Toby hale

Trans RINA, Vol 151, Part B1, Intl J Small Craft Tech, 2009 Jan-Jun

THE TRANSACTIONS OF THE ROYAL INSTITUTION OF NAVAL ARCHITECTS International Journal of Small Craft Technology

THE INNOVATIVE EVOLUTION OF MODERN PRESS ADAPTIVE FORMING, OPTIMISING THE EFFICENCY OF SMALL METAL CRAFT CONSTRUCTION THROUGH VARIABLE BED ANGLE BENDING TECHNIQUES T J Hale, Falmouth Marine School, UK SUMMARY Through a joint project, IMD have utilised the adaptation of modern press adaptive forming in the small craft construction sector. A newly designed and built machine purely for forming boat hulls from singular sheets has revolutionised the capabilities of press break forming, through a new unique process of Variable bed height bending.

In recent times within the small craft construction sector, a press break has still yet to be used in the produce small metal Boats. Scale models have been produced using new methods of variable bed angle bending. V.B.A.B, has enabled opposing anti-parallel uniform creases to form chine’s in sheet material with excellent accuracy and fairness.

Scale clean aesthetically pleasing bent boats have been produced boasting 0 longitudinal distortion increasing the overall appearance of theses newly designed and built vessels. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ press brake can make a definite difference in the quality NOMENCLATURE of the finished product” [2] P [Pressure (Psi ] Press brakes started to be used in the manufacturing Fold [Parallel uniform bend] industry roughly 40 years ago. The press brakes of that Crease [Anti parallel uniform bend] era were simple but effective using basic hydraulic VBAB [Variable Bed Angle Bending] human controlled shut off valves and simple tooling.

RIB [Rigid Inflatable Boat] The machines were only capable of uniform folding limiting their capabilities. Since then press brakes have 1.

INTRODUCTION evolved around the automotive aerospace, land base and the marine industry. Roughly 20 years ago saw the There exist common issues in the labour costs, turnaround for presses; a new revolutionary system production costs, health and safety aspects, and distortion called CNC (Computer Numerically Controlled). this issues in the production of small metal boats. Until breakthrough was soon to be adapted re-launching the recently there have only been ways of minimising theses press breaks as high volume production line machines. common issues.

Over the past 2 years IMD has looked at the possibilities 2.1 INTEGRATION OF CNC to reduce these expensive and time consuming processes With CNC ram positioning, “air bending” became in order to maximise efficiency increasing profit, and possible thereby eliminating much of the set-up required reduce time scales in the production of Rigid inflatable for bottom bending or “coining”. Parts could be formed boat type of craft. in one handling without as much time spent readjusting A new production method has been developed the ram stroke for each bend or stage bending with surrounding the idea of sheet metal forming with the aid custom matched dies that all bottomed at the same of using brake press technology And VBAB techniques. stroke. “As controls became more sophisticated, extra 2

PRESS BRAKE TECHNOLOGY

2.1 INTRODUCTION Metal processing technology evolves to meet the demands of industry and press breaks are of no exception. It has been said “Whenever practical use brake press forming to reduces welding and improve overall appearance” [1] “A brake formed plate crease is a straight line, free from weld distortion, and smooth and pleasing to the eye.

There are many areas of the boat where wise use of the

©2009: The Royal Institution of Naval Architects

benefits—like bend allowance calculations and extra back gauge axes made set up faster and easier. The objective was to lower the cost of labour by reducing set up and part handling time” [3] 2.2 TECHNOLOGY TODAY Morden systems now boast “Adaptive Corrective Forming”, effective offline programming and proofing software and some permit streamlining integration of robots.

