Introduction, Waterjet, Hydroforming

1. INTRODUCTION

ADVANCED MANUFACTURING PROCESSES

ADVANCED MANUFACTURING is the use of innovative technologies and methodologies for improved competitiveness in the manufacturing sectors.

4 JUMPS in manufacturing:

1. Steam engine → England, local development → 1^st INDUSTRIAL REVOLUTION
2. Mass production, after WWII → 2^nd INDUSTRIAL REVOLUTION
3. Computers invaded manufacturing processes → 3^rd INDUSTRIAL REVOLUTION
4. Internet → 4.0 INDUSTRY

Example: MACHINING

• Conventional: add tools to remove material through mechanical forces
• Unconventional: any other forms of energy and usually not solid tools

TECHNOLOGY

• PROCESS (physical transformation that takes place)
• SYSTEM (machine, tool, features belonging to the machine, all the devices: mech, electronics, also operator...)
• PRODUCT what we want to obtain at the end of the process
  • WORKPIECE = while working
  • PART = only after we have finished it

The interaction of these 3 makes a technology.

WHY?

Why do we need unconventional processes?

The main drivers of manufacturing are: COST, QUALITY, TIME

We need FLEXIBILITY = capability to rapidly changing the production

to obtain CUSTOMIZATION.

This is the era of MASS CUSTOMIZATION, so we need PRODUCTIVITY and FLEXIBILITY.

New processes are being developed for these reasons:

• MATERIAL ADVANTAGE to make technically and economically feasible the manufacturing of new advanced materials (ceramics, titanium, alloys,...)
• GEOMETRICAL AND PERFORMANCE ADVANTAGE
  • Complex part geometries not obtainable with conventional processes (large undercuts, thin and small workpieces)
  • Higher tolerances or lower roughness needed
  • No residual stresses on the part

• FLEXIBILITY ADVANTAGE

to reduce fixed and setup costs and times

• reduce costs of tooling and fixtures, dies...
• reduce time-to-market of a new product

Especially when you have low productions (batches)

• aerospace manufacturing
• medical devices

Product Volume Mass Production Product Variety Craft production

PROCESS

SYSTEM

Network of Factories Factory Shop Module, Tools, Fixtures, Components, Operation

PRODUCT

PERFORMANCE can be increased by increasing:

• Quality Q
• Flexibility f

by decreasing:

• Cost €
• Time t

4 variables that help to evaluate a choice

QUALITY = for a mechanical part, it is tolerance, mechanical properties, finishing...

The variability is in a ± range, it means you can have different qualities

FLEXIBILITY = ability of a given technology to work with different materials, geometries...

It means VERSABILITY, ability of quickly changing the setup (short times of setup).

Reducing times → higher flexibility and lower costs

OPTIMIZE

• Quality: no optimization, I have to reach the quality asked by the customer
• Costs: minimize reduction, first by reducing time
• Time: being quicker I minimize them

Poor cutting speed when optimizing

PROCESS PARAMETERS

WJ and AWJ are mechanical unconventional material removal processes. The physical principle they are based on is the conversion of pressure energy into kinetic energy in the primary nozzle. The high speed of water provides a high erosive/abrasive cutting power.

WJ

• High-pressure water
• Nozzle (held stone)
• Stand off distance
• Workpiece (flexible clamping)
• Catch (deeper cause residual energy very high)

AWJ

• Water
• Particles
• Mixing chamber

600 m/s higher than sound

Hydraulic Parameters

• Pump pressure p
• Water-orifice diameter d₀

Cutting Parameters

• Traverse rate V [mm/min] ➔ orbital movement of the cutting head
• Number of passes m_p
• Stand off distance x ➔ as small as possible, not to devour and loose power density
• Impact angle φ (angle of attack) ➔ Not 0 (there will be scratches)
• ➔ Not 0.1 (because of vibrations) ➔ Minimum distance instantly necessary but as small as possible

Mixing and Acceleration Parameters

• Focus diameter d_f ➔ diameter of mixing tube
• Focus length l_f

3

Other designs:

• multiple workjets and external mixing
• multiple workjets and orifice plate
• annular jet

Abrasive Suspension Jet (ASJ)

How to avoid the presence of air = mixing grains and water before the nozzle

Abrasive Injected Jet

Air entrained

Lower efficiency

Abrasive Suspension Jet

• Nozzle Ø: 0.6 – 2 mm
• Pressure: up to 2000 bar
• Working time: < 1 hour

Advantages

• very efficient (higher momentum transfer)
• no air
• Efficiency!
• Portability
• Use in critical environment (Firefighter, Shipyards)
• Cleaning

Disadvantages

• frequent downtimes (to refill abrasive or change the nozzle now in contact with abrasive)
• Higher components wear
• Low pressures (up to 2000 bar)
• Abrasive concentration variable on time → variable cutting quality

AWJ Suction Process

Process in which the workjet creates vacuum in the mixing chamber. Pv lower than Pa. If workjet velocity increases, there’s more drag, Pv decreases and the difference of pressure increases → more vacuum.

Experimental setup for AWJ nozzle suction includes:

Different experiments at different pressures (changing the diameter of plastic tube)

To do this, a pressure higher than the osmotic pressure is applied.

The diluted solution is collected in a tank, while the more concentrated stream is drained.

PUMPING SYSTEM

SINGLE ACTING INTENSIFIER

When retracting, it doesn't pump water.

More than 1, usually 3 in parallel to avoid interruptions.

DOUBLE ACTING INTENSIFIER

One single double acting piston or more than one in parallel to increase the flow rate.

1. DIRECT DRIVE PUMP

   • We directly pressurize water without a double hydraulic circuit.
   • Used for low pressure applications (tens of MPa).
   • High flow rate (even more than 100 l/min).

2. DOUBLE-ACTING INTENSIFIER

   • Lower flow rate (2 l/min).

ACCUMULATOR

The piston has to slow down, stop and invert the motion.

So the pressure signal is fluctuating.

To compensate fluctuations of signal, an accumulator is needed.

It is a reservoir of pressure, an elastic accumulator of energy, an high pressure vessel.

This component reduces water pressure fluctuations and supplies water flow when needed.

Handling System

• Cover: to reduce noise and for safety
• 2 axis cartesian machine
• 2 1/2 axis
• 3 axis
• 6 axis: robotic head, difficult to be programmed (collision problems)

Catcher

The catcher is a water tank, a basin, that has to:

• Dissipate jet residual energy (that can be up to 75% of initial energy)
• Avoid jet back reflection - very deep, 1m or more
• Reduce noise (especially in submerged AWJ cutting)
• Catch and flush the machining scraps

To reduce the volume of the basin, there can be ceramic balls inside it that damp residual energy or catcher plates of TiB₂

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