Embedded Files
- Marking Out
When marking to size all marking should be done from the datum edge.
A datum edge is a straight edge, running the length of the piece of metal, from which the project is marked to size.
A datum edge, in thin sheet metal, may be prepared as follows:
Rule a straight line with a rule and scriber.
Carefully cut along the line with guillotine.
Test for straightness with a rule.
Mark the edge with a datum edge mark (essentially a 'V' pointing to the datum edge).
An engineering datum used in geometric dimensioning and tolerancing is a feature on an object used to create a reference system for measurement. In engineering and drafting, a datum is a reference point, surface, or axis on an object against which measurements are made.
These are then referred to by one or more 'datum references' which indicate measurements that should be made with respect to the corresponding datum feature .
In geometric dimensioning and tolerancing, datum reference frames are typically 3D. Datum reference frames are used as part of the feature control frame to show where the measurement is taken from. A typical datum reference frame is made up of three planes. For example, the three planes could be one "face side" and two "datum edges". These three planes are marked A, B and C, where A is the face side, B is the first datum edge, and C is the second datum edge.
2. Plasma Cutting
2. Plasma Cutting
Plasma Cutting
Plasma Cutting
If you’ve ever seen Star Wars, then you’ll know what a light sabre is, and (even if you don’t admit it) you’ve probably wanted to have a go of a real one. What’s the closest you’re ever going to get to waving around a super destructive beam of light? Plasma cutting. Except you absolutely shouldn’t wave it around, and they’re not quite ‘destructive’, but they will shoot out a beam of light that cuts through things, which is just as cool.
Plasma is a super-heated column of gas (and the fourth state of matter). It’s formed when compressed air or compressed gases (like nitrogen or argon) make contact with the electrode (which is inside the torch) and ionise to create plasma.
Plasma cutting (plasma arc cutting), therefore, is a melting process that uses plasma and an outside power source to create an electric arc between the electrode and the metal being cut to melt and eject it from the cut.
Plasma can cut through anything electrically conductive; steel, stainless steel and aluminium are all fair game. In comparison, oxy cutting will only work on metals that contain iron, as it works through chemical reactions, such as oxidisation (it’s like a sped-up version of rusting) instead.
Clean Cut vs Severance Cut
Clean Cut vs Severance Cut
You can get two types of cut with your plasma cutter: a clean cut or a severance.
Clean cut: precisely what it says, a smooth, clean cut on the metal.
Severance: a cut all the way through, but it won’t be smooth, and if you plan on working on it after, you’ll need to clean it up.
Every plasma machine will have a maximum clean cut thickness and a maximum severance. These indicate how thick the metal can be if you want a good quality cut and how thick the metal can be if all you need is to get through it. The severance thickness will always be more than the clean-cut thickness.
The metal thicknesses will vary depending on how many amps you can use (your machine model will determine your max amps) and what kind of metal you’re using. Aluminium is the softest metal, steel is harder and stainless steel is the hardest of the three. Despite their hardness, aluminium and stainless steel have a higher viscosity (which is a fluid’s resistance to flow) than mild steel. Their max cutting thickness is usually smaller than steel’s max thickness because of their viscosity.
Travel Speed
Travel Speed
Your travel speed will depend on how thick the material is that you are cutting. The sparks should be coming out straight down on the other side of the plate when travelling at the correct speed.
If you’re cutting too fast, the sparks will spray at a very steep angle in the opposite direction than you’re cutting. Some sparks might even fly out from the top.
If they’re flying out of the top, it means your plasma arc isn’t cutting all the way through, and the sparks are bouncing off the part that is still joined together.
If they are coming out straight down, but you’re getting stuck in grooves, you’re cutting too slow. Cutting too slow results in a wider kerf (the material lost due to the cutting process) and dross (excess metal from the cut that hardens on the bottom of the piece and needs to be cleaned off). Cutting too slow also makes the cut much harsher; it won’t be as smooth as it could be.
Cutting Your Metal
Cutting Your Metal
Before you cut, make sure to mark out where you want to cut, whether it’s a straight line or a shape; freehand cutting will always be worse than a guided cut.
To do the actual cut is relatively easy. Once your machine and torch are all ready to go, place the tip of your torch flush with the metal where you’re cutting, pull the trigger and away you go.
For extra accuracy on your cuts, add a piece of sheet metal to push the torch up against to keep your lines straight (if you want straight lines). You can also measure from the shield’s outer edge to the centre of the cutting tip opening and add that width between the line you wish to cut and the sheet metal you’re leaning against. This will mean that your cut will be dead on, rather than slightly to the side of where you drew it. You can get circle cutting attachment kits for some plasma torches to help you make perfect circles.
