Metal Forging Guide: Processes, Materials and Design

This metal forging guide is written for engineers, procurement managers and founders who need to specify, source and compare forged components. It covers the main process routes, the alloys most often quoted, the design and tolerance decisions that drive feasibility, the cost drivers behind a quotation, and the checks to run before placing an order.

Forging suits parts where directional strength, fatigue resistance and material integrity matter. It is not automatically the right answer for every geometry: open-die work can need extensive machining, closed-die work carries die cost and die-fill limits, and cold forging demands high forming loads and substantial tooling. The guide sets out those trade-offs so you can state a route on the drawing instead of leaving it to the supplier.

The guide is split into four chapters plus this overview. Each chapter answers one sourcing question end to end, so you can read them in order or jump straight to the decision you are facing.

If you already know the route and grade, skip to the design, cost and supplier sections below. If you are still choosing between processes, start with the chapter on open die, closed die and ring forging.

Forging processes differ mainly in how the metal is constrained and at what temperature it is formed. The table below summarises the six routes most often quoted for custom steel and alloy parts, with the practical advantage and the main penalty of each.

How to read the table

Treat the route as a specification decision, not a supplier preference. Open-die work is normally chosen when the part is large or the volume is low and machining capacity is available. Closed-die work pays back when annual volume justifies die cost and the geometry respects draft and parting-line rules. Cold forging is chosen for finish and dimensional control on smaller parts where the alloy has enough ductility.

In this metal forging guide, material choice sets the achievable strength, corrosion resistance and service temperature before any process decision is made. The grades below are typical starting points for forged steel and other custom forging components; confirm the applicable specification and heat-treatment condition.

A metal forging guide is a practical reference for specifying forged parts: it links alloy, forging route, heat treatment and inspection to the drawing so every supplier quotes the same scope.

Most routes start from a billet. In impression-die forging, the billet is pressed in shaped dies, and the excess metal that escapes the cavity forms flash, which is trimmed afterward.

Specifying the material on the drawing

• Name the alloy and grade, not just the family: a typical example is that "ASTM A105" is a specification, while "carbon steel" is not.
• State the heat-treatment condition and the required mechanical properties, including tensile, elongation, reduction of area and hardness where relevant.
• State the acceptance standard for the forging itself, for example the ASTM A788 general requirements.
• State the surface examination required, such as visual or magnetic-particle testing (MT), where relevant.
• State whether material certificates and heat-number traceability are required.
• State any service conditions that affect grade choice, such as temperature, corrosive media or weight limits.

Forging tolerances are part-specific. There is no universal value that can be applied across sizes, routes and geometries, so the drawing must carry the tolerances you actually need and the standard they are judged against.

Design rules to apply before quoting

• Add machining allowance to surfaces that must finish to a tolerance tighter than the forging route can hold.
• Respect draft and parting-line requirements on closed-die work; die-fill limits constrain thin sections and sharp corners.
• Keep the datum structure consistent between the forging drawing and the machined drawing.
• Specify surface finish and inspection responsibility where the part is supplied machined.
• State the examination method explicitly: visual, magnetic particle, dye penetrant or ultrasonic.
• Do not assume a tolerance from a previous project transfers to a different size, route or alloy.

Forging cost is driven by the route, the tooling it needs, the material, and the amount of post-forging processing the part requires. Two quotes for the same drawing can differ substantially because the suppliers assumed different routes or different levels of machining and testing.

Primary cost drivers

• Tooling: closed-die work carries higher die cost, while open-die work keeps tooling low but may push cost into machining.
• Route and temperature: cold forging needs high forming loads and substantial tooling; hot forging adds scale, distortion, energy use and post-forging heat treatment.
• Material: alloy grade, section size and the buy-to-fly ratio all affect the material line.
• Machining allowance: extra stock on critical surfaces converts into machining time.
• Heat treatment: required condition and the equipment needed to achieve it.
• Testing and examination: mechanical testing, magnetic particle, dye penetrant and ultrasonic testing each add cost and lead time.
• Volume and lot size: die cost is amortised differently at low and high annual quantities.

How to make quotes comparable

Give every supplier the same drawing revision, the same alloy and grade, the same annual quantity and lot size, the same forging route or an explicit statement that the route is open, and the same testing and certification requirements. Ask each supplier to break out tooling, piece price, heat treatment, machining and testing so you can see where the differences sit.

Supplier selection for forgings comes down to whether the supplier can hold your drawing, document the material and prove the result. Work through the checklist below before you release a purchase order.

1. Confirm the route and the equipment Ask which forging route the supplier proposes and whether the equipment can handle your part size and alloy. A supplier who cannot state the route clearly cannot be compared with one who can.
2. Review material certificates and heat-number traceability Heat-number traceability links the forging to its melt, material certificate, processing records, heat treatment and inspection results. Ask to see a sample certificate pack.
3. Check the quality-system certification Request the applicable quality-system certification, such as ISO 9001, and confirm it covers the site doing the work. Certification does not replace product inspection.
4. Agree the inspection and testing plan Confirm which mechanical tests, surface examinations and volumetric examinations apply, who performs them, and what reports are delivered with the parts.
5. Confirm machining and finishing responsibility If the part is supplied fully machined, agree the datum structure, tolerances, surface finish and inspection responsibility in writing.
6. Verify the documentation package Ask for the material certificate, heat-treatment records, inspection reports and NDT reports that will ship with the order.

A complete RFQ is the fastest way to get comparable forging quotes. Include the drawing, alloy and grade, annual quantity, lot size, forging route, heat treatment, machining scope, tolerances, testing, certification and delivery requirements.

1. Send the current drawing revision with tolerances, datums and surface finish stated.
2. State the alloy and grade, plus the heat-treatment condition and required mechanical properties.
3. State annual quantity and lot size, and whether the forging route is fixed or open.
4. State the machining scope and who owns final inspection.
5. State the testing, examination and documentation package required.
6. State the delivery destination and required date.

Sourcing Repository collects quotes from a vetted supplier network, manages quality and inspection, and delivers the parts. Send your RFQ to killol@sourcingrepository.com or use the quote form, and we will come back with supplier quotes, typically within 5-7 working days.