“Adaptive forming refers to the press brakes ability to monitor material thickness and angle variations, while

Trans RINA, Vol 151, Part B1, Intl J Small Craft Tech, 2009 Jan-Jun

making corrections in real time. The method for thickness detection that drastically improves the formed sections use’s the ram as a micrometer. During a production run, the ram transitions an approach speed a couple of millimetres above the work-piece while the CNC unit closely monitors the pressure as the tool contacts the material” [4] 2.3 PRODUCTION LINES Press brakes of today are slowly being replaced with modern Press adaptive forming machines running on scripted software with integrated robotic arms requiring minimal human input once the systems are set up. These systems are well suited to production lines where one part can be made over and over again requiring little or no human input if robots are integrated.

2.4 SHEET METAL SIZES Modern day sheet metal mills have the ability to manufacture aluminium sheets larger now than they have been able to in the past. [5] Alco the United Kingdoms largest importer of aluminium alloy can supply sheets up to 2.5m wide and up to 14m long These large sheet sizes have posed a possible opportunity in the small metal craft construction industry with a new concept forming process using a newly design press brake that has the capabilities for folding complete boats from singular sheets.

3.

PROCESS DESCRIPTION

3.1 OVERVIEW The process begins with the design selection. Many types and variations of hull can be produced using the press that has been designed. Currently sheet sizes have restricted hulls to be formed up to 14m in length and widths are restricted from 2-2.5m. The press designed has a maximum capacity to form a 9m hull.

The process for selecting the template radius is key to the final design altering the external and internal radius on the design will draw the bow sections differently to form different shapes and characteristics to the final hull shape. Key points are that the internal and external radiuses have to be mirrored across the centreline symmetrically but internal radius can be different to the outer radius. The basic rule is Shallower larger radiuses will form longer sleeker hulls. Shorter smaller external and internal radiuses will draw the bow sections to form more traditional displacement type vessels. The aft and midship sections are limited to hard chine and gull wing chine construction, consisting of large flat areas perfect for planeing craft ideally suiting the method to aluminium rib and workboat construction.

3.1a SLECTING BOW SHAPE Using a modern cad program a selection of radius are laid out at scale with intersecting lines these geo-sim lines once arced off with the necessary inputs for hull form marked on the chart give the points at which the

©2009: The Royal Institution of Naval Architects

chine creases must end. This process will also give the position where the radius must start and end for both sides of the net and inner and outer radius. For the bow sections to pull together this process is highly important to the finish look and fairness of the hull. If the fold point were to be slightly out kinks or creases will occur in the hull.

3.1 b NET CRETION The following process is the net creation using cad again a planner curve is used to draw a surface. This surface must be the exact size of the full size sheet. From process 3.1c, a radius has been chosen for the type of hull form and bow characteristics. The start of the radius is located on the rectangular sheet and drawn using the radius command on the net. Using the mirror command this section is copied across. With the mirrored section in place select the trim command and cutting object and cut away the excess material.

3.1d CREASE AND FOLD LINES For an example for a rib a simple single chine construction method incorporating a single anti-parallel crease tapering from the transom on each side of the hull will form a good basic shape for the hull form. Using the chart from process 3.1a, this will give the optimum crease start point for the different hull forms obviously for a rib the hull form is planning. With the location known the two crease lines can be marked on the rib and centreline fold.

3.1e ANGLES To find the optimum angles the chart in 3.1a is used again. Using a protractor the angle between the geo-sim lines that intersect the radius arc are directly proportional to the length of line for the creases and folds for the hull when selected at the beginning. Using the chart measure the length of the creases and use the chart to find the angle. Once an angle has been obtained using an angle depth chart will find the corrected press brake depth to form that angle. (This will be different for each model of press brake) The chart will show a material thickness, tooling application, and bending process “Air bending” in this case and a depth will be shown to achieve the angle selected. For an example a 90 degree fold on a 30mm V die will be about 20mm in depth for 1mm steel. for most boats the steepest angle is roughly 110 degrees this is important when selecting tooling. On thicker material maximum bend radius are imperative or stress fracturing will occur or material tear or cracking. Largely effect the strength of the structure.

Formula for spring back Spring back occurs due to the metals elastic limit resisting bending this is a common problem and must be compensated for using the formula below.

