Large Machine Frame Manufacturing: How to Choose Between Casting, Welding, and Machining

Last updated: September 22, 2026 · Reviewed by the Openex Engineering Team

When an industrial machine frame becomes several meters long and weighs many tons, choosing the manufacturing process is not simply a question of casting versus welding.

The better question is:

Which manufacturing route can turn the engineering design into a structurally sound, dimensionally stable, precision-machined, inspected, and shippable machine frame at the required production volume and cost?

For large customized frames, the practical options usually include:

• welded steel fabrication followed by stress relief and CNC machining;
• cast construction followed by machining;
• machining from heavy plate or solid material;
• or a hybrid design combining two or more of these methods.

The correct choice depends on geometry, production volume, material, structural loads, dimensional tolerances, design-change risk, available manufacturing equipment, and logistics.

For buyers of large industrial equipment, there is another issue that is often more important than the initial fabrication method:

Can one manufacturing partner actually handle the complete process from raw material through final inspection?

That means considering cutting, welding, heat treatment, heavy lifting, CNC machining, dimensional inspection, NDT, finishing, assembly, and shipment as one connected manufacturing chain.

Quick answer: There is no single best method. Welded fabrication suits large, custom, low-to-moderate-volume frames. Casting suits complex geometry at high volume where tooling cost is justified. Machining from plate suits simple sections in available material thicknesses. Most large industrial frames end up as a welded-then-machined structure, not a pure casting or a pure weldment.

Openex Metal Fabrication is set up around this type of large-scale manufacturing workflow. Its published capabilities include heavy structural welding, thermal stress relief, large-part CNC machining, CMM and laser-tracker inspection, and heavy material handling. Its facility information lists a 180-acre manufacturing operation, 55 lifting cranes, and lifting capacity up to 250 tons.

Explore Openex Heavy Equipment Base Frames · Talk to an engineer about your frame

Large welded frames often require both structural fabrication and precision machining before they are ready for installation.

The Short Answer: Which Manufacturing Method Should You Choose?

There is no universal winner.

A useful engineering starting point is:

• Choose welded fabrication when the frame is large, customized, structurally complex, produced in relatively low or moderate quantities, or likely to change during development.
• Consider casting when the geometry is highly integrated or complex and the expected production volume is sufficient to justify tooling and foundry development.
• Consider machining from plate or solid material when the required section is commercially available and the geometry can be produced without an unnecessarily complicated welded or cast structure.
• Consider a hybrid design when different areas of the frame have fundamentally different manufacturing requirements.

For a large welded frame, the manufacturing route should normally be evaluated as:

cutting → fit-up → welding → stress relief → rough machining → precision CNC machining → inspection → finishing → assembly

The cost of welding alone is therefore not an appropriate comparison against the price of a finished casting.

1. Start With the Machine Frame, Not the Manufacturing Process

Before selecting a process, define what the frame actually has to do.

A machine frame may provide:

• structural support;
• resistance to static loads;
• resistance to cyclic loads;
• vibration control;
• mounting surfaces;
• bearing alignment;
• guideway alignment;
• motor and gearbox interfaces;
• tooling or die support;
• access and service openings;
• lifting and transportation points.

These functions determine the frame’s geometry and tolerances.

For example, a frame that only supports a static enclosure does not have the same requirements as a press frame that must maintain alignment under repeated high loads.

A frame for a large generator, mining machine, stamping press, marine system, or production machine may therefore require very different structural designs even when the overall dimensions are similar.

This is why the manufacturing process should be selected after the functional requirements and critical datums are understood — not before.

2. Casting Is About Geometry and Production Strategy

Casting becomes attractive when the geometry itself benefits from being created as one integrated shape.

Typical reasons to consider casting include:

• complex three-dimensional geometry;
• internal ribs and cavities;
• large numbers of repeated parts;
• geometry that would require many fabricated pieces;
• requirements for a particular cast material or damping characteristic;
• a mature design that is unlikely to change.

The major consideration is tooling.

A casting pattern or mold requires engineering, manufacturing, maintenance, and validation. That investment can make sense when many substantially identical parts will be produced.

For a one-off industrial frame, however, the tooling cost can become a significant part of the total project cost.

A buyer should therefore ask:

How many finished frames will we actually purchase over the life of the product?

The answer can change the economic comparison dramatically.

