Welding heavy-gauge material handling parts

A forklift overhead guard in 8 mm plate is welded with a 5 mm fillet at every bracket. It passes visual inspection, passes a dimensional check, and cracks at the toe of the mast bracket after 4,000 hours because the bracket carries a bending moment that needs a 6 mm throat, and 5 mm of leg gives 3.5 mm.

Heavy gauge welding for material handling parts is where a drawing habit becomes a fatigue failure. Above about 6 mm the weld stops being a surface joint: the plate restrains the contraction, the pass count matters, and the difference between a fillet and a full-penetration groove is a factor of three in weld metal and a factor of five in distortion.

The bending and welded assemblies hub covers the rest of this cluster on fixture, sequence and inspection.

What changes above 6 mm plate

Three things. The joint needs preparation, because a square butt cannot penetrate 10 mm in one pass without a current that overheats the plate. The weld needs more than one pass, so interpass temperature and slag or spatter cleaning between passes become process controls rather than housekeeping. And the plate is stiff enough to resist contraction, which means the distortion comes out as angular movement and residual stress rather than a gentle bow.

The current that one pass can carry is limited by the wire and the puddle. A 1.2 mm solid wire runs comfortably at 200–260 A, which on a 10 mm V-groove fills 3–4 mm of depth per pass. Pushing a single pass through 10 mm needs 350 A or more, and at that current the arc digs a deep finger into the root while the sidewalls stay cold. The result is a joint that looks full and fails on a macro section at the fusion line.

The economics follow the bevel. A 60° single-V in 10 mm plate with a 2 mm root gap has a cross-section of about 78 mm², so a metre of weld is 78,000 mm³ of steel, roughly 0.61 kg before reinforcement and 0.65 kg with it. A 7 mm fillet on the same plate is 24.5 mm² and 0.19 kg/m. Full penetration costs 3.4 times the weld metal, plus the passes, the cleaning and the extra straightening.

The numbers that decide a heavy-gauge joint

Heat input is the number most often quoted and least often calculated. It is:

HI = (V × A × 60) / (1000 × travel speed in mm/min)

At 24 V, 220 A and 350 mm/min: 24 × 220 × 60 = 316,800, divided by 350,000 gives 0.905 kJ/mm. Drop the travel speed to 250 mm/min and the same settings give 1.27 kJ/mm, still inside the range. Raise the current to 280 A at that speed and it goes to 1.61 kJ/mm, which is outside the range for a restrained 10 mm joint and increases the risk of a hard, crack-sensitive heat-affected zone.

Heavy-gauge welding starts at the bevel

The bevel angle is a compromise between access and volume. At 60° included, a 2.4 mm electrode can reach the root with a 10–15° work angle. At 45° the volume falls but the electrode cannot reach the root of a 10 mm groove without gouging a sidewall. Below 30 mm plate, 60° single-V is the standard; above 16 mm, a double-V at 60° included with the same 2 mm root faces puts half the weld metal on each side and halves the angular pull.

The root face is the fitter's number. Two millimetres is enough to prevent burn-through at 200 A and thin enough to fuse on the root pass. A 4 mm root face on a 10 mm plate leaves a 6 mm groove that four passes cannot fill properly, and the joint ends up narrower at the root than the drawing shows.

The gap is the other half. A 2–3 mm gap gives the root pass somewhere to sit; a zero gap means the root pass is a bridge. Tack welds should be on the root face, not across the gap, and they should be ground to a feather before the root pass runs over them.

Fit-up is where most heavy-gauge defects originate. Two plates cut on the laser to 20 mm will fit within ±0.3 mm on a straight edge, which is why laser cutting a 12 mm bracket is cheaper overall than burning it and grinding the edge. A flame-cut edge with a 0.5 mm taper and a hard scale layer needs cleaning before welding, and the scale is a hydrogen source.

Multi-pass technique and interpass control

Run the root pass hot enough to fuse both sidewalls and cool fast enough not to sag. 200–220 A at 300–350 mm/min on a 10 mm groove is a working range, with a slight weave no wider than three electrode diameters.

Clean between passes. Slag, spatter and silica islands trap in the next pass and produce lack of fusion that no visual inspection finds. A wire brush and a chipping hammer are not enough on a 4-pass joint; a grinder with a dedicated wheel is the reliable method, and the wheel should not be the one used on aluminium.

Control the interpass temperature. Above about 250 °C on structural steel the heat-affected zone coarsens and toughness falls, and on a 10 mm joint in summer the plate can reach that after the second pass. A contact thermometer on the plate beside the weld, not on the weld cap, is the measurement.

Balance the sequence across the part. A bracket with welds on both sides of a web should be welded alternately, and a long seam should be backstepped in 200–300 mm increments. The alternative, welding one side fully and then the other, leaves the first weld's angular pull uncorrected and the part bows in one direction.

Fillet size, throat and when full penetration is justified

The 0.7 × thickness rule gives a fillet that is roughly as strong as the plate in shear along the throat. On 10 mm plate that is a 7 mm leg, a 4.95 mm throat, and a design strength that matches the parent for most bracket loads. On 6 mm plate it is a 4 mm leg, and on 16 mm plate an 11 mm leg, which is three passes rather than one.

