Final Production / 4.4 /
Manufacturing Processes
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Different manufacturing processes have been developed to innovate existing products and create new products. Designers sometimes engineer products in such a way that they are easy to manufacture. Design for manufacture (DfM) exists in almost all engineering disciplines but differs greatly depending on the manufacturing technologies used. This practice not only focuses on the design of a product’s components but also on quality control and assurance.
4.4.1 | Additive techniques
4.4.1 | Additive techniques
Paper-based Rapid Prototyping (PRP) technology is only really used for prototyping purposes and despite restrictions has a low build material cost. Paper prototyping is often used as the first step of the rapid prototyping process, used to identify early issues or problems with the concept before advancing the design idea into more expensive and complex types of prototypes.
Laminated object manufacturing (LOM) is a form of PRP and is used to make 3D paper-thin polymer models. It is a form of 3D printing. LOM is often used to create scale models and conceptual prototypes that can be tested for form and design. It can also be used to make patterns and templates used in traditional manufacturing, such as sand mould casting.
Stereolithography (SLA or SL) - also known as optical rapid prototyping or resin prototyping - is a type of adhesive manufacturing used for creating models, prototypes, patterns, and production parts in a layer-by-layer fashion. Is an additive manufacturing technology that builds objects layer by layer, curing a photoreactive resin with a UV laser or other similar light source. Starting from a 3D image, the model is built slice-by-slice from the bottom to the top in a vessel of liquid polymer that hardens when struck by a laser beam.
Stereolithography requires the use of supportive structures which attach the model to the building platform, and support internal parts in complex structures. Supports must be removed from the finished product manually.
Fused Deposition Modelling (FDM) constructs three-dimensional objects directly from 3D CAD drawings. A temperature-controlled head extrudes thermoplastic material like PLA or ABS layer by layer in a semi-liquid state. The material cools and hardens to produce the final 3D product.
FDM starts with importing a CAD file of a model into pre-processing software. The model is orientated and mathematically sliced into horizontal layers. A support structure is created where needed, based on the model's position and geometry. The model needs support until the hot thermoplastic cures enough to support itself. More complex shapes and designs also require supporting structures so they don’t fall over while being printed.
4.4.2 | Wasting/subtractive techniques
4.4.2 | Wasting/subtractive techniques
Cutting describes the action of sawing, chiselling, or planning that removes material in the process of cutting. The tool must be harder than the material being cut or abraded.
Machining refers to cutting with powered machines. Machine tools operate on unfinished parts, such as rough metal castings or timber, and perform shaping and finishing operations that produce precisely dimensioned parts. Most machine tools function in one or more basic categories that can be either computer or manually controlled: Drilling, turning and milling.
Turning is most commonly carried out using a lathe. Lathes are used primarily to cut metals and wood. They work on a horizontal axis where the workpiece rotates at speed and the tools such as chisels remove the waste material to the desired shape.
Milling is more commonly carried out on the vertical axis and is used for cutting slots, grooves, and complex shapes, usually out of metal. different to a lathe, the workpiece is placed is fixed and the cutting head is moved (commonly computer controlled) to remove the desired waste material.
Abrading involves the use of abrasive materials to wear away the material using friction. This can be done using abrasive paper or emery cloth. It can also involve the process of grinding using a wheel or abrasive stone. Synthetic materials such as silicon carbide, aluminium oxide, or industrial-tipped diamond tools can be used.
4.4.3 | Shaping techniques
4.4.3 | Shaping techniques
Laser cutting is a technology that uses a laser to cut or engrave materials. It is typically used for industrial manufacturing processes, but as the technology has become more commonplace, and significantly reduced in cost, schools, small businesses, and hobbyists can now afford the equipment.
The focused laser beam is directed at the material, where the material either burns, melts or evaporates. This leaves the edge of the cut with a high-quality and precise finish. Industrial laser cutters are used to cut flat sheet material, as well as piping material.
Advantages
Highly accurate.
Quick production time.
Repeatability.
Can cut and engrave materials.
A wide range of materials can be used in laser cutters.
Fairly simple to set up and operate.