D=R/(2.1 x S) [6] Where R is the radius of the angle in mm and S is the sheet thickness in mm. using this formula, a steel sheet 0.8mm thick, and given a bend radius of 20mm and a bend angle of 90 deg., has a spring back value of 11.9 deg. Input 0.68 for aluminium opposed to 2.1 for steel.

Trans RINA, Vol 151, Part B1, Intl J Small Craft Tech, 2009 Jan-Jun

3.1f NET CUT OUT There are a number of ways to cut out the net once marked out. The more preferable way and highly more accurate way would be to use a water jet, laser or plasma cutter. The water jet method would be the more accurate method and the plasma method the cheaper option.

These methods use the cad drawing of the net to produce a cutting file which is sent to the CNC machine this process usually takes less than a minuet to create a cutting file from a 2d cad drawing if done correctly.

3.1g BENDING Before bending the finished full size boat a 10th scale model would be a good idea to produce as this will give a good insight to the fairness of the finished full scale hull.

Another way of checking the model is using the rotate feature on a cad program this will allow the net to be folded into the finished boat and analysed. The digital model can then be imported into a fluid flow prediction program such as max surf, for further hydrostatical analysis.

Check list • Net is correctly sized • Radius are correct • Crease marks checked • Crease and fold angles checked • Depth angles checked • Brake press fully operational • Feeler gauge at hand • Pressure sensors calibrated • Check minimum bend radius if bottoming • Spring back calculation allowance 3.2h IN TO THE PRESS Depending on the amount of creases or chine’s at this stage a crease order will need to be decided on. For an example the rib will have its delta pad folded first followed by its main chine and then the centre fold.

It is important the press has a facility to measure the depth of the tooling for crease angles and a pressure back facility is a major advantage when it comes down to VBAB. The pressure back facility enables the press to pressure relieve an individual ram when it reaches a certain pressure this stops the crease line from over extending and forming parallel. In an event of failure the pressure relief can also stop series damage occurring to the press if the spool valves were to lock open.

3.2i FIRST FOLD  Tooling 90 degree dies  Process Air Bending  Pressure relief left ram.  Bow to the left With the press set for the first bend the ram pressures will be adjusted. Using the rams adjust the bed height to the crease line. Using a feeler gauge check the clearance at the max crease point. The ram to the left will need to be set so the pressure will not rise above the set pressure or uniform parallel bending will occur. The right hand

©2009: The Royal Institution of Naval Architects

ram’s centreline must run through the transom. Using the feeler gauge adjust the bed height so the tooling dies are holding the net in place and crease angle is set. Set the pressure relief 5-10psi (varies with material thickness) grater than the current setting on the pressure relief valve on the left hydraulic ram. Using the depth angle chart a depth should be acquired for the angle of the crease (angle) measured at the transom. As the press is already holding the net firmly the depth datum point can be taken And a depth required will be the datum + depth. The elastic limit of the material will need to be calculated and added on to this depth to counteract spring back. Some brake presses will do this automatically if CNC controlled. Once happy open the spool valves on the hydraulic rams and watch the first chine be created. A thick length of rubber can be laid into the tooling bed to create a softer “gull wing” chine if proffered. Repeat this step for the other side and check angles.

The centre fold is achieved using both rams folding uniformly parallel. The pressure relief can now be bypassed so both rams will be working at the same pressure. Using the feeler gauge and depth gauges at each end of the press adjust the bed height and check the datum’s once the press firmly has hold of the net. In this step the boat will try to form its self drawing the bow sections together. Check the datum measurement and add the necessary depth from the depth angle chart. Open the spool valves and check the gauges constantly as the ram bed rises. As soon as the height is close adjust the final mm’s with the pressure valves instead of the spool valves as this is more accurately controlled. Once the fold is done the relief valves can be set to 0psi to allow the bed to drop and the newly formed hull be removed.

3.2j BOW SECTION WELDING As the boat is not press stamped there is still a section of the hull which will need to be welded. This Section will also have a stem plate added for welding.

