Manual shears
Bench mounted manually operated shears are often referred to as guillotines.
Their purpose is to cut sheet metal and small plate within the thickness of 5mm.
Although the cut is reasonably accurate, an allowance normally should me made for the pull/tilt on the metal caused by the bow twist and camber movements of the waste metal. Different bench shears will incorporate different rake angles (the angle of the moving blade in relation to the fixed blade), this has a direct impact to the quality of the cut.
Bench shears are mainly used for small scale production for one off or prototypes. This is because all the work is manual and the workpiece requires a small amount of finishing off.
The overall cost of purchasing and maintaining bench mounted shears is low. The shears can be purchased from around £100, with regular lubrication the shears can last on average up to 5 years depending on the usage.
Pop riveting systems
Pop rivets are used to join two pieces of material together, normally sheet metal but can also be plastics. Occasionally it is used to join more than two but this is not common.
When the rivet is placed in the holes of each of the materials, a tool is used to extract the mandrel from the shank. As the mandrel is attached to the bottom of the shank, it deforms the metal creating a large surface area and thus bringing the pieces together.
Each rivet costs around £0.40 and the cost of a pneumatic setup (which is less labour intensive and quicker) can vary from £200 – £1000. Riveting systems are generally used for better quality products. For example, rivets can be ground down and removed to allow for parts to be changed. Also, with riveting, as opposed to spot welding, no heat is produced and materials like GRP and Fiberglass can be joined. Pop riveting system also require much less power than with spot welding as the only electrical system is the compressor.
Box and Pan Brake
A box and pan brake, often referred to as a folding machine, is used to fold sheet metal of a low carbon content.
The work piece is placed on the machine bed and the desired bend location is lined up. The work piece is them clamped and a counterweighted lever is pushed or pulled to bend the material. Nose bars can be adjusted laterally and are used to clamp the workpiece. When bending steel, the angle on the nose bar can be used as an indicator to compensate for spring back.
This piece of machinery is only used for one off, prototyping or small-scale production. The process can become tiring and the quality of the bend is completely dependent on the operator as there are no guides. If a piece of sheet metal need to be bent uniformly on a large scale, a die could be used which is much quicker than using the Box pan brake and produces consistent results.
A box and pan brake will cost around £200 – £1000
Laser cutting systems
With laser cutting systems there are many different types that can be used including; vaporising, melt- blow and melt-blow-burn. The most common being melt-blow.
A laser (usually co2) is focused using either lenses of curved mirrors onto the workpiece, as the metal becomes molten a high-pressure gas forces the molten metal out of the kerf forming a perforation.
Once the CNC program has been created for the required cut, the machine is operated easily, and minimal set up is required.
As laser cutting is one of the most precise methods of cutting, it is commonly used by large companies for medium/large scale production. The power consumption of laser cutting systems is the highest of all cutting systems excluding plasma cutting (24-40 kW).
The cost of a laser cutting system is around £223,068. This is the most expensive cutting process in comparison to other processes such as water jet cutting and plasma cutting. However, if the intended task is to produce large scale metal cut-outs, laser jet cutting is the most beneficial. Very little clean up is required as a product of laser cutting, mostly consisting of dust which is collected in filters or lays in the work area. Laser cutting produces very low noise pollution and machines can be left to run over night which yields great production values. Eye protection is not necessarily required and the only realistic health hazard is fumes/gasses produced by the material.
Spot welding
Spot welding is one of the most commonly used joining processes throughout industry, mainly being used in the aerospace and automotive industry. The process enables two pieces or edges of sheet metal (varying in thickness between 0.5 – 3mm) to be joined together by means of a small welded area.
Little setup is needed for a spot welder, the correct current needs to be selected in correspondence to the metal thickness.
The two pieces are placed between two electrodes (most commonly copper alloy) and clamped in place using a lever, when the lever is pressed a final time a high current is passed through the metal causing it to melt and form a weld. Spot welders are usually bench operated as they are heavy due to the transformer.
Spot welding is the preferred method for joining due to many properties. The finished spot weld is neat and free from splutter, the process is extremely quick (a result being minimum distortion in the material caused by prolonged exposure to heat).
The main downside to spot-welding is the power consumption. Although it is the most efficient type of welding, it requires much more power than other processes such as riveting where pneumatics can be used.
Spot welders start from around £400 but get cost up to £5000 for more reliable systems.
Water jet cutting
Water jet cutting is a commonly used cutting method, it is such a preferred method due to the complete diversity of materials and thicknesses it can handle.
An abrasive is added to water (usually garnet) which is dispensed at a high pressure in a small diameter jet. The process is simply a precise, expedited form of erosion.
The setup is quite complicated as the correct water pressure and quantity of abrasive added needs to be set. However, when the CNC program has been set correctly, it is easy for an operator to work the cutter.
The most appreciated properties of water jet cutting are that there is no heat affected zone. This is sometimes a problem in processes like oxyacetylene cutting or laser cutting as the heat affects the properties of the metal (i.e. heat treatments/temperedness).