Full penetration is justified when the load path crosses the joint in tension perpendicular to the plate, when the joint is in a fatigue-critical location, or when a standard requires it. A mast bracket on a forklift, a boom pivot on a telehandler, and a lifting lug all qualify. A stiffener inside a counterweight cover does not, and specifying full penetration there adds cost and distortion for nothing.

When full penetration is required, say which side is welded and whether a backing bar is permitted. A ceramic backing allows a wider root gap and a cleaner root; a steel backing becomes part of the joint and must be the same grade. The drawing should also state the acceptance level to ISO 5817, because quality level B and level D are different processes and different prices.

Distortion, restraint and straightening

Heavy plate resists contraction, so the distortion appears as angular movement at the joint and as residual stress in the plate. A single-V butt in 10 mm plate typically pulls 1–3° of angular distortion, and a bracket welded on one side of a web bows the web toward the weld.

Three controls work. Balance the weld about the neutral axis, using a double-V or welding both sides alternately. Pre-set the part against the expected pull, which for a 2° angular pull over a 300 mm bracket is about 10 mm at the free edge. And restrain with a fixture that allows contraction along the seam but not rotation about it.

Straightening after welding is a legitimate operation on mild steel, using a press or local heat, but it has limits. Cold straightening beyond about 2% strain work-hardens the plate and can start a crack at a weld toe. Heat straightening with a rosebud is gentler but changes the heat-affected zone again. Neither belongs after coating, and a part that arrives at the paint line out of flat is held, not forced.

The forklift overhead guard guide covers the specific geometry of a ROPS-style frame, where the welds are the load path rather than a connection.

Inspection that matches the load path

Visual inspection to ISO 5817 covers the cap, the toe and the profile of every weld. It does not cover the root, and on a full-penetration joint the root is where a defect matters. Where the drawing calls for it, magnetic particle inspection on the finished weld finds surface-breaking cracks at the toe; ultrasonic testing finds lack of fusion and slag in the body of the weld.

Plan the inspection before the weld, not after. A joint that will be UT-inspected needs a cap profile that lets the probe couple, and a joint that will be MPI-inspected needs the surface clean and uncoated. Both are cheap at the weld station and expensive after shot blasting and powder coating.

Dimensional inspection on a heavy weldment should follow the same datum logic as any assembly: measure the mounting faces and the hole pattern, record the diagonal where the part is a frame, and check the flatness of any face that carries a bearing or a mating plate. The welding inspection guide covers the record set for a repeat programme.

Welding for heavy-gauge material handling parts at Ganesh

Plate is cut on a 12 kW fibre laser with a 40 ft × 16 ft bed, which handles mild steel, CRCA, stainless, aluminium, brass and copper up to 20 mm, and on the iron worker for plate work in the 30–40 mm range. Forming stops at 10 mm on the 200 T, 5-axis brake with a 4,450 mm bed, so anything thicker is fabricated from cut and welded plate rather than bent.

Welding runs across three CLOOS robotic MIG cells for repeat assemblies and more than 30 manual MIG/MAG, spot and special-purpose stations for the heavier and lower-volume work, with fixtures designed and built in-house. Finished weldments go through a 16 ft × 16 ft shot blast chamber, then seven-tank pretreatment and the 18 ft × 14 ft powder booth, or through the wet paint booth where the specification calls for it.

Customer work in this shape includes material handling and genset base structures for Mahindra and Mahindra Powerol, and rail and infrastructure weldments for Indian Railways. The welded assemblies capability sets out the station and cell range, and the forklift parts page shows the part families.

Ganesh has manufactured sheet metal since 1992 across five units in Mumbai (Vasai) and Nagpur, with ISO 9001:2015 and ISO 14001:2015 certification. PPAP and first article inspection are available, and a first article for a heavy weldment includes the bevel and gap record, the pass log and the dimensional report against the stated datums.

What to put on the drawing

• Plate grade and thickness with the standard, such as IS 2062 E250 or E350, and the carbon equivalent if it is critical.
• Joint detail with bevel angle, root face, gap and whether a backing bar is permitted.
• Weld symbols to ISO 2553 with size, length and whether the weld is full or partial penetration.
• Acceptance level to ISO 5817, and the inspection method and extent for any full-penetration joint.
• Preheat and interpass requirements, or a note that the supplier proposes them from the grade and thickness.
• Datum faces and the dimensions that matter at assembly, measured after welding.
• Distortion allowance and the straightening limit, if straightening is permitted at all.
• Coating system and any face that must remain uncoated for a sliding fit or an earth.

The weight calculator gives the plate weight per part, which is the first number a handling and freight comparison needs.

When heavy-gauge welding is the wrong route

Welding is wrong when the shape can be a casting. A counterweight, a mast pivot housing or a complex bracket at volume is often cheaper and more accurate as a casting, and the weld that joins three plates becomes one part with no heat-affected zone.

It is wrong when the joint could be bolted. A bolted connection avoids the heat-affected zone, allows disassembly and needs no preheat, and on a maintenance item that is usually the better choice even at a higher piece price.

It is wrong when the plate could be thinner. A 12 mm bracket that carries a 3 kN load is usually a 6 mm bracket with a gusset, and the gusset costs less than the extra plate, the extra passes and the straightening.

Send the weldment drawing with the plate grades, joint details and the load path. The engineering team will return the bevel, the pass plan, the preheat and the inspection route, with full penetration specified only where the load actually crosses the joint.