Manufacture of Compression Springs Part Two

Finishing a Compression Spring (by hand)

Part 2 of 2

You have to continue counting until you achieve the active target coils in the completed compression spring. Then let it wind a couple of more coils. Keep counting and unfasten the lead screw. The wire lays on itself and starts forming closed coils.

  • Turn off the lathe machine after allowing about two closed coils to wind on the arbour. Don’t allow the end of the pin past your wire guide. Note down the number of final coils done for your reference.
  • Slowly rewind the chuck a little to loosen the spring on the arbour. Don’t allow your pickup pin or chuck jaw to catch the wire front because the spring will loosen on the arbour.

If you have additional wire left, cut it. Afterwards, you have to put the compression spring in the oven to reduce any stress. In this trial process, you have to leave it inside for about thirty minutes. Remember that this process of relieving stress will make the music wire springs contract a little. In the case of stainless steel springs, it expands a little.

After completing the process, allow the compression spring to cool down at room temperature, i.e. by air-cooling. You can measure the spring to find out how near you are to the target. You should check the diameter initially. If the diameter is not correct, you need not bother to do any more measurements. You will require a different arbour which changes all the remaining dimensions of the compression spring.

However, if the diameter is perfect, count the active coils of the compression spring. If would be nice if you ended up quite close to your target. It is fair to be one-fourth of it off on either way for a smaller figure of springs. If it has more than 25% variation, you have to calculate how much additional or lesser you require and try achieving the target coil count next time.

Winding While Not Using a Lead Screw

You may also coil compression spring on your lathe without using the lead screw. But here the problem is that you may not make the same springs. Let us learn how to do it without a lead screw.

  •  Find the required value of spring pitch. Take the wire length and subtract 5.5 times of dia and divide the resulting figure by the figure of active target coils.
  •  As earlier, bring the chalk at your tool post. Move it closer until the arbour puts a couple of marks on the chuck.
  •  Switch on your lathe and allow the chalk to mark a full circle on the arbour.
  •  Bring your tool post slowly towards right using the handwheel by still allowing the chalk touching the arbour. The chalk keeps on marking almost the same place where you want the spring to be made.
  •  You can count the coil marks made by chalk as per your target and halt the rightward movement.
  •  The lathe should run till the chalk marks are there all over the arbour.
  •  Make a winding of trial spring by following the chalk marks as close as possible.
  • If the spring dimensions are incorrect, clean the chalk marks from the arbour and attempt again by recalculating the target pitch.

Making a Compression Spring by Hand

(Part 1 of 2)

This article will explain the process of manufacturing compression springs. The best way to learn the manufacturing process is to try making them by hand. This way, you will be able to appreciate what the machine does. You can find errors in the mechanical process, make the required changes to make it better, and apply your experience from your manual spring-making trials. Since its manufacturing is a little complicated, we are looking in a little more depth than you might expect. After all if you can do this manually, you know “what good looks like” when a machine does it. So, here we discuss in greater detail to catch this process’s nuances and subtleties.

Before we proceed further, we need to gather some information about how the equipment works while manufacturing compression springs. First of all, let us have a word about the pitch of a compression spring. The pitch is the distance from one open coil to another open coil of a compression spring. It is essential to understand that you need to control the wire guide’s speed travelling from the left side to right side when the arbour turns around. By controlling this speed, you can quickly make a spring with a required pitch.

It is easier to do so using a lathe. You can manage the speed by engaging its lead screw. It will automatically maintain the required pitch. However, you will probably be using a hand winder or a drill to control the manual process speed. It is quite challenging to manage it manually. We are not saying that it is impossible to manage it by hand, but comparatively, it is only a little more complicated.

To get around this problem, the spring shops buy a hand winder machine. Such winding equipment can manufacture lightweight springs easily. The hand-winding machine manufacturers have designed the machine in such a way that you can manufacture any quantity of compression springs after setting up that machine. The best part is that all the springs manufactured so will be precisely the same.

However, in the case of a lathe machine, although you may believe that you are doing the similar process every time, you are highly likely to generate different springs, especially in the case of a light wire. That is the differentiation between manufacturing the spring by visual observation and using professional equipment.

Calculating Wire Length

To begin the manufacturing process, you need to estimate the amount of wire required to make one compression spring. You can use the following method:

1. Multiply the wire’s outside diameter (OD) with 3.3 (An approximation of Pi – plus a little extra)

2. Decide the number of coils needed in the resulting spring

3. Multiply the figures for the above two results to give you the required wire length

4. Increase the result of by a little buffer. You can take it as 6 feet for a heavy wire, 3 feet for a medium wire, and 6 inches for a light wire. Here though you are best using your judgement and taking your surrounding’s and the tolerances of your equipment into account.

5. You should note down this resulting figure. If it is much higher than you expect, take a second look at your calculations. They are probably correct. The amount of wire in a spring is often a surprise to someone who has not made seen one being made, However, if you are over by a substantial amount remember to recut. It will save you time in the long run.

 

Before beginning, you need to ensure two things: firstly, engage the back gear, and secondly, put the lead screw in a correct position. Keep in mind that the lathe speed depends upon the wire dia. The higher the diameter, the slower is the lathe speed. Now, let us learn to set the speed of your lead screw.

You have to ensure the lead screw to go left to right on engaging it.

The lead screw speed should be set such that you get appropriate coil spacing along the arbour. You can guess it or measure it mathematically to decide the pitch.

 

The easiest way to estimate the coil distance is as follows:

* · Subtract 5.5 times Wire dia from the wire length

* · Divide this figure by the figure of active coils

Switch on the lathe to involve the lead screw. Tightly hold chalk on the tool post to bring the post near the arbour so that the chalk touches it. Allow the chalk to mark the arbour for at least two turns. Now halt the lathe machine.