If you are starting in the middle of a plate and piercing straight through, it’s a good idea to angle the cutter at roughly a 45° angle so that the metal doesn’t jump back at the shield and clog it up.
Once you’ve pulled the trigger and the plasma has pierced all the way through the metal, you can angle back up to 90° and begin cutting. If you’re just starting from an outer edge, you can just start at 90°.
If you’re gouging instead of cutting, the process is almost the same. You’ll still run your torch along in a line, but rather than hold it straight up and down, keep it at a roughly 45° angle from the metal (as if you’re pushing a MIG torch), as this helps avoid going through the piece.
Even if you have the right travel speed, which corresponds with the amps and air pressure, plasma cutting will leave a bit of dross (leftover metal) on the bottom. This can be removed with a chipping hammer; it’s generally not too thick, so it’s easy to clean up.
Click on the following link for '9 Tips and Tricks to improve your Plasma cutting'.
Oxy cutting vs. Plasma cutting
There are quite a few differences between the two methods, from gas requirements to preheating, travel speed, and portability. So, which is going to work best for you?
Plasma Cutting
Pros
Cuts through all metals – ferrous and non-ferrous
No preheating
Only needs compressed air
Some machines come with a built-in air compressor
Stop/start with a single button press
Less mess and less clean up
Machines are generally lightweight
Faster travel speeds, especially on thin materials
It’s safer
Cons
Max cut thickness is determined by the machine
The machine and air compressor require a power source
Oxy Acetylene
Pros
It doesn’t need a power source
Cuts through thick material
It’s multipurpose – you can weld, gouge, braze, heat and solder, as well as cut
Cons
Only cuts through ferrous metal (steel)
Metal needs to be preheated before it’s cut
It requires two (flammable) gases
Longer setup time
The torch needs to be manually lit and extinguished
Incredibly messy with lots of clean up
3. Machining
3. Machining
Turning Basics (Lathe)
Turning Basics (Lathe)
Turning may be used to produce a constant diameter, a tapered diameter, or a contoured diameter (sphere, radius, or other non standard shape). Straight turning (parallel turning) of a constant diameter is a very common operation performed on the lathe. During straight turning operations, the workpiece can be held in a chuck, collet, between centres, or on a mandrel. A steady or follower rest may also be used for extra support of very long work.
When performing parallel turning, the turning tool must always be set on centre just as when facing. Most turning is done from the tailstock toward the headstock using a right-hand tool. To turn from the headstock toward the tailstock, use a left-hand tool.
Shouldering combines turning and facing to creat a step where two different diameters meet. Three common shoulder types are square, filleted and angular. To machine shoulders, first rough the smaller diamter and shoulder length with the cutting tool set in the positionn recommended for turning. Be sure to left enough material for finishing the shoulder to the desired shape.
To finish a square shoulder, the tool position needs to be changed so only the tip will contact the shoulder when the cross slide is fed across the shoulder. Touh off the tool against the roughed diameter and set the cross slide dial to zero. Take small depth cuts across the should to establish a flat surface, using the cross-slide zero to avoid touching the diameter.
Facing
Facing
A very basic operation is called ‘facing off’. A piece of steel has been placed in the chuck and the lathe cutting tool is used to level the end. This is done by turning the cross-slide handle so that the cross-slide moves and the cutting tool cuts the surface of the steel. Only a small amount of material should be removed - each pass of the cross slide. After each pass of the cutting tool the top slide can be rotated clockwise to move the tool forward approximately 1mm. This sequence is repeated until the steel has been levelled (faced off).
Taper
Taper
When turning a short taper the topslide is set a the required angle. This is normally done by loosening two small allen screws and then rotating the topslide to the angle and tightening back up the two allen screws.
When the chuck is rotating the topslide handle can be rotated slowly by hand in a clockwise direction. A small amount of metal is removed each time until the taper is formed. If too much steel stands out from the chuck the steel will vibrate and the surface finish will be very poor.
Parting
Parting
The lathe will often be used to perform cutoff or parting operations that use a special narrow cutting tool to cut off the end workpiece to a desired length. However, you should never perform parting operations on work that is mounted between centres.
Sometimes the same tool can be used for both standard grooving and parting operations. Parting tools are available with a cutting face that is angled either to the left or right to minimise the amount of uncut material left on the part that is cut off. These tools are available in HSS or inserted carbide types.
