Specifying a Custom Ship Small-Assembly Welding System: Start with the Weld Map

Begin with the weld map, not the robot count

A shipyard evaluating small-assembly welding should first describe what has to be welded, where the joint is accessible and how completion will be accepted. A plate with several stiffeners can look simple in a general arrangement drawing while containing very different welding tasks: long accessible fillets, short interrupted runs, crowded intersections and end returns with restricted torch approach. Treating these as one undifferentiated length produces an equipment enquiry that is easy to price imprecisely and difficult to verify later.

The practical starting document is a weld map linked to the current assembly drawing. Each required weld receives a persistent identifier, a location, a joint description and an acceptance route. TWI separates the welding equipment from the robot that positions the heat source; that distinction explains why reach alone is an incomplete specification. [1] The recommendations below turn a drawing into a project review package. They are proposed engineering controls, not a description of functions already installed on a particular machine.

TitanWeld's supplied marine brief describes double-sided, double-arc fillet welding with two arms forming the basic coordinated unit. Its current coordination ceiling is 2 + 2, meaning four welding units and eight arms. This is a highly non-standard project with no off-the-shelf single machine. The number of units, their physical arrangement and their assigned welds require a project-specific discussion.

Define a useful assembly family

Select representative assemblies by welding difficulty rather than by overall length alone. A useful family record includes plate and stiffener geometry, material identification, required weld symbols, loading orientation, available datums and the expected condition at handover from fitting. Record which details repeat and which change between orders. If one family includes both open flat panels and crowded brackets, identify the subfamilies explicitly instead of expecting one average model to describe both.

Include at least one ordinary assembly, one with the most restricted access and one with the most demanding start, stop or return detail. These are proposed sampling categories, not a prescribed qualification sample count. The responsible project team must decide how many trials represent the actual work. Provide the expected production mix so that a supplier does not optimize a demonstration around the easiest and least frequent component.

State the boundary of supply around the incoming workpiece. A robotic welding project might receive a fully tacked assembly, or it might include additional locating and clamping operations. These are different workloads. A proposal should identify who establishes fit-up, who checks it, where unacceptable assemblies wait and how accepted parts are released to the next operation. Otherwise apparent robot idle time may actually originate from an undefined upstream responsibility.

Give every seam a stable identity

A weld identifier should survive changes in robot assignment. For example, a yard may choose a structure such as assembly revision, stiffener identifier, side and segment. The exact syntax is less important than the relationship: a weld remains the same required joint even if a different arm performs it during recovery. Keep operation identifiers separate so that a restart or repair can be recorded without overwriting the original weld identity.

For each segment, record the specified weld size and its interpretation from the approved drawing, whether the weld is continuous or intermittent, the intended start and finish regions, and any return or termination requirement. Do not convert a leg-size requirement to an effective-throat value by assumption. Refer ambiguous symbols to the design authority. Also record whether the opposite-side weld is part of the same planned operation or a later stage.

Add a status for welding access: provisionally reachable, requires verification, or allocated to another approved method. This prevents a visually attractive coverage percentage from hiding difficult short welds. The current IACS Recommendation 47 is a shipbuilding and repair quality reference; the contract must identify the quality requirements actually adopted for the work. [2] The weld map should point to those requirements rather than inventing a universal tolerance table.

Describe the usable process envelope

A seam is usable only when the torch can maintain the required relationship to the joint over its complete path. Check the approach, working motion, departure and servicing movement. Include the nozzle, contact tip, sensor, wrist, cables and any fixture that occupies the space. A point that the robot can reach with its bare flange does not establish that the welding tool can reach it with an acceptable orientation.

Map local constraints beside the seam: adjacent stiffeners, brackets, lifting attachments, clamps, end stops and already deposited welds. Distinguish a collision problem from a welding-position problem and from a sensing problem. The remedies differ. Moving a clamp may solve access but weaken location; changing approach may clear the nozzle but obstruct the sensor; dividing a seam may make motion possible but add another start and stop.

Specify the evidence required to close each unresolved item. A simulation can demonstrate the intended geometric route using the modelled tool and fixture. A representative welding trial can examine deposition at a restrictive detail. A production readiness review can confirm the approved procedure and operating instructions. Keeping these records separate helps the buyer understand exactly what has been shown and what remains to be demonstrated.

