Specialist Techniques and Processes

Tools, Equipment and Processes

There are a range of tools, equipment and processes that can be used to shape, fabricate, construct and assemble high quality products and prototypes.

__Wastage __– where material is cut away to form a shape:

Die cutting is the cutting of a shape by pressing a die cut shape through the material. Dies are a sharp metal blade fixed into a block in the shape of the cut, rounded metal edges can also be in the block to create creases. Can be used on paper, thin wood and polymer sheets.

Perforation is a line of cuts through thin material which create an easily folded and ripped line such as cheque books and raffle tickets. A perforating blade can roll over the material or press down like a die cutter.

Lathes turn a long length of material with specialist shaped tools. Turning spins the material round whilst layers are shaved off. Turning is used for items like furniture and stair spindles.

Milling is a similar technique mainly used for metal work, a thin layer of metal is removed each turn at a carefully measured depth and speed. It can produce a really accurate finish.

Sawing is the oldest and most basic wastage technique, saws are used to cut away material. Different saws are available for different materials, which have a variety of shaped blades depending on what you’re cutting. Tenon, jigsaw, scroll and coping are all different types of saws.

Drilling uses a circular bit to create holes in materials, hand or electric drills can create holes through all materials. Drill bits come in a variety of standard sizes to fit other standard components. The tip of a drill is shaped differently to suit different materials such as wood and stone.

Shearing is a method of cutting sheet material, particularly metal or flexible polymers. Shears use the same method as scissors but stronger to cut through tougher materials.

Specialist Techniques and Processes, figure 1

__Addition __– Where materials are added to form shape:

Brazing,__ soldering__ and__ welding__ all use molten metal to join metal together. Soldering uses solder melted at a relatively low temperature to join metal. It’s particularly used for electrical circuits and plumbing joints. Brazing heats joints to a higher temperature and uses brass to flood the joints. The strongest of all of the addition joints is welding which uses an electrical current to melt welding rod to flow together and cool between joints. Polymer can also be welded with plastic rod.

Lamination sandwiches layers together to strengthen or protect, plastic laminated paper, foam board, goretex fabric and plywood are all examples of lamination.

3D printing adds material in layers suirted through a nozzle to print the CAD drawing sent to it. 3D printing mainly prints plastic but metal, resin and food printing is all being developed.

Batik is a decorative textile technique where hot wax is painted onto cotton fabric with a brush or Tjanting tool, this creates a resist where dye cannot soak in. The areas around the wax are dyed and when dry the wax is ironed and melted off.

Sewing is an addition that can be done by hand or on a sewing machine, it can be used to join fabric or add decoration on the fabric.

Bonding any material together takes adhesive glue to stick it. Different glues are developed for different jobs, PVA for wood and paper, epoxy resin for most materials and liquid solvent cement for polymers.

Printing adds ink to decorate paper and board. Lithography is where an oil based ink and water are transferred onto an aluminium plate which has the image areas treated with a chemical which repels water and attracts the ink. Flexography uses a flexible printing roller to coat surfaces. Screen printing squeezes ink through a frame which has a mesh image on it. Digital printing uses cyan, magenta, yellow and black (CMYK) to create all the colours necessary, inkjets and laser printers enable you to send an image directly from your computer to print.

Specialist Techniques and Processes, figure 2

Deforming and reforming __materials __can also produce shapes:

__Vacuum forming __heats sheet polymer until it is flexible and then sucks out the air between it and the mould to create a vacuum and an accurate copy.

Creasing, bending __and folding__ fabrics, card, plastic, metal and paper can create shape, these can be decorative or strengthen a structure. Fabric can be pleated and gathered to form shape in clothing and upholstery.

Pressing metal between an upper and lower mould under high pressure can form an accurate and intricate shape such as metal plates and trays.

Drape forming is used to shape thermoforming polymer by heating sheet plastic until it is soft enough to drape over a mould, when it cools it sets into the shape and the mould is removed.

Blow moulding takes softened polymer and blows it into a mould with air like a balloon, used to mould bottles and containers.

Casting pours molten material into a mould (the die), this can be used with metal, plastic or plaster for things like motor parts, toilets and plastic soldier toys.

Injection moulding injects liquid plastic into a mould under high pressure, it creates accurate and quick products such as buckets and washing up bowls.

Extrusion squeezes molten plastic or metal through nozzle to create a long continuous shape such as plastic beading or wire.

When cutting, forming and measuring manufacturers put tolerance measurements in place, these are the allowances of accuracy that need to be followed to keep the quality of the product high and the ability to accurately join pieces together. For instance, a reasonable tolerance between button holes on a shirt would be plus (+) or minus (-) 5mm. The tolerance of a large cupboard would be more than a small engine part. These tolerances would be worked out using a prototype before production.

The application and use of quality control includes measurable and quantitive systems during manufacture:

Paper, board and fabric printing rely on registration marks to check print rollers and plates are in place. This is usually a circle with a cross in it. Visual accuracy is checked for quality throughout by comparing it with an original sample.

Go/No go fixtures are used to check whether a part fits within its limits. They are mostly used in timber products and are usually double ended with the minimum at one end and maximum at the other and are very quick to use.

Depth stops are used for machine drilling and cutting. A depth stop can be put on a drill to stop it cutting passed the limit set on the bit. It is usually adjustable and can be changed depending on the task.

Polymers cut on a laser cutter can have tiny variations in thickness so the laser needs to be focused and set to the correct feed rate and power for the material. The laser moving too fast or at low power will not have enough power to cut through the polymer.

PCBs manufactured through chemical etching all need to have the same exposure time to ensure the correct amount of copper track is exposed, too little will not expose a circuit and too much will uncover too much and cause a short circuit.