ME5603 Metal Forming TechnologyMETAL SPINNING, FLOW TURNING &

FLOW FORMING

By: A/P Lee Kim Seng

METAL SPINNING, FLOW TURNING & FLOW FORMING

Flow turning or spinning is the plastic deformation of metal to the shape of a rotating mandrel with forces applied by a tool or roller.

A/P Lee Kim Seng

It is an efficient and economical way of producing radial symmetrical parts such as cones, hemisphere and cylinders etc.

METAL SPINNING, FLOW TURNING & FLOW FORMING (Cont..)

A/P Lee Kim Seng

A/P Lee Kim Seng

A/P Lee Kim Seng

Tools Used in Metal Spinning, Flow Turning & Flow Forming

A/P Lee Kim Seng

Metal Spinning, Flow Turning & Flow Forming Processes in action

A/P Lee Kim Seng

A/P Lee Kim Seng

A/P Lee Kim Seng

In conventional metal spinning, a flat blank or preform is formed into another rotationally symmetrical rotationally symmetrical shapeshape with the aid of a stick tool or spinning roller. Each element in the blank undergoes appreciable radial displacement from its original position whereas the change in the thickness is virtually zero.

A/P Lee Kim Seng

A/P Lee Kim Seng

Flow turning (sometimes known as power spinning, shear spinning, shear forming, spin forging and hydro spinning), resembles conventional spinning, in that a flat disc is transformed into final shape by localized plastic deformation between a mandrel and a roller.However, during flow turning, each element in the blank retains its radial position.

A/P Lee Kim Seng

The final wall thickness of the component is given by

tf = to sin ααααo

For preformed cone

(t1 = to sin ββββ)

tf = t1sin ααααo

sin ββββ

A/P Lee Kim Seng

The pre-requisite for flow turning is axial symmetry, thus all conic sectionsall conic sections can be formed provided a mandrel is made for the required section and the roller can be made to describe the required profile.Only one thickness can be produced when flow turning a flat blank with a given thickness at a certain cone angle.

A/P Lee Kim Seng

A/P Lee Kim Seng

Flow forming, sometimes referred to as flow turning of tubestubes, is a rotary point extrusion process. There are two modes of operations, namely the forward and backward methods.

A/P Lee Kim Seng

A/P Lee Kim Seng

Flow Turning Spinning

1. Flow turning is a shearing operation whereasconventional spinning is one of bending and drawing with the inherent problems of spring back and wrinkling.

2. Flow turning requires much higher forcescompared to conventional spinning.

A/P Lee Kim Seng

Flow Turning Spinning

3. In conventional spinning, the deformation zone extends into the unspun flange, and theproblem of instability of the flange arises as a result on induced stresses, whereas in flow turning the deformation is localized.

4. In conventional spinning, the thickness remains virtually constant while the blank diameter changes. In flow turning, thethickness is reduced but the blank diameterremains unchanged.

A/P Lee Kim Seng

Flow TurningSpinning

In addition, flow turning process has considerable advantages over the conventional spinning process in forming axi-symmetrical conical components. These advantages include:

• Close dimensional accuracy.

• Higher output rate because only a single pass is needed.

A/P Lee Kim Seng

Flow TurningSpinning

• Base and unformed rim retain original thickness giving the component added rigidity.

• Simple machine operation by semi-skilled personnel.

• Lower material and labor cost (less wastage).

• Improved metal properties due to work hardening.

• Flexibility in production as resetting of the machine is easy and takes little time.

A/P Lee Kim Seng

Flow Turning

• It is limited to the forming of radially symmetrical, hollow conical parts only.

• The ductility and elongation of the material is reduced.

• It requires higher forces, thus larger machine capacities, when compared to spinning.

• Machine costs are higher.

The disadvantagesdisadvantages of flow turning process are:-

A/P Lee Kim Seng

Perhaps one of the greatest drawback to the wider adoption of flow turning or spinning as a production method is the comparatively slow rate of production when compared with other forming processes, such as deep drawing.

A/P Lee Kim Seng

Some practically aspects:

i) Flow turning machine and its applications

ii) Flow formability

iii) Accuracy, tolerance & surface finish

iv) Material properties

v) Lubricant

vi) Costs

vii) NC & CNC machineA/P Lee Kim Seng

• Horizontal & Vertical model with various capacities.

• 1 to 3 forming rollers.

A/P Lee Kim Seng

Flow turning machines are suitable or adaptable for metal spinning as well as flow forming – able to form more complex components; often combining spinning, flow turning & flow forming in 1 machine cycle – thus making the process much more flexible & economicalmore flexible & economical.

