formulation and process variables are selected so that no significant polymerization occurs until the mold cavity has been completely filled. This is achieved by the ad-... 

Undercut Whether external or internal, undercuts should be avoided if possible to reduce mold cost (by about 25 to 30%) and simplify melt flow during molding. However many molds use external and/or internal undercuts. In cases where it is essential to incorporate them in a design, appropriate mold design is required. The mold will include action such as sliding components on tapered surfaces, split cavity cam actions to produce the needed undercut, etc. (Chapter 8, TOOLING)... 

If a self-threading screw can be substituted, it will not only appreciably decrease mold maintenance and mold cost but most likely, with proper type selection, also give better holding power. A screw that has a thin thread with relatively deep flights can give high holding power. If the screw or plastic is preheated... 

Cost When it is necessary to equal the production rates of other processes, the mold cost with RM may exceed that of other processes such as flow molding. The plastics used in RM are generally more expensive than the pelleted plastics used in many other processes, because they must be more finely and evenly powdered, such as to a 35 mesh. However, this process generates low levels of regrind or scrap, even when it is operating poorly. Products can have no flash at all if properly designed molds are used. 

Next is to make sample prototype tooling and sample prototype products for the test. Samples made by machining or other simplified model making techniques do not have the same properties as the product made by molding or extrusion or whatever process is to be used (Chapter 3, PROTOTYPES). A product made this way is a sample rather than a testable prototype. Simplified prototypes may reduce trial mold cost and produce adequate test data in some cases. Its main value is appearance and feel to determine whether the aesthetics are correct. Any testing has to be done with considerable reservation and caution. 

This interplay of the many variables is extremely complex and involves a matrix of the many variables. As an example in the molding simulation TMconcept system programmed Molding Cost Optimization (MCO) of Plastics Computer Inc., Dallas, TX, there are well over 300 variables. It is not reasonable to expect a person using manual methods to calculate these complex interactions even if molding only a modest shaped product without omissions or errors. Computerized process simulation is a practical tool to monitor the influence of design alternatives on the processability of the product and to select molding conditions that ensure the required product quality (3). 

Using low cost material to meet high performance requirements will compromise their integrity. As an example, the cost of a mold cavity and core materials, for more than 90% of the molds, is less than 5% of the total mold cost. Thus it does not make sense to compromise mold integrity to save a few... 

Disadvantages include higher initial mold cost, the need for both injection and blow molding units and lower volume production. 

The fabrication of polyurethanes into complex shapes is much easier than with metals. Large casting of up to 500 to 1,000 kg can be made from relatively simple molds and buckets, with minimal labor. The energy input into the production of a cast polyurethane part is low compared to the melting of a metal alloy. The actual molding costs are also lower. 

Tooling cost for the production of all polyurethane parts is much lower than that for making plastic parts by either compression or injection molding. The molds do not have to withstand the pressures involved when compression and injection molding is carried out. These lower molding costs can be used to prepare prototypes of a new concept for general evaluation prior to the expense of an injection molding die. 

Latex rubber can be poured like polyurethanes, but they generally are only poured in thin sheets. Even thicker sheets such as Linatex require a very long cure time. Pouring is the method of choice for cast polyurethanes. Normally, rubbers require a compression molding press or injection molding machine to produce parts. This has high capital and mold costs. 

Permanent mold casting is generally similar to die casting, except that gravity rather than pressure is used to fill the mold cavity. This process is employed where larger, or heavier, section castings are needed. Mold costs are still high, so this process is economical only in volume as well. 

Draft on the cavity wall such as 1° is recommended to facilitate product removal. Lower-shrinkage plastics like PC and PMMA requires l1 to 2°. Undercuts are possible, but they should be kept to a minimum. Making provisions for undercuts or no drafts usually requires higher mold costs because the mold will require action such as core pulls or splitting a mold to allow separation parallel to the undercut groove. This type of mold action usually requires additional cycle time thus increasing cost. 

There may be a requirement for surface finish, molded-in color, textured surface, or other conditions the plastic material is to meet (Chapter 2). The different processes may be able to provide only one surface to be smooth or both sides are smooth. Important that smooth be identified since it has many meanings to different people. Surface finish can be more than just a cosmetic standard. It can also affect product quality, mold cost, and delivery time. The Society of Plastics Engineers/Society of Plastics Industries standards range from a No. 1 mirror finish to a No. 6 grit blast finish. A mold finish comparison kit consisting of six hardened tool steel pieces and associated molded pieces is available through SPE/SPI. 

Many different processing methods are used, all with the essential element of heat. These processes permit products to be made that would otherwise require costly and heavy melt processing complicated molds and/or equipment. Different types of dispensing equipment are used to meet different flow rates and delivery amounts. No pressure or mixing is necessary. This means that mold costs are very low and the overall processing equipment costs are low. They are very versatile materials in that almost any additive can be incorporated for special... 

Another compromise is made when blowing multiple bottle sizes from the same preform. This may not be optimum from the perspective of polymer utilization, but it may save lots of money on inventories and mold costs. As shown in Section 12.3.2, one can design the preform for optimum wall thickness distribution by using finite element analysis. Sometimes polymer is less expensive than molds. 

The fabric s unidirectional fibers are constructed in a way that increases resin flow during molding, and wet-out is up to 40% faster than with other products. So that molders don not have to modify their existing laminate designs, the fabrics are based on traditional knitted fabric technology and have comparable properties. Channels are built into the fabric structure to ensure a fast, even resin distribution. The faster flow rate can lead to higher production and mold turnover and because there is no need for local resin distribution media, the fabric can potentially decrease molding costs. A continuous filament mat version of the fabric is said to offer even faster surface flow. 

Note 1. Ratio based on sheet metal weight as 1 2. Relative comparison for 400-500 kg 3. Mold cost for sheet metal. Symbols Excellent O Good A Fair xNogood... 

Table 9.1 Mold costs, output, and life expectancy...

Process Mold cost (UK j Daily output Life of mould... 

Resin transfer molding Low mold costs, low pressure molding, two good surfaces providing quick manufacture of wood molds and producing rather complicated small and particularly large parts to rather tight tolerances... 

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