A search for a metal drawing manufacturer can land on three quite different suppliers, because metal drawing is not one process. Pulling wire or tube through a die to reduce its diameter, forming a flat blank into a cup, and shaping a shell over a rotating mandrel are all called drawing, and a shop that does one of them well usually does not do the others. The first useful step is to name the process the part actually needs, because that decides which supplier can quote it, what tooling is required and which tolerances are realistic.
What is a metal drawing manufacturer?
A metal drawing manufacturer forms metal by pulling or pressing it into shape instead of cutting it away. In sheet metal the term nearly always means deep drawing: a flat blank is formed into a hollow cup, housing or shell by a punch and die, then thinned and lengthened by further draws and ironing. In bar, wire and tube the same word means pulling stock through a die to reduce its diameter, which is a separate trade with separate equipment. A deep drawing manufacturer works from flat sheet on presses from 25 t to 350 t, with drawn diameters up to 250 mm, and quotes from a drawing rather than a catalogue. Balford is a deep drawing manufacturer: dies are designed and built in house, and the blank, the draw stages and the secondary machining run in the same plant.
Metal drawing is a family of processes, not one
Three groups of process share the name. Sheet metal drawing deforms a flat blank into a three-dimensional shape. Wire, bar and tube drawing reduces the cross-section of long stock by pulling it through a die. Metal spinning forms a disc over a rotating mandrel with a roller. They use different machines, different tooling and different people, so a quotation from one group says nothing about the others. Most industrial enquiries that use the words metal drawing manufacturer are about the first group, because that is the process that produces housings, shells, sleeves and end caps from sheet.
Deep drawing compared with wire, bar and tube drawing
- Deep drawing. Starts from flat sheet or coil. A blank is drawn into a cup, and the wall is thinned or the part lengthened by further draws. Output is a hollow part: housings, shells, sensor sleeves, end caps. Balford does this in house on presses from 25 t to 350 t.
- Wire, bar and tube drawing. Starts from rod, wire or tube and pulls it through a die to reduce the diameter or change the section. Output is long stock rather than a formed part. This is a separate trade and is not carried out at Balford.
- Metal spinning. Starts from a disc and forms it over a rotating mandrel with a roller. Suited to large, thin, round parts at low volume. Also a separate trade.
- Ironing. Often described as its own process, but it usually runs as a stage inside deep drawing, where the wall of an already drawn cup is thinned between a punch and a die to raise the wall height and tighten the wall thickness.
Key point
If the part is a hollow shell, housing or sleeve formed from flat sheet, the process to ask for is deep drawing, not wire drawing or spinning. Naming the process first removes most of the ambiguity from the enquiry, and it is also what decides whether a supplier can quote at all.
Which tolerances are realistic on a drawn metal part
Forming and machining hold different tolerances, and a drawing that mixes them without saying which is which is the usual cause of a dispute. Dimensions created by the draw itself depend on material, thickness, draw ratio and springback, so they are wider than machined dimensions and are normally held to a general tolerance block. Dimensions created after forming, by turning, boring, drilling or thread cutting, can be held much tighter: 0.01 mm is achievable on selected critical machined features where the process, geometry, material and inspection method support it, and it is quoted per feature rather than as a blanket tolerance. Wall thickness, roundness and concentricity on a deep drawn part sit in the first group and should be specified as drawn requirements with the datum they are measured from.
How to specify a drawn metal part so it can be quoted
- State the material and its temper or grade, not only the family, because drawability changes with both.
- Give the finished geometry and mark which dimensions are formed and which are machined.
- Say which dimension is the datum, and what roundness, concentricity or wall-thickness variation is acceptable.
- List the finish and any heat treatment, and say which of them may be batched with other part numbers.
- Give the annual volume and the first-order quantity separately, so the recurring price and the first lot are each priced on the right basis.
- State the documentation package: dimensional report, material certificate, PPAP level or nothing beyond a shipping inspection.
What to put in the RFQ to a metal drawing manufacturer
Send the drawing, the material and thickness, the annual volume, the first-order quantity, the finish and the documentation package. Ask for the process route to be stated, and ask which operations are outsourced. Balford designs and builds the dies in house, runs the blank, the draw stages and the secondary machining in the same plant, and quotes from the drawing with the process route written out. Bulk heat treatment, slow-wire EDM, passivation, electropolishing, plating, phosphating, painting and e-coating are carried out by qualified external partners and are shown as their own lines, and pre-forms such as hot forgings, cold extrusions, castings and powder-metallurgy blanks are bought in and finished by machining in house. A complete enquiry is normally answered within 24 hours.
Frequently asked questions
What is the difference between metal drawing and deep drawing?
Metal drawing is the broad term. Deep drawing is the sheet metal version of it, where a flat blank is formed into a hollow shape by a punch and die. The same word is also used for pulling wire, bar or tube through a die, which is a different process on different equipment. When the part is a hollow shell made from sheet, the process to ask for is deep drawing.
Can a metal drawing manufacturer work from a drawing only?
Yes. Deep drawing is quoted from a drawing rather than a catalogue, because the blank size, the number of draw stages and the tooling all follow from the part geometry, the material and the volume. A 2D drawing with the material, the thickness and the critical dimensions is enough to start; a 3D model speeds up tooling design but is not required for the first quotation.
What tolerances can be held on a drawn metal part?
Dimensions created by the draw itself depend on material, thickness, draw ratio and springback, so they are held to a general tolerance block. Dimensions created afterwards by machining can be much tighter, and 0.01 mm is achievable on selected critical machined features where the process, geometry, material and inspection method support it. It is quoted per feature, not as a blanket tolerance.
Are heat treatment and plating done in house?
No. Bulk heat treatment of dies and production parts, slow-wire EDM, passivation, electropolishing, plating, phosphating, painting and e-coating are carried out by qualified external partners. Each has its own minimum batch and lead time and is quoted as its own line rather than absorbed into the drawing price.
How do I know whether a drawn part needs one draw or several?
The limiting draw ratio for a single draw is roughly 2.0 to 2.2 depending on the material, which means the first draw can reduce the blank diameter by about half. A part deeper than that is made in two or more stages, with an anneal between them if the material work-hardens. Sending the finished geometry and the material is enough for a supplier to work out the draw count and quote the tooling.