Disadvantages
In general limited to sheet materials.
High power machines can be very expensive.
Cutting metal can be difficult - copper, aluminium, gold, silver, brass and bronze for example.
Mainly 2D objects can be made.
Advantages
Ideal for thermosetting plastics.
Long production runs.
Low set up and mould costs in comparison to injection moulding.
Little waste material.
Ideal for creating solid parts with thick walls.
Disadvantages
Limited complexity of shapes.
Shapes need ‘thicker’ walls.
Can be labour intensive.
Compression molding is a method of molding in which the molding material, generally preheated, is first placed in an open, heated mold cavity. The mold is closed with a top force or plug member, pressure is applied to force the material into contact with all mold areas, while heat and pressure are maintained until the molding material has cured
Injection moulding is a manufacturing process for producing parts, by injecting material into a mould. Injection moulding can be performed with a variety of materials, including metals, glass, elastomers, confectionary, and most commonly thermoplastics and thermosetting plastics. Materials for the part are fed into a heated barrel, mixed, and forced into a cavity of the mould, where it cools and forms the shape of the mould.
Parts to be injection moulded need to be carefully designed to facilitate the moulding process. The part must be designed so it complies with the desired shape of the finished component, but also can be easily removed from the mould.
Disadvantages
High set up cost.
Expensive moulds.
Limitations on size of parts.
Some shapes can not be made.
Maintenance costs.
Retooling time and cost.
Advantages
Precision parts.
High repeatability.
Low cost per part.
Little or no waste.
Fast production time.
Large volumes can be made.
Smooth surface finishes.
Highly automated.
Advantages
Once set up, blow moulding is a rapid method for producing hollow objects.
Well suited to low and high production runs.
Many types of plastic can be used.
Can be less expensive than injection moulding
Disadvantages
Limited to hollow parts.
Moulds can be expensive.
Difficult to produce triangular shapes.
Certain shapes can not be produced because the process will not allow it.
Blow moulding is a manufacturing process for forming hollow plastic parts. It is also used for forming glass bottles or other hollow shapes.
The blow moulding process begins with softening plastic by heating a preform or parison. The parison is a tube-like piece of plastic with a hole in one end through which compressed air can enter.
The plastic workpiece is then clamped into a mold and air is blown into it. The air pressure inflates the plastic which conforms to the mould. Once the plastic has cooled and hardened the mould opens and the part is ejected. Water channels within the mould assist cooling.
Rotational molding involves a heated mold which is filled with a charge or shot weight of material. It is then slowly rotated, causing the softened material to disperse and stick to the walls of the mold forming a hollow part.
Advantages
A hollow part can be made in one piece without seam lines or joints.
Ideal for ridged, tough and flexible shapes.
No material wastage, as the correct amount is weighed out for each mould.
Different types of products can be moulded on one machine.
Surface texture can be added to the mould surface.
Moulds tend to be cheaper than blow and injection moulding.
Disadvantages
Only hollow shapes can be made. More complex shapes would need to use another manufacturing process.
The plastic used needs to be ground down into a fine powder, in many cases the addition of special additives is required. This can increase the manufacturing costs.
Advantages
High-speed production.
Material optimization.
Cost-effective.
Material flexibility.
Low cost of tooling.
Disadvantages
Shape and size -restrictions.
Matching of the edges is required.
Thermoforming is a manufacturing process where a plastic sheet is heated to a pliable forming temperature, formed to a specific shape in a mould, and trimmed to create a usable product. The sheet, or "film" when referring to thinner gauges and certain material types, is heated in an oven to a high-enough temperature that permits it to be stretched into or onto a mould and cooled to a finished shape. Its simplified version is vacuum forming.
Vacuum forming is a simplified version of thermoforming, where a sheet of plastic is heated to a forming temperature, stretched onto a single-surface mould, and forced against the mould by a vacuum. This process can be used to form plastic into permanent objects such as turnpike signs and protective covers
(Plastic) extrusion is a high-volume manufacturing process in which raw material is melted and formed into a continuous profile. Extrusion produces items such as pipe/tubing, weatherstripping, fencing, deck railings, window frames, plastic films and sheeting, thermoplastic coatings, and wire insulation.
