huck versus welding
DESCRIPTION
Comparativa entre uniones remachadas (HUCK) y uniones soldadasTRANSCRIPT
Huck vs. Welding
Welding compared to boltingBolting Welding
Flanges required Seam welds possible
Pre-coated parts Cleaned parts, paint afterwards
Pre-manufactured parts Often fabricated on site
Assembly Fabrication
Joint responsibility with design engineer
Joint responsibility with welder (easy to add that little bit more, quality)
Cost visible on Bill of Material Cost mainly in labour time
Normally more flexible joint Joint can be stiffer than material
Welding compared to bolting
F
F
� Seam joint for welding or lap joint for bolting
The Welded situation
� Preparation of joint
� Welding of joint
� Painting after assembly
– Often done by same skilled labour
� Cracking of weld
– repair
Joint failure� Cracking of end of joints
� Highest stress levels
� Weld impurities
� Hydrogen embrittlement)*
� Warping of material possible
� Fatigue or brittle failure
)* Source: The welding Journal, Feb 1990, Hydrogen-Induced Cracking along the Fusion Boundary of Dissimilar Metal Welds, M.D. Rowe et all
Cracking and hardness traverse near the fusion boundary
Joint failure
Dual Phase HAZ
Course Grained HAZ
Weld Material
Source: Oil & Gas - Microstructural change in high t emperature heat-affected zone of low carbon... D.Ca rrouge
Even it seems that the materials are joined together, there is still differences in grain structure, especially in the Heat Affected Zone, creating higher internal stresses. The HAZ is normally the point of failure of a weld.
Cost comparison: Welding vs Huck
Welding cost mainly labour costs
� Labour time:
– Grinding
– Cleaning
– Rigging up
– Cleaning, inspecting weld
– After-painting
� Labour rate
� Increase in material cost (+50%)– Pre-punched holes
– Fasteners
� 26% Saving compared to welding
72.3
16.1
11.3 0.4LabourMaterialsEnergyOther
)* Source: Welding-Related Expenditures, Investments, and Productivity Measurement in U.S. Manufacturing, Construction, and Mining Industries May 2002
Welding related production expenses)*
26
43
1
24
6SavingLabourMaterialsEnergyOther
Huck bolting related production expenses
(-20%)
(-30%)
Bolting compared to welding
� A more ductile and flexible joint is created.
� Stress limitations down to maximal contact loads between parts and maximal performance of fastener.
� In a ‘good’ designed joint, the forces travel through the joint and not the fastener, due to the high friction between the plates
Blind rivet versus welding
Bulbing blind fasteners:
• Wide bearing area
• Thin sheet applications
• No pull through during impact
• Controlled failure (of sheet material)
• High energy uptake
• Brittle failure of weld
Huck versus Welding
Pro’s:Easy visual inspectionNo brittle failure, the fastener will fail ductile (compared with welding)Joining of different materials possible, using the appropriate cathodic protectionNo Heat Affected Zone as with weldingJoint is vibration proof
Con’s:Perceived expensive toolingAddition of parts on Bill of MaterialWeakening of material due to necessity of holes to install fasteners inOverlap necessary, no overlap necessary with welding.
Maximum allowed stress levels
� Fatigue:
Tokyo Institute of Technology
Maximum allowed stress levels
� Bolted joints can have same or higher stress levels than welding
In the long term: convincing evidence
Lockbolt grade 8.8
BOM blind rivetBolt and retaining
nut grade 8.8
Summary
• Welds difficult to inspect• Expensive equipment needed• Or not inspected
• Specialized workers• Expensive• Training
• Increased human error• More chance of making
mistakes
• Time for complicated welds• Production time decrease• Possible interference with
multiple welders
• Secondary cleaning and polishing etc.• Higher production time.• More expense
• Tooling• Expensive• Safety issues
• And of course:
SAFETY…
Environment, Health and Safety
• Expense• Costly ventilation systems to
remove harmful gases:• 20-40% Iron Oxide• 2-8% Manganese• Arsenic• Lead• Chromium• Nickel
• Protection such as aprons, gloves and masks:
• Health Risks• Even with ventilation and
masks, the risks of illnesses are high:
• Lung cancer• Skin cancer• Retina damage• Asthma• Bronchitis• Renal Failure• Infertility• Possible hearing problems
Final note
� To change from a welded design to a bolted/riveted design, in many cases, a full redesign is required to suit lap joints and calculate the load cases.
� Changing over from welding to threaded fasteners might be an intermediate solution which is eventually easier to convert.