Matched-die forming

A variation of thermoforming which does not involve gas pressure or vacuum is matched die forming. The concept is very simple and is illustrated in Fig. 4.53. The plastic sheet is heated as described previously and is then sandwiched between two halves of a mould. Very precise detail can be reproduced using this thermoforming method but the moulds need to be more robust than for the more conventional process involving gas pressure or vacuum. 

Fluoropolymers such as PVDF, FEP, PFA, and modified polytetrafluoroethylene can be thermo-formedl J by vacuum forming, pressure forming, and matched-die forming (Fig. 7.19). In all methods, a... 

Matched Die Forming - A type of thermoforming process consisting of preheating the plastic sheet prior to forming and then subjecting it to simultaneous motion of the two mold halves. 

Figure 1 Schematic views of (a) matched-die forming, (b) diaphragm forming.

Part Design Blow Molding Casting Compression Extrusion Filament Winding Injection Matched Die Molding Rotational Thermo- forming Transfer Compression Wet lay-up (Contact Molding)... 

Rigid caul plates are typically constructed of thick metal or composite materials. Thick caul plates are used on very complex part applications or cocured parts where dimensional control is critical. Many rigid caul plates result in a matched die configuration similar to compression or resin transfer molding. Parts processed in this manner are extremely challenging because resin pressure is much more dependant on tool accuracy and the difference in thermal expansion between the tool and the part. Tool accuracy is critical to ensure no pinch points are encountered that would inhibit a tool from forming to the net shape of the part. 

A second method to efficientiy produce mediyl esters of carboxylic acids is to heat die acid with potassium carbonate and mediyl iodide. The mediyl ester is produced under mild conditions and is easily separated from die reaction byproducts. This method is somewhat different in tiiat die ester is formed by a nucleophilic displacement of iodide by die carboxylate ion. Normally carboxy-lates are not thought of as good nucleophiles—and tiiey are not—but mediyl iodide is a quite reactive electrophile which matches die poor nucleophilicity of die carboxylate satisfactorily. 

Polyesters of this class vary from heavy, sticky gums to brittle but tacky solids. For this reason they are seldom handled in this form but are immediately diluted with the monomer of choice. The resins are available in a wide range of viscosities. Most of the marketed resins yield rigid materials when cured. Flexible resins are available but are used for blending with rigid ones to impart flexibility. The properties of a typical general-purpose resin for matched die-molding work are lisied in Table 15-9. 

Also prepared is mat preforming. It is the usual flat fiber mat that is formed into a shape usually using a set of matched dies (often made of fiber reinforced epoxy). A mat is cut to the correct dimensions and... 

Part design Blow molding Casting Compression Extrusion Filament winding Injection Matched die molding Rotational Thermo- forming Transfer compression Wet lay-up (contact molding)... 

Bhattacharyya et al. [26] showed that wood fibre-polypropylene composites are indeed formable. The sheets they manufactured used pinus radiate fibres along with polypropylene powder, for a total through thickness of 1.3 mm. Two types of composites were made, layered and homogeneous with polypropylene and wood fibres mixed during formation. Results showed a tensile modulus increase of up to 250% with a 25-30% fibre mass fraction. Several formability tests were studied, dome forming with matched die and cup drawing being most relevant. For both... 

Matched-die molding n. A reinforced plastic manufacturing process in which close-fitting metal matching male and female molds are used to form the part using pressure, temperature, and time cycle. 

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