Parting (and grooving) operations require special care because of the substantial width of the cutting tool and the large amount of contact between the tool and the workpiece. They require extremely rigid setups, ensuring the tool tip is on centre and the tool is kept as short as possible to minimise vibration and chatter. The tool must be set 90 degrees to the lathe's ways so that the sides of the tool will not rub the sidewalls of the groove and create excessive heat.
When parting, lock the carriage to the ways to prevent any unwanted carriage movement. Spindle speeds are also reduced to about 1/4 to 1/3 of the nominal turning speed. Use plenty of cutting fluid and continuously feed the tool with the cros slide to the desired depth or until the part is completely cut off.
Knurling
Knurling
Knurling is producing a raised pattern on the circumference of a workpiece. knurling is accomplished by pressing a knurling tool with two wheels, called rolls, against a rotating workpiece. Basic knurl patterns are straight and diamond, with both available in fine, medium, and coarse types. The pattern is raised because instead of the material being cut as in most machining operations, the knurling tool forms the material by applying pressure.
The most common reason for producing a knurl is to proivde a gripping surface on handles, knobs, or levers. Knurling can be used for decorative purposes or to slightly increase the diameter of material to repair worn cylindrical parts.
Milling Basics
Milling Basics
Many different operations can be performed using the different types of milling cutters, but there are a few basic principles that apply to all operations. Face milling is using the face of a cutting tool to machine a surface as shown in the image to the right. Peripheral milling is using the outside periphery of the cutting tool to machine a surface.
When peripheral milling, two different types of situations can exist depending on the relation between the cutter rotation and the feed direction. Conventional milling is feeding the workpiece against the rotation of the cutting tool. This method is normally used when machining on the vertical mill. It provides a measure of safety because the tool tends to push away from the workpiece, requiring constant feed pressure to continue cutting. The drawback to conventional milling is that the surface finish is often not as smooth as desired.
The other machining process occurs when the workpiece is fed with the rotation on the cutting tool. This is called climb milling. Climb milling should only be used under certain conditions on the vertical mill because the work can be pulled into the tool uncontrollably and cause tool breakage and workpiece damage. One advantage of climb milling is that is provides a smoother surface finish than conventional milling when performed properly. It is normal to rough a surface using deeper cuts close to the final size by conventional milling, then take light cuts using climb milling to reach the final size and create a smoother surface finish.
4. Welding
4. Welding
GMAW Welding
GMAW Welding
Gas Metal Arc Welding (GMAW) is often called MIG welding. MIG stands for metal inert gas. This form of arc welding is used extensively in the metal and engineering industry.
MIG welding is a semi automatic arc welding process in which an electric arc is struck between a continuously fed electrode wire and the work.
Electric current is transferred to the wire through the contact tip in the welding gun or torch. The electrode is not flux-coated. It is, in most MIG welding applications, a bare solid wire that becomes the filler material as it is continuously fed to the weld area during the welding process.
The wire, weld pool and the general weld area are protected from atmospheric contamination by a shielding gas which is fed through the welding torch. Shielding gases are selected to suit the particular job. Argon and CO2 mixtures are generally used when welding steel.
MIG welding combines the use of electrical energy, continuously fed filler metal and shielding gas into a fast, efficient and economical process that is used throughout industry.
Advantages of MIG Welding
Advantages of MIG Welding
Gas metal arc welding has numerous advantages over other types of welding. Advantages which relate to the use of solid filler wire in the MIG welding process are included in the list which follows:
faster welding speed
flux is not used
there is no slag to be chipped off the finished weld
very little smoke or fumes are produced
welding can be performed in all positions
in some applications, the MIG process is capable of welding mild steel without edge preparation if necessary
most metal can be welded by changing the electrode wire and sometimes the shielding gas
there is less distortion than with other welding processes
spot welds can be performed very efficiently
there is very little wastage of consumables (filler wire).
Duty cycle is a term used to describe current output rating over a given period of time. The duty cycle time on most MIG welding plants is five minutes, however, some late models have a ten-minute cycle. For example, a duty cycle of 60% at 200 amps over a 5-minute cycle indicates that the power source can be used at 200 amps for 3 minutes in every 5-minute period, then off for 2 minutes. Similarly, a duty cycle of 100% at 180 amps means that the machine can be used continuously at 180 amps.