Some welding options are pulsed mig pulsed tig friction stir and tracked welding. All these methods are more than sufficient for achieving both strength and a clean aesthetically pleasing weld.

3.1k Deck, transom, engine bearers, propulsion system.

A bonus with working with aluminium is that the deck can be fitted after the hull is formed. Custom lockers hatches can be welded and press formed to suit each individual’s needs and usage for the boat. The transom can be made to accommodate a variety of engines and outboard options and a large advantage is that most boats produce by VBAB come out with parallel aft sections ideally suiting the boat for a water jet propulsion systems. Engine boxes and consoles have the option for being press formed reducing welding costs and improving overall appearance.

Trans RINA, Vol 151, Part B1, Intl J Small Craft Tech, 2009 Jan-Jun

4. BENEFITS Variable bed angle bending technology is aimed at sheet metal applications involving the fabrication of three dimensional boat hulls out of singular aluminium sheets.

The key Benefits of the technology are.  Reduction in distortion  Reduction in labour costs  Reduction in welding and costs up to 75%  Reduction in manufacturing processes  Reduction in shape complexity  Reduction in age hardening  Improvement in appearance  High tech material usage  The ease of application  The application to modern press brakes  Re sale value of hulls  Evolving design processes  Precision accuracy  The implementation of VBAB 4.1a APPERANCE By forming the hulls out of a single sheet a large gain is achieved in the overall appearance of the hull totally eliminating distortion in the aft sections and massively reducing distortion in the bow. The symmetry of the hull is increased dramatically this is down to the crease and fold angles being exactly measured both angular and physically marked out with a laser or CAM devise.

4.1b WELDING Welding is used to join bow folds and add other parts to the structures to the hull. This process forms complex shapes that VBAB would not be able to form.

However the heating involved in the process produces heat affected zones and can lead to warpage. The heat affected zones generally have inferior properties to the unaffected material and can result in significant weakening of the structure as well as being susceptible to corrosion. The thermal expansion due to heating can lead to warpage of the surface of the hull this in turn becomes more problematic as the hull becomes larger and more complex. Loss of precision may be significant. Welding complex curves often involves difficult fixturing that can be labour intensive and slow. In many cases it is also difficult to be certain of the weld quality because it is hard to inspect with out expensive devices. Because VBAB technology can be used to form relatively complex shapes and curves from a single sheet of material, without needing to join separate pieces together, the need to weld can be reduced or eliminated entirely in places. This avoids the issues associated with heat affected zones and the lack of warpage due to heating increases precision. In some cases welding may benefit VBAB. Instead of making the hull out of one sheet, it may be possible to weld two sheets together for example a 2.5m sheet by 14m to form a 5m by 14m sheet this would allow a much larger boat to be produced. In putting a fold down the centreline of the weld, weld strength will be tested and sealed in the folding process.

©2009: The Royal Institution of Naval Architects

Even with the complexity of a 14m weld this still greatly simplifies the standard hull forming process.

4.1c LABOUR To produce a single 6m rib hull from the sheet arriving to putting it into the gantry system and receiving a finished boat out of the press would take 2.5 hours with two skilled men. This compared to building a scantling frame structure on which hull platting is added, would take two skilled welders 1 week at quickest. So it is very easy to see that labour costs would dramatically drop when using this method of construction.

4.1d ALUMINIUM THE 5000 SEREIS ALLOY The commonly used aluminium alloys used for marine applications are found in the 5000 series, which use a high percentage of magnesium as their primary alloying element. Their resistance to saltwater corrosion is excellent; they have a high welded strength and are fairly ductile this is largely down to the alloys strain hardening rather than being heat treated. This is why the 5000 series alloys are a popular alloy to use in welded boats as they will retain their high strength when heated by welding.

With the 5000 series being a popular alloy of choice within the marine industry this has aided the production for larger sheets to be formed. Currently sheets are available in a number of standard sizes up to 2.5m by 14m sheets. These large sheet sizes have been the key and only reason why a brake press is able to form a hull out of a single sheet. Alco the UK’s largest importers of aluminium keep stock sizes up to 2m by 6m sheets. This is the size a typical 6.5m rib would use.

