Compression molding tooling

Both thermoplastics and thermoset materials can be injection compression molded. Tool patterning is particularly accurate on thermoplastics. It is also simple to produce very large parts using this method. Figure 3.20 shows the usual process flow. 

During the press operation, which is actually a form of compression molding, the resin-treated laminate plies are heated under pressure and the resins cured. The initial heating phases cause the resin to melt and flow into voids in the reinforcing ply and bond the individual plies together. The applied heat simultaneously causes the resin to polymerize and eventually to cross-link or gel. Therefore, resin viscosity reaches a minimum during the press cycle. This is the point at which the curing process becomes dominant over the melt flow process. Dynamic mechanical and dielectric analyses (11) are excellent tools for study of this behavior. 

This section will illustrate the tools taught in the above sections in the form of examples applied to steady state problems. Example 8.3 applies the finite difference method to a simple one-dimensional fin cooling problem and illustrates the nature of the system of equations that is normally achieved. Example 8.4 present a 2D compression molding problem where an iterative solution method is introduced. 

Since the in-mold pressures in RIM are generally relatively low [50 to 150 psi (0.4 to 1.1 MPa)] a variety of tooling constructions have been used. These include machined steel or aluminum, cast aluminum or kirksite, sprayed metal or electroplated shells, and reinforced or aluminum filled epoxy (Chapter 17). With mold pressures usually below 100 psi (0.7 MPa), mold-clamp-pressure requirements can accordingly be low when compared to injection and compression molding. 

Compression-molding equipment consists of a matched mold, a means of heating the plastic and the mold, and some method of exerting force on the mold halves. For severe molding conditions molds are usually made of various grades of tool steel. Most are polished to improve material flow and overall part quality. Brass, mild steel, or plastics are used as mold materials for less severe molding conditions or short-run products. 

RTM is an excellent process choice for making prototype components. It allows representative prototypes to be molded at low cost, unlike processes such as compression molding and injection molding, which require tools and equipment approaching actual production level. 

BMC, PREMIX PREFORMS AND PREPREGS ALL MATCHED TOOL COMPRESSION MOLDING... 

When the molding cycle is complete, the press opens and the molded part is removed and, if required, trimmed. It is probably moved to a jig for post-cure. This is normally carried out in a vertical press (compression molding), which is also convenient for loading inserts into the molding tool. 

Bmc, premix preforms and prepregs all matched tool compression molding ... 

Relative tooling cost, single cavity Lowest. Machined aluminum may be variable, depending on quantity required 20 percent more. Hardened-steel tooling 20 percent to 25 percent more. Compression-molding steel tools... 

Compression molding is a relatively simple and inexpensive procedure for the manufacture of moderate piece counts. For the production of bipolar plates compression molds with surface structured inserts were designed and manufactured. For the molding, the granulate can directly be molded in a heated mold under high pressure. Another way is the direct extmsion of a profile (semifinished material) into the structured mold, forming the plates from this plasticized polymer. In this variant the tool temperature is kept constant. With a multicavity-mold the cycle time can accordingly be shortened, and the output quantity of plates per cycle increased (Fig. 12). 

The highly crystalline nature of the polymer persists up to, ...625°P. At that temperature, the polymer undergoes a broad endotherm which most likely corresponds to the loss of order in one dimension. However, even above this transition, the flow is extremely limited and is insufficient to meike compression molding a useful tool for fabrication. Only very thin sections can be molded 1/4") and the resultant... 

A compressed air thermoforming machine is essentially a deep drawing machine with a controlled heat shield, except that, in place of an upper ram, a pressure bell is used. The heated rubbery material is pressed into the molding tool using a differential pressure of up to 100 psi. After cooling and demolding, the formed part is precisely shaped. 

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