Modes of metal transfer
Modes of metal transfer
The mode, or type of metal transfer in the MIG welding process depends on the current, arc voltage, electrode diameter and the type of shielding gas used. Metal transfer can be genereally described as falling into one of four categories:
short arc transfer
spray transfer
globular transfer
pulsed arc transfer
Transfer comparisons
Short arc metal transfer is also known as dip transfer. In the short arc range, low current and voltage settings are used to produce a short-circuiting arc. When welding commences, an arc is struck and a weld pool if formed. The tip of the electrode wire dips into the weld pool and causes a short circuit.
This results in a rapid temperature rise in the wire and the end of the electrode wire is melted off. An arc is immediately formed between the tip of the wire and the weld pool. This arc maintains the electrical circuit and produces sufficient heat to keep the weld pool fluid.
The wire continues to feed and the tip once again dips into the pool. This sequence is repeated at a frequency of up to 200 times per second until the welding torch trigger is released. The short arc method of transfer is suitable for positional welding and has the advantage that the heat input to the work piece is kept to a minimum. This limits distortion and enables thin sheet materials to be welded.
Identifying welding defects
Identifying welding defects
Undercut could be caused by voltage that is too high, welding speed that is too slow for the current, or a torch angle that is too low.
Lack of penetration results from current that is too low, inconsistent current pickup at the contact tip, stickout that is too great, joint angle too narrow or insufficient gap.
Excessive spatter is often caused by voltage that is either too high or too low, incorrect shielding gas or a blockage in the gas delivery system.
Irregular weld shape may be caused by the operator's technique, current that is too high for the voltage, excessive stickout, travel speed too slow, or excessive gas flow.
Porosity can result from insufficient shielding gas, dirty weld area, arc voltage too high, excessive gas flow rate or air getting into the gas shielding system.
Metal Preparation
Unfortunately, MIG isn’t as forgiving as stick welding, so you’ll need to either wire brush or grind your workpiece so that it’s clean. Otherwise, you won’t get a quality weld.
Starting Your Weld
Now that your machine and workpiece are set up, you’re ready for the next step: starting the weld. With the voltage and wire speed set, the rest of the welding is up to you.
There are three main factors to consider when doing a weld:
Work angle
Travel angle & distance
Travel speed
This is true regardless of whether you are TIG, MIG or stick welding.
1. Work Angle
Your work angle is your torch in relation to the angle of the joint. There are a few different joint types, and several positions these joints can be found.
2. Travel Angle & Distance
When MIG welding, you can travel at a pushing or a pulling angle, though it does depend on which wire is in the machine.
If you’re using mild steel, stainless steel or aluminium, you’ll want to travel at a pushing angle (torch over the weld pool pushing towards the metal).
If you’re using flux-cored wire (gasless), you’ll want to travel at a pulling angle (torch in front of the weld pool and dragging towards the metal).
Whether you’re pushing or pulling, you want to keep your torch at a 10° to 15° angle. If your angle becomes too deep or parallel with the metal you’re welding, you increase the spatter amount, decrease penetration, and create more mess that you’ll have to clean up later.
For example, say you’re welding in a fillet joint (a corner join) with a standard steel wire. Your torch will be angled into it at a 45° angle, and then you’ll angle slightly to the side (in a push direction) so that your gas can cover the weld pool and in front of the weld as you go.
The other important thing to watch is the distance of your wire ‘stickout’. You want to maintain the 1cm of stickout throughout the joint for the best weld. If your wire is sticking out too far as it’s feeding and your torch nozzle is getting further away from your workpiece, it will cause a few problems.
The first problem is that your feeding wire acts as a resistor, so the longer it is coming out of the torch and into the weld pool, the lower your machine will drop the amps, so it won’t run as well. The second problem is that your shielding gas will no longer be able to reach your weld pool, and you’ll increase the number of defects – like porosity – in your weld.
3. Travel Speed
Travel speed is how fast you are moving the torch along the weld. This is separate from the wire speed, but the two do impact each other.
If you’re moving too fast for your set wire speed, then there’ll be nothing being fed into the weld pool to create a proper weld.
On the other hand, if you’re moving too slowly or you have too much wire being fed through, you’re going to have a fat weld join that will need to be ground back, causing a lack of fusion on the toes (edges of the weld).
You want to move at a speed that corresponds with your settings. Keep your travel speed consistent across the entire weld for the best quality result.
Making the Weld
Place your cleaned workpiece in front of you in a way that when you begin welding, your hands can move freely and steadily all the way along the joint. It’s a good idea to have something to steady your hands against as they go along the weld so that you can maintain your angle and distance.
