Single-Source Fabrication: How Drawing-to-Assembly Under One Roof Cuts Project Risk

Most fabricated parts need more than one operation. A single bracket, frame, tank or welded assembly might need cutting, then forming, then machining, then welding, then finishing, and finally assembly. The question buyers rarely ask early enough is who is responsible for the work between those steps.

When each step is done by a different supplier, the part moves between companies several times before it is finished. This article looks at what happens at each of those handovers, and at what changes when one supplier does every step. That approach is called single-source metal fabrication.

Where a chain of several suppliers goes wrong

Consider a typical job that has been split between suppliers. One supplier laser-cuts the flat blanks and ships them to a second supplier for bending. A third machines the features that must fit other parts, and a fourth welds the assembly. A fifth polishes the part and passivates it, which is a chemical treatment that helps stainless steel resist corrosion. Each supplier may be good at its own process, but every time the part moves from one company to the next, something can go wrong.

Each handover means the purpose behind the design has to be passed on again. The next supplier has to read the drawing again, check the material again, and be told again what finish is needed. Small misreadings add up. A cut edge that suited one supplier's bending tools may behave differently in another supplier's tools. A weld preparation that suited one workshop's welding process may not suit the next workshop's process.

None of these problems needs poor work at any single step. Each supplier can meet its own part of the drawing and still pass on a part that causes trouble later, because it did not know what the next step needed.

When the problem finally shows at assembly, the part has already passed through several companies. No single company is responsible for it, so nobody takes charge of the fix.

The costs that do not appear on the quote

A split chain looks cheaper, because you can buy each process from the supplier with the lowest price. The costs that reduce that saving tend to arrive later, and they are hard to see on a purchase order. They include:

• Quality drift: each supplier works to its own reading of the drawing. Small differences build up along the chain, and no one checks the whole part in one place.
• Scheduling delays: each supplier has its own queue of work. If the second step is late, the third, fourth and fifth steps have to wait, and no single company is managing the overall schedule.
• Communication gaps: a change agreed with the welder may never reach the finisher, because no single conversation covers the whole job.
• Unclear responsibility: when a finished part is wrong, the cutting supplier blames the bending supplier, and the bending supplier blames the machinist. You then have to settle a dispute that you did not cause.

The list is not complete, but it shows the pattern. The more handovers a job has, the more of your time goes into managing the suppliers instead of getting the part you need.

That time is easy to overlook, because it does not appear on any supplier's invoice. It includes the phone call to find out where a part is, and the email that passes a change from the welder to the finisher. It also includes the meeting held to decide whose mistake caused a bad fit. Each of these tasks is small, but across a job with five suppliers they add up to many hours of your own staff's time.

Every handover you remove is one less place for a part to go wrong, and one less thing for you to manage.

What changes when one supplier is responsible

TH Steel does cutting, forming, machining, welding, finishing and assembly in-house, in one workshop. The practical result is not a longer list of machines. It is fewer handovers, and so fewer places where a project can go wrong.

When one workshop controls the whole sequence, each step is planned with the next one in mind. The cut edge is prepared for the weld that will follow. The bend is planned around how the part will be held for machining. The welder and the finisher work to the same understanding of the surface the part needs. Decisions that would otherwise pass between two companies, and might be lost on the way, are made by people working in the same building.

There is also one company responsible for the result. If something needs to change, you have one conversation, instead of a round of emails between suppliers who each see only their own step.

Quality is handled differently too. Because the same team carries the job from drawing to finished assembly, the part is checked throughout the process by people who know what the next step needs. In a split chain, each supplier checks its own work before sending it on, and then has to trust that the next supplier will do its step correctly.

This approach suits different volumes of work. With a one-off or a prototype, what the team learns stays in one place and goes straight into the next version. With a production run, the process is the same from start to finish, so the parts stay consistent from the first batch to the last. Accurate in-house cutting is the starting point, because parts that are cut accurately make every later step easier.

The same workshop also handles the choice of material and finish. We work with grades including 304, 316/316L, 430 and duplex 2205. Finishes include 2B (the standard smooth mill finish), No. 4 (a brushed finish with fine parallel lines) and mirror. Where the application needs it, the part can be pickled, which chemically cleans the surface after welding, and passivated.

When you send an enquiry, please describe the whole part, not just the first operation. Include:

• the drawing, or a sketch, sample or photograph if the drawing is not complete
• the material grade
• the finish
• how the part will be used

With that information, the workshop can plan cutting, forming, welding and finishing as one job, instead of making one step as efficient as possible on its own.

Why single-source fabrication helps overseas buyers

Buyers who purchase parts across borders, including those who work for the original manufacturer of a machine, find a split chain even harder to manage. Coordinating five suppliers is difficult even from the next town. When the buyer is in another country, a question may not be answered until the next working day, and each supplier holds only part of the information. A fabrication order can then turn into a full-time coordination job.

One responsible supplier removes most of that work. You have one relationship, one specification and one conversation from drawing to finished assembly. When a question comes up, it goes to the company responsible for the whole job, instead of to whichever supplier happens to be at work in its own time zone.

The specification benefits in a simple way. In a split chain, the drawing and the specification are sent to each supplier separately. When something changes, every copy has to be updated, and one out-of-date copy is enough to spoil a batch. With one supplier, there is only one current version to keep correct.

Evidence matters more when you cannot visit the workshop, because a remote buyer is making the decision from a screen. Photographs of similar finished work have to do the work of a site visit. So do a clear account of how quality is checked and clear answers about what can and cannot be done.

For shipping and delivery, we prefer to discuss each case rather than make general claims about export. Tell us where the work needs to go, and we will discuss how to support that requirement.