Another key benefit of aluminium is that of the boats Re sale value. “A properly maintained three year old boat in good condition can return nearly 95% of the original purchase price” “in some cases, particularly with jet sleds, 12 year old boats have sold for more than their original cost. “Such potential appreciation can make a well-designed aluminium boat a good investment.” [7] 4.1e DURABILITY In addition to lightweight high strength, aluminium is also durable and very ductile (Able to be bent and drawn without breaking ideal for press forming) “Aluminium is more impact-resistant than steel or fibreglass. In fact, aluminium has 3 times the elasticity of ship steel and 5 times the elasticity of reinforced polyester laminates in the working stress range” [8]

4.1f REDUCING SHAPE COMPLEXITY Because the net shape, crease and folds are all marked out while the aluminium sheet is in the flat state, there are no access issues and it is highly possible with correct tooling to fold far more highly intricate shapes such as spray rails, which previously could not even be attempted on a standard press break using standard bending processes. In addition to enable the fabrication of complex curves this process allows hulls that previously had to me made up in several sections to now be formed

Trans RINA, Vol 151, Part B1, Intl J Small Craft Tech, 2009 Jan-Jun

as one piece. Fewer components lead to fewer welds, and fewer pieces to cut out, keep track of, and manage all this leads to a reduction in bills, amenities and labour costs.

4.1g REDUCED MANUFACTURING PROCESS By combining multiple hull plates into one and eliminating, or at least greatly reducing welding operations, it is possible to simplify the overall manufacturing process. Fewer pieces of aluminium need to be cut and managed. Resulting in fewer manufacturing operations are needed to make each part. Reducing the number of factors that may influence the final hull quality, making it easier to reduce errors and manage quality. Eliminating a joining operation, for example a weld eliminates a set up welding process, weld preparation process, health and safety risk assessment process, skilled welder intensive process, labour weld finishing process, clean up process, welder maintenance process, and an electrical consumption process.

4.1h EASE OF VBAB APPLICATIONS Variable Bed Angle Bending press break technology can be implemented in a very flexible way. The ease of tooling set up and eases of switching from planeing hulls to displacement hulls quickly enables rapid design iteration and makes the process viable for low production volume applications. Since hulls can be made at scale in lighter gauge materials, prototypes can be made quickly without requiring heavy machinery.

4.1i THE IMPLEMENTATION OF VBAB Variable bed angle bending technology was developed around an existing standard C shape press brake design.

Therefore as “Air Bending” is key to VBAB it is merely an issue of reconfiguration of a spool and pressure relief valves to enable some press brakes to use VBAB. 4.1j THE PREES BRAKE A Modern press adaptive forming machine is not capable of forming a 6.5m rib of this size. A modern 6m press would have no trouble forming a boat from pressure or power requirement, the problem is the physical size of the press. To accommodate a 6m boat within a standard press brakes jaws would not be possible due to the press brakes traditional C shape design. The UK’s largest press at 14m is large enough but lacks the forming ability of variable bed Angle bending to form anti parallel uniform crease which make up the chine’s of the hull. This issue has forwarded the design and build of a new press brake.

This newly designed machine will be 7m long and able to form up to a 9m boat out of a 9m by 2.5m sheet. The newly designed press will consist of two 6m 610mm by 229mm steel beams running longitudinally housing one of the 100 ton hydraulic rams. A boxed Colum T shape section consisting of another two 610mm by 229mm beams 4m long one above each other will form the top and bottom and then two 250mm Colum’s will form the 3m verticals, forming the box support structure hosing the other 100ton ram. The press will be powered by two 100 ton hydraulic rams running on a hydraulic spool

©2009: The Royal Institution of Naval Architects

valve system with pressure regulating relief valves at each ram to allow for “VBAB”.