Plan the two sides as related work

For a double-sided fillet, give each side its own weld identifier and link both to a paired operation. This preserves the ability to describe different start locations, length interruptions or access restrictions without pretending that the sides are identical. Identify whether simultaneous welding is proposed throughout the seam or only where both sides satisfy the process and clearance conditions.

The pair record should contain a proposed response when one side cannot start or must stop. Questions include whether the other side finishes its current segment, how the workpiece state is recorded, how the interrupted bead is assessed, and which checks precede a restart. These decisions belong in the engineering review before an output guarantee is negotiated. A normal-cycle animation seldom reveals the consequences of an asymmetric interruption.

Pairing also affects fixture design and inspection access. A clamp that is harmless for one torch may block the opposite torch or make a completed fillet inaccessible to the required examination. Review the pair with the fitter, welding engineer, automation engineer and inspection representative using the same drawing revision. Assigning these review roles is a suggested project method; it does not imply that an independent review of the TitanWeld configuration has already occurred.

Connect the map to procedures and inspection

Attach the proposed WPS reference and its revision to each weld family. TWI describes the WPS as the document that defines the welding variables and distinguishes it from the supporting qualification evidence. [3] An equipment supplier's preferred program name is therefore insufficient as the only process reference. The project should explain how a selected robot recipe corresponds to the applicable controlled welding instructions.

For each family, identify the required inspection method, timing and release authority. Some checks occur before welding, some during the operation and some after cooling or release from the fixture. Keep the actual acceptance criteria in the controlled inspection documentation and link to them from the map. This avoids copying criteria into several spreadsheets that subsequently drift apart.

A useful completion state has more detail than welded or not welded. Consider separate states for fit-up accepted, welding completed, examination pending, accepted, repair required and repair accepted. The vocabulary can follow the yard's existing system. The essential requirement is that a completed motion program cannot silently advance the assembly to accepted status when required examinations remain outstanding.

Make exclusions measurable

An enquiry should contain an explicit exception register. Each exception needs a location, reason, proposed alternative operation and effect on the complete assembly cycle. A short return finished manually is different from an inaccessible longitudinal seam that forces the whole assembly to be repositioned. Both count as incomplete robotic coverage, but their production implications are not comparable.

Record the basis for any coverage percentage. Weld length, deposited volume, count of weld identifiers and labor content answer different questions. A system may cover most of the length while leaving a substantial number of short details. Present the underlying map so that the buyer can examine these details instead of relying on a single headline figure. State whether repair and inspection activities are included in the comparison.

Resolve exclusions before freezing the trial plan. If an inaccessible seam is discovered during a demonstration, update the map and repeat the affected cycle estimate. Do not hide the change inside a revised travel speed. The practical commercial objective is a shared understanding of the finished assembly and the operations needed to deliver it, including any agreed work outside the automated cell.

Use the map as the acceptance backbone

Build the acceptance trial from the map: load the identified assembly, verify its incoming condition, execute the agreed weld families, record exceptions and assess the specified results. Include normal production variation that has been explicitly accepted for the trial. Keep the test drawing, material record, procedure revision and robot program revision together so that a successful result can be reproduced or a failure investigated.

Ask the supplier to report completed and accepted weld identifiers, elapsed cell time, interventions and unresolved details. Review the evidence against the original scope before discussing additional units. Expanding from one two-arm unit to several units changes scheduling, shared access and recovery obligations; it does not remove the need to qualify the individual joint tasks.

The finished specification should let a new project engineer answer three concrete questions without guessing: which welds are included, under what incoming and process conditions, and what evidence releases the assembly. When those answers are clear, the custom equipment discussion becomes productive. Robot count then follows a defined manufacturing task, and the buyer can compare proposals against the same work rather than against different interpretations of a drawing.

Project review checklist

• Identify the drawing revision and representative assembly families.
• Assign a weld ID to every included joint and required end return.
• Record material, thickness, weld details and incoming assembly conditions.
• Mark fixture obstruction, torch access and any excluded welds.
• Agree trial assemblies, acceptance evidence and responsibility for exceptions.