There are 5 main types of Plastic Molding these are:
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Injection
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produced by melted plastic is injected into a closed male/female tool and cooled forming a shape
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most widely used and utilized in most products (e.g. Device Exteriors)
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poor tooling and insufficient parameter control resulting in flash and shiny marks are the main issues
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Blow
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pre-formed plastic tube is inserted into a tool onto a nozzle, tool is closed and air is blown to form a shape
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low-cost and used items with 1 or 2 apertures (e.g. Bottles or Extendable Tubes)
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leakage, tearing and uneven wall thickness are the main issues
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Extrusion
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melted plastic is pushed through a nozzle to form a single shape
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lowest cost and used for tubes or single-direction simple shapes (e.g. Shelving Tubes)
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wall thickness can vary after molding and consistency of finish are the main issues
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Thermoforming
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Compression Molding
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utilizing a male/female mold material is compressed or liquid is poured into the space forming a shape
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cheaper than injection but also less precise, it is strong and durable but lacks precision (e.g. Clamshell)
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Vacuum Forming
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a sheet is heated and then secured, it is pulled via vacuum pressure over a mold to form a shape
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low-cost and useful (widely used for appliance covers e.g. Fridge Fronts)
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edge finishing and dimensional control are the main issues in thermoforming
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Rotational
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produced by powder added into a rotational tool which is heated as it rotates, can cause shrinkage issues
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for large-sized small volume products, it is useful but becomes an issue at scale (e.g. Kayak)
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limited material options and high cycle times are the main issues
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It is also possible to produce silicone cast Resin housings which are very customizable and cheap in small quantities but require thick wall thicknesses and handwork finishing
The best method depends on the design and its final use along with what material is desired, each method is useful in its own way