Due to the shear size and weight of the press it will be built and kept in its own work shop this building will have a gantry system running the full length of the shed consisting of 4 electric 250kg chain hoists running on two beams with carriages which will allow a 2 axis movement above the press for moving hulls and sheets into position.

The hoists will have glass suction pads to protect the aluminium sheets from scratches; also picking a 2m by 6m sheets up with slings is near impossible when the sheets are on the ground this is why the suction pads really are a necessity.

4.1k CAD DESIGN The design process started with the idea surrounding a rib. A rib design when broken down is quite simple consisting usually of only 1 chine and most ribs consist of a parallel aft section which is why the design suited itself so well to press brake forming. The early designs started out simple and worked but not so aesthetically pleasing as hoped. It wasn’t until the integration of cad when relationships were found between end creases and radius angles; this find enabled smoother flowing surfaces to be formed. Now it was apparent that by changing inner and outer radiuses, bow height and hull form could be altered to perfect and maximise hydrostatic particulars using Delft ship. Cad has also helped compare and contrast a number of different hull forms generated from this process when proving the method.

6.

CONCLUSION

This project is unusual in that it is a craft designed around a manufacturing process that in itself is unique to IMD. By design, the hull is a compromise. A form as near to perfect as Variable Bed Angle Bending allows.

The minor trade off for fuel, speed or weight inefficiency, could be said is more than made up for by massive production savings in bills, materials and labour.

As the design process progresses onto other models, the press can produce any sequence of shapes and sizes in succession, on the same press.

Aluminium as a choice of material gives the craft a high strength to weight ratio, durability practicality, as well as good looking.

With a direct build ie no plugs or moulds to be bound by, the craft can evolve at its own rate.

The production method allows the build to advance and improve on a one off basis.

Little or no deterioration means far less depreciation and ultra violet damage becomes a thing of the past, holding the boats re sale valve.

With diminishing oil stocks and ever increasing prices, resin prices can only increase. This together with health and safety legislation particularly when employing workers makes aluminium the material for the future?

Trans RINA, Vol 151, Part B1, Intl J Small Craft Tech, 2009 Jan-Jun

7.

ACKNOWLEDGEMENTS

Slade, K.S., 1979 steel boat construction. 1st ed. London: Butterworth & co Kemmish R.E.W 1980 Yacht and Boat design. 1st ed.

London: Butterworth & co [8] Larsson, L.L. & Eliasson, R.E., 2007. principles of yacht design. 3rd edition. London: Adlard Coles Nautical.

Skene, N.S., 2001 Elements of yacht design. 5th ed. New York: Sheridan House.

Jones, C.J., 1992. Rigid inflatable boats. 1st ed. London: Thomas Reed.

Nicolson, I.N., 1986. Small Steel Craft. 2nd ed. London: Adlard Coles Nautical.

Press Brake Bending: Methods and Challenges," Metalforming magazine, Precision Metalforming Association, August, 2008.

Tool and Manufacturing Engineers Handbook (TMEH), Volume 2, Forming. Society of Manufacturing Engineers, 1984.

©2009: The Royal Institution of Naval Architects

8.

REFERENCES

1. [Pollard, S.P], ‘[statement why press forming]’, [Boat building with Aluminium. 2nd ed], [2007].

2. [Benson, S.B], ‘[press formed crease description]’, [Press Brake Technology. 1st ed], [1997].

3. [Schlachter, C.S], ‘[Adaptive forming]’, [forming fabrication journal.], [2005] 4. [Schlachter, C.S], ‘[Integration of CNC]’, [forming fabrication journal.], [2005] 5. [Roberts, B.R], ‘[sheet sizes]’, [Metal Boats. 3rd ed], [2006] 6. [Benson, S.B], ‘[spring back formular]’, [Press Brake Technology. 1st ed], [1997].

7. [Pollard, S.P], ‘[Re-Sale]’, [Boat building with Aluminium. 2nd ed], [2007].

8.

[Pollard, S.P], ‘[Strength comparison]’, [Boat building with Aluminium. 2nd ed], [2007].