Check that your earth clamp has been attached to a metal surface, such as a (clean) metal workbench or the workpiece, because if your earth clamp isn’t grounded, your machine won’t start.
If you’re making a fillet join, you can use a magnetic welding clamp to hold your two pieces of metal together. Aluminium isn’t magnetic, however, so a manual clamp will be needed.
The kind of wire you are using will determine the technique required when welding.
Push Technique (Gas-shielded Wires)
The wire is located at the leading edge of the weld pool and pushed towards the un-melted work surface. This technique offers a better view of the weld joint and direction of the wire into the weld joint.
The push technique directs the heat away from the weld puddle, allowing faster travel speeds and providing a flatter weld profile with light penetration – useful for welding thin materials. The welds are wider and flatter, allowing for minimal clean up/grinding time.
Fusion Welding
Fusion Welding
In fusion welding the edges of the parts to be joined are melted and fused together to form a high strength joint. Additional weld metal can be added from a hand held filler rod.
Filler rods are available in several sizes (diameters). Different types of rods are manufactured to provide a range of weld metal properties. Filler rods should be selected to suit the type of metal and the requirements of the job. Always refer to the manufacturer's specifications when you are selecting filler rods for a particular job.
For all mild steel welding operations, mild steel filler rods are used and no flux is necessary. The mild steel rods provide sufficient strength and ductility for the job. The size of the filler rod used will dpend on the thickness of the parent metal. For work up to 3mm thick a 1.5mm rod is satisfactory and a 3mm rod would be suitable for 5mm plate. If the rod is too small it will melt before the parent metal reaches welding temperature and if the rod is too big the parent metal may overheat before the rod can melt. A neutral heating flam should be used and the gas mixture adjusted to produce the heat required for the job.
Forward welding (leftward welding) is the technique most suited to the types of projects undertaken in the metal workshop. When this welding technique is used you move the filler rod ahead of the torch which travels from right to left (for a right hand welder). point the flame in the direction that the weld is being made, hold the tip at about 60 degrees to the surface of the plate and hold the filler rod at around 35 degrees to the work.
The edges of the plate must be heated uniformly just ahead of the molten puddle. Move the tip and filler rod in half circular weaving movements. This technique helps you control the heat and enables he rod end and side walls of the plate to be melted into a uniformly distributed molten puddle. The envelope of the flame protects the molten weld pool from contamination by the atmosphere.
Soldering
Soldering
Soldering is a process of joining two metal surfaces together using a filler metal called solder. The soldering process involves heating the surfaces to be joined and melting the solder, which is then allowed to cool and solidify, creating a strong and durable joint.
Soldering is commonly used in the electronics industry for the manufacture and repair of printed circuit boards (PCBs) and other electronic components. It is also used in plumbing and metalwork, as well as in the manufacture of jewelry and other decorative items.
The solder used in the process can vary in composition, with different alloys used for different applications. Common solder alloys include tin-lead, tin-silver, and tin-copper, among others. Lead-free solder has also become more widely used in recent years due to health and environmental concerns associated with the use of lead.
Tinning soldering bits
Tinning the tip means covering the tip with a layer of solder. Most modern soldering tips are composed of a copper core (copper conducts heat excellently) encased with nickel-plated iron to repel solder. However, iron tends to oxidize quickly. Tinning the tip extends the life of the tip by preventing oxidation and corrosion, but it also causes the solder wire to melt and flow more easily over the parts you are joining, making the overall soldering process go smoothly. You will want to tin your tips when you first purchase them before use, when the iron is sitting idle in the holder during use and when you finish soldering, before you pack your tips for storage.
First you will want to heat the iron up to operating temperature and wipe the tip on a damp soldering sponge to gently clean it. If the tip is very dirty you may want to dip the tip in a commercial tip cleaning paste and then wipe it clean on the damp soldering sponge. Once the tip is clean let it return to the operating temperature. Apply a small bead of solder to the copper part of the tip. Wipe away any excess solder on the damp sponge. A small amount should remain on the tip giving it a shiny appearance. The tip is now tinned and ready for use.
Brazing
Brazing
Braze welding, or bronze welding, is a process of joining similar or dissimilar metals by using the heating flame and a copper-tin-zinc (bronze) filler rod. Braze welding is not a fusion welding process since the parent metals to be joined are not heated to their melting points. The bronze filler rod has a lower melting point than the parent metal or metals.