You can compare your target pitch with the measurement of the distance of chalk marks. It would be best if you regulated the speed until both measurements are the same.

 

Making The First Trial Spring

After the lead screw speed setting is done, you can proceed with making your first spring.

 

  • Cut the wire length you calculated above. Ensure that nobody else is around to minimise danger during the remaining process. Simultaneously, arrange to heat your oven as well.
  • Feed the wire and bring the wire guide on the left side close to your pickup pin to ensure that your wire engages both of them.
  • Please ensure that you read and understand this step fully well before going further.

You can start coiling. Let the chuck move slowly to one complete coil. Make a minimum of two complete coils, and they should touch each other. You can do so by keeping the wire guide slightly on the left where your wire is put on the arbour.

After making two full coils on the arbour, you should ensure the following two things simultaneously.

 

  • Occupy the lead screw. Provided you wind wires above 0.187 inches, you should not grasp the lead screw controls from above the wire but instead below the wire. It is so because the wire will not cause any injury if it flicks back if your wire guide accidentally breaks.
  • Count you coils from here onwards. Count it once every time the active coil leaves the point which separates it from the end coils passing the chuck top.

Transworld Engineering Ltd. supplies manufacturing solutions through the sale of high quality machinery and engineering support for spring makers and end users in the UK and European market.

To assist our clients, we are providing a database of information related to springs and spring manufacturing solutions. This article represents part one of this database.

Our first part looks at the different types of spring. Each has its set of applications and performs a different basic function. There are fundamental differences between Spring types, how they are made, the materials they may be manufactured from and their application.

 

Compression Springs

“A compression spring resists a load pushed against or onto it”

Compression springs are perhaps the type of spring you are most likely to see in everyday life. They are found in household objects, engines, manufacturing control and have many domestic and commercial uses.

Compression springs provide some flexibility of movement white the force they provide attempts to return the object or objects the spring is attached to back to its original position.

Compressions springs are used in most forms of automation, cars, trains, aeroplanes. They provide such mundane functionality as door-stops. They can provide basic shock absorption functionality. Providing a load with just enough freedom of movement to prevent fixed stress under vibration, while always looking to return the load to its ideal position.

Hole and Rod. Typically, a compression spring is anchored with a rod which runs through its centre, inside the diameter. This rod prevents the spring from distorting, bulging, or fouling under load.

The free length of a spring refers to the length of the spring material unwound

Compression springs can be manufactured in different shapes. Conical, convex, concave and pipe.

 

Extension Springs

“An extension  spring is used to bring things together or place 2 objects attached to the spring under a fixed diametrically opposing load”

Extension springs are most commonly used in situations where some degree of movement should be allowed between 2 objects or one object and its anchor point where the force of the spring encourages the objects to return to their original proximity

For example. In a traditional  “up and over” garage door, closing the door extends the spring. Someone closing the door will feel the tension despite having gravity on their side. The door wants to return to its open position. Only when vertical does the mechanism lock, leaving the spring extended and the locking mechanism preventing the door from opening.

It is the initial tension that determines how tightly together the spring is coiled. This initial tension can be manipulated to achieve the load requirements of a particular application. Designs normally have hooks, eyes, or other interface geometry at the ends which attach to the opposing components. They are frequently used to provide a return force to components that extend in an actuated position.

The reverse is true when opening the door. Once started, with the momentum of the first lift, the door easily returns to its up and over position.

Torsion Springs

“Torsion springs provide a rotary (tangential) force are most typically anchored at both ends and providing  radial resistance (torque) to movement.”

These anchors, sometimes known as legs provide radial resistance. Unlike the lateral forces that other spring types provide or resist, torsion springs provide or resist bending stress.

A good example in everyday use that might visualise this is the common office clip board. The clip at the side or top of the board uses a torsion spring, one leg attached to the board itself, the other to the clip. When the clip is lifted it provides pressure which ensures that, once paper is placed between it and the board the pressure ensure the paper remains fixed.

Torsion springs provide an angular  torque around their circumference. This force is measured ion kilograms per degree around this circumference.

Torsion springs have a maximum deflection. This is the amount of force needed to overstress the spring. The point at which it will fail in terms of providing too much movement or material stress within the spring itself will occur which usually permanently damages the spring

Maximum Load is the amount of force that can be placed on a spring before maximum deflection is reached

 

Principles of Spring Design

There are three core principles in spring design.

  • Heavier gauge spring wire provides a stronger spring
  • The more tightly wound a coil is, the strong the spring will resist
  • More active coils mean less force is required to move the spring a specific distance from its resting point.

There are some caveats to these rules.

Firstly, they apply to springs made from the same material. Depending on the spring type there are materials suitable for different applications that provide different properties. The rules above apply to springs made with the same material.

The same is true for the age and lifetimes uses of any spring. Due to the stresses of use, the material in any spring will degrade in relation to its ability to perform over time. Different materials provide different projected lifetimes depending on their use case.

The endurance limit is defined for ferrous (steel and iron) material as the stress level below which the material can be cycled infinitely without failure. (Shigley et al., 2003)

http://mech.sharif.edu/~mechengdesign/Shigley’s%20Mechanical%20Engineering%20Design_TextBook.pdf

Extended lifetimes can be expected if the spring is made with the correct material for its application. For example, a stainless-steel spring can provide both corrosion resistance and an expected lifespan that can be longer than the application or device it is used in.

However, the correct material for any spring in any given application can vary. There is usually a best material for the job.

Based in Birmingham with a small but highly skilled team, we work to ensure the machines we supply are of top quality, without charging over the odds. Once a machine is sold, we continue to provide manufacturers with expert engineering support and after-sales care.

If you have any queries, please contact us on 0121 772 9796 or using the contact button at the top of any page of this website.

 

 

 

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