3. Welded Fabrication Changes the Economics of Large Custom Frames

A welded machine frame is constructed from manufactured steel products such as:

• heavy plate;
• structural sections;
• machined plates;
• rolled sections;
• tubes;
• bars;
• reinforcement members.

The individual components are cut and prepared, fitted together, welded, stress-relieved where required, and then machined.

This approach is particularly useful when the design is:

• customized;
• produced in small or moderate quantities;
• still undergoing engineering changes;
• extremely large;
• made from readily available steel plate;
• or divided into sections for manufacturing and transport.

Large welded structures can be built from plate and sections without first developing a dedicated casting pattern.

Openex’s heavy welding operation reports weldments up to 250 tons and uses processes including SAW and FCAW for heavy structural work. Its welding capabilities also include AWS D1.1 and ASME Section IX environments.

See Openex Heavy Welding Services

4. The Real Comparison Is Finished Frame vs. Finished Frame

One of the most common purchasing mistakes is comparing two incomplete manufacturing costs.

For example:

Casting quotation

casting + rough machining

versus

Welded quotation

plate + cutting + welding

This is not an apples-to-apples comparison.

A finished large machine frame may require:

1. Raw material
2. Material certification
3. Cutting
4. Edge preparation
5. Fit-up
6. Welding
7. Weld inspection
8. Stress relief
9. Rough machining
10. Precision machining
11. Dimensional inspection
12. NDT
13. Surface treatment
14. Assembly
15. Packing
16. Transportation

The buyer should ask every supplier to quote the same finished scope.

Key takeaway: a “cheaper” welding quote and a “cheaper” casting quote are only comparable once both cover identical downstream steps — machining, inspection, and finishing included. This often changes the apparent cost difference between manufacturing methods.

5. Large Frames Have a Manufacturing Envelope

A supplier’s maximum machine size is only one part of the equation.

For an oversized frame, at least six physical envelopes need to be considered:

1. Fabrication envelope

Can the shop physically assemble and weld the structure?

2. Heat-treatment envelope

Can the complete welded frame fit into the furnace if stress relief is required?

3. Lifting envelope

Can the supplier safely rotate and position the complete frame?

4. Machining envelope

Can the CNC machine reach every required surface?

5. Inspection envelope

Can the finished frame be measured at the required accuracy?

6. Transportation envelope

Can the completed frame leave the factory and reach the project site?

A supplier may be able to weld a 20-meter structure but still be unable to stress-relieve or machine it as a complete assembly.

That is why buyers should qualify the entire manufacturing chain — not just the welding shop.

6. What Openex Can Handle at Large Scale

Openex publishes specific capacity data rather than describing its large-scale manufacturing capability only in general terms.

Its heavy CNC machining operation lists:

These are facility limits, not a promise that every 250-ton frame can be machined to every listed tolerance. Actual capability depends on geometry, material state, datum strategy, workholding, thermal conditions, and drawing requirements.

See Openex Heavy CNC Machining Capacity

Large machine frames require machine tools with sufficient travel, rigidity, workholding capacity, and access to the required surfaces.

Have a drawing already? Send your 2D/3D files for a capability and cost review →

7. Why Welding Does Not Finish the Job

For a precision machine frame, welding creates the structural body. It does not automatically create the final functional geometry.

Critical surfaces may include:

• mounting pads;
• bearing seats;
• guide rails;
• gearbox interfaces;
• motor mounts;
• die surfaces;
• bolting patterns;
• reference datums.

These surfaces frequently require machining after fabrication.

This means a buyer should not ask only:

“Can you weld a frame this large?”

A better question is:

“Can you fabricate, stabilize, machine, and inspect this frame at its finished size?”

That distinction separates a welding supplier from a large-frame contract manufacturer.

8. Stress Relief Is Part of the Machining Strategy

Welding heats the material locally. As the weld cools, contraction creates residual stress.

In a large structure, accumulated residual stress can become important when precision machining removes material.

If the workpiece moves during machining, a surface that was correct at the beginning of the operation may no longer be correct after the remaining stress is released.

This is why the manufacturing sequence should be designed before machining begins.

A typical large welded frame workflow is:

Fabrication → welding → stress relief → machining

rather than:

Fabrication → welding → precision machining immediately

The exact heat-treatment requirement depends on material, weld procedure, geometry, code requirements, service conditions, and the engineering specification.

Openex reports in-house stress-relief and PWHT capability for assemblies up to 250 tons, allowing applicable welded structures to be treated before large CNC machining.