A/P Lee Kim Seng

Applications:Flow turning process is used in aircraft and aerospace industries to produce engine, rocket and missile components, such as shrouds, nose cones and motor case cylinder, because of material and cost savingmaterial and cost saving.

A/P Lee Kim Seng

Many automotive and truck parts such as wheel rims, shock absorber tubes and brake cylinders are being flow turned or flow formed.

A/P Lee Kim Seng

The process is also adopted for production of convex and concave hollow components, such as sound reflectors, ventilator parts, inlets and container covers.

A/P Lee Kim Seng

Other applications of spinning, flow turning and flow forming include air handling components such as diffusers, tank ends, centrifuge bowls, radar screen, light reflector, kitchen utensils, washing machine parts and musical instrument components.

A/P Lee Kim Seng

The main manufacturers of flow turning & spinning machines are Lodge & Shipley Co., Cincinnati Milacron, and Leifeld U. Co.

A/P Lee Kim Seng

Materials:

• Aluminum and their alloys• Silver and their alloys• Copper and their alloys• Zinc and their alloys• Steel, carbon and alloys such as low carbon steel (< 0.5% C)• Stainless steel• Nickel• Titanium (normally hot 500 – 1100 °°°°C)• Lead

The range of materials which can be spun and flow turned include most ferrous and non-ferrous materials, such as:

A/P Lee Kim Seng

• Defined as the maximum reduction achievablemaximum reduction achievable during the flow turning processes so as not to confuse with the term spinnability.

• Increase with ductility at room temperature.

• Deterred by flange wrinkling and wall fracture.

Maximum reduction in thickness ≅≅≅≅ 75% (2αααα ≅≅≅≅ 30°°°°)In general, semi-cone angle 12°°°° ≤≤≤≤ αααα ≤≤≤≤ 80°°°°

Thinning, metal working required become excessive and problems may occur.

< 12°°°° –

> 80°°°° – Amount of ‘working’ of the metal is insufficient to ensure stability.

Small cone angle can also be achieved by starting off with a pre-formed.

A/P Lee Kim Seng

AccuracyAccuracy – Influence by the feed and the amount of reduction.

Surface FinishSurface Finish – Inversely proportional to feed.

ToleranceTolerance – up to ±±±±0.025mm is claimed in some literature depending on the size and the complexity of the part flow turned.

A/P Lee Kim Seng

The crystal lattice structure in the metal is distorted; this results in an increase in hardnesshardness, yield stressyield stress & tensile strengthtensile strength, with a concurrent reduction in elongationelongation.

Metallurgical properties of the final part are better better than those produced by normal press-drawing processes.

A/P Lee Kim Seng

High nickel alloys & steel components – lubricant is needed to withstand the high pressure and temperature develop due to the intense working.

Commonly used lubricant – Beeswax – tallow– yellow soap

1 part of heavy oil to 2 parts of paraffin has proved ideal in flow turning of drums for spin-dryers.

A/P Lee Kim Seng

Tool friction may also be reduced by flash copper-plating difficult shape.

Sulphur or lead lubricant should never be used where annealing is to follow, because their presence causes embrittlement to annealing temperatures.

A/P Lee Kim Seng

Blank for flow turning & spinning can be flat sheets or plates, forgings, extrusions or castings. Preformed blanks drawn on presses or machined are also widely used. Thus there is considerable material choice and consequently a high potential for cost reduction.

A/P Lee Kim Seng

E.g. At the Bristol Siddley Engines Ltd., (Now part of Rolls Royce), large material saving occurred when using the flow turning process.

A/P Lee Kim Seng

Although flow turned components can reduce both the material cost and labour cost it is influenced by the batch quantities. Batch as low as 50 off can be economically formed or flow turned, but normally runs of several hundreds are required to justify flow turning.

A/P Lee Kim Seng

Before deciding on any process, for example flow turning, spinning and deep drawing, for the production of axi-symmetrical components, there are several factors which may influence the choice, namely:

1) Material and Tool cost per unit (This may vary with batch size)

2) Labour and overhead costs

3) Lead time and delivery requirements

4) Dimensional accuracy of the product and limits of each process

5) Batch quantity

6) The availability of machine equipmentA/P Lee Kim Seng

Comparative cost chart for producing 6 x 6 in. aluminum shell by spinning and deep drawing

A/P Lee Kim Seng

The application of NC & CNC machines had a great effect on the spinning & flow turning – permit components to be produced which previously would have been considered impracticable.