Bond strength of the weld depends on the surface penetration of the molten bronze filler rod and the parent metal. three distinct factors contribute to bond strength between bronze and the parent metal:
Tinning: The clean surafce of the parent metal should be properly 'tinned'. A thin film of molten bronze is applied with the aid of flux. The bond is produced by the molecular action at the faces of the molten bronze and the parent metal.
Interalloying: In a narrow zone at the join, the constituents of the bronze diffuse into the parent metal while a corresponding diffusion of the parent metal into the bronze takes place, forming an alloy of the bronze and parent metal.
Intergranular penetration: The action of the bronze in the parent metal opens up the crystalline grain structure of the parent metal allowing the bronze to penetrate, producing a physical bond between the bronze and parent metal.
Braze welding should not be used where the part is subject to temperatures above 340 degrees celsius because of the decreased strength of the bronze at these temperatures.
5. Modifying Properties
5. Modifying Properties
Anodising
Anodising
Anodising is an electrochemical process that converts a metal surface into a decorative, anodic oxide finish. The anodic oxide structure is made up of a layer of aluminium oxide on the surface of the aluminium which slightly increases the thickness of the metal.
The aluminium oxide is not attached to the surface like paint or plating. It is fully integrated with the underlying aluminium substrate, which stops it chipping or peeling. It has a porous structure that allows for secondary processes such as colouring and sealing.
Anodising is achieved by immersing the aluminium into an acid electrolyte bath and then passing an electric current through it. A cathode is mounted to the inside of the anodising tank; the aluminium acts as an anode, so that oxygen ions are released from the electrolyte to combine with the aluminium atoms at the surface of the part being anodized. Anodising is effectively a process of highly controlled oxidation.
It requires both a specialist skill and an exact grade of metal to achieve the desired result, so it's not an easy technique to perfect! Accordingly many manufacturers steer clear of the method and only offer plated finishes, albeit the number of finishes possible is more limited using this process.
Anodising can only be applied to aluminium. This finish is ideal in external environments due to its durability because its UV stability will protect the light frame against weathering, subject to being installed away from acidic materials such as mortar or saline environments. Despite being durable, any small scratch can cause this to corrode quickly. Anodising is the most premium finish, compared to plating and powder coating and can achieve a variety of finishes which are authentic to the material they are mimicking.
Advantages
It's easy to maintain; it can be cleaned with water and mild detergents to restore the original lustre,
UV stable and will not peel or flake, as it is integral to the metal,
Protects the base metal to offer a deeper, richer metallic appearance,
Offers a wide range of high quality architectural finishes.
Disadvantages
Can only use specific grades of aluminium for this process,
Cannot be used on Stainless Steel, which is durable to mortar, salt, chlorine and marine environments,
This method draws from the base metal so it can be subject to colour variations. In high grade metals a 95% match is possible between batches, in low grade metals no match is possible,
Consequently harder to replicate consistency between batches compared to plating,
The most expensive solution for small quantities (requires a higher-grade alloy in addition to the already high set up costs).
Plating
Plating
Plating is a hydrolysis process, popular for specific architectural finishes that coats a metal with a thin layer of another metal.
There are two types of plating processes:
Electroplating – This process involves passing an electric current through a solution called an electrolyte. This is done by dipping two terminals called electrodes into the electrolyte and connecting them into a circuit with a battery or other power supply. The electrodes and electrolyte are made from carefully chosen elements or compounds. When the electricity flows through the circuit they make, the electrolyte splits up and some of the metal atoms it contains are deposited in a thin layer on top of one of the electrodes. When this is done it becomes electroplated.
Electroless Plating - Involves several simultaneous reactions in an aqueous solution, which occur without the use of external electrical power. Nickel plating is an example of common electroless plating method.
Common materials used for plating include:
Gold, Silver, Copper, Rhodium, Chrome, Zinc, Nickel, Tin, Alloy, Composite, Cadmium
Advantages
Can plate a range of high quality metals,
Offers a protective layer against corrosion,
Nice range of specific but limited popular architectural finishes,
Cost effective,
Provides increased strength and hardness.
Disadvantages
Subject to cracking and chipping in hard wearing environments,
Can be a lengthy process as many of our finishes are subsequently hand polished to achieve the desired high quality effect,
The process if not managed carefully can show up surface imperfections such as pitting marks or scratches. This is even more profound on cheaper metals.
What are treatments?
What are treatments?
Annealing is a process that involves heating and cooling which is usually applied to induce softening. The method and temperature range for heating and cooling varies for different metals. In non-ferrous metals cold working usually induces hardening. Annealing realigns the crystalline structure and softens the metal. For example, copper can be annealed by heating to a dull red and then quenching in water.
