Contact Molding
Contact molding is the simplest method used for the manufacture of compositestructures.
This method requires a minimum of equipment and consequently a minumum of invesment. These advantages were the origin of the success of glass fiber composites in both industry and crafts.
Contact molding can be used to manufacture both small and large composite structures such as boat hulls, vehicle bodies, building panels,tanks, etc., where small production runs are required. Although the proportion of fibers may vary it nevertheless stays low, usually between 30% and 35% by weight of reinforcements.
(Jean-Marie Berthelot,Composite materials: mechanical behavior and structural analysis,p.54 )
Compression Molding
In compression molding, the compound, in powder or preform shape, is loaded directly in to a hot cavity at an average temprature of 340 F.
The required compression molding pressure depents upon: (1) the type of material, (2) the conditioningand preheating of material before molding,(3) temprature of the mold,(4) part design, and (5) mold design. Most thermoplastic materials are not suited for tihs process, so compression molding is used for molding thermosetting resins.
There are four methods of molding by the compression(and transfer) process.These are: (1) hand, (2) semi-hand, (3) seemi-automatic, and (4) automatic. Many different types of presses are made for compression molding.
The requirement of a press is to apply the needed pressure and provide sufficient heat to plasticize and cure (make infusible) the plastic materials. Heat is applied by transferring heat from heated platens, or it can be applied directly to mold.
The basic procedure for compression molding consist of placing the molding compound into the open mold cavity, closing the mold, and the applying heat and pressure through a down-ward-moving force-plıug to the material until it softens and is forced to fill the mold cavity.In closed mold a chemical reaction thet cross-links the polimer chains takes place and the materail hardens in to the required shape.
(Harold V. Johnson,Manufacturing Process, p.558)
Vibration Welding
vibration welding is a well-established process that can join large,sealed, and mechanically strong weld seams with cycle times of only a few seconds.It is mainly used when short cycle times are demanded and the part is too large for the use of ultrasonic welding.However, because the process reqires relatively flat (planner) joining surfaces, some applications are not suited for vibration welding.A slight incline in the jint 10 degree can be tolerated in the linear vibration welding components, although it is not recommended.in some cases the vibration welding process can be used to solve warpage issues of glass-fiber-filled polyamide parts, because it is possible to clamp the parts,so that they are forced in the correct geometry.vibration welding can also used as an alternative to adhering or mechanically joining different materials such as wood fiber reinforced matherials to thermoplastic.
ın vibration welding, the two parts to be joined are clamped together under a relatively high force.At a preset force, one part is vibrated relative to the seconf, usually with a displacement between 0.5 and 1.5 mm (0.020 and 0.060 in.). The motion results in the joining surface melting and fusing together.
(Avraham Benatar, Welding, p.36)
Hobbing
A hob is machined from tool stell desired form of the part to be molded, heat-treated, and polished. The operation consist of pressing the hob By means of a hydrolic press(capacity from 250 to 8,00 tons) into a blank of soft steel mounted in a cavity of a specified size. A retainingh ring prevents the mold mold from spreading out of shape. This method of cold forming can produce identical cavities economically.
(Harold V. Johnson,Manufacturing Process, p.181)
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