A/P Lee Kim Seng

Advantage of NC & CNC machine over conventional machine include:

1) Faster set-up & change over time

2) Operation by unskilled labour

3) Uniform parts spun or flow turned at high production rate

4) Simplified part programming when using CNC

A/P Lee Kim Seng

The introduction of NC & CNC greatly increases the complexity & flexibility of the flow turning process. Although NC & CNC has been introduced only recently to metal spinning & flow turning machine, they promise to make an important impact to future high production application.

A/P Lee Kim Seng

With the use of an idealized model of flow turning and assuming simple shear deformation under the roller.

General power consumed = Specific energy

VolumeUnit time

××××

i.e. P = udTdV

A/P Lee Kim Seng

Specific energy, u =Energy

Unit volume

= ��������

γγγγ = cot αααα

0ττττ dγγγγ ----- (1)

where ττττ = shear stressdγγγγ = shear strain

Shear strain is the distance an element moves axially divided by the thickness of the element(γγγγ = cot αααα)

i.e.dtdx

= γγγγ

A/P Lee Kim Seng

Assuming a Von Mises / Henky Yielding Criteria:

σσσσ = [(σσσσx - σσσσy)2 + (σσσσy - σσσσz)2 + (σσσσz - σσσσx)2 + 6(ττττxy2 + ττττyz

2 + ττττzx2)] ½

√√√√21

All stresses except ττττxy are zero

∴∴∴∴ τ τττ =σσσσ

√√√√3----- (2)

A/P Lee Kim Seng

The flow turning action will produce a shear strain of cot ααααwhere αααα is one-half the total included angle

From Equation (1) u = ��������

cot αααα

0ττττ dγγγγ

ττττ =σσσσ

√√√√3

∴∴∴∴ ----- (3)σσσσ√√√√3

∴∴∴∴ u = ��������

cot αααα

0dγγγγ

Assuming non-strain hardening, perfect plastic material =σσσσ σσσσo

u = σσσσo √√√√3∴∴∴∴

1cot αααα ----- (4)

A/P Lee Kim Seng

Alternatively, Specific energy = Area under σσσσ / εεεε curve

u = ��������

σσσσ d εεεεεεεε

0

For simple shear

εεεε =√√√√3

cot αααα

=√√√√3

cot αααασσσσo

u = ��������

σσσσ d εεεεεεεε

0∴∴∴∴

= σσσσo √√√√31

cot αααα

=σσσσ σσσσo For

A/P Lee Kim Seng

= 2ππππR to sin αααα f NdTdV ----- (5)

where f is measured parallel to the cone face

∴∴∴∴ P = udTdV

dTdV ����

����σσσσ d εεεε

εεεε

0

=dTdV ����

����

γγγγ

0ττττ dγγγγ

=

or

P = Power

A/P Lee Kim Seng

From Equations (4) & (5)

∴∴∴∴ P = udTdV

= 2ππππR to sin αααα f N√√√√3

cot αααασσσσo

----- (6)

----- (7)Power P = ππππN to R f σσσσo cos αααα√√√√32

∴∴∴∴

P = T θθθθ.

θθθθ.

= 2ππππNA/P Lee Kim Seng

----- (8)Torque T = to R f σσσσo cos αααα√√√√31

∴∴∴∴

----- (9)Tangential force = to f σσσσo cos αααα√√√√31

∴∴∴∴

√√√√3cot αααα

σσσσo= to f sin ααααor

��������

σσσσ d εεεεεεεε

0

A/P Lee Kim Seng

Tangential force = to f sin αααα ��������

σσσσ d εεεεεεεε

0

In general

For simple shear, εεεε =√√√√3

cot αααα

=σσσσ σσσσo i.e.

=√√√√3

cot αααασσσσo

��������

σσσσ d εεεεεεεε

0, thus

Torque = Tangential force ×××× radius

= to f R sin αααα ��������

σσσσ d εεεεεεεε

0

Power = Torque ×××× 2ππππ N= 2ππππN to f R sin αααα ����

����σσσσ d εεεε

εεεε

0A/P Lee Kim Seng

NOTE :

The effective strain consider above does not include any redundant straining and is solely on simple shear.

A/P Lee Kim Seng

In practice, the loads may often be much greater than those predicted, due to constraint imposed by the necessity for the metal to flow in a particular way.

In general, the more curve the shear lines, the higher the pressure required to make the metal flow.

The work done in overcoming this excess constraint cannot be found from the overall change in shape, and is known as redundant workredundant work.

Surface stress analysis takes no account of redundant work, and there is in fact no general analytical theory.

A/P Lee Kim Seng