The tolerances of water jet cutting are 0.05mm which is not as precise as those produced by laser cutting (0.002)
The cost of a water jet cutter is the highest if operational costs are considered. A water jet cutter will initially cost around £30,000 – £150,000. Then the cost of running needs to be acknowledged. This includes the price of: water, power, abrasive and parts wear. When compared to laser cutting, the power consumption is less. However, the waste produced from water jet cutting is substantial, meaning longer clean-up and disposal of waste times.
methods Batch size Repeatability/ Energy consumption/
sustainability Accuracy/tolerances Required skill Overall cost
Box/pan brake Small batch Low, the desired bend needs to be lined up by the operator. Manual labour/no waste produced medium accuracy, the operator determines where the bend is made so can be inaccurate Low, training can be done in hours £200-£1000
Manual/bench shears Small batch Low, the cut is sometimes inaccurate and determined by the oporator Manual labour/ medium/large amount of waste produced Medium, the quality of the cut depends on the blade condition and the operator manually cuts so can be inaccurate Low, training can be done in hours £100
Pop riveting systems Varies depending on tool used and whether cnc is encorporated Pop riveting can a fast process, the only waste produced is the shank that snaps off. Low, if pneumatics are used, an air compressor can be run on under 1kWH Accurate, results are consistant Low, training can be done in hours, with the addition of an understanding of pneumatical appliances To produce
100 riveted holes will cost around £600
Spot welding Varies depending on tool used and whether cnc is incorporated If the voltage and time are constant the results are consistent. Medium energy consumption, however the lowest of welding processes The spot weld produced is usually between 5 – 10mm Medium, an engineer could learn the skill in a matter of hours although spot welding in usually automated For 100 spot welds will cost around £800
Water jet cutting Large scale production There is usually a long cleanup time meaning the process can be time consuming Medium-high energy consumption around 25kWH Highly accurate, tolerances within 0.05 mm High, a course would need to be attended, and knowledge of CNC machining and CAD are compulsary Around £50,000t
Laser cutting Large scale production Machines can be left to run with minimal cleanup. High energy consumption
Usually around 24-40 kWH Extremely accurate, tolerances within 0.002 mm High, a course would need to be attended, and knowledge of CNC machining and CAD are compulsory Around
£230,000
Mild steel toolbox
The production of the mild steel toolbox incorporates; cutting, folding and joining techniques.
When the box is made initially, tools from the workshop can be used (maybe with the addition of a box, pan fold machine). Although the work required will be labour intensive there will practically be no costs other than labour and materials. The only machinery that may require power is a drill press which would only be used for a minute period so the power consumption need not even be considered. This method of fabrication will usually take around 2-3 hours to produce 1 box.
When 120 boxes are required to be produced, the previous method is completely ineffective. There are machines/controlled processes out there that would be able to yield 100 times more units, with better tolerances and less waste produced. However, the overall cost of purchasing and operating an industry standard machine (such as a laser cutter) is disproportionate to the profits made by the product. If more toolboxes were made and sold then this method could be considered but otherwise it would take decades for a profit to be made. With this being said, the most cost appropriate way of manufacture would be to take a set of engineering drawings to a manufacturing company would be able to produce 120 boxes in a matter of days.
When 1000 units need to be produced, it is worth purchasing precision industrial machinery, such as a laser cutter, hydraulic brake press and robotic spot welder.
Considerations need to be made such as costs and required skills.
Aluminium pc casing
With the production of the aluminium pc casing it would be ineffective to fabricate using workshop tools.
The pc casing contains lots of holes which would take too long to cut using hand tools such as metal shears and hand files. For the prototyping of the product I would recommend sending the engineering drawings off to a laser cutting company who would be able to make a couple. Although the cost may be high with respect to profits, the pc case could me produced in a matter of days saving time on the whole process.
Once produced with the cut outs of aluminium a box/pan/fold brake could be used to fold the pc casing into shape. If the constructed pc casing is within tolerances and fit for use, it will then be worth purchasing a laser cutter and a hydraulic brake press with dies.
The cost of the laser cutter will be around £223,000, the cost of the hydraulic brake press with dies will be £1500 (second hand quote) and the running cost will be 30kWH x electricity cost.
Although this is a very expensive fabrication process, it is the quickest. With benefits such as minimal waste, highest precision and un-manned operation. This process could yield up to 1000 pc cases in under a week.
Health and safety
For the operation of all if not most of the machinery that has been listed, PPE is required. PPE is an abbreviation of Personal Protective Equipment. In 1992 it became the law that PPE must be used sufficiently in a work environment. The legislation is called “The personal protective equipment regulations 2002” and “the personal protective equipment at work regulations 1992”. This must be enforced by employers and implemented by employers otherwise fines can be issued. Here is a list of the most commonly used PPE. Throughout all operations it is important to follow all regulations including CHIP, COSHH, HASWA, FIRE, PUWER, RIDDOR, First aid, and risk assessments.