See Openex Thermal Stress Relief & PWHT

9. Machining Strategy Matters as Much as Machine Size

A 25-meter machine does not automatically mean a 25-meter frame can be machined to the required tolerance.

The manufacturer must determine:

• where the primary datum will be established;
• how the frame will be supported;
• whether the structure can be machined in one setup;
• which surfaces need common-reference machining;
• where the part must be repositioned;
• how machining allowances will be distributed;
• how thermal expansion will be controlled;
• how distortion will be monitored.

For some frames, machining critical surfaces in one setup can reduce datum-transfer errors.

For other designs, sectional machining followed by assembly and final machining may be more appropriate.

The correct method is a process-planning decision, not simply an equipment-selection decision.

10. Large-Part CNC Machining Requires Heavy Handling and Metrology

Oversized CNC machining starts before the cutting tool touches the workpiece.

A 100-ton or 200-ton frame must first be:

1. lifted;
2. rigged;
3. positioned;
4. supported;
5. aligned;
6. referenced;
7. machined;
8. measured.

Openex’s large-part machining workflow uses its heavy crane infrastructure to position large fabrications on CNC machine beds, followed by gantry or boring-mill machining and large-scale metrology. The company reports 55 overhead/gantry cranes and lifting capacity up to 250 tons.

See Openex Large-Part Machining

Large-frame manufacturing is not complete until the finished geometry has been verified against the engineering requirements.

11. Inspection Should Be Designed Into the Project

For large machine frames, inspection should not be an afterthought.

A strong inspection plan may include:

Material inspection

• material certificates;
• heat numbers;
• MTRs;
• traceability.

Welding inspection

• visual inspection;
• MT;
• UT;
• RT where required;
• weld procedure documentation.

Dimensional inspection

• critical dimensions;
• flatness;
• parallelism;
• perpendicularity;
• position;
• bore alignment;
• datum relationships.

Final metrology

Large structures may require:

• CMM measurement;
• laser tracking;
• portable metrology;
• in-process measurement.

Openex’s quality operation reports climate-controlled CMM capability and FARO laser-tracker systems for oversized components, together with in-house NDT personnel and methods including UT, RT, and MT.

Explore Openex Quality Assurance & NDT

12. A Real Large Press Frame Shows the Difference Between Welding and Manufacturing

A useful way to understand the complete process is to look at a large welded press frame.

Openex documents a straight-side H-frame press structure with approximately:

• 6.0 × 4.0 × 8.0 meters overall envelope;
• 80–140 metric tons mass;
• 60–120 mm primary plate thickness;
• 10,000–20,000 kN press-force range;
• approximately 2,500 × 1,800 mm clear opening.

The engineering challenge is not simply joining thick plates.

The structure must maintain its geometry under demanding loads, control welding-related distortion, stabilize the completed weldment, and then provide accurately machined machine-bed and mounting interfaces.

That is why the documented workflow includes heavy plate preparation, controlled welding, post-weld stress relief, and precision CNC machining.

Read the Openex Large Welded Press Frame Case Study

This type of project illustrates an important purchasing principle:

The value of a large-frame supplier lies in controlling the complete manufacturing chain, not just performing the welding operation.

Have a similar frame in mind? Get a project review based on your press-force and envelope requirements →

13. When Machining From Plate Makes More Sense

There is a third option that is often forgotten in casting-versus-welding discussions.

Some components can be manufactured from heavy plate or solid material and then machined.

This can make sense when:

• the geometry is relatively simple;
• the required plate thickness is commercially available;
• the material removal volume is acceptable;
• welding would introduce unnecessary joints;
• casting tooling would be difficult to justify.

However, machining from solid material is not automatically cheaper.

For very large components, removing a large volume of material can create:

• high material cost;
• long machining cycles;
• significant chip volume;
• high tooling consumption;
• greater machine occupancy.

The correct comparison is therefore between complete manufacturing routes, not manufacturing labels.

14. Hybrid Construction Can Reduce Unnecessary Manufacturing Complexity

Some industrial frames do not need to be entirely cast, entirely welded, or entirely machined.

A hybrid design may combine:

• welded steel structure;
• cast local components;
• machined plate;
• forged interfaces;
• bolted subassemblies;
• precision-machined inserts.

This can be useful when one part of the design benefits from a manufacturing process that would be inefficient for the rest of the structure.

The design question becomes:

Which portions of the geometry actually benefit from each manufacturing process?

That is often more productive than trying to select one process for the entire assembly.