This process starts by feeding raw material (pellets, granules, flakes or powders) from a hopper into the barrel of the extruder. The material is gradually melted by the mechanical energy generated by turning screws and by heaters arranged along the barrel. The molten polymer is then forced into a die, which shapes the polymer into a shape that hardens during cooling.
Advantages
Fast production.
Material colour flexibility.
Low wastage.
Design flexibility.
Best way to make long products with the same profile (shape).
Low unit cost as large production runs can help achieve this.
Disadvantages
High initial capital cost.
Part and size design restriction.
Restricted to long products with the same profile (shape).
Not suitable for small-scale production runs.
Advantages
Low cost process.
Easy to operate.
Advanced sand casting can produce very detailed and intricate parts.
Flexible levels of production.
Complex shapes can be made.
Disadvantages
Can be labour-intensive.
Unit cost can be high for one-off or small-scale production.
Parts may require a lot of finishing.
Sand casting, also known as sand molded casting, is a metal casting process characterized by using sand as the mold material. The term "sand casting" can also refer to an object produced via the sand casting process. Sand castings are produced in specialized factories called foundries. Over 60% of all metal castings are produced via sand casting process.
High-pressure die casting is a process in which molten metal is forced under pressure into a securely locked metal die cavity, where it is held by a powerful press until the metal solidifies. After solidification of the metal, the die is unlocked, opened, and the casting ejected.
Advantages
Ideal for complex shapes.
High level of detail can be achieved.
Excellent surface finish.
Highly accurate.
Can produce small, thin parts.
Fast production.
Disadvantages
Suitable for metals with low melting points.
Expensive set up costs.
Only suitable to high production levels.
Parts produced can not guarantee high structural strength.
Excess material requires trimming.
Advantages
Suitable for one-off, bath and mass production.
Can accommodate a range of thicknesses.
Creates lightweight and strong products.
Relatively quick, easy and cheap to set up.
Can incorporate different materials into its veneers - skateboards for example
Disadvantages
Moulds can be labour intensive to construct.
Can be restricted to bends in one direction at one time.
Laminations take long to dry.
Wood laminating is the process of forming multiple sheets of veneer, chips or solid timber using moulds and bonded together by very strong adhesives, to produce rigid, lightweight structures.
Weaving is a method of fabric production in which two distinct sets of yarns or threads are interlaced at right angles to form the fabric or cloth. Other methods of shaping materials or cloths are knitting, lace making, felting, braiding or plaiting. The longitudinal threads are called the warp and the lateral threads are the weft or fill. The cloth or fabric is usually woven on a loom, these can be either manual or mechanically driven. A device called the ‘shuttle’ holds the weft threads and is passed through the moving ‘warp’ threads. The pattern of the finished cloth is determined by this movement. The way that the warp and the weft threads are interlaced with each other is called the ‘weave’.
Knitting is another way of shaping yarns or threads into material. Knitted fabric consists of a number of consecutive rows or loops, called stitches. As each row progresses, a new loop is pulled through an existing loop. The active stitches are held on a needle until another loop can be passed through it. This process eventually results in a fabric, often resulting in blankets or clothing. There are numerous styles or methods that can be made by hand or machine.
4.4.4 | Joining techniques
4.4.4 | Joining techniques
Advantages
Low cost.
Does not affect the properties of the material being brazed.
Suitable for one-off to mass production.
The joint is very strong.
Can produce a clean joint without need for secondary finishing.
Complicated and intricate joints can be achieved.
Joints can be reworked if faults are found.
Disadvantages
Requires a high level of cleanliness.
The joint colour is often different to the base metal.
Can require a level of skill.
Obvious danger risk.
Personal protective equipment is a must.
Wider joints or thicker materials can take a long time to weld.
Soldering and brazing are semi-permanent joining processes used to join different types of metals together by melting solder. Solder is a metal alloy usually made of tin and lead which is melted using a hot iron.