Hardening and tempering of engineering steels is performed to provide components with mechanical properties suitable for their intended service. Steels are heated to their appropriate hardening temperature (usually between 800-900°C), held at temperature, then "quenched" (rapidly cooled), often in oil or water. This is followed by tempering (a soak at a lower temperature) which develops the final mechanical properties and relieves stresses. The actual conditions used for all three steps are determined by steel composition, component size and the properties required.
Hardening and tempering can be carried out in "open" furnaces (in air or combustion products), or in a protective environment (gaseous atmosphere, molten salt or vacuum) if a surface free from scale and decarburisation (carbon loss) is required ("neutral hardening", also referred to as "clean hardening").
All tool and die steels must be treated to develop optimum properties in terms of hardness, strength, toughness and wear resistance. Almost all are hardened and tempered.
Hardening involves controlled heating to a critical temperature dictated by the type of steel (in the range 760-1300 C) followed by controlled cooling. Dependant on the type of material, appropiate cooling rates vary from very fast (water quench) to very slow (air cool).
Tempering involves reheating the hardened tool/die to a temperature between 150-657 C, depending on the steel type. A process which controls the final properties whilst relieving stresses after hardening, tempering can be complex; some steels must be subjected to multiple tempering operations.
What are the benefits?
What are the benefits?
Hardening and tempering develops the optimum combination of hardness, strength and toughness in an engineering steel and offers savings in weight and material. Components can be machined or formed in a soft state and then hardened and tempered to a high level of mechanical properties without having to pay for more expensive heavier materials.
What are the limitations?
What are the limitations?
The response of a steel component to hardening and tempering depends on steel composition, component size, and method of treatment. Every steel has a "limiting" section size above which full hardening cannot be achieved. A higher grade of steel will be required to ensure optimum properties in a larger section. It may be possible to harden larger components in lower-grade steels by using non-standard treatments such as faster quench rates or lower-temperature tempers. Faster quench rates always increase the risk of distortion or cracking, and low-temperature tempers can seriously impair mechanical properties such as toughness. Serious consideration should be given to these facts before asking for non-standard treatments to be carried out. Almost all engineering steels containing over 0.3% carbon will respond to hardening and tempering.
Other limiting factors include the presence of other alloy metals such as aluminium, nickel and chromium; and the steel conditions, shape, size and availability of suitable equipment.
Hardening: Quenching Process
Hardening: Quenching Process
Tempered Steel
Tempered Steel
6. Thread Cutting
6. Thread Cutting
Threading taps are a tool used to create screw threads (tapping) into a pre-drilled hole, to create a clean fitting for bolts in metals and plastics. Used in engineering and manufacturing, threading taps work like a drill but due to the unique shape of a tap, when screwed into a piece of material, screw threads are created. Threading taps must be used in a predrilled hole and cannot be used for drilling entire holes.
The difference between taps and dies is that taps are used to create or repair threads in holes which is ideal for nuts. Dies are used to cut threads on materials such as steel rods to allow a fitting to be screwed on and attached (threading).
The tap is designed for internal thread cutting, so this would be used on the fastener hole or a nut, whereas a die is used for the external thread, like on a bolt. In other words, tapping uses the tap part of the set and creates internal threads and threading is the process used by the die to cut external threads.
What is the difference between an Intermediate, Tapered and Bottom Tap?
There are three common types of taps; Taper Taps, Intermediate taps and Bottoming taps. Taps are held in tap wrenches so you can apply the rotational force necessary for the threading process.
Taper Taps are used to start the thread. They usually have an eight to ten thread lead. This means that the thread on the tap is ground back to taper the teeth over seven to nine threads.
Intermediate taps are used after the thread has been started with a taper tap. These taps usually have a three to five thread lead.
Bottom taps are used to finish the thread in a blind hole. They have a one to one and a half thread lead and are often called plug taps.
Technique
The tapping hole is pre-dilled and should be smaller than the tap. The exact drill size required can be found from a tapping drill chart. However, for most metric threads the size can be calculated by the following formula:
Tapping hole = D - p.
D is the outside diameter of the tap and
p is the pitch.
Always use a suitable cutting oil when you are tapping and back off the cutting action when you feel resistance, every half turn, to break off the waste material. Taps are very hard and therefore very brittle. They will break if you apply too much pressure, particularly if you allow the waste material to build up.
7. Finishing
7. Finishing
Powder Coating
Powder Coating
Powder coating is a type of coating that is applied as a free-flowing, dry powder. Unlike conventional liquid paint which is delivered via an evaporating solvent, powder coating is typically applied electrostatically and then cured under heat or with ultraviolet light. The powder may be a thermoplastic or a thermoset polymer. It is usually used to create a hard finish that is tougher than conventional paint. Powder coating is mainly used for coating of metals, such as household appliances, aluminium extrusions, drum hardware, automobiles, and bicycle frames.
Properties
Because powder coating does not have a liquid carrier, it can produce thicker coatings than conventional liquid coatings without running or sagging, and powder coating produces minimal appearance differences between horizontally coated surfaces and vertically coated surfaces. Because no carrier fluid evaporates away, the coating process emits few volatile organic compounds (VOC). Finally, several powder colors can be applied before curing them all together, allowing color blending and bleed special effects in a single layer
While it is relatively easy to apply thick coatings that cure to smooth, texture-free coating, it is not as easy to apply smooth thin films. As the film thickness is reduced, the film becomes more and more orange peeled in texture due to the particle size and glass transition temperature (Tg) of the powder.
Most powder coatings have a particle size in the range of 2 to 50 μm, a softening temperature Tg around 80 °C, a melting temperature around 150 °C, and are cured at around 200 °C for a minimum of 10 minutes to 15 minutes (exact temperatures and times may depend on the thickness of the item being coated). For such powder coatings, film build-ups of greater than 50 μm may be required to obtain an acceptably smooth film. The surface texture which is considered desirable or acceptable depends on the end product. Many manufacturers prefer to have a certain degree of orange peel since it helps to hide metal defects that have occurred during manufacture, and the resulting coating is less prone to showing fingerprints.
Advantages
Powder coatings contain no solvents and release little or no amount of volatile organic compounds (VOC) into the atmosphere. Thus, there is no need for finishers to buy costly pollution control equipment. Companies can comply more easily and economically with environmental regulations, such as those issued by the U.S. Environmental Protection Agency.
Powder coatings can produce much thicker coatings than conventional liquid coatings without running or sagging.
Powder coated items generally have fewer appearance differences than liquid coated items between horizontally coated surfaces and vertically coated surfaces.
A wide range of speciality effects are easily accomplished using powder coatings that would be impossible to achieve with other coating processes.
Curing time is significantly faster with powder coatings compared to liquid coatings especially when using ultraviolet cured powder Coatings or advanced low bake thermosetting powders.
Oiling
Oiling
Oil not only lubricates metal parts and allows them to move with less friction, but oil also forms a protective barrier against rust. The principle here is pretty simple; with a coating of oil, moisture can't react with the iron in the metal and cause rust.
Although the theory behind this process works, the steel must be thoroughly cleaned of scale and moisture prior to oiling. The oiling process is ongoing, requiring reapplication to ensure the product always has a protective coating.
The benefit of this finishing process is it is cheap and easily accessible. If rust appears, the steel simply needs to be filed or ground to remove the rust and oil reapplied.
Polishing & Buffing
Polishing & Buffing
Polishing and buffing are finishing processes for smoothing a workpiece's surface using an abrasive and a work wheel or a leather strop. Technically polishing refers to processes that use an abrasive that is glued to the work wheel, while buffing uses a loose abrasive applied to the work wheel. Polishing is a more aggressive process while buffing is less harsh, which leads to a smoother, brighter finish. A common misconception is that a polished surface has a mirror bright finish, however most mirror bright finishes are actually buffed.
Polishing is often used to enhance the appearance of an item, prevent contamination of instruments, remove oxidation, create a reflective surface, or prevent corrosion in pipes. In metallography and metallurgy, polishing is used to create a flat, defect-free surface for examination of a metal's microstructure under a microscope. Silicon-based polishing pads or a diamond solution can be used in the polishing process.
The removal of oxidization (tarnish) from metal objects is accomplished using a metal polish or tarnish remover; this is also called polishing. To prevent further unwanted oxidization, polished metal surfaces may be coated with wax, oil, or lacquer. This is of particular concern for copper alloy products such as brass and bronze.
While used less extensively than traditional mechanical polishing, electropolishing is an alternative form of polishing that uses the principles of electrochemistry to remove microscopic layers of metal from a base surface. This method of polishing can be fine-tuned to give a wide range of finishes, from matte to mirror-bright. Electropolishing also has an advantage over traditional manual polishing in that the finished product will not experience the compression and deformation traditionally associated with the polishing process.
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