15. Production Volume Can Change the Answer

Production quantity should be discussed early.

One-off frame

For a prototype or one-off machine, avoiding large tooling investments can be important. Welded fabrication may allow the manufacturer to work directly from engineering drawings and CAD data.

Small production run

For several to several dozen frames, fabrication and machining can remain attractive, especially when the geometry is customized.

Repeated production

At high production volumes, tooling and process optimization can make casting more economically attractive for certain geometries.

However, high-volume welded fabrication can also benefit from fixtures, standardized components, automated welding, and repeatable machining programs.

Production volume changes the economics, but it does not determine the answer by itself.

16. Design Changes Are a Procurement Risk

Large machine frames are often designed alongside the machine they support.

That means the frame may change because of:

• revised load calculations;
• motor changes;
• different gearbox dimensions;
• modified access openings;
• new mounting interfaces;
• transportation restrictions;
• customer requirements;
• updated FEA results.

A welded design can be relatively adaptable before material is cut.

A casting pattern can be more difficult to change after tooling has been completed.

This does not mean welded construction is always better. It means the expected design-change risk should be included in the manufacturing decision.

17. How to Compare Large Machine Frame Suppliers

Do not qualify a supplier only by asking:

“How many tons can you weld?”

Use a complete capability checklist.

A supplier that can perform all or most of these operations within one manufacturing organization can reduce the number of handoffs between vendors.

Openex describes its operation as a one-stop manufacturing hub with cutting, forming, welding, machining, painting, heavy lifting, and inspection capabilities.

See Openex Facilities & Equipment

The manufacturing facility itself becomes part of the supplier qualification process when the component is too large for a conventional machine shop.

18. What Should Be Included in a Large Machine Frame RFQ?

A good RFQ lets the manufacturer evaluate the actual manufacturing route before pricing the job.

Send as much of the following as possible:

Engineering files

• 2D manufacturing drawings;
• 3D STEP/IGES/CAD model;
• assembly drawing;
• BOM;
• critical section views.

Material information

• material grade;
• plate thickness;
• mechanical requirements;
• material certificates;
• heat-treatment requirements.

Welding requirements

• welding code;
• WPS/PQR requirements;
• weld class;
• NDT percentage;
• preheat/interpass requirements;
• PWHT requirements.

Machining requirements

• critical datums;
• GD&T;
• flatness;
• parallelism;
• hole position;
• bore tolerances;
• surface finish.

Quality requirements

• inspection standard;
• CMM requirements;
• laser-tracker requirements;
• NDT reports;
• dimensional report;
• certificate of conformity.

Commercial information

• prototype quantity;
• annual quantity;
• delivery schedule;
• destination;
• required Incoterm if applicable.

For a large-frame project, providing the 3D model together with the 2D drawing can make the early manufacturing review much more useful.

Start your RFQ with Openex →

19. Five Questions to Ask Before You Award the Project

If you are buying a large machine frame, ask every shortlisted supplier these five questions.

1. What is the largest finished frame you have actually manufactured?

Ask for dimensions and weight — not just a general capability statement.

2. How will you control welding distortion?

The answer should address welding sequence, joint preparation, fixturing, thermal control, and post-weld treatment where applicable.

3. Where will the final machining be performed?

Ask for the machine type, travel, workholding strategy, and setup sequence.

4. How will you prove the final dimensions?

Ask for the inspection method and sample dimensional report.

5. How many external suppliers are involved?

If welding, heat treatment, machining, inspection, and painting are all subcontracted to separate companies, the project has more interfaces to manage.

These questions reveal whether the supplier has a credible plan for delivering the finished component.

20. Why an Integrated Manufacturing Route Can Matter

For a large frame, moving the workpiece between suppliers is not the same as moving a small machined component.

Every additional transfer can require:

• heavy transport;
• crane loading;
• temporary supports;
• re-rigging;
• dimensional re-establishment;
• additional insurance;
• schedule coordination.

For very large structures, keeping major operations within one manufacturing site can reduce these interfaces.

Openex’s published workflow specifically connects:

heavy fabrication → stress relief → large CNC machining → dimensional inspection

and its large-part machining operation is designed around heavy workpiece handling and oversized machine tools.

Explore Large Part CNC Machining

21. Frequently Asked Questions About Large Machine Frame Manufacturing

Is a welded machine frame better than a cast machine frame?

Neither is universally better. Welded fabrication is often useful for large customized and low- or moderate-volume structures, while casting can be attractive for complex repeated geometries where tooling can be justified. The decision should also consider final machining, stress control, inspection, and logistics.

Can a welded machine frame be precision machined?

Yes. Critical mounting pads, bearing interfaces, guideways, bores, and other functional surfaces can be CNC machined after fabrication. The machining strategy should account for welding distortion, residual stress, workholding, and datum control.

Does a large welded machine frame need stress relief before machining?

It may. The requirement depends on the material, weld procedure, geometry, applicable code, service conditions, and machining tolerances. For large precision weldments, stress relief can be an important part of the dimensional-stability strategy.

What is the maximum size of machine frame Openex can manufacture?

Openex’s base-frame page lists general facility capacity up to approximately 25 meters in length, 6 meters in width, and 250 tons for a single assembly. Actual manufacturability depends on the detailed design, machining requirements, handling, heat treatment, inspection, and transportation plan.

What is the maximum size Openex can CNC machine?

Openex’s heavy CNC machining page lists gantry milling capacity up to 25,000 mm in length, 6,000 mm in width, and 5,000 mm in height, with workpiece weight up to 250 tons. Actual machining capability depends on the geometry and required process.

Can Openex stress-relieve a large welded machine frame?

Openex reports thermal stress-relief and PWHT capability for assemblies up to 250 tons. The applicable heat-treatment cycle should be established from the engineering specification and material requirements.

How are large machine frames inspected?

Inspection can include material traceability, visual weld inspection, UT/MT/RT as specified, dimensional inspection, CMM measurement, and laser tracking. The appropriate inspection plan should be defined by the drawing, applicable codes, and customer requirements.

How long does it take to manufacture a large welded machine frame?

Lead time depends on plate procurement, welding hours, required stress-relief cycle time, machining setups, and inspection scope. Because these steps are sequential rather than parallel, an early RFQ with complete engineering data allows the most accurate schedule estimate.

What should I send for a large machine frame quotation?

Send the 2D drawings, 3D CAD model, material specification, approximate dimensions and weight, quantity, critical tolerances, welding requirements, NDT requirements, surface-treatment requirements, and delivery destination.

Can one supplier fabricate and machine a large welded frame?

Yes. Some heavy manufacturing facilities are structured to combine fabrication, stress relief, CNC machining, inspection, finishing, and assembly. This can reduce transportation and supplier-interface requirements for oversized components.

Is casting always cheaper for high-volume production?

Not necessarily. Casting tooling can be amortized across high production volumes, but welded fabrication may also become economical when fixtures, standardized components, automated welding, and repeat machining programs are used. The finished part cost should be compared using the same scope and production assumptions.

22. Ready to Discuss Your Large Machine Frame?

If your project involves a large machine frame, welded machine base, press frame, equipment skid, heavy structural frame, machine bed, or other oversized industrial weldment, the most useful first step is not choosing a manufacturing process from a generic comparison chart.

Send the engineering package to a manufacturer that can evaluate the complete route.

For an Openex engineering review, provide:

• 2D drawings
• 3D CAD model
• material grade
• approximate dimensions
• estimated weight
• production quantity
• critical machining tolerances
• welding/NDT requirements
• delivery destination

Openex can then evaluate the requirements for heavy fabrication, welding, stress relief, large-part CNC machining, dimensional inspection, finishing, and assembly.

Request a Project Review / Contact Openex

Email: sales3@openex.com.cn Phone / WhatsApp: +86 186-5928-0806

Final Takeaway

For large machine frames, the most useful question is not:

“Casting or welding?”

It is:

“Which manufacturing route can deliver the required structural performance and final geometry with a controlled, inspectable, and economically practical production process?”

For a customized large frame, that evaluation should include:

geometry → production volume → material → welding → stress relief → machining → inspection → finishing → lifting → transportation

Welded fabrication can be highly practical for large customized structures, particularly when the design is produced in relatively low or moderate quantities and the final interfaces can be precision-machined.

Casting can make sense when complex geometry is repeated enough to justify tooling and when the foundry and machining route meet the project’s dimensional and material requirements.

Machining from plate or solid material can be appropriate when the geometry and material availability make it efficient.

And for some projects, a hybrid approach is the most rational solution.

The key is to evaluate the finished machine frame, not just the first manufacturing operation.

For oversized industrial components, supplier capability should therefore be measured by the complete chain:

fabricate → stabilize → machine → inspect → finish → deliver.