The only difference between soldering and brazing is the temperature at which each process takes place. Soldering takes place at a temperature below 450°C, and brazing occurs at a temperature above 450°C.
Welding is a fabrication process that permanently joins materials, usually metals or thermoplastics, by using high heat to melt the parts together and allowing them to cool, causing fusion. Welding is distinct from lower temperature techniques such as brazing and soldering, which do not melt the base metal (parent metal)
Advantages
Little preparation of materials.
It is a fast process.
Strong bond.
No harmful fumes
Easily automated.
Ability to join different metals.
Disadvantages:
Expensive equipment.
Limited size of joints.
Machinery requires high stiffness.
High forces involved.
Can mark the material due to excessive clamping pressure
Friction welding (FRW) is a class of solid-state welding processes, in which heat is generated by mechanical friction between a moving component and a stationary one, and at the same time a lateral force is applied to the parts, in order to plastically displace and fuse the material. There are two forms, linear and rotational welding and they are used in the production of cars, ships and trains, and is the preferred method for fusing turbine fans in jet engines. FRW is a permanent joining method.
Pop or blind riveting is a technique primarily used to join thin pieces of metal. It can also join plastic sheets and materials (denim jeans). The rivet has two parts; the pin and the rivet. The pop rivet pliers or the gun is used to pull the pin through the rivet. This process slightly deforms the rivet so it joins the two materials together.
This technique is used where the material is very thin and the joint does not have to be very strong. It is ideal for joining aluminium, and the technique is commonly used where weight considerations are an important factor in design. Pop rivets could be considered a semi-permanent jointing technique, as they can easily be drilled out to release the joint.
Cold and hot riveting are used in more ‘industrial’ manufacturing processes where thicker materials need to be connected, in comparison to the lighter applications of pop riveting.
Hot riveting is mostly used where high strength and low weight are critical. The medical technology and automobile industries use it on a large scale. It is also used in electronics production. Hot riveting can also be used in aircraft and window furniture or where a liquid-tight seal is required.
Cold riveting has largely been replaced by welding as a metal jointing technique but was extensively used in ship and train building in the past. The Titanic had a cold riveted hull. Cold riveting is still extensively used in the automotive industry though.
An adhesive is a substance that is applied between two surfaces in order to bond them together. Adhesives may come in either natural or synthetic forms. Some modern adhesives are very strong and are becoming increasingly important in the modern construction industry and industry in general. Adhesives you need to know:
PVA Glue - Polyvinyl acetate has different varieties, Type II is water resistant. Type I is waterproof. Commonly used for a variety of applications. Usually found in schools - the white glue. PVA glue is water-based and easy to clean up. It dries transparent and has a low life span. The curing time is long: 24 hours.
Contact adhesive - A contact adhesive (also known as 'contact cement') is a rubber-based adhesive. Once the surfaces over which a contact adhesive has been applied make contact, the bonding is permanent. Contact cement is different from other adhesives because it needs to air-dry for 15 to 20 minutes before assembling. The cement needs to be applied to both parts so that the glue actually bonds to itself. The most common purpose for contact adhesives is the connection of two non-absorbent surfaces or the bonding of surface materials
Liquid solvent cement - Joints plastics such as perspex together permanently. The glue is applied along with clamping pressure and allowed to fully cure for 24 hours. It has a permanent hold and usually is the best option for joining plastics. The bond is irreversible. The glue can have strong fumes. It works only on smooth surfaces. The bond is not very strong bond and therefore requires a large glue surface area.
Epoxy resin - Thermosetting plastic made using resin and hardener. Used for joining completely different materials, like wood and metal. Very strong and heat resilient in comparison to other adhesives. Can chemically combust if not combined properly. Multi-purpose.
Superglue (cyanoacrylate) - A type of fast-bonding, high-strength, instant adhesive engineered to bond almost any material. Super glues are valued for their resistance to temperature and moisture and are commonly used with stone, metal, wood, plastic, glass ceramic, paper and most other common substances.
Temporary jointing methods allow materials to be joined together, but not permanently. They can be taken apart when needed - with